More Black Hole Questions

1. Dec 25, 2005

ThomasFuhlery

Ok...
Let's say there is a star with a planet orbiting it which supports life. If, somehow (never mind how), the star within an instant became massive beyond the Chan. Limit...
1) how long would it take to form a black hole (assuming that the mass kept increasing until it reached a black hole state, or, in other words, could this process be accelerated by the addition of more mass?), and
2) how would this affect the life on the planet orbiting the star? (or exactly how would they die and how long would that take?)
thanks for any input.

2. Dec 25, 2005

pervect

Staff Emeritus
It's perfectly possible for a star to be more massive than the Chandrasekhar limit if it has fuel to burn. It's only when the star runs out of fuel and becomes a white dwarf that the Chandresaekhar limit becomes important.

The closest scenario to what you describe would be an existing white dwarf star, gaining mass by pulling it off from a companion star. In this situation, when the white dwarf star gains enough mass, it explodes in a supernova (type I, I think). I'm not sure of the exact details of the process or how long it takes - white dwarfs are pretty small, so it probably happens fairly quickly.

Anyone on a nearby planet will be thouroughly fried.

3. Dec 27, 2005

ThomasFuhlery

Ok, so...
If there is a star that runs out of the fuel it takes to remain stable, then depending on its mass it will either supernova, collapse into a white dwarf, or collapse into a black hole, correct? So a white dwarf is a star that has run out of fuel, collapsed, but not violently enough (because it didn't have enough mass/crushing power) to form a black hole...and then heated up from the collapse to form a semi-stable ultra dense white dwarf. still correct? If so, then I guess what I'm asking is this:

1. If there is an existing white dwarf, can it have planets in orbit of it?

2. If it were to continually gain mass (and thereby use its fuel faster), whether by drawing it from another companion star or whatever else, could it collapse from a white dwarf into a black hole (as opposed to a supernova)?

3. what would happen to a planet in orbit of a white dwarf were it to collapse into a black hole?

4. Is there any concievable way (whether it has been observed or not) for a white dwarf to be forced back onto the main sequence once it has collapsed?

I know this is a lot to answer but I would appreciate anything you could give me. Thanks again!

4. Dec 27, 2005

Chronos

A stellar mass black hole would gravitationally behave just like the star from which it collapsed, gravtationally.