Astronomers have discovered a star speeding at about 1.3 million miles per hour across our Milky Way galaxy.
The star is just 400 light-years from Earth. As well as the smallest “hypervelocity” star known, it’s now the closest to the solar system.
Escape Velocity
The star is an intriguing target for astronomers because its fast speed and odd trajectory mean it could escape the Milky Way altogether.
The star, catalogued as CWISE J090552.38+01 365806.8, but also known as J1249+36, was found by citizen scientists and followed up by astronomers using ground-based telescopes. The research has been published as a pre-print paper and accepted for publication in The Astrophysical Journal Letters.
“I can’t describe the level of excitement,” said Martin Kabatnik, a citizen scientist from Nuremberg, Germany, to NASA’s Jet Propulsion Laboratory. “When I first saw how fast it was moving, I was convinced it must have been reported already.”
Mysterious Origins
How J1249+36 got to be moving so fast is challenging for astronomers to explain. One theory is that it may have been a part of a globular cluster— tightly bound balls of ancient stars that orbit the Milky Way and are thought to be the remains of an ancient galaxy—then had a close encounter with two black holes, which hurled it out of the system.
“When a star encounters a black hole binary, the complex dynamics of this three-body interaction can toss that star right out of the globular cluster,” said Kyle Kremer, an assistant professor at the University of California San Diego and a co-author of the paper.
The weird star is also an L subdwarf, the oldest type of star in the Milky Way.
Supernova Kick
Another theory is that it may have been a part of a binary star system of two stars, the other being a dense white dwarf—the compressed core of a dying star. As the white dwarf inevitably exploded as a supernova, it ejected the star.
“In this kind of supernova, the white dwarf is destroyed, so its companion is released and flies off at whatever orbital speed it was originally moving, plus a little bit of a kick from the supernova explosion as well,” said Adam Burgasser, a professor at the University of California San Diego, and lead author on the paper. “Our calculations show this scenario works. However, the white dwarf isn’t there anymore, and the remnants of the explosion, which likely happened several million years ago, have already dissipated, so we don’t have definitive proof that this is its origin.”
Keep On Moving
Nothing in space is stationary. Just the other planets in the solar system orbit the sun—with the Earth traveling at 67,000 miles per hour—the sun orbits the center of the Milky Way galaxy. However, the sun travels at about 560,000 miles per hour. That’s about a third of the speed of this newly found hypervelocity star.
The star’s unusual speed was noticed by the 80,000 members of the citizen science project Backyard Worlds: Planet 9 project, who search through reams of data collected over the past 14 years by NASA’s Wide-field Infrared Survey Explorer (WISE) mission. That mission ended last week. Follow-up observations were made at the Keck Observatory on Maunakea and Pan-STARRS on Haleakalā, both in Hawaiʻi and several other ground-based telescopes.
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