Cosmic Queries: General Astrophysics 101

Curious about general astrophysics? Then join us for class this week as Professor Neil deGrasse Tyson and teaching assistant Leighann Lord explain some of the basics.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:21Neil deGrasse Tyson?

  Welcome to StarTalk Radio. I'm your host Neil deGrasse Tyson. I'm an astrophysicist with the American Museum of Natural History, right here in New York City, where I also serve as Director of the Hayden Planetarium. Come by and check us out sometime. I've got with me Leanne Lord, comedian extraordinaire. Leanne, welcome back to StarTalk.

• 0:41Speaker 01

  Thank you, Neil. Good to be back.

• 0:43Neil deGrasse Tyson?

  I got you for this special needs of this hour. Not special needs, that didn't come out right. Special needs. Are you a special needs?

• 0:53Speaker 01

  Well, you know what, actually, I think it did come out right, because these questions make me feel very special.

• 0:57Neil deGrasse Tyson?

  Oh, because this is the cosmic queries part of StarTalk Radio.

• 1:00Speaker 01

  Yes, and these questions, woo.

• 1:02Neil deGrasse Tyson?

  These are questions from our listeners, and we've got some like seriously knowledgeable listeners out there.

• 1:08Speaker 01

  Yes.

• 1:09Neil deGrasse Tyson?

  Very impressed.

• 1:10Speaker 01

  These questions are very challenging.

• 1:11Neil deGrasse Tyson?

  Yeah, and so what we try to do is spend some time of our StarTalk airwaves, just receiving and responding to cosmic questions shared with us on our Twitter stream, on our Facebook page. You can find us on Facebook and like us there, of course, or find us on the web at starTalkRadio.net. And we have a Twitter stream, StarTalk Radio, and all these places you can send in questions and we collect them. In this particular case, we've got all ones just about general astrophysics.

• 1:38Speaker 01

  Yes.

• 1:39Neil deGrasse Tyson?

  Yeah, and you're gonna read them to me, and I haven't seen any of these questions in advance.

• 1:43Speaker 01

  And I wish I had, because I need some help. I don't know when I've ever felt this inadequate mentally.

• 1:49Neil deGrasse Tyson?

  All right, mentally was the clarifying word there. All right, so give it to me. What do you got?

• 1:54Speaker 01

  Okay, our first question is from, I believe this is Jen or Justin Divs, CBS. Could the Big Bang be the destruction of supermassive black holes?

• 2:06Neil deGrasse Tyson?

  Ooh, so the Big Bang itself is what birthed all the space, time, energy and matter of the universe?

• 2:13Speaker 01

  Yes.

• 2:14Neil deGrasse Tyson?

  So, once the universe began to expand and the matter coalesced, the matter coalesced into objects like stars and galaxies and every large galaxy we know has a supermassive black hole in its center. Only one, there's no room for two. If there's ever two, they will soon merge.

• 2:33Speaker 01

  Okay.

• 2:33Neil deGrasse Tyson?

  And become one mondo.

• 2:35Speaker 01

  The alpha?

• 2:36Neil deGrasse Tyson?

  The alpha.

• 2:36Speaker 01

  The uber?

• 2:37Neil deGrasse Tyson?

  Yeah, so what happens is you can have galaxies that collide with each other and their black holes sure as night follows day will find each other, merge and become the new center of that mega galaxy that just formed. Because galaxies collide, they go bump in the night.

• 2:51Speaker 01

  Right.

• 2:51Neil deGrasse Tyson?

  Yeah, so can they destroy supermassive black holes? No, a black hole is a black hole until it evaporates using the special, did you know evap- holes evaporate?

• 3:02Speaker 01

  No.

• 3:03Neil deGrasse Tyson?

  You didn't know that?

• 3:03Speaker 01

  I had no idea.

• 3:04Neil deGrasse Tyson?

  You gotta come more often.

• 3:05Speaker 01

  That's what I'm saying.

• 3:06Neil deGrasse Tyson?

  Or get out more, you know? If you get out more, you would learn this.

• 3:10Speaker 01

  Yes, but this is general casual conversation. Hey, everybody, black holes evaporating over on 15th Street.

• 3:18Neil deGrasse Tyson?

  They, they, they, so it turns out, Stephen Hawking showed, among many discoveries of Stephen Hawking, we all know Stephen Hawking, the brilliant physicist at University of Cambridge, England. So, he proposed, he, he discovered, using quantum physics, the laws of quantum physics, that sort of particle by particle, a black hole slowly evaporates. And the black hole in the center of a galaxy is large enough, it would take about 10 to the hundredth years, a googol years, to evaporate. Did you know 10 to the hundred is a googol?

• 3:53Speaker 01

  I had no idea.

• 3:54Neil deGrasse Tyson?

  Yeah.

• 3:54Speaker 01

  Does Google know that?

• 3:55Neil deGrasse Tyson?

  Google, they're spelled differently. They put the L in front of the E. Google, the number 10 to the hundredth power, a one with 100 zeros, is spelled G-O-O-G-O-L, googol, as opposed to googul.

• 4:09Speaker 01

  Oh, got it.

• 4:10Neil deGrasse Tyson?

  Yeah, googol, a googol. So, that's way longer than the age of the universe. So, this is not something you should wait around to watch happen.

• 4:17Speaker 01

  That's not a quick cup of tea.

• 4:18Neil deGrasse Tyson?

  Right, no, no. And so, in the birth of the universe, there's no reason to think that if somehow another universe got born, that it would destroy. A black hole that was adjacent to it because black holes really have their own agendas. And it is matter gone bad.

• 4:32Speaker 01

  I love that. They have their own agenda.

