Questions tagged [gravitational-collapse]

Use for questions related to the creation/possibility of black holes in a certain situation, singularities, the contraction of an astronomical object due to its own gravity, and the re-collapse of our universe. Do not use for questions relating to normal gravitational attraction.

Filter by
Sorted by
Tagged with
36
votes
1answer
2k views

How can dark matter collapse without collisions or radiation?

I understand that dark matter does not collapse into dense objects like stars apparently because it is non-interacting or radiating and thus cannot lose energy as it collapses. However why then does ...
27
votes
4answers
3k views

Throwing a micro black hole into the sun: does it collapse into a black hole or does it result in a supernova?

What do we know about accretion rates of micro black holes? Suppose a relative small black hole (mass about $10^9$ kilograms) would be thrown into the sun. Eventually this black hole will swallow all ...
14
votes
1answer
522 views

Gravitational collapse of a photon cloud

The Schwarzschild solution shows that a spherically symmetric, static fluid will undergo gravitational collapse if too much mass-energy is concentrated together (i.e. if the fluid's radius is less ...
13
votes
1answer
11k views

What happens to atoms inside a black hole?

Black holes have very high gravitational force that tends to crush everything. So as we know atoms in a molecule have inter-atomic spacing between them and further electrons also revolve at a certain ...
11
votes
0answers
230 views

In realistic gravitational collapse, can we have an absolute horizon without a trapped surface?

In gravitational collapse, it seems that there is no close or simple logical relationship between the formation of an event horizon (absolute horizon) and formation of a trapped surface (which implies ...
9
votes
2answers
626 views

Gravitational waves and chirp waveform

When two neutron stars collide emitting gravitational waves, what exactly does the chirp waveform represent and how is it used to infer the distance to the source?
8
votes
1answer
274 views

Is it possible for a black hole to form for an observer at spatial infinity? [duplicate]

To my knowledge if you calculate the coordinate time (time experienced by an observer at spatial infinity) it takes an infinite amount of time for an object to fall past the horizon of a Schwarzschild ...
6
votes
1answer
123 views

Do galaxies have a halo of neutrinos and cosmic microwave background?

If virial arguments as in "How can dark matter collapse without collisions or radiation?" allow concluding that dark matter could collapse to galactic halos purely gravitationally, then is this true ...
5
votes
2answers
154 views

Comoving system of expanding or collapsing dust-like particles

I have a question on co-moving and synchronized reference systems. I read the corresponding section (97) in Landau/Lifshitz's second book "Field Theory" on it. In particular it is said that space ...
5
votes
1answer
158 views

Numerical relativity resources - Adaptive Mesh Refinement

I have, in the past few months, been studying numerical relativity, specifically the problem of spherical collapse of a scalar field as studied by Choptuik. I have also taken a look at some books that ...
5
votes
1answer
293 views

Electron degeneracy pressure

Why is it that in stars undergoing gravitational collapse electron degeneracy kicks in? Why couldn't the electrons form energy bands like in semiconductors?
5
votes
2answers
955 views

Questions about the Jeans length

I have a couple of questions about the Jeans length. Suppose the universe has a homogeneous energy density, except there's a spherical region that is overdense. I understand that if the region is ...
5
votes
0answers
222 views

What does black hole formation and evaporation actually look like as viewed from far away?

Many people on Physics SE (myself included) have been confused about what black hole formation and evaporation look like when viewed from far away. For example: Does any particle ever reach any ...
4
votes
1answer
373 views

How come gravity generates enough pressure to start a fusion reaction in stars even though it is the weakest force?

Given the fact that gravity is the weakest of all forces, how does a gas cloud manage to collapse on itself under gravity and start a fusion reaction, outweighing the electromagnetic and nuclear ...
4
votes
4answers
942 views

White Holes and Time-Reversed Oppenheimer-Snyder collapse

So, the canned explanation that I always hear about why the white hole solution of the extended Schwarzschild solution is non-physical is that "The matter distribution cuts off the white hole solution....
4
votes
1answer
594 views

Oppenheimer-Snyder Collapse

I have read the Oppenheimer-Snyder collapse is significant in the sense that it was the first work which treated the problem of black hole formation under gravitational collapse. The model assumes a ...
4
votes
2answers
1k views

What is the main thermal energy source for a protostar, the contraction or the deuterium burning energy?

