Date: February 22, 2010
Title: Jonathan McDowell Visits Thayer Academy
Podcaster: Jamie Formato
Organization: Thayer Academy, Braintree, Massachusetts. Harvard-Smithsonian Center for Astrophysics, & Cahall Observatory: cahallobservatory.wordpress.com
Description: Chandra X-ray Center Astrophysicist Jonathan McDowell is interviewed by a high school senior from Thayer Academy in Braintree, Massachusetts. Jonathan describes what the Chandra X-ray Observatory is, how it works, and what his job as a working scientist in the field is like. Prompted to discuss his work on supermassive black holes, Jonathan describes the physics of black holes, challenging the audience to imagine how the extreme gravity fields in a black hole cause space and time to commingle, and what it would be like on the inside of such a place.
Bio: I am the director of the Cahall Observatory at Thayer Academy. I teach physics and astronomy at the school.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Craig Clark.
This episode of “365 Days of Astronomy” has also been sponsored by Tom Foster.
Transcript:
Jamie Formato: Thank you for listening, my name is Jamie Formato and I am a physics and astronomy teacher at Thayer Academy in Braintree, Massachusetts. On January 21st, 2010, we hosted a visit from Chandra x-ray center astrophysicist Jonathan McDowell. He gave a lecture to fifty of our twelfth-grade astronomy students, in which he took them on a tour of the Universe and was then interviewed by one of our twelfth graders, Jake Bock. The following podcast is an excerpt from the interview portion of Jonathan’s visit, and you can see the entire video of his slideshow and of the interview on our observatory website, which is cahallobservatory.wordpress.com. Thanks very much for listening!
Jake Bock: Could you explain a little bit more of what you do at the Chandra X-ray Center?
Jonathan McDowell: Sure. So the Chandra Observatory is a spacecraft that’s a bit like the Hubble. Everyone knows about the Hubble telescope, which went up in 1990. The Hubble sees ordinary light, so it looks at the ordinary stars and galaxies. Chandra sees x-rays, and with x-rays we see the weird stuff. Most things in the Universe don’t put out x-rays, but the things that do are the really interesting things- exploding stars, black holes, these clusters of galaxies. So we get to complete the picture that Hubble begins by getting to look at the most extreme physics.
So we operate the spacecraft from the Harvard-Smithsonian in Cambridge. And anyone in the world can apply to use the telescope, where every year we have a competition where people write in with their four-page essays on ‘this is the thing I want to look at and this is why I should look at it and this is why it will revolutionize astronomy’. We usually get about seven or eight hundred applications and pick a hundred, so its pretty competitive. And then we operate the spacefcraft; we tell the spacecraft “okay this week you’re looking at this one, that one and that one” and it goes and takes the pictures, we analyze the data and send it out to the astronomers who requested it. But the neat thing is because its so expensive to do this, the astronomers get it for a year. If they haven’t published within a year, the data goes public. So, the first nine years of Chandra data are already public and you can just go to cxc.harvard.edu and download it and see if you can make any discoveries yourself.
Jake: Formato, that’s for the blog right there. So, basically its not that you’re shooting x-rays as we would think of an x-ray machine- you’re kind of capturing and collecting x-rays.
McDowell: Right. Exactly. If you think of a medical x-ray, what you do is you shoot x-rays through a person at some film. We’re trying to make the picture not of the person, but of the thing shooting the x-rays. So a star is putting out the x-rays and the x-rays cross the universe, and they would normally be stopped by the Earth’s atmosphere. So, we just poke our nose a little bit above the atmosphere and catch the x-rays before they get stopped and figure out what the thing is that is making them.
Jake: Hmm. That’s interesting. So, what is your specific job at the X-ray center?
McDowell: So most of the people that work for Chandra have jobs where part of their job is to support the mission and part of their job is just to go and make some discoveries. And so the part of my job that is supporting the mission, I actually get to design the software that astronomers around the world use to take this data from space and turn it in to scientifically valid numbers. So I’ve got to figure out, given that we get the raw data from the spacecraft, what do you need in order to get a scientific paper out of that? What software do you need? What math do you need to apply to make corrections for different problems in the camera? And so on the other side of my job which actually is to study black holes in distant galaxies I get to try doing that, and every time I run into a problem I put my other hat on and tell the programmers that we need to make a program that will solve this problem. So that’s pretty much what I do.
Jake: So, I kind of interested in this actually, for the black holes. Black holes, basically, is it just kind of like a space, uh.., a place in space that’s extremely dense, right, and it kind of pulls everything into it?
McDowell: What happens in a black hole is when a star collapses… let’s go back to what a star is. A star like the sun, the sun is a star, and its really a beautiful balance between the weight of all the material in the star, which is trying to crush it… right? The star is so heavy that its trying to collapse under its own weight. But its so hot inside, you’ve basically got an H-bomb going off inside that’s trying to blow it apart. And it’s a nice balance: if the H-bomb gets a little hotter and blows it apart a little further, the weight… as the thing gets bigger the weight is more and so it crushes back… if you crush it, you squeeze it and it gets even hotter and the H-bomb pushes back harder. So it’s a nice balance until the day that you run out of fuel. And then gravity wins, and if the star is big enough, gravity wins sufficiently impressively that the star collapses until the umm… the strength of gravity is enough to close it off from the universe entirely. And what you end up with is a region of space where space has become like time. And, this is kind of a weird concept, so let me take you through that one.
So you may know that Einstein said that space and time are basically the same thing. But, there’s a slight difference, which is that in space I can go forward and I can come back. Whereas in time, I can get to tomorrow really easily, but I can’t get to yesterday. And, what’s happened in a black hole is that the space direction has been turned around into the time direction, so that the direction into the black hole is in a very strict, mathematical sense, not in a woofly analogy sense, like going to tomorrow. And the direction out is like going to yesterday, i.e., you can’t get there.
So what happens as you go towards the black hole is that you see the directions around you start shrinking. It’s a bit like tunnel-vision, but its not an optical illusion- that as you get close to the horizon of the black hole, the directions to your left and to your right and behind you kind of start shrinking and the directions ahead of you take up more and more of your surroundings. And as you go through the horizon the direction ‘out’ disappears and every direction you turn is still ‘in’. So its not that you can’t run fast enough to get out, its that there is no out direction anymore. And the weird thing: Einstein’s theory of gravity tells us that gravity is intrinsically tied up with geometry; that in the regions of strong gravity that the angles in a triangle don’t add up to 180 anymore- all of your high school geometry is just out the window and ….. (microphone slips). And so you get these really bizarre counter-intuitive experiences. So that’s the story of the black hole.
Jake: That is one confusing explanation. But I got it. I mean, that is serious stuff.
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.