After a 20-year search, the Hubble Space Telescope has brought back the first photograph of a planet-like object orbiting a nearby star, exuberant astronomers announced here Wednesday.
The object - a gaseous ball of hydrogen about the size of Jupiter but 20 times heavier - is the first confirmed “brown dwarf.” While it’s too big and hot to be a planet, it’s too small and cool to be a star.
Brown dwarfs are the “missing link” between stars and planets, said Shrinivas Kulkarni of the California Institute of Technology in Pasadena, a member of the team that discovered the object.
Astronomers have had previous clues to brown dwarfs’ presence, but this is the first time one has been definitely identified and photographed. An image-sharpening device invented by a former astronaut played a big part in its discovery.
“The evidence is overwhelming - 100 percent strong,” said Alexander Wolszczan, an astronomer at Pennsylvania State University.
Two other “very likely” brown dwarfs have been found, Kulkarni said, but definite confirmation has not been made.
In addition, at least four planets outside the Earth’s solar system have recently been discovered by indirect means.
However, these new planets could not be seen or photographed by even the most powerful telescopes. Instead, their presence was detected by observing minute irregularities in the activity of their parent stars.
Tagged with the unglamorous name, GL229B, the newly discovered brown dwarf is located near a faint red star known as Gliese 229, 18.6 light years (about 100 trillion miles) from Earth in the constellation Canis Major (the Big Dog). It is a little farther from its companion star than Pluto is from the Earth’s Sun.
The Sun is at least 250,000 times brighter than GL229B, which is the faintest object ever seen orbiting another star. To spot it required a new image-sharpening device invented by Sam Durrance, a former astronaut now at Johns Hopkins University in Baltimore.
The device enabled the Caltech and Hopkins astronomers to screen out the overpowering light from the star so they could look for a nearby dwarf. They used this technique to survey about 100 stars within 30 light years of Earth, using a ground-based telescope on California’s Mount Palomar.
They spotted the brown dwarf in October 1994, but could not be sure what they had found.
“We’ve had a lot of false alarms before,” said Steve Maran, an astronomer at the Goddard Space Flight Institute in Baltimore.
But on Nov. 17, a camera on the Hubble telescope snapped a stunningly clear picture of GL229B from space, confirming that the object was real.
The final proof that it was a brown dwarf was the detection of methane, a gas found in the atmosphere of giant planets like Jupiter but not in stars.
“The difference between Jupiter and a brown dwarf is very slim,” Durrance said. “The radius is the same, but the dwarf is hotter.”
Jupiter’s temperature is 170 degrees Fahrenheit below zero. The Caltech and Hopkins astronomers said their brown dwarf is about 1,300 degrees above zero, about half the temperature of the smallest star. The sun is about 8,000 degrees at the surface, millions of degrees inside.
Canis Major is visible in the winter sky, below and to the right of Orion. Sirius, the brightest star in the sky, is in the same constellation.
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