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Can the Cosmological Parameters be Determined from Supernovae?

Date: Mon Mar 16 10:29:25 1998
Posted by konrad alfred
Grade level: undergrad
School: univ of cambridge
City: cambridge State/Province: cb
Country: uk

Message: deceleration parameter, cosmological constant and hubble constant of particular interest

type 1a supernovae seem most useful

Supernovae are very useful for many things in astronomy, but recently they are coming into their own as distance indicators. There are two types of supernovae; what we call Type II are the kind most people are familiar with. This is a bright, massive star that explodes after fusing all the light elements in its core. The other kind is called Type I, and we believe the precursor is a binary star system. In this case, two stars orbit closely around each other, one of which is a white dwarf. A white dwarf is basically the tremendously dense core of a star which started out much like the Sun, but is very old and has lost a lot of its mass.

The white dwarf can strip gas from its neighbor, and that gas piles up on the surface of the dwarf. If it piles up at the right rate, BANG! The star fuses the gas pretty much all at once. The resulting explosion rips the star to pieces and releases a lot of energy, so much energy that we can see the explosion clear across the Universe.

The current thinking is that it is possible to calibrate how bright a Type I supernova actually is. That means we can calculate how far away it is. That's why we can use it as distance indicator! If we know how bright it really is, and how bright it looks to us, we can determine how far away it is.

Right now, there are many theories dealing with the details of how the Universe was born and how it is evolving. Will it expand forever, or eventually contract? How fast is it expanding? Questions like this can be answered, or at least clues to the answer can be found, by looking as far away as possible.

Imagine you are looking at wall from one centimeter away, and want to know if it is flat or curved. If it is slightly curved, you can't tell easily because you are too close to it. If you look down the wall, you can see the curvature more easily. This is exactly what we are trying to do with these supernovae; look far enough away that any deviations from flatness of the Universe can be seen.

By finding the distance to these supernovae, we have milestones placed at various points around the Universe. We can measure how fast these supernovae are receding from us due to the expansion of the Universe, and this in turn can tell us things like how fast the Universe itself is expanding and if it is slowing down.

For more info about supernovae, and links to people that study them, I welcome you to take a look at my website.

Phil Plait
Keeper of the Bad Astronomy website.

©2008 Phil Plait. All Rights Reserved.

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