Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Evidence that black holes gain in mass?

  1. Jan 2, 2012 #1
    Please correct me if I am wrong, as I have little more than a highschool knowledge of physics until I start at university this year - virtually no knowledge of the quantum side of things just yet. ^^

    My thought is, as spaghetification occurs as you approach the centre (not using singularity for reasons specified below) of a black hole, all matter breaks down until it reaches the level of the Higgs-Boson particle, theorised to give all other particles mass (Correct?). At this point, the mass will simply vanish.

    As I understand it, the working theory is that black holes gain in mass as they take in mass. If mass is instead, destroyed, then what sustained the gravitational pull of the black hole? Unless there is a core of massless (matter-sourceless) force preventing it from coming any closer that the minimum distance at which the structural integrity of the particle can hold, the matter would be obliterated, and the mass lost.

    So here is my question. Is there any observable (not theoretical, unless it voids my above reasoning) evidence to show that black-holes gain mass? That is, if they gain mass, net mass would not be lost, so the force of the net gravitational pull of the black hole and the matter between a body and a black hole would remain unchanged. If the mass of absorbed matter is ultimately destroyed, the force towards the black hole at a fixed point would decrease to approach the actual, CONSTANT force caused by the mass of the black hole.

    Of course, we have no way of actually measuring for this, as this would required a fixed point around a black hole. The only theoretical way I could see to measure this is to have some spacecraft putting out a constant thrust away from the black hole, to measure the force required to REMAIN in the fixed point. Obviously, this can not yet be tested.

    Is there anything I may have overlooked, either in my theoretical reasoning, or in methods for observing for this phenomenon? Perhaps there are implications this theory would mean that are untrue?

    Thankyou, Kael.
  2. jcsd
  3. Jan 2, 2012 #2
    Also, if mass is destroyed, would this not mean that there is a super-concentrated supply of Higgs-Boson particles stored in the core of a black hole?
  4. Jan 2, 2012 #3
    Mass cannot be created or destroyed, it can only change form. Matter can become energy, and energy can become matter, but always according to e=m2.

    So, if matter was destroyed by a black hole, the mass of the matter is converted to energy of equal mass, but then as the black holes gravity is so strong the energy cannot escape and therefore the mass remains.
  5. Jan 2, 2012 #4
    The evidence would be the event horizon of the hole getting bigger as stuff falls in. I don't think this has been observed directly yet.
  6. Jan 3, 2012 #5
    Rollcast, part of the point of this post is to question this axiom. This is an accepted law, yet what mathematical, observable, undeniable proof have you of this? It has never been observed, only it being converted into energy, and thus is assumed to be true. Yet whatever occurs anywhere inside of the event horizon has never been observed.

    What you have provided is theoretical information based on axioms under question, making a circular argument. Unless there is some law that is completely unrelated to the conservation of matter that I have overlooked, or some observable phenomenon to show otherwise, the possibility that matter/energy is actually destroyed at the core of a black hole cannot be entirely refuted.
  7. Jan 3, 2012 #6


    User Avatar
    Science Advisor
    Gold Member

    We can verify black holes have mass by virtue of bodies in orbit around them.
  8. Jan 3, 2012 #7
    Yes, that is very obvious. But does it remain constant, or grow as it takes in more matter? Observable evidence, not theoretical claims based on the laws of conservation of matter/energy.
  9. Jan 3, 2012 #8
    There are various factors which govern how long a given BH will live on for , size , angular momentum, the amount of stellar dust surrounding one. You have supermassive black holes and others not so large ones. According to a recent study scientists have acknowledged that early black holes ate up cold gas to grow bigger , BH M87 is said to have fed on other smaller Black holes. All this among other finds suggest BH do have fluctuation of mass.

    What makes them exotic heavenly bodies is when we approach beyond the event horizon out of which they act as normal bodies, have their own orbit and in fact a binary BH system has been observed. I think you seemed to have a misunderstanding , it's not always true that whenever a BH has any mass going in that it gets larger, they may evaporate if my memory serves me right. Take a look over the bekenstein-hawking formula..

    [itex]S_{BH}[/itex] [itex]\propto[/itex] Area of the event horizon.
    Last edited: Jan 3, 2012
  10. Jan 3, 2012 #9
    Nope. At this point something weird happens, but it's unlikely that mass will just vanish. In any event, what happens inside the black hole doesn't effect what's happening on the outside.

