English: This animation gives an insight into the method astronomers used to uncover a pair of supermassive black holes lurking 89 million light-years away from Earth in the NGC 7727 galaxy — and to measure their masses. The pair is the closest found to date, both with regards to the distance to Earth and the distance between the two supermassive black holes. Astronomers studied the spectra of the bright stars around each of the black holes using the MUSE instrument on ESO’s Very Large Telescope (VLT). More massive black holes have a stronger gravitational pull on the stars around them, causing them to move faster. This effect is reflected in the spectra of the stars, with the spectral lines being broader if the stars are moving faster. By measuring the width of the spectral lines for the groups of stars surrounding each black hole in the pair, astronomers calculated the masses to be about 154 million and 6.3 million times that of the Sun.