What exactly are they?

I was on a website featuring shots from the Hubble, and there was this one featuring a "bow shock of a young star"

Here's the URL for the picture.

http://oposite.stsci.edu/pubinfo/PR/2002/05/index.html

Thanks

The Incubus

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<font size=-1>[ This Message was edited by: The Incubus on 2002-05-09 17:21 ]</font>

If you watch a boat, moving through the water, the faster it goes, the more the water piles up in front of the boat. That pile of water is the bow shock, induced by the fact that the water has to go around the boat, not through it. It takes time for the water to respond to the boat, so the faster the boat moves, the more water stacks up. The same thing happens with airplanes moving through the air. A sonic boom is the bow shock induced by an object moving through air faster than sound does (the air can't react to the plane faster than the speed of sound).

So, as the solar wind rams into the earth's magnetic field, it piles up and forms a bow shock (here's an animated model, and here's an explanation). The sun has a bow shock in the plasma of the interstellar environment, just as the earth has a bow shock in the plasma of the interplanetary environment. The HST image shows the sun-like bow shock of another star.