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Black holes for beginners

An artist's conception shows a
massive black hole in action.

If big black holes are so scary, why do scientists think it's not a problem to be around teeny-tiny black holes? Astrophysicist Neil deGrasse Tyson literally wrote the book on "Death by Black Hole," so he ought to know. He also ought to be good at explaining the difference, since he's the director of the Hayden Planetarium at New York's American Museum of Natural History as well as the host of "NOVA scienceNOW," the TV magazine show that begins its summer season on PBS tonight.

If you're wrestling with all the claims and counterclaims over matter-gobbling black holes, this is the guy you want on your side.

Tyson, who turns 50 in October, is used to wrestling with scientific puzzlers - and just plain wrestling, for that matter. He was captain of the wrestling team at the Bronx High School of Science as well as editor-in-chief of the school's Physical Science Journal.

More recently, he has wrestled with America's future space policy as a member of several advisory commissions. But you could argue that his most challenging match found him pitted  against the scientists and second-graders who are fans of the planet Pluto. Eight years ago, Tyson had to take the heat when the remodeled Rose Center for Earth and Space (which serves as the Hayden Planetarium's home) dropped Pluto from its planet display.

David Britt-Friedman / msnbc.com file
Astrophysicist Neil DeGrasse Tyson is director of
the Hayden Planetarium in New York.

Tyson defended the demotion, saying that the discovery of other icy worlds on the solar system's edge implied that the littlest planet should be reclassified as the biggest member of a new class of celestial objects. In 2005, it turned out that Pluto wasn't even the biggest: Another ice world, eventually dubbed Eris, was found to be even bigger. That set off new rounds of decisions and debates that are still raging.

Tyson says he's taking the subject head-on in a book titled "The Pluto Files," due for publication next year. "It's a study of the public's reaction to the scientific demotion of a planet," he explained in an interview this week.

But enough about Pluto: On tonight's installment of "NOVA scienceNOW," Tyson and his team will be wrestling with the mysteries of dark matter as well as the causes of Alzheimer's disease, the scientific methods for detecting fake imagery and the "wisdom of crowds." If you miss the show, or if you don't live in an area that gets PBS, you can watch the whole show online beginning Thursday.

About those black holes...
As a warmup for tonight's show, I asked Tyson about one of the subjects that's closest to his heart: black holes, the phenomenon that's created when an object collapses into a gravitational singularity so powerful that not even light escapes its pull.

We've known for decades that such things should exist out in the cosmos, based on a reading of relativity theory. There's increasing evidence that supermassive black holes lurk at the core of many galaxies, including our own. And now there's talk that an atom-smasher known as the Large Hadron Collider might blast subatomic particles into each other so energetically they turn into incredibly tiny black holes on Earth.

Is this something we should be worried about? Some people think so, but Tyson has a different view, as reflected in this edited Q&A:

Cosmic Log: You've written the book "Death by Black Hole," and now people have been talking about the black holes that might eat the planet. What can you say about the risks involved, and the different sizes of black holes? Is a microscopic black hole as dangerous as a galaxy-sized black hole?

Tyson: Well, black holes are undeniably scary things. Let's just start with that fact. They eat what comes near them, and that's it. Black holes are dangerous. You want to avoid them at all cost. That's No. 1.

No. 2: Yes, there are black holes of different sizes. The one most commonly discussed is the one that would be the endpoint of the life of a star of very high mass. The sun is not one of those, so the sun will not end its life as a black hole. That's the most commonly discussed, and that's what would be the most common in the galaxy. Wherever there was once a high-mass star, there would now be a black hole in its place. You want to map those out, ultimately, and not run into them.

When I say "common," these types of stars are themselves rare. They're common for black holes, but they're rare for a cosmic object. Only one out of 1,000 or even 10,000 stars is a high-mass star. That's a small fraction of the total.

There's this other type of black hole that one imagines one might make in a particle accelerator. That's what you'd call a micro black hole. It turns out that black holes evaporate. That was discovered by Stephen Hawking. The phenomenon is called Hawking radiation in his honor.

The way this happens is kind of cool. The gravitational field is so intense in the vicinity of a black hole that the gravitational energy spontaneously becomes particles, according to E=mc2. They become particles in the field outside the event horizon of the black hole. Gravity extends well beyond the event horizon. So the energy becomes particles, one of those particles escapes, and the other one falls into the black hole. And so, all right, that just took mass away from the black hole. So black holes actually become lighter over time.

Now here's the catch: The smaller a black hole is, the faster it evaporates. So, micro black holes evaporate practically instantaneously.

There's this worry that at CERN, they're going to turn on the accelerator and create states of matter as never before – which is true – at higher energies than ever before – which is true – and possibly produce micro black holes. What happens if one does not evaporate, but just sort of hangs around? Whatever it touches, it eats, then it gets more massive. The more massive it gets, the less likely it will be to evaporate, because they evaporate quickly only when they're small. This worry that it will create a runaway black hole that will eat the Earth is what some people have been concerned about.

You can do a calculation to show how quickly the black holes will evaporate. You're sort of protected there. But suppose you made a mistake. There's a big cost if you made a mistake. The cost is the end of the Earth. However, there's another separate experiment that's going on all the time. And that is, there are these mysterious particles in space called cosmic rays, and they hit Earth all the time. They have energies rivaling and exceeding the energies that will be created in this new supercollider, the Large Hadron Collider in Switzerland. They would be making black holes all the time as they slam into our atmosphere.

If the collider were somehow deadly to Earth – so, too, would the rest of these particles striking us from space. Yet, at no time have we had a black hole emergency.

