Exploring Black Holes: Formation and Facts

[haileyparikh]

I've been reading 'A brief history of time' and want to know more about how black holes are formed. Please help?

 

[e.bar.goum]

I've been reading 'A brief history of time' and want to know more about how black holes are formed. Please help?

There are some pretty great websites around that introduce black holes:
http://www.universetoday.com/33454/how-do-black-holes-form/
http://hubblesite.org/reference_desk/faq/category.php.cat=exotic
https://en.wikipedia.org/wiki/Black_hole

PF is really much better at answering specific questions, so I encourage you to do some reading, and come back with whatever questions you have!

 

[newjerseyrunner]

There are two main ways black holes form: direct collapse or a dying star. Just after the moment of creation, energy was spread more or less uniformly through space, but some places were slightly denser than other. As things got jostled around, some of these areas got so dense that they collapsed into a primordial black hole. It's thought that these probably were the anchors that created the galaxies. When a really really big star starts to finish it's fuel and sputter out, it's internal heat can't keep gravity at bay anymore and as the star collapses in on itself, the core gets so dense it forms a black hole.

 

[Abullais Ghazi]

When the escape velocity of a star becomes extremely high then it starts consuming itself or starts degrading itself and a time comes when their is no existence of star at that place but there is a very high concentration of Gravitational force at that point and finally it starts attracting everything even light! I hope you got the answer.

 

[newjerseyrunner]

When the escape velocity of a star becomes extremely high then it starts consuming itself or starts degrading itself and a time comes when their is no existence of star at that place but there is a very high concentration of Gravitational force at that point and finally it starts attracting everything even light! I hope you got the answer.

This is not accurate. When stars get too big, they don't collapse, they explode: the nuclear forces overwhelm gravity at the radius of even the most densely packed star. Only the core gets crushed enough to turn into a black hole, and it's not simply gravity doing that. Gravity keeps the hole collapsed, but the momentum of the rest of the star falling onto the core is what crushes it into a hole.

 

[Abullais Ghazi]

I simply want to say that when the escape velocity of that star exceeds the velocity of light then there is a formation of black hole takes place. I want to end my answer in simple language other wise it takes a lot of problem to the questioner. You are throwing light on the stages of black hole. The stellar nebula first becomes the massive star then in the red super giant then into supernova and then either in black hole or in neutron star. There many conflicts on theories of black hole and even on there existence. Everyone wants to explain the fundamentals of black hole in his own way. Researches are still going on but still we are unaware of a extremely vast part of universe...

 

[phinds]

I simply want to say that when the escape velocity of that star exceeds the velocity of light then there is a formation of black hole takes place. I want to end my answer in simple language other wise it takes a lot of problem to the questioner. You are throwing light on the stages of black hole. The stellar nebula first becomes the massive star then in the red super giant then into supernova and then either in black hole or in neutron star. There millions of conflict on theories of black hole and even on there existence. Everyone wants to explain the fundamentals of black hole in his own way. Researches are still going on but still we are unaware of a extremely vast part of universe...

I think your attempt to simplify the explanation of "what is a black hole" is just making it more confusing. You make it sound like magic, whereas it is a well understood physical process and no, there are not "millions of conflicting theories"

 

[Chronos]

Any region of space where the escape velocity = c, is a black hole by definition.

 

[newjerseyrunner]

Any region of space where the escape velocity = c, is a black hole by definition.

Isn't this the definition of the event horizon? Isn't a black hole escape velocity >= c?

There are not many conflicting theories, as far as I know there are three: collapse stellar core, direct collapse of primordial black holes, and merger of two preexisting black holes. There are conflicting theories about what's inside the hole, but not how it comes to be. And their existence is certainly known, there is a monstrous one in the middle of our galaxy, we can see stars flying around it.

 

[SteamKing]

This is not accurate. When stars get too big, they don't collapse, they explode: the nuclear forces overwhelm gravity at the radius of even the most densely packed star. Only the core gets crushed enough to turn into a black hole, and it's not simply gravity doing that. Gravity keeps the hole collapsed, but the momentum of the rest of the star falling onto the core is what crushes it into a hole.

This description isn't accurate, either.

