Black holes take a bite out of galaxies

AGN Feed in Distant GalaxiesAstronomers usually try to educate the public that black holes do not go around actively eating the hearts out of galaxies. Usually. On July 24, astronomers announced that in the early days of the universe large numbers of young supermassive black holes actually spent their days feeding on galaxy cores. (image credit: NASA/CXC/Ohio State Univ./J.Eastman et al.)

“The black holes in these early [galaxy] clusters are like piranha in a very well-fed aquarium,” said Jason Eastman of the Ohio State University and first author of this study.

While there are some feeding supermassive black holes (technically called Active Galactic Nuclei or AGN) in the modern universe, they are rare. Using the Chandra X-ray Observatory, Eastman’s team found that when the universe was 8 billion years old there were 20 times more AGN than there were when it was 11.2 billion years old. Today, the universe is 13.7 billion years old and there are no nearby AGN.

In the early universe, galaxies were rich in dust and gas that could be used to form stars or to feed AGN. When the AGN gobble the dust and gas, they often burp out high-energy jets and expel blasts of X-rays that stifle star formation, leaving galaxies devoid of stellar nurseries.


  1. Astrogeek July 28, 2007 at 2:24 am #

    yow! There’s either a black hole munching on this post, or something’s wrong with the code, because I’m seeing a bunch of HTML instead of your usual smooth writing.

    What are the theories as to the cause for the current rarity of AGN? Is it simply that the black holes have consumed all of the nearby matter in the galactic cores and are therefore quiescent, or is there another mechanism?

  2. Kevin July 28, 2007 at 8:15 am #

    Yeah, Pamela, lots of html codes showing up by mistake. Makes it a challenge to read. 🙂

    According to what I read, as a galaxy gets older there is less gas, nearby stars, etc. for the “piranha black holes” to feed upon. When the galaxy’s newer, there’s lots of yummy snacks.

  3. Joanna July 28, 2007 at 8:23 am #

    I’m slightly disturbed by the idea of black holes as piranhas *shudder*

    BTW whilst your new layout looks lovely in firefox, it’s horribly broken in opera 🙁

  4. pamela July 28, 2007 at 8:58 am #

    Okay, so I’m clearly still getting used to the new version of WordPress I installed. I’m sorry for the confusion. I think the HTML chaos is now fixed.

    Joanna, if you could email me a screen shot of what it looks like in opera, I would be very grateful.

  5. Torchwood July 28, 2007 at 9:00 am #

    That’s better, lol!

  6. Torchwood July 28, 2007 at 9:04 am #

    Everything looks fine in Explorer
    Seems that ‘p’ before the image link was what sent the whole thing helter skelter.

  7. Kevin July 28, 2007 at 9:45 am #


    Did you get my email about the layout problem I’m seeing in Firefox?

    Not that I personally care to look, but if I want to see the ads on the right side of the page I would have to scroll right.

  8. Krishna July 28, 2007 at 10:57 am #

    “While there are some feeding supermassive black holes (technically called Active Galactic Nuclei or AGN) in the modern universe, they are rare.”

    Really? For some reason, I thought that most galactic cores, including our own Milky Way, had a supermassive black hole at the center. Did I just make that up (entirely possible), or did the scientific consensus change in some way recently.

  9. pamela July 28, 2007 at 2:00 pm #

    As far as we know, all galaxies have supermassive black holes. Feeding supermassive black holes are called AGN, and those are what are rare. (I guess that means most supermassive black holes are fasting)

  10. Quasar9 July 29, 2007 at 3:44 am #

    lol Pamela,
    also most pictures or animations of galaxies and blackholes can be a little misleading. Rather than a pin prick in the middle of the galaxy – we are talking of circumferences far greater than that of our solar system. It could be that there is a limit to the reach of a blackhole (its boundary) – and once it has consumed or recycled everything within its grasp, it cannot reach for anything more, and becomes dormant … (until more reaches its path)
    or simply once its had its fill it becomes stable and cannot accrete anymore, and like the Sun in our Solar system it settles into a somewhat ‘peaceful’ mode, with the galaxy orbiting around it.
    Maybe we’ll get a closer look one day.

  11. Astrogeek July 31, 2007 at 2:28 pm #

    *All* galaxies, or all *large* galaxies? What about the Sgr Dwarf that our Milky Way is currently consuming, or the SMC and LMC?

  12. pamela July 31, 2007 at 3:04 pm #

    Not all supermassive black holes are created equal. There are small ones in small galaxies and large ones in large galaxies. Only the ones in large galaxies (and the LMC, CMC, and dSph Sag don’t count) are known (as near as I can tell) to have AGNs.

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  14. Astrogeek August 2, 2007 at 11:03 am #

    Wow, I hadn’t known that. So does that tend to tip the ‘which came first’ question more toward the idea that ‘galaxies form around black holes’ over the ‘black holes are formed in the center of galaxies’ school of thought?

  15. pamela August 2, 2007 at 11:10 am #

    We still don’t know the chicken and the egg of galaxies and supermassive black holes. What we do know is dark matter over densities came first, and the other stuff fell into those over densities.

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