The discovery of CWISE J124909.08+362116.0, moving at 1 million miles per hour, marks the first identification of a hypervelocity object with a mass comparable to or smaller than a small star escaping the Milky Way.
TL;DR
A hypervelocity object named CWISE J124909.08+362116.0, found by NASA’s Backyard Worlds project, is speeding out of the Milky Way at about 1 million miles per hour. This is the first known object with a mass similar to or smaller than a small star that is escaping the galaxy’s gravitational pull. Its unusual composition suggests it might be one of the galaxy’s earliest stars. Scientists are investigating whether its high speed is due to a supernova or a black hole encounter.
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While most stars quietly orbit the center of the Milky Way, a remarkable discovery by citizen scientists working on NASA’s Backyard Worlds: Planet 9 project has revealed an object so fast it will break free from the Milky Way’s gravitational pull and venture into intergalactic space. This hypervelocity object is the first of its kind to be found with a mass comparable to or smaller than that of a small star.
W.M. Keck Observatory/Adam Makarenko
The Backyard Worlds project uses images from NASA’s WISE (Wide-field Infrared Survey Explorer) mission, which mapped the sky in infrared light from 2009 to 2011. WISE was later reactivated as NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) in 2013 and decommissioned on August 8, 2024.
A few years ago, dedicated Backyard Worlds citizen scientists Martin Kabatnik, Thomas P. Bickle, and Dan Caselden identified a faint, fast-moving object named CWISE J124909.08+362116.0 in the WISE images. Subsequent observations with ground-based telescopes confirmed and characterized the discovery. These citizen scientists are now co-authors on the study published in the Astrophysical Journal Letters (a preprint version is available here).
“I can’t describe the level of excitement,” said Kabatnik from Nuremberg, Germany. “When I first saw how fast it was moving, I was convinced it must have been reported already.”
CWISE J1249 is racing out of the Milky Way at about 1 million miles per hour. Its low mass makes it challenging to classify; it could be a low-mass star or, if it doesn’t sustain hydrogen fusion in its core, it might be a brown dwarf, placing it between a gas giant planet and a star.
Ordinary brown dwarfs are relatively common—Backyard Worlds: Planet 9 volunteers have discovered over 4,000 of them!—but none have been found to be leaving the galaxy.
This new object also has an unusual characteristic. Data from the W. M. Keck Observatory in Maunakea, Hawaii, reveal that it contains significantly less iron and other metals compared to typical stars and brown dwarfs. This rare composition suggests that CWISE J1249 could be one of the earliest generations of stars in our galaxy.
The reason for its high velocity is still under investigation. One theory is that CWISE J1249 originated from a binary system with a white dwarf, which exploded as a supernova after pulling too much material from its companion. Another possibility is that it came from a globular cluster and was ejected after a close encounter with black holes.
“When a star encounters a black hole binary, the intricate dynamics of this three-body interaction can expel the star from the globular cluster,” explains Kyle Kremer, an incoming assistant professor at UC San Diego’s Department of Astronomy and Astrophysics.
Scientists will further analyze the elemental composition of CWISE J1249 to determine which scenario is more likely.
This discovery represents a collaborative effort involving volunteers, professionals, and students. Kabatnik acknowledges the contributions of other citizen scientists, such as Melina Thévenot, who inspired him with her personal blog on astronomical data queries, and Frank Kiwy, whose software was crucial to this discovery.
The study is led by Adam Burgasser, a professor at the University of California, San Diego, and includes co-authors Hunter Brooks and Austin Rothermich, astronomy students who started their careers as citizen scientists.
