Black holes

[Lizwi]

1. Is there an evidence for black holes

2. Is singularity possible?

3.If the Sun becomes a blackhole, will the planet's continue to revolve as if the Sun is still present?

[swansont]

1 hour ago, Lizwi said:

1. Is there an evidence for black holes

2. Is singularity possible?

3.If the Sun becomes a blackhole, will the planet's continue to revolve as if the Sun is still present?

1. Yes.

2. Unknown. AFAIK the thinking is no, it's not physical, which us why other approaches are being investigated.

3. The planets wouldn't notice, gravitationally, since gravity wouldn't be different.

[mathematic]

Note that the sun is too small to become a black hole.

[Lizwi]

Okay, thanks, the Sun is too small.

Is there a general Shwarzchild radius for objects to become a black whole?

[swansont]

2 hours ago, Lizwi said:

Okay, thanks, the Sun is too small.

Is there a general Shwarzchild radius for objects to become a black whole?

R = 2GM/c²

[Lizwi]

[Endy0816]

13 hours ago, Lizwi said:

Yes, that is correct.

[Strange]

On 11/12/2019 at 9:12 AM, Lizwi said:

Okay, thanks, the Sun is too small.

Is there a general Shwarzchild radius for objects to become a black whole?

It is not really that the sun is too small. There is, in principle, a Schwarzschild radius for any mass. The problem is that there is no mechanism to make the sun turn into a black hole.

A black hole with the mass of the sun would have a radius of about 3km. [Edit: sorry, I see you have already worked this out.]

Edited November 13, 2019 by Strange

[swansont]

As Strange notes, it's the "US New England driving directions" problem of "you can't get there from here" because of all the steps that prevent collapse. You could, in principle, have a primordial black hole that grows in size to have the mass of the sun

[Janus]

On 11/12/2019 at 3:20 AM, Lizwi said:

More correctly, it would have to have this radius with it present mass.

As indicated by others here, this won't ever happen.  Stars all have life cycles which they follow and the staring mass of the star determines the end state.  For example, as our star fuses hydrogen, helium builds up in its core.  Eventually, all the hydrogen at the core is used up, the remaining helium cools and collapses. This allows the hydrogen in the shell surrounding the core to fuse.  The Sun swells in to a Red giant.  At some point after that enough pressure builds up in the core to cause the helium to fuse into Carbon.  But that's the end of it.  The remaining mass of the Sun just isn't enough to cause the Carbon to fuse.  The Sun shrinks, slowly using up its remaining fuel.  But it never gets small enough to form a black hole. The forces between the atoms are always going to be enough to prevent this.  By this time, the Sun will have lost almost 1/2 of its mass, and will have shrunk to about the size of the Earth (well short of what is needed to form a black hole).

If a star is massive enough, it will not only fuse the carbon, but it continue to fuse the elements that build up in its core all the way up to Iron*.  Now up to Iron fusion releases energy, which helps support the weight of the star. From Iron upwards, it takes a net input of energy for fusion to occur.

With these stars, the Iron core will build up larger and larger.  eventually it gets so big, that it is forced to fuse. This sucks energy from the star, which was previously "holding up" the outer layers. These outer layers crash down on to the suddenly shrunken,  which cause them to ignite in a huge supernova explosion, both blowing away a good part of the star and exerting  lot of pressure on the core, collapsing it even further.  If the core is massive enough to start with, it can be compressed enough to reach a point where no known force will hold it up against it own gravity and it collapses into a black hole (if it not quite that massive, the process stops with the formation of a neutron star.)

*Keep in mind that this is a somewhat of a "Cliff notes" version of what happens, the actual dynamics are a bit more complicated.