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How did supermassive black holes get so big and chonky? Scientists still don't know.

An artist's depiction of a supermassive black hole.
An artist's depiction of a supermassive black hole.
(Image: © NASA/JPL-Caltech)

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of "Your Place in the Universe." Sutter contributed this article to's Expert Voices: Op-Ed & Insights

Active galaxies are by far the brightest objects in the universe, and they are powered by monster black holes that lie at their centers. But finding the origins of those giant black holes has proven challenging for astronomers. New observations underscore that difficulty.

Although simulations suggest that black holes should grow quickly in the early universe, when astronomers look back in time they simply cannot find many such structures. That struggle continues even now, with new research that describes a hunt for such objects.

The making of a monster

Let's backtrack. The largest black holes in the universe are real whoppers, millions and even billions of times more massive than the sun. To reach such incredible sizes they've consumed an all-you-can-eat buffet of gas over billions of years, constantly gorging themselves on whatever falls into their gravitational embrace.

But these supermassive black holes must have also started off larger than average, to give them a jumpstart in their path to cosmic corpulence. We're not exactly sure what seeded the universe's supermassive black holes, but there are two main schools of thought.

Related: Images: Peering back to the Big Bang & early universe

In one line of thinking, supermassive black holes got their start with the first generations of stars to appear in the cosmos. These stars, made of pure hydrogen and helium (because there weren't any heavier elements around back then), grew to massive proportions, perhaps as much as hundreds of times the size of the sun. They lived fast and died quickly in titanic supernova explosions, leaving behind collapsed cores — the first big black holes.

Or, perhaps the first and biggest black holes were never stars at all. Instead, perhaps such objects formed when a cloud of gas went unstable and collapsed. That would explain why massive black holes appear so early in cosmic history, and how they could get so big so quickly.

Blaze of glory

Whatever the case, the seeds of today's monsters were laid in the very early universe, when it was less than a billion years old. But, as big as these objects were when they were born, they still had to gorge themselves to become the true monsters that they are today. Computer simulations of the behavior of stars, black holes, galaxies and gas in the early universe suggest that these black holes grew quickly, reaching their hulking state within just a few hundred million years of their formation.

Astronomers know how to spot such gorging black holes: Feeding black holes form the hearts of active galaxies. As all that gas crams down the throat of a black hole's event horizon, it compresses and heats up to millions of degrees. That hot gas emits scorching X-rays so bright they can be seen from billions of light-years away. So when we see a giant, glowing source of X-rays in the sky, we know that trillions of tons of gas are falling into a black hole.

But whereas scientists have spotted hundreds of thousands of active galaxies in the nearby universe, we have only seen a handful in the young cosmos. (Because light takes time to travel, studying distant corners of the universe is the equivalent of looking back in time.) 

That said, the active galaxies that scientists have found at extreme distances and therefore in the past are extremely powerful. For example, the most distant known active galaxy, dubbed ULAS J1342+0928, was alive and well when the universe was only 690 million years old and hosted a supermassive black hole with a mass of 800 million times that of the sun.

Searches in the deep darkness

Although these giant active galaxies are awesome, what scientists really want to know is whether they are typical of the early universe or off-the-chart extremes.

In a recent study, scientists suggest that the known active galaxies in the young universe are the exception, not the rule. Using a combination of observations taken by NASA's Chandra X-ray Observatory and probes that see in longer wavelengths, the astronomers were able to identify possible candidate active galaxies in the young universe across a wide chunk of the sky.

And after sifting and sorting through data, they made a list of all their candidates. That is, all five of them. That's right, in their entire search field of the early universe they only found five active galaxies, and due to uncertainties in measurements those galaxies may actually be much closer to us and much more recent after all.

These findings seem to contradict simulations that suggest that supermassive black holes should have experienced growth spurts before the universe turned two billion years old and thus be common at such vast distances. While we can point to a few, they seem more like oddballs than a stop along the typical journey of a supermassive black hole.

So how do we go from seeds in the very early universe to the giant black holes we see today? As of now, we're all in the dark. 

The research is described in a paper posted to the preprint server on Jan. 16 and accepted for publication by the Astrophysical Journal.

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  • dfjchem721
    Like father, like son, or is it grandson?

    Once again, did primordial black holes (PBHs) appear from the get?

    As noted by more than a few cosmologists*, the formation and existence of PBHs is an active study of research and this new data adds more support for their existence. Yeah, I know, there will be a lot of "oh brother"s out there on this one, but this data indicates PBHs are more "in the running" then ever before.

    The link below gives a good overview on how they are considered, but cannot include all PBH sources since this stuff is too wild to know what other sources might have existed way back when. Note that there is no limit to the size of a PBH.

    As someone once noted, "All models (aka simulations) are wrong, but some are useful." And as rod has so famously pointed out, the Department of Cosmology doesn't like alternatives to their perceived "Laws of the BB."