When a massive star reaches the end of its life, its core is no longer capable of using nuclear fusion to create enough energy to support itself against gravity wanting to collapse it further. When fusion ceases, gravity wins the battle and collapse occurs rather suddenly. As the collapsing core gets denser and denser, eventually a point is reached in some stars where the core cannot collapse further, and it stops abruptly. The envelope of the star, having rushed into fill the void left by the collapse of the core, strikes the surface and rebounds. The shock wave created by the rebound is sufficient to blow the star's envelope into space, leaving the neutron star core behind:

https://en.wikipedia.org/wiki/Type_II_supernova

If the core is sufficiently massive, when collapse occurs, there will be no rebound, and a black hole will be created:

https://en.wikipedia.org/wiki/Black_hole

Sometimes, even if a dead star leaves a neutron star behind, this star can collect enough additional mass from surrounding gas to collapse into a black hole.

It's also possible for two neutron stars to collide and, because their combined mass is so great, only a black hole is left behind.

 

[|Glitch|]

This description isn't accurate, either.

When a massive star reaches the end of its life, its core is no longer capable of using nuclear fusion to create enough energy to support itself against gravity wanting to collapse it further. When fusion ceases, gravity wins the battle and collapse occurs rather suddenly. As the collapsing core gets denser and denser, eventually a point is reached in some stars where the core cannot collapse further, and it stops abruptly. The envelope of the star, having rushed into fill the void left by the collapse of the core, strikes the surface and rebounds. The shock wave created by the rebound is sufficient to blow the star's envelope into space, leaving the neutron star core behind:

https://en.wikipedia.org/wiki/Type_II_supernova

If the core is sufficiently massive, when collapse occurs, there will be no rebound, and a black hole will be created:

https://en.wikipedia.org/wiki/Black_hole

Sometimes, even if a dead star leaves a neutron star behind, this star can collect enough additional mass from surrounding gas to collapse into a black hole.

It's also possible for two neutron stars to collide and, because their combined mass is so great, only a black hole is left behind.

That works with stars in the 10 to ~130 solar mass range, or stellar remnants with a combined mass greater than ~3 solar masses (such as the collision of two neutron stars). However, once you get stars that are greater than ~130 solar masses the temperature, pressure and gamma-rays from the collapsing core it is sufficient to create electron-positron pairs, which annihilate each other. The thermal energy released by the electron-positron pairs overcomes the gravitational binding energy of the core and the core also explodes, leaving nothing behind. So like neutron stars, which have a range between 1.44 and ~3 solar masses, black holes also appear to have a minimum and maximum range with regard to stellar remnants. Obviously another mechanism, other than a stellar core collapse, is required to produce black holes greater than ~39 solar masses.

 

[phinds]

Obviously another mechanism, other than a stellar core collapse, is required to produce black holes greater than ~39 solar masses.

Since supermassive's seem to all be at the heart of galaxies, it seems very reasonable that they grew from scratch by accreting new material from the very dense area at the center of the galaxy. First enough to create a BH and then more until they had cleared out a large area around them (small fraction of the galaxy's diameter but a good sized volume in absolute terms).

I guess there would have had to have been a star there at some point along the way, but then just more and more feeding.

 

[Neon]

A black hole IS actually just a 'hole' in the fabric of the universe and is black as no light escapes it. Creation of a black hole is more complex depending on the mass of the star of other stuff.

 

[davenn]

A black hole IS actually just a 'hole' in the fabric of the universe

do you have a reference for that ummm interesting comment ?

 

[Neon]

do you have a reference for that ummm interesting comment ?

Well, It will be easier to imagine gravity with the universe as a fabric. I read it somewhere,couldn't remember.

 

[nuuskur]

Any region of space where the escape velocity = c, is a black hole by definition.

How come popular literature writes "nothing can escape, not even light". Light does travel at c, doesn't it? Or is, perhaps, my conception of c at fault here, then?

 

[Neon]

How come popular literature writes "nothing can escape, not even light". Light does travel at c, doesn't it? Or is, perhaps, my conception of c at fault here, then?

He meant >c
nuuskur you are also right too.

 

[davenn]

He meant >c
nuuskur you are also right too.

no he meant c meaning light DOESNT escapeyou really need to stop and think and maybe do some reading before you keep making these regular oddball comments throughout many of your posts

Dave

 

[Neon]

no he meant c meaning light DOESNT escape

So if i reach Earth's escape velocity exactly, i will not get out of earth? exclude friction.

 

[Drakkith]

A black hole IS actually just a 'hole' in the fabric of the universe

It is not. There is no such thing as a 'fabric of the universe'.

