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The Question

(Submitted August 05, 1997)

How has it been demonstrated that black holes are real? What are the various positions that astrophysicists take regarding black holes? Are black holes related to the big bang? How or in what way?

The Answer

Astrophysicists generally agree that black holes exist. There is good observational evidence from X-ray observations and from the Hubble Space Telescope that there are massive black holes (with masses more than a million times that of the Sun) exist in the centers of some galaxies. For further information, check the Active Galaxies topic of the Level 1 or Level 2 sections of our web site. (http://imagine.gsfc.nasa.gov)

In addition, there is also evidence for black holes which result from the final stage of a star's life. These "galactic" black holes (so called because they are in our Galaxy), are usually 3 - 10 times the mass of the Sun. They also often orbit a companion star, and by observing the X-rays emitted from the region near the black hole and/or the visible light from the companion, a mass can be determined for the black hole. If it is larger than the accepted mass for a neutron star (about 1.5 times the mass of the Sun), then astronomers generally agree the object is a black hole. There are quite a number of these objects known in our galaxy.

For further info, check the Black Holes topics on our web site.

No, black holes are not related to the big bang.

Jim Lochner
for Ask an Astrophysicist

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