Saturday, May 7, 2011

The Totally Possible Planet

Hey! So, science fiction and astronomy just collided, and I thought you might find this interesting.

Ummm... So. I've been watching episodes of Dr. Who from seasons 2 and 3 to get my fix, as it were, and I just went back to "The Impossible Planet". Still one of my favorites, but as it turns out, it would be perfectly possible for the planet to be there even without a Satan gravity-field holding it there. Stars orbit around black holes all the time, the way anything else orbits around anything, and they don't fall in for the same reason the Earth doesn't fall into the Sun just offhand. The planet presumably has way less of a mass than any self-respecting star would, but all that means is that it 'd have to be farther out from the black hole than a star would.

Now, the planet is probably closer than it ought to be and the Satan-field is what's keeping it in place, so it's still shocking, but in principle stuff can totally orbit around a black hole and not fall in. That's how we know about them in the first place; indeed, the only way we can observe them directly is by the actions of stuff moving around them. But apparently if you're not within the Schwartzchild radius (point of no return) you won't get sucked in. Black holes don't intrinsically have more gravity than other objects; a black hole with the mass of three suns has the same gravitational attraction as a regular star with that mass, which blew my mind. It's only when you're inside that radius that you're absolutely screwed and cannot escape.

Also, see the way the matter just pours over the edge of the black hole? As it turns out, matter and energy swirl into a black hole like water down a drain. But if you get sucked in, you won't have a chance in hell of surviving anyway. What fun!

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