Dead Star Engine May Explain Why Some Supernovas Stay Blindingly Bright
“For nearly 20 years, astronomers have searched Fermi data for gamma-ray signals from thousands of supernovae, and while a few intriguing hints have been reported, none were definitive until now,” That line is significant because the mystery really has been about this explosion. It’s been the missing source of energy inside a structure of unusual stars, which seem to explode too bright to be understood by conventional supernova physics.
Superluminous supernovae, one of the most prominent examples, is called SN 2017egm, which is a supernova explosion in the galaxy NGC 3191 approximately 440 million light-years distant. The supernova was ?-ray bright enough to also be visible with NASA’s Fermi Gamma-ray Space Telescope, which captured the gamma rays from the event. The team says that the new gamma-ray data backs up the theory that an unusually compact engine is driving the extra light in superluminous supernovae, which can be up to 10 times brighter than more common core-collapse supernovae.
The top suspect is a magnetar, a newborn neutron star that spins at a rate matched by many orders of magnitude that of a kitchen blender, and has an enormous magnetic field. The collapse of the core of a large star can crush matter into a mass as large as a city, about 10-12 miles in diameter. In some cases this left-over seems to be born spinning for millisecond, and to be encased in magnetic fields four times as strong as those of normal pulsars. It dissipates its rotational energy and may shoot charged particles into the debris that’s expanding, inflate a magnetar wind nebula, and inspire gamma rays that then help account for the supernova’s dazzling optical brightness.
It’s the time that makes the appeal. Gamma rays may start to leak out 3 months after collapse, if the debris that expands after the collapse is cool enough and thin enough to allow some of the radiation to escape, said Acero. The researchers’ model of the luminosity of the gamma-ray emission in SN 2017egm was the earliest, however, to predict the early arrival of the gamma rays, while a magnetar-based model was the most successful at describing both luminosity and early arrival.
The magnetar theory continued with another result in 2026, after which the scientists reported seeing a “chirp” in the light curve of a superluminous supernova. The light of SN 2024afav decreased and the distance between the 4 dim spots kept decreasing. Based on their interpretation, they concluded that this wobbling was likely the Lense-Thirring precession, a relativistic phenomenon created by a compact object that spins, dragging spacetime with it, into a disk of matter called an accretion disk. The study concluded that the spin period was estimated to be 4.2 milliseconds, and that the magnetar properties are compatible from the magnetic strength of the field. That didn’t disprove the concept of all superluminous supernovae being the same, but it surely provided a much more robust set of observational rules to operate by. There’s still depth in the image.
Certain supernova remnants can also experience enhanced brightness as they plow through material ejected from the star prior to its death and in some scenarios, black holes can enhance brightness. Over time, however, the calculations based on the magnetars have become more sophisticated, including simulations that investigated the effects of energy injection to cool a supernova later than the expected rate and how this delay could change the light curves of such an explosion, as well as making hydrogen-rich supernovae appear much brighter than expansion speed alone would predict.
The next gain may be a-plus instrument rather than event. The Fermi result pointed one way because it proved that gamma rays can investigate the occult engine directly. The main team was also able to show that the Cherenkov Telescope Array Observatory can also see such outbursts from more than 500 million light-years away using long exposures, which means astronomers would have greater opportunities to observe these stellar remnants while they are engaged in the brightest show in the sky.
