I created this page. I'm not a member of the LIGO collaboration, but
I'm at the same institution as many who are. That's arguably close
enough to a WP:COI that I'll confine further additions to this talk
page. NormanGray (talk) 15:48, 11 February 2016 (UTC)
@NormanGray:[1] says 12 September, rather than 14th. Do you have a reference for the more precise time and different date you've added here, please? A reference for the rest of the content would also be very useful, please. Thanks. Mike Peel (talk) 15:58, 11 February 2016 (UTC)
@Mike Peel: It might be worth a pointer to the 'Science summary', potentially replacing the media references. That provides references for the detection date and time, as well as the remark about 10x the rest of the universe – the current ‘citation needed’ – and is more generally intelligible than the PRL paper. The first notes were extracted from a paper version of this. NormanGray (talk) 16:59, 11 February 2016 (UTC)
Does merely having LIGO colleagues really imply COI? The connection seems a bit indirect compared to the examples listed in COI; you only know someone who is involved in the topic, but you're not involved yourself. I suppose we have to make that judgment each for ourselves. Like half the astrophysical community, I also have LIGO colleagues (and so far I did not make major contributions to this article). And what about astronomy in general, can we write about topics in our own fields (not about our own scientific results of course)? Most of Wikipedia is written by people with some connection to the topics they write about, even if only as a hobby. Gap9551 (talk) 19:00, 11 February 2016 (UTC)
I'd agree, I don't think there is a COI here (since you aren't part of the LIGO collaboration), and I'd encourage you to help improve the article (while providing references for additions/changes). :-) It would probably be useful if you could ask your colleagues to have a look through the article in a day or so to spot any inaccuracies in it, though, and to post any comments that they might have here rather than making them directly. Thanks. Mike Peel (talk) 19:05, 11 February 2016 (UTC)
I also agree that working at an institution that employs people in the LIGO collaboration is not COI for this page. Geogene (talk) 23:47, 11 February 2016 (UTC)
Well, I'm in the same research group rather merely the same institution. I myself don't think there's a real conflict of interest, but it seems proper to note the relationship nonetheless. I'll take this conversation as licence to edit the page. Also, as @Mike Peel: suggests, I'll solicit appropriate commentary from collaboration members. NormanGray (talk) 16:09, 12 February 2016 (UTC)
Scope (section Future detection) and article title
I think that the section 'Future detection' may not be within the scope of this article. This article should probably be just about this specific event, i.e, the properties of the progenitor binary, the merger event, the GW signal of the merger event, the formed black hole, and a short description of the detectors. Future prospects of (similar) events and the expected rate of such events are probably better located in the detector articles, and/or the GW article. Gap9551 (talk) 17:40, 11 February 2016 (UTC)
Agreed on all fronts. I have to go back to work so feel free to either make the edits yourself or I will get to it in a couple of hours time. Seddontalk18:05, 11 February 2016 (UTC)
I renamed the section to "Implications for future detections" before noticing this discussion. I think that's good to include - it's the brightness of this signal that implies that many more will be detected by more sensitive instruments in the future. So long as it stays focus on the implications from this detection, rather than trying to be more general than that. Thanks. Mike Peel (talk) 18:56, 11 February 2016 (UTC)
I agree. I also wrote this section when the article was still named Gravitational wave detection, February 2016. The current title 'Gravitational wave detection' is more general. When more detections are announced, maybe we should rename this article again to make it clear that this is only about this first event. A general overview of detections should probably go into Gravitational wave. Or maybe we can create a separate article about all detections. Gap9551 (talk) 19:05, 11 February 2016 (UTC)
That makes sense. Given that the article on the first pulsar is at PSR B1919+21, it may be worth thinking about having this at GW150914 at some point. But that's a problem for the future, when (hopefully) there are more detections. Thanks. Mike Peel (talk) 19:08, 11 February 2016 (UTC)
I agree. When I created the page, I did consider naming it Gravitational wave detection of GW150914 or similar, but in the end patterned it after the more low-key discussion of the Higgs discovery. However since this easily ranks with the observation of PSR B1919+21, since unlike the Higgs discovery this was more clearly An Event, and since a page on GW detections in general would also be reasonable, then a page devoted to this specific first event would seem to be entirely warranted. Who wants to make the change? NormanGray (talk) 16:09, 12 February 2016 (UTC)
I move my discussion here because I think that this article should be renamed into "First direct observation of gravitational waves" or something like this? Actually, I translated this article in French and I choose a title like this. Indeed, the current title refer to the observation in general whereas the article talk only about the detection that happens on 14 September 2015. Do you plan to write about the next detection in this article? IMHO, I think this event (the first detection of such wave) is enough important to have its own article. Pamputt (talk) 00:21, 13 February 2016 (UTC)
I agree with Pamputt; the scope of this article is the first detection of gravitational waves, so the title should define that. On a side note, probably, an additional subsection is the resulting controversy on who might be entitled to the Nobel price for this event. Cheers, BatteryIncluded (talk) 00:29, 13 February 2016 (UTC)
The current edition of the article contains the phrase "Across the duration of the detectable signal, the relative velocity of the black holes increased from 30% to 60% of the speed of light with the objects orbiting each other at a distance of ≃350 km." which doesn't sound well. Figure 3 of the article at https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf has green line named "black hole relative velocity" that really shows this increase. What means "relative velocity" in this context? Dobrichev (talk) 18:53, 11 February 2016 (UTC)
I think it means the velocity of one black hole relative to the other. It would either be that, or the relative velocity to earth, but in this context it looks like the former. Thanks. Mike Peel (talk) 18:58, 11 February 2016 (UTC)
There are already many references to the event in pop culture, including a segment on Saturday Night Live, a New Yorker cartoon, two segments in the Feb 13 broadcast of A Prairie Home Companion, and a popular Twitter parody account (@iagw150914). — Preceding unsigned comment added by 193.205.74.131 (talk) 15:04, 15 February 2016 (UTC)
On the contrary, a list of pop-culture references to the announcement serves to highlight the immediate impact of the news in the non-scientific community. This is one of the palpable elements of the detection that will otherwise be forgotten. The scientific details are well-documented, and will remain so; the interpretation of the achievement by the general public (who, it should be noted, paid for this research) is an important aspect of major science news like this and should be recorded. — Preceding unsigned comment added by 193.205.74.131 (talk) 10:17, 17 February 2016 (UTC)
What does the name "GW150914" imply? Gravitational-wave event 150914? Who controls that numbering? Is it unique only to the one observatory, or all observatories? i.e. what name will be given to the next one, if it is detected at a different observatory? John Vandenberg(chat)21:04, 11 February 2016 (UTC)
@John Vandenberg: "GW" = "Gravitational Wave". "150914" is the date, 2015-09-14. There's no guarantee that any future detections will follow the same convention, but it does (mostly) match the convention that has been used by Gamma-ray bursts. Thanks. Mike Peel (talk) 21:10, 11 February 2016 (UTC)
Blimy, why on earth do they knock the '19'/'20' off the front, still. Saving previous space on their hard disks?? ;-)
Thanks. It would be good to write up this convention. What happens when there are two different observations on the same day? It hasn't happened yet? GRB 790305b looks like the first instance with an article in English, but ja:GRB 670702 is about the 'first' detection. John Vandenberg(chat)21:32, 11 February 2016 (UTC)
I mentioned the origin of the name in section 'Event detection' (as this information may be too detailed for the lead). Gap9551 (talk) 21:49, 11 February 2016 (UTC)
The origin of the name GW150914 in event detection has disappeared, the sources after the name description do do not verify the name origin and description.CuriousMind01 (talk) 23:25, 21 February 2016 (UTC)
New York Times
I've removed this reference as the NYT article is, to be frank, appallingly bad. For example, see their statements that "physicists who can now count themselves as astronomers" and "scientists have finally tapped into the deepest register of physical reality, where the weirdest and wildest implications of Einstein’s universe become manifest"... Thanks. Mike Peel (talk) 21:31, 11 February 2016 (UTC)
That first statement is something I've heard involved people say too, tongue-in-cheek, as they actually detected an celestial body now. Either way, we are not short on RS so this is fine. Gap9551 (talk) 21:52, 11 February 2016 (UTC)
Four events
NYT says
Shortly after the September event, LIGO recorded another, weaker signal that was probably also from black holes, the team said. According to Dr. Weiss, there were at least four detections during the first LIGO observing run, which ended in January.