 

[nuuskur]

What makes the black hole have such intense gravity? Is it correct to think a black hole is made of compacted matter? How does that look like exactly? Are the elementary particles, neutrons, protons, electrons smashed together? If so, isn't there a limit for how "dense" a black hole could get, yet we speak of black holes and then Supermassive black holes, quasars and whatnot.

 

[Drakkith]

What makes the black hole have such intense gravity? Is it correct to think a black hole is made of compacted matter?

A black hole forms as a result of the extreme compression of matter, which forces a large amount of mass into a tiny area, enough to bend spacetime around it (gravity) so that not even light can escape.

How does that look like exactly? Are the elementary particles, neutrons, protons, electrons smashed together?

We don't know. We don't know how physics works at the extreme scales of energy and gravity found within black holes. Once a particle goes beyond the event horizon, it is essentially 'lost' to us.

If so, isn't there a limit for how "dense" a black hole could get, yet we speak of black holes and then Supermassive black holes, quasars and whatnot.

We don't know of any limit. We've measured supermassive black holes with billions of solar masses, so it seems unlikely that there is some upper limit unless it is staggeringly enormous.

 

[phinds]

A black hole IS actually just a 'hole' in the fabric of the universe and is black as no light escapes it. Creation of a black hole is more complex depending on the mass of the star of other stuff.

There is no "fabric of the universe", that's just a pop-sci type description that is badly overused.

Well, It will be easier to imagine gravity with the universe as a fabric. I read it somewhere,couldn't remember.

"I read it somewhere" is not a valid citation for this site. We all forget where we read things, but when you are defending something that is pop-science, not actual science, you need to do better.

 

[Neon]

Well, It will be easier to imagine gravity with the universe as a fabric. I read it somewhere,couldn't remember.

There is no "fabric of the universe", that's just a pop-sci type description that is badly overused.
"I read it somewhere" is not a valid citation for this site. We all forget where we read things, but when you are defending something that is pop-science, not actual science, you need to do

I am talking about that.Took me a while to find it. If you find what i said eailer confusing.

 

[Drakkith]

I am talking about that.Took me a while to find it. If you find what i said eailer confusing.

The fabric in that video is used as a visual analogy to help explain the variable geometry of space. In other words, it's just showing that a 2d surface can bend and alter the path of objects, much like spacetime can 'bend' and do the same thing. I put bend in quotes because it's not a literal bending. It's a change in geometry, nothing more.

 

[Neon]

Well, It will be easier to imagine gravity with the universe as a fabric. I read it somewhere,couldn't remember.

As i said, it makes it easier tovisualize

 

[Nugatory]

What makes the black hole have such intense gravity?

You don't need any general relativity or exotic science for that. Just take a look at Newton's centuries-old law for classical gravitational attraction, $F=Gm_1m_2/r^2$. There are two ways of making $F$ greater: make one or both masses larger; or make $r$ smaller. For example, gravity at the surface of the Earth is what it is because the radius of the Earth is about 6400 kilometers; if we took the same mass and squished it down into a radius of 3200 kilometers while keeping the mass the same, the gravitational force at the new surface closer to the center would be four times as great.

Although Newton's law breaks down under the conditions that you'll find around a black hole, the basic principle that the force gets stronger as you get closer to the gravitating mass still holds and that's how neutron stars and black holes create their intense gravitational forces. An ordinary star with a radius of many hundreds of thousands of kilometers collapses down to a few kilometers across - and suddenly you can get a lot closer to it and therefore find much stronger gravitational forces.

Is it correct to think a black hole is made of compacted matter?

Most of the space inside a back hole (that is, the space inside the event horizon which is what we generally think of as the surface of the black hole) is actually vacuum. All of the matter is concentrated in a very small area (general relativity says it's a point of zero size, but that just tells us that even the theory of GR isn't accurate under those extreme conditions and we need some new physics) at the center; as Drakkith says, we have no idea what's going on there,and we won't until we figure out some new physics.

However, the most sensible definition of the density of a black hole is to divide its mass by its volume (that is, the volume "inside" the event horizon, and I'm using scare-quotes because there's a subtlety here that we don't need to go into). Most of that volume is empty space bevause the mass is concentrated at the center... And somewhat counterintuitively, the more massive the black hole the lower its density. The supermassive black holes at galactic centers have densities much less than that of air.

