The coldly warm glow of star birth

By Phil Plait | August 23, 2010 10:05 am

For centuries, scientists have wondered how stars were born. There were lots of ideas, but precious little evidence to back them up.

That’s changed recently. Oh baby, how that’s changed. Check out this gorgeous image of the star-forming compact gas cloud called GL490:


You have to click that to get the ginormous 6000 x 6000 pixel version! It’s stunning.

This image is a combination of pictures taken by the Spitzer Space Telescope and the 2 Micron All-Sky Survey, or 2MASS. Both telescopes scan the sky in the infrared, well outside what our eyes can see. In this false-color image, blue represents 2.2 microns (the reddest light our human eyes can detect is about 0.7 microns, so this is three times that wavelength), green is 3.6 microns, and red is 4.5 microns. At these long wavelengths, what you tend to see are objects that astronomers call "warm", but that’s compared to empty space. In non-geek terms, these objects are colder than 100 Kelvin: about -170°C, or -280°F!

The green glow is from PAHs, or polycyclic aromatic hydrocarbons. Again, in non-geek lingo: big molecules of stinky soot. These are created in lots of conditions in space, but are common where stars are being born. Another indication we’re seeing star birth here is that the cloud is pumping out infrared light: it glows in the IR with thousands of times the Sun’s total energy, which is what you expect if young, hot stars are embedded in thick layers of dust. The dust absorbs that light, warms up, and glows in the IR.

And we know the dust is incredibly thick: it stops so much visible light that if you were to create a filter with the same light-blocking ability, it would be darker than a welder’s mask. If you walked outside and held it up, it would totally prevent any sunlight from reaching your eyes. If you were to ask how much more black it could be, the answer would be none: none more black.

spitzer_gl490_zoomBut in the infrared GL490 glows! And that glow reveals a lot about what’s going on. There are little blobs of material all over the cloud, like the two shown here. See how the blobs tend to line up, like a stream of glop in space? That’s yet another indication we’re seeing young stars. When a star is born, it spins rapidly, has strong magnetic fields, and is generally surrounded by a disk of material from which it (and maybe any planets it has) formed. This sets up conditions where twin beams (what astronomers call "jets") of matter can be blown out of the star from its poles. Since the gas is moving outward from the poles, it’s called bipolar outflow*.

In some cases there are clearly jets of matter coming from the stars, but using radio telescopes astronomers have looked at GL490 and seen that some of the outflow is perhaps not as well focused. Some stars may be blowing vast winds, like the solar wind, in all directions which expand and sweep up the gas around them. Blobs also seen to emit radio waves may be clumps of that material as it gets snowplowed by the spherically-expanding winds.

spitzer_gl490_zoom2Also, I have to point out the very cool star near the top of the image. See how it’s surrounded by a yellower dust (remember, these are false colors; the green is really way out in the IR, and the yellow not quite so far)? That’s probably not the dust glowing, but reflecting the light from the star itself. Some objects in space glow on their own, and some are bright because they’re lit up by something bright nearby. That latter is the case here.

Interestingly, the dust appears to be laid out in long, thin ribbons. That may be due to the star’s magnetic field; the dust grains line up along the field lines like iron filings on paper with a magnet underneath. I’ll also note that if you look at the big picture, that star appears to be near the center of a huge, battered loop of dust. I suspect it’s a young star blowing out a wind that’s sweeping up the material in the cloud, carving out that cavity. I can’t be positive though, since it may simply be a coincidental distribution of dust in the cloud… but it appears to be happening on a smaller scale around at least one other star in that cloud, too.

Obviously, there’s a lot going on here! The good news is that GL490 is relatively close — about 3000 light years — which gives us a pretty good view of what it’s doing. Amazingly, the Spitzer data was taken after the telescope had run out of the helium coolant it used to keep its cameras cold; since it’s looking at cold objects, the mirror itself had to be kept cold or else it would’ve been like shining a flashlight down the tube! So even though the helium ran out a while back, Spitzer is still capable of producing great science, and very, very pretty imagery.

