No fear of 2012, Part 3

I've been discussing one of the scenarios I've heard, giving supposed astronomical reasons why the world will end in 2012. Here are Part 1 and Part 2.

From a family friend: Will the Sun (or Earth) be swallowed by a black hole in 2012?

Follow up:

The only reason I don't just give a flat "No!" to this is that scientists hardly ever give a flat no to anything, even when the odds are trillions to one against it happening. Not coincidentally, that's around where the odds are against a black hole coming close to the Sun, or the Earth. But to explain that, I have to back up a moment and explain a few things about black holes.

Black holes, of the type that one might find moving around in our Milky Way galaxy, are formed when a star maybe ten or more times the mass of our Sun loses a long battle against gravity. During the star's life, the pressure of its own superheated gas held it up against collapse; but when the nuclear fusion furnace at its core gives out, gravity wins a decisive victory. The entire star collapses in on itself with incredible speed, and rebounds in a titanic explosion called a supernova. While the outer parts of the star are blown away, the core dwindles down, all that mass packed down into something the size of a planet...

.. of a city...
.. of a pinhead...
.. of an atom...
.. and smaller, and smaller, and smaller....

Here's where it starts getting weird. When I say nothing stops the collapse, that's pretty much literally true. It ends up so small that you can't even properly think of it as having volume at all. This weird state is known as a "singularity." You could think of it as an infinitely small point, as in mathematics, but it might be more accurate to say that a singularity operates on the space around it in a way that defies conventional geometry and gives most of us headaches to think about.

What you end up with is a huge amount of mass in this singularity. Now, mass warps space, and a lot of mass in one place will warp space a lot. That's why we end up with the headache-inducing singularity to begin with. However - and this is the really important point - this effect is very limited by distance. Get a little way from the black hole, and it would just be like any other massive object in space. You could have planets orbiting around a black hole (very COLD planets, since it gives off no light or heat) and they could continue orbiting it for billions of years or more.

Black holes aren't vacuum cleaners - they don't suck things in. It's like a gradual slope leading down to a hole - if you're not on the steep part of the slope, you don't fall in. It's when you get too close - inside the steep part - that the trouble starts. Fortunately, "too close" is actually a very short distance, compared to the usual distances in space. If our Sun turned into a black hole (it won't; much too small) you'd have to get within, oh, maybe ten kilometers before you really hit the downhill slide of gravity. (In astronomer-speak, that's roughly where the "last stable orbit" around the Black Hole Sun would be.) Keep in mind that Mercury is 46,000,000 km from the Sun at its closest!

In order to affect our solar system, then, a black hole would have to pass shockingly close. It would take me a lot of work to calculate just what the odds of that are. Fortunately, a fellow astronomer has already done the work on that. Dr. Phil Plait, in his great book Death from the Skies! has a very scary chapter on black holes. Then, in the last chapter, he gives you the punch line. (Which I will now give away; sorry, Phil.) Given the number of black holes in our galaxy, the odds are that one would black hole pass that close to our solar system only once in a hundred trillion years. For perspective - our solar system is less than five billion years old!

So the odds against a black hole coming into our solar system and swallowing the Sun - or the Earth - are fantastically small. You might say, astronomically small. (Heh.) Dr. Plait calls Death By Black Hole a lifetime risk of one-in-a-trillion. That number may not exactly equal "no chance", but it's surely close enough. It's definitely not worth wasting any worry on. For U.S. residents, here are some comparison risks: you're ten billion times more likely to die in traffic, ten million times more likely to die from a lightning strike, or two million times more likely to die ina tsunami. Overall, my advice would be: wear your seatbelt - and don't shorten your lifespan by worrying over this incredibly unlikely chance.