on Protostellar Disks

My wife made me this new quilt for the door of my office:

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DG Tau B as quilted by Jamie McDonald/The Paperbook Rose

It’s a star called DG Tau B, and she made an incredible likeness.

But what, exactly, are we looking at here? If you’d like to know more about how the quilt was made, take a look at my wife’s blog. Read on to find out more about what you’re looking at.

DG Tau B is indeed a star, but we’re not actually seeing the star itself here. We’re actually seeing a disk of gas and dust AROUND the star. The deep black portion in the middle is where the dust is so thick that it blots out the entire star system. It’s a flared disk, which means it’s thin near the middle and wider at the outer edges: the star is illuminating the top and bottom sides of the disk, and the portion you CAN see is the far side of the inner edge of the disk, shining through the thinner near edge of the disk.

DG Tau B
DG Tau B as seen by the Hubble Space Telescope in 1999

In the center is a very young star and (if there are any) planets in the process of forming. In the case of DG Tau B (a member of the nearby Taurus-Auriga star-forming region roughly 150 parsecs away), the star is so young it’s still gaining mass from the disk of material, and some of that matter is being swept up by its magnetic field and beamed outwards as giant jets (the green things). My wife actually quilted the piece along the contour lines of the outflowing gas actually takes, and you can see that in the picture.

This is a bit easier to see with a high resolution image of a star. This star is called Gomez’s Hamburger (yes, really…) and consists of a massive disk surrounding a protostar* 250-ish parsecs away.

Gomez's Hamburger
Gomez’s Hamburger, as seen by the Hubble Space Telescope in 2002.

Gomez’s Hamburger is named for its discoverer, Arturo Gomez, one of the long-time observatory support staff at the Cerro Tololo Inter-american Observatory in Chile. As for the star, it’s the astrophysical equivalent of the Burger King logo. The disk is thinner in the middle (and toward us), and that’s how we’re seeing the star’s light reflecting off the dust.

Viewed from the top, this would probably look like this ALMA image of HL Tau (shown here with the central star removed; all the gaps in the rings are probably planets): ALMA image of the protoplanetary disc around HL Tauri

And since these are fun to look at, here’s another called “Flying Saucer” (astronomers really do name things well sometimes) as seen here in an image from Grosso et al. 2003.

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2MASSI J1628137-243139 (Flying Saucer). Image from the Astrophysical Journal

It’s… well, you can see why they’d call it that. Here again, we can see a young star where we can’t actually see the star itself.

These kinds of stars are downright fascinating to study, because somewhere within these disks we’ll be able to watch planets forming. As someone who studies star forming regions, these are the perfect things to put on my office door.

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The finished quilt

*There is apparently still some controversy over whether Gomez’s Hamburger really is a protostar or if it’s a dying star at the end of its life blowing material off into space.

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