Garik Israelian: What's inside a star?

47,516 views ・ 2009-10-01

TED


Please double-click on the English subtitles below to play the video.

00:18
I have a very difficult task.
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I'm a spectroscopist.
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I have to talk about astronomy without showing you
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any single image of nebulae or galaxies, etc.
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because my job is spectroscopy.
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I never deal with images.
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But I'll try to convince you
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that spectroscopy is actually something which can
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change this world.
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Spectroscopy can probably answer the question,
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"Is there anybody out there?"
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Are we alone? SETI.
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It's not very fun to do spectroscopy.
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One of my colleagues in Bulgaria,
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Nevena Markova, spent about 20 years
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studying these profiles.
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And she published 42 articles
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just dedicated to the subject.
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Can you imagine? Day and night, thinking,
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observing, the same star for 20 years
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is incredible.
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But we are crazy. We do these things.
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(Laughter)
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And I'm not that far.
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I spent about eight months working on these profiles.
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Because I've noticed
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a very small symmetry
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in the profile of one of the planet host stars.
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And I thought, well maybe there is Lithium-6 in this star,
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which is an indication that this star
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has swallowed a planet.
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Because apparently you can't have this fragile isotope
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of Lithium-6 in the atmospheres of sun-like stars.
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But you have it in planets and asteroids.
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So if you engulf planet or large number of asteroids,
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you will have this Lithium-6 isotope
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in the spectrum of the star.
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So I invested more than eight months
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just studying the profile of this star.
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And actually it's amazing,
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because I got phone calls from many reporters asking,
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"Have you actually seen the planet going into a star?"
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Because they thought that if you are having a telescope,
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you are an astronomer so what you are doing
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is actually looking in a telescope.
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And you might have seen the planet going into a star.
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And I was saying, "No, excuse me.
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What I see is this one."
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(Laughter)
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It's just incredible. Because nobody understood really.
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I bet that there were very few people
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who really understood what I'm talking about.
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Because this is the indication that the planet went into the star.
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It's amazing.
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The power of spectroscopy
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was actually realized
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by Pink Floyd already in 1973.
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(Laughter)
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Because they actually said that
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you can get any color you like
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in a spectrum.
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And all you need is time and money
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to make your spectrograph.
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This is the number one high resolution,
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most precise spectrograph on this planet, called HARPS,
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which is actually used to detect
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extrasolar planets and sound waves
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in the atmospheres of stars.
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How we get spectra?
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I'm sure most of you know from school physics
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that it's basically splitting a white light
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into colors.
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And if you have a liquid hot mass,
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it will produce something which we call a continuous spectrum.
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A hot gas is producing emission lines only,
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no continuum.
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And if you place a cool gas in front of a
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hot source,
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you will see certain patterns
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which we call absorption lines.
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Which is used actually to identify chemical elements
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in a cool matter,
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which is absorbing exactly at those frequencies.
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Now, what we can do with the spectra?
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We can actually study line-of-sight velocities
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of cosmic objects.
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And we can also study chemical composition
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and physical parameters of stars,
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galaxies, nebulae.
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A star is the most simple object.
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In the core, we have thermonuclear reactions going on,
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creating chemical elements.
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And we have a cool atmosphere.
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It's cool for me.
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Cool in my terms is three or four or five thousand degrees.
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My colleagues in infra-red astronomy
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call minus 200 Kelvin is cool for them.
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But you know, everything is relative.
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So for me 5,000 degrees is pretty cool.
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(Laughter)
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This is the spectrum of the Sun --
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24,000 spectral lines,
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and about 15 percent of these lines is not yet identified.
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It is amazing. So we are in the 21st century,
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and we still cannot properly understand
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the spectrum of the sun.
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Sometimes we have to deal with
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just one tiny, weak spectral line
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to measure the composition of that chemical element in the atmosphere.
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For instance, you see the spectral line of the gold
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is the only spectral line in the spectrum of the Sun.
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And we use this weak feature
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to measure the composition
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of gold in the atmosphere of the Sun.
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And now this is a work in progress.
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We have been dealing with a similarly very weak feature,
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which belongs to osmium.
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It's a heavy element produced in thermonuclear
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explosions of supernovae.
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It's the only place where you can produce, actually, osmium.
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Just comparing the composition of osmium
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in one of the planet host stars,
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we want to understand why there is so much
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of this element.
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Perhaps we even think that maybe
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supernova explosions trigger formations of planets and stars.
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It can be an indication.
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The other day, my colleague from Berkeley,
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Gibor Basri, emailed me
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a very interesting spectrum,
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asking me, "Can you have a look at this?"
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And I couldn't sleep, next two weeks,
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when I saw the huge amount of oxygen
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and other elements in the spectrum of the stars.
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I knew that there is nothing like that observed in the galaxy.
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It was incredible. The only conclusion we could make from this
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is clear evidence that there was a supernova explosion
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in this system, which polluted the atmosphere
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of this star.
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And later a black hole was formed
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in a binary system,
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which is still there with a mass of about
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five solar masses.
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This was considered as first evidence that actually black holes
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come from supernovae explosions.
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My colleagues, comparing composition of chemical elements
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in different galactic stars,
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actually discovered alien stars in our galaxy.
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It's amazing that you can go so far
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simply studying the chemical composition of stars.
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They actually said that one of the stars you see in the spectra
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is an alien. It comes from a different galaxy.
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There is interaction of galaxies. We know this.
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And sometimes they just capture stars.
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You've heard about solar flares.
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We were very surprised to discover
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a super flare,
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a flare which is thousands of millions of times
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more powerful than those we see in the Sun.
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In one of the binary stars in our galaxy
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called FH Leo,
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we discovered the super flare.
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And later we went to study the spectral stars
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to see is there anything strange with these objects.
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And we found that everything is normal.
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These stars are normal like the Sun. Age, everything was normal.
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So this is a mystery.
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It's one of the mysteries we still have, super flares.
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And there are six or seven similar cases
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reported in the literature.
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Now to go ahead with this,
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we really need to understand chemical evolution of the universe.
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It's very complicated. I don't really want you to
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try to understand what is here.
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(Laughter)
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But it's to show you how complicated is the whole story
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of the production of chemical elements.
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You have two channels --
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the massive stars and low-mass stars --
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producing and recycling matter and chemical elements in the universe.
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And doing this for 14 billion years,
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we end up with this picture,
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which is a very important graph,
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showing relative abundances of chemical elements
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in sun-like stars
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and in the interstellar medium.
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So which means that it's really impossible
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to find an object where you find about 10 times more sulfur than silicon,
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five times more calcium than oxygen. It's just impossible.
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And if you find one, I will say that
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this is something related to SETI,
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because naturally you can't do it.
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Doppler Effect is something very important
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from fundamental physics.
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And this is related to the change of the frequency
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of a moving source.
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The Doppler Effect is used to discover extrasolar planets.
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The precision which we need
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to discover a Jupiter-like planet
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around a sun-like star
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is something like 28.4 meters per second.
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And we need nine centimeters per second
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to detect an Earth-like planet.
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This can be done with the future spectrographs.
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I, myself, I'm actually involved in the team
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which is developing a CODEX,
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high resolution, future generation spectrograph
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for the 42 meter E-ELT telescope.
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And this is going to be an instrument
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to detect Earth-like planets
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around sun-like stars.
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It is an amazing tool called astroseismology
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where we can detect sound waves
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in the atmospheres of stars.
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This is the sound of an Alpha Cen.
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We can detect sound waves
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in the atmospheres of sun-like stars.
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Those waves have frequencies
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in infrasound domain, the sound actually nobody knows, domain.
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Coming back to the most important question,
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"Is there anybody out there?"
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This is closely related
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to tectonic and volcanic activity of planets.
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Connection between life
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and radioactive nuclei
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is straightforward.
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No life without tectonic activity,
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without volcanic activity.