• 4:34Neil deGrasse Tyson?

  Well, they don't care what's happening around them. They don't care. They're super massive centers of gravity and mass at very high density. Some new law of physics would have to rise up that we would then discover to show how you would then tear apart a black hole or destroy it. But there's no known force large enough to accomplish this.

• 4:53Speaker 01

  Hmm. All righty then. Moving on.

• 4:55Neil deGrasse Tyson?

  What else you got?

• 4:56Speaker 01

  All right. This is from Mikel Garbaks about the accuracy of the age of the universe and the Hubble constant.

• 5:04Neil deGrasse Tyson?

  Mm hmm.

• 5:05Speaker 01

  How are we able to refine the 12 to 14 billion year estimate to 13.75 billion? Which, that's really rude. Not, lady doesn't like to tell her age. Does the universe really want you knowing that it's 13.75? Couldn't we go with the estimate?

• 5:22Neil deGrasse Tyson?

  For the longest time, in fact, my entire time as an undergraduate and in graduate school, we didn't know the age of the universe by a factor of two. There was some research that indicated that we might be 10 billion years old. Other research that indicated we might be 20 billion years old. And there were warring camps at every conference. There were the 10 billion year old people, the 20 billion year old people.

• 5:45Speaker 01

  What did that fight look like in the lunchroom?

• 5:47Neil deGrasse Tyson?

  In the lunchroom? What, what food stuff did we reach to throw at each other? And this all relates to what's called the Hubble constant.

• 5:55Speaker 01

  Okay.

• 5:56Neil deGrasse Tyson?

  Named in honor of Edwin Hubble, the man. There was a human being that predated the telescope, whose name was Hubble.

• 6:03Speaker 01

  What you say?

• 6:05Neil deGrasse Tyson?

  Now, here's an interesting case. He had an affected British accent.

• 6:09Speaker 01

  Did he really?

• 6:10Neil deGrasse Tyson?

  Yes, yes. He was so fake and wore all these tweety things. He smoked a pipe.

• 6:15Speaker 01

  I love it.

• 6:15Neil deGrasse Tyson?

  And he was, wait, and he was a misogynist racist. Totally.

• 6:20Speaker 01

  Well, if you're gonna be one, you should be the other.

• 6:22Neil deGrasse Tyson?

  They go together.

• 6:23Speaker 01

  Two for one.

• 6:23Neil deGrasse Tyson?

  They often go together. And the good thing about science is that none of that's relevant. What matters is how good was his science? In many other walks of life, you fold all that together and you say the person is reprehensible.

• 6:35Speaker 01

  Right.

• 6:36Neil deGrasse Tyson?

  I don't want any part of them. I don't want them speaking to my children. And in science, science distinguishes itself from other activities of the human condition for that reason.

• 6:46Speaker 01

  Right.

• 6:47Neil deGrasse Tyson?

  It's got nothing to do with culture. That's right. So, he in 1920s discovered that galaxies in the universe were moving away from one another in all directions. And so, you look this, you look one direction, they're moving away from you. Look, another direction is still moving away from you.

• 7:03Speaker 01

  I want my space. I'm out of here.

• 7:05Neil deGrasse Tyson?

  You need, I need my space. They're not coming towards you in one direction and away from you in another. They're going away from you in all directions. If you plot this up, the line that is drawn has a slope.

• 7:16Speaker 01

  Okay.

• 7:17Neil deGrasse Tyson?

  The slope of that line is the Hubble constant. And if you know the slope of that line, you know the age of the universe. So, the Hubble telescope was first designed to get the best, most accurate measurement of the Hubble constant. So, the battle of the Hubble constant went from 10 billion to 20 billion, and then it was like 10 billion to 15 billion, and it got narrower and narrower and narrower. And finally, we refined that slope of that plot, and we can say the universe is 13.7 billion years old. We gotta take a break. We'll come back, more cosmic questions on StarTalk Radio.

• 8:14Neil deGrasse Tyson?

  This is StarTalk Radio. We're back. I'm Neil deGrasse Tyson. My co-host today, Leanne Lord.

• 8:19Speaker 01

  Yes.

• 8:20Neil deGrasse Tyson?

  Comedian.

• 8:22Speaker 01

  Extraordinaire.

• 8:23Neil deGrasse Tyson?

  Do people come up to you, they know your profession, they say, "Tell me a joke."

• 8:25Speaker 01

  Yes.

• 8:26Neil deGrasse Tyson?

  Yeah, you don't want to hit them?

• 8:27Speaker 01

  All the time. And I, and I have. So, there's an issue.

• 8:31Neil deGrasse Tyson?

  You're still resolving this.

• 8:32Speaker 01

  It's still resolving. Case is pending. I can't discuss.

• 8:36Neil deGrasse Tyson?

  So I've got you here to read me these questions. They came in from the internet. And I haven't seen them before, but they're all about modern astrophysics.

• 8:43Speaker 01

  Yes.

• 8:44Neil deGrasse Tyson?

  And they came from our listeners and we're just trying to give back in this, the cosmic queries part of StarTalk. So what do you got?

• 8:51Speaker 01

  I have a question from Tony Schultz, and he says regarding a subject brought up on the Origins TV series.

• 8:57Neil deGrasse Tyson?

  The TV series that I hosted for PBS Nova.

• 9:00Speaker 01

  Nice plug.

• 9:01Neil deGrasse Tyson?

  I'm just, I'm sure people know, just so they know.

• 9:04Speaker 01

  Uh huh.

• 9:05Neil deGrasse Tyson?

  Okay, go.

