Confirming The Existence Of A Black Hole
November 28, 2011 1:08 p.m.
Dr. Jerry Orosz, Associate Professor of Astronomy, San Diego State University
Take a tour of Cygnus X-1
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CAVANAUGH: This is KPBS Midday Edition. I'm Maureen Cavanaugh. Cygnus X1 is described by some astronomers as iconic black hole. In theory, it displays the quintessential of characteristics of what a black hole is supposed to be. The only problem was until recently, some scientists were not convinced that Cygnus X1 really contain aid black hole. Due in part to the work of SDSU's Astron no department, the evidence seems overwhelming. Joining me to talk about this research and what black holes mean to our understanding of the universe is my guest, doctor Jerome Orosz, associate professor of astronomy state university. And thank you so much for being here.
OROSZ: Thank you for having me.
CAVANAUGH: What is Cygnus X1 where this black hole is located?
OROSZ: Well, Cygnus X1 was the name given to a very powerful X-ray source discovered in rocket flights in 1964. And eventually, it was determined that this was a binary system containing a star that we can see and a dark companion that we can't see.
CAVANAUGH: Ah, the dark companion --
OROSZ: Being the black hole
CAVANAUGH: And how far from earth is this?
OROSZ: It's about 6,000 height years
CAVANAUGH: And it's in the Cygnus constellation?
CAVANAUGH: What role did SDSU play in developing this new evidence for a black hole in Cygnus X1?
OROSZ: Well, the recent break through came in a series of three papers. And the first breakthrough was getting an accurate distance. Once we have the accurate distance, I took all available observations, you know, the optical data, how the star's brightness change, how its velocity changes, and using the scans, we were able to trial get a very good mass estimate. Previously, there was lots of uncertainties in the mas of the black hole. And with the distance, we were able to actually calculate the size of the star that we see, and that information in turn allows us to get a very accurate mas for the black hole
CAVANAUGH: And these calculations together therefore confirm that there is a black hole in this location?
OROSZ: Well, basically it removes any doubts. I think most people had assumed that there wassed in a black hole. But the mass was -- it had a huge range in possible values
CAVANAUGH: I see.
OROSZ: So now it's really penned down
CAVANAUGH: Now you study data from NASA's Chandra X-ray observatory to get details about the mass and the other calculations. And also about the birth of this black hole. What does an X-ray observatory mean? I think we all know what a regular observatory is. What's an x-ray observatory?
OROSZ: Well, basically it's the analogue of a telescope that's sensitive to X-ray light instead of visible light. Since X-rays don't pen straight the atmosphere, the X-ray telescopes have to be in orbit. Chandra observatory is one of NASA's great observetories. It's basically the analog of Hubble, except it's sensitive to X-rays
CAVANAUGH: I see. When you get these X-rays, what does an X-ray from this observatory look like?
OROSZ: Well, backing up, the black holes in a binary system with the star that we see, and the stars are so close together that the normal star is losing mas. And some of that mass is falling towards a black hole. Since the black hole has such strong gravity as the mass borrows in, it gets very, very hot and emits X-rays. So in fact, we're seeing the gas, basically right before it disappears into the black hole
CAVANAUGH: So the black hole is basically sucking the energy from its companion stars?
OROSZ: Yeah, it's attracting mass from the companion, and it gets so hot that it's a very strong X-ray source
CAVANAUGH: I see. Now, papers published this month, including yours, revealed how this black hole was born. How did that happen?
OROSZ: Well, so the third paper in the sequence was led by Liu Cheng of the Harvard center for astrophysics. He is looking at the X-ray data. By looking at the X-ray spectrum and some calculations, we basically could measure the size of the so called accretion dist of the black hole. When we put all the numbers together, we find it's spinning something like 800 turns per second, which is close to its maximum value as allowed by Einstein's theory.
CAVANAUGH: And so how was it created? How does that tell you how it was created?
OROSZ: Well, the companion star that we see probably isn't any older than about 6 million years. So a quick calculation shows that if the black hole were born with a low spin, it would not have time to spin up through the matter it accretes. So it basically has to have been born at that high spin.
CAVANAUGH: It's my understanding, and I have very little of it when it comes to black holes, that black holes can be formed by either sort of an implosion or explosion. Which one would this be?
OROSZ: Well, the binary system, since we got a good distance, we can calculate what we call its peculiar velocity. And that velocity is very small, which indicates that whatever formed the black hole did not give the binary system a very large kick velocity. And so it's possible that this black hole formed via just a direct collapse, and really made very little noise, so to speak. Very little, if any, super nova explosion
CAVANAUGH: Exactly. No explosion but a collapse.
OROSZ: Just a direct collapse.
CAVANAUGH: Tell us again what a black hole is.
>> Well, a black hole is an object whose gravity is so powerful that basically escape velocity exceeds the speed of light. And since nothing can go faster than the speed of light, once you cross into the black hole, you can't go fast enough to get back out. So it's like a one way ticket
CAVANAUGH: To where?
OROSZ: To the singularity, to the center. All the mass, according to theory should be concentrated at a single point, which is called the singularity. And then surrounding the singularity is this imaginary surface called the event horizon. Basically the event horizon is sort of the gateway, if you're you're past the event horizon, you can't get back out
CAVANAUGH: There have been a number of Hollywood movies based on concepts like this events horizon and singularity. How do you watch those movies? Do they have any relevance at all to what is the actual size in
OROSZ: I love science fiction even though it's most often wrong. A movie from about 1980 or so called the black hole, that had a pretty realistic view of what a black hole -- you don't trial see the hole itself, but you see material as it falls in. So you get this accretion dist, it's basically like a spiral as the water runs out in your bathtub
CAVANAUGH: I would imagine you would see something like that and the scientific errors in it would drive you crazy
OROSZ: From a purely theoretically point of view, a block hole is very simple. Only three numbers you need to describe a black hole, the mass, the spin rate, and the charge. If you think about it, anything else in real life is really complex. For example, can you describe your dog in three words?
