General size comparison between a low mass star, a brown dwarf, and the planet Jupiter.

Coldest Star ever Found

General size comparison between a low mass star, a brown dwarf, and the planet Jupiter.
Terrence Aym's image for:
"Coldest Star ever Found"
Caption: General size comparison between a low mass star, a brown dwarf, and the planet Jupiter.
Image by: NASA/JPL-Caltech/UCB
© This file is in the public domain because it was created by NASA.

WD 0806-661 B may not replace Florida or Hawaii as getaway hotspots for vacation-seeking Americans, but it could be one of the galaxy's most unusual hotspots.

Although astronomers have recently discovered Earth-like planets during deep space observations, WD 0806-661 B is not a planet, but a star. Amazed scientists describe its surface temperature as the coldest ever found, "like a summer day on Earth."

Stillborn, brown and white dwarf stars

WD 0806-661 B is what's known as a brown dwarf, a star that began as other stellar objects, but failed to achieve enough mass from the dust and gases it condensed from to ignite a nuclear furnace.

The Solar System has a planet several orders of magnitude below a brown dwarf: Jupiter. Like WD 0806-661 B, the Jovian world failed to accumulate the mass needed to start burning. It also failed to become a star and remained a giant world with many of the attributes of a protostar.

On the other hand, the brown dwarf WD 0806-661 B can be thought of as a star somewhere between the stillborn star, Jupiter, and the sun.

The coldest star ever was discovered by Kevin Luhman, a Penn State Associate Professor of Astronomy and Astrophysics, using NASA's Spitzer infra-red space telescope. After scanning nearly 600 stars close to Earth, Luhman found WD 0806-661 B sitting 63 light years away.

Luhman and his astronomical team first published their discover in Spring of 2011. Now they are publishing a follow-up paper in the Astrophysical Journal confirming the brown dwarf's record smashing cool surface temperature.

Another surprise was the discovery that the cold brown dwarf is orbiting a white dwarf. White dwarfs are stars that go through a normal cycle like the sun and then collapse after using up all their nuclear fuel. Having the approximate mass of the sun, white dwarfs compress to roughly the size of Earth. They're made up primarily of electron-degenerate matter.

Small star with a very big orbit

Describing the cold star, Luhman said, "It is a very small star with an atmospheric temperature about as cool as the Earth's. The distance of this white dwarf from the sun is 63 light-years, which is very near our solar system compared with most stars in our galaxy."

Scientists say the tiny brown dwarf's orbit is huge. They calculate WD 0806-661 B's orbit is 2,500 times the distance between the sun and Earth.

For an astronomer, finding the coldest brown dwarf is like winning an unofficial contest. Since 1995 astronomers and astrophysicists have competed with each other to find the coldest stars.

There's a real science behind their efforts, though. Brown dwarfs have been recognized—since their discovery in 1995—to be like little space laboratories that help scientists better comprehend the nature of Earth-like planets and determine the composition of their atmospheres.

More about this author: Terrence Aym

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