This doesnt appear to be covered in the article yet, and seems significant. Would be good to get more info on the other events, with additional sources. John Vandenberg(chat)01:12, 12 February 2016 (UTC)
Yes that is important, although possibly outside the scope of the article. I added a note in 'Announcement' for now. The NYT is a reliable source, even if we may not like some parts of their article, there is no reason to question the statement which they attribute to Rainer Weiss. To be on the safe side, I attributed the statement to NYT. Gap9551 (talk) 01:58, 12 February 2016 (UTC)
I think you're right, and this probably is outside the scope of this article, to the extent that this article is about this particular detection. There will doubtless be plenty of other detections yet to be discovered and/or announced, either as good as this one or more marginal. It might be worth a note, based on the team's remarks, that this detection is unlikely to be absolutely unique, but beyond that it's surely speculation. I've taken the liberty of pruning the Announcement section to what's been formally published by the collaboration. NormanGray (talk) 17:58, 12 February 2016 (UTC)
Use of boldface in first sentence
Currently 'GW150914' is in boldface, but that does not meet MOS:BOLDTITLE. Still, it feels right as the article is about the object/event, even though it is not named as such (yet). Previously I had bolded 'observation of gravitational waves' as it is close to the title. Maybe that is close enough? Gap9551 (talk) 22:05, 11 February 2016 (UTC)
My understanding was that redirects from alternative names should be marked in bold in the article that the redirect points to. But I guess I'm outdated here? Thanks. Mike Peel (talk) 23:53, 11 February 2016 (UTC)
Maybe only if the title is also bolded? (Mumbai/Bombai example). But there's also the Azaria Chantel Loren Chamberlain example which seems to apply here, so I think you may be right. I'll bold the GW150914 again like you did before, please revert if I misinterpret the guideline. Gap9551 (talk) 00:26, 12 February 2016 (UTC)
If I understand it correctly, they numerically simulated a large range of binaries with varying parameters such as mass and spin (and also redshift, distance) using general relativity, covering the realistic parameter space, calculated the resulting GW signal, and looked which simulations best matched the observed signal. Apparently the signal from begin to end is consistent with a certain group of GR simulations, and those are the ones on which the published parameter ranges are based. Gap9551 (talk) 00:35, 12 February 2016 (UTC)
I see. That makes sense.
In addition though, according to Black hole, the "size" (insofar as holes has a diameter) of a 10 solar-mass hole is ~30km. A 30M hole will be a bit bigger. The article text says that the holes merged while 350km (i.e. nearly 10 radii) apart. Why is this? Surely they could have got down to ~50km apart before merging? Fig (talk) 11:36, 12 February 2016 (UTC)
The Schwartzschild radius of a black hole is about 3 km for each solar mass. So, these black holes would have had radii of about 85 and 105 km, respectively, which is 190 km put together. That's not yet 350 km, but you'd need a proper GR simulation to find out the details of the merger. Gap9551 (talk) 15:57, 12 February 2016 (UTC)
Thank you for this explanation. Do you think you could add something in the article to explain above (how did they determine the resulting black hole properties)? I asked myself the same question so the detailed explanation should be given in the article in order to avoid treading here to find the information. Pamputt (talk) 06:55, 13 February 2016 (UTC)
At first I wondered if he would be notable, but that Science article is pretty much about him, so that's a big step towards notability. Gap9551 (talk) 02:00, 12 February 2016 (UTC)
Yeah that's what I thought too, being the first person to notice the observation and having had an article in such a publication dedicated wholly to him is enough to make him notable for Wikipedia. Sardeis (talk) 11:43, 12 February 2016 (UTC)
Also related to Drago, is the fact he took note of the signal first significant enough to be mentioned in the lede (The waveform, detected on 14 September 2015[3] by Marco Drago, physicist at the Albert Einstein Institute in Hannover, Germany,[4] [...])? This fact wasn't mentioned in the press conference, for example. Also, I'm not sure if we can say that one specific person 'detected' the signal. Gap9551 (talk) 22:36, 12 February 2016 (UTC)
I disagree. I am sure he is a very competent professional, but, the list of authors is longer than 1000, of a large international effort. He just happened to be doing his shift at the computer. Keep the perspective. Cheers, BatteryIncluded (talk) 00:49, 13 February 2016 (UTC)
The number of first observers is increasing. University of Padua claims: "The first to notice the event a few minutes after its arrival on Earth was Gabriele Vedovato, INFN Padova member of the Virgo group, in conjunction with Marco Drago at the Albert Einstein Institute in Hannover, former student and postdoc in the group of Padova-Trento".
University of Florida reports:
The coincident detection was reported by Coherent WaveBurst within three minutes of the signal arrival. Coherent WaveBurst reconstructed the signal shape revealing a spectacular signature of two colliding black holes. In a fraction of a second they merged into a single more massive black hole releasing energy equivalent to a few times the mass of our Sun in a burst of gravitational waves. Coherent WaveBurst, was developed at the University of Florida by physics professors Sergey Klimenko and Guenakh Mitselmakher, and their graduate students and postdoctoral research associates. Klimenko and Mitselmakher have been leaders in LIGO’s search for gravitational-wave bursts since 1997. The burst search seeks to detect short gravitational-wave signals from supernovae, gamma-ray bursts, mergers of binary neutron stars and black holes, and other catastrophic astrophysical events.
Sergey Klimenko told to the Russian news agency TASS that on 6:30 Florida time he read an E-mail report from his program and on 7:15 sent a warning to the people working with the detector. - Ace111 (talk) 23:37, 13 February 2016 (UTC)
I've modified the ‘Event Detection’ section to remove all names. LIGO/LSC/LVC is a hundreds-strong collaboration, and they all get the credit, not individuals. NormanGray (talk) 11:38, 14 February 2016 (UTC)
Observation vs detection
From what I see, there was no observation in the sense of direct visualization, video recording or naked eye observation of the waves. Rather the waves were detected, so I think the previous title "Gravitational wave detection" was more correct. Brandmeistertalk09:01, 12 February 2016 (UTC)
Your definition of observation is strange, how is a video recording (electromagnetic phenomena, detected by electronics, converted to digital media and displayed in a screen) different to the LIGO detections (gravitational phenomena, detected by electronics, converted to digital media, displayed on a screen)?
Semantically, it is just as much a direct observation as the hubble telescope beaming photographs back to Earth. Scientifically, detection IS observation.
