Brian Cox
speaker
1,719 appearances
13 recordings
8 series
first heard Oct 2024
last heard 16 Jun
Brian Cox’s voice in public audio — every appearance, attributed to the second.
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recordings per month · last 12 monthsRecordings per month over the last 12 months — 9 in all, peaking in Jun 2026 with 3.
Appearances
From BBC Radio 4, listen now on BBC Sounds.
Exciting, I would say. I've been doing some work on black holes recently, which I hadn't started last time I saw you, actually. So I got interested in it. And the amount of the progress that's been made in trying to understand how they work. And a question that was posed by Stephen Hawking a long time ago, really 1970s, early 1980s, which is what happens to stuff that falls in?
The simplest question you could possibly ask. Right. There's progress being made on that now, which I think is profound and exciting.
I mean, it's mainly theoretical, although we have now got photographs of them. So we have two photographs, which are radio telescope photographs. One of the one in the center of our galaxy, which is a little one. It's called Sagittarius A star. It's a little supermassive black hole. So it's about 6 million times the mass of the sun, which makes it a little supermassive.
And then there's another one, the first photo that was taken. It's a collaboration called Event Horizon. And they took a photo of one in the galaxy M87, 55 million light years away. That thing is around 6 billion times the mass of the sun. I mean, imagine that, 6,000 million times more massive than our sun. Is that the largest black hole we've ever discovered?
No, there are bigger ones than that, but that's the scale of them. It's a big-ish one, that. But if you think about it, I mean, so there's a number. It's called the Schwarzschild radius of the thing.
So if you took our sun, which you can fit a million Earths inside, and collapsed it down to make a black hole, it would form a black hole when it shrunk within a radius of three kilometers, about two miles. So you've got to take this thing, which is what I have to convert from kilometers to miles. That's okay. 700,000 kilometers. It's about 500,000 miles radius or something like that, the sun.
So you squash it down until it's about two miles, and then that would form a black hole. Wow. Six billion times the mass of the sun means you multiply that by six billion. So these things, the so-called Schwarzschild radius is, I don't know, larger than our solar system, basically. Oh, my God. This thing that sits in a galaxy. So we've got these two photographs. Larger than our solar system.
Yeah, the event. So it's a big structure. Now, that's a Chandra X-ray image of... There it is. That's it. So that one there, that's the M87 black hole. So what you're seeing there is the emission from the material that's swirling around it. It's called the accretion disk. So you have material that's orbiting very fast, emitting a lot of radiation. And that's what you see.
It's a flat disk, by the way. So you think Saturn's rings. So this material is very flat. But what you're seeing in that photograph is the light rays being bent around the black hole from that flat disk. So that was a prediction from Einstein's theory, basically. He published it in 1915. And you can predict that that's what one should look like.
And then just about, what was that, four years ago now, maybe five years ago, for the first time in history, we get an image of one. And it looks like the prediction. So it's a remarkable thing. How phenomenal is that?
So we've had those two photographs. The other thing we've had is so-called gravitational wave detections. So these are colliding black holes, and they collide and merge together. And obviously that's quite a violent event in the universe. And so that event, that process ripples space-time. So it sends ripples out in the fabric of the universe, space and time.
And actually, Kip Thorne, I've spoken to him several times. He's one of the greats, right, won the Nobel Prize for this. And he calls it a storm in time. So you get a time storm. So really, we're to think, as we speak now, there will be these very tiny ripples from violent cosmic events passing through this room. And they're changing the rate that time passes as they go through.
And we can detect that now. So we have detectors that can pick that up. And so we've seen those collisions as well.
Oh, millions of light years away.
Yeah, to a tiny extent. So there's an experiment called LIGO, which stands for something like gravitational interferometer. I can't remember exactly what the word is. So basically, it's laser beams. And there's one in Washington State, north of Seattle, and one in Louisiana. And they're laser beams, four-kilometer-long laser beams at right angles.
And they can detect these very tiny shifts in the, effectively, you could say the length of the laser beam. It's a bit more fiddly and complicated. It essentially measures the distortion in space-time caused by these ripples. And it's way less than the diameter of an atomic nucleus, by the way. Way less. These little sort of... Oh, my God.
And so we've started to... We've observed many of those... There it is. There's LIGO. So it's just basically two laser beams, that, but these ultra high precision thing. And so we've got data now of the collision of black holes and those event horizon pictures with radio telescopes. So that's part of it. But the main bit has been theoretical advances in understanding exactly...
In a sense, it was what's wrong with Stephen Hawking's calculation, which is a weird thing to say sometimes because people think Stephen Hawking, sure, he didn't get his math wrong. But he did actually. So what he calculated back in 1973, 1974. is that a black hole, so we picture this thing from which nothing can escape, even light. So when you go in, you're gone, basically.
What he calculated is that even though these things are just a distortion in space and time, that's the description of them. So it's almost as if there's nothing there apart from a distortion in space and time. He calculated that they glow, so they have a temperature of... So they emit radiation. It's called Hawking radiation. And so important was that discovery.
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