Cosmic Secrets of the Supernova | Robert P. Kirshner | Big Think

Cosmic Secrets of the Supernova

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Robert Kirshner’s research into supernovae overturned decades of scientific assumptions about the universe, and how it is mysteriously expanding at a rapid rate.

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Robert P. Kirshner:

Robert P. Kirshner is Harvard College Professor of Astronomy and Clowes Professor of Science at Harvard University. He graduated from Harvard College in 1970 and received a Ph.D. in Astronomy at Caltech. He was a postdoc at the Kitt Peak National Observatory, and was on the faculty at the University of Michigan for 9 years. In 1986, he moved to the Harvard Astronomy Department. He served as Chairman of the Department from 1990-1997 and as the head of the Optical and Infrared Division of the CfA from 1997-2003.

Professor Kirshner is an author of over 200 research papers dealing with supernovae and observational cosmology. His work with the "High-Z Supernova Team" on the acceleration of the universe was dubbed the "Science Breakthrough of the Year for 1998" by Science Magazine. Kirshner and the High-Z Team shared in the Gruber Prize for Cosmology in 2007. A member of the American Academy of Arts and Sciences, he was elected to the National Academy of Sciences in 1998 and the American Philosophical Society in 2004. He served as President of the American Astronomical Society from 2003-2005. Kirshner's popular-level book "The Extravagant Universe: Exploding Stars, Dark Energy, and the Accelerating Cosmos" won the AAP Award for Best Professional/Scholarly Book in Physics and Astronomy and was a Finalist for the 2003 Aventis Prize.

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TRANSCRIPT:

Question: What are supernovae and why does your research focus on them?

Robert Kirshner: Yeah. So, stars have a lifetime. It’s very long compared to ours, so stars seem permanent. For poets, stars are kind of symbols of permanence. The speed of light is a symbol of something going fast. But for astronomers, the speed of light is slow, that’s what lets us see the past and the stars are not permanent; they are changing over time. It’s just the time scales are much longer than human lifetimes. So, a star, like the Sun, gets its energy from nuclear fusion. Down in the center of the Sun, hydrogen, which is what the sun is made of, is being converted into helium, the next element up. When you do that – when the sun does that, it generates energy. Energy is released because the helium in the nucleus has a little less mass in it then the ingredients, the hydrogen nuclei that went into it. So, hydrogen goes in and helium comes out, and the difference shows up as energy.

You know that equation that Einstein has, E=MC2, that’s not just a symbol of scientific inscrutability. That is actually an equation where the thing on the left is equal to the thing on the right, the amount of energy that you get out is equal to the change in mass times the speed of light, squared. Well, the speed of light is a pretty big number and when you square it, it’s big, big. And that means you get a lot of energy out from a small change in the mass. This is really important. So this is nuclear fusion. This is how the sun works and since the sun is made of that fuel, it can last for a very long time.

We think the lifetime for a star like the sun is about 10 billion years. So, the sun formed about 5 billion years ago, along with the planets like we’re on, and it has about 5 billion years to go. So check you’re homeowner’s policy, but I think we’re going to be okay for awhile. The interesting thing is that the more massive stars have shorter lifetimes. So, a star that has ten times the mass that the sun has a lifetime that is not measured in billions of years but only millions of years. And the very massive stars have very short lifetimes compared to the age of the earth, or compared to the age of the sun. so that means that there’s a complicated story. When stars form, the massive stars live fast, dies young; blow up, it turns out at the end. They explode as supernova explosions.

There’s another path that also leads to explosion where a star uses its fuel and crunches down in the center to become a white dwarf, which is a very dense kind of star that is left over after an ordinary star has used its nuclear fuel. The sun will probably be a white dwarf five billion years from now. In between, it will become a red giant. It will swell up and it will vaporize all of the planets, so if you’re worried about this sort of thing. You should worry.

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