Last June, the All-Sky Automated Survey for Supernovae (ASAS-SN — think “assassin”) discovered a faint flicker of starlight in an unremarkable galaxy in the far southern constellation of Indus the Indian. Hundreds of supernovae are discovered every year, but this one was different. Once it was determined the exploding star lay 2.8 billion light years from Earth or more than a thousand times farther than the Andromeda Galaxy, astronomers realized they had happened on the biggest supernova blast ever seen.
At peak brightness, if SN 2015L had been the same distance as Alpha Centauri, it would have shone nearly as brightly as the sun! To this day, it radiates more energy per second than all 300 billion stars of the Milky Way. So where does it fit in the scheme of stellar explosions? Astronomers still don’t know what powered such an enormous explosion, but they have ideas.
Normal supernovae are a big deal, but they pale next to the superluminous variety sometimes called hypernovae which shine 5 to 50 times times more brightly. ASASSN-15lh was several times brighter yet. Supernovae either occur in pairs of stars, where one star “feeds” its tiny, superdense companion white dwarf until the dwarf exceeds a certain weight limit and burns explosively or in a single supergiant star that depletes all the nuclear fuel in its core. Without heat and pressure to combat the force of gravity, the giant collapses and then rebounds in a titanic blast that blows the star to smithereens.
To explain ASASSN-15lh’s super-bright light, it’s possible its core imploded with all the matter crunched into a fantastically compact, rapidly-spinning object about 10 miles across called a neutron star. If you could scrape it up, a thimbleful of neutron star matter would weigh about 1oo million tons.
During the collapse, the former star’s magnetic field (all stars have them) would have been crunched and intensified along with material in the star’s core to create a rare magnetar, a neutron star with an incredibly powerful magnetic field up to a trillion times that of the sun. As the magnetar spins, it gives off strong bursts of X-rays and gamma rays which may help to explain why this supernova is so doggone bright.
Or not. It’s already cranked out more energy that even current models of magnetars predict, leading some astronomers to consider other possibilities, including a strange quark star, a hypothetical stellar remnant made of quarks, the tiniest of things that compose the neutrons and protons in the nucleus of an atom.
Somehow, we’ve traveled from supergiant stars to quarks — nature’s way of telling us that the behavior of the biggest things in the world depends upon their tiniest parts.
For more details on this unique star, check out the scientific paper.