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The Question

(Submitted May 27, 2004)

If a large star collapses into a singularity, I've been told that it indeed becomes infinitesimally small. What area of space would the black hole at the center of M87 occupy? Is it as small as a one solar mass black hole or is there a difference in sizes as far as singularities go? Is the black hole at the center of M87 considered a singularity?

Many thanks if you can please clarify this for my public who have asked about this quandry many times

The Answer

According to classical physics, the size of the singularity of any black hole would be zero. However, when you factor in quantum physics, the singularity does, indeed, have a size.

I'm not sure what the size of the singularity of the black hole at the center of M87 would be, but there would be a dependence on the mass of the black hole. According to the Cosmology Primer on the Berkeley web site:
http://cosmology.berkeley.edu/Education/IUP/Big_Bang_Primer.html
the singularity that started our whole Universe was about the size of a dime (!)

We hope this helps!

Barbara & Stefan
For the "Ask an Astrophysicist" team

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