No. 99: May-Jun 1995
Like the Big Bang, black holes are an astronomical staple. Most scientists and laymen assume that black holes are proven, well-observed denizens of the cosmos. Certainly the media entertains no doubts! Let us take a skeptical look.
Does theory require black holes? In 1939, R. Oppenheimer and H. Snyder showed on paper that a massive star could collapse and create a black hole, assuming the correctness of stellar theories and General Relativity. Initially, scientists were skeptical about black holes because of their bizarre properties: They emit no light and inhale unwary starships. Black holes are also singularities, and singularities make scientists nervous. In the black-hole singularity, thousands of stars are swallowed and compressed into an infinitesimally small volume. (Ref. 1) This grates against common sense.
The philosophical uneasiness about black holes is worsened by the discovery that they:
"...threaten the universe with an irreversible loss of information, which seems to contradict other laws of physics." (Ref. 2)
Adding to these problems are nagging doubts about General Relativity, which underpins black-hole theory. Recently, some theorists have shown that General Relativity requires that two bodies of approximately equal size not attract one another! (Ref. 2)
Despite all these qualms, black holes have become a fixture of astronomy because they promise to explain the incredibly powerful energy sources seen in the cores of galaxies.
Do astronomers really observe black holes? The answer is: MAYBE. And even if YES, there are not nearly enough of them to satisfy theory.
To illustrate, according to present theory, when stars weighing in at less than three solar masses collapse, they become neutron stars; if larger, the stars turn into small black holes. Theoretically, there should be one small black hole for every three neutron stars. But with some 500 neutron stars already pin-pointed, only 3 "possible" small black holes have been given votes of confidence; namely, Cyg X-1, LMC X-3, and AD 620-00. All objects previously proclaimed to be small black holes have instead turned out to be neutron stars. (Ref. 1)
The case for massive black holes weighing in at millions of solar masses is not overwhelming either. These are supposed to lurk in the centers of galaxies. To find them, astronomers look for intensely bright spots in galaxies, around which swirl stars at speeds approaching the speed of light as they are sucked into the black hole's maw. Such fantastic celestial maelstroms do seem to exist, as evidenced by "something" in the giant elliptical galaxy M87. (Ref. 1)
New claims for massive black holes are always being put forward. The spiral galaxy NGC 4328, for example, is thought to harbor a supermassive black hole weighing in at 40 million solar masses! (Ref. 3) However, claims for massive black holes are also being shot down all the time. Several have thought they had found a massive black hole at the center of our own galaxy. This no longer seems likely. (Ref. 4)
Conclusion. Don't be too quick to accept such bizarre constructs as black holes, whether small or massive.