Q: You get all these questions about how the LHC will be producing this phenomenon down on Earth, and people talk about how the black holes would be moving slowly in relation to Earth rather than zooming past like a cosmic ray. The counterargument to that is generally, "Gee, there are so many reactions going on over the history of the universe …"

A: "… that you would catch them." That's right. Nature is already conducting this experiment, with Earth as its target. These are the cosmic rays that fly back and forth, whose origin is still a mystery – but we do know they're there, and we know they're hugely energetic. It's that kind of test that gives you the confidence that nothing bad will happen with the Large Hadron Collider.

By the way, it's not new for people to be concerned when we open up new scientific vistas. Back in the early 20th century, people warned that we shouldn't split the atom. This was a fundamental building block of nature, and splitting it would be bad. Well, yes, it was bad because we made bombs out of it, but nature was just fine. Nature does it all the time. There was this worry that the atom was someplace we should not go. Yet atomic physics is the foundation of modern technology.

Q: Right. And people talk about the first nuclear detonation, and the concern that that would destroy the world.

A: That it would ignite the atmosphere. So, yes, the fear is understandable if you're otherwise unfamiliar with a subject. People need to know, however, that the fears are not somehow uniquely applied. There are fear factors at every turn, at every advance in our understanding of the universe. So that should temper the singularity of a person's concern.

Q: Do you find that's a particular challenge when you engage the public in scientific discussion? That a little bit of knowledge can be a worrisome thing?

A: It can breed fear. A little bit of knowledge about something that people don't understand, or that is more powerful than they are, can breed fear. And that's understandable. I'm not critical of the public for that. I'm critical of myself and my colleagues for our failed efforts to try to create a comfort zone around the frontiers of scientific discovery.

Q: I guess that gets right into the show. Do you feel as if you're making a difference? Have you gotten feedback from the general public?

A: What I get is e-mail and other correspondence from people who say, "I always viewed science as something beyond my ability to understand." And they see "NOVA scienceNOW" as a fun, interesting and entertaining way to become scientifically literate. "NOVA scienceNOW" is conceived to bring science to the viewer in such a way that you don't feel as if you have to take your medicine. It doesn't mean dumbing it down. It doesn't mean dropping out all the jargon, to try to simplify things. It just means having fun with the frontier of discovery. I'm there as your guide and as your host. Because I'm a scientist, I have a foot in the scientists' camp. But I also feel strongly for what's going on in the mind of the public, so I have a foot in your living room as well.

I see myself as a conduit between you and that frontier that we're sharing with you. By the way, I'll get on the scientists' case for using jargon. I'll say, "Don't you mean it's the blah-bla-blah-bla-blah?" Because I know enough to come at them that way, right? And they'll say, "Yeah, I guess you could say it that way." And we just did. So we have fun, and the public sees scientists just having fun.

Q: And you get a sense of the process behind the science.

A: The process. That's the word. Too many journalists will only report the scientific discovery, leading the public to think that science is all about the discovery, when in fact it's all about the process. Sometimes it's long and drawn out. Sometimes there's no eureka moment at the end of the day. But the scientists love the work, they love the process, they love the quest.

It's a metaphor for life. People might say, "Oh, when I get my degree…" or "When I get my pay raise…" or "When I retire…" But life happens between now and then, and that's what you should be paying attention to. As a scientist, so much of your time is spent in the lab, or in the field, or on the computer, trying to grapple with the boundary of ignorance.

Occasionally, you make discoveries that grab something from the unknown and bring it into the world of the known. Then you've made a contribution to our understanding of the universe. That doesn't happen every day.

Q: Dark matter is a perfect example of that – where you have something you know that's out there, and yet it's unknown.

A: And it's still unknown. We do a whole segment showing that we don't know what it is. Most science programs wouldn't do that. They'd wait until it was known, and then they'd report the results. We go right in there to this mine that's more than 2,000 feet below Earth's surface. You've got to go that deep so that the bedrock above you shields the experiment from particles that could masquerade as dark matter.

Particle physicists are confident that dark matter is a new family of exotic particles that do not interact with ordinary matter. But I look at that with the idea that when you're a hammer, all your problems look like nails. When you're a particle physicist, the solution to dark matter looks like particles. I try to stay open to what other possible solutions might exist.

Q: Right, and as an astrophysicist, you probably have your own brand of hammer – the idea that dark matter might be MACHOs [massive compact halo objects] rather than WIMPs [weakly interacting massive particles].

A: That's true. But if I were a betting man, I'd probably give the nod to the particle physicists. I don't care which it is, as long as it has the right properties. If it works, we're good.

Q: That brings us around full circle to the Large Hadron Collider. With all this talk about micro black holes, people may not realize that the LHC might detect dark-matter particles.

A: If there are dark-matter particles, they should be within reach of the Large Hadron Collider. So the people at CERN are anxious to be the first to discover dark matter through that means, rather than natural dark matter that happens to be passing through the earth.

Q: I suppose the good thing about the "NOVA scienceNOW" format is that you could always come back with an update.

A: Exactly. I think of it as having the style of CBS' "60 Minutes," where there are different segments, and I do the parts that lead from one segment to the next – right on down to the Andy Rooney part, where at the end of the show, I give my "Cosmic Perspective." I offer a point of view that enhances your understanding of where we fit in the universe, drawn on themes that have just appeared on the program.

Q: And as you get closer to Andy Rooney's age, you can become more and more of a curmudgeon.

A: Ha! I'd have to get bushier eyebrows – and get an old Underwood typewriter. The counterpart would be an old oversized PC, I guess.

Hungering for more? In earlier interviews, Tyson discussed Einstein's and Darwin's theories, subjects ranging from black holes to black history, and life, the universe and everything. And in last Sunday's Parade magazine, Tyson discussed the legacy of the Hubble Space Telescope.