A supernova 440 million light years away has become the first ever to send a clear gamma ray signal to NASA's Fermi telescope, and the source of its extraordinary brightness appears to be one of the most extreme objects in the universe: a newborn magnetar.
The explosion, cataloged as SN 2017egm, belongs to a rare class called superluminous supernovae. These blasts can shine at least 10 times brighter in visible light than ordinary supernovae. Until now, astronomers had only hints of what powered them. Fermi's detection may have settled the debate.
A gamma ray signal from deep space
SN 2017egm erupted in the galaxy NGC 3191, located in the constellation Ursa Major. Even from that enormous distance, it remains one of the closest superluminous supernovae ever observed from Earth.
An international research team led by Fabio Acero at the French National Centre for Scientific Research and the University of Paris-Saclay analyzed 16 years of data from Fermi's Large Area Telescope. They focused on the six nearest superluminous supernovae visible during the mission. Only SN 2017egm showed evidence of gamma rays.
Guillem Marti-Devesa, a researcher previously at the University of Trieste in Italy and now at the Institute of Space Sciences in Barcelona, Spain, said the detection confirms earlier hints that some supernovae can be as luminous in gamma rays as they are in visible light. The findings were published in the journal Astronomy and Astrophysics.
A magnetar engine at work
Core collapse supernovae happen when a massive star runs out of fuel. Its core collapses under gravity, triggering a violent explosion. Depending on conditions, the collapse leaves behind either a neutron star or a black hole.
In the case of SN 2017egm, scientists believe the remnant is a magnetar: a rapidly spinning neutron star with magnetic fields so powerful they can turbocharge the explosion from within. This magnetar, formed during the star's collapse, would explain why the supernova became extraordinarily bright.
For nearly 20 years, astronomers searched Fermi data for gamma ray signals from thousands of supernovae. A few intriguing hints appeared, but none were definitive until now.
What this means for understanding cosmic explosions
Fermi is part of NASA's network of observatories designed to track changing events across the universe. This detection opens a new window for studying superluminous supernovae and the exotic objects that power them. By confirming that gamma rays can be emitted years after the initial explosion, researchers now have a new tool to probe the inner workings of the most extreme stellar deaths in the cosmos.
