A couple of weeks ago, on May 19th, Koichi Itagaki, an amateur astronomer in Japan, was taking a picture of the galaxy M101. This galaxy, known as the Pinwheel Galaxy, is a very popular object for astronomers to capture, and it would not be the first time Itagaki took a picture of it. As a dedicated variable star observer, Itagaki puts in long hours with his imaging equipment. These dedicated hobbyists devote themselves to capturing the sky night after night. And why would they pursue such a thankless task? Well, as the name suggests, variable star observers look for variations in the brightness of stars. Certain stars, called variable stars, fluctuate in brightness over time. In some cases, these fluctuations can be instrumental in determining the distances to these stars. (That’s a whole topic which I won’t delve into here). But sometimes, they discover something more exciting. And when Itagaki looked at the images he had just captured of M101, he knew that this was going to be big news.
In his picture, there was a bright star clearly visible where there was not one before. Itagaki knew that he was witnessing a supernova. This was not the first time he had seen such a phenomenon. Since 2000, he has discovered 172 supernovas. In 2014, he discovered a supernova in the galaxy M82, another very famous galaxy. Supernova like this occur when a star suddenly explodes. This typically happens either when a very high mass star reaches the end of its life (known as a Type II supernova), or when a white dwarf absorbs enough hydrogen to restart its fusion (a Type Ia supernova). In either case, this will cause a sudden burst of light, which can outshine the entirety of the star’s host galaxy. NASA’s Astronomy Picture of the Day (APOD) has a good image comparing what M101 looked like before and during the supernova here (mouse over the image to see the “before” shot). (As an aside, our sun will not go supernova when it dies, it will form a planetary nebula. And that won’t happen for another 5 billion years).
Below is an image I took of M101 in the early hours of Friday, May 26th. The supernova is labeled with a red arrow. Here you can clearly see how bright it is compared to the rest of the galaxy. It’s so bright that it could be mistaken for one of the foreground stars in our galaxy. However, that star is about 23 million light years away, whereas the foreground stars are only a few hundred to a few thousand light years away.
Although supernova in our galaxy only happen roughly every 200 years or so, there are trillions of other galaxies out there in the universe. As a result, we can quite regularly see supernova occurring in other galaxies. However, a supernova in a galaxy this close to us (yes, astronomers consider 20 million light years “close”) only happens about once a decade.
While this supernova event is expected to remain bright for at least a few months, unfortunately the full moon does make seeing it very challenging. M101 is a very faint, diffuse galaxy to begin with, so even on the darkest night, it is not easy to make out. But if you have a telescope at home, get it out and try to spot it! M101 is not too challenging to find, being located very close to the handle of the Big Dipper. Eventually, though, the supernova’s brightness will fade, and things will go back to normal.
There are many, many things I could talk about when it comes to supernovas, but I think I’ll leave it at this for today. I mostly want to share with everyone that there is something cool happening right now, and that you should go check it out if you have a chance. By the way, I am working on setting up a profile on Flickr so that I can share my photos of space objects, as well as terrestrial subjects. Once it’s ready, I’ll update this post with a link to it. Please check it out if you are interested!
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