A jaw-droppingly fast star that is one of the oldest in the galaxy has been spotted racing across our galaxy by astronomers—who were looking for something else entirely.
The scientists noticed the speedy star traveling at 1.3 million miles per hour, nearly three times the speed of our own sun, which orbits around our Milky Way galaxy at around half a million miles per hour.
This rapid star, which has been named CWISE J124909+362116.0 ("J1249+36"), is moving fast enough to potentially escape the gravity of the galaxy entirely. That's according to the new research, which was announced at the 244th Meeting of the American Astronomical Society in Wisconsin and will soon be published in The Astrophysical Journal Letters.
This discovery was made by accident, with the astronomers spotting the star racing across the cosmos when they were poring through data looking for evidence of "Planet 9" in our solar system. This was part of a citizen science project named Backyard Worlds: Planet 9, which involved 80,000 volunteers looking through NASA's Wide-field Infrared Survey Explorer (WISE) mission data from the past 14 years in the hopes of discovering a secret hidden planet in the outskirts of our solar system. Instead, J1249+36 was spied as it tore across the galaxy at its 372 miles per second velocity.
This star's impressive speed makes it a potential "hypervelocity" star, an extremely rare star moving fast enough to eventually leave the galaxy entirely.
"Its speed and trajectory showed that it was moving fast enough to potentially escape the Milky Way," researcher Adam Burgasser, a professor of astronomy and astrophysics at the University of California San Diego, said in a statement.
According to the researchers' models, the star was discovered to be an L subdwarf, which is a rare type of low-mass, low-temperature star, known to be among the oldest in the Milky Way.
"It was exciting to see that our models were able to accurately match the observed spectrum," University of California San Diego researcher Efrain Alvarado III said in the statement.
Exactly how this star started traveling so fast remains unclear, though the astronomers have suggested a number of theories. One posits that J1249+36 could have been in a binary star system with a white dwarf—the remnant core of a star that has exhausted its nuclear fuel and shed its outer layers—which collected enough mass from its companion to explode in a huge explosion called a nova.
"In this kind of supernova, the white dwarf is completely 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 Burgasser. "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."
Alternatively, they suggest that J1249+36 had originated in a close group of stars known as a globular cluster, which contained a black hole, and this black hole had ended up catapulting the star out at immense speeds.
"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," Kyle Kremer, an assistant professor at UC San Diego, said in the statement. "It demonstrates a proof of concept, but we don't actually know what globular cluster this star is from."
The researchers hope to further study the star and look for proof of either of these scenarios, such as the traces of a white dwarf nova or a globular cluster in its wake.
"We're essentially looking for a chemical fingerprint that would pinpoint what system this star is from," UC alumnus Roman Gerasimov, a researcher at the University of Notre Dame, said in the statement.
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