Also, the main source (the Physical Review Letters paper) uses 'observation' in the title, and the 'O' in LIGO stands for 'observatory'. But overall the terms are used interchangeably. Gap9551 (talk) 16:03, 12 February 2016 (UTC)
I am not a scientist, but my feeling for the language is that an observation is more detailed than a detection. The reports that we are talking about are more detailed than a mere detection. The experimenters did more than find that there was a gravitational wave, they measured it and saw it changing over time. And there is reasonable expectation that they can repeat the observations. FWIW. TomS TDotO (talk) 00:47, 13 February 2016 (UTC)
There is also the question of whether gravitational waves were detected through measurements of binary pulsars. Perhaps changing the title of the article to GW150914 would remove ambiguity? — BobQQ (talk) 16:34, 14 February 2016 (UTC)
You're right: It's true that the orbital decay of the Hulse-Taylor binary provides (and provided) important corroboration of the existence of gravitational waves, in the sense that GW radiation provided the most adequate explanation of that decay. Perhaps that point should appear explicitly somewhere in the Gravitational wave article. However I doubt anyone would suggest that was a detection of GW: detection would be reserved for the case where there was a pretty much ‘direct’ detection of a phenomenon, rather than a measurement which could merely be best explained (indirectly) in terms of the phenomenon. Turning from there to the point at issue in this subsection: although there's probably an idiomatic difference between ‘observation’ and ‘detection’ (people would probably use the former, in conversation, for a more direct/detailed/unmediated detection), I can't think of a stable distinction between the two in a formal context. Thus, I think the difference is stylistic rather than substantial, and GW150914 is comfortably on the direct/detailed/unmediated side of the line. NormanGray (talk) 17:37, 14 February 2016 (UTC)
Detection and observation are similar words. Observation also means making measurements and records and inferences. It seems in science detection is the process and act of identifying an event. An observation is the additional act of making measurements and records and inferences of the event detected.CuriousMind01 (talk) 15:18, 15 February 2016 (UTC)
English
Hi, sorry but does this sentence sounds English "It was first seen by Italian post-doctoral researcher Marco Drago who was receiving data from LIGO while in Germany and initially did not think the signal was real;". For a non-native speaker like me, it sounds a bit weird, in particular the end. Am I misunderstanding something? Pamputt (talk) 23:05, 12 February 2016 (UTC)
I noticed that the Compton wave length mentioned, 1013 km, is roughly numerically equivalent to 1 light-year. Is that worth mentioning? TomS TDotO (talk) 04:49, 13 February 2016 (UTC)
There should be more information included about the test signal injection mechanism. How often are these test performed? Do they modulate the laser signals directly or do they manipulate only the signal output? Can these tests generate signals, that cannot be distinguished from original signals? What is the probability, that the detected first signal is generated accidentally or intentionally by the test signal injector. Does the benefit of a test signal injector also include the risk of misuse and how are the protection means? PANAMATIK (talk) 08:00, 13 February 2016 (UTC)
The Science article discusses these injections, though not in much detail. As that suggests, the test injections (can) happen very close to the origin of the signal (the article refers to ‘mechanical systems’, meaning very close to the test masses at the ends of the arms). The article also describes the collaboration verifying that there were no test injections scheduled at the time of the detection – the systems to do so weren't yet ready – and the processes of ruling out the possibility that the signals were the result of a mistake or a prank. — Preceding unsigned comment added by NormanGray (talk • contribs) 14:00, 13 February 2016 (UTC)
The lack of any detection in neutrinos or e.m. waves yet is interesting. Would we expect neutrinos from merging black holes? Why? - all their nucleons were long since crushed? Re e.m. might intervening matter have slowed e.m. waves by an amount that might add up to years of travel over a billion years? Also do gravitational waves get deflected/lensed by mass in the same way as e.m.? If not, that adds another delay to the em signal? Fig (talk) 10:56, 13 February 2016 (UTC)
This is not the place for this discussion - this Talk Page is for the discussion of the use of Reliable Sources for the improvement of the article - only. See WP:FORUM. Also, read the statement at the top of this (and every) Wiki Talk Page. 68.19.8.105 (talk) 17:03, 13 February 2016 (UTC)
1.3±0.6 billion light years or light travel distance years? Comment
Is "1.3±0.6 billion light years" supposed to be "1.3±0.6 billion light travel distance years"? The research publication gave a luminosity distance but not a distance in any light year units, that I could find. I see the 1.3 billion light years in news reports, but new reports tend to not report the term "light travel distance". --CuriousMind01 (talk) 15:10, 13 February 2016 (UTC)
That 1.3 number seems to be converted from the luminosity distance in parsecs by multiplying by 3.26. For a redshift of 0.09 (given in the PRL paper), the light travel time is 1.187 billion years according to [3] (not rounding to significant digits). But that number would be original research if the sources don't mention it. Gap9551 (talk) 17:21, 13 February 2016 (UTC)
Section 'Future observatories'
I don't think this section should exist. I wrote the eLISA paragraph in the 'Implications' section because the GW150914 signal has direct implications for eLISA. I still think it belongs there. Now the eLISA paragraph has been moved to the new section, and in addition a paragraph on the Einstein telescope has been added, without any connection to GW150914. I think the Einstein telescope paragraph should be deleted. In fact I deleted it before with explanation but it was re-added without explanation. Gap9551 (talk) 17:36, 13 February 2016 (UTC)
User:Gap9551, The name of the article is Gravitational wave observation not GW150914 event. Because the name is Gravitational wave observation, so I think that means the observation work in the past, present and future of gravitational waves, which is a broader topic than the GW150914 event. The Einstein telescope is a future Gravitational wave observatory with a mission to observe Gravitational waves, so I think its 1 sentence mention fits in an article named Gravitational wave observation. In the future there may be more wave events observed, so the GW150914 event may be the first of more wave event observations in the future to be documented.
A suggestion is for someone, if interested, to split the current article into 2 articles: 1. Gravitational wave observation (history, and methods in the past present & future) 2.GW150914 event.--CuriousMind01 (talk) 18:55, 13 February 2016 (UTC)
Yes, I agree it would be good to rename this page to focus it on just this (first, special) observation, and so make it clearer that such discussion of future observations might be better elsewhere. This suggestion was floated earlier, near the top of this talk page. The Gravitational_wave#Detection page has a section on detection in general. So I propose that someone who knows how to do it, and how to ensure cross references are updated to match (I don't) renames this to, perhaps, First gravitational wave detection, GW150914 or something like that. Note that there's a GW150914 redirection in place, so at least one person has been WP:BOLD about this already. NormanGray (talk) 20:47, 13 February 2016 (UTC)
Mike gives the better article to describe the many GW observatories that are in development or have merely been proposed. Also, why single out Einstein telescope? Gap9551 (talk) 21:42, 13 February 2016 (UTC)
Across several discussions on this talk page, I think there is consensus to settle the scope of this article to only the first observation. That also makes sense given the huge amount of media coverage on specifically the first event. To make the scope clearer, I moved the article to First observation of gravitational waves. A title like this seems to have more support than GW150914 at this point, but maybe we need to move there in the future. Gap9551 (talk) 00:08, 14 February 2016 (UTC)
I agree with Gap9551; the first observation is historic, the future ones will be statistics. I support the move to "First observation of gravitational waves". Cheers, BatteryIncluded (talk) 01:20, 14 February 2016 (UTC)
ELF wave background
I've reverted this subsection twice ([4][5]) but it is re-added (slightly edited, without explanation, and incompletely sourced). Input from another editor would be welcome here, in order to avoid an edit war. Gap9551 (talk) 02:06, 14 February 2016 (UTC)
Removed again, Although toned done, it is more lkke a forum content. The reference supplied is a general one and not applicable directly to this event. The investigators did measure environmental disturbances anyway and dismissed them. If an accademic paper or news item appears on this, we could include coverage, but I don't see such a thing after searching. Graeme Bartlett (talk) 02:38, 14 February 2016 (UTC)
I think scientists from LIGO collaboration could exclude ELF waves of Schumann resonances if they had really occured at that time because how can we interpret the similiar waveforms detected by two sites which 3,002 km apart, how can ELF waves penetrate through concerete and steel shields to reach detectors?Earthandmoon (talk) 02:38, 14 February 2016 (UTC)
The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section.