• 9:05Speaker 01

  Moving on. Why is it even a question whether our solar system came from a supernova explosion? I mean, how else would heavy elements like gold on Earth come from?

• 9:15Neil deGrasse Tyson?

  Well, how, what a luxury it is to retrospectively assert that of course our heavy elements came from supernovae.

• 9:24Speaker 01

  I know, right?

• 9:25Neil deGrasse Tyson?

  This was not known for a while. Do you know when I was a kid and I'm in chemistry class and you ask the chemistry teacher, where did these elements come from that sit up there on the periodic table? So we find them in the ground.

• 9:39Neil deGrasse Tyson?

  That was the chemistry teacher's answer. You don't get the real answer that, to that question until you take astrophysics. We say, where do these elements come from? They are cooked in the crucibles of high mass stars forged from low, from, from small elements like hydrogen and helium. They are fused together to make high mass elements. And you, they ride their way up the periodic table of elements. And then that same star explodes, scattering its guts into the galaxy, out of which you make subsequent solar systems. Somebody had to discover this. A Nobel Prize was awarded for that discovery.

• 10:16Speaker 01

  You know, if they explained it like that in high school, that was like the opening of a movie. It was forging and explosions and, oh my god.

• 10:25Neil deGrasse Tyson?

  Is this how it goes?

• 10:26Speaker 01

  My science class was not that interesting.

• 10:28Neil deGrasse Tyson?

  And so, but in a, in a TV series on Origins, you got, you can't assume people know that in advance. And how heroic it was to deduce the fact that these heavy elements owe their origins to stars that have given their lives for, so that we can live.

• 10:45Speaker 01

  Wow. I love that.

• 10:48Neil deGrasse Tyson?

  You have it.

• 10:49Speaker 01

  Move it on.

• 10:50Neil deGrasse Tyson?

  Startalk, the Cosmic Queries session.

• 10:52Speaker 01

  Hello.

• 10:52Neil deGrasse Tyson?

  Leanne, what else you have?

• 10:53Speaker 01

  Don't assume, I like that. Okay, this next question is from William M. Sacrin. And he says, this is a Google Nexus commercial where a girl asked Google, yeah, Google, how much does the Earth weigh? And the device responds with, the Earth has a mass of. I mean, obviously, mass and weight are not the same measurement, but this made me wonder, how do you measure the weight of a planet when it's the planet itself that provides the gravitational force by which you make the measurement?

• 11:21Neil deGrasse Tyson?

  Ooh, well, a couple of things. So if you say, what is the weight of something that's, that's a physical object? We assume you mean, what is its mass? We have to assume that, yes.

• 11:33Speaker 01

  Really?

• 11:34Neil deGrasse Tyson?

  Hence, the answer comes back with a mass number, not a weight number. Earth is in free fall towards the Sun with sideways motion that keeps it in orbit. And anything that's in free fall towards anywhere is weightless. So you could justifiably say the Earth is weightless in space, because that's true.

• 11:56Speaker 01

  Wow.

• 11:56Neil deGrasse Tyson?

  Earth has no weight, any more than an astronaut has weight in orbit around Earth itself. So in other words, for the same reason that astronauts and space stations and the space shuttle is weightless in orbit around Earth, Earth is weightless in orbit around the Sun. The Sun is weightless in orbit around the center of the galaxy.

• 12:15Speaker 01

  So the minute we stop moving fast enough.

• 12:18Neil deGrasse Tyson?

  Oh, if we stop moving sideways, then we fall directly towards the Sun. If the space shuttle, space stations, no more space shuttle, space station stops moving sideways, it'll fall directly down towards Earth and crash about 15 minutes later.

• 12:33Speaker 01

  So the, the Earth is as felt, nothing, is what you're saying?

• 12:36Neil deGrasse Tyson?

  It weighs nothing, but it's got mass. So when people go on weight loss programs, what they're really doing is trying to lose mass. Because if you want to lose weight, just go into orbit, and then you, you weigh nothing. But what we're really trying to do is remove atoms from your body.

• 12:53Speaker 01

  Yes.

• 12:54Neil deGrasse Tyson?

  That's what you're trying to do.

• 12:55Speaker 01

  I really am.

• 12:55Neil deGrasse Tyson?

  Fat atoms.

• 12:57Speaker 01

  Yes.

• 12:58Neil deGrasse Tyson?

  Fat, they're molecules, fat molecules. That's what you're trying to remove from, you know, there's no element on the periodic table called fat. It's a, it's a rather complex.

• 13:05Speaker 01

  We have a different table, sir.

• 13:06Neil deGrasse Tyson?

  It's a, it's a rather complex molecule that has a lot of stored energy. That's why.

• 13:13Neil deGrasse Tyson?

  Fat is, it's an extraordinary, that's why you can go for days and days before you burn off all the fat layer that might have accumulated on your belly or on your butt. So, getting back to the person's question, Earth is weightless because it's in free orbit around the sun, as in anything that's freely falling towards anything else. So the moon is weightless in orbit around the Earth, just as Earth is weightless in orbit around the sun. So now you want to measure the mass. Mm-hmm. Okay, that was done by a fellow named Cavendish, and he's a British, actually, I think he was a chemist. But real British, not affected. No, I always get it confused if you're British, or English, or from the UK. I always get, every time I learn it, I never retain it.

• 13:58Neil deGrasse Tyson?

  Right. And so, I'll say he's from somewhere in the United Kingdom, alright? But, the point is, he was the first to measure the mass of the Earth. Okay. And, it's a hefty number. It's, you know what's useful about- The Earth is a little chunky. Yeah, so the mass of the Earth, we got 6 times 10 to the 27 grams. So if you want this in tonnage, that would be, uh, let's see here, that would be 6 times 10 to the 21 tons, so 6 sextillion tons. Wow. Yeah. The Earth is a brick house. Now, what's useful about that number is, if you want to know what happens to Earth if we get hit by an asteroid, find the mass of the asteroid.