And if you like this, I strongly urge you to take a look at the Related Posts below. Each shows incredible infrared images of the sky, some of which are destined to be your new desktop wallpaper.

Image credit: NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin)

* Which is also the term used when astronomers get food poisoning or a norovirus.

Related posts:

When a star struggles to be free of its chrysalis
The unfamiliar face of beauty
The terrible beauty of star birth
The first spectacular views of the sky from WISE

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (26)

Links to this Post

  1. The coldly warm glow of star birth « Paola comenta | August 25, 2010
  1. Gary Ansorge

    Dang! Even with my 6 meg dsl line, that took several minutes to download but it WILL be excellent wall paper.

    Gary 7

  2. What does GL490 look like in visible wavelength? A DARK cloud, only visible because it covers background stars?

  3. Daniel Snyder
  4. That is one of the many reasons I come to this blog! :) Just mind blowingly stunning!

  5. Awwww baby pictures are always so cute!

  6. Justin

    “If you were to ask how much more black it could be, the answer would be none: none more black.”

    Yeah, well my star birth goes to 11!

  7. Drivethruscientist

    So the material around the stars is comparatively cold, right? The actual stars themselves have formed but are still carving out their heliosphere and would be hot, like what we would normally think of when we think of the temp of a normal star?

  8. jim moore

    How are the magnetic fields being generated?

  9. andy

    Actually GL 490 (=Gliese 490) is one of the stars in that image, not sure what the designation of the cloud itself is.

  10. Nice write up. And just to add something else, thanks to the Herschel space telescope and our friends across the pond at ESA, we have seen chains of protostars forming along the shreading filaments of dust and gas in collapsing clouds, like beads on a string.

    It’s really remarkable. We always knew that must be the case, but now we can see it.

    But that’s the part of astronomy I love: you figure out something on such a deep level that you know what it MUST look like; you build a better telescope and look; and there it is!

  11. Wayne Robinson

    I’m happy (as a pseudogeek) that my ADSL+wireless didn’t take that long to download a 20 MB file to a laptop as I had feared.

  12. Brian Too

    Hey Phil, I don’t understand.

    The Spitzer is out of coolant, and yet it can still take IR pictures? Wha?

    I had understood that once out of frozen OJ, a telescope like the Spitzer was just a clumsy paperweight. What gives?

  13. George Martin

    Brian @ 12 says:
    The Spitzer is out of coolant, and yet it can still take IR pictures? Wha?

    It is still functioning, just not at the longer IR wavelengths. See:

    However, the telescope’s two shortest-wavelength detectors in its infrared array camera will continue to function perfectly. They will still pick up the glow from a range of objects: asteroids in our solar system, dusty stars, planet-forming disks, gas-giant planets and distant galaxies. In addition, Spitzer still will be able to see through the dust that permeates our galaxy and blocks visible-light views.


  14. Jamey

    How many lightyears of that black PAH dust does it take to make it that dark?

  15. Messier Tidy Upper

    Magnificent image, news & article there – thanks BA, I love this. :-)

    Thanks also to the astronomers and engineers operating Spitzer & the 2 Micron All-Sky Survey.

    If you were to ask how much more black it could be, the answer would be none: none more black.

    Poetic – but true only at visual wavelengths. ūüėČ

    What is black in infra-red?

    Makes you wonder.

    Do what know how massive these stars are going to be & what their spectral types are – or will be when they hit the main-sequence? How far evolved are they and when will they join the main-sequence (dwarf) star ranks?

  16. Messier Tidy Upper

    Did I mention how much the “coldly warm” line – a true paradox appeals to me? ūüėČ

    Hope y’all enjoy this bit of doggrel inspired by this:

    Seeing the Invisible stars of GL490 :

    Coldly warm the new star glows
    Coccooned its light concealed
    The nuclear fires stoke up to burn
    With frozen grains congealed!

