One of the closest stellar explosions for years has been spotted in a relatively nearby galaxy that is a favourite target for amateur astronomers. The supernova appeared in the galaxy Messier 82, or M82 for short, which lies about 11.4 million light-years away, right on our doorstep in cosmic terms.
Early images show it as a bright blob against the cigar shape of the galaxy, which can be found in the constellation of Ursa Major and which is visible as a smudge in binoculars or a small telescope.
Estimates of its brightness put it at a little above 12th magnitude, making it a telescopic target. However, supernova experts say it was discovered early in its explosive outburst and so could reach magnitude 8, which would make it visible in binoculars.
Our map shows the northern sky as it appears from mid northern latitudes at around 9pm local time. The galaxy M82 is easy to find using the familiar star pattern of the Big Dipper (also known as the Plough) which is part of the constellation of Ursa Major. Just imagine a line extended through the stars gamma (γ) and alpha (α)and it will point to where the galaxy lies. (You may see two smudges as M82 appears to lie close to another galaxy, M81).
The image of the supernova above was taken by UK amateur astronomer Robin Scagell, remotely using a telescope in New Mexico. The supernova seems to have been discovered on Tuesday night by tutor Dr Steve Fossey and his students, of University College London, when they imaged the galaxy from the university’s teaching observatory at Mill Hill, north London.
It was later confirmed by Russian astronomers L Elenin and I Molotov, using a 0.4-metre telescope at the ISON-NM Observatory at Mayhill, New Mexico. Its position is measured as 09h 55m 42s, +69d 40’ 25.8”, and the discovery brightness was given as magnitude 11.7.
News of the supernova spread swiftly thanks to social media such as Twitter, with excited professional astronomers comparing notes to help themselves understand its significance! They will also be scouring old Hubble images to see if they can see the star that produced the supernova.
Dr Fossey modestly described his discovery as “entirely a fluke”. He told Skymania: “I was with a group of students and we wouldn’t normally have observed because the conditions were getting bad. But we had a brief chance to acquire some data and so I picked M82 to look at. We only managed to get two or three images before the clouds rolled in.
“You look at these galaxies so often that they become familiar. When I looked at the image we’d got of M82, it struck me that it didn’t look quite right. So I got the students to help check that it wasn’t an asteroid or something in the way. Then when I felt confident that this was a supernova, I emailed an alert to the International Astronomical Union so that other observatories could check it out.”
Chris Lintott, of the University of Oxford, and presenter of The Sky at Night, told Skymania today: “This is a nearby supernova, by astronomical standards, and so we have the chance to learn about the causes and processes that drive these spectacular events. Early indications are this might be a type Ia – they’re the type we use to measure the expansion of the Universe and so that would be especially exciting.”
On the other side of the world, supernova specialist Brad Tucker, of Mount Stromlo Observatory, Australia, was looking forward to learning valuable new information about supernovae and galactic expansion from the discovery.
Brad said the supernova appeared to have been caught early and so might brighten to magnitude 8 which would put it easily within the reach of binoculars.
He told Skymania: “Any supernova that we catch early will help us understand how they explode and what the star is that explodes, as the earlier we can observe a SN, the more clues we get. For instance, at very early times, between an hour and a couple of days, we may be able to see the shockwave of the explosion propagate through the star, much like the shockwave from a nuclear bomb occurs before the nastiness follows.
“This type of supernova is a type Ia, the ones we use to measure distances across the Universe. This use was what led to the 2011 Nobel Prize – the discovery that the expansion of the Universe is accelerating, which implies the Universe consists of 70 per cent Dark Energy, something we have no idea about.
“In order to figure out what Dark Energy is, the cause of the acceleration, we need to improve our distances measurements using these objects, i.e. we need a more precise measurement. The two large problems with using Ia for distance measurements, are the progenitors, what the star that explodes actually is, and how dust affects these measurements.
“So the fact that this SN is a type Ia, caught young, means we have a good chance of finding clues to the explosion. Since it is so close, the Hubble Space Telescope has pre-imaging of the galaxy, images long before the star would have blown up, which may allow us to directly see the star.
“Also, it is a “reddened” Ia – meaning it occurs in a known dusty environment. By knowing there is lots of dust, we can analyze out how the dust is impacting the colors of the SN and therefore the distance measurements, and use this to calibrate other SN. In short, this is the Holy Grail.”
The closest supernova of recent times was seen to explode in 1987 in the Milky Way’s companion galaxy the Large Magellanic Cloud. Labelled SN1987A, it was of a different type to the new supernova, and reached magnitude 3. In 2011, a supernova appeared in another well-known galaxy, M51, which lies 23 million light-years away from us.