Brown dwarf stars are often referred to as “failed stars” because they were born with insufficient mass to light their nuclear-fusing stellar fires–even though they formed just like their more massive, fiery, glaring, hydrogen-burning “true” star kin. Because of their puny size, astronomers have found it difficult to distinguish brown dwarfs from giant planets, such as our own Solar System’s brightly banded behemoth, Jupiter. This is because gas-giants like Jupiter and “failed stars” possess some of the same characteristics. In June 2019, a team of astronomers using preliminary results obtained from a new Gemini Observatory survey of 531 stars, released their findings that it appears more and more probable that brown dwarfs and large planets have very different origins. Hence, gas giants and brown dwarfs are much too distantly related to be “kissing cousins.”
The GPI Exoplanet Survey (GPIES) is one of the most sensitive and largest direct imaging exoplanet surveys to date, and is still ongoing at the Gemini South Telescope in Chile. “From our analysis of the first 300 stars observed, we are already seeing strong trends,” commented Dr. Eric L. Nielsen in a June 11, 2019 Gemini Observatory Press Release. Dr. Nielsen, of Stanford University in Palo Alto, California, is the lead author of the new study.
Back in November 2014, GPI Principal Investigator Dr. Bruce Macintosh, who is also of Stanford University, and his international team started to observe almost 600 nearby stars with the newly commissioned instrument. GPI is funded with support from the Gemini Observatory partnership, the most coming from the US National Science Foundation (NSF). The NSF and the Canadian National Research Council, funded scientists participating in GPIES.
Imaging a distant alien planet, that is in orbit around a star beyond our Sun, is extremely challenging. Indeed, the difficult task is made possible only with the use of a handful of instruments. The problem is that these faraway worlds are small, dim, and reside close to the overwhelming glare of their roiling, broiling stellar parent. Indeed, the challenge of observing a dim and distant exoplanet can be compared to spotting a moth flying in front of a street lamp when the observer is 10 miles away. Even the brightest planets are overwhelmed by the glare of their parent star. Although the brightest planets emit a tender glow, they are still about ten thousand times dimmer than their star. The good news is that GPI has the ability to observe planets that are as much as a million times dimmer–it is much more sensitive than earlier planet-imaging instruments. “GPI is a great tool for studying planets, and the Gemini Observatory gave us time to do a careful, systematic survey,” Dr. Macintosh commented in the June 11, 2019 Gemini Observatory Press Release.
GPIES is now at the end of its mission. Out of its first batch of 300 stars, GPIES detected half a dozen giant planets and a trio of brown dwarfs. “This analysis of the first 300 stars observed by GPIES represents the largest, most sensitive direct imaging survey for giant planets published to date,” Dr. Macintosh added. Even though brown dwarfs are more massive than planets, they are still the runts of the stellar litter because they have not accumulated sufficient mass to fuse hydrogen into heavier atomic elements–like true stars. “Our analysis of this Gemini survey suggests that wide-separation giant planets may have formed differently from their brown dwarf cousins,” Dr. Nielson explained in the same Gemini Press Release.