    You can't destroy mass without killing GR, and if you kill GR (which isn't necessary bad), then all bets are off.

    Also whatever happens in the black hole isn't going to get noticed by the outside.
  11. Jan 4, 2012 #10
    I must disagree here, what happens inside the black hole does have relevance to the rest of the U; they may not be causally connected but a black hole that is gaining mass must have a noticeable effect on its nearby surroundings (extension of the EH and increased gravitational driven curvature) Which could be noticed and measured. So while there is no causal interaction between a Black Hole and the U there is a matter interaction. Causality may flow in but so does the mass.

    I hope this makes sense? As a layman I am open to corrections.
  12. Jan 4, 2012 #11
    Nope. By definition something that is not causally connected has no noticeable impact on the outside world so what happens inside of a black hole does not influence anything else in the universe (assuming GR is correct).

    What happens *just before* something falls into the black hole does, so if you have falling into the black hole, the gravitational effects of that matter just before it crosses the event horizon will influence the outside universe.

    One other point is that GR is local so what happens at the black hole is irrelevant. If you replace the sun with a one solar mass black hole, then it won't strongly change the orbit of the earth.

    Kip Thorne worked this all and for "ordinary black holes" you aren't interacting with material that has fallen across the event horizon, but rather with the material right before it falls into the EH. See


    Now whether or not there are some weird situations in which can can interact with the insides of a realistic black hole is an open question. Most people strong suspect that you can't, but the mathematicians haven't come up with a proof yet. There are some solutions in which you can form a naked singularity, but people have argued that those are not physical.
  13. Jan 4, 2012 #12
    Ok thanks for clearing that up - its a very subtle difference though. The fact that Black Holes grow in mass does affect the outside world - regardless of the mechanism for growth, this was my point. I think this can be seen most clearly with SMBH's at galactic cores. While I agree that anything that goes in does become causally disconnected, the fact that the Mass/Spin/Angular momentum are the variable measurable properties of a BH gives it a causal influence on the U. I will do more reading on the subject and take into consideration these comments.

    Thanks for the link - I have done some minor reading on Naked Singularities but currently the maths for most black hole equations are a little out of my grasp (I am a computer engineer by trade.)
  14. Jan 8, 2012 #13
    I don't really understand this or the concept of the black hole information paradox, which i believe is related.


    I'll can start a thread for this, if required. But it seems to be saying that information can gradually leak out of a black hole as it evaporates: not as a thing falls in, but that things that "fell in" a long time ago may leak their information out. Which seems to imply to a layperson such as myself that there is a causal connection.
  15. Jan 8, 2012 #14
    @Kael42 (please do not confuse my bluntness for derisiveness) you don't seem to understand some key aspects of how science works.
    There is no such as '100% proof' or certainty, ever. It's always a matter of how much evidence there is for a theory; and how much lack there is of alternate, viable, theories.

    You are correct that there is no direct observation of the growth of black holes, there also won't be anytime soon. None-the-less, observations are entirely and incredibly consistent with the hypothesis that BH's grow; and the inverse argument would lead to lots of huge problems---thus it seems highly unlikely.

    It is important to note that none of this is in any way circular. Any logical framework necessarily moves from assumed axioms to derived conclusions -- as in this case. The scientific method is based on dispensing with axioms which contradict observations, and maintaining those consistent ones.
  16. Jan 8, 2012 #15
    To get back to this question in the OP, we have good observational evidence of extragalactic supermassive Black Holes, of up to 21 billion solar masses. We also have good evidence of a (approximately) 4 million sm BH in our own galaxy. Unless you're going to postulate that they formed from a singular gravitational object, accreation of mass seems to be the only explanation for their existence.
  17. Jan 9, 2012 #16
    This is a good point, as we see measurable differences in the mass of BH's and we theorise them to be created via a specific mechanism, if they cannot grow this would assume, either different mechanisms or a mechanism which functions exactly the same given an immense variatin in mass.
  18. Jan 10, 2012 #17
    It is indeed an excellent point, but it should be pointed out that there are two missing pieces to our understanding of BH growth---the existence of supermassive quasars at high redshift; and less significantly, but still conspicuous, the lack of IMBHs....
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook