Date: July 26, 2009
Title: Gravity Wave Astronomy
Podcaster: Ivan Semeniuk
Organization: Dunlap Institute for Astronomy and Astrophysics, University of Toronto http://www.di.utoronto.ca/journalist/
Description: Gravity waves promise an entirely new way to perceive the universe, more like hearing rather than seeing. So far no gravity waves have been detected, but this year the world’s biggest gravity wave experiment, LIGO, is moving into an enhanced phase with improved sensitivity. By 2013 it will become Advanced LIGO, which will be 10 times more sensitive.
All of this means the first detection of gravity waves could be just around the corner. To “hear” what gravity waves might sound like and to find out more about the implications, host Ivan Semeniuk speaks with gravity wave astrophysicist Neil Cornish.
Bio: Ivan Semeniuk is science-journalist-in-residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto where he blogs and podcasts about astronomy and related topics.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Moreton Bay Regional Real Estate, Queensland, Australia, on the web at www.mbrrealestate.com.au, and is dedicated to Jonathan Bowden.
Transcript:
[IVAN]
Hi, I’m Ivan Semeniuk, host of the Universe in Mind podcast…
Since it’s very beginnings astronomy has been the ultimate seeing science… In a way the Universe is a kind of silent movie that we can watch with better and better telescopes.
But now some scientists are hoping to add a soundtrack to that movie using gravity waves. These are perturbations in the fabric of spacetime. If they’re detected they would give us a completely new way to perceive the Universe. More like hearing rather than seeing.
So far that hasn’t happened yet… but this year the world’s biggest gravity wave experiment, known as LIGO is moving into a more enhanced phase, with improved sensitivity. And by 2013 it will become Advanced LIGO, which will be 10 times more sensitive.
So the first gravity wave detection could be getting closer… and to find out what that could means I’m joined by Neil Cornish, he’s an associate professor of astrophysics at Montana State University in Bozeman and he specializes in gravitational wave astronomy.
Neil Cornish welcome.
[CORNISH]
Thank you.
[IVAN]
I’d like to start with this idea that detecting gravity waves would be like adding a soundtrack to our movie of the universe… what does that really mean?
[CORNISH]
It’s an analogy that’s surprisingly close, of course there’s no sound in space… there’s no air molecules… but these gravity waves, the idea is that when you have violent events in the Universe, larger concentrations of mass moving around… that actually stirs up waves in the fabric of spacetime itself. So these are fluctuations in the curvature of spacetime, and so you’ll have, say, two black holes crashing together and they’ll throw off ripples into the fabric of spacetime which then move out like ripples in a pond and the vibrations are in space itself.
We can take those, and then convert them to sounds and listen to the sounds of black holes colliding.
[IVAN]
Well, I’d love to hear an example of one of these sound analogs. I know no gravity waves have been detected yet, but what might they sound like?
[CORNISH]
Right, so we’re able to use Einstein’s equations to understand what sounds should sound like. Basically, you’ve got a system with two black holes, they’re orbiting around one another. In doing so they’re emitting these gravitational waves, but the gravitational waves carry energy. They also carry away the spin or angular momentum of they system. So as they emit the waves they spiral in toward each other. Their orbits become tighter and tighter so they start moving faster and faster and they also get into a regime where they’re moving faster and it’s a much stronger gravitational field so the gravitational waves coming out get louder… So basically … the characteristic sound is increasing in pitch, so going up in frequency and also increasing in amplitude or loudness
[IVAN]
OK… we’ve got that sound cued up, so let’s listen to it right now.
///— sound—///
[IVAN]
So that’s the sound of two black holes converging… if we converted their gravitational waves into sound waves that the human ear can perceive?
[CORNISH]
That’s right their really speaking to us. They are actually telling us a very complex story. The human ear isn’t able to discern all of the features that were in those waves that we just heard played. In fact, by measuring a system like that with, say, one of these future space detectors we’re actually able to measure the masses of the black holes to incredible precision—much less than 1% precision—so it’s actually a very high precision form of measurement that can be done using these sounds.
[IVAN]
Now light waves have a spectrum that human eyes can perceive from red to violet and even more wavelengths that we can’t see… is there an equivalent spectrum for gravity waves?