• 14:42Neil deGrasse Tyson?

  I was about to say, doesn't it depend? Well, yeah, exactly. So you look at the mass of the asteroid compared to the mass of the Earth, it's like a mosquito flying full speed ahead into the buttock of an elephant. That's an image. So, or a gnat, a gnat is better than a mosquito, because gnats are just kind of annoying and they fly into you. So, so the relative mass, I think, when the last time I did that calculation, that was about right. Okay. Alright, so asteroids are bad for life, but they're not going to harm Earth. When people say save Earth, Earth does not need saving from anybody.

• 15:15Speaker 01

  She eye.

• 15:16Neil deGrasse Tyson?

  They mean save life on Earth.

• 15:17Speaker 01

  Right.

• 15:18Neil deGrasse Tyson?

  Yeah, yeah. So, uh, so, so you could buy this. So you do it with a, with special, an experiment. If you, if you Google Cavendish, you'll read all about his experiment where you can measure what's called the gravitational constant, which was first predicted by Isaac Newton.

• 15:34Speaker 01

  Okay.

• 15:34Neil deGrasse Tyson?

  And once you know that constant, you can calculate the mass of the Earth. It rolls out of the equation that you just used.

• 15:41Speaker 01

  Wow. All right, William.

• 15:42Neil deGrasse Tyson?

  You got it.

• 15:43Speaker 01

  Thank you for your question.

• 15:44Neil deGrasse Tyson?

  Uh huh.

• 15:44Speaker 01

  Moving on, I have a question from Ken Duncan.

• 15:47Neil deGrasse Tyson?

  Yeah.

• 15:47Speaker 01

  And he says, Dr. Tyson, where does all the spin in the universe come from? Planets, solar systems, galaxies? I'm thinking Madison Avenue.

• 15:57Neil deGrasse Tyson?

  Spin from Madison Avenue? That's the best place for spin? There he is. Everything spins. Everything.

• 16:05Speaker 01

  So when little kids do it, mommy shouldn't say stop?

• 16:07Neil deGrasse Tyson?

  Everything. Mommy should never tell kids to stop doing anything.

• 16:10Speaker 01

  Oh, well, hold on now.

• 16:13Neil deGrasse Tyson?

  So everything spins and here's, but you say, well, that's odd. Why is, or is there anything that doesn't spin at all? Take a huge gas cloud, all right, for example, in the galaxy.

• 16:24Speaker 01

  Mm hmm.

• 16:25Neil deGrasse Tyson?

  If there's any movement at all, like one atoms width per year in the, in the, if anything is moving in it, as the gas cloud collapses, the speed of movement increases. This is why, if you suck a strand of spaghetti through your lips, it is guaranteed to flap you in the face.

• 16:55Speaker 01

  Guaranteed?

• 16:56Neil deGrasse Tyson?

  Guaranteed. Try it.

• 16:57Speaker 01

  I know what I'm eating for dinner tonight.

• 16:59Neil deGrasse Tyson?

  Try it, okay? Put, start at the bottom of the spaghetti.

• 17:02Speaker 01

  Okay.

• 17:03Neil deGrasse Tyson?

  Make sure there's not a loved one at the other end of the spaghetti.

• 17:05Speaker 01

  Oh, that would have made it wrong.

• 17:06Neil deGrasse Tyson?

  This experiment wouldn't work.

• 17:07Speaker 01

  Okay.

• 17:08Neil deGrasse Tyson?

  It's got to dangle below. You suck it up in your mouth. Initially, it's wiggling just gently.

• 17:14Speaker 01

  Mm hmm.

• 17:15Neil deGrasse Tyson?

  As you suck it more and more, it starts wiggling more violently.

• 17:19Speaker 01

  Yes.

• 17:19Neil deGrasse Tyson?

  And then eventually it slaps you in the face.

• 17:23Neil deGrasse Tyson?

  I'm just saying.

• 17:24Speaker 01

  Yes.

• 17:24Neil deGrasse Tyson?

  Okay, so, this is a major principle in physics called the conservation of angular momentum. That's what it's called. And skaters know-

• 17:31Speaker 01

  It's not called flapping spaghetti.

• 17:35Speaker 01

  That would be so much easier to remember.

• 17:36Neil deGrasse Tyson?

  I should rename it, yeah, the flapping spaghetti rule. It's skaters that pull in their arms and they spin faster.

• 17:41Speaker 01

  Oh yeah, of course.

• 17:42Neil deGrasse Tyson?

  If you start out with even the slightest speed, you will speed up as you collapse. And everything in the universe, because of gravity, collapses. And whatever speed it had before, it speeds up. This is why everything in the universe rotates. We gotta take a quick break. More from Cosmic Queries when StarTalk Radio continues.

• 18:21Neil deGrasse Tyson?

  We're back on StarTalk Radio. Of course, we're on the web, starTalkRadio.net. You can download our archival shows. They're fun. If you've just, if you're a new listener to StarTalk Radio, we've been at this only for a couple of years, but there's some cool guests that we've had in the past. Check it out. And we're also, of course, findable on iTunes. Just find us on StarTalk Radio. Leanne Lord, you're my co-host today.

• 18:45Speaker 01

  Yes, I am.

• 18:46Neil deGrasse Tyson?

  Great to have you.

• 18:46Speaker 01

  And I'm loving it.

• 18:47Neil deGrasse Tyson?

