Bizarre supernova completely normal in every way, find astronomers
A nearby white dwarf went supernova in 2011, giving scientists an unprecedented look at a rare Type Ia supernova. They discovered that it's remarkably, stunningly, perfectly 'normal.'
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When big stars die, they go supernova. When small stars die, their outer layers expand into a planetary nebula (which, remember, has nothing to do with planets) and the surviving core collapses into a white dwarf.Skip to next paragraph
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White dwarfs are also known as degenerate dwarfs. (No, not Tyrion Lannister.) These are very old, Earth-sized stellar remnants under so much pressure that it's literally impossible to squish them any further without collapsing the atoms into neutrons.
They're also thieves. If another star wanders close enough to a degenerate dwarf, the dwarf will start stealing mass from it. (If two white dwarfs find each other, they collide in what's called a "double-degenerate" system.) The stolen mass leads to fusion explosions on the white dwarf's surface, called novae.
Remember how astronomers give weird names to things? Novae and supernovae really have nothing in common except for fusion. A nova is a fusion explosion on the surface of a star. A supernova is the explosion of a star.
But a degenerate dwarf can only steal so much. Once it gets to 1.4 times the mass of our sun, it'll collapse into a Type Ia supernova. (Hat tip to Subrahmanyan Chandrasekhar, who calculated the 1.4 solar mass limit, named the Chandrasekhar limit in his honor.)
Of course, these are theoretical models, based on all the Type Ia supernovae observed before. “The 2011fe observations can be used to test these models,” says Aldering. “For 2011fe, the existing models of the double-degenerate scenario agreed best at some epochs, but the single-degenerate scenario was better at others. And for some epochs both agreed very poorly with the data, suggesting these models have a way to go.”
What's so cool about Type Ia supernovae?
Thanks to the Chandrasekhar limit, we know that every single Type Ia supernova starts with a mass of 1.4 stellar masses. All of them. No matter how far away they are.
In astronomy, it's surprisingly difficult to calculate interstellar distances. When you see a pale dot in the sky, is it a supergiant star that's very far away, or a little planet nearby? Ships at sea had the same problem: Is that dim glow a lighthouse on the horizon or a firefly in front of your nose?
Knowing the mass of a Type Ia supernova, we can calculate exactly how much energy it will release over its supernova lifespan. That means we can measure any Type Ia supernova's brightness and back-figure exactly how far away it is. That gives us distances to anything nearby, too.
This prompted astronomers to call Type Ia supernovae "standard candles" – not lighthouses, not fireflies, but perfectly standard candles with a perfectly predictable light pattern.
That's why the astronomers were so excited to find 2011fe and get a crystal-clear view of a Type Ia supernova, right in our backyard: it gave them a "standard candle" light curve that hasn't been subjected to any of the assumptions necessary to correct fuzzy data.
The team hopes 2011fe will answer many questions about Type Ia supernovae, including exactly what causes these titanic thermonuclear explosions. "We've never had data like this," says Aldering. "It’s a dream opportunity to stimulate deeper thinking about these markers of the expansion of the universe.”
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