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Some supermassive black holes may not be so super after all

The views expressed are those of the author and are not necessarily those of Scientific American.


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Black hole with accretion disk and jetBlack holes are the most massive compact objects in the universe—the supermassive variety are millions or even billions of times the mass of the sun. But new research may take these cosmic colossi down a peg or two.

According to an analysis in the February 17 issue of Nature, the masses of supermassive black holes at the cores of distant, luminous galaxies, known as active galactic nuclei (AGNs), have been overestimated by a factor of at least two. (Scientific American is part of Nature Publishing Group.)

Active galaxies give off bright radiation from their cores, where gas heats up as it is compressed into a swirling accretion disk encircling the black hole. The radiating region is too small to resolve telescopically at intergalactic distances, so researchers have turned to spectroscopy—splitting the radiation from an AGN into its component wavelengths—to get an idea of what goes on near an AGN’s black hole.

Spectral signals of individual atoms—say, the light emitted when a hydrogen atom is ionized—do not show up as discrete, narrow spikes at a specific wavelength. Rather, Doppler shifts spread them into wide lines surrounding that wavelength. The Doppler effect arises as the material swirls around the disk at thousands of kilometers per second. (The effect is analogous to standing at one end of a speedway—the pitch of a race car’s engine will rise and fall as it continuously approaches and then recedes from your vantage point.) Wolfram Kollatschny and Matthias Zetzl of the Institute for Astrophysics Göttingen in Germany used those smeared spectral lines from 37 AGNs to determine how much of the widening results from the disk’s rotation around the black hole, and how much results from turbulence and other phenomena.

Kollatschny and Zetzl’s analysis found that rotation is the primary driver of spectral line widening, allowing them to use the width of measured hydrogen lines to infer the velocity of the swirling gas and hence the mass of the object at the disk’s center. Their method indicates that the mass of distant AGN black holes as estimated by other spectral methods is two to 10 times too high.

That is not enough to cost supermassive black holes their title as heavyweight champs of the universe, but it may nonetheless affect studies of the formation and growth of black holes and the galaxies that feed them.

Artist’s conception of gas swirling around a black hole: NASA/Dana Berry, SkyWorks Digital





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  1. 1. Wayne Williamson 5:20 pm 02/23/2011

    stew6302…where’s the center?…if everything came from a point(big bang) then anywhere is the center…

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  2. 2. mo98 2:45 pm 02/24/2011

    What is not clear is whether this changes the estimate of the mass of any of the galaxies studied as whole or does it simply redefine the inflated distribution of it near the black hole? Would the uneven distribution of dark matter then possibly follow some sort of reversal and display a proportionality to its density when it borders the Schwarzschild radius as well?

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  3. 3. bucketofsquid 4:14 pm 02/24/2011

    If the super massive black hole is only half or less the mass it was originally assigned then the entire "dark matter" situation has just changed. Either we need a lot more or a lot less of it to explain the bad math of galactic expansion. I’m not skilled enough in cosmology to know which way the change goes but it means a lot if these researchers are correct.

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  4. 4. MTpackrat 7:12 pm 02/24/2011

    The current expansion of the universe hypothesis states that space itself is expanding everywhere. Why doesn’t the mass that occupies that space not expand also? Does this mean that gravity overcomes the expansion? or is the concept of space just a convenient fiction to explain some observations?

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  5. 5. Wilhelmus de Wilde 4:03 am 02/25/2011

    I am not a professional cosmologist , but when we look at the limites of our observable (measurable) universe then we reacht the Planck scale which means the lenght of 10^-33cm, use this as the diameter of a sphere, take the Planck mass 2,18.10^-8kg, take the diameter of a given black hole (assumed) and the product of the two will give you the maximum mass of the black hole, or am making a serious mistake ?

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  6. 6. suitti 10:03 am 04/7/2011

    At the time of the Big Bang, the Universe must have been at least as large as the currently visible portion. If that was not true, we would not see the Cosmic Microwave Background Radiation, which has been coming toward us since nearly the start. But, the Universe was so dense that the stuff in the currently visible portion was about the size of a proton (more or less a point). This means that 1) the Universe is really big, and 2) the idea of a center of the Universe is not very helpful even if it exists. The Universe may be infinite in size.

    The Milky Way’s millions of solar masses central black hole is a tiny fraction of the mass of the 100′s of billions of stars galaxy. So while there may be some modification to the estimate of how much Dark Matter there may be, my guess is that the change is less than the current error bar of the estimate. The estimate for Dark Matter would go up. Dark matter distribution isn’t uniform across galaxies. Current thinking is that if you can get Dark Matter particles into the event horizon, they become part of the black hole. But as Dark Matter particles don’t engage in friction, black holes do not efficiently consume dark matter.

    The expansion of space does not create matter. It’s not at all clear that Dark Energy is anything that can power a toaster even in principal. So Dark Energy, which is increasing as the Universe expands, can not be converted into matter. The energy budget of the Universe isn’t changing. Gravity is not slowing the expansion of the Universe as expected. Dark Energy, whatever that is, is causing the Universe’s expansion to accelerate. Galaxies aren’t expanding – they’re gravitationally bound. The Universe’s expansion is a very small effect on the scale of a galaxy.

    The event horizon (Schwarzschild radius) increases as mass is added to a black hole. Oddly, the density of the black hole (as measured at the event horizon) goes down as mass is added. While it isn’t known what exactly goes on inside a black hole, there are no known mass limits for black holes. You can always add more. There is a growth speed limit for accretion of gas. But you can easily increase the mass faster by having a black hole eat a star, a neutron star, or have two black holes merge, for example.

    Having better ways to get measurement estimates is a good thing. Hopefully the Nature article stimulates further research to confirm or refute this finding.

    Black holes are hard to find, because, well, they’re black. Look in black socks?

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  7. 7. Wilhelmus de Wilde 11:54 am 04/7/2011

    Dear Suiiti,

    Was there a BB ? I dont think so, if you agree that the BB exists you agree on singulairities in our Universe, they cannot exist because we have limits (see my post above), you are right when you say that the origin of our universe is "now" everywhere, going back to the limits Planck length and time) of our Universe we meet the same limit of comprehensability. (see also my essay on FQXi (http://www.fqxi.org/community/forum/topic/913)

    Dark matter is a theory, it isn’t a fact, we are troubled by the fact that the movement of the milky ways and so is not in accordance with the the Newton gravitational laws, perhaps MOND is better, but also that is a theory, scientists just don’t know, so it not at all good to take for truth dark matter.

    You say : "The extension of space does not create matter", if there is more space there is more vacuuum, so more particles "pop up".
    It is not at all sure that dark matter increase when the universe expands (see above), this is just as many other rhings in physics an assumption based on a theory .

    There are mass limits for black holes as we have limits in our universe, this is the same error as in the existence of a singulairity.

    When your toes are in a black sock, there are still a part of yourself, obeing the same "laws" that your body is listening to,your consciousness is aware of your toes even if they are far away from your brain. Everything that seems to be far away from your brain, toes, black hole of our milky way, origin of our Universe (or point of rebundance ?) CAN be reality if not in our reality then in another…

    have fun… (took that from dr. Cosmic Ray)

    Wilhelmus

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