 

[stewart brands]

Is it not true that within the event horizon of a so called Black Hole,the mass is confined to an extrodinarily small space relative to other mass distributions everywhere else?
Is it not true that there is so much mass confined that the pressure forces cause limited degrees of freedom for the atoms such that massive amounts of heat derived from atomic motion is dissipate?
Is it not also true that the models go further and describe the elimination of all electrons and the nucleii themselves disassociate into their constituents(bosons subsequent to fermion ejection)?
Is it not true then that this degree of freedom starved mass of energy would have very little heat and be extremely cold?
The question that now follows is :would this mass have the properties and nature of a Bose-Einstein Condensate with very small S / entropy?
If not how would the two states differ?
If the nucleus of a Black Hole is not cold then why not?
If the entropy in this domain does shrink in an extraordinarily unique way then does that mean the bosons travel faster within this medium than they ordinarily would/(compared to a laboratory Bose-Einstein Condensate)?
If they conserve the second law with heat of motion then waht happens if the confinement becomes so great that they must exceed or almost exceed c to conserve the heat?

 

[Chronos]

You make extraordinary assertions without extraordinary evidence - in fact, you offer zero evidence.

 

[Nugatory]

Is it not true that within the event horizon of a so called Black Hole,the mass is confined to an extradinarily small space relative to other mass distributions everywhere else?

That is the result that we get if we take the Einstein Field Equations at face value. Everything inside the event horizon must end up at the central singularity. It is impossible for anything to remain in the region of spacetime "between" the event horizon and the central singularity, for about the same reason that I cannot remain at 12:00 noon today - like it or not, I'm going to move from 12:00:00 to 12:00:01.

However, the answer to all of the "Is it not true...?" questions below is "No, there is no reason to believe that it is true".

Is it not true that there is so much mass confined that the pressure forces cause limited degrees of freedom for the atoms such that massive amounts of heat derived from atomic motion is dissipate?
Is it not also true that the models go further and describe the elimination of all electrons and the nucleii themselves disassociate into their constituents(bosons subsequent to fermion ejection)?
Is it not true then that this degree of freedom starved mass of energy would have very little heat and be extremely cold?
The question that now follows is :would this mass have the properties and nature of a Bose-Einstein Condensate with very small S / entropy?
If not how would the two states differ?
If the nucleus of a Black Hole is not cold then why not?
If the entropy in this domain does shrink in an extraordinarily unique way then does that mean the bosons travel faster within this medium than they ordinarily would/(compared to a laboratory Bose-Einstein Condensate)?
If they conserve the second law with heat of motion then waht happens if the confinement becomes so great that they must exceed or almost exceed c to conserve the heat?

 

[AleksanderPhy]

Well on physics we have rule what says: when objects mass is very big then it have's strong gravity so black hole must be have very big mass

 

[Bernie G]

Sometimes, even if a dead star leaves a neutron star behind, this star can collect enough additional mass from surrounding gas to collapse into a black hole.

It's also possible for two neutron stars to collide and, because their combined mass is so great, only a black hole is left behind.

Not so. The most massive neutron star which has been observed is about 2 solar masses. The smallest black hole observed is about 5 solar masses. Draw your own conclusions.

 

[SteamKing]

Not so. The most massive neutron star which has been observed is about 2 solar masses. The smallest black hole observed is about 5 solar masses. Draw your own conclusions.

There may be BHs which are smaller than 5 solar masses, but we just haven't observed them. There's no violation of any fundamental physics laws if smaller BHs exist.

Two neutron stars have been shown in simulation to merge into a single object which forms a BH.

http://www.iflscience.com/space/what-happens-when-neutron-stars-collide

 

[Neon]

There may be BHs which are smaller than 5 solar masses, but we just haven't observed them. There's no violation of any fundamental physics laws if smaller BHs exist.

Two neutron stars have been shown in simulation to merge into a single object which forms a BH.

http://www.iflscience.com/space/what-happens-when-neutron-stars-collide

Bhs smaller than 5 sm are possible.Those bh are so light than few clues are released ( x ray...) so maybe in the future we will find super light bhs.

 

[|Glitch|]

Gravity effects the entire electromagnetic spectrum, not just photons or objects with mass, correct? Therefore, would not the gravity of a black hole, once the event horizon is crossed, also "consume" infrared radiation? If that is true, than would not the temperature of a black hole at its event horizon always be absolute zero? Would that not contradict quantum field theory in curved space-time that predicts that event horizons emit radiation like a black body with a finite temperature?