Astronomers have imaged a very young brown dwarf, or failed star, in a tight orbit around a young nearby sun-like star.
An international team led by University of Hawaii astronomers Beth Biller and Michael Liu with help from University of Arizona astronomer Laird Close and UA graduate students Eric Nielsen, Jared Males and Andy Skemer made the rare find using the Near-Infrared Coronagraphic Imager, or NICI, on the international 8-meter Gemini-South Telescope in Chile.
What makes this discovery special is the proximity between the 36 Jupiter-mass brown dwarf companion, dubbed PZ Tel B, and its primary star, named PZ Tel A. They are separated by only 18 Astronomical Units, or AUs, similar to the distance between Uranus and the sun.
Most young brown dwarf and planetary companions found by direct imaging are at orbital separations greater than 50 AUs – larger than the orbit of Pluto, at 40 AUs.
In addition to its small separation, in just the past year the researchers observed PZ Tel B moving quickly outward from its parent star.
An older image, taken seven years ago and reanalyzed by Laird Close, a professor at UA's Steward Observatory and the department of astronomy, showed PZ Tel B was obscured by the glare from its parent star as recently as 2003, indicating its orbit is more elliptical than circular.
"Because PZ Tel A is a rare star being both close and very young, it had been imaged several times in the past," said Close. "So we were quite surprised to see a new companion around what was thought to be a single star."
Lead author and UA graduate Beth Biller said, "PZ Tel B travels on a particularly eccentric orbit – in the last 10 years, we have literally watched it careen through its inner solar system. This can best be explained by a highly eccentric, or oval-shaped, orbit."
The host star, PZ Tel A, is a younger version of the sun, having a similar mass but a very young age of only 12 million years (about 400 times younger than the sun). In fact, the PZ Tel system is young enough to still possess significant amounts of cold circumstellar dust, which may have been sculpted by the gravitational interaction with the young brown dwarf companion.
This makes the PZ Tel system an important laboratory for studying the early stages of solar system formation. With an estimated mass of 36 times that of Jupiter, PZ Tel B's orbital motion has significant implications for what type of planets can form (and whether planets can form at all) in the PZ Tel system.
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The discovery of PZ Tel B is described in a paper being published by Astrophysical Journal Letters.
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