[CORNISH]
Yes, there’s a spectrum of gravitational waves. In terms of where we expect to find signals it spans everything from the Hubble frequency, which is one over the age of the universe, down at 10-16 Hertz, some ridiculously tiny frequency… all the way up to the MegaHertz range which might be possible signatures from the processes when the early expansion of the universe slowed down. The end of the inflationary period has been predicted to produce, in some scenarios, quite high frequency gravitational waves… and in between you’ve got a whole spectrum of astrophysics sources such as black holes of various sizes colliding, supernova explosions… more esoteric possibilities like whip-crack sounds from cosmic strings, thin filaments of energy that some theories of the early universe predict might be out there.
So there’s a whole potential orchestra out there that we’re waiting to hear.
[IVAN]
Well and speaking of waiting—the LIGO detectors have been running for a while now, is it that they’re no yet sensitive enough to pick up the waves that should be passing through…
[CORNISH]
That’s right. Even when they were first designed, it wasn’t expected that they would be guaranteed to make a detection. There were predictions of what kind of strength of signals we might expect to find and the first generation detectors were just a little bit below the level where we could be confident that we would definitely make a detection, so I think the hope was we’d get lucky, that there would be a rare even that’d happen or there’d be something that we hadn’t thought of that would be louder than anything that we’d predicted… we’re still looking for that… But the plan was to use the first generation as a stepping stone to understand the technology and use it as a way to get towards these advanced detectors and they’ve been very successful in that, they’ve reached already absolutely phenomenal sensitivities, they can track the distance between these mirrors, which are separated by four kilometers in a vacuum tube… they track the distance between those mirrors to an accuracy of a thousandths the width of a proton. So it’s a phenomenally sensitive measuring device and it’s going to get better still so…
[IVAN]
So now we’re moving into enhanced LIGO… How much better will it be?
[CORNISH]
So in terms of the distance tracking of these mirrors, it will be an improvement of somewhere in the factor of two or three in accuracy, which actually translates into the volume of the Universe that allows you to explore. It goes as the cube of that factor so its somewhere between eight and almost 30 perhaps increase in the volume of the Universe that you’re able to explore with the enhanced range of detectors, so you’re just seeing more galaxies, more stars… so your chances of seeing something just go up by that factor, so it’s 30 times or 10 times more likely to see something on any given day than the previous generation.
[IVAN]
And to get a sense of how much Universe we’re talking about, what is the range of the detectors and so how much larger will it be?
[CORNISH]
So the range for detecting something like two neutron stars merging is about 15 Megaparsecs, which is those crazy units we like to use. You’ve gotta multiply that by 3 to light years so its of order 50 million light years… which, in astronomical terms, that’s still nearby… that’s known as the local group of galaxies is basically what that’s probing. And so the next range detectors… for the advanced detectors, which are a factor of 10 or so better than the initial detectors… that’ll take you out into the 100’s of Megaparsecs region, and for black hole systems even further yet out into Gigaparsecs and once you start talking Gigaparsecs you’re really talking cosmology type scales. That’s really getting back to when the Universe was significantly younger than it is today.
[IVAN]
So instead of looking at a handful of galaxies you’re looking at thousands and thousands of galaxies and whatever’s going on in those galaxies you’ll be able to pick them up…
[CORNISH]
Right
[IVAN]
So Neil, now that technology is moving forward, how long do you think before the first gravity waves are detected?
[CORNISH]
I am very confident that we’ll have the first detection before 2015 and I would even be as bold as to say that enhanced LIGO might have something by 2011.
[IVAN]
Well… bold is a great note on which to end our conversation. Thanks for that prediction. I hope you’re right, Neil Cornish, in which case we’ll I’m sure we’ll be speaking again. Thanks so much.
[CORNISH]
Thank you.
[IVAN]
Dr. Neil Cornish is at Montana State University. He joins us today at the University of Toronto, at the Dunlap Institute for Astronomy and Astrophysics, which sponsors the Universe in Mind podcast.
If you like to hear more of The Universe in Mind show you can find us on iTunes or visit www.di.utoronto.ca/journalist
I’m Ivan Semeniuk, thanks for listening.
End of podcast:
365 Days of Astronomy
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