Date: October 17, 2011
Title: The Acclerating Universe and the Nobel Prize
Podcaster: Rob Sparks and Tom Matheson
Organization: the National Optical Astronomy Observatory (NOAO)
Links: http://www.noao.edu
http://twitter.com/#!/NOAONorth
www.facebook.com/USNOAO
Description: A discussion of the concept of the accelerating expanding Universe. The discoverers of this recently won the 2011 Nobel Prize for Physics.
Bios: Rob Sparks is a science education specialist in the EPO group at NOAO and works on the Galileoscope project (www.galileoscope.org), providing design, dissemination and professional development. He also blogs at halfastro.wordpress.com.
Tom Matheson is an associate astronomer at the National Optical Astronomy Observatory. He received his PHD in astronomy from the University of California Berkeley.
Sponsor:This episode of “365 Days of Astronomy” has been sponsored by the National Optical Astronomy Observatory. NOAO is a US national research and development center for ground-based nighttime astronomy. We provide astronomers access to world-class observing facilities on a peer-reviewed basis. Our mission is to engage in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe. For information on observing proposals or our public programs, please visit www.noao.edu for more information.
Transcript:
Rob: Hi, this is Rob Sparks of the National Optical Astronomy Observatory and I would like to welcome you to this edition of the 365 Days of Astronomy podcast. I am sitting here with Tom Matheson of NOAO. Good afternoon, Tom.
Tom: Hi, Rob.
Rob: So first could you tell me a little bit about your background.
Tom: I got my PHD at Berkeley working with Alex Fillipinko on various explosive things, mainly supernova and I went and did a post Doc at the Center for Astrophysics at Harvard with Bob Kirshner, also doing explosive things. Then I came out here to NOAO with a job as a staff astronomer.
Rob: What all do you do here at NOAO?
Tom: My time at NOAO is split. I have half my time to do research and the other half is service to the organization. The service time is trying to help people use the Gemini observatory and to help and trying to help sort out things for the LSST project that we are hoping comes along pretty soon. For research I am still working on things that explode and go bump in the night. It is fun to have things that change and keep you on your toes when you are trying to work on them.
Rob: Today we are here to talk about the recent Nobel Prize that was awarded in Physics for the discovery of the accelerating universe and you were involved in that project with both teams I understand. Could you tell me how you got involved with that and what you did for the project?
Tom: When I was in grad school in Berkeley I was in the right place at the right time because both teams were finding supernova using the telescopes down at Cerro Tololo. They would use those to find the supernova. But if you wanted to make sure they were the right kind of supernova and to get the redshift which you needed to have to do this test on it to see how the universe was expanding, they needed to have a spectrum. And since we were at the University of California we had access to the Keck telescope which was the best way to do it because we were looking at faint things and when you are looking at faint things you need the biggest telescope you can get. That meant that we were really in the best position to do this in the best way. There were other big telescopes that could do this too, but the Keck was the one you really wanted to do this. We ended up helping both teams. They would find supernova, we would get the spectra and provide them with the information, what kind of supernova it was, the redshift and then they would use this for the projects that came out of that. There were other facilities that were used at the same time so its this odd quirk that I am actually a co-author on the Supernova Cosmology project paper, this was Saul Perlmutter’s group, but I am not on the Reiss et al paper because the Reiss et al paper did not have any supernova where we took the spectrum of it. So it’s just the odd quirk about how things work out because after tha I worked almost exclusively with the High-Z team and everything subsequent to that was working with the Brian Schmidt team instead of the Saul Perlmutter team. It’s just the random way that things work out some times.
Rob: But you had your hand in both cookie jars so to speak.
Tom: Yeah, that’s true. But my advisor, Alex Fillipinko, he had both arms in both cookie jars. I just had a finger in!
Rob: As you mentioned, the telescope down at Cerro Tololo did the discovery of the supernova and that is run by NOAO South.
Tom: That is right. And it turns out that this was a critical element of success for both teams and that’s because the telescope at Ceroo Tololo offered a wide field of view because you wanted to look at a large area of the sky to encompass as many distant galaxies as you could because supernova are rare but if you look at enough galaxies you are likely to find one. So you needed that wide field capability and that doesn’t exist at a lot of telescopes. And they also had CCD cameras that were large format that could take advantage of this.
So it was exactly the right telescope for them to be able to do this searching and finding and so both teams recognized this and used it to do that. And then other NOAO facilities were also used, not for finding the searching but for some of the follow up observations.
Namely the Kitt Peak 4 meter was used early on, not as much as the four meter down at Tololo, and then the WIYN 3.5 meter was used extensively because at that point it was actually a cue scheduled telescope and the ability to get an image whenever you wanted it without it having to be your particular night to be observing was a valuable thing for both teams.
Rob: So why don’t you tell us what the teams actually found for our listeners not as familiar with this topic.
Tom: Well, the original goal of this project was to find out why the universe was slowing down because everyone expected that was going to be the result.
Rob: Yeah, gravity slows things down, right?
