cosmic spiral visuals
August 28, 2009 7:56 AM   Subscribe

The Anatomy of Spiral Arms, shows how galaxies naturally evolve to form grand-design two-arm spirals. The Hubble Ultra Deep Field in 3D. posted by nickyskye (18 comments total) 19 users marked this as a favorite

 
That first link features what I think we could generously call a nonconsensus theory. The authors are unaffiliated and it's not clear to me that the work is peer reviewed (of course, arXiv makes it damn hard to tell).

Not that this means that it's wrong; they're just red flags.
posted by mr_roboto at 8:10 AM on August 28, 2009 [1 favorite]


Man. Very little tightens my scalp and makes me chortle with tears in my eyes like a mental patient, but show me some 3-D galaxies whose existence turns me to dust, and I can't think of anything better to do.
posted by cmoj at 9:51 AM on August 28, 2009 [3 favorites]


I've made too many Total Perspective Vortex quotes in the past month here on MeFi, so I'll just mention it briefly and let everyone's brain fill in the specific quote from the radio series or books that they prefer the most.
posted by hippybear at 10:12 AM on August 28, 2009 [1 favorite]


Man. Very little tightens my scalp and makes me chortle with tears in my eyes like a mental patient, but show me some 3-D galaxies whose existence turns me to dust, and I can't think of anything better to do.

I read this as "When I'm down, mental patients make me laugh uncontrollably; the vastness of the universe, on the other hand, puts me at a loss for words."
posted by lumensimus at 10:15 AM on August 28, 2009 [1 favorite]


Seeing an image of M104 is one of the reasons I decided to major in astrophysics in college.

My first thought was "God, that's beautiful!" and the second was "I want to know its secrets..."
posted by vacapinta at 10:18 AM on August 28, 2009 [4 favorites]


Ahh the good ole sombrero galaxy...
posted by Mister_A at 10:51 AM on August 28, 2009


"nonconsensus at best" is the right way to put it. The paper is all over the place and contains far more assertions than actual arguments supporting their claims. They fit the milky way data "by eye" and claim that it rejects the models proposed by people who actually use some statistics. They identify streams in hipparcos data, but again show no statistics about whether or not the streams are real or just statistical artifacts. The section on streams doesn't really tie in with the discussion of spiral arms. I don't see one single physical simulation to back up their model. All their talk about gas is confused (no physics, just assertions), and their assertion that star formation and HII regions don't trace spiral arms is wacky and counter to the evidence.

If you read the website of the authors a bit more, you find that their real effort is to replace the idea of dark matter with what they call "relational quantum gravity". Their evidence for doing so is super, super slim, and they pretty much ignore the features of the CDM which make it reasonable. This kind of explains why they're going through the weird spiral arm stuff and not just running a simulation: they hypothesizing a different model for gravity, but they don't tell you that in the spiral arms paper. Then they tie it all in with the pioneer anomaly, and so on and so forth. Wacky is the only word I know to describe it.

I was originally going to post a warning that all theories of spiral arms are to be treated with some skepticism. It's a really challenging problem that I don't think anyone has completely nailed down yet. But these folks are really out there. Please look elsewhere if you want a more well-accepted (though still not perfect) explanation of spiral arms.
posted by kiltedtaco at 10:51 AM on August 28, 2009 [2 favorites]


These folks have posted a lot on the arXiv, but only one work has actually been refereed. This one hasn't. Wacky indeed.
posted by pizzazz at 11:04 AM on August 28, 2009


Just wanted to chime in with the "crackpot" alert on paper 1 up there. The rest of the post is awesome though!
posted by kms at 12:52 PM on August 28, 2009


kiltedtaco, are the first couple of visuals in that first link accurate or sound science based?
posted by nickyskye at 2:29 PM on August 28, 2009


The Deep Field image in 3D was amazing, I've been thinking about it off and on all day.
posted by sleevener at 3:50 PM on August 28, 2009


Looking at it by eye, the rotation curve for that galaxy is completely whacko. If it is, I think we can safely say it's not just out there but it's just plain wrong.
posted by edd at 4:01 PM on August 28, 2009


To continue my reminisces, as an undergraduate I ended up working on Interstellar Matter problems, grabbing time on millimeter-wave telescopes when I could (I was looking for absorption lines at 116 GHz) Anyways, they gave me my own desk at the Harvard-Smithsonian Center for Astrophysics. Except, it wasn't my own desk. I had to time-share it with a grad student named Fred Adams.

I was sort of in awe of Fred - not because of anything he had (yet) done - but because when we were both there at the same time, he was sometimes chatting on the phone with "Frank." I knew that meant Frank Shu. So, I was -this- close to Frank Shu who was a towering genius in my eyes. When he, Frank Shu, was an undergraduate, that is when he was in the same position I was at the time, he was developing Density-Wave Theory to explain the structure of spiral galaxies. And what was I doing?

At the end of my undergraduate years I was asked by a professor I had been working with if I was interested in staying at Harvard as a graduate student in astrophysics. He asked if I wanted to work for him. I thought about it and I declined. At that cocky young age I recall thinking: I'm 22 years old. If at this age, I haven't already produced something significant in this field then I probably never will.

For me, astrophysics is that ex-girlfriend that you abandon impetuously when you are young and later, in your more mature years, look back and wonder about what might have been.
posted by vacapinta at 4:47 PM on August 28, 2009 [3 favorites]


Ok, I've had some time to collect more links. Here's a basic description of spiral arms. A sketch of the epicycle theory for spiral arms can be found in these notes [PDF], go to starting around page 5. Also have a look at the pretty figure on page 15, which is the classical explanation for how eccentric orbits lead to spiral arms. But don't believe it too seriously! Spiral arms are more than just a phenomenon of stars; gas has to be involved too (This is where Lin and Shu's density wave theory is needed), and so any treatment has to handle lots of processes going on. Epicycles can describe the formation of some spiral arms, but there are also plenty of examples of galaxies where the spiral arms don't fit the description we get from epicycles.

The big thing that's causing the most problems for spiral structure these days is that it's becoming more apparent that stars don't sit in their orbits receiving minor perturbations over time. There's evidence for stars migrating radially towards or away from the center of the galaxy by large distances. It's very cool but very messy stuff. Did I mention that spiral structure is complicated?

As far as the figures on the website: I can't figure out what the first movie is supposed to show at all. The stuff about procession of orbits is OK. The last figure about gas is unsubstantiated, as far as I know.

Just a little bit more: vacapinta's story is great. I wish I could better convey what big names both Adams and Shu are in astronomy.
posted by kiltedtaco at 5:56 PM on August 28, 2009 [1 favorite]


Thanks kiltedtaco for your informed, interesting comments in this thread.

And thanks vacapinta for that meaningful anecdote.
posted by nickyskye at 7:12 PM on August 28, 2009 [1 favorite]


Shu's Physical Universe was the textbook in my undergraduate astrophysics course, circa 1983. It's one of my cherished possessions. I reread it last year. I then read the new edition of Carroll & Ostlie, which was fine, but Shu is better.


Physical Universe **ISBN: 9780935702057** (Hardcover)
by Frank H. Shu (Author)
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posted by neuron at 9:48 PM on August 28, 2009


Beautiful images on a Saturday morning.

Thanks nicky for keeping an eye on the sky.
posted by bru at 7:27 AM on August 29, 2009




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