Date: June 1, 2009

Title: Supernovae

Podcaster: Maureen Teyssier

Organization: Columbia Astronomy
http://outreach.astro.columbia.edu

Description: Supernovae are the largest explosions in our Universe today. Not only have they helped us understand the Universe, but they play a crucial role in it.

Bio: Maureen Teyssier is a Ph.D. candidate at Columbia University. Her undergraduate degree is a double in Physics and Astrophysics from U.C. Berkeley. Her research interests include large scale structure, galactic dynamics, and accretion feedback.
Her website is: http://astro.columbia.edu/~maureen

Today’s sponsor: This episode of 365 Days of Astronomy is brought to you by AAVSO.

Transcript:

Hello everyone, and welcome to Columbia Mondays! My name is Maureen Teyssier and I’m a 4th year astronomy graduate student here at Columbia University in New York.

Supernovae are the largest explosions in our Universe today. They play an immense role in the way humans have come to understand the Universe. They give us insight into the physics of the universe, they tell us about it’s overall behavior. They also tell us about physics under extreme conditions, i.e., incredibly high temperatures and densities. They contribute to star birth and evolution, and even to life on Earth as we know it. Not only have they helped us understand the Universe, but they play a crucial role in it. As we understand it now, we could not exist without these massive explosions.

A supernova is the explosion of a star- it is extremely bright, brighter than the cumulative light of billions of stars. When a supernova occurs, a star that we couldn’t even see will become the brightest beacon in a galaxy. Each explosion has a light signature as unique as a fingerprint, but just as fingerprints have commonalities, like having a loop or whorl, you can group the explosions into different ‘flavors’ or ‘types.’ The explosions can be caused by several different mechanisms, and every explosion resultant from one type of mechanism is similar enough that we can group them together.

One of the main types of supernova explosion comes from the collapse of an evolving star. As it ages, the star becomes unable to support it’s own weight -it can no longer generate enough energy in it’s core to support itself, so it implodes. This then causes a massive explosion.

The other main type of supernova explosion comes from a white dwarf star and a red giant star closely orbiting each other. The red giant is a huge, ‘fluffy’ star that is sloughing off it’s outer layers. These layers then fall onto the surface of the white dwarf which is already supporting as much as it can. The white dwarf then explodes due to the additional weight.

A supernova of this type is an unusual situation, but there are enough stars in the universe that we have detected hundreds of them. In fact, because these supernovae are so bright and unique, we can use them as ‘standard candles,’ meaning that the only difference in their brightness is due to their distance from us. Just as if we’d opened a box of 100 Watt light bulbs and placed them different distances away. In the 20th century we used these supernovae to determine distances out to further than we ever could have before. Supernovae usually exist within a galaxy- we could now obtain distances to the furthest galaxies we could see. Once we knew how far away objects in the sky were, we could figure out their size, and begin to understand their physics.

It was using the distance measurements to distant supernovae that we first learned that space itself was expanding. This discovery essentially created the field of cosmology, a word used by astronomers to describe the study of the behavior of the universe on a grand scale. We learned that the universe was not only expanding, but expanding at an increasing rate!!

Now let’s talk about how supernovae are involved with the universe on it’s smallest scales.

Supernovae are an excellent place to test atomic and subatomic physics. We cannot hope to create the same extreme densities and temperatures that exist in a star before, or as, it goes supernova. Even scientists sometimes forget that you cannot strap a star down to a test bench and take measurements.

Before we began to build large particle colliders these supernovae were one of the best ways to study particle physics. Let me tell you an instance of this:

Super-light, fast particles called neutrinos pass through the earth constantly. They rarely ever interact with anything, and when they do, it releases a tiny amount of energy. Initially very mysterious, neutrinos are known to originate from stars going supernovae We have observed an 11 second burst of neutrinos pouring out of a supernova in 1987 just before it exploded. Because neutrinos fly out of the star so easily, they give us an idea of what is happening in the core of a star. The core becomes so dense that new particles, pions and kaons, are created. These decay into neutrinos. The neutinos easily escape, carrying away more than 90% of the gravitational energy of the star, greatly hastening it’s collapse. We learned a lot about particle physics in those 11 seconds.

We also learn a great deal about a supernova by looking at the remnants of the explosion left around the star. As a star blows its layers off, it creates shock waves of gas that pummel material like gas of dust surrounding the star. The energy from the shock waves cause the dust to radiate, making it bright enough to create the glowing nebulae that made the Hubble Space Telescope famous among the public. Although the explosion itself is very short, the remaining nebula will last for thousands of years or more, slowly blooming across titanic distances, forming strange hoops, or bubbles, with marble-ized or glassy surfaces. The strange shapes of these nebula give us more insight into the way stars explode. There are many contributing factors: magnetic fields, rotation, metallicity, mass, cosmic age and binarity. Humans do not currently have the computing power to fully model how these factors interact during a supernovae explosion.

Supernovae are critical to the formation of other stars. Shock waves from supernova push outside gas clouds to higher densities- this change triggers a collapse of the cloud, which may then heat to high enough temperatures to ignite, creating a new star. Not only do supernovae create more stars, but they do an excellent job of illuminating their environment, allowing us to see the areas where stars are born.

In addition, the material flung out from a supernova explosion ‘enriches’ the gas environment around it by adding heavy metals, iron, nickel, gold, etc. – meaning that objects forming out of the gas would have these elements in them. This changes how second or third generation stars evolve. It also changes the elements in planets around these stars. Heavy metals that we mine on Earth, the metals that are essential for life here on Earth, are created, then redistributed by the exploding deaths of stars.

There is direct evidence that this is true- meteorites found on the surface of the Earth contain unique aluminum deposits which are created in supernovae explosions. Because this aluminum inclusion decays quickly, the meteorite must have formed quickly out of supernovae ejecta. This seems to indicate that a supernovae event triggered the collapse of our own solar nebula.

Supernovae not only influence life as we know it, but also allow us to understand the Universe around us, from the smallest to largest scales.

This has been a podcast of Columbia University here in the City of New York. For more information about our public events at Columbia Astronomy visit outreach.astro.columbia.edu. Our next ‘Columbia Monday’ podcast will be on Monday, June 8th, where Erika Hamden will be speaking about “The Universe in Ultraviolet”. Have a great day and keep listening.

End of podcast:

365 Days of Astronomy
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