Black Holes Can Spawn Large, Odd Stars, Model Suggests

August 22, 2008

Black holes, with their overwhelming gravitational pulls, generally aren't considered good neighbors for the types of dusty gas clouds where new stars are born.

But sometimes stellar nurseries can escape the maws of supermassive black holes and spawn abnormally large stars on eccentric orbits, a new model suggests.

The stars would be so massive that they'd die relatively young, burning out before the black hole had time to crush them with its gravity.

The finding could help explain why two unexpected groups of young stars, called disk stars, exist near the supermassive black hole at the center of our Milky Way galaxy.

One population contains stars that are just six million years old, and the other has stars that are even younger. (See an updated map of the Milky Way released in June.)

"The high tidal shear from the black hole should tear apart the molecular clouds that form stars," wrote the Scotland-based study authors Ian Bonnell from the University of St. Andrews in Fife and Ken Rice from the University of Edinburgh.

The computer simulations show that when a starmaking cloud approaches a large black hole like the one at our galaxy's heart, the tidal shear can cause the type of celestial commotion that's needed to make new stars. The oversize newborns then circle the black hole on the same bizarre, oblong orbit as their parent gas cloud.

The findings, reported in today's issue of the journal Science, could yield insight into the life cycles of black holes.

"Hopefully, by studying these things, we'll get a better insight into how black holes grow and form," Bonnell said.

Escape Artists

The black hole at the center of the Milky Way has the mass of about a million suns—small by supermassive black hole standards.

Still, its range of influence is wide, Bonnell said. Gas is drawn toward the black hole from a distance of up to 20 light-years.

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