1 December 2010

Numbers of stars in universe tripled

Cosmos Online
There are three times as many stars in the universe as they had previously supposed - and "possibly trillions of Earths orbiting these stars" - say astronomers.
elliptical galaxy

SYDNEY: There are three times as many stars in the universe as they had previously supposed – and “possibly trillions of Earths orbiting these stars” – say astronomers.

The startling find, published in the British journal Nature, has exciting implications for the discovery of new planets as well as theories on galaxy formation and dark matter.

Astronomers Pieter van Dokkum and Charles Conroy found greater than expected numbers of faint, small stars known as red dwarfs in relatively close galaxies as observed with Hawaii’s twin Keck Telescopes.

“Possibly trillions of Earths”

More stars means potentially many more planets, says lead author and astronomer van Dokkum, from Yale University, Connecticut: “There are possibly trillions of Earths orbiting these stars,” he said.

There are currently 504 known exoplanets, most of which are large gaseous planets similar to or larger than Jupiter. But Earth-like planets have been found around red dwarf stars, including Gliese 581, a red dwarf whose planet count was recently [Sept] updated to six.

The red dwarf stars that the team discovered are typically more than 10 billion years old, old enough for complex life to have evolved, van Dokkum points out. “It’s one reason why people are interested in this type of star.”

More red dwarfs in elliptical galaxies

In terms of sheer numbers, stars of low mass are more dominant that hotter stars such as the Sun, which is five to 10 times more massive than a red dwarf, according to University of Sydney astronomer Scott Croom, who was not involved in the research.

Although there is no reason for red dwarf stars to have more Earth-like planets than Sun-like stars, “if there are more stars, there are more stars that can support life,” Croom says.

Van Dokkum and Conroy found 80% of stars within eight elliptical galaxies 50 million and 300 million light-years away were red dwarfs. Elliptical galaxies are egg-shaped galaxies that generally evolved earlier than spiral galaxies like the Milky Way.

Major impact on theory of dark matter

“No one knew how many of these stars there were,” says van Dokkum.

The results show elliptical galaxies have 20 times the number of red dwarfs as the Milky Way, which has a “major impact” for theories on galaxy evolution and calculations of the amount of dark matter required to ‘balance’ observations of the galaxies, says Conroy, from the Harvard-Smithsonian Center for Astrophysics in Massachusetts.

“We usually assume other galaxies look like our own. But this suggests other conditions are possible in other galaxies,” he says. If red dwarfs are more abundant that astronomers realized, it may mean less dark matter is required in models that look at how star mass and galaxy rotation are linked.

Astronomers first postulated the existence of dark matter after observations of physical factors such as motion of galaxies didn’t fit with galaxies’ supposed mass.

This ‘missing mass’ became known as dark matter and is intrinsic to theories of galaxy evolution. “It’s telling us elliptical galaxies have less dark matter than we originally thought and more of the mass is provided by stars,” said Croom.


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