  You're reading me Cosmic Queries.

• 18:49Speaker 01

  I am.

• 18:49Neil deGrasse Tyson?

  And this session, they're just general astrophysics. It's the grab-bag bin of cosmic questions that's sent to us by listeners from our Facebook page. So what do you got?

• 18:58Speaker 01

  Well, you know, I'm feeling richer and smarter with every question.

• 19:02Neil deGrasse Tyson?

  Excellent.

• 19:02Speaker 01

  You know, I've done the spaghetti thing. I gotta be honest.

• 19:06Neil deGrasse Tyson?

  Oh, the spaghetti, yeah, coming off the break, yeah, yeah. You suck spaghetti through your lips and it flaps in your face.

• 19:10Speaker 01

  And I had no idea there was a physics principle going on with this fun.

• 19:15Neil deGrasse Tyson?

  Major law of physics operating, getting spaghetti sauce in your face. Now, I think as adults, we don't do it as often, right?

• 19:22Speaker 01

  Oh, right, yeah.

• 19:23Neil deGrasse Tyson?

  Because you flap food in your shirt and all this sort of thing. So, but kids, kids certainly remember this. And it's a major law of physics. It's the conservation of angular momentum.

• 19:32Speaker 01

  Wow.

• 19:32Neil deGrasse Tyson?

  And so what it means is if you're rotating slowly and you have a big extent to your physical system, and then you start pulling things in towards your axis of rotation, something's gotta compensate for that. And the way you compensate is you end up spinning faster. And there are equations that prescribe this with precision.

• 19:52Speaker 01

  I'm a roller blader, so yes.

• 19:54Neil deGrasse Tyson?

  Oh, yeah, you know it. Oh, yeah.

• 19:55Speaker 01

  So I didn't know. I should have known it was physics. I just know, oh, wow, I'm faster.

• 20:01Speaker 01

  All right, I have more questions, if that's okay.

• 20:03Neil deGrasse Tyson?

  Yeah.

• 20:03Speaker 01

  William Jesse Miller has a question. And William asks, how does a planet-

• 20:08Neil deGrasse Tyson?

  It's another three-name person.

• 20:09Speaker 01

  Another three-name person.

• 20:10Neil deGrasse Tyson?

  Maybe they're feeling it with my Neil deGrasse Tyson, so they gotta come in with three names.

• 20:13Speaker 01

  Yeah, I feel that's how I gotta get their entree.

• 20:16Neil deGrasse Tyson?

  William Jesse Miller, go.

• 20:17Speaker 01

  How does a planet have four suns? Wouldn't some stars be ejected? I thought three or more star system is unstable.

• 20:27Neil deGrasse Tyson?

  How does a planet have four suns? Okay, yeah, sure. So, the universe, if you look up at night, most of the stars you see are not alone.

• 20:39Neil deGrasse Tyson?

  More than half of the stars in the night sky are multiple, double and multiple star systems.

• 20:44Speaker 01

  Okay.

• 20:45Neil deGrasse Tyson?

  And so, the solo star like Earth, or like our sun, is, I don't wanna call it rare, but it's not the most common case in the galaxy.

• 20:53Speaker 01

  Really?

• 20:54Neil deGrasse Tyson?

  Yeah. And what a surprise that was to the first person with a telescope who looked up and saw, hey, that's not one star, that's two. Oh, it must be a chance alignment of a star in the foreground and a star in the background, they said to themselves. Then they looked around and they said, wait a minute. Way too many stars are close to each other than statistics, than the randomness of stars in the galaxy should allow. If you just randomly throw stars up on the sky, how often are they that close to one another?

• 21:23Speaker 01

  Right.

• 21:23Neil deGrasse Tyson?

  It should be rare, yet it was common. So, the original research paper did this statistical calculation and concluded, this must be real. There must be actual double stars up there. Hey, there's a triple star. There's a quadruple star. You keep looking, whoa, we have a whole cluster of stars. A beehive of stars. In fact, there's an actual cluster called the beehive cluster. And all these stars orbiting a common center of gravity. Yes, occasionally you get an ejected star, cuz not all orbits are stable when you have all this action. But there is what we call a parameter space where, think this through, right? Two stars orbiting close to one another, it's a tight orbit.

• 22:05Speaker 01

  Right.

• 22:05Neil deGrasse Tyson?

  Now, you pull one out a little, kinda far, have that orbit, that pair. It's orbiting so far away, it thinks it's orbiting one star. So that's stable.

• 22:16Speaker 01

  Okay.

• 22:17Neil deGrasse Tyson?

  Now you get a fourth one, pull it far away. Make it so far away, it thinks it's orbiting sort of one gravity field. The, the, the questioner is right. Jesse's right. When you orbit really close, the path, what path are you gonna take?

• 22:32Speaker 01

  Right.

• 22:32Neil deGrasse Tyson?

  Who are you next to now, some indifferent tomorrow? That could be hugely turbulent, hugely unstable to the, to the, to the, to the orbits within the system. But you can configure a system where you have a whole set of stable orbits and everybody's happy. You know, another set of stable orbits, a pair of stars here and a pair of stars there, and those pairs orbit each other.

• 22:54Speaker 01

  Oh.

• 22:54Neil deGrasse Tyson?

  Right? Isn't that cute?

• 22:55Speaker 01

  Like dancers.

• 22:56Neil deGrasse Tyson?

  So that'd be a double double star.

• 22:57Speaker 01

  A double.

• 22:58Neil deGrasse Tyson?

  And they're actual stars in the night sky, visible to the naked eye, that are double double.

• 23:02Speaker 01

  I feel like I'm ordering Tim Hortons coffee. That's great.

