Three times as many stars – and many more planets – possible

Astronomers have peered into eight relatively nearby elliptical galaxies and made a discovery suggesting that small, dim red dwarf stars in these sorts of galaxies might be 20 times more plentiful than in our spiral-shaped Milky Way galaxy.

Messier 87, a giant elliptical galaxy. Galaxies like these might have 20 times more small, dim stars than our spiral Milky Way. (Anglo-Australian Observatory)

If they’re correct, the total number of stars in the universe might be three times bigger than previously thought.

If that’s true – if red dwarf stars are so plentiful – planets orbiting these small, dim stars be expected to be more numerous as well. Astronomers recently discovered a planet orbiting a red dwarf star called Gliese 581, which they believe might support life. More stars … more planets … more possibility for a universe teeming with life.

“There are possibly trillions of Earths orbiting these stars,” van Dokkum said, adding that the red dwarfs they discovered, which are typically more than 10 billion years old, have been around long enough for complex life to evolve. “It’s one reason why people are interested in this type of star.”

Until now, astronomers hadn’t been able to detect them in galaxies other than our own Milky Way and its nearest neighbors. Astronomers have used powerful instruments on the Keck Observatory in Hawaii to detect the faint signature of red dwarfs in eight
massive, relatively nearby galaxies called elliptical galaxies, which are located between about 50 million and 300 million light-years away. They discovered that the red dwarfs, which are only between 10 and 20 percent as massive as the sun, were much more bountiful than expected.

“No one knew how many of these stars there were,” said Pieter van Dokkum, a Yale University astronomer who led the research, which is described in Nature’s Dec.1 Advanced Online Publication. “Different theoretical models predicted a wide range of possibilities, so this answers a longstanding question about just how abundant these stars are.”

The team discovered that there are about 20 times more red dwarfs in elliptical galaxies than in the Milky Way, said Charlie Conroy of the Harvard-Smithsonian Center for Astrophysics, who was also involved in the research.

“We usually assume other galaxies look like our own. But this suggests other conditions are possible in other galaxies,” Conroy said. “So this discovery could have a major impact on our understanding of galaxy formation and evolution.”

For instance, Conroy said, galaxies might contain less dark matter — a mysterious substance that has mass but cannot be directly observed — than previous measurements of their masses might have indicated. Instead, the abundant red dwarfs could contribute more mass than realized.

So the universe might have three times the number of stars – and many more planets – than we knew. As with all astronomical discoveries, this one is waiting for confirmation from other astronomers.

December 1, 2010

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