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And we know very well that geothermal energy
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is mostly produced by decay of uranium, thorium, and potassium.
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How to measure, if we have planets
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where the amount of those elements is small,
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so those planets are tectonically dead,
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there cannot be life.
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If there is too much uranium or potassium or thorium,
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probably, again, there would be no life.
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Because can you imagine everything boiling?
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It's too much energy on a planet.
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Now, we have been measuring abundance
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of thorium in one of the stars with extrasolar planets.
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It's exactly the same game. A very tiny feature.
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We are actually trying to measure this profile
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and to detect thorium.
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It's very tough. It's very tough.
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And you have to, first you have to convince yourself.
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Then you have to convince your colleagues.
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And then you have to convince the whole world
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that you have actually detected something like this
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in the atmosphere of an extrasolar planet
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host star somewhere in 100 parsec away from here.
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It's really difficult.
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But if you want to know about a life on extrasolar planets,
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you have to do this job.
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Because you have to know how much of radioactive element you have
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in those systems.
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The one way to discover about aliens
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is to tune your radio telescope and listen to the signals.
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If you receive something interesting,
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well that's what SETI does actually,
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what SETI has been doing for many years.
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I think the most promising way
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is to go for biomarkers.
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You can see the spectrum of the Earth, this Earthshine spectrum,
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and that is a very clear signal.
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The slope which is coming, which we call a Red Edge,
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is a detection of vegetated area.
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It's amazing that we can detect vegetation
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from a spectrum.
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Now imagine doing this test
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for other planets.
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Now very recently, very recently,
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I'm talking about last six, seven, eight months,
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water, methane, carbon dioxide
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have been detected in the spectrum
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of a planet outside the solar system.
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It's amazing. So this is the power of spectroscopy.
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You can actually go and detect
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and study a chemical composition of planets
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far, far, far from solar system.
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We have to detect oxygen or ozone
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to make sure that we have all necessary conditions
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to have life.
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Cosmic miracles are something
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which can be related to SETI.
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Now imagine an object, amazing object,
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or something which we cannot explain
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when we just stand up and say,
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"Look, we give up. Physics doesn't work."
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So it's something which you can always refer to SETI and say,
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"Well, somebody must be doing this, somehow."
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And with the known physics etc,
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it's something actually which has been pointed out
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by Frank Drake,
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many years ago, and Shklovsky.
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If you see, in the spectrum of a planet host star,
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if you see strange chemical elements,
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it can be a signal from a civilization
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which is there and they want to signal about it.
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They want to actually signal their presence
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through these spectral lines,
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in the spectrum of a star, in different ways.
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There can be different ways doing this.
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One is, for instance, technetium
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is a radioactive element
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with a decay time of 4.2 million years.
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If you suddenly observe technetium
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in a sun-like star,
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you can be sure that somebody has put this
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element in the atmosphere,
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because in a natural way it is impossible to do this.
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Now we are reviewing the spectra of about
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300 stars with extrasolar planets.
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And we are doing this job since 2000
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and it's a very heavy project.
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We have been working very hard.
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And we have some interesting cases,
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candidates, so on, things which we can't really explain.
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And I hope in the near future
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we can confirm this.
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So the main question: "Are we alone?"
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I think it will not come from UFOs.
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It will not come from radio signals.
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I think it will come from a spectrum like this.
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It is the spectrum of a planet like Earth,
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showing a presence of nitrogen dioxide,
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as a clear signal of life,
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and oxygen and ozone.
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If, one day, and I think it will be
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within 15 years from now, or 20 years.
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If we discover a spectrum like this
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we can be sure that there is life on that planet.
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In about five years we will discover
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planets like Earth, around sun-like stars,
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the same distance as the Earth from the Sun.
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It will take about five years.
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And then we will need another 10, 15 years
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with space projects
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to get the spectra of Earth-like planets like the one I showed you.
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And if we see the nitrogen dioxide
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and oxygen,
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I think we have the perfect E.T.
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Thank you very much.
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(Applause)
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