In paleontology, the supposed missing link between birds and dinosaurs was discovered in the form of a feathered but lizard-like fossil. Now, astronomers have found an interesting missing link of their own.
Scientists using the United Kingdom Infrared Telescope and the Sloan Digital Sky Survey have recently discovered three new types of brown dwarf or "failed stars," objects greater in mass than giant gas planets like Jupiter, but smaller in mass than true stars. The newly discovered objects represent the first sighting of an intermediate link between hot, young brown dwarfs and cooler, older ones.
"Previously, brown dwarfs were known in two different spectroscopic flavors," said Sandy Leggett of the Joint Astronomy Center in Hawaii and one of the astronomers involved in the discovery. The two flavors in question included an "L" type, a cool, more star-like brown dwarf, and a "T" type, which more closely resembles gas-giant planets. "We were very excited because the objects we found link these two types," said Leggett.
Brown dwarfs are of great interest to astronomers because they themselves represent an intermediate form between gas planets and stars. Brown dwarfs are more massive than gas giants like Jupiter and Saturn, but do not reach the minimum mass (8 percent of our suns mass) needed to become a true star. Therefore, while stars are able to sustain nuclear reactions necessary to shine bright for billions of years, brown dwarfs shine for a brief initial period, but then they soon cool off, becoming fainter and fainter as time marches on.
The discovery of an intermediate type of brown dwarf was particularly pleasing to astronomers working on the project because they were lucky enough to find not one, but three new brown dwarf types which, according to Leggett, "form a very clear sequence" between young, intermediate and old brown dwarfs.
"The lack of previous identifications had suggested that [the intermediates] might be very rare objects," explained Tom Geballe of the Gemini Observatory in Hawaii, who was also involved in the discovery. "Having found three of them in succession, we are not so sure that they are so rare."
Brown dwarfs are difficult for astronomers to find at short, optical wavelengths because they are so dim. As a result, researchers studying these objects must search the skies using infrared, or long-wavelength, detectors. The new "missing-link" brown dwarfs were discovered this way, with the United Kingdom Infrared Telescope in Hawaii.
"We found three objects in images taken by the Sloan Digital Sky Survey as being extremely red and faint," said Jill Knapp, a Princeton astronomer who also worked on the project. "We then measured their brightness at infrared wavelengths, using the United Kingdom Infrared Telescope. The infrared data showed that the objects are intermediate in their properties between L-type dwarfsand T-type dwarfs."
Though the find is revolutionary, it is just one more in a string of recent discoveries about brown dwarfs, which had, until recently, been objects of complete mystery to astronomers. "This is part of a small revolution going on in stellar and planetary astronomy right now," explained Knapp.
Still, astronomers say there is much that remains unknown about brown dwarfs, like their chemistry, abundance and exact distances from Earth and our solar system. Researchers say this recent detective work to find the missing links between young and old brown dwarfs will advance the understanding of these mysterious objects.
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