• 23:05Neil deGrasse Tyson?

  So now I'm thinking about it, the question was, how does a planet orbit safely around four suns? That's what the question, that's what his question actually asked. I'm talking about how do you get four stable suns to begin with?

• 23:16Speaker 01

  Oh, yeah.

• 23:17Neil deGrasse Tyson?

  So now, if a planet were among the stars, it's not stable. It'll fly away. Right?

• 23:23Speaker 01

  The planet will fly away.

• 23:24Neil deGrasse Tyson?

  Yeah, if the planet's orbiting within the orbits of the stars themselves, it's gonna fly away.

• 23:29Speaker 01

  So you're saying the planet is commitment phobic?

• 23:30Neil deGrasse Tyson?

  It's, it's totally commitment phobic. It needs one sort of committed feeling.

• 23:35Speaker 01

  So it can't be big love?

• 23:36Neil deGrasse Tyson?

  It's gotta, it's gotta go in one direction. So in Star Wars, where they had the double sunset planet, the, the double sunset, those two stars are close enough to each other, and the planet is far enough away from both, so it executes one orbit around both.

• 23:50Speaker 01

  Okay, okay.

• 23:51Neil deGrasse Tyson?

  That's how you pull this off.

• 23:53Speaker 01

  But four, not gonna work.

• 23:54Neil deGrasse Tyson?

  Your four, if you can't start moving in and out, what's your allegiance? As you get pulled to one star versus another, and it wreak havoc on the planet, and you just get ejected. In fact, you know something? We think most planets in the universe were ejected in their early solar system. And they're floating free in space, and they're called planetary vagabonds.

• 24:12Speaker 01

  Oh.

• 24:12Neil deGrasse Tyson?

  And if any of those planets have internal heat sources, like geothermal heat that doesn't require a host star, maybe there's life on those planets. And it might be that life is teeming far away from stars in this galaxy.

• 24:27Speaker 01

  Wow, that's a possibility?

• 24:30Neil deGrasse Tyson?

  Yeah.

• 24:34Neil deGrasse Tyson?

  So we gotta take a break. StarTalk, the Cosmic Queries Edition. We'll see you in a moment.

• 24:56Neil deGrasse Tyson?

  This is StarTalk Radio. I'm Neil deGrasse Tyson, here with Leanne Lord, comedian Leanne.

• 25:01Speaker 01

  Hey.

• 25:02Neil deGrasse Tyson?

  Thanks for being here on StarTalk, and you're reading me questions today.

• 25:05Speaker 01

  I am.

• 25:05Neil deGrasse Tyson?

  On the universe, submitted by listeners, posted on our Facebook page, and I'm ready for them.

• 25:13Speaker 01

  Well, are you ready for Ryan Smith, who wants to know if light has no mass, why does the gravity of a black hole affect it?

• 25:20Neil deGrasse Tyson?

  Ooh.

• 25:22Speaker 01

  This is right up your alley, sir.

• 25:23Neil deGrasse Tyson?

  Ooh, bring it on. Bring it on. Yeah, light has no mass, but light has energy.

• 25:31Speaker 01

  Oh.

• 25:31Neil deGrasse Tyson?

  Oh, and you need to rethink of what mass is. Mass, this is how to, let's move forward into the future, thinking about the universe in this way.

• 25:44Speaker 01

  Okay.

• 25:45Neil deGrasse Tyson?

  Okay. Mass can reveal itself as either matter or energy.

• 25:54Speaker 01

  Okay.

• 25:55Neil deGrasse Tyson?

  All right. That's a way to think about it. And so therefore, light, which has energy, has a mass equivalent to that energy. And since a mass has gravity, a gravitational field will pull a beam of light into it. Not very well, it turns out, unless you're a black hole. You gotta totally tear a new one through the fabric of space to pull a beam of light into your surface. So light beam coming by Earth bends a little bit, barely perceptibly. Light coming by the sun bends perceptibly. That got measured in 1919 when, after Einstein predicted it,

• 26:40Neil deGrasse Tyson?

  Sir Arthur Eddington, an astrophysicist, brilliant dude from England, measured the bending of starlight as it came by the sun during a total solar eclipse. You can't see the stars, you can't see the stars in broad daylight. But you want to see a beam of light coming by the sun to see if the sun tugs on it in a measurable way. Wait for a total solar eclipse. The light of the sun is blotted out. There's starlight behind it.

• 27:05Speaker 01

  Mm-hmm.

• 27:05Neil deGrasse Tyson?

  You know where the, the image of that star should be? You measure it, it's in a different place. The light bent on its way coming around the edge of the sun to get to your telescope. You measure how much it bent? Bang on. It's Einstein's general theory of relativity with gravity field bending the curvature of space and it curves the path of light. But I shouldn't say it that way. You know how I should say it? I should say-

• 27:27Speaker 01

  With a deeper voice?

• 27:30Neil deGrasse Tyson?

  I'll say it with a deeper voice. Gravity curves the fabric of space and time. And light travels on that fabric. So it's not that gravity curves light. It's that gravity curves the very nature of the spacetime continuum. And all light is doing is following that form.

• 27:53Speaker 01

  Hmm.

• 27:55Speaker 01

  Wow.

• 27:55Neil deGrasse Tyson?

  Yeah, so that's why. That's why. Light is following the path of space. In a black hole curved space, light goes in right alongside it.

• 28:02Speaker 01

  So light is along for the ride.

• 28:04Neil deGrasse Tyson?

  It's along for the ride, exactly. So it's wrong to say that, that gravity curves the path of light. Gravity curves space. Light, as far as it's concerned, is always traveling in straight lines.

