AAS #17: A rolling moth gathers no stones

Bad Astronomy
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Jan. 11 2008 11:30 AM

AAS #17: A rolling moth gathers no stones

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When I worked on Hubble data, lo these many years ago, some of the most fun I had was working on protoplanetary disks. Stars form when local bits of an interstellar cloud collapses. Random eddies and whorls amplify as the blob shrinks under its own gravity. The swirling junk forms a disk, and the central region compresses and forms the nascent star. The outer part of the disk spins around the central star and forms planets. As you can imagine, the disk can be pretty big, many billions of miles across. That means that even from light years away, telescopes like Hubble can see them fairly clearly. They come in many shapes, but usually they are relatively symmetric and round. However, one was recently found around the nearby star HD 61005 (which is about 100 light years away), and it was a bit of a surprise:

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Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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It's squished! The astronomers who found it call it "The Moth". It's extended on the sides, almost as if it's being swept back by something.. and it turns, it is. The whole system is moving through the galaxy, and as it sweeps through the thin gas between the stars, the pressure pushes on the disk, giving it those graceful arcs. Here's an annotated version of that image showing what's what.

As you can see, the disk is plowing through space pretty much face-on, which is why it's warped. Just so's you know, the part labeled "coronographic hole" is where a small piece of metal block out the light from the star, which is far brighter than the disk, allowing us to see the much fainter circumstellar material. The scale is huge; the size of Neptune's orbit is shown for comparison. The wings of The Moth are 35 billion kilometers across! The disk is probably in the middle of forming planets now, and it's unclear how this will affect whatever planets are being born. It's quite possible planet formation will be suppressed, and eventually the disk will blow away entirely... which, I hope, explains the title of this post.

I'll note that the astronomers who made these observations -- Dean Hines and Glenn Schneider -- are friends of mine. I worked with Glenn in particular on several very cool protoplanetary disks. They were fun for a lot of reasons: they were interesting scientifically, they were pretty, and I just plain enjoyed working on the images where the coronograph was blocking the starlight and letting the disk light through. Plus it was simply a true and clear joy to gaze upon the light from planets and stars in the throes of birth, knowing that there was literally a bright future ahead of them for the next few billion years.

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