(A version of this piece appeared on The Hindu, Chennai, website on January 22 as written by me.)
A Type 1a supernova was spotted a few hours ago by stargazers in the starburst galaxy M82, which is only 11.4 million light-years away from Earth (here’s an interactive map and a helpful sky-chart). This is the closest such supernova that has been detected since 1972, 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.
The supernova is a Type 1a supernova (SN1a), which means it’s not the explosion that happens when a star runs out of fuel and blows itself apart. Instead, it’s what 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.
That M82 is a starburst galaxy means it’s rapidly producing stars. This also means it has a lot of old stars, many of which are continuously dying. They could either be dying as Type 2 supernovae—which is the run-out-fuel kind—or Type 1. The SN1a that’s gone off now (i.e. so many millions of years ago) has chosen to go off as Type 1a, and that’s a good thing because we haven’t spotted a Type 1a since 1972 that’s so close.
When the 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 from the explosion 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. On the other hand, the M82-SN1a could be our big chance to study SN-origin gamma rays in the best detail for the first time in more than four decades.
However, since we haven’t had our detectors trained for neutrinos from M82 particularly, how do we know when that white dwarf in M82 blew up? We measure how its brightness varies over time. Using that information, we know the thing blew up 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. In fact, according to 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, and I quote, ‘too bright’. As Brad Tucker, an astronomer from Berkeley, tweeted,
So, hadn’t it been for amateur astronomers, who’ve made this remarkable observation, too, we wouldn’t have spotted this beauty. Already, according to Skymania’s Paul Sutherland, astronomers believe they’ve caught this supernova early in its act and think it could brighten even further.
This particular find was made by Russian amateur astronomers on January 22, and later confirmed by multiple sources. In fact, M82-SN1a seems to have appeared in the photographs taken by noted Japanese amateur astronomer Koichi Itagaki on January 14 itself (beating Patrick Wiggins by a day). And if you’re interested in reporting such discoveries, check this page out. If you want to keep up with the social media conversation over M82, follow @astrokatie. She’s going nuts (in a good way).