Black Hole: Conservation of energy

  • Thread starter darkside00
  • Start date
  • #1
83
0

Main Question or Discussion Point

If black holes exist, they cant consume infinite amount of matter, so where does this energy go if it is not dissipated?
Is it gamma ray bursts that dissipate this huge amount of energy?
Or maybe a better question is, once a black hole is created, how long can it last? or do they last forever?
 

Answers and Replies

  • #2
1,254
3
I don't exaclty understand where you see conservation of energy being violated. The energy still exists.... in the black-hole and the space-time (gravity) around it---its not being 'dissipated' necessarily (although generally a good deal of energy is 'radiated' when material is consumed by a BH).

I don't see how you are relating this to the lifetime of blackholes, but what you are alluding to is correct: black-holes do not last forever---they slowly evaporate (but this gets very complicated, and large-black holes will essentially always being gaining more than they're losing). The micro-black holes which could hypothetically be created at the LHC would evaporate in the smallest fraction of a second. And if I recall the numbers correctly, a stellar-mass black hole would take about a Hubble-time (14 billion years) to evaporate.
 
  • #3
83
0
Can there be a limit of the amount of mass it can pull in (consume)? and
How do supermassive black holes evaporate?
 
  • #4
bcrowell
Staff Emeritus
Science Advisor
Insights Author
Gold Member
6,723
423
Can there be a limit of the amount of mass it can pull in (consume)?
General relativity doesn't have any preferred scales such as a mass scale or a distance scale, so there can't be any such limit.

and
How do supermassive black holes evaporate?
The same way less massive ones evaporate...?
 
  • #5
Chronos
Science Advisor
Gold Member
11,408
738
You are ascribing black holes 'supernatural' properties. A black hole is entirely well behaved at the Newtonian limit, and equally well up to the GR limit. It only becomes unruly at the event horizon. At that point it behaves reasonably well up to the quantum limit. Inside the event horizon, all bets are off.
 
  • #6
9
0
can a black hole be destroyed using the same property of evaporation ???
 
  • #7
gneill
Mentor
20,793
2,773
can a black hole be destroyed using the same property of evaporation ???
What do you mean by "be destroyed"? Black holes evaporate. That is, they gradually lose mass over time until they disappear if they aren't constantly fed at a rate greater than the evaporation rate.

The rate of evaporation gets smaller (but never zero) as black holes get larger. The rate goes higher as the mass goes down. Really big black holes can 'feed' adequately on just the ambient radiation in the current universe (CMBR). Really small ones can't get enough mass down their gullets to sustain themselves. The 'end game' for black hole evaporation is a rapid flash of energy as the last of the mass within its minuscule event horizon is converted to particles and energy immediately outside of it. Boom!
 
  • #8
83
0
ok, so once there done feeding, how are they releasing their mass energy?
would it be similar to a dying star? or supernova? there would have to be some fusion to release the energy in the event horizon and eventually become visible...otherwise there is no evaporation rate while its feeding

or become just a big chunk of mass that is stagnant or dead. That would mean it didn't evaporate?
 
Last edited:
  • #9
gneill
Mentor
20,793
2,773
ok, so once there done feeding, how are they releasing their mass energy?
would it be similar to a dying star? or supernova? there would have to be some fusion to release the energy in the event horizon and eventually become visible...otherwise there is no evaporation rate while its feeding

or become just a big chunk of mass that is stagnant or dead. That would mean it didn't evaporate?
The evaporation is continuous, no matter what. No fusion required. It's just evaporation. If the mass influx is greater than the evaporation rate, the black hole grows. If it's less, it shrinks.
 
  • #10
If black holes exist, they cant consume infinite amount of matter, so where does this energy go if it is not dissipated?
Is it gamma ray bursts that dissipate this huge amount of energy?
Or maybe a better question is, once a black hole is created, how long can it last? or do they last forever?
hey buddy its the one and only black hole where physics law's goes wrong or one can simply say the human limits,so there is nothing like conservation of energy in a black hole and there lifetime may very from few nanoseconds (as in case of pie-meson particle interactions) to infinity depending upon amount of matter present around them(IN there intense gravitational field) once they end up eating matter around them they die.
 
  • #11
You are ascribing black holes 'supernatural' properties. A black hole is entirely well behaved at the Newtonian limit, and equally well up to the GR limit. It only becomes unruly at the event horizon. At that point it behaves reasonably well up to the quantum limit. Inside the event horizon, all bets are off.
its only for darksidee00 man who put up such a silly question
 
  • #12
Can there be a limit of the amount of mass it can pull in (consume)? and
How do supermassive black holes evaporate?
its when there is nothing left around them in their gr field (as dark energy is pushin things apart slowly but efficiently).
 
  • #13
2,471
1
When BH evaporates it is converted into hawking radiation.
Conservations laws hold.
 
  • #14
12
0
Black Holes has a temperature; any object that has a temperature emits radiation, emitting radiation=loosing mass. Black Hole radiations is also called as Hawking's Radiation.

Space around the black hole is usually colder. Hot flows into colder objects, therefor the space's heat flows into the black hole because black hole has a lower temperature. In addition with the black holes constant absorbing of matter, so therefor the black holes absorb more energy than they loose them.

When space is expanded enough, eventually the temperature around the black hole will become colder than the black hole. Remember hot flows to colder object? So black hole's heat will be carried into space, eventually the black hole will evaporate but this cycle will take a long time as described in the 1st post.

Small black holes= High Temperature=they die(evaporate) faster
Big black holes= Low Temperature=they die(evaporate) slower

I am not entirely sure, so experts please correct this if this is wrong.
(Excuse me for my bad English)
 
Last edited:
  • #15
83
0
Haven't heard an expert yet

Will have to look more into this hawking radiation
 
  • #16
2
0
Q;Could this evaporation be induced?forinstance by Excitation.
 
  • #17
1,254
3

Related Threads on Black Hole: Conservation of energy

  • Last Post
Replies
8
Views
2K
Replies
24
Views
9K
Replies
16
Views
4K
  • Last Post
Replies
5
Views
5K
Replies
8
Views
2K
Replies
10
Views
6K
  • Last Post
Replies
6
Views
876
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
6
Views
4K
Top