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rw4pt6
2008-Sep-25, 02:07 AM
Is it true that if a large star becomes a black hole, the black hole's
mass is slightly less than the original star?
Thanks,
roy

neilzero
2008-Sep-25, 02:26 AM
Yes, perhaps half of the mass is ejected by the blast, but some is recaptured within a year. Several percent is not recaptured even in a billion years. Neil

Spaceman Spiff
2008-Sep-25, 03:30 AM
Is it true that if a large star becomes a black hole, the black hole's
mass is slightly less than the original star?
Thanks,
roy

He might also be referring to the effects of the gravitational binding energy. As the mass sinks deeper into the potential well, the resulting mass diverges from (and becomes smaller than) that computed with the same total material spread out to infinity. If I recall correctly, the mass ratio is a factor of 2 for a black hole.

astromark
2008-Sep-25, 07:54 AM
As a star ends its hydrogen burning period great instability is common. If the mass of the star is high enough when it sheds its outer layers into space the core begins to collapse under the gravity pressure of its mass. If that gravity force accelerates mater ( Photons ) to greater than C. Then it has formed a black hole. Yes the mass of this black hole must be less than the original star., BUT it does not need to stay that way. N.B. We do not now that all black holes are formed this way. Its not unreasonable to assume that matter and its density could form black holes at the core of galaxies without ever having formed a star.

Spaceman Spiff
2008-Sep-26, 12:32 AM
As a star ends its hydrogen burning period great instability is common. If the mass of the star is high enough when it sheds its outer layers into space the core begins to collapse under the gravity pressure of its mass. If that gravity force accelerates mater ( Photons ) to greater than C. Then it has formed a black hole. Yes the mass of this black hole must be less than the original star., BUT it does not need to stay that way. N.B. We do not now that all black holes are formed this way. Its not unreasonable to assume that matter and its density could form black holes at the core of galaxies without ever having formed a star.

What the heck? Neither photons nor matter can be accelerated to speeds greater than c.

And this shedding of the "outer layers" is generally referred to as an explosion, called a supernova. Other than that point, what did the rest of your post have to do with the question?

Spaceman Spiff
2008-Sep-27, 04:23 PM
rw4pt6: Have we answered your question? If not, could you please clarify what it is you are trying to understand?

rw4pt6
2008-Sep-30, 01:00 AM
Sorry for the delay. My question was answered.
If a star-one star only-became a black hole, the mass and gravity of
the black hole would be less than the original star.
Thanks,
Roy

sohh_fly
2008-Sep-30, 01:17 AM
why wouldn't the mass of the blackhole be more than the original star, if in the creation of the BH the fabric of spacetime was somehow altered from it's pre BH state? . could the puff's of gas that is shedded from the star contain more mass than the energy of ripping space-time leaving several times the size of the BH in the after effect?

what i mean is , if there is a mass in the BH?
how is it determined what has more mass???