Black Holes Can Only Get So Big

Article written: 5 Sep , 2008
Updated: 24 Dec , 2015

Black holes are thought to exist throughout the universe, with the largest and most massive found at the centers of the largest galaxies. These supermassive black holes have been shown to have masses upwards of one billion times that of our own Sun. But an astronomer studying black holes says there’s an upper limit to how big a black hole can get. Priyamvada Natarajan, an associate professor of astronomy and physics at Yale University has shown that even the biggest of these gravitational monsters can’t keep growing forever. Instead, they appear to curb their own growth – once they accumulate about 10 billion times the mass of the Sun.

These ultra-massive black holes, found at the centers of giant elliptical galaxies in huge galaxy clusters, are the biggest in the known universe. Even the large black hole at the center of our own Milky Way galaxy is thousands of times less massive than these behemoths. But these gigantic black holes, which accumulate mass by sucking in matter from neighboring gas, dust and stars, seem unable to grow beyond this limit regardless of where – and when – they appear in the universe. “It’s not just happening today,” said Natarajan. “They shut off at every epoch in the universe.”

Natarajan’s study is the first time an upper mass limit has been derived for black holes. Natarajan used existing optical and X-ray data of these ultra-massive black holes to show that, in order for those various observations to be consistent, the black holes must essentially shut off at some point in their evolution.

Artist's conception of a black hole.  Credit:  U of Tel Aviv

Artist's conception of a black hole. Credit: U of Tel Aviv

One possible explanation, says Natarajan, is that the black holes eventually reach the point when they radiate so much energy as they consume their surroundings that they end up interfering with the very gas supply that feeds them, which may interrupt nearby star formation. The new findings have implications for the future study of galaxy formation, since many of the largest galaxies in the universe appear to co-evolve along with the black holes at their centers.

“Evidence has been mounting for the key role that black holes play in the process of galaxy formation,” said Natarajan. “But it now appears that they are likely the prima donnas of this space opera.”

Source: PhysOrg

22 Responses

  1. quantum_flux says

    Well this just opens all sorts of questions concerning the Big Bang then.

  2. Jim says

    AFAIK it’s hardly possible for two black holes to consome eachother, they rather attract eachother untill the bigger one repels the smaller one from the host galaxy in a renegade escape.

  3. quantum_flux says

    I wonder if Black Holes can diverge or split?

  4. td says

    it is possible for two black holes to merge…this is one of the main locations that “we” hope to detect gravitational waves…

  5. Chuck Lam says

    Hmm . . . how can a black hole radiate energy in any form if light can’t escape. How is it another part of the energy spectrum can? If nothing can escape the gravitational pull of a black hole, then why would there be an upper limit to its size or mass? Maybe in time, the universe might evolve into an infinitely large black hole. Natarajan’s study of black hole radiation interference with the consumption of matter appears to be flawed.

  6. Mark says

    “I wonder if Black Holes can diverge or split?”

    Maybe in a collision of two of these upper limit black holes one of them could be split in two?
    That would be awesome! If we don’t see gravity waves from something like that…

  7. Simon says

    What kind of mechanism could split a black hole in two?

    Surely an ultra massive black hole could still get bigger in collisions with other black holes moving at high speed towards each other.

    Though I can see why it would not get bigger from absorbing stars, sort of a photoevaporation effect only for black holes instead of stars.

  8. tomS says

    Seems to me I read many eons ago that black holes radiated (due to zero-point energy in space and virtual particles) and that the smaller they got the greater the radiation. When they got small enough, the would explode leaving nothing.

    This implies that there is greater radiation from larger black holes. Does this contradict the above? Is the above still true?



  9. Matthias says

    @Chuck Lam:

    It’s called Hawking Radiation. basically, particle-anti particle pairs form spontaneously; sometimes one gets sucked in and the other escape; due to conservation of energy (=mass) what it carries away is taken from the black hole


    This process is connected to the tidal forces near the event horizon, and therefore is actually stronger, the smaller a black hole is. That’s why those they hope to make at the LHC won’t do any harm, as they will radiate away within fractions of a second.

    There is a “magical barrier”. If a black hole manages to grow beyond a certain size it will absorb more energy from the cosmic microwave background than it radiates away; i.e. any black hole not actively feeding and smaller than that wil evaporate; bigger than that and it will grow (*very* slowly).

    Be aware that this critical mass is sinking over time due to the cooling of the CMB, so over time (*lots* of time) even big black holes might radiate away still.

    If I grasp the article right Natarajan just says that black holes beyond a certain age would be so violent when swallowing something, the radiation put out in the process would clear it’s vicinity, so that it’s no longer actively feeding, thus reducing its growth to being immeasurable.

    It will probably still grow (see Cosmic Microwave Background), but compared to 10^15 solar masses this won’t make much of a difference.

    This is not a “hard” barrier, so they might grow further through mergers.

  10. Star Geezer says

    I’m glad we cleared that urrrp!!…. I mean up… So I can continue to feed until I’ve consumed – or merged with… other black holes… then space.. .dark matter…dark energy… time…


  11. David says

    I have also read that black holes can radiate energy.
    In this case though, I wonder if the observed limit to the growth of black holes could just be a natural part of the lifecycle of black holes and their surroundings. In other words, new physics, associated with super massive black holes, may not be needed to explain the observation.

  12. bob says

    No, this is NOT the first time someone has put an upper size limit on black holes. Amy Barger and Lennox Cowie drew the same reasoning about 3 years ago.