CAVANAUGH: No. Maybe, maybe. But it wouldn't really describe him very well.
>> What breed is it, what gender, how old. But a black hole is very, very simple. So if you made a black hole, one the solar mass of peanut butter, and one the solar mas of jelly, you couldn't tell the difference. Once it's inside the black hole, there's no way to know what it was
CAVANAUGH: I'm speak requesting doctor Jerome ors
RIH2: Associate professor of astronomy at SDSU. We're talking about a paper that he published with -- a total of three papers that are basically showing the existence of a black hole and confirming the data that they have been receiving from NASA's Chandra X-ray observatory. Bill is calling from Chula Vista. And hi bill, welcome to the conversation.
NEW SPEAKER: Hi. Thank you very much. My question was when the professor is talking about the fact that the black hole was born at such a high rate of spin, is it possible that instead of being an actual binary system, it's just a closely occurring individual star system, meaning that the star that's formed the black hole could bed in 2 or 3 billion years old and have died and then from that either a new star formed or attracted the star that we see this closely in conjunction with the black hole?
OROSZ: That's a very good question, bill. Basically we can see the optical star, we can see its orbital motion. So it's basically coming and going. So it's no doubt that there's a binary system. Now, because of the huge mass of the galaxy, it's very, very unlikely that two stars would actually come together and form a binary system after they're formed. So the most likely explanation was that we had a binary system of two massive stars that formed close together. The more massive star evolved first, and eventually made the black hole that we see today. So capture is very, very unlikely.
CAVANAUGH: Bill, thank you very much for that very informed question. Where do black holes fit into our understanding of the universe? How important are they to our understanding of the universe?
OROSZ: Well, black holes represent sort of the ultimate extreme state of gravity. And so Einstein in the early 19 hundreds came up with his theory of general relativity, which is -- sort of pushed aside Newton's theory of gravity. And Einstein's theory has been tested in it motions of solar system bodies, and the remaining place to test his theory is in strong field limit. Near very dense objects like neutron stars and black holes. And black holes also represent the end state of the most massive stars as the star goes through its evolution. Of eventually, the core cannot support itself, and it has to collapse. And there's no known force to support the core after they finish the evolution. So they become black holes
CAVANAUGH: Cygnus X one was the place of a famous bet by Steven hawking. He said that there was no black hole in this area. Is it certain -- is science certain now that there is because of this research data?
OROSZ: Well, in some sense, there is -- I think there is beyond a reasonable doubt. So we measure the system that we see with a dark companion, and that dark cam ponnion is about 15 times the mass of the sun. We don't know any other object it could be. White dwarfs are too unstable, and neutron stars. So what's raft is a black hole. We don't know what else it could be.
CAVANAUGH: How much of a problem is it for a physicist for the stature of Steven hawking to be wrong abouting this something like this?
OROSZ: Oh, I don't think he's at all upset from it. What I understand it, the reason he bet that way, is either way, he would be happy. If he lost the bet, black holes would exist, and that's his field. And if he won the bet, he'd win the wet. And he'd be happy that way too.
CAVANAUGH: I have read that this Cygnus X1 has been described as an iconic black hole. Why? Why do they put those two terms together?
OROSZ: Well, it was the first really good source that you could plausibly point to that -- and say this contain ace black hole. It was discovered in 1964 as a strong X-ray source, and it took decades for the observations -- the technology to catch up. So if you look at any Astron no test book, Cygnus X one is mentioned as the possible case of a black hole we can observe
CAVANAUGH: And you said from the data we have, it behaves classically along the principles of what a black hole should do.
OROSZ: As far as we can tell, it does, yes.
CAVANAUGH: I think people often hear about scientist headlines about black holes, and it's interesting but it doesn't seem to have much to do with answering problems we have here on earth. I wonder what do you say to people who ask you for the relevance of discoveries like this?
OROSZ: I think we all have some basic urge to understand what's going on. And so we look because we're curious about what's out there. And in the process of carrying out scientific investigation, there's also progress, and technology, and spin-off technologies and things like that. The mathematically techniques we develop, computer programs, the software, that has a wide application outside of just the narrow purpose that it was developed for.
CAVANAUGH: And when you're doing pure science like this, you don't often know what's going to be developed from it. It's just the quest to know more about how things work, right?
OROSZ: That's usually the case. And so we, for example, we got a very good distance of the source, and we penned down the mass, and we were able to calculate the spin, and discover it's really spinning rapidly. That raises the question, how did it get that spin? Was it born that way? So each question that's answered raises two more.
CAVANAUGH: My last question to you, how important is it to you and SDSU's program to be involved in a project like this?
OROSZ: Well, it's very exciting for me I've had my eye in this source for the last 10 to 15†years. Unlike other system, this one had still -- even though it was a textbook example, it still had huge uncertainties, and its possible masses and other properties. I've had my eye on it since I left graduate school, and only within the last five years has the technology developed such that we can actually get the distance.
CAVANAUGH: Well, I want to thank you so much for coming in and explaining this to us. I've been speaking with doctor Jerome Orosz, associate professor of astronomy at SDSU. Thanks again.
OROSZ: Thank you for having me.