According to the virial theorem, when a protostar contracts, half of the gravitational potential energy is radiated and half is kept as kinetic energy of the falling material which in turn heats the ...
4
votes
1answer
143 views

Negative mass thin shell collapse

Suppose we have a collapsing light-like (ingoing) shell with negative mass and decreasing further. The shell is radiating and so the exterior region is that of the outgoing Vaidya solution. $$ds^2 = -...
4
votes
2answers
122 views

Direct rocky planet formation without protostellar disk?

Inspired by this question, which sort of asked what I'm asking, but emphasized a different point (and the answers accordingly addressed that). Can a rocky planet form directly from the collapse of ...
4
votes
0answers
198 views

Situation after Saini & Stojkovic's paper on unitarity in gravitational collapse and non-formation of black holes?

In their paper, Anshul Saini and Dejan Stojkovic [1] claimed that by calculations it is possible to demonstrate that in a gravitational collapse of a disk, an event horizon is never made for a far ...
3
votes
2answers
152 views

Gravity/Energy relationship

I understand that gravity is not energy, but is force, but my question revolves around if the presence of gravity in the universe results in a continuous amount of energy, from gravity-induced ...
3
votes
0answers
105 views

Gravitational waves from collapsing rotating mass? [closed]

According to the Birkhoff’s theorem, a non-rotating mass does not radiate gravitational waves during a spherically symmetric collapse. There is, however, no equivalent of the Birkhoff’s theorem for a ...
2
votes
4answers
3k views

What happens during gravitational collapse to cause the formation of a star?

I know that stars are formed from dense regions in large gas clouds. I know that when gravity causes the mass of the clump to get so big that its internal pressure can't sustain it, it collapses and ...
2
votes
1answer
80 views

Black holes from gravitational collapse without matter

A collapsing star or mass shell or photon shell can eventually form a black hole. Are there any examples of BH formed from purely gravitational condensation of energy, like from focused gravitational ...
2
votes
1answer
62 views

Would a neutron star-like celestial body made of bosons collapse because of missing Pauli repulsion?

Imagine the neutron star-like celestial body would be built up of bosons (assume that neutrons would be bosons). In that case there would be no Pauli repulsion (the exchange force of the exchange ...
2
votes
1answer
234 views

Free fall time of collapsing non-rotating star in GR according to a distant observer

Suppose a star with a spherically symmetric mass distribution, mass $2\cdot M_{sun}$ and initial radius $R$, undergoes a gravitational collapse after all gas pressure has vanished. The final radius ...
2
votes
1answer
78 views

Can a theoretical object exist as such that its mass overcomes gravitational collapse

A daydream the other day led me to the question if "a universe filled with water (or any other substance for that matter), instead of being mostly void" could exist within the rules of our current one....
2
votes
0answers
42 views

how to create a kinetic energy kugelblitz in theory? [duplicate]

Black holes form when enough mass gets packed so close together that its gravity gets so strong that even light cannot escape it. Mass and energy are equivalent, so theoretically it is possible to ...
2
votes
0answers
151 views

What is more dense, Neutron Star material, or Black Hole material? [duplicate]

What is the most Dense material in the Universe? Is it Neutron Star Material? I would think that the Singularity in a Black Hole would be the densest material, or the material that exists moments ...
2
votes
1answer
303 views

Gravitational collapse (conservation of energy)

During gravitational collapse, gravitational potential energy of the gas is converted to its internal kinetic energy so the internal energy of the clous of gas is said to be increased But isn't ...
1
vote
2answers
102 views

Need proper interpretation of imploding/exploding self-gravitating sphere

While searching for some nice and simple problems in Newton's theory of gravity, I've made this trivial calculation for which a proper physical interpretation is lacking. Some pieces are missing and ...
1
vote
2answers
344 views

So gravity turns things round

It makes sense, since gravity tends to push the surface of a body towards it's center. Unless I'm mistaken, everything with mass has it's own gravity, every atom and for instance, our own bodies ...
1
vote
1answer
32 views

What is the Effect of Gravity in Preventing Macroscopic Quantum Superpositions?

