Wednesday, February 18, 2009

A Glimpse Of Our Future

500 light years away form us, a star very much like our sun is slowly dying. It's converted most of it's Hydrogen fuel into heavier elements. Because the nuclear fission has slowed, gravity is starting to win out over pressure and the star is starting to collapse into a White Dwarf. The cool part of all this is that we now have a picture of it!

This image is of T Leporis, a Miri type star in the constellation of Lepus (The Hare) was taken by an amazing technique called Interferometry with the European Space Organization's VLTI telescope Array. Interferometry uses multiple telescopes all pointed to a single target. By using an extremely complex process that combines the light recieved by the different 'scopes and treats them all as a single scope with an apature equal to the distance between the individual telescopes. For more information on the VLTI, here's the Wikipedia entry on it.

Now that we know a little of how the image was taken, let's take a look at what it actually is. In order to interpret the image, we need to have a basic understanding of how a star works. Let's see if we can cram a couple of weeks of Astronomy 101 into a paragraph. Drum Roll Please!

A star is, at it's most basic level, a huge fusion reactor. It works by fusing Hydrogen atoms into other atoms and generating photons. A photon is a packet of electro-magnetic energy and depending on it's frequency, may be anything from an x-ray to the particle of visible light that we capture in our telescopes to microwaves that can cook an astronaut in orbit. It's these photons that push out against the gravity of the sun's mass. A more energetic star will be larger than a less energetic one because there is more pressure pushing out. As the star ages and the fuel is used, the light pressure that inflated the stellar atmosphere begins to lessen and gravity starts to take over as the defining force of the star's physical shape.

The star begins to collapse on itself. Think of a balloon, you blow it up and the pressure of the air inside the balloon pushes the rubber skin out. If you let the air out of the balloon, the skin of the balloon will start to shrink into it's origninal, un-inflated state. In a star though, when it starts to collapse, strange things begin to happen. As the inner layers start to collapse, the individual atoms (mostly Helium at this point) start to move together and when the pressure of the collapse is high enough, they begin a new round of fussion. This time, instead of Hydrogen fusing into Helium, it's Helium fusing into Carbon. Just like striking a match, the star erupts with a burst of energy blows out it's own outer layers of atmosphere. This is where we get the beautiful planetary nebulas like this one.

M57 - The Ring Nebula

So, back to T Leporis. We are looking at a picture of the collapsing core of the star with the outer layers of stellar material being blown off it's surface. For a sense of scale, the inner part of that image (the stellar core) is about as big around as the orbit of the Earth around our Sun! If you consider the size of objects in the Universe, capturing an image as small as T Leporis is an amazing feat and the ESO scientist have good reason to be proudly celebrating.

Universe Today has a lot more details along with a picture of another VLTI image shoing a binary star system in the Great Orion Nebula.