Black holes reloaded

[Aphex_Twin]

Having read Hawking's "Brief history of time" I was left with some unanswered dilemmas:

1. Are black holes stable? If a black hole evaporates to a mass below it's Chandrasekhar limit will it turn into something like a neutron star?; or if someone uses a ridiculous ammount of energy input to compress an object to a black hole, once the compression is stopped, will the miniature black hole continue to exist? (that is, will it decay at a normal rate).

2. Do object truly ever fall into a black hole?
If an object is never actually "seen" to fall into a BH (although it is redshifted), can we say it never falls in? Say I am that object, an unfortunate astronaut ready to pass through the event horizon. As I am aproaching the event horizon, time, from my perspective is dilated, which means that the few meters before I will collapse into the BH will take me a fraction of a second (depending on the size of the BH), but a gzillion years in "outside time". But what if by the time I reach the BH the BH has evaporated?

3. If an object is capabile of crossing the EH in finite time, how much time will it take to reach singularity? If we say time is extremely dilated around the EH, if it is infinitely dilated at the EH beyond it... more than infinity? Can we say thus that a BH can never accumulate more than it's initial matter into it's singularity (or that all new mass will be concentrated solely around the EH)?

 

[Blackbird_SR-71]

Having read Hawking's "Brief history of time" I was left with some unanswered dilemmas:

1. Are black holes stable? If a black hole evaporates to a mass below it's Chandrasekhar limit will it turn into something like a neutron star?; or if someone uses a ridiculous ammount of energy input to compress an object to a black hole, once the compression is stopped, will the miniature black hole continue to exist? (that is, will it decay at a normal rate).

2. Do object truly ever fall into a black hole?
If an object is never actually "seen" to fall into a BH (although it is redshifted), can we say it never falls in? Say I am that object, an unfortunate astronaut ready to pass through the event horizon. As I am aproaching the event horizon, time, from my perspective is dilated, which means that the few meters before I will collapse into the BH will take me a fraction of a second (depending on the size of the BH), but a gzillion years in "outside time". But what if by the time I reach the BH the BH has evaporated?

3. If an object is capabile of crossing the EH in finite time, how much time will it take to reach singularity? If we say time is extremely dilated around the EH, if it is infinitely dilated at the EH beyond it... more than infinity? Can we say thus that a BH can never accumulate more than it's initial matter into it's singularity (or that all new mass will be concentrated solely around the EH)?

1)Black holes are pretty stable. They evantually evaporate into nothing but that happens later. and neutron star has a mass less than a black hole so a black hole can never turn into a neutron star. To make this more clear:

Stars that have a mass like the Sun become White Dwarfs after they die.
Stars that have a mass of 3 times more of the Sun become Neutron Stars.
Stars that have a mass of 5+ times more of the Sun become black holes.

2)Things never fall into the black hole. A recent discovery shows that when a black hole sucks you in you dont pass the singularity point and you are broken down and spitted out. although you still have the same mass you particles are misarranged to the point you are seen as nothing. the Black hole takes a long time to evaporate. some of the earliest black holes to date haven't yet evaporated. the time it takes you to get in the black hole will be long to the outside world but the black hole will never actually evaporate while your reaching the BH.

3)The mass that it takes in is spit right out in the form of Jet stream of particles. So yes it will never acculmulate more mass than it already has.

 

[Aphex_Twin]

Subsequent questions:

Does the singularity actually hold ANY matter?
Does the shape of the event horizon contort and/or inflate/dilate in the presence of a material object in it's vicinity?

What kind of Maths are necessary for a reasonable understanding of BHs?

 

[Bluemofia]

singularities are a point in space/time with infinite density. they occupy absolutely no space whatsoever.

the shape of the event horizon is generally a certain distance from the singularity. since ring shaped singularities exist, there are probably singularities that are more flattened than others.

 

[Aphex_Twin]

Infinite density, IF they hold any matter. If singularities hold no matter their density would be zero, even if spacetime in that point is infinitely twisted.

