This morning I woke up with a jolt as I saw on Twitter that a supernova had been discovered in the relatively nearby galaxy M82. This is one of the best chances to observe a supernova for professional and amateur astronomers in the Northern Hemisphere in recent history!
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Things in the night sky are fairly static thanks to the long, long timescales of most astrophysical phenomena. So a supernova, the death knoll of a star blowing itself apart, is jarring and exciting when it happens so close by.
11.4 million light-years away might not seem close-by, but by cosmological standards, that's right next door. M82 is the nearest "starburst galaxy," meaning that it is undergoing a high rate of star formation. Such sites are typically home to core-collapse supernovae, or the event where a massive star runs out of nuclear fuel and explodes. This supernova, however, is not that type.
The spectrum shows this to be a Type 1a supernova, or a white-dwarf supernova. These can happen anywhere there are old stars, since white dwarfs are the remnants of smaller stars that have run out of fuel and finished their main life cycles.
Type 1a supernovae have distinguished themselves in astronomy as "standard candles." That is, their peak brightness is predictable based on observations of the light curve, or how the brightness changes with time. These white dwarfs probably detonate when they collect too much mass, getting closer and closer to the Chandrasekhar limit where they can't support themselves anymore.
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This predictability in brightness means that they can be used to accurately measure the distance to very distant galaxies. They are an important rung in the "cosmological distance ladder," or the way we measure distances in astronomy, and were famously used in the discovery that our Universe's expansion was accelerating due to dark energy.
Are all Type 1a supernovae really alike, though? There is evidence that the amount of heavy elements in the progenitor white dwarf can affect the brightness, introducing an uncertainty in distance calculations. These uncertainties haven't been enough to overthrow indirect observations of dark energy, especially in light of other lines of evidence, but astronomers are always after more accuracy.
There is also some debate about the exact nature of a white dwarf supernova explosion. In one case, it may be a white dwarf collecting material from a nearby massive star, such as a red giant. However, it could also be the result of the in-spiral and collision of two white dwarfs. Having such a nearby explosion means we'll get a much better look at the details in the way that Supernova 1987A is still giving us an amazing view of core-collapse supernovae.
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The supernova itself doesn't appear to have reached peak brightness just yet, so it is expected to get brighter. It is already in range of amateur optical telescopes, as demonstrated by the image below, taken during the Virtual Star Party last Sunday night, two days before the announced discovery. Astronomers can report their measured magnitudes to the IAU's Central Bureau for Astronomical Telegrams.
I don't have an imaging camera myself, but I'll be sure to look for it during my public observing nights in the coming weeks with our school's 8-inch telescope! Universe Today has a map that can help you find M82 in the night sky. Phil Plait at Bad Astronomy also has more information on this exciting discovery.
Sometimes it pays to check Twitter when you're dealing with insomnia. It may lead to a breathless early morning blog post, such as what I already wrote up for CosmoQuest. We'll be following this story as it unfolds. Happy observing!