NASA’s Fermi mission sees no gamma rays from nearby supernova

A close-by supernova in 2023 provided astrophysicists a superb alternative to check concepts about how a majority of these explosions enhance particles, known as cosmic rays, to close light-speed. However surprisingly, NASA’s Fermi Gamma-ray House Telescope detected not one of the high-energy gamma-ray mild these particles ought to produce.

On Might 18, 2023, a supernova erupted within the close by Pinwheel galaxy (Messier 101), positioned about 22 million light-years away within the constellation Ursa Main. The occasion, named SN 2023ixf, is probably the most luminous close by supernova found since Fermi launched in 2008.

“Astrophysicists beforehand estimated that supernovae convert about 10% of their total power into cosmic ray acceleration,” mentioned Guillem Martí-Devesa, a researcher on the College of Trieste in Italy.

“However we now have by no means noticed this course of instantly. With the brand new observations of SN 2023ixf, our calculations lead to power conversion as little as 1% inside a couple of days after the explosion. This does not rule out supernovae as cosmic ray factories, however it does imply we now have extra to find out about their manufacturing.”

The paper, led by Martí-Devesa whereas on the College of Innsbruck in Austria, will seem in a future edition of Astronomy and Astrophysics.

Trillions of trillions of cosmic rays collide with Earth’s ambiance each day. Roughly 90% of them are hydrogen nuclei—or protons—and the rest are electrons or the nuclei of heavier components.

Scientists have been investigating cosmic ray origins because the early 1900s, however the particles cannot be traced again to their sources. As a result of they’re electrically charged, cosmic rays change course as they journey to Earth because of the magnetic fields they encounter.

“Gamma rays, nonetheless, journey on to us,” mentioned Elizabeth Hays, the Fermi venture scientist at NASA’s Goddard House Flight Heart in Greenbelt, Maryland. “Cosmic rays produce gamma rays after they work together with matter of their atmosphere. Fermi is probably the most delicate gamma-ray telescope in orbit, so when it does not detect an anticipated sign, scientists should clarify the absence. Fixing that thriller will construct a extra correct image of cosmic ray origins.”

Astrophysicists have lengthy suspected supernovae of being high cosmic ray contributors.

These explosions happen when a star not less than eight instances the sun’s mass runs out of gas. The core collapses after which rebounds, propelling a shock wave outward by the star. The shock wave accelerates particles, creating cosmic rays. When cosmic rays collide with different matter and light-weight surrounding the star, they generate gamma rays.

Supernovae significantly affect a galaxy’s interstellar atmosphere. Their blast waves and increasing clouds of particles might persist for greater than 50,000 years. In 2013, Fermi measurements showed that supernova remnants in our personal Milky Way galaxy have been accelerating cosmic rays, which generated gamma-ray mild after they struck interstellar matter. However astronomers say the remnants aren’t producing sufficient high-energy particles to match scientists’ measurements on Earth.

One principle proposes that supernovae might speed up probably the most energetic cosmic rays in our galaxy within the first few days and weeks after the preliminary explosion.

However supernovae are uncommon, occurring just a few instances a century in a galaxy just like the Milky Way. Out to distances of round 32 million light-years, a supernova happens, on common, simply yearly.

After a month of observations, beginning when seen mild telescopes first noticed SN 2023ixf, Fermi had not detected gamma rays.

“Sadly, seeing no gamma rays does not imply there are not any cosmic rays,” mentioned co-author Matthieu Renaud, an astrophysicist on the Montpellier Universe and Particles Laboratory, a part of the Nationwide Heart for Scientific Analysis in France. “We’ve to undergo all of the underlying hypotheses relating to acceleration mechanisms and environmental conditions with a view to convert the absence of gamma rays into an higher restrict for cosmic ray manufacturing.”

The researchers suggest a couple of eventualities that will have affected Fermi’s potential to see gamma rays from the occasion, like the best way the explosion distributed particles and the density of fabric surrounding the star.

Fermi’s observations present the primary alternative to review situations proper after the supernova explosion. Extra observations of SN 2023ixf at different wavelengths, new simulations and fashions primarily based on this occasion, and future research of different younger supernovae will assist astronomers hone in on the mysterious sources of the universe’s cosmic rays.