The result of the move request was: No move. There's much to consider in this RM, but it seems clear that there's not (yet) consensus to move from the current descriptive title to the wave's designation number. As noted by several participants, this should probably be revisited in the future. Cúchullaint/c15:15, 4 April 2016 (UTC)
First observation of gravitational waves → GW150914 – This article currently uses a descriptive title, but the gravitational wave detected actually has a designation (an objective name), which is "GW150914", which is what the article should be called, same as how FRBs, SGRs, GRBs etc are named, and not using descriptive titles. -- 70.51.200.135 (talk) 06:32, 14 February 2016 (UTC)
Support. Descriptive names should really only be used when there is no proper name for an article's subject, which is not the case here. — Huntster (t@c)08:45, 14 February 2016 (UTC)
Oppose. According to the article, "the signal was named GW150914", but, as can be seen in the contents table, this article is about much more than about the signal alone. I think the current title, flanked by the redirect from GW150914 is perfect. - DVdm (talk) 10:20, 14 February 2016 (UTC)
Our cited skyandtelescope source says: "The passing gravitational waves slightly altered the path lengths in the arms of both detectors by about 1/1,000 the width of a proton. That slight change created a characteristic interference pattern in the laser light, an event LIGO scientists have dubbed GW150914." So they say that GW150914 is a change, creating a characteristic interference pattern in the laser light. Whether that change is the observation, or led to the observation is not clear.
Still, in a publication by LSC or the title of the paper published in The Astrophysical Journal("Astrophysical implications of the binary black-hole merger GW150914"), "GW150914" seem to be read as the name of the event at least by relevant researchers.--LeoTschW (talk) 11:55, 14 February 2016 (UTC)
GW150914 would be regarded as the astrophysical event rather than specifically the signal on-disk (as with PSR B1919+21). One could be more subtle about this, but to me, this page is at least in part about the social and media event, and its status as The First, as well as the astrophysical one, and the current name reflects that better than the object designation would (I wouldn't go to the wall for it, though). NormanGray (talk) 12:34, 14 February 2016 (UTC)
The event in question is the gravitational wave passing through the detectors, hence GW150914 is the name of the signal. (This is why it has the date in the name). — BobQQ (talk) 16:41, 14 February 2016 (UTC)
Support: Personally, I think the case of "GW150914" is somehow like the case of PSR B1913+16, where the discovery of the event (or system) seem to be more important than the event (or system) itself, but I support the move, considering the main readers in the long run, even if the title "GW150914" seem not to be able to express the historical importance of the observation as the present title. --LeoTschW (talk) 12:04, 14 February 2016 (UTC)
Oppose as the code name is not that cpommonly used in any popular publications. Barely anyone would know it, however many more would have an idea what the current name means. Graeme Bartlett (talk) 13:53, 14 February 2016 (UTC)
Oppose 1) commonly known as "the first detection"; 2) no layman would enter that code in the search bar, and 3) the code is non-descriptive as a title. BatteryIncluded (talk) 14:20, 14 February 2016 (UTC)
Oppose The article subject is more than the code name event, the code name is not well known. The code name could be entered in () in the title. The article subject is gravitational waves and their first detection, so I think the current name matches the subject. CuriousMind01 (talk) 14:33, 14 February 2016 (UTC)
Not yet. As I said above, I think this is a problem for the future, when (hopefully) there are more detections, at which point moving it to the GW ID would make sense, but for now I think the article is fine where it is (although the inclusion of 'First' in the article name could be argued if you want. ;-) ). Thanks. Mike Peel (talk) 16:02, 14 February 2016 (UTC)
Support This avoids any conflict over whether gravitational waves were already detected through observations on binary pulsars. General gravitational wave observations should be added to gravitational-wave astronomy. As more detections is made, perhaps we can make a list, but since this is the first, it is significant enough to merit its own page, and implications can be discussed here. — BobQQ (talk) 16:39, 14 February 2016 (UTC)
Oppose The audience for this encyclopedia is not astrophysicists. As things stand for the moment, this title will direct the interested reader to the desired information. When more is learned, then there is ample opportunity to change the title. TomS TDotO (talk) 16:48, 14 February 2016 (UTC)
Not intending to single you out amongst the other similar replies (more of a broad response), but this argument seems unusual. It feels like saying we should call the Bell X-1 article "First supersonic jet aircraft" or Amundsen's South Pole expedition article the "First successful South Pole expedition". Our article titles are just not named as such when a more precise name can be given. — Huntster (t@c)19:43, 14 February 2016 (UTC)
I am not a fan of the present title, for reasons something like yours. I would prefer something like "January 2016 announcement of observation of gravitational waves". Not that I'm going to propose that - I know that that will be shot down. But aside from that, I only have the choice of the present or GW150914, so I'm sticking with the flawed present until we get much more information which will enable us to decide on what would be more precise and permanent title. TomS TDotO (talk) 21:52, 14 February 2016 (UTC)
Wavering Support: Per WP:NC, the current title matches Recognizability and Naturalness, while GW150914 fits Precision, Conciseness, and possibly Consistency. That tips the scales slightly toward the latter title, but I'm mostly indifferent really. Praemonitus (talk) 18:00, 14 February 2016 (UTC)
Oppose The current article deliberately covers more than just the event/signal. There is a lot of context; on GWs, the first indirect evidence (the Hulse-Taylor system), a LIGO description, implications. The current title more accurately covers the content. Gap9551 (talk) 22:02, 15 February 2016 (UTC)
Oppose I agree with what's been said about the article covering more than that specific signal, and that we should keep it accessible for a general reader. The current title is much more natural than the technical classification for the signal. I also wonder if we still need "first", but that's another debate. :) Julietvbarbara 05:38, 19 February 2016 (UTC) — Preceding unsigned comment added by Julietvbarbara (talk • contribs)
Support tentatively based on first the pulsar observation and second that we're now also talking about gamma observations of the same event. The context that was brought out could just be part of the Gravitational wave article. The key here is that a specific event was observed. It should still landmark the event as the first direct observation of gravitational waves.--Smkolins (talk) 09:57, 19 February 2016 (UTC)
@Martin Hogbin and Gap9551: I'm not sure I follow this line of argument: this article does focus on the event, and the context is at the level of what should included in any article about an event... Thanks. Mike Peel (talk) 22:10, 21 February 2016 (UTC)
It was just an idea. Have one article focusing on what the world sees as a major event in the history of science, mainly for the general reader, with a link to a more detailed article specifically on the details of GW150914. Martin Hogbin (talk) 22:20, 21 February 2016 (UTC)
Support Per WP:COMMONNAME. Even if descriptive names of the event are more common in general, the pretty much endless possible variations of the description mean individually these are a LOT less common than the proper name for the event. Google counts are not the end all for such a discussion but as a case in point searching for "GW150914" gives over 300,000 hits, while searching for the articles current title give just under 15,000 hits. In the end user is much more likely to look for "GW150914" than any individual descriptive title. In the future, a more human friendly common name my surface for the event (cf. "Hulse-Taylor binary" for "PSR B1913+16").TR11:00, 22 February 2016 (UTC)
Oppose, by coincidence I read much of the page today after seeing the title on the main page. It's a very good descriptive title and draws the reader to it. The suggested name may be an official designation, but it doesn't do justice to the magnitude of this discovery. Randy Kryn15:06, 22 February 2016 (UTC)
If interested, here are ideas for alternate titles, I took from the title and words used in the research article:
1. "Observation of Gravitational Waves" (where the gravitational wave event GW150914 is the first event observed)
2. "Gravitational wave event GW150914"
3. "Observation of Gravitational wave event GW150914"
I think just "GW150914" as a title is not descriptive, just "GW150914" requires prerequisite specialized knowledge.
The technical research paper has a plain descriptive title:"Observation of Gravitational Waves from a Binary Black Hole Merger" I notice the authors themselves did not use the event number in the title "GW150914" or call the paper "GW150914" by itself.--CuriousMind01 (talk) 20:21, 14 February 2016 (UTC)
Except our naming standards are radically different from the personal preference standard used in research papers, so that's not really an argument. Saying "GW150914" is not descriptive, while true, is also a non-argument considering the, well, vast number of proper noun article titles that exist here and are the naming standard. — Huntster (t@c)20:28, 14 February 2016 (UTC)
The article title naming "standards" are actually subjective general principles:
"A good Wikipedia article title has the five following characteristics:
Recognizability – The title is a name or description of the subject that someone familiar with, although not necessarily an expert in, the subject area will recognize.
