Waves of star birth sweep through tiny galaxies

By Phil Plait | April 30, 2009 11:21 am
It’s the Genesis Wave! They’re on a build-up to detonation!
— David Marcus
Star Trek II: The Wrath of Khan

Stars are born when gas clouds in galaxies collapse. Eddies form, clumps and knots of higher density gas a hundred billion kilometers across, which then contract under their own gravity and form stars. Sometimes, galaxies undergo violent bursts of star formation, making huge numbers of stars all at once.

What does it look like when that happens?


Credit: NASA, ESA, K. McQuinn (University of Minnesota, Minneapolis), and I. Karachentsev (Special Astrophysical Observatory of the Russian Academy of Sciences, Russia)


This is Hubble’s view of the nearby dwarf galaxy IC 4662. At 8 million light years distant, it’s one of the closest galaxies in the sky, and that makes it a perfect target for all kinds of investigations. In this case, astronomers targeted IC 4662 and several other nearby dwarf galaxies — smaller-than-usual galaxies, much smaller than our Milky Way — to try to understand how stars form in them.

IC 4662 is undergoing a current burst in star formation even as we watch. See those two big red regions? Those are gigantic clouds of gas furiously forming new stars. Take a close look at them: you can see how they appear to be less red in the middle, and there are lots of stars there. That’s because massive stars born inside the clouds blast out ultraviolet light and strong winds of subatomic particles (like a super solar wind), eating away at the gas and carving out a giant bubble in the cloud. That kind of structure is a sure sign that stars are being born at a high rate*.

But we already knew this! What’s new here is that it appears that in these dwarf galaxies, star formation happens in waves, starting in one place and sweeping across the entire galaxy over time. That’s very interesting, and surprising. It was thought that these starbursts, in general, just happened in one location and lasted for a few million years. Now it looks like they start that way, but then spread out from there like an infection, with the whole process lasting for two hundred million years or more!

That tells us something about the way stars form in these galaxies, which also tells us about their structure, how the gas clouds are laid out, and how these galaxies behave. We care about this for two reasons: one is that we are pretty sure that big galaxies, like our own, form by the collision and merger of smaller dwarf galaxies like this one. The more we understand about dwarf galaxies, the better a picture we get of the history and composition of our own.

But we also care because this is just so very cool. We can watch as stars are born in other galaxies! We can understand how this happens, why it happens, and what the implications are… and we do it using an observatory orbiting our planet, pointed toward a cosmic collection of stars and gas that lies 80 quintillion kilometers away!

Always try to remember that when you read something about science. We do this stuff because it’s important, but we also do it because it’s so tremendously wonderful.

*If you download the ginormous version of this image (it’s 5Mb) you can see faint, arc-shaped extensions to the two reddish gas clouds (above the one at the top of the picture, and below the one at the bottom). I suspect that’s where the furious winds from the stars have literally popped the bubbles; what astronomers call a blowout for obvious reasons. You can see that the hollow parts of the clouds "point" toward those blowouts, just as you’d expect if the stars inside had pushed on the cloud itself and caused it to pop in that direction. Tres, tres cool.

CATEGORIZED UNDER: Astronomy, Pretty pictures, Science

Comments (22)

  1. Herschel and Planck have been delayed until next month!

  2. DrFlimmer

    Tres, tres cool.

    Phil, are you trying to learn French? 😉

    But, très cool, indeed.
    Just like the launch of Planck and Herschel – as far as I know launch is due on May 14th. Just hope that everything goes well with the rocket and the cargo. Fingers crossed.

  3. 😀 You had to quote one of the best ST movies… But yes, that is some great astronomy there too!

  4. Dan Roy

    Phil, or others who might know,
    have we ever observed a star that ignites. It ought to be a pretty instantaneous process right? First a cloud of gas invisibly contracting under its own gravity, next second a shining star? Or what does the theory on star formation say on this?

  5. Big Al

    “The stars, like dust….”

  6. Eddie Janssen

    “”Eddies form clumps and knots of higher density gas a hundred billion kilometers across, which then contract under their own gravity and form stars.”
    Yes, we Eddies are a remarkable lot.

  7. coolstar

    “subatomic particles”? you couldn’t just say, uh, protons and electrons as those are the primary constituents of stellar winds…….

  8. Chris A.

    @Dan Roy:
    The problem is that stellar ignition takes place deep inside molecular clouds, thoroughly hidden from our view (even the longer wavelengths struggle to get through). We only see newly-ignited stars after they’ve had a chance to blow away their birth clouds a bit with their rambunctious stellar winds (which form these things we call “Herbig-Haro objects”).

  9. Dan Roy,

    It’s not quite like flicking a switch. Instantaneous is all relative. For humans it’s not at all, but over the lifespan of a star it sure would be that way. If you look at the wiki entry on protostar, that may give you a good starting point for more stuff to consider.

