NASA Fermi telescope captures first clear gamma rays from a superluminous supernova, confirming magnetar engine
Astronomers have for the first time directly observed the engine powering the universe's brightest exploding stars. NASA's Fermi telescope caught gamma rays from SN 2017egm, a supernova 440 million light-years away in Ursa Major, confirming a newborn magnetar drives the blast.
Astronomers have for the first time directly observed the engine driving the universe's brightest exploding stars. A team led by Louisiana State University, using data from NASA's Fermi Gamma-ray Space Telescope, detected high-energy emissions from SN 2017egm, a so-called superluminous supernova that briefly outshone its entire host galaxy NGC 3191, located about 440 million light-years away in the constellation Ursa Major. The findings appear in Astronomy & Astrophysics. For more than a decade, theorists have argued that the most luminous stellar explosions cannot be powered by ordinary radioactive decay alone. The favored explanation is a freshly born magnetar, a type of neutron star with a magnetic field roughly a trillion times stronger than Earth's, embedded inside the expanding debris. As the magnetar spins down, it pumps energy into the surrounding material, lighting up the supernova far beyond normal levels. Until now, that scenario remained an inference from light curves and spectra. Gamma rays offered a more direct test, but they only escape the explosion once the ejecta becomes transparent, and no superluminous supernova was close enough to study at that resolution. SN 2017egm finally provided one. According to LSU's Manos Chatzopoulos, the gamma-ray signal matches what the magnetar models predicted. The detection moves the field from indirect modeling to a measurement of the central engine itself, and gives astrophysicists a new tool to study magnetar formation and the death of the universe's most massive stars.