Tom: Exactly. That was what everyone expected. The idea was that you could use supernova to map out the universe. And the reason that you could do that is supernova are extraordinarily bright so you can see them all they way across the universe and you can’t do this with most other astronomical objects because they are just not bright enough.
Rob: But there was a specific type of supernova you were looking for.
Tom: That’s right. One particular type of supernova called a type 1a. There’s a usual problem in astronomical nomenclature that name makes no sense. But that’s what we’re stuck with because someone in the 1940s said “We’re going to call that type 1 and this one type 2”.
Rob: For historical reasons before they quite knew what they were looking at.
Tom: Precisely. This looks like that, and this looks different so we will call it something different. Anyway, it turns out these type 1a supernova we think are a thermonuclear disruption of a white dwarf. And it turns out a white dwarf can only be of a certain size before that happens, it will destroy them in this thermonuclear explosion.
Since that size is a constant, that means whenever one of these things goes off, it’s about the same amount of matter that is burned in this thermonuclear fusion. If it’s about the same amount of matter, it’s about the same amount of energy, therefore it’s about the same brightness and that’s they key to using them. We can say if it appears this bright, that’s how far away it is. People do this all the time without thinking about it. If you are out driving on a highway and you see a headlight in the distance, you know that a faint headlight is further away than a bright headlight just because they are further away. It’ something we all understand, but there is a mathematically correct way to do this so you can say exactly how far away it is as long as you know how bright it is and that’s the key thing, you have to be able to tell how bright it is. With the 1as, they are all about the same and it turned out the differences among the 1as, and there are differences, can be taken out by looking at how the light curve changes which is basically how the explosion brightens and then fades away. You can use that information to tell exactly how bright it is. In fact, a lot of that work was done using data that was taken down at Cerro Tololo as well. In fact, it was mainly CTIO scientists who did that groundbreaking work to do the calibration that enabled both teams to do this work in the end. So that’s really important. So it’s not just that CTIO was used to find them, it’s that you couldn’t have done the project without the stuff they had done beforehand. So it was really important to the whole thing.
Rob: So you got all these supernova, you know how far away they are, you got their spectra. How do you put it all together?
Tom: If you believe the universe is expanding without anything changes, it follows what is called the Hubble Law which basically means the further away things are, the faster they are moving. They are further away because they were moving faster. It essentially means that it follows a linear relationship. If you plotted velocity versus distance, it’s a straight line. That’s sort of what you expected to have happen in this case. But it turns out if you look at these supernova at high redshift, they didn’t quite fall on that line. They were fainter than they should have been. They were further away and if they were further away that means the velocity had to be increasing to put in that extra distance between us and that distant supernova. It was that subtle change away from what we might call a regular expansion of the universe that showed that the velocity was changing and that it was increasing. So that’s why there is this acceleration of the universe and that’s what both teams found. When you look at these supernova, they weren’t as bright as you expect them to be and this little difference means that the universe is accelerating apart right now.
Rob: It’s a good thing both teams found it, right?
Tom: Yeah, if one team had thought the other way then it might not have been as accepted. It has since been confirmed by other astronomical techniques that this acceleration has to be happening.
Sure those first couple of years people might have been a little dubious but now it’s generally accepted that there is something going on. We don’t understand it, but there is something going on.
Rob: And that’s a big area of research right now, finding out what this stuff is.
Tom: Yeah, and there is a lot more work being done trying to determine exactly how this stuff deviates from a general expansion, how that changes with time, because that might tell you if this is a constant thing in the history of the universe, if it is something that changes with time in the history of the universe. These are all things we would like to know but we don’t know the answers to those yet.
There is a lot of work being done trying to sort that out, some of it still using supernova, and to do that you need to go to even more distant objects and it turns out that is very hard to do from the ground. A lot of what is done with the most distant supernova is done using HST (Hubble Space Telescope) because once you are above Earth’s atmosphere you get a sharper picture, you can work at wavelengths that don’t come through Earth’s atmosphere and so you can look at much much more distant supernova.
Rob: That’s a nice segue to my next question. We have Hubble, but that’s only going to be around for a few more years, so what’s the next step in this reearch?
Tom: Well, I think we will continue to use Hubble as long as we can. It’s still a really valuable tool for this and still providing answers in areas where we don’t have a lot of information. The next step will be the James Webb Space Telescope and it will operate at infrared wavelengths and as you go to things that are more distant that redshifts the light so it moves the optical light into the infrared so it makes a lot more sense to move to the infrared for these high redshift objects. The James Webb Space Telescope will be a tremendous tool to actually do this at the very beginnings of the universe to try and see if we could see things back that far. Now that’s going to be hard to do, but you can certainly go farther than we have gone so far. I really think that would be really valuable to have that as a tool to do this kind of study.
Rob: Thanks, Tom. I wish you much luck in your future studies and to get to the bottom of this whole dark energy puzzle.
Tom: That would be great. We would love to know what it is. Thanks
Rob: Thanks for joining me. This is Rob Sparks for the 365 Days of Astronomy podcast.
End of podcast:
365 Days of Astronomy
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