Galaxy Interactions Could Cause Overweight Black Holes


Yep. It’s true. Almost all galaxies are guilty of having a supermassive black hole in their centers. Some even tip the scales at millions – or even billions – of times more mass than the Sun. However, how they came to be so weighty is a true enigma. Thanks to research done by Dr. John Silverman (IPMU) and the international COSMOS team, the Chandra X-Ray Observatory and the European Southern Observatory’s Very Large Telescope have revealed that galaxy interactions may be responsible for the growth of supermassive black holes – and they’ve left behind some very important clues…

If you’re big – you’re big. As a general rule, supermassive black holes like to hang out in massive galaxies. Their mass is usually directly related to the central bulge. Now the consensus is that massive galaxies gained their girth (at least in part) by mergers and interactions with smaller galaxies. This act of cannibalism in galactic evolution has been postulated to explain how matter gathers toward the middle, eventually resulting in a supermassive black hole.

How do we determine this? One way is to take a closer look at galaxies currently in merger as compared to ones in isolation. While the concept is easy, carrying out the test hasn’t been. A supermassive black hole leaves visual observations “blinded by the light” while a quasar can effectively “outshine” an entire host galaxy, leaving an interactor almost impossible to detect. But, like a bulging waistline, such interactions should distort the overall contours of the galaxy.

Now the COSMOS team might have an answer to the riddle.. by assuming a galaxy is interacting if it has a nearby neighbor. It’s a test that can happen without needing to know if distortion is present in optical images. What makes it possible are accurate distance measurements of about 20,000 galaxies in the COSMOS field as provided by the zCOSMOS redshift survey with the European Southern Observatory’s Very Large Telescope. Isolated galaxies are used to give a comparison sample to lay the foundation as to whether an active galactic nucleus is common to interacting galaxies. With help from NASA’s Chandra Observatory, X-ray observations pinpoint galaxies which host an AGN. The X-ray emission signature dominates in growing SMBHs and X-rays are capable of cutting through the gas and dust of star-forming regions.

In their report to The Astrophysical Journal the team states that galaxies in close pairs are twice as likely to harbor AGNs as compared to galaxies in isolation. This answer may prove that beginning galaxy interactions can lead to “enhanced black hole growth”. Because it’s not a drastically common occcurrance, it means that only about 20% of SMBHs that break the scale happen via a merger event and that “final coalescence” might also play a role.

One thing we do know is that galaxies and their black holes, like people and their waistlines, all get a little heavier with time.

Original Story Source: Institute for Physics and Mathematics of the Univserse.

8 Replies to “Galaxy Interactions Could Cause Overweight Black Holes”

  1. Just how big can a black hole get, can it keep growing forever or is there a critical mass, if so when reached or exceeded what happen’s

    1. I don’t think there is prediction of a mass limit in theory. (Layman here.)

      In practice, it seems the limit is how much mass can feed the SMBH. Galaxy cluster masses and speeds becomes only so much, and that decides the maximum possible SMBH mass assuming everything else alike.

  2. “…only about 20% of SMBHs that break the scale happen via a merger event and that “final coalescence” might also play a role.”

    This brings up the question of what accounts for the other 80% of AGNs. Besides the “final coalescence” stages of a major merger, accretion of materiel from the nearby galactic environment (or the IGM) and minor mergers with dwarf galaxies may be mechanisms to feed these AGNs.

  3. Of course the egg comes before the chicken, how else? It’s that first chicken that raises eyebrows – like how and where?

    Been going thru the data over and over.. thinking about it and dreaming about it. I’ve read and re-read all the currently reasonable explanations I can lay my hands on (and understand) and yet none of them provide the final-final definitive answer(s). It seems as though the logic and the numbers simply don’t add up by themselves… yet, here we are. (Just goes to show, that no matter where you are, there you are!)

    As a result, I’ve decided to follow my intuition, which goes something like this analogy. In nature, all life begins from a seed stock – that being the germination by two separate yet compatible (For lack of a better term) zygotes. In biology, it’s the sperm and the egg, while in the sub atomic world it appears to be the neutron and the proton (Or conversely the neutron and anti-proton) forming the basic atom or particle of anti-matter? This observation does not take into account scale differences where the ‘zygote’ is almost infinitely larger in comparison to individual sub-atomic particles or waves but joined conceptually, seem to indicate evidence of a fractal continuum.

    Back to the atom: Were the above ‘logic’ to be continuously applied (I AM addressing this article!), then each atom might contain a quantum scale ‘black hole’ at it’s gravitational center… thus forming the primal ‘seed stock’ around which particles/waveforms are drawn into an aggregation. This ‘seed stock’ eventually congealing ‘upwards’ into molecules. Which might then appear to be an exponentially scaled fractal ‘seed stock’ for ever larger scaled physical bodies… all the way up to and including galactic clusters and even larger structures.

    Whew! Still with me? So where did the original atom come from? so spontaneously and ubiquitously throughout the known universe? Am leaning toward the ‘quantum foam’ concept and slightly away from the ‘big boom’ – that idea being that all matter (in space/time) is representative of a multi-dimensional phenomena where infinite yet disparate elements of those dimensions collide…

    Please forgive my naivete in the above simplistic rendering. The bottom line that I wished to establish with this comment is that ‘the egg came before the chicken’, or rather, that black holes must have come before galaxies…. later joining to form ever larger black holes.. and that our universe is part of a much larger reality… I hear brain cells popping, and see dead people turning over in their graves… ~*~

    1. Of course the egg comes before the chicken, how else? It’s that first chicken that raises eyebrows – like how and where?

      Since this is a science blog, if I may: this is nonsense biologically.

      Egg use evolved long before the first birds. (With all of us fishes, actually.) Likewise, the first populations evolved way before sexuality, hence plant or fungal spores or animal eggs, evolved.

      The observation of bottlenecks such as chicken-and-egg problems points to evolution as the natural resolution, while trying to resolving it as a static system is based on creationist ‘poofing’ ideas.

      The rest of your comment is like that. Standard cosmology makes a prediction of how the first particles appear: inflation makes a universe homogeneous and reheating after inflation creates elementary particles everywhere.

      In the end you make a claim ultimately based on such creationist fantasies, clothed in terms of processes. Good luck with convincing anyone of that.

      1. Creationist? Not…. My analogy was bent toward taking a common folk idiom and using it to make sense of the growth of a black hole. However you want to look at it life on Earth is undoubtedly _part_ of the cosmos! As such, it’s continual evolution MAY provide clues into external processes… i.e. the microcosm mimicking the macrocosm through a fractal growth analogy.

        The controversial part of my statement is not related to creationism at all, instead the idea of quantum level black holes, as MAY be found to exist in every atom as part of a ‘quantum foam’, is at the core of my entire statement.

  4. To bad sound waves do not travel through vacuum – otherwise we could just put our very sensitive microphones on those fat BHs just to check if we could hear… “Om Nom Nom Nom”.


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