 

[Bluemofia]

then how can they evaporate if they hold no matter? that would result in no mass, thus no density, and no gravity.

 

[Aphex_Twin]

I mean the singularity NOT as a synonim for "black hole" but the singularity, as the construct consisting of one geometric point (for static BH's) or torus (for rotating ones), which lies INSIDE the event horizon. Theory says all the matter of a star should collapse into the singularity, but what I don't understand is IF the matter ACTUALLY collapses, or just tends to. It's like being attracted to a BH, you aproach it, but never actually fall in.

 

[Bluemofia]

well, where would the matter go if not in the blackhole singlularity?

 

[Shaihulud]

Its theorised that black-holes leak energy in the form of "Hawking Radiation". Pairs of virtual particles are created in quantum vacumn all the time but they annihilate back into nothingness so there is no expression of energy, this happens at very short interval of time. In a blackhole it is possible for one of the pair to fall into the singularity, this net increase in energy from the gravity promotes it from virtual into real particle. The other pair also promoted to real particle escapes. Part of the energy form the blackhole is therefore lost.

 

[Aphex_Twin]

I mean, could the BH hold it's matter in the space between the EH and the singularity (or perhaps at the very edge of the EH), but not in the singularity?

In the process of the formation of a BH, the radius of the star shrinks up to a point where it is smaller than the Schwarzchild radius, at which point it has become a a BH, trapping all it's matter inside. However, will the matter "inside" continue to move towards the singularity, once the event horizon has been formed? Or is this collapse instantaneous?

 

[Bluemofia]

wait. steven hawkings mentioned baby universes. what if he means that the matter in the black hole goes into the baby universe? that would make so much sense now.

 

[Shaihulud]

I remember reading once that Hawking theorized that the Universe existed based on humans existence. When humans gone "Poof" goes the universe, can't say I understand some of the things he said though. The Hawking radiation wsa some bet he made with some guy about how information could leak from singularities.

 

[Bluemofia]

so we are holograms? is that what you are sudjesting?

 

[Shaihulud]

No the Universe are based on a Wavefunction that is dependent on Human existence.

 

[Aphex_Twin]

I remember reading once that Hawking theorized that the Universe existed based on humans existence. When humans gone "Poof" goes the universe, can't say I understand some of the things he said though. The Hawking radiation wsa some bet he made with some guy about how information could leak from singularities.

It's called the Anthropic principle. Wiki link: http://en.wikipedia.org/wiki/Anthropic_principle

It basically says that the universe is as it is because any other configurations would not allow the development of sentient beings, like ourselves, to ask the question of why the universe is as it is. A little bit of circular logic to tie up the theoretical loose ends; or the 20th century scientist version of the medieval geographers brand - "there be dragons", to make complete maps.

 

[Shaihulud]

Okay I always knew the creation of the Universe is the so that such marvellous ppl like ourself owuld ponder upon the fate of the Universe

 

[Blackbird_SR-71]

wait. steven hawkings mentioned baby universes. what if he means that the matter in the black hole goes into the baby universe? that would make so much sense now.

I think some guy disproved this theory. He said that what ever matter goes into a black hole is torn apart and spit right out as Particle Jet Streams. thats were all the energy of a black hole comes from. though i can't remember the guy who did this but he was an Indian.

 

[Yom]

I think some guy disproved this theory. He said that what ever matter goes into a black hole is torn apart and spit right out as Particle Jet Streams. thats were all the energy of a black hole comes from. though i can't remember the guy who did this but he was an Indian.

http://www.msnbc.msn.com/id/5452537?GT1=4244
Doesn't sound like an Indian to me.

 

[Bluemofia]

actually, only some of the material is shot out in jet streems. others get sucked in.

 

[Blackbird_SR-71]

http://www.msnbc.msn.com/id/5452537?GT1=4244
Doesn't sound like an Indian to me.

No i'm saying is that before Hawking changed his mind another scientist proved to him that he was wrong. That scientist may have been an Indian but i don't remember so i may be wrong.