There have been two big stories in Astronomy this week, a visible supernova and a planet made of diamond.
The supernova shown in the top picture is in M101 or the Pinwheel Galaxy, which is 21 million light years away. That means this star died 21 million years ago and the light has only reached us this week. It will get brighter over a fortnight and should be visible with small telescopes and possibly even binoculars. It was discovered within days of the explosion and is giving astronomers a fantastic opportunity to observe it as it happens.
M101 is in the Ursa Major constellation, if I’m using my StarWalk app correctly then it should be visible in the US for most of the night. In Australia it is up during the day and sets about an hour after sunset, so chances to see it yourself are unlikely. And it isn’t something you’re going to be seeing from an urban backyard.
This is a Type Ia supernova, and here’s where it gets technical. You have to realise that stars have an incredible amount of gravity – they can control enormous solar systems. The only reason their own gravity doesn’t pull them in to collapse is because their energy is constantly pushing them out, think of them as unimaginably large, long lasting nuclear explosions.
When a star runs out of hydrogen for these reactions in the core it blows out to a red giant and burns hydrogen in the outer shell. When the sun becomes a red giant the earth might be inside this tenuous outer atmosphere (and therefore disappear). The core will begin to burn helium and eventually produce carbon. The outer atmosphere slowly drifts away and the core is left as a white dwarf. This is how almost all stars will end, quietly and undramatically.
White dwarfs are so incredibly dense that at first astronomers couldn’t believe what they had. A ton of material from a white dwarf would easily fit inside a matchbox. Normal atoms could not make a material that dense, and this is where we start getting into quantum effects. The electrons are stripped away from the atomic nuclei which are packed very closely together. This means the electrons are likewise packed tightly, which means there are very few places they can go and their positions are relatively known. According to the uncertainty principle*, this means there must be high uncertainty in their movements, which means some of them will be moving extremely fast. It is this extreme energy that stops the star from collapsing because of its own gravity.
Most white dwarfs will stay like this, but some of them will be large enough or will get more material from another star to push them over the limit where the electron energy can stop them from collapsing. The carbon nuclei will fuse, and it may take just a few seconds to react a large amount of the remaining star. This catastrophic explosion is the Type Ia supernova we are seeing now.
The diamond planet is probably extremely rare and closely related to the mechanisms that created the supernova we’re seeing. A few stars are large enough that rather than forming white dwarfs, they explode in different types of supernovas. The remnants of the core collapse and are pulled together even more than in white dwarfs – so much that the protons and electrons actually join and the stars are made entirely of neutrons. A neutron star has more mass than the sun but is only 10-20 km across.
What appears to have happened in this system is that the neutron star had a white dwarf companion. They are very close and some of the matter from the white dwarf has been pulled into the neutron star, and combined with the massive explosion next door brought the ex-white dwarf into the planet size range. Because it now has less mass, its particles are no longer being packed together so densely by gravity and can form atoms.
Remember that white dwarfs are mostly built of carbon and it is still incredibly dense. The densest form of carbon is crystalline, otherwise known as diamonds. Voila, a planet made of diamond.
Of course it is being blasted by extreme radiation and has the gravity of Jupiter, so I don’t think we’ll be visiting anytime soon. And I’ve just compressed several years of astronomy into less than 1000 words! Any questions?
* The simplest explanation of the uncertainty principle (which will probably make quantum physicists turn green) is that for small particles you can’t know everything about them, the act of trying to measure them changes something else. So if you observe/measure where an electron is, that will change its direction, spin or speed. In this case because there are very few places the electrons can be, it makes their position relatively certain, which means their movement will be relatively uncertain. Uncertain means there is a wide range of possible values, so some of them will be going very slowly and some will be going very fast.
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