Scientists sifting through archival data captured by NASA's former NEOWISE mission found an unusual star that quickly disappeared, fading to nothing more than a wispy shell. Their conclusion: The star, a dying supergiant named M31-2014-DS1 located in the Andromeda Galaxy, imploded into a black hole instead of undergoing the more common scenario in which a star dramatically explodes in a supernova before forming a neutron star or a black hole. While astronomers had previously predicted that some massive stars might quietly implode in this manner, observational evidence has been limited.
"This star used to be one of the most luminous stars in the Andromeda Galaxy, and now it was nowhere to be seen," says Caltech alumnus Kishalay De (PhD '21), a professor at Columbia University and an associate research scientist at the Simons Foundation's Flatiron Institute. "Imagine if the star Betelgeuse suddenly disappeared. Everybody would lose their minds! The same kind of thing [was] happening with this star in the Andromeda Galaxy."
The findings were reported today in the journal Science.
While a graduate student at Caltech working with Professor of Astronomy Mansi Kasliwal (PhD '11), De began searching through more than a decade of infrared data captured by NEOWISE to look for stars and other objects that changed in brightness. NEOWISE, which operated from 2009 to 2024 (with a two-year hiatus from 2011 to 2013), was managed by NASA's Jet Propulsion Laboratory, which is managed by Caltech for NASA. The data from the mission were processed and archived at IPAC , a data and science center for astronomy at Caltech.
"Kishalay used the untapped NEOWISE data to look for all kinds of interesting stellar variables, supernovae, and more," explains co-author Jacob Jencson (PhD '20), a staff scientist at IPAC.
Those data revealed that infrared light from M31-2014-DS1 increased in brightness beginning in 2014 before fading dramatically and mostly disappearing in 2016. "It didn't look like anything we'd seen before," Jencson says.
One of Jencson's roles was to analyze data taken of the star by NASA's Hubble Space Telescope between 2008 and 2022. "Hubble saw the star many times after its initial outburst, and the star was basically gone. It was 10,000 times fainter in visible light," Jencson says.
The scientists concluded that the massive dying star failed to go supernova (for reasons that are not fully understood) and instead collapsed inward. As it collapsed, the star would have shed its outer layers, which glow with infrared light. Currently, the stellar remnant is only one-tenth as bright in infrared light as it was before it imploded, and it continues to fade into the darkness.
The discovery provides the clearest insights into the formation of a black hole via implosion and indicates that this kind of stellar death may happen more often than scientists had thought.
"Imploding is much harder to see than exploding," Jencson says. "Makes you wonder what else we have missed and what we might find in the future."
The paper, titled "The disappearance of a massive star marking the birth of a black hole in M31," was funded by NASA, the Clay Postdoctoral Fellowship at the Smithsonian Astrophysical Observatory, the Simons Foundation, and the Gordon and Betty Moore Foundation.
Data from Caltech's Palomar Observatory near San Diego and the W. M. Keck Observatory in Hawaiʻi provided valuable insights into the nature of this source.
