Supermassive Black Holes are Not Fussy Eaters

The core of M81 (Chandra/NASA)

By combining observations from a multitude of observatories, all looking at spiral galaxy M81, astronomers have taken a very close and intimate look at a supermassive black hole’s feeding habits. As supermassive black holes (of tens of millions of solar masses) and stellar black holes (of a few solar masses) exist in entirely different environments, astrophysicists were uncertain as to what supermassive black holes feed on. Stellar black holes eat away at the gas from companion stars, creating an accretion disk, generating a range of emissions as stellar gas falls into the disk. But where do supermassive black holes get their food? It turns out they feed off gas in the central region of galactic cores, generating similar emissions as their smaller stellar cousins. What’s more, this finding supports Einstein’s theory that all black holes, regardless of mass, share the same characteristics…

Supermassive black holes have only recently been discovered to live in the majority of galactic cores, so it is little wonder astronomers are only just beginning to understand what is on the supermassive’s menu. There has been some strange and wonderful research looking at supermassive black holes hiding in the depths of galactic nuclei. My favourites include the theory that black holes dislike dark matter and the observations of the “death scream” of a star falling into one of these galactic heavyweights. However, this is the first time that astronomers have been able to work out that supermassive and stellar black holes consume similar material. This is important when characterizing the range of black holes that are possible in the Universe and gives a special insight to the dynamics of the most massive known bodies in the cosmos.

New observations by the Chandra X-ray telescope and Earth-based telescopes have been combined with advanced theoretical models during a campaign looking deep into the M81 spiral galaxy. And the result? It turns out the M81 supermassive black hole feeds just like a stellar black hole.

Chandra was backed up with data from three radio telescope arrays (the Giant Meterwave Radio Telescope, the Very Large Array and the Very Long Baseline Array), two millimetre-wavelength telescopes (the Plateau de Bure Interferometer and the Submillimeter Array) and the optical Lick Observatory to detect the range of emissions coming from the heart of M81. It was very important to take simultaneous observations with all instruments so any transient events or other brightness variations did not cause observational error. Chandra was chosen as the ideal X-ray observatory as the spacecraft’s instruments can distinguish between the faint X-ray emissions from a feeding supermassive black hole and the rest of the parent galaxy.

On studying data from the observatories, Sera Markoff from the University of Amsterdam and research team leader, used theoretical models that simulate a disk of material spinning around the supermassive black hole. In the model, as the disk gases fall toward the black hole they should generate X-rays and optical light. Just outside the black hole’s event horizon there should be a volume of hot gas generating ultraviolet and X-ray emissions. In addition to this, the black hole should be generating radio and X-ray emitting jets. By using different simultaneous studies of the emissions from the supermassive black hole in the centre of M81, these theoretical results match up with observation. It seems that the M81 emissions match the emissions from the smaller stellar black holes.

This confirms that the feeding patterns for black holes of different sizes can be very similar. We thought this was the case, but up until now we haven’t been able to nail it.” – Sera Markoff, Astronomical Institute, University of Amsterdam in the Netherlands, research leader.

These results should help astronomers identify illusive intermediate black holes, also supporting Einstein’s theory of general relativity in that it helps to explain that black holes, no matter what their mass, develop via similar mechanisms.

Sources: Chandra, Chandra press release

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