  10. Everything that we peek at in the big, wide universe is wondrous and tres cool. Phil et al, Here’s another way to explore the image. Toggle the button on the far right bottom for a full-screen view. It’s like being on the bridge of a starship.

  11. DrFlimmer

    Also @ Dan Roy,

    but thanks to our spaceships we have detected almost every little step of the star birth. We cannot detect the “flash” of one star, but combining our results of many young stars gives us a very good picture. Interesting regions, where we can see almost every step, are M17 and the Orion Nebula (a friend of mine is working on one of the deepest pictures ever taken of M42 for his master thesis – it’s gonna be very interesting :) ).

  12. Flying sardines

    Ja ist ‘tres’ cool, herr Doktor Phil!

    Vot should dat ber Monsieur Doctore Phil? 😉

  13. Flying sardines

    ber = be.

    Unless ber means ‘be’ in another foreign language!

  14. Spectroscope

    @ Dr Flimmer :

    Awesome masters thesis your friend is working on – lucky bloke!

    @ Dan Roy : As others here have already noted, astronomers have observed many snapshots in the process of star birth – from Bok globules to Herbig-Haro objects to infant (T-Tauri) stars. Like almost everything stellar*, the timescale is immensely long – millions of years – and star birth as noted is hidden within the dark cocoons of dust and gas from which stars form. These cocoons remain opaque until after the star has lit up – although they can make good nebula once they’ve been cleared a bit such as Hinds Variable Nebulae around, I think, T-Tauri itself.

    There are many good articles, chapters in astronomy books and other sources on this if you wish to research further. It is a pretty amazing thing to follow even if we do this via numerous examples at slightly different ages rather than catching one star at the exact moment of ignition.

    Here’s three questions for the BA and others here :

    1. Do we know what might have started this wave of starbirth within IC 4662? Is it interacting with other galaxies or showing increased activity at its core or something?

    2. Is IC 4662 a satellite galaxy like the Magellanic clouds or the famous starburst galaxy M82? Could this be connected with its starburst status? Or is it alone in space?

    3. Do we know if this dwarf galaxy is likely to merge with another galaxy -even our own Milky Way at some later stage? Could some of these stars ultimately end up as part of our own Galaxy one millennia?

    Finally, just a very tiny nit to pick – beautiful as it is, it looks like only *half* the galaxy is in the photo to me. Is there a “zoomed-out” image somewhere or composite picture putting together the “missing” half of IC 4662 to the right-hand side of the photo?

    Hmm.. It does remind me of the Large Magellanic Cloud.


    * the notable exceptions to this long timescale re stars being novae, supernovae and stellar variables.

  15. Ah Wikipedia – M82 link via my name here -aka tge cigar galxy companion to the spiral M81.

  16. That’s

    -a.k.a. the cigar galaxy, companion to the spiral M81.

    of course.

    Editing capability .. *sigh*

    Now click on my name in this post for Wikipedia article on ‘star formation’ – there are also lots of links off there for everyone who may be interested.

    Oh & I checked & it is indeed T-Tauri itself that boasts Hind’s Variable Nebula. I also recall reading in ‘Constellations’ (Motz & Nathanson, 1991, Page 147) that an infra-red object possibly even of planetary mass named TIRC – T-Tauri Infrared Companion had been discovered around the star. Motz & Nathanson wrote that “within the next ten years” TIRC’s identity should be established. That was 1991, we’re now in 2009 so .. anyone know what happened there?

  17. DrFlimmer


    Awesome masters thesis your friend is working on – lucky bloke!

    Yes, indeed. If I were on the “experimental” side, I would have been so lucky as well. But I like playing around with equations and thus turned to the “theoretical” side. My masters thesis will be about Synchrotron-Self cooling of electrons. Yes, that sounds rather boring 😉 but “applications” are jets of AGN and such things – a topic I find VERY interesting. :)

    But, I’m sorry. I don’t know anything to help you with your questions, although they are quite interesting…

  18. David Martin Degner

    Where do the atoms, presumably H, that form stars come form?

  19. DrFlimmer

    @ David Martin Degner

    Every single hydrogen atom was created in the Big Bang.
    In the beginning there was only energy, but with the expansion came the cooling and finally elementary particles condensed and over time they happened to form hydrogen and in smaller amounts helium and a little bit of lithium.
    And then there was darkness – but that’s a different story…

  20. Flying sardines

    @ Dr Flimmer :

    “.. but “applications” are jets of AGN and such things – a topic I find VERY interesting.”

    Wouldn’t you need rather a *l-a-r-g-e experimental laboratory to create an artificial Active Galactic Nucleus with its light years long jets, supermassive black hole & all? 😉

    Wait till the mob who shudder at the LHC hear about you experimenting on that scale! 😉

  21. DrFlimmer

    Since I am a theoretician I don’t have to build such a tremendous experiment 😀 Too bad!

  22. Dan Roy

    Thanks Chris, Larian, Dr. Flimmer and Spectroscope for excellent answers.


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