A young star in the midst of a dramatic growth phase has been observed with the help of ESA’s Gaia satellite and NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) and Spitzer telescopes. Named Gaia 17bpi, the newfound star belongs to a class of stars that gain mass when matter swirling around the star falls onto its surface. The in-falling matter causes the star to appear about 100 times brighter. The discovery will be published in the Astrophysical Journal.
This illustration shows a young star undergoing a type of growth spurt. Upper panel: material from the dusty and gas-rich disk (orange) plus hot gas (blue) mildly flows onto the star, creating a hot spot. Middle panel: The outburst begins — the inner disk is heated, more material flows to the star, and the disk creeps inward. Lower panel: the outburst is in full throttle, with the inner disk merging into the star and gas flowing outward (green). Image credit: Caltech / T. Pyle, IPAC.
Gaia 17bpi belongs to a group of stars known as FU Ori stars, named after the original member of the group, FU Orionis found in the constellation of Orion.
Typically these FU Ori stars, which are less than a few million years old, are hidden behind thick clouds of dust and are therefore hard to observe.
However, University of Exeter’s Professor Tim Naylor and co-authors spotted the star undertaking a dramatic phase of evolution, whereby matter swirling around falls onto the star, and so bulking up its mass. They were able to see this stellar outburst through both infrared and visible light.
“It’s taken a lot of patient waiting and careful sifting of data to uncover this star, but once we realized what was going it has exceeded expectations,” said Professor Naylor, co-author of the study.
“It also gives us insight into events which may have happened as the planets in our own Solar System were beginning to form from a disc of material around the Sun.”
Gaia 17bpi was first spotted by ESA’s Gaia satellite, which scans the sky continuously and makes precise measurements of stars in visible light.
NASA’s NEOWISE spacecraft serendipitously observed the star’s brightening at the same time that Gaia did.
Additional searches in NEOWISE’s data archives and the archives of NASA’s Spitzer Space Telescope showed that these spacecraft had detected the flare-up in infrared light more than one year earlier.
“These FU Ori events are extremely important in our current understanding of the process of star formation but have remained almost mythical because they have been so difficult to observe,” Caltech’s Professor Lynne Hillenbrand, lead author of the study.
“This is actually the first time we’ve ever seen one of these events as it happens in both optical and infrared light, and these data have let us map the movement of material through the disk and onto the star.”
Gaia 17bpi is only the 25th member of the FU Ori class found to date, and one of only about a dozen caught in the act of an outburst.
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Lynne A. Hillenbrand et al. 2018. Gaia 17bpi: An FU Ori Type Outburst. ApJ, in press; arXiv: 1812.06640