    You cannot see its nebula
    Too dark it blocks the stars
    By absence you detect its presence

    It gives itself away by hiding
    Except in infra-red
    What would we see if eyes we had
    That saw in heat and cold?

    These new born stars and planets round
    What do they have in store?
    Will there be life on worlds they birth
    What possibilities might be foresaw
    If we look close enough to tell
    What stories lie ahead?

    These planets still forming now, their suns begin to blaze
    Will still young be as our earth dies, our Sun’s red giant phase!
    Could we ever meet up if life starts over there?
    Will they ever somehow know we’ve caught them at this stage?

    – Steven C. Raine (Messier Tidy Upper here.)

    PS. Yeah, I know it doesn’t always rhyme & is sort of free verse / stream of consciousness / limerick mixed style. Hope it’s still amusing /entertaining / thought-provoking / okay anyhow.

  17. MadScientist

    Colder than 100K? I don’t believe it; have you calculated the radiance of an object at 100K? There’s not much 2.2, 3.5, or even 4.5 micron radiation. I can’t remember Spitzer’s bands but there were bands much longer than 4.5 microns. The Planck and Herschel observatories go out into the millimeter band so I do expect them to see very cold objects. Sure if you had an extensive enough source you would get enough photons back here on earth, but you’d get an awful lot more photons at the longer wavelengths – say 20 microns or longer. Hmm … do I have time to do these calculations of how many photons reach the earth for a galaxy-sized object or nebula-sized object at 100K and at a variety of distances …

  18. Jeeves

    The green glow is from PAHs, or polycyclic aromatic hydrocarbons. Again, in non-geek lingo: big molecules of stinky soot.

    See, I told you space has a smell.

  19. procyan

    Jeeves, the term aromatic is an anachonism in this case. In its day, it refered to newly discovered “organic” (another anachonism) molecules that were volatile and had a distinctive smell. But over time is has taken a place in the chemist’s lexicon to describe molecules with a ring structure, such as benzene or other more complicated cyclic structures, PAHs included. However the high molecular weight of PAH’s means that they are not likely to be very volitile at STP and therefore not too smelly. nevertheless there are lots of references to the cordite aroma that attends astronauts after a “stroll about the policies”.

  20. Nigel Depledge
  21. Nigel Depledge

    To build on what procyan (19) said:

    A molecule or functional group is desrcibed as aromatic if the electrons in its pi-bonding orbitals are delocalised.

  22. Jeeves

    Hey, I didn’t call it “stinky soot”!

    But point taken about the meaning of “aromatic” to a chemist. Didn’t know about that.

  23. Charlie in Dayton

    Multiple kudos to ya, BA — this site gives me a wondrous source of scientific wallpapers for the computer here at the club ham radio station. I get questions regularly about what’s what, referring them to the BA website.
    We might get an astronomonomoner out of this yet…

    When ya coming back to ScopeOut? We miss you here in flyover country…

  24. Wayne Conrad

    Outstanding picture, as usual. Well, maybe better than usual for this one. Wow.

    I’ve got a question out of my own ignorance of how astronomy works: How do astronomers pick what visible colors to assign to the components of a false-color image? Are there conventions? Is it all about making the information visible, and the beauty is just a side-effect of that pragmatism, or does beauty ever come into it?

  25. MadScientist

    @Wayne #24: You can color things however you want to make them pretty – or to highlight the things of interest. People will *usually* color the shorter wavelengths blue and the longer red (or even black) but although that is very common, there are really no set rules. With instruments viewing the earth at invisible wavelengths, for example, I color things however I please. Also keep in mind that some images are produced from a set of differences between measurements. In such a case people often color the positive numbers blue and the negative red, but once again there is no set rule and some friends of mine like to color them from yellow to brown and other such schemes. In fact if you strictly use a red-to-blue scheme for differences I think the result is usually awful.


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