Naturalness – The title is one that readers are likely to look or search for and that editors would naturally use to link to the article from other articles. Such a title usually conveys what the subject is actually called in English.
Precision – The title unambiguously identifies the article's subject and distinguishes it from other subjects. (See § Precision and disambiguation, below.)
Conciseness – The title is no longer than necessary to identify the article's subject and distinguish it from other subjects.
Consistency – The title is consistent with the pattern of similar articles' titles. Many of these patterns are listed (and linked) as topic-specific naming conventions on article titles, in the box above."
So I, per the subjective "standards", subjectively think the 3 ideas for names 1-3 above, or the existing article name, are better names than "GW150914" for "recognizability (descriptiveness)","naturalness","precision","conciseness" and "consistency". I think using the words "gravitational wave event" in the title is consistent with other gravitational wave articles that exist, as there are no other event articles. CuriousMind01 (talk) 21:02, 14 February 2016 (UTC)
I think the title of "Gravitational-wave observations" as a future article proposed by user:Drbogdan is a good future title. I think user:Hunster has a good point with the analogy of titling Amundsen's South Pole expedition article the "First successful South Pole expedition", but at the time, year 1911, the "First successful South Pole expedition" may have been the best title, and then after more successful expeditions changed the article title to "Amundsen's South Pole expedition".
I understand this article is about the scientific observation(process+measurements+inferences) of the detection(identification) of the event GW150914. I don't consider the GW150914 event as an astronomical object like PSR B1913+16. I think the astronomical objects would be Object Black Hole 1, (which merges with) Object Black Hole 2, (generating the GW150914 gravitational wave event), (and then forming) Object Black Hole 3. In the future hopefully there will be more observations of detections of gravitational wave events and the title could be "Gravitational-wave observations" to include these observations, then leading to a "List of Gravitational-wave observations."
The survey question was only about an article title rename to GW150914, so I opposed the rename to GW150914 since the article is not only about the event, but also about the observations and detection of the gravitational wave event.CuriousMind01 (talk) 15:46, 15 February 2016 (UTC)
CuriousMind01, see, I don't understand your last sentence. Yes, "GW150914" is about the event. "Northrop Grumman X-47B" is about the aircraft. Both articles discuss the histories and happenings surrounding each. Again, this is the standard for Wikipedia articles. — Huntster (t@c)17:29, 15 February 2016 (UTC)
User:Hunster. I agree with you about an article's structure. I think the current article is broader than the event "GW150914". I think like User Drbogdan wrote, this article could be split, in time, into several articles in the future: "Gravitational-wave observations", "List of Gravitational wave observations", "Gravitational-wave observation GW150914", "Gravitational-wave observation GWxxxx" etc. Then the "Gravitational-wave xxx' articles, except the list, each would have a content structure history, methods, etc sections.
I think the newness of the "first" that may have led to the editors to pick a title describing the significance of the event, and the article growing to contain multiple subjects. In time the article will evolve to more articles. Probably there would have been a "first solo flight", and in the future there will be more "first" article titles.
I also opposed the title "GW150914" itself, because I think "GW150914" is a bad title name, it is a code and not descriptive, and conciseness does not mean fewest characters in a title. CuriousMind01 (talk) 14:52, 17 February 2016 (UTC)
I don't see it as any more of a "code" than the names of stars and exoplanets. It's just another proper name. But yes, I definitely see that eventual article structure coming, it just makes logical sense. There's no need for *this* article to hold as much as it currently is. — Huntster (t@c)16:03, 17 February 2016 (UTC)
Oppose. Over-abbreviated jargon. "First observation" is meaningful, including the date of measurement is not normal for an article. --SmokeyJoe (talk) 04:26, 22 March 2016 (UTC)
The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.
About the diagrams in infobox
Hi, I'm one of the editors of the corresponding article in zh-wiki. Here I want to ask a question about the diagrams in infobox: Are the diagrams in the second row theoretical prediction or fitting curves?--LeoTschW (talk) 07:32, 14 February 2016 (UTC)
In the paper PhysRevLett.116.061102 authors describe diagram read as:
Second row: Gravitational-wave strain projected onto each detector in the 35–350 Hz band. Solid lines show a numerical relativity waveform for a system with parameters consistent with those recovered from GW150914[37,38]confirmed to 99.9% by an independent calculation based on[15]. Shaded areas show 90% credible regions for two independent waveform reconstructions. One (dark gray) models the signal using binary black hole template waveforms [39]. The other (light gray) does not use an astrophysical model, but instead calculates the strain signal as a linear combination of sine-Gaussian wavelets[40,41]. These reconstructions have a 94% overlap, as shown in[39].
So they are both theoretical prediction (numerical relativity) and fitting curves (shaded areas reconstruction) that overlap in these diagram.Earthandmoon (talk) 07:50, 14 February 2016 (UTC)
Observing gravitational waves: I'm not a doctor in physics, but it seems to me that gravitational waves can be observed just by going down to the beach and watching the tide go in and out. The gravitational waves are created by the Moon as it orbits the Earth and you can observe the gravitational wave the Moon creates. Granted the gravitational waves created by the Moon are very low frequency compared to the detection noted in the main thrust of this article; but, to my way of thinking they are gravitational waves just the same. My understanding gravitational waves are fluctuations or ripples in the space/time continuum caused by the movement of massive bodies in space. The variations of the Moon's gravity on the Earth fits this concept.— Preceding unsigned comment added by 24.217.10.33 (talk • contribs) 08:53, 14 February 2016
No. In electrostatics, when you move a charge, its electrostatic field changes accordingly, immediately. Still, this is particle dynamics plus field statics. Not a field dynamics yet. A wave exists independently of the charge that created it. Similarly, in gravitation. Boris Tsirelson (talk) 09:30, 14 February 2016 (UTC)
I believe the best way to explain it to the OP is that gravity moves at the speed of light. If a new mass, let's say a moon, were to pop into existence the pull of its gravity would expand outwards at the speed of light. The expanding ripple of gravity in the pond is called a gravitational wave. Pairs of white dwarfs, neutron stars, and/or black holes very near to each other tend to orbit each other around a barycenter. If you were near, and off to the side of this pair, you would feel the gravitational pull of one and then the other, alternating. The pulses of those "pulls" are continuously expanding away from the pair at the speed of light. When viewed from overhead it looks like a double spiral. This ripple of the gravity pulses are called gravitational waves. The image to the right is a two-dimensional representation of gravitational waves generated by two neutron stars orbiting each other.
Apparently our gravity sensors are not sensitive enough yet to detect and discriminate the "ordinary" ripple of pairs of black holes orbiting each other throughout the universe. We needed to wait until a pair of large black holes spiraled down and merged to create a spike in the ripples that continuously surround us that was unique enough that we could discriminate it from the background noise. A merger does two things that help us discriminate them from the background noise. 1) As they are about to merge a large amount of the mass in the stars or black holes involved is getting burned off and per the physics law conservation of energy the system's mass is getting converted into energy. What I don't understand is apparently a significant amount of the energy released is form of gravitational energy. Thus, in the last few tenths of a second prior to merger the size of the ripples increases greatly. 2) The second thing that helps us discriminate a merger from the background noise is that the last few tenths of a second the orbiting pair is going faster and faster. Thus what we saw was a sudden increase in both the size and frequency of the ripples followed by some much smaller ripples as the pair was a single though misshapen blob and then it's a spherical though rotating blob and there are no more ripples from that source. The entire event took less than two tenths of second. We saw the last five orbits of the pair prior to the merger followed by first four rotations of the merged pair. --Marc Kupper|talk10:55, 15 February 2016 (UTC)
That is an interesting and possibly useful image. Correct me please if I am wrong, but aren't the waves spherical, with no directionality? This image illustrates nicely the double spiral but really should be seen as a cross section through the spherical waveform and here the amplitude is illustrated by the height of the wave, whereas a spherical wave would be better illustrated with dense and less dense zones radiating outward. Zedshort (talk) 00:27, 19 February 2016 (UTC)
As far as the Moon affecting the Earth in the form of tides, I think that effect is more akin to a dynamic response of the Earth's oceans to the rotation of the Earth in the presence of the Moon and would not be useful as a means of detecting gravitational waves. Zedshort (talk) 00:21, 19 February 2016 (UTC)
Signal and Astronomical Event get the same name? Comment
Does anyone know if the Name GW150914 is being applied to both the astrophysical event and the signals detected from astrophysical event GW150914?
