astronomy

Red dwarfs increase star total threefold

YALE (US) — Small, dim stars known as red dwarfs are much more prolific than previously thought—so much so that the total number of stars in the universe is likely three times bigger than realized.

Because red dwarfs are relatively small and dim compared to stars like the Sun, they haven’t been detected in galaxies other than the Milky Way and its nearest neighbors before now.

Astronomers 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, located between about 50 million and 300 million light years away.

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,” says Pieter van Dokkum, professor of astronomy and physics at Yale University. “Different theoretical models predicted a wide range of possibilities, so this answers a longstanding question about just how abundant these stars are.”

The research appears online in the journal Nature.

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

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

For instance, Conroy says, 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.

In addition to boosting the total number of stars in the universe, the discovery also increases the number of planets orbiting those stars, which in turn elevates the number of planets that might harbor life. In fact, a recently discovered exoplanet that astronomers believe could potentially support life orbits a red dwarf star, called Gliese 581.

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

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