A Type 1a supernova was spotted a few hours ago (on the night of January 22) by stargazers in the starburst galaxy M82, which is 11.4 million light-years away from Earth. This is the closest such supernova that has been detected in the last four decades, and is poised to give astronomers and cosmologists some invaluable insight into how such stellar explosions pan out, and what we can learn about neutrinos, gamma rays and dark energy from them.
A Type 1a supernova (SN1a) happens when a white dwarf pulls in too much material from a nearby star and blows itself apart, having bitten off more than it could chew. A white dwarf itself is what is left over when a small-to-medium mass star dies, blowing away its outermost layers and retaining only a dense core of carbon, oxygen and electron degenerate matter. When a heavier star dies, it blows up as a Type 2 supernova to leave behind a neutron start or a black hole.
M82 is a starburst galaxy, which means it is rapidly birthing new stars. This also means it has a lot of old stars, many of which are continuously dying. They could either be snuffing off as either Type 1 or Type 2. The SN1a that has been spotted now (i.e. so many millions of years later) has chosen to go off as Type 1a. This is fortuitous because we haven’t spotted a Type 1a that is so close since the 1970s. Moreover, we also seem to have caught it in the early days of the cataclysm, giving us enough time to spot details about this event we haven't had a chance to naturally do so before.
When a supernova explosion releases light, it doesn’t immediately start its journey and head straight for Earth. Instead, the light gets trapped in the explosion behind lots of matter, and is delayed. In fact, the ‘ghost particles’ that can pass through matter almost undetected, neutrinos, get a headstart. They reach us before light does.
However, a Type 1a supernova produces far fewer neutrinos than does a Type 2, so while the neutrinos flying our way will still be valuable, they might not be valuable enough to study a supernova with, corroborated by the team of the IceCube neutrino detector, located under the South Pole. On the other hand, the M82-SN1a could be our big chance to study supernova-origin gamma rays in the best detail for the first time in more than four decades.
Since we have not had our detectors trained for neutrinos from M82 particularly, we know when the white dwarf in M82 blew up by measuring how its brightness varies over time. Using that information, we know it happened 11.4 million years ago. Because a 1a’s variation of brightness over time consistently follows a well-established pattern, white dwarfs across the universe can be used as cosmic candlesticks: astronomers use them to judge the relative distances of nearby objects.
In fact, white dwarfs did play an important role in astronomers discovering that the universe was expanding at an accelerating rate due to dark energy. Paraphrasing astronomer Katharine Mack’s tweet: “With a better estimate of the distance [as judged from their brightness], we get a better link between the distance and the universe’s expansion.”
M82's relative closeness is useful because it provides a lot more information to work with before it could get (more) adulterated through the distance of space. According to German astronomer Daniel Fischer, the supernova’s been going on for a full week now, and was missed by the bigger budget telescopes because it was ‘too bright’. As Brad Tucker, an astronomer from the University of California, Berkeley, explained, it was too bright in the sense that it saturated in the images, leading observers to believe it was light from the Milky Way galaxy.
So, hadn’t it been for amateur astronomers, who have made this remarkable observation, we wouldn’t have spotted this supernova. Already, according to Skymania’s Paul Sutherland, astronomers believe they have caught this supernova early in its act and think it could brighten even further.
M82-SN1a, soon to be designated 2014J according to Tucker, was detected by amateur astronomers in Russia, and was later confirmed by multiple sources. Interestingly, it seems to have appeared in the photographs taken by noted Japanese amateur astronomer Koichi Itagaki on January 14 itself.