    Did they arise intact from the BB, or form shortly afterwards from ultra-dense clouds? Sadly, it is likely no one will ever know. But perhaps, if and when that blasted Webb Telescope** makes its appearance in the seemingly ever distant future, it might provide an answer, or two. Or at least more suggestions for the modelers.

    Happily then, for those who believe they exist, they can never be disproven! So to any nay-sayers out there, the preemptive answer to their intransigence? Prove that they do not exist. Because all those models of SMBHs forming shortly after the BB might have just fallen into a SMPBH, never to return.

    Au contraire?!

  • Torbjorn Larsson
    Admin said:
    Although simulations suggest that black holes should grow quickly in the early universe, when astronomers look back in time they simply cannot find many such structures.

    Something similar odd is seen in star formation rates, since to fit cosmological simulations the rate should be close to the natural for molecular clouds and we should see more large early galaxies overall. Several early galaxies that are large and fit the estimated rate has been found, but the general early population is more modest in szie and rate AFAIK.

    But tensions have been naturally resolved before. E.g. when Milky Way seemed to have much fewer satellite galaxies than the average simulated galaxy, but now the discrepancy is just a factor of two. And the unseen population is estimated to be extremely small and hard to distinguish.
  • Torbjorn Larsson
    dfjchem721 said:
    As noted by more than a few cosmologists*, the formation and existence of PBHs is an active study of research and this new data adds more support for their existence. Yeah, I know, there will be a lot of "oh brother"s out there on this one, ... "Laws of the BB."

    Oh brother. 😎

    The Wikipedia article is a long list of exclusion results. Most importantly, "tight limits on their abundance have been set up from various astrophysical and cosmological observations, so that it is now excluded that they contribute significantly to dark matter over most of the plausible mass range. " And the big bang expansion is what we live in - it's an observation, but there is no law saying it had to be so - so even if it had been a law, what would be the problem?

    There is no good connection between the unseen primordial black holes and the ones in the center of galaxies. The one proposed paper in Wikipedia present a model based on other physics than LCDM (wrong type of inflation; supersymmetry).

    What does "they can never be disproven" refer to? We can test and reject observations and so theory (but not everything predicted by an effective theory may be testable - c.f. Planck masses of quantum field theory). But I can't parse that part, does it suggest that we can't see black hole mergers? We can see some nearby already today, LISA will probe the SMBHs we discuss in a few decades, and the sky is the limit from there.
  • dfjchem721
    Re-reading my post T, I made no mention specifically referring to dark matter in any of this, only the early formation BHs in general.

    Read all about the "tight limits on their abundance have been set up from various astrophysical and cosmological observations, so that it is now excluded that they contribute significantly to dark matter over most of the plausible mass range. " , and found reasonable alternatives which circumvent such limits. One is the micro-lensing studies. There are alternate explanations for the lack of any observational data. From wiki:

    "However, these limits are model-dependent. It has been also argued that if primordial black holes are regrouped in dense halos, the micro-lensing constraints are then naturally evaded."

    Indeed, was so surprised by the back and forth on these "tight limits" that they don't look so tight anymore. I am not a complete fool. It is the only reason I am posting such heresy!

    It is PBHs that can never be disproven. If you read that Wiki link I posted, they have a considerable following with serious notions about them and how they formed etc. Whenever I see such a thing, I have to check it out. I trend contrarian if there is reasonable doubt about a subject, and there certainly is here.
  • dfjchem721
    By the way, T, I was truly impressed by your treatment of magnetic field involvement in the formation of the solar system Had never heard such a thing. If true, very remarkable.

    But no one answered my question. I suppose it was a trivial and boring post to most of you guys, but where did the angular momentum come from? Is it how I guessed, by an asymmetric pressure wave on the gas/dust fragment that condensed, or by some other means.
  • abdelhalimhosney886@gmail
    I think that scientists are seeking for a mirage, because the solution of this problems did not need super massive star to be black holes , so I put very strong hypothesis to solve this question it is depends on these points:
    The presence of black holes in the core of galaxies is inevitable.
    mass does not depends on matter
    mass depends on position of body in universe
    mach's principle is correct.
    inertia is measurement of mass
    Einstein theory said that the mass generates gravity and gravity generates space curvature so the vice verse is correct.

    let mass of spider man is equal 60 kg ,so spider man inertia can't stop any big pushes to move him in space, so let now spider man connect a trillions of his strong wires to all stars in the galaxy , now try to move him,so you need to move this stars also, so it's inertia and mass will be very very high, black holes appear have no any matter but have a huge masses which gain from stars around them . barycenter is point between planets act like a massive star which planets move around it . may be inertia come from that every body connect to other bodies in space by unseen strings like gravity strings .this wires make all body in space stay in his place and resistant motion(inertia) .and from Einstein theory, imagine the space texture and we put high massive bodies around point in the middle, this point suffer a big strains so the space around it will curvature so this curvature makes big gravity and big gravity makes big mass points.
    It is small part of my hypothesis( space strings) but I can't found site to publish it ( I hope some one help me)