I am trying to understand how gravity might prevent the creation of macroscopic quantum superpositions, such as a Schrodinger Cat state. I am not asking about decoherence. Also, Penrose has a great ...
1
vote
1answer
375 views

Gravitational collapse of dark matter [duplicate]

The gravitational lensing evidence suggests the existence of massive and relatively dense regions of dark matter. However, if dark matter interacts only gravitationally, what would stop it from ...
1
vote
1answer
319 views

Why doesn't Brooklyn expand? (Or “Is the expansion of the universe kinematic?”) [duplicate]

Possible Duplicate: Why space expansion affects matter? Imagine two tiny spacecrafts that are moving with the Hubble flow and so are moving away from each other. Let's assume that they've been ...
1
vote
3answers
65 views

What happens at the atomic level when a black hole forms?

As I understand it, during a gravitational collapse, the star stops fusion and gravity overcomes the radiation pressure. At that point, there is a point in space where there is a lot of gravity in a ...
1
vote
1answer
60 views

Naive question about Gravitational collapse

Suppose that you have a probe orbting a $10M_{\odot}$ star in the final moments before gravitational collapse. In a time $t$ the collapse event occurs. So do you really would see all the matter "...
1
vote
1answer
92 views

What are the conditions for non-spherically symmetric gravitational fields in GR?

This may seem like a silly question. However, what are the conditions for a matter source to produce a non-spherically symmetric gravitational field? More specifically, can a spherical source ...
1
vote
1answer
320 views

What does singularity mean in the context of black holes? [duplicate]

Non-rotating big stars can be subject to a gravitational collapse increasing their density. When the density is so high that the mass volume shrinks below the event horizon, a black hole is formed. ...
1
vote
1answer
184 views

Gravitational time delay and contraction of matter [duplicate]

How can any matter contract to its Schwarzschild radius if gravitational time dilation clearly states that all clocks stop at that point. So any contraction any movement would stop. If that is so why ...
1
vote
0answers
29 views

What is the assumption of conservation of rest mass in gravitational collapse?

I have been reading up a paper on gravitational collapse, where a particular equation $$ 4\pi \rho R^2 b = 1 $$ means the assumption of conservation of rest mass. Here the spacetime interval is ...
1
vote
1answer
88 views

How does a distant observer see matters that “form” an initial black hole?

I did see Can black holes form in a finite amount of time? but it does not seem to discuss how a distant observer would see evolution of collapsing matters that form a black hole. Does it view these ...
1
vote
0answers
64 views

Elementary flatness - Gravitational collapse of a massless scalar field

Choptuik pioneered numerical studies of the gravitational collapse of massless scalar fields in spherically symmetric, asymptotically flat spacetime. In his papers (e.g. https://arxiv.org/pdf/gr-qc/...
1
vote
0answers
156 views

In what sense is ''Oppenheimer-Snyder collapse a time reversed closed FRW model"?

In what sense is ''Oppenheimer-Snyder collapse a time reversed closed FRW model" ? That is, "Are closed FRW metric (k=1) and the geometry inside the collapsing homogeneous matter same?" If yes, how? ...
1
vote
1answer
92 views

Photon gas into a Black hole

Can a photon gas have so much energy that it collapse into a black hole just like a regular star?
1
vote
2answers
104 views

Is there an equation for the amount of energy from a collapsing star BEFORE it creates a black hole?

(I could be phrasing my question incorrectly, so bear with me as I try to explain it.) Recently I've been very interested in the geometry and physics of black holes, so I started messing around with ...
0
votes
3answers
355 views

How does gravity cause nuclear fusion in stars?

I am a bit confused regarding the nuclear fusion that occurs during star formation. For example, suppose there is a huge hydrogen cloud. It gets more mass and therefore pulls in more and more hydrogen,...
0
votes
1answer
33 views

Gravitational waves of spherical body with mass $M$ which collapses to a black hole with mass $m<M$

Consider a body with spherical symmetric mass distribution in asymptotically flat space with a total mass $M$. Assume it collapses to a black hole with mass $m<M$. Does this body emit ...
0
votes
1answer
58 views

Do binary black holes mergers emit light?

I am not referring to Hawking radiation and although I see there should be no way the collision can produce electromagnetic wave after all, a black hole is simply a region of space right?
0
votes
1answer
175 views

Are physicists still ignorant of the existence of real singularities?

(1) Is the gravitational singularity (or space-time singularity) the same as the black hole singularity? (2) The wikipedia page says Physicists are undecided whether the prediction of ...