Turning On A Supermassive Black Hole

Article written: 14 Jul , 2011
Updated: 24 Dec , 2015
by

[/caption]

ESO’s Very Large Telescope and ESA’s XMM-Newton X-ray Space Observatory has just opened our eyes once again. While we thought that the massive black holes that lurk at the center of large galaxies (and they always lurk, don’t they? they never just lay about, lallygag, or loiter…) for the last 11 billion years were turned on by mergers, we’re finding out it just might not be so.

For all astronomers, we’re aware that galactic structure involves a mostly quiescent central black hole. But as we reach further out into the Universe, we’re finding that early, brighter galaxies have a middle monster – one which appears to be noshing on a material that emits intense radiation. So if a galaxy merger isn’t responsible, then where does the material originate to ignite a quiet black hole into an active galactic nucleus? Maybe the omni-present dark matter…

Viola Allevato (Max-Planck-Institut für Plasmaphysik; Excellence Cluster Universe, Garching, Germany) and an international team of scientists from the COSMOS collaboration have studied 600 active galaxies in an intensively mapped region called the COSMOS field. Spanning an area consisting of about five degrees of celestial real estate in the constellation of Sextans, the COSMOS field has been richly observed by multiple telescopes at multiple wavelengths. This gives astronomers a great “picture” from which to draw data.

What they found was pretty much what they had expected – most of the active galaxies in the past 11 billion years were only moderately bright. But what they weren’t prepared to understand is why the majority of these more common, less bright active galaxies weren’t triggered by mergers. It’s a problematic situation that had previously been tackled by the Hubble Space Telescope, but COSMOS is looking back even further in time and with greater detail – a three-dimensional map showing where the active galaxies reside. “It took more than five years, but we were able to provide one of the largest and most complete inventories of active galaxies in the X-ray sky,” said Marcella Brusa, one of the authors of the study.

These new charts could help further our understanding of distribution as the universe aged and further refine modeling techniques. The new information also points to active galactic nuclei being hosted in large galaxies with abundances of dark matter… against popular theory. “These new results give us a new insight into how supermassive black holes start their meals,” said Viola Allevato, who is lead author on the new paper. “They indicate that black holes are usually fed by processes within the galaxy itself, such as disc instabilities and starbursts, as opposed to galaxy collisions.”

Alexis Finoguenov, who supervised the work, concludes: “Even in the distant past, up to almost 11 billion years ago, galaxy collisions can only account for a small percentage of the moderately bright active galaxies. At that time galaxies were closer together so mergers were expected to be more frequent than in the more recent past, so the new results are all the more surprising.”

Original News Source: ESO Press Release.


6 Responses

  1. Anonymous says

    AGN triggering is a very complex question, and in reality, we are probably looking to establish the relative contributions to triggering of multiple different mechanisms and the circumstances under which each dominate, rather than figuring which mechanism is solely responsible for the phenomenon.

    For example, internal stochastic processes such as bar instabilities should be able to trigger the moderate and lower luminosity AGN, but it’s hard to get them to feed enough material to the central regions of galaxies to power the high luminosity beasts. That at the moment still seems to require mergers. Certainly though, the evidence is mounting that in most circumstances, AGN can be triggered through mechanisms other than mergers.

    Another interesting possibility are minor mergers – mergers between galaxies and small gas rich companions. These are hard to detect and even harder to study, but both computer simulations and observations seem to suggest they are a viable triggering mechanism.

    Anyway – the rabbit hole goes deeper and deeper still… 🙂

  2. Anonymous says

    I have pondered this some. The merger of two galaxies with 10^8 solar mass black holes is likely not to provide much “friction” to slow the relative motion of the two SMBHs enough so they would coalesce. A 10^8 solar mass black hole is not likely to be slowed down much by gobbling up stars or nebula. So the two SMBHs are then likely to keep orbiting about each other with little to perturb their orbits into a tighter inspiral and merger.

    LC

  3. Anonymous says

    I have pondered this some. The merger of two galaxies with 10^8 solar mass black holes is likely not to provide much “friction” to slow the relative motion of the two SMBHs enough so they would coalesce. A 10^8 solar mass black hole is not likely to be slowed down much by gobbling up stars or nebula. So the two SMBHs are then likely to keep orbiting about each other with little to perturb their orbits into a tighter inspiral and merger.

    LC

    • Torbjörn Larsson says

      OTOH if every galaxy bears an initial SMBH, and a late large galaxy such as ours is a merger of some ~ 30 dwarf galaxies (IIRC), where are all the SMBHs?

      Also, isn’t SMBH mergers supposed to explain most of SMBH spin?

      Conversely, SMBHs should be able to merge without having the whole galaxy start to feed them towards becoming an AGN.

      • Anonymous says

        I spend most of my time worried about supersymmetric BPS black holes and nilpotent orbits on moduli spaces for extremal black holes and the like. I and a colleague have worked out some elliptic curve cohomology for quantum fields with these and … . These are quantum black holes, so my focus tends to be on the string-field theory aspects of black holes. These thundering huge things are classical black holes, which is on the other scale of things.

        It is hard to grow a black hole, in spite of the enormous gravity they have near their event horizons. A projectile sent into a black hole has to be pretty much dead on to get in. If not the projectile goes into an orbit. So to grow a black hole you must have “friction.’ An accretion disk is a nice way to grow a black hole. If you have two galaxies which collide their SMBHs are likely to miss each other by thousands of light years. The two will go into a mutual orbit, which is perturbed by the large amount of matter in the coalesced galaxy. I am not a modeler of these things, but my physical sense is that it would take an enormous amount of time for the two SMBHs to merge by the interaction of these two black holes with the rest of the merged galactic material. The rest of the material provides the friction.

        On of these UT topics a week ago was the assessment that galaxies grew more by accreting on gas than by violent mergers. So this might explain the absence of other SMBHs. Maybe dwarf galaxies do not so much violently collide with a larger galaxy, but have a number of grazing collisions where they lose material and stars, but they persist as reduced objects.

        These questions tend to involve astrophysical modeling that is a bit out of my league. Yet my sense is that with galaxy collisions it probably takes a long time for their black hole cores to eventually coalesce.

        LC

  4. Member
    IVAN3MAN_AT_LARGE says

    For convenience, click here for the direct link to the research paper (PDF).

Leave a Reply