Reader’s Digest published a debunking of 15 common science myths, and you might recognize one of the people they interviewed about the dark side of the Moon and toilets flushing the opposite way in the southern hemisphere.

I was a guest on the podcast “Mission Implausible”, hosted by ex-CIA officers John Sipher and Jerry O’Shea. We talked about various misconceptions about space and astronomy, and it was fun! It’s available on all your favorite podcast venues, like IHeart. You can get a list of them by searching to find the one you like best.

A supernova is one of the most violent and powerful events in the Universe. The explosion of an entire star, one can blast out so much energy it can briefly outshine an entire galaxy.

When you think of one, you likely picture a massive star like Betelgeuse blowing its top. We call those core collapse supernovae, because the core of the star collapses and explodes.

But there’s another kind, involving previously dead stars. When the sun finally dies about 7 or so billion years from now it’ll shed its outer layers, exposing its hot, dense core to space. That kind of object is called a white dwarf, and they’re bizarre. The size of Earth but with roughly the mass of the Sun, they’re incredibly dense and are born very hot. As they cool over time they get dimmer; there are several white dwarfs pretty close to us but so dim they can’t be seen without a telescope.

When the Sun dies it’ll leave behind a white dwarf with about half the mass it has now. But some can be more massive, depending on how massive the star was that died. Critically, some white dwarfs can gain mass, too, if they’re in a binary system. Orbiting another star like the Sun, their powerful gravity can pull material off the normal star, which then piles up on the white dwarf. Sometimes that can result in a nova, where the material periodically explodes like a thermonuclear bomb (T Coronae Borealis is a good example of this).

If they gain enough mass they reach a peculiar limit. The electrons inside a white dwarf support it against its fierce gravity. It’s not so much that they repel each electrically (after all, like charges repel), but are subject to a weird quantum force called degeneracy. Try to pack electrons too tightly together and they resist hard, enough to prevent the star from collapsing. But if you add too much mass, that force can be overcome. The electrons inside the star merge with protons and antineutrinos to become neutrons. The star collapses and explodes: supernova.

This mass, about 1.4 times that of the Sun, is called the Chandrasekhar Limit, after the astronomer who first derived it. There’s another way to get there besides siphoning material off a normal star, too. If two white dwarfs orbit each other, and their total mass is more than the Chandrasekhar Limit, there could be trouble. If they’re close enough together, then over time they emit energy in the form of gravitational waves and their orbit tightens up. If they get close enough together, one can disrupt the other, steal its matter, and then KABOOM.

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