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COSMOLOGISTS are this week beginning to rethink their ideas about how
galaxies form after the discovery that a nearby galaxy lacks a giant black hole
at its core.

Astronomers can detect giant black holes in galaxies by looking for their
effect on the motions of stars close to the galactic nucleus. All of the 30 or
so galaxies previously investigated contain black holes with masses more than a
million times that of the Sun.

But a study of the spiral galaxy M33鈥攖o be published in
Science鈥攈as drawn a blank. A team led by David Merritt of Rutgers
University in New Jersey calculated that if it had a central black hole, it
could be no heavier than 3000 solar masses.

Until now, the apparent ubiquity of supermassive black holes suggested that
the black holes form first and then pull in material to form a galaxy around
them. 鈥淚 don鈥檛 know if we would have expected this,鈥� says Douglas Richstone of
the University of Michigan. 鈥淚 think it鈥檚 a problem for the black hole story.鈥�
Merritt says M33 may be evidence that astronomers have been getting the chicken
and egg the wrong way round. 鈥淢33 looks like a fairly young galaxy,鈥� he says.
Perhaps a supermassive black hole may yet form in M33.