• 28:14Speaker 01

  As far as it's concerned.

• 28:15Neil deGrasse Tyson?

  As far as it's concerned. But if the space happens to take it in a curved path, that's space's problem, not the light.

• 28:23Speaker 01

  Officer.

• 28:24Neil deGrasse Tyson?

  All right, yeah.

• 28:24Speaker 01

  I was in the car. I had no idea what was gonna happen.

• 28:29Neil deGrasse Tyson?

  Think about it, on NASCAR, because I know you're a big NASCAR fan.

• 28:32Speaker 01

  Huge. Huge. As I get in my hoopy speeding down the Belt Parkway. Huge.

• 28:39Neil deGrasse Tyson?

  So in NASCAR, there's a joke about NASCAR drivers, you know, can they, in real life, are they always just turning left? Do they ever know how to turn right? Well, that's actually not an accurate joke. That's like a scientifically flawed joke, right? The track is banked in a NASCAR track. Right? Of course it is. Right? It's banked. You know why it's banked?

• 29:02Speaker 01

  Hmm.

• 29:03Neil deGrasse Tyson?

  I'll tell you why it's banked. If you are driving at the right speed for that bank, you do not have to turn the steering wheel and the track will turn you. So as far as the car is concerned, it's going in a straight line.

• 29:17Speaker 01

  Yes. Wow.

• 29:20Neil deGrasse Tyson?

  They don't ever have to turn the steering wheel to bank those turns.

• 29:24Speaker 01

  But they've got to be going at the right speed.

• 29:26Neil deGrasse Tyson?

  At the right speed, exactly. And so it's banked for a particular speed and depending on the slope of the track. So when they're steering, they're steering just to maneuver in front and behind each other on the track.

• 29:38Speaker 01

  Right.

• 29:38Neil deGrasse Tyson?

  Yeah. Oh, yeah. So that's a car driving in a straight line with the spacetime continuum of the NASCAR track curving its path into a U-turn.

• 29:48Speaker 01

  Oh, man.

• 29:49Neil deGrasse Tyson?

  Oh, yeah.

• 29:49Speaker 01

  That is so cool.

• 29:50Neil deGrasse Tyson?

  Yeah, it feels good. Good for you. It's good. Okay. So, wow, did we finish that segment already? My gosh, you have more questions for me when we come back?

• 30:01Speaker 01

  I do, I do have more questions.

• 30:02Neil deGrasse Tyson?

  All right, yeah, you're listening to StarTalk Radio and, like I said, find us on the web at startalkradio.net. And Leanne, you tweet.

• 30:10Speaker 01

  I do.

• 30:11Neil deGrasse Tyson?

  Leanne Lord, L-E-I-G-H-A-N-N.

• 30:14Speaker 01

  Yes.

• 30:15Neil deGrasse Tyson?

  Messing with people. So more when we come back. StarTalk, after hours, the cosmic queries.

• 30:38Neil deGrasse Tyson?

  You're back. We're back on StarTalk Radio. I'm your host, Neil deGrasse Tyson. I'm an astrophysicist, and this is StarTalk, the Cosmic Queries Hour. And I'm with Leanne Lord, who is delivering me questions culled from the internet, from listeners, from you, the listeners of this show. And in this particular satchel of questions, these are all just general questions about the universe.

• 31:02Speaker 01

  General astrophysics questions?

• 31:04Neil deGrasse Tyson?

  I'm happy to serve, if you're happy to deliver.

• 31:06Speaker 01

  I am.

• 31:07Neil deGrasse Tyson?

  All right, go for it.

• 31:08Speaker 01

  I have a question from Angie Suave. I love that name.

• 31:12Neil deGrasse Tyson?

  She's Rico Suave's sister.

• 31:13Speaker 01

  Sister, absolutely. And she wants to know...

• 31:16Neil deGrasse Tyson?

  Why do you say it? Rico Suave.

• 31:18Speaker 01

  Suave. How sad is it that we know that?

• 31:21Neil deGrasse Tyson?

  I know. That is so sad. We gotta get a life.

• 31:23Speaker 01

  We're lame. We lost our street cred.

• 31:25Neil deGrasse Tyson?

  Mm-hmm.

• 31:26Speaker 01

  All right. "Could we send a probe of some kind into a black hole? I realize it would be destroyed, but couldn't it transmit some relevant data, at least for a short time, on its approach? And have we already done this?"

• 31:37Neil deGrasse Tyson?

  We have not already... Excellent question. We haven't already done that. We're not close enough to a black hole to even think about that experiment.

• 31:45Speaker 01

  Really?

• 31:45Neil deGrasse Tyson?

  Now, the dangerous part is, suppose a black hole comes our way. Like, first, how would you know it was coming, if it's black? Space is black. Well, I'm saying. So what you have to do is, you look for the distortion of space around it, right? So you have a star field. If all of a sudden, the star field starts looking like a funhouse mirror?

• 32:04Speaker 01

  Mm-hmm.

• 32:05Neil deGrasse Tyson?

  Run.

• 32:06Speaker 01

  Run. Just pack up the planet.

• 32:08Neil deGrasse Tyson?

  Pack up the planet, and get the hell out of that solar system, because a black hole is on its way. Most... Just as a quick aside, most of the black holes we know, we detect from... Because they're in a binary star system. There's another star adjacent to them, being flayed.

• 32:25Neil deGrasse Tyson?

  Love that word.

• 32:26Speaker 01

  I do.

• 32:26Neil deGrasse Tyson?

  A rare word. It means getting skinned alive, by the way.

• 32:29Speaker 01

  Yes, yes, very Middle Ages.

