Aha. Here is what they were basing that speculation on (in 2000):
"Careful analysis reveals that each [putative] black hole is approximately six times the mass of the Sun. If they were ordinary stars with this bulk they would be bright enough to outshine the more distant background star. The masses are also too large to be white dwarfs or neutron stars. This leaves a black hole as the most likely explanation."
..."most likely" if you do not know of, or accept the reality of mirror matter. Nor did they consider quark stars then. A couple of years later quark stars were becoming 'trendy':
http://www.wired.com/science/discoveries/news/2002/04/51943 Maybe HH, the champion of MM will weigh-in on this...? Robin van Spaandonk wrote:
Suppose that the Sun orbits about a black hole once every 27000 years
approximately.
Although that cannot be ruled out, there seems to be no good evidence AFAIK that a black hole has been documented nearby (and perhaps cannot be situated anywhere other than a galactic core) ... or is there?
http://hubblesite.org/newscenter/archive/releases/2000/03
