Recent gamma-ray observations from NASA’s Fermi Space Telescope indicate that supermagnetic neutron stars, known as magnetars, could be responsible for superluminous supernovae—rare stellar explosions that shine with a peak luminosity 10 to 100 times greater than conventional nuclear collapse supernovae.

A nuclear collapse supernova occurs when the energy-producing core of a massive star runs out of fuel, collapses under its own gravity, and subsequently explodes.

During this collapse, city-sized neutron stars and potentially smaller black holes may form.

The resulting blast wave ejects the remaining star material, expanding rapidly as a cloud of hot, ionized gas.

Over the past few decades, nearly 400 remarkable nuclear collapse supernovae have been cataloged.

These events, termed hyperluminous supernovae, emit over ten times the visible light typically observed from standard supernovae.

A 2026 research paper suggests that Fermi’s large-area telescope has detected gamma rays from the superluminous supernova SN 2017egm.

This phenomenon occurred in the barred spiral galaxy NGC 3191, located approximately 440 million light-years away in the constellation Ursa Major.

Dr. Guillem Martí Debesa, a researcher at the Institute of Space Sciences in Barcelona, Spain, commented, “We searched for gamma rays from the six nearest superluminous supernovae observed during the first 16 years of Fermi’s mission.” He added, “Only SN 2017egm exhibits gamma-ray evidence, reinforcing earlier indications that certain supernovae can be as luminous in gamma rays as they are in visible light.”

This discovery unlocks new avenues for studying these fascinating astrophysical events.

The explosive energy sources driving these powerful explosions have been a matter of theoretical debate.

The formation of magnetars—neutron stars with unparalleled magnetic fields, 1,000 times stronger than typical neutron stars—is a leading candidate.

Astronomers conducted an in-depth analysis of the optical and gamma-ray characteristics of SN 2017egm, comparing different theoretical models to evaluate their accuracy.

Their model tracked how light and particles produced by the nascent magnetar interacted with the expanding supernova debris.

They anticipate that the newly formed magnetar will rotate hundreds of times per second, producing a powerful outflow of antimatter equivalents of electrons and positrons, thereby creating a substantial cloud of energetic particles.

This cloud, referred to as the magnetar wind nebula, drives various interactions responsible for both gamma-ray production and absorption.

For instance, an electron and a positron may annihilate, producing a pair of gamma-ray photons, or two gamma rays may collide, resulting in particle formation.

Through these mechanisms, gamma rays interact with the remnants of the supernova, becoming reprocessed into lower-energy visible light, thereby enhancing the supernova’s brightness.

Dr. Fabio Acero from the University of Paris-Saclay and CNRS stated, “Around three months after the collapse, as the supernova debris expands and cools, gamma rays may start to escape.” He went on to say, “This magnetar model most accurately models the supernova’s brightness and gamma-ray arrival timings during the initial months, but we believe there is potential for refinement in the later phases when visible light fades erratically.”

“Additional mechanisms may have had an impact during the prolonged decay phase of SN 2017egm,” he added.

Factors such as debris interaction with the magnetar and blast waves emitted over centuries could contribute to these observations.

The study team’s research paper is published in the latest issue of Astronomy and Astrophysics.

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F. Acero et al. 2026. Gamma-ray signatures of ultraluminous supernovae: Fermi-LAT GeV detection of SN 2017egm and evidence for a central engine. A&A 709, A229; doi: 10.1051/0004-6361/202558547