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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:
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.
January 11th, 2008 at 12:48 pm
The accretion disk thing has interested me since back when Dole did his simulation in 1970. Looks like he was wrong and Sagan and Isaacman (1977) were right, most of the planetary systems out there don’t look very much like the solar system. Now if we can figure out why…
January 11th, 2008 at 1:08 pm
Phil, great entry even for an astronomy dummy like myself. I often kick myself for not going into the field, but chose another branch of science (optical physics and EE) instead. Thanks!
Anyway, I was wondering what you guys thought about the Hubble discovered double Einstein ring — being as how I am “light” guy, I thought it an incredible sight… http://presscue.com/node/38728
January 11th, 2008 at 1:55 pm
Charles
Phil covered this one already
January 11th, 2008 at 2:38 pm
Speaking of planetary disks, I hear that the first verified planetary prediction since the 1840s has been made.
Assuming it isn’t a fluke among the other similar attempts, the theory is really exciting I think: planets forms where they can. (I.e. where they find stable orbits.)
It’s in the stars, but there may be lots of planets.
January 11th, 2008 at 3:27 pm
I’m curious about the corn hole. It’s a small piece of metal (relatively) and I’m guessing it actually blocks more light (from our perspective) that it’s true size would indicate (due to prismatic effect?). What properties indicate that it’s metal? When we say ‘small’, is there a way to scale it in the model or in the picture? Any guess as to its composition?
Thanx in advance to any help.
January 11th, 2008 at 6:10 pm
@Jeffersonian
The coronagraph is a part of the telescope that blocks out the direct light from the star. It creates an artificial eclipse. The same type of thing is used in SOHO to view the solar corona.
http://en.wikipedia.org/wiki/Coronagraph
January 11th, 2008 at 10:08 pm
what are the discrete black blobules? they seem to align into some sort of structure. Have these been observed before or are they artifacts of photo?
January 11th, 2008 at 10:13 pm
OK, I get it (as in, the apparent hole caused by the coronagraph itself). For a shot like this (this one really grabs me), is there a specific coronagraph, or just the same one always used on this ‘scope?
Are they ever used on common amateur ‘scopes (I’m currently shopping)?
January 12th, 2008 at 2:16 am
The “hole” is the occulted area from the coronagraphic hole that is part of NICMOS instrument on HST. There are some residual black “blobs” that are artifacts from the processing. In order to construct this image, we have to subtract a similar image of a star that does NOT have a disk. This is called PSF-subtraction, and it allows us to remove MOST of the artifacts that are introduced by the diffraction of the telescope… but its not perfect.
This would be virtually impossible to image on an amateur scope, mostly because HST has a very stable point-spread-function (no seeing) enabled by being in space. The telescope is also quite large, so collects lots of photons. Very few images of disks like this are possible from the ground, even with 8 and 10 meter telescopes equiped with adaptive optics.
January 12th, 2008 at 5:08 am
I’m worried that by looking at this protoplanetary disk we are collapsing it’s potential to what we can actually measure. A pessimistic amateur astronomer could become the Destroyer of Worlds. Perhaps we could build a big coronagraph to restict who sees it. I think it would be shaped like a cone.
January 12th, 2008 at 10:15 am
Hey! You made dailykos’ Science Friday!
http://feeds.dailykos.com/~r/dailykos/index/~3/215474373/25618
January 12th, 2008 at 10:21 am
Okay, so it’s Saturday…. still. They’re talking about this post on dailykos.
January 12th, 2008 at 11:06 am
[...] Bad Astronomy with the tale of the strange looking proto-planetary disk just 100 light years away called The Moth. [...]
January 12th, 2008 at 3:35 pm
[...] Bad Astronomy with the tale of the strange looking proto-planetary disk just 100 light years away called The Moth. [...]
January 12th, 2008 at 3:35 pm
[...] Bad Astronomy with the tale of the strange looking proto-planetary disk just 100 light years away called The Moth. [...]
January 12th, 2008 at 7:54 pm
What’s the stars spectral type and thus luminosity, lifespan?
Is it visible with binoculaers or unaided eyesight & where?
Anyone know?
Minor~est of nitpicks but isn’t Neptune’s orbit much more circular and less elliptical than shown with the image?
January 13th, 2008 at 5:13 am
Rob, why are you posting links to every thread IN every thread? We’re READING BA, we don’t have to be told where it is. Seems to me you’re using up an awful lot of bandwidth to no purpose.
January 13th, 2008 at 9:03 am
Arnaud, thanks. I missed that somehow.
To answer the comment Barton made about Rob, it’s just the way that WordPress (BA’s blog software) works. When someone links to an article in their own blog, those comments are auto-generated and posted. They are called “trackbacks.” When it comes to bandwidth, the bytes the generate is probably less than a few square centimeters of the
photos of “anatomy and physiology lessons” that proliferate on the ‘Net like so many weeds.
January 13th, 2008 at 9:21 am
Phil,
Working with Glen, did he subject you to his bad puns? I remember being in a van with him after driving from Baltimore to Florida to see the shuttle launch for the first Hubble servicing mission in Dec. 1993. He came up with some real groaners.
Cool image!
January 18th, 2008 at 12:42 pm
Hi Phil et al.,
A mutual acquaintance pointed me to this discussion. I see Dean (Hines) has already commented – but just to clarify a few points…
1. “Some of the most fun I had was working on protoplanetary disks”…”I worked with Glenn in particular on several very cool protoplanetary disks”. Indeed it was (fun) an they are “cool” (but not thermally, of course), but for clarity the circumstellar dust structure around HD 61005 is unequivocally NOT a protplanetary disk. It is a debris disk — interacting with the local interstellar medium. The distinction (between protoplanetary and [evolved] debris disks is very important, as the material around HD 61005 is not like interstellar grains or those around gas-rich (young) T Tauri stars, but result from collisions of planetesimals in orbit around the star.
2. “the part labeled ‘coronographic hole’ is where a small piece of metal block out the light from the star”. Well, no. STIS (the Space Telescope Imaging Spectrograph; Phil’s favorite HST instrument) does (or did, since it is now in slumber) use a “small piece of metal” (a “occulting wedge”) in a re-imaged focal plane to suppress central starlight. The “Moth” images we took are with HST’s NICMOS (the Near Infrared Camera and Multi-Object Spectrometer) coronagraph (a true Lyot coronagraph also with a pupil plane mask to control diffracted light), and literally has a hole in a first image plane mirror where the central starlight passes through and is not reflected “downstream”. That NICMOS internal mirror is at the f/24 focus of HST’s secondary mirror. And the central starlight falls into it so it is not scattered downstream before coronagraphic suppression of diffractive light in the pupil. Bottom line, it is a hole, not a piece of metal (FYI – physically the hole in the mirror is 165 microns in diameter). Oh, and coronagraph is with an “A” as in “corona”, both an “o”.
As Jeffersonian asks… projected onto the sky, the “hole” (region onbscured) is 0.3 arcseconds in radius. At the distance of HD 61005 that is about 10 Astronomical units – so we do not actually see the inner 10 AU of the dust structure. That is the size of the black region at the “head” of the moth. Procyan asks about the “discrete black blobules” — those are just noise in the image – don’t read anything astrophysical into that (again discussed in the context of residual image artifacts in our paper).
Cheers,
Glenn Schneider
NICMOS Project Instrument Scientist
Astronomer, Steward Observatory University oif arizona
http://nicmosis.as.arizona.edu:8000