The terrible beauty of chaotic starbirth

By Phil Plait | January 5, 2010 9:00 am

Orbiting our Milky Way galaxy like two bickering siblings are the Magellanic Clouds, galaxies in their own right, though far smaller than ours. The smaller of the two — named, shockingly, the Small Magellanic Cloud — is also the farther of the two, about 200,000 light years to the Larger cloud’s 180,000 or so. The SMC is loaded with gas and dust, and is actively churning out stars.

The Spitzer Space Telescope, which observes infrared light from astronomical sources, took this incredibly beautiful image of the SMC:

[Click to embiggen, including getting access to a huge 7800 x 7000 40Mb version.]

Remember, this is not a visible light image! In the picture, blue represents light at a wavelength of 3.6 microns, about 5 times longer than what the human eye can see. Green is 8 microns, and red 24. So what you see here as blue is really what we would think of as red stars if we saw them with our eyes. Green shows light from big organic molecules called PAHs, for polycyclic aromatic hydrocarbons. Red is light from stars deeply embedded in dust, and is where stars are busily being born.

All together, this image shows starbirth on a vast scale, thousands of light years across. And this may be a new phenomenon for the SMC: measurements of the elements in the stars there show that they have far fewer heavy elements (like oxygen, iron, and so on) than stars in the Milky Way, as little as 1/5th as abundant. Since these elements are created inside of stars over time, this indicates that stars in the SMC are on the whole younger than in the Milky Way.

Even though the two Clouds are the closest galaxies we can see — and you can spot them easily with the unaided eye in the southern hemisphere — there’s still a lot we don’t know about them. In fact, we’re not even sure if they are orbiting the Milky Way, or just passing by! Even over decades, measuring their actual motion across the sky is very difficult; their mind-numbing distance of quintillions of kilometers away shrinks any real motion into apparently microscopic amounts. It may be quite some time before this question is finally resolved.

Another image from Spitzer also shows a tail of gas streaming away from the SMC, material ripped out of the body of the galaxy itself by the gravity of the Milky Way. It’s possible that interactions with the Milky Way and the other Magellanic Cloud are what triggered the star formation in the SMC, too.

It’s rather convenient to have such a nice laboratory for dwarf galaxies and starbirth so close to us. That makes it easier to study, giving us access to really high resolution images like this one. And the bonus? They’re pretty, too.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (13)

  1. I’m glad I don’t have to vaccinate those babies.

  2. It’s rather convenient to have such a nice laboratory for dwarf galaxies and starbirth so close to us

    Praise be to His Noodliness for granting us such a convenience! Indeed, His wisdom is all…uh…wise.

  3. D.Rose

    41.1MB Hot damn that’s a big jpg. I even see a few galaxies hiding in there.

  4. @murmur55

    Thank you science for all that you do…

  5. In fact, we’re not even sure if they are orbiting the Milky Way, or just passing by!
    Say what? Don’t we have detailed maps of tidal tails from the two galaxies that clearly orbit around the Milky Way several times?

  6. Charles Boyer

    I love the big files, they print very nicely and make the office walls a little more cheerful.

    This and news of a star exploding because of anti-matter have made for an interesting day in astronomy.

  7. Ooh, pretty. Another image to add to my wallpapers folder.

  8. Plutonium being from Pluto

    Great picture BA & good article. :-)

    Do folks realise we’re seeing the Small Magellanic Cloud end on & that is a lot longer than it looks – about 5 X longer than we see it but we only see it from one end? (If I recall right.)

    Please BA a request if I may – can we have another top 10 pictures for 2009 as you hinted back in your original best pics post? Please? :-)

  9. Kelin

    Beautiful! I have a probably stupid question: how do we know that there are “big organic molecules”? I an aware of the spectral/absorbtion lines idea but thought that only applies to atoms. How can the composition of the molecules be determined? e.g. couldn’t it all just be basic methane and CO2? sorry, if this is a stupid question. cheers

  10. Spectroscope

    @ 9 Kelin:

    No such thing as a stupid question. Molecules can indeed be detected via spectroscopy as well – for instance we’ve detected titanium oxide in cool red giant (M III) stars & methane in brown dwarfs. We’ve even detected water vapour in the atmosphere of at least one exoplanet (HD 189733 b) & in sunspots while formaldehyde and all sorts of other chemical compounds have been discovered in nebulae.

    James Kaler’s Stars website has a good and clear page which may help :

  11. Kelin

    @10. Spectroscope: Thanks a lot!
    Your linked website does not specifically mention how it differs, but it was a good explanation!
    However, I disagree on one point: stupid questions _do_ exist! ;-)

  12. RegnRotational spectroscopyer Trampedach

    @9+11: Kelin: In some ways, molecules give spectra that are easier to study than atoms do, since the former have hundreds of narrow lines arranged in bands with accurately known line-strength ratios within each band. You can try to “Wikipedia” “Rotational spectroscopy” which has a (pretty poor) plot of a molecular spectrum.
    There are lots of molecular bands in the infra-red (shorter wavelength neighbour to micro-waves), and also some in the optical and even in the ultra-violet, depending on the molecule/kinds of transitions. I hope this helped.


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