• 32:30Neil deGrasse Tyson?

  And you're a word person, because you tweet word of the week. It's very Middle Ages, right? It's very like Spanish Inquisition. So a black hole can flay an adjacent star. If it becomes a red giant and its outer shells expand too much, that it'll then remove those outer layers and those layers will descend into the black hole. Our X-ray telescopes detect material descending into a black hole that gets heated on its way down because of the friction of the disk that it makes. It basically gets flushed toilet bowl style.

• 33:01Speaker 01

  Right.

• 33:02Neil deGrasse Tyson?

  And as it descends down, it releases energy that it has from falling. And that energy is very high. It's like X-rays. X-ray telescopes detect black holes in the galaxy. There's none that we know of that are nearby.

• 33:16Speaker 01

  Lucky for us.

• 33:16Neil deGrasse Tyson?

  Lucky for us. But if we did send a probe, yeah, we could get some fascinating data on the gravitational field, the radiation field. And we get it all the way until it hit the point of no return, the event horizon.

• 33:30Speaker 01

  Ah.

• 33:31Neil deGrasse Tyson?

  I love that.

• 33:32Speaker 01

  Clearly.

• 33:33Neil deGrasse Tyson?

  It's a poetic term for the place where you're never coming back.

• 33:36Speaker 01

  Right.

• 33:36Neil deGrasse Tyson?

  Because within the event horizon, even if you could travel the speed of light, it's not fast enough to escape the gravitational field of the black hole. So there you have it.

• 33:46Speaker 01

  Is there something, I mean, are there plans to do this? And can we really get some knowledge from this?

• 33:52Neil deGrasse Tyson?

  Oh, yeah, we could get knowledge, but I'm saying there's no plan. I mean, we don't know our own solar system, much less trying to poke around in a black hole.

• 33:59Speaker 01

  Right.

• 33:59Neil deGrasse Tyson?

  Right? It's like, stay out of that. Don't play, you know? We gotta choose our playpens and our sandboxes.

• 34:04Speaker 01

  Don't poke the bear.

• 34:05Neil deGrasse Tyson?

  Don't. Until that day comes. If we were to find a black hole, I'd try to find a way to exploit its gravitational field for the purposes of the production of energy.

• 34:15Speaker 01

  Nice.

• 34:16Neil deGrasse Tyson?

  That'd be cool. Yeah.

• 34:17Speaker 01

  Reduce my light bill.

• 34:18Neil deGrasse Tyson?

  That'd be good.

• 34:19Speaker 01

  I have a question from Gary Ralph. And I love this. Is there dark matter in my bedroom right now?

• 34:27Neil deGrasse Tyson?

  I love it.

• 34:28Speaker 01

  Dark energy? Is it inside of me right now? Dark energy is, I guess, but dark matter, I'm not sure about. Also, if the universe is expanding, does that mean that I'm expanding too? This is a Dexter question.

• 34:42Neil deGrasse Tyson?

  This is golly.

• 34:43Speaker 01

  Dark matter in me right now.

• 34:45Neil deGrasse Tyson?

  I got like two minutes left and I gotta like, I don't know that I can answer all three in two minutes, but I'll try.

• 34:50Speaker 01

  Okay.

• 34:51Neil deGrasse Tyson?

  Okay. Uh, dark matter, we don't know what it is, but we know where it, where we can find it. Uh, but I can tell you that if it's in your room, there's not much of it.

• 35:02Speaker 01

  Okay.

• 35:02Neil deGrasse Tyson?

  Dark matter does not interact with our matter. It doesn't interact even with itself. That's assuming that it's matter at all. So you don't have solid dark matter planets.

• 35:13Speaker 01

  Okay.

• 35:14Neil deGrasse Tyson?

  What does it take to make a planet? Matter has to interact with itself and make molecules and cling together and make rocks and molecule and people and places and things. Dark matter has no such properties. That's why it's diffuse across the galaxy. We have what's called a dark matter halo around our galaxy and all the dark matter is scattered into this halo. Huge quantities of matter. I don't even know if it's matter, but it has gravity and is huge, but it's so dispersed and so that you, there's not a meaningful amount of it in any localized place that you're gonna find.

• 35:49Speaker 01

  Very antisocial.

• 35:50Neil deGrasse Tyson?

  Yeah, very antisocial. And dark energy, that's everywhere you find the vacuum, you have dark energy, the vacuum of the cosmos itself.

• 35:58Speaker 01

  Hmm.

• 35:59Neil deGrasse Tyson?

  Yeah. So, and is it, when the universe expands, are we expanding with it? The molecular forces that keep your body together, those molecular forces are stronger than the force that's expanding the universe.

• 36:11Speaker 01

  Thank goodness.

• 36:11Neil deGrasse Tyson?

  So as the universe expands, you don't.

• 36:14Speaker 01

  Oh.

• 36:15Neil deGrasse Tyson?

  Neither does our galaxy.

• 36:16Speaker 01

  Until you hit middle age and then it's all downhill from there.

• 36:18Neil deGrasse Tyson?

  Or the solar system. We've gotta wrap this up. Leanne Lord, thanks for coming.

• 36:23Speaker 01

  Thank you for having me. I have so much fun here and I learn so much.

• 36:27Neil deGrasse Tyson?

  And, and I hope people will follow you because I follow you on Twitter. So I hope others will follow you too. You learn a lot and laugh a lot.

• 36:34Speaker 01

  Yeah.

• 36:34Neil deGrasse Tyson?

  You've been listening to StarTalk Radio. I'm your personal astrophysicist, Neil deGrasse Tyson, bidding you as always farewell and compelling you at all times to keep looking up.