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Monday, October 22, 2007

The science behind black holes

The science behind black holes
One late October morning several years ago, I received an interesting phone call.A Canadian radio station - I want to say it was from Vancouver, but don't quote me - wished to interview a black hole astronomer for its Halloween morning show.

I'm pretty far down the list from Steven Hawking and the like, so they must have dug quite a while before reaching me.

Nevertheless, I am a black hole astronomer, so they did land an expert.

I'd like to say I'm a media darling, but it's not so. Not counting this column, I average about one radio/newspaper interview every two or three years. But I'm a hog for the limelight, so I agreed.

Following some standard spooky music, the radio host asked me about all the weird things that black holes can do. I think I talked with him and an unseen audience of millions - or maybe hundreds - for a few minutes.

People joke about getting 15 minutes of fame. I can truthfully say that all the interviews I've ever done like this together don't reach 15 minutes.

Black holes

Because Halloween is again nigh, I thought I'd revisit this spookiest of objects with you.

A short definition of a black hole is "an object from which nothing can escape." In other words, once you fall in, you can't come back out.

The modern idea of a black hole is that its gravity is so intense that not even light can leave it. We pick light as the standard because we know of nothing that can travel faster than the speed of light.

Imagine you are an astronaut approaching a black hole. What would happen to you?

Ocean tides on Earth come from an imbalance of gravity from the moon and sun. Because your feet are closer to the Earth's center than your head (while standing), you experience tides every day, though these tides are far below any threshold of sensation.

But if you got close to a black hole, the pull on your feet would get substantially larger than its pull on your head. Before falling in, you'd be stretched out like a strand of spaghetti.

Time changes

Also, light can't go any faster than it already does, but it can be made more energetic.

Visible starlight would become X-rays as it fell in. So if being ripped apart wouldn't work, being fried by induced radiation ought to take you out.

It's even possible for light to orbit the hole, pulled around by the hole's gravity. At the right position, you wouldn't need a mirror to see the back of your head.

The weirdest part of being near a black hole is that time changes. Your astronaut buddies would see you slowing down until you froze in place. You would see the opposite - time outside the hole would speed up enormously, until the universe itself came to an end. All the Halloweens that ever can be would be pass by in an instant.

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