This may be a fine point that doesn't matter, but the sources seem to use the name GW150914 for both the astronomical event and the signal from the event, but differentiate "signal" and "event".
Examples:
"To successfully detect a gravitational wave event like GW150914..."
"The gravitational-wave event GW150914"
"ARE WE SURE THAT GW150914 WAS A REAL ASTROPHYSICAL EVENT? The short answer is “yes”,
"GW150914 was indeed a real gravitational wave event"
OUR LIGO OBSERVATIONS AND WHAT THEY MEAN: "On September 14, 2015 at 09:50:45 Greenwich Mean Time the LIGO Hanford and Livingston Observatories both detected a signal from GW150914."
"signal GW150914"
"the coincident signal GW150914"
"observatories detected the coincident signal GW150914...recovered GW150914 as the most significant event from each detector for the observations reported here."
Yes, I said that before. Perhaps some will (or already do) use the name GW150914, not for the astronomical event, and not for the signal, but for the detection-of-the-signal-of-the-astronomical-event. Wait till the dust settles. Give it a few months before they find a new GW. Won't take long. - DVdm (talk) 16:57, 15 February 2016 (UTC)
Final orbital frequency
The text says: "The chirp signal lasted over 0.2 seconds, and increased in frequency and amplitude in about 8 cycles from 35 Hz to 250 Hz" and also, later: "The orbital frequency of 75 Hz (half the gravitational wave frequency)". 75 is not half of either 35 or 250. What's up there? Fig (talk) 16:53, 15 February 2016 (UTC)
The article states: "The waves given off by the cataclysmic merger of GW150914 reached Earth as a ripple in spacetime that changed the length of a 4-km LIGO arm by a ten thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star by one hair's width." Is this nearest star the Sun? The answer to this question would change the scale significantly... 206.186.37.200 (talk) 17:12, 16 February 2016 (UTC)
Maybe this is not the place for a general discussion, but in reading this article it brings to mind questions.
If a mass is stationary, I assume it warps space-time just by being. Would that mass, if large enough, be detectable or must it be moving?
It is believed that the three solar masses were converted into their energy equivalent at the wavelength of gravitational waves. Did this emission take place before they merged? I would assume that once combined, nothing would be emitted from the resulting black hole. Zedshort (talk) 17:39, 16 February 2016 (UTC)
Please read our article on black holes to see how to detect black holes. Since warping space means you bend light, the correctly placed light sources make black holes visible. (Or are you only referring to gravitational waves?) -- 70.51.200.135 (talk) 04:30, 17 February 2016 (UTC)
Geo600
This article says "GEO600 (near Hannover, Germany) was not sensitive enough to detect the signal", but GEO600 says "However, the Virgo interferometer in Italy, and the GEO600 were not operating at the time and so could not confirm the signal". Which is correct? Fig (talk) 23:18, 17 February 2016 (UTC)
Just as aLIGO, the GEO600 was in engineering mode when the signal was detected ([6]) (the official observations also started on Sep 18) But GEO600 was not sensitive enough anyway. "Not operating at the time" line must be changed. Cheers, BatteryIncluded (talk) 00:44, 18 February 2016 (UTC)
Hypothesis by Loeb
It seems to me the progenitor star was a binary, as I wrote initially.
Quote from Loebe's paper:
"We therefore conclude that the progenitor star must be rapidly rotating, not much below its break-up frequency. Such a progenitor could result from the merger of a binary star system with a common envelope. The appearance of a dumbbell configuration in a collapsing, rapidly rotating system was considered in the literature as a path towards the formation of common envelope massive star binaries through fission (Tohline 2002). For a sufficiently hard equation of state, a rapidly rotating configuration could produce a bar that breaks into two clumps of comparable masses (New & Tohline 1997), consistently with the similarity between M1 and M2 in GW150914."
I did that revert based on browsing mostly the introduction of the paper, which says
Below we explore the possibility that the GW and Gamma-Ray Burst (GRB) signals originated from a common origin, namely a single, rapidly-rotating, massive star.[2] As the core of the star collapsed, it broke into two clumps in a dumbbell configuration. The two clumps collapsed separately into two BHs which eventually merged due to GW emission.
On reading slightly closer (unfortunately my eyes are giving me trouble lately), the part you quoted speaks about how such a single star could form, initially, and mentioning a different but related question considered by Tohline. As far as I can see, all the rest of paper speaks about a single massive star. Over the whole history of the system, maybe it's just a matter of perspective, but Loeb clearly chooses to view it as a single star. --Ørjan (talk) 04:44, 21 February 2016 (UTC)
Maybe I understood incorrectly. I took the term "progenitor" binary star as the system that collapsed producing 2 black holes that merged immediately after the two stars' collapse. Perhaps he meant that the binary star merger formed a single massive star that much later gave rise to two black holes? Cheers, BatteryIncluded (talk) 06:26, 21 February 2016 (UTC)
That's how I interpreted it, at least. It seems to me that the initial merger could happen at any time from right after the stars are born, while the final split happens only when the merged star exhausts its fuel. A young merger also seems somewhat suggested by
Given that the core of the star needs to be more massive than M ∼ 65M⊙, the progenitor must be a very massive star with a total mass of hundreds of M⊙ or more. Such stars could form via collision runaway in young dense star clusters (Pan, Loeb & Kasen 2012; Vink 2015), and their mass loss through winds would be reduced at low metallicities.
I reverted another edit to this section that I am not convinced corresponds to what the article says:
An accretion from a long-lived disk (e.g., originating from the tidal disruption of an ordinary star) around the BH binary would be typically limited to the Eddington luminosity (Kamble & Kaplan 2013), which for a binary mass of M ∼ 65M⊙ amounts to ∼ 1040 erg s−1, a factor of ∼ 109 lower than the inferred γ-ray luminosity in GW150914-GBM.
I.e. this seems to me to imply that the GRB could not have been triggered "from the disk of matter that surrounded the original star", as the edit added. My previous impression was that the hypothesis derives the GRB from the infalling matter of the star itself. --Ørjan (talk) 02:19, 4 March 2016 (UTC)
As it stands the article gives undue weight to a single possible formation channel for the binary. There quite a few plausible formation channels out there (and more far fetched scenarios are appearing at the usual post big discovery rate). The more boring (but fairly likely) scenario is binary formed dynamical in dense cluster. We need to bring some more balance here.TR09:56, 4 March 2016 (UTC)
A misleading sentence...I think
I found and tagged the following for clarification: "At the very end of this process, the two objects will reach extreme velocities, and in the final fraction of a second of their merger a substantial amount of their mass[clarification needed] would theoretically be converted into gravitational energy, and travel outward as gravitational waves, allowing a greater than usual chance for detection."
