In Search of Elusive (or Illusive?) Black Holes
Cowen, Robert C., The Christian Science Monitor
Last year was a good year for black holes.
After two centuries of speculation and two decades of inconclusive data, a Hubble Space Telescope research team appeared finally to have nailed one. Now a radio-astronomy team reports that it probably has pinned one down too.
A black hole is a mass that has collapsed to such a density that its gravity is too strong for anything - including light - to escape its immediate vicinity. Einstein's theory of general relativity says that these bizarre things should exist. Many astronomers would like them to exist. They would provide a handy explanation for the massive energy pouring out as radiation and sometimes as jets of matter from so-called active galaxies and other objects. So black-hole enthusiasts feel gratified to finally have what both research teams call compelling evidence of these wonders.
But wait a minute. As sometimes happens at a "eureka moment" in science, skeptics have arisen to dampen the celebration. Last year also brought new challenges to Einstein's theory. These modifications suggest that there's no theoretical basis for black holes after all. And that would please a host of skeptics who don't like the appearance of flimflam in astrophysics.
Black holes have smelled a bit like a "too-good-to-be-true" confidence game. Like an investment scam that promises outrageously high returns, a proposed black hole can be shaped theoretically to account for any amount of power an astronomer wants.
It works like this. Stars, dust, and gas caught in a black hole's gravity orbit in a so-called accretion disk. As this orbiting matter eventually falls into the black hole, it releases gravitational energy just as does water flowing over a hydroelectric dam. Moreover, the in-falling matter adds to the black-hole mass and increases its gravity. So, by gobbling up matter, a black hole can be any size needed to account for observed energy outpourings.
But there's a catch. If you look inside this black-hole scheme, you find that, like an investment scam, there is, in a sense, nothing there. …