Trapezium Cluster

For other stars with this Bayer designation, see θ Orionis.

Trapezium
Trapezium in optical (left) and infrared light (right) from Hubble. NASA photo
Observation data (J2000 epoch)
Right ascension	05h 35.4m
Declination	−05° 27′
Distance	1,344±20 ly (412 pc)
Apparent magnitude (V)	4.0
Apparent dimensions (V)	47 (seconds of arc)
Physical characteristics
Mass	? M☉
Radius	10 ly
Estimated age	300,000 years
Associations
Constellation	Orion

Three of the main stars of the Trapezium, with the triple star in the top right, as sketched by Galileo. The letters do not correspond to the current designations.

The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta¹ Orionis (θ¹ Orionis), is a tight open cluster of stars in the heart of the Orion Nebula, in the constellation of Orion. It was discovered by Galileo Galilei. On 4 February 1617 he sketched three of the stars (A, C and D), but missed the surrounding nebulosity. A fourth component (B) was identified by several observers in 1673, and several more components were discovered later like E, for a total of eight by 1888. Subsequently, several of the stars were determined to be binaries. Telescopes of amateur astronomers from about 5-inch (130 mm) aperture can resolve six stars under good seeing conditions.

The Trapezium is a relatively young cluster that has formed directly out of the parent nebula. The five brightest stars are on the order of 15 to 30 solar masses in size. They are within a diameter of 1.5 light-years of each other and are responsible for much of the illumination of the surrounding nebula. The Trapezium may be a sub-component of the larger Orion Nebula Cluster, a grouping of about 2,000 stars within a diameter of 20 light-years.

Identification

The Trapezium is most readily identifiable by the asterism of four relatively bright stars for which it is named. The four are often identified as A, B, C and D in order of increasing right ascension. The brightest of the four stars is C, or Theta¹ Orionis C, with an apparent magnitude of 5.13. Both A and B have been identified as eclipsing binaries.

Infrared images of the Trapezium are better able to penetrate the surrounding clouds of dust, and have located many more stellar components. About half the stars within the cluster have been found to contain evaporating circumstellar disks, a likely precursor to planetary formation. In addition, brown dwarfs and low-mass runaway stars have been identified.

Possible black hole

A 2012 paper suggests an intermediate-mass black hole with a mass more than 100 times that of the Sun may be present within the Trapezium, something that could explain the large velocity dispersion of the stars of the cluster.

• 
  One of the components of the cluster (Theta¹ Orionis F, lower left) is a double star.
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  The Chandra X-ray Observatory view of the Orion Nebula
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  Trapezium star identification
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  Hubble detail of a region west of the Trapezium, showing arcs and bubbles formed when stellar winds collide with existing interstellar material
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  A wider shot of the core details showing the trapezium in context of the surrounding nebulae
• 
  Core detail of the nebula with all the stars identified

List of stars

Main article: Theta Orionis

Star	Stellar components
A	A1, A2, A3
B	B1, B2, B3, B4, B5
C	C1, C2
D	/
E	E1, E2
F	F1, F2
G	/
H	/

Further reading

• Lada, E. A.; et al. (1996). "Circumstellar Disks in the Trapezium Cluster". Bulletin of the American Astronomical Society. 28: 1342. Bibcode:1996AAS...189.5301L.
• Poveda, Arcadio; et al. (2005). "Low-Mass Runaway Stars from the Orion Trapezium Cluster". Astrophysical Journal. 627 (1): L61–L64. arXiv:astro-ph/0506002. Bibcode:2005ApJ...627L..61P. doi:10.1086/432053. S2CID 1145928.

External links

• Chandra Observatory Uncovers Hot Stars In The Making, MIT Press Release, 2000.
• Astronomy Picture of the Day - In the Center of the Trapezium 2003 March 2
• Observing the Trapezium