The energy released was expressed as its mass equivalent, which I guess led someone to say that mass was in fact converted and radiated away as gravitational waves. I'm pretty sure that is wrong but am uncertain enough to not change it. Any mass within the black holes are completely lost to the rest of the universe and stays within the black hole as is any energy. There is essentially no radiation produced by conversion of mass to energy during this event. I doubt that there was much mass in the vicinity that could be converted. The energy converted has something to do with the warping of space-time and the ticking down of the orbits of the two masses. In expressing the energy conversion in terms of mass it might leave the casual reader to conclude that mass was in fact converted into energy. I think this needs to be be clarified. I see there is a great expansion of the section about mass, energy and momentum, but that requires a good deal more in depth reading. It might be useful to mention that the energy did not evolve from the conversion of mass as we know it into energy. I would assume that once combined, nothing would be emitted from the resulting black hole, not even gravitational radiation. Zedshort (talk) 18:37, 21 February 2016 (UTC)
I think the mass lost during the merger is radiated out as energy from the surfaces of the two event horizons, as they merge to become a single event horizon. Tayste (edits)18:57, 21 February 2016 (UTC)
That sound very vague. Do you know that for a fact? Neither mass nor energy can leave the black hole. Saying the mass is on the surface of the event horizon is obfuscation. Zedshort (talk) 20:52, 21 February 2016 (UTC)
I'm no expert, with only undergraduate physics training. Saying that mass cannot leave a black hole is an oversimplification, I suspect, and also a misunderstanding of general relativity in the context of two black holes merging. The references clearly say that a large amount of energy was radiated away via the gravitational waves. The only possible source for the energy is that the black holes lose mass somehow, via mass–energy equivalence. Black holes also lose mass via Hawking radiation. I'll leave it to the experts to clarify the article on these points. Tayste (edits)22:46, 21 February 2016 (UTC)
Once mass or energy crosses that horizon it is in to stay regardless of merging with another black hole. Hawking radiation is very, very, very weak. Yes, energy was radiated away but was a result of the degradation of the orbits of the two objects, which is apparently a function of something more basic about space-time. Zedshort (talk) 02:03, 22 February 2016 (UTC)
No clarification needed because Einstein already clarified it long ago: E=mc2. So yes, mass inside a black hole can be converted to energy. For a fact, we have observed X-ray jets ejected from many black holes, and now, gravitational waves. Cheers, BatteryIncluded (talk) 02:08, 22 February 2016 (UTC)
I believe that those X-ray jets are the result of normal matter (outside the BH boundary) interacting with the BH, they are not emitted by the BH. Zedshort (talk) 17:05, 22 February 2016 (UTC)
I'm no expert either, but from my impression of discussions elsewhere and assuming that black hole thermodynamics works analogously to normal thermodynamics, the thing that fundamentally cannot escape a black hole is neither mass nor energy but information, or equivalently (except for very slowly through Hawking radiation) entropy. For a single, non-rotating chargeless black hole, the entropy is proportional to the square of the mass, so such a black hole cannot lose mass/energy alone. But when two black holes merge, the square of the sum of their masses is greater than the sum of their squared masses, so then you can lose energy without increasing the total entropy. Also, it is supposedly possible to extract energy from a rotating black hole by the Penrose process. (I don't know about charged ones.) --Ørjan (talk) 05:00, 22 February 2016 (UTC)
The observation here is simple: The (rest) mass of the final black hole is smaller than the sum of the (rest) masses of the binary components. (The is completely as expected from theory).
So what is going on? Is energy escaping from inside the BHs? No not really. What is going on then? As the binary orbits its center of mass, energy is radiated away in GWs. As a consequence the binding energy of the binary is increased. Note that the total energy of the system is (Mass1) + (Mass2) [b]-[/b] binding energy. The mass of the final BH is simple the total energy in its center of mass frame (divided by c^2). In some sense you view this situation as the total mass of the BHs decreasing because they are absorbing negative energy. This is similar to what happens in the Penrose process. This OK aslong as the total area of the BHs does not decrease.TR10:34, 22 February 2016 (UTC)
Can this process be viewed as analogous to the rotation of two opposite sensed electric charges about a common point? Their orbiting would cause the emission of EM radiation. You say this is similar to the Penrose process. Are you using an analogy or is that in fact the process? I suppose you could view the orbit of one of those BH relative to the other. If one is entering the ergosphere of the other it would pick up energy from the one it is orbiting and in this case it would radiate energy. Would it radiate the energy over the entire spectrum including gravitational frequencies? I guess the Penrose process is the result of the twisting of space-time? In the article, it was suggested that 3 solar masses were converted to energy, while in the referenced article, it simply stated that the amount of energy was (3 solar mass)*c2. Should the article avoid the first and express the idea in the latter form? The universe is a weird place.
Also, could the waves be viewed as two spherical waves propagating isotropically i.e. with no directionality? In the illustrations in the article the waves are depicted as propagating in a plane. I suppose that illustration is a convenient cross section through the spherical wave and the amplitude of the waves illustrate the compression and expansion of space. Zedshort (talk) 17:05, 22 February 2016 (UTC)
The comparison with the Penrose process was by analogy, both involve BHs absorbing negative energy to lose mass (while still satisfying the area law). In the case of binaries losing mass in GWs during merger, there is no need for the BHs to be rotating. In fact, I'd have to doublecheck but I think even if you merge the BHs in a head on collision (i.e. without any angular momentum) you would still lose some mass.
The GWs produced by a binary are certainly not isotropic. (In fact it is not possible to spherical gravitational waves!) Roughly speaking at any time the GWs will be focussed along the directions of motion of the components. The final pattern ends up being quite complicated. TR20:22, 22 February 2016 (UTC)
"Gravitational wave speed" section and quote
The "Gravitational wave speed" section contains the following incorrect and misleadingly presented quote from the PhysicsWorld.con article:
The Institute of Physics member magazine Physics World reports that the first observation of gravitational waves on 14 September 2015 confirms "that gravitational waves travel at light speed and that [gravitons have] no mass, as predicted by general relativity."
Here is the actual quote from the article:
"... the LIGO researchers were also able to check a key prediction made by general relativity, which is that gravitational waves travel at the speed of light and that the currently unknown carriers of the force – often dubbed "gravitions" – are massless." ... "However, the [LIGO] data show no evidence that the gravitational waves were anomalously dispersed, as they would if gravity had some small mass."
It does not say that gravitons were proven to be massless, only that no evidence of mass was found. Failing to detect mass does not show that they are massless to arbitrary precision. All experiments have uncertainties and error bars. Is that clear? WolfmanSF (talk) 20:13, 23 February 2016 (UTC)
This is the quote that I drew from (last sentence third paragraph): "The data also showed that gravitational waves travel at light speed and that gravity has no mass, as predicted by general relativity."
I originally included the quote as:
The Institute of Physics member magazine Physics World reports that the first observation of gravitational waves on 14 September 2015 confirms "that gravitational waves travel at light speed and that gravity has no mass, as predicted by general relativity."
That is a faithful and accurate quote. Someone with handle BatteriesIncluded changed it to put in "gravitons have" without the standard use of square brackets. I fixed that and put in square brackets as per MOS.
Sorry, I looked at the "Testing Einstein" section and did not see the mention of the subject earlier in the article. So, forget what I said about quoting. However, my original objection is valid: it doesn't make sense to have have 2 consecutive subsections in the article that are discussing exactly the same subject. Furthermore, the first paragraph is more detailed and accurate, giving historical context. If there is something about that section that needs clarification, then lets deal with that, but we don't need a duplicate discussion under a new heading. WolfmanSF (talk) 01:54, 24 February 2016 (UTC)
You're wrong. The wavespeed of gravitational waves is what is salient. It's what people understand. It's also more adherent to the Theory of General Relativity, which says nothing about gravitons or mass thereof (which is a quantum phenomenon). We have a section about "Implications" of the detection of gravitational waves. This is one of the most salient implications, confirming a prediction of GR. 98.118.36.105 (talk) 03:03, 24 February 2016 (UTC)
Massless gravitons and gravitational waves traveling at the speed of light are 2 sides of the same coin. While the original wording of the first paragraph did not state that, it now does. That paragraph, sourced from technical articles rather than a press release, also explains that we already knew gravitons would have to be close to massless, i.e. that gravitational waves would have to travel at close to the speed of light, before the recent observations, and now we've reduced the uncertainty in that equivalence in some respects. That context is lost in the quote you favor, which makes it sound like this new measurement came out of the blue and there is now no uncertainty in the equivalence. WolfmanSF (talk) 05:15, 24 February 2016 (UTC)
Even though Battery got the last word in and no one attempted to violate 3RR and change it back, the page is protected for 24 hours. We should consider this:
Under the section "Implications", we have a subsection titled with and solely about a hypothetical elementary particle that does not exist in the canon of elementary particles. Not yet, anyway.
Now, unlike gravitational waves which were hypothetical until last September, gravitons continue to be hypothetical. They might not even exist. What is more, there is no need for gravitons in the theory of General relativity. But gravitational waves propagating at the same speed of lightdo exist in GR. And a salient property of these waves is their speed. Just as it would be for EM.
What is this LIGO (and others, such as VIRGO) trying to verify? A quantum gravity theory with particles? Or the established theory of General Relativity?
Why are we hiding, to the best of Battery's and Wolfman's ability, the salient finding, as reported in reliable sources, that this LIGO result confirms the reality of gravitational waves and a salient and fundamental property of those gravitational waves? And why are we trying to replace that salient finding, that is easily understood by the general public, with a more obscure finding about hypothetical particles that might not even exist, that relate to this salient property in an obscure manner (from the POV of the general reader, most readers do not know that particles that mediate action must be massless if they move at speed c)?
Now, from what I know, with only two detectors, perhaps this wavespeed of c is not verified. With that 7 ms delay and 3000 km separation between observatories (I dunno if that is the chord length or the arc length between the two), I can imagine a wavespeed possibly at 140% c. It seems to me that perhaps a third detector observing the same GW event is needed to verify both wavespeed and angle of incidence or direction of location of the source. But I am not a "reliable source". However there are reliable sources that are saying that this observation confirms the wavespeed of gravitational waves to be c and that is an extremely salient property of this fundamental interaction. Why is this being hidden from readers of this article. What is the technical authority that is obscuring this reported fact from a verifiable and reliable source?
The speed estimate did not come from the timing disparity between the two detectors (which would have comparatively low precision), but from the lack of observed dispersion in the waveform of the merger signal, via the reasoning presented in the paragraph. This reasoning is based on gravitons (see pp. 13-14 of "Tests of general relativity with GW150914"). WolfmanSF (talk) 08:00, 24 February 2016 (UTC)
I think we could make it clearer that limits set are limits on anomalous dispersion of GWs, which can be parameterized by a hypothetical graviton mass. In particular we should be clearer that this is a limit on "classical" physics and does not necessarily involve any form of quantum physics. But certainly this should all be discussed in a single section not two.TR12:57, 24 February 2016 (UTC)
Can we derive, under classical physics, a relation between vg/c, mg and gravitational wave frequency? Presenting the lower limit of vg/c for the stated upper limit of mg for the observed frequency (range) would largely resolve the main issue here. WolfmanSF (talk) 03:02, 25 February 2016 (UTC)
From [7] one easily gets with the "Compton wavelength of the graviton" (which is the classical, ie. h independent measure, of the "mass" of a classical field.)TR09:10, 25 February 2016 (UTC)
Note that any limit on the speed of light in this way is model dependent. In particular it depends on the functional form of the dispersion relation you get from introducing a mass term to the field. Other more exotic dispersion relations could lead to different limits on v_g.TR10:55, 26 February 2016 (UTC)
Effects
Can we say what the effects of these gravitational waves were for any locations near (relatively) to the merger? At our distance a billion light-years away, space-time stretched by "a thousandth of the width of a proton" - which obviously had no effects; but what about for an observer a couple of ly away? Would the huge intensity of the gravitational wave there have ripped planets apart as it passed? What would have been the space-time stretch at that location? Fig (talk) 13:07, 24 February 2016 (UTC)
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The second paragraph of this article contains the following words,
"The energy released during the final fraction of a second of the event was immense, with the energy of 3.0±0.5 c2 solar masses (1.8×10e54 ergs) radiated in less than half a second"
What is the reasoning behind the value of energy being quoted in ergs in parenthesis instead of the SI unit of energy, as in one of the companion papers published with the PRL paper? I would like to see it changed to 5.4x10e47 J as stated in this paper http://arxiv.org/abs/1602.03838
SJ 130.159.27.91 (talk) 12:55, 3 March 2016 (UTC)
The conversion is not currently correct. It is also not correct that this was emitted during the final half a second as this number is for the complete history. Hopefully now fixed. — BobQQ (talk) 18:16, 3 March 2016 (UTC)
Billions of years? The number is calculated as the difference in between the energy if the two black holes were infinitely separated and the final energy of the black hole, that is the energy radiated is E = [(m1 + m2) - Mf]c2, where m1 and m2 are the masses of the two black holes of the binary and Mf is the mass of the final black hole. (The calculation looks simple, but the tricky part is working out Mf). Most of the energy is radiated in the last second or so though, as the luminosity increases as the binary comes together, peaking around merger. — BobQQ (talk) 11:10, 4 March 2016 (UTC)
Thanks much for the explanation, but I still do not understand the origin of the energy that manifests itself as gravitational waves. Is the origin of the energy the potential energy that is converted into kinetic energy which is then converted into gravitational waves? Are the waves the result of the rotation of those masses about their Barycenter rather like how if two electrical charges orbited a center they would generate electromagnetic waves? As a result of those EM waves the rotation rate of those charges about each other would decline in proportion to the energy radiated a EM waves? As I understand it, mass that enters a BH is there to stay. Rotational kinetic energy can be extracted from a BH via the Penrose process if some external mass enters and leaves the ergosphere of the black hole. Are the two BH removing rotational energy from each other via that process? But if that is so they would need to escape their companion's ergosphere while they in fact don't as they merge. Is the energy radiated result of the decline of their orbits about their Barycenter the source of the gravitational wave energy or is the decline of their orbits the result of gravitational waves being generated. Inquiring minds would like to know. Zedshort (talk) 16:55, 4 March 2016 (UTC)
Heuristically, the energy in the GWs comes from the decreasing potential energy of the binary.TR19:53, 4 March 2016 (UTC)
This is probably the best way of thinking about it. It is difficult to pin down potential energy in general relativity, but you can think of it as like the mass defect when you fuse two atomic nuclei together (this time with gravitational binding energy). — BobQQ (talk) 10:25, 7 March 2016 (UTC)
It seems to me the authors of the original (Physical Review) paper simply label the inspiralling dense objects as black holes because they are denser than neutron stars. This is reasonable in a journal paper meant to be read by other astronomers, but in an encyclopedic article it might be better to refer to them as black hole candidates. Especially when their physical properties lie somewhat outside current black-hole models of formation. Some sort of reference may be wise to the "alternate candidates" discussion in the black hole article, so that readers of this article can get that background.
There is more to it than the objects simply being very dense in this case. The lack of (strong) EM counterpart signals for example excludes almost any alternative model involving material objects. (This event produced much more power in GWs than the rest of the visible universe produces in EM radiation, if even a fraction of this energy was released as EM radiation we would have seen it.)TR18:05, 5 March 2016 (UTC)
We can count this as the first direct observation of black holes. Model matching established the type of object. Anything as dense as a black hole, is a black hole afawk. Models of formation will have to change to accommodate the observation. After all formation has not been observed directly yet. Supernovae have been observed, but not so much is known of the remnants. Graeme Bartlett (talk) 11:19, 6 March 2016 (UTC)
. - DVdm (talk) 11:31, 14 February 2016 (UTC)