  13. dennis says

    Duh- Conservation of energy? it can neither be created nor destroyed, therefore it cannot leave behind nothing.Given the velocity of moving black holes, the odds of it’s energy repelling an oncoming supermassive black hole are slim- THe 2 must collide and create a massave wave of some sort of energy and moswt likely massive quantities of particles. particles

  14. The fact is there is a complete misunderstanding of the actual structure of any mass object, not just the black hole. But you will all have to wait for a little longer to read more.

  15. David Madison says

    The article raises two separate but related questions. One is why we have not observed ultramassive black holes more massive than about 10 billion solar masses. The second issue is whether there is a reason, a law of physics, which forbids a supermassive black hole from growing greater than this observation.

    Priyamvada Natarajan answered the first one well; we have not seen a more massive object. However, he misses on the second. The idea that energy radiation disrupts further growth of an ultramassive black hole is lame. That radiation results because the object grows. If it stops growing, then it stops radiating. There is now no reason for it not to start growing again.

    One problem is that Natarajan just may not be thinking in the necessary time frame. He is only looking at supermassive blackholes since the beginning of the universe. He is not capable of observing any object older than the current age of the universe. Hawking Radiation will evaporate a small black hole, but a large one will continue to grow as it absorbs more energy, more mass, than it evaporates. As the universe cools, the dividing line between small and large ones gets larger. The time though is beyond any human comprehension. We are talking about maybe a trillion trillion trillion trillion times as long as the universe has existed yet before the stellar sized black holes evaporated. It would take maybe a million trillion trillion trillion times longer than that for the supermassive ones to evaporate.

    Given sufficient time, there is no reason why these ultramassive black holes cannot grow. Given more time, they too will go away, but I will not be around to see it happen.

  16. LLDIAZ says

    It seems reasonable. I mean if it were’nt so the universe would be littered with black holes, something must be keeping them in check. The universe could not have let these “behemoths” grow unchecked for so long it would (eventually with enough time)swallow everything.

  17. John in Missouri says

    Okay, if I’m reading this right, what Professor Natarajan is really saying is not that a black hole can grow no larger than XXX, but that the mechanics of normal growth of a black hole prevent it from getting fed once its reached XXX level of massiveness, which is not the same. What if an extreme condition arises, say a small black hole, not really affected by normal interstellar pressures, wanders by close enough to be attracted to the big guy. if it approaches at the right angle and speed can’t it still be consumed?

    Another possibility; is it possible that at mass XXX consumption of whatever the universe throws at the black hole is so negligible compared to its mass that the effects of so doing are not seen? Kinda like throwing a pea against the side of a skyscraper compared to a wreckers’ ball? This last one I see as a bit far-fetched, but its food for thought.


  18. astrobob says

    Why didn’t the universe collapse into a black hole right before the big bang?

  19. Starman says

    W’r ll gnn d vntlly. t’s jst mttr f whn.

    I’ve never understood how Hawking Radiation would work. I mean, don’t matter and anti-matter behave in a similar way under gravity?

    That being the case, when a particle pair spontaneously appears near a black hole’s event horizon, it’s gonna be a 50-50 chance as to which one of the particles falls in.

    If the matter particle fell in, the black hole would gain mass. On the other hand, if the anti-matter particle fell in, it would cancel some of the matter inside the black hole, so the black hole would lose mass.

    If the two processes have an equal chance of happening, there should be no overall effect upon the mass of a black hole, because the two would cancel each other out.

    Or am I missing something?

  20. willie says

    Maybe my Karate chop.

  21. PSYCHONAUT says

    Black holes continue to enlarge until the “big crunch” which occurs after all matter in a space-time continuum is completely eradicated by blackholes through something i will call time-void phasing. During some of my early ego death experiments into the true nature of reality, i discovered much insight into this area cosmology. A fair analagy is that black holes are to physical universes as plant life is to earthlings (plants take animal CO2 waste and give lifeforms oxygen fuel) Black holes absorb matter and then “phase” as it into the next universe as energy for the next big bang.

    Also bare in mind that matter is energy slowed down to a certian speed or frequency with photons being the highest frequency for physical matter. Time slows down for matter the nearer it approaches the center of the black hole which is a time void (time axis is warped so badly it no longer is connected to any of the 3 spacial axes). Eventually, the devoured matter is naturally changed by the gravity into pure energy (matter vibrating at an infinite speed/frequency) due to the particle breakdown with the law of conservation allowing it to pass out of our universe using the time void into another one (sometimes back into our own). the energy that doesnt get radiated back into ours as hawkings radiation becomes the fuel for:

    1 the next universe’s big bang that occurs after our own crunches
    2 a previous one that crunched before our own
    3 and even recycled for the big bang responsible for our own universes creation.

    Essentially this process allows an infinite number of physical universes to exist using the same finite amount of energy (pure energy mind you with infinite speed & frequency) that was created from the opposal creation of conciousness and nothingness which is what happened before the first big bang and way too complicated & abstract to explain with langauge in a timely manner on a forum. I’d imagine i’d have to use vague references to things like thought cancellation from redundant opposal awareness and chain reacting shifts in the will. It’s only completely understood while experiencing ego death (or actually dying!) since your conciousness is then existing in that same non-physical reality that the time-voids in black holes contain* but without the maecrocosmic shell limit of time’s linear sequencing effect that prevents
    At least not in this universe anyway…

  22. c henry says

    this coincides with my theory that galaxies are nothing more than a seed pod for future universal creation bangs…. i’m glad 2 see that im not the only person who sees this correllation… keep up the good work… chris

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