Do black holes have energy?

  • So black holes are created by certain dying stars and when the star runs out of nuclear energy gravity wins out and the star implodes. An entire star’s mass collapses down into a smaller and smaller volume of space. Which then creates a black hole, so my question is, do black holes actually have energy to create that type of vacuum to suck light in?



    If a black hole was created by a huge star running out of fuel and then collapsing in on it self, would the black hole have energy and if so where would it come from, or is it just like the vacuum in space with no energy at all?



    (Please correct me if I said anything wrong about the black holes as I am very young and don't quiet grasp the concept of it yet.)


    I think you should at least try to read Wikipedia or something of the like to grasp the basic ideas. You have many errors in your question. Correcting them would take long. You could also go through other questions here in astronomy.stackexchange.com about black holes. Here is the link http://astronomy.stackexchange.com/questions/tagged/black-hole.

    If I'm reading your question right, you're asking if gravity requires energy. If the "sucking" requires an energy source and where does gravity's "sucking" energy come from. I'm pretty sure this has been asked before. In a nutshell, A massive object with gravity in and of itself has no "sucking" energy. If you have 2 objects, a heavy body and a smaller body some distance away, the 2 body system has potential energy, And the potential energy can explain the object falling towards a black hole. That's an oversimplified version of Stan Liu's post - just thought I'd put it out there.

  • Stan Liou

    Stan Liou Correct answer

    7 years ago

    An isolated black hole is a vacuum solution of general relativity, so in a very direct sense it does not contain any energy anywhere in spacetime. But perhaps somewhat counter-intuitively, that does not imply that such a black hole has no energy.



    Defining the total amount of energy is usually very problematic in general relativity, but in some special cases it is possible. In particular, the usual black hole solutions are all asymptotically flat, i.e., spacetime is just the usual flat Minkowski when far away from the black hole.



    Here (or in general when we have a prescribed asymptotic form of the spacetime), we can calculate the total energy-momentum, by essentially measuring the gravitational field of the black hole at infinity. The energy just be one component of energy-momentum.



    There are actually two relevant different kinds of 'infinity' here: spatial infinity and null (lightlike) infinity, depending on whether we are 'far away' from the black hole in a spacelike or lightlike direction. There's also timelike infinity, but that just corresponds to waiting an arbitrarily long time, so it's not relevant here. The two different infinities beget different definitions of energy-momentum, giving the the ADM energy and the Bondi energy, respectively. In a vacuum, the intuitive difference between the two is that Bondi energy excludes gravitational waves.



    So the short answer is 'yes', with the caveat that in a more complicated situation, where we can't attribute everything to the black hole itself, the answer to how much energy is due to the black hole may be ambiguous or ill-defined.



    Note that the ADM and Bondi energy-momenta also define their corresponding measures of mass, as the norm of those energy-momenta ($m^2 = E^2-p^2$), but for a black hole we can also define mass more operationally in terms of orbits around the black hole. There are also other alternatives for addressing mass specifically.


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