A Cosmic Tadpole … in More Ways Than One

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Jun 9, 2014
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Star birth is a difficult process. It’s hard enough in the best of times to get a few octillion tons of gas and dust to collapse and form stars; you need all kinds of special circumstances to make it work. The good news is there’s so much of that stuff in space that star birth is relatively common in our galaxy.

But the Universe can make it harder … like, say, if you happen to be a gas cloud floating a few light years from a bustling cluster of hot, young, massive stars. Such is the fate that has befallen the little gas cloud called IRAS 40324+4057, nicknamed The Tadpole, for obvious reasons.

That image (using observations from Hubble as well as the Isaac Newton Telescope in the Canary Islands) shows just how bad things can be. The cloud itself is the bright fuzzy knot of material (colored orange-ish) you see on the right. It’s surrounded by a larger head, and then has a tail streaming away to the left (both in blue).

The evolution of the Tadpole is being profoundly altered by a nearby cluster of hot stars. The stars blast out a huge amount of ultraviolet light, which zaps the Tadpole, lighting it up. That’s what’s causing the bright ridge along the top of the cloud. Not only that, the light is bright enough that it’s photoevaporating the material, literally dissolving it, eating it away. This material expands around the forming stars in the Tadpole and forms the bigger, fuzzier head.

But wait a second. The star cluster is above and to the right of the Tadpole. Why isn’t the tail pointing away from it, down and to left? Instead, it points straight to the left!

That had me confused for a moment, but then I figured there must be something off to the right that isn’t obvious. Happily I was able to find a journal paper on the Tadpole, and the authors concur: There is most likely a wind of material being blown from stars off to the right that is creating the tail. That explains the ripples in the tail too—that’s called a Kelvin-Helmholtz instability, which happens when one fluid moves past another; it’s what causes waves in water and ripply clouds.

What a mess! Those stars in the Tadpole deserve to be left alone to form in peace, but instead their cocoon is being evaporated by one clump of stars nearby, and then that material blown away from a second group of stars. That’s a rough neighborhood.

But it’s a pretty one. The Tadpole is part of the much, much larger Cygnus Molecular cloud, which is so big the Tadpole gets totally lost in it:

In that image, the Tadpole is barely a pixel across; here’s a guide to finding it. I’ll note this is only one part of the ridiculously huge cloud; the whole thing is hundreds of light years across, and is home to some of the largest and most brilliant stars in our galaxy. But the thick dust choking the region hides them from us, making it a very difficult volume of space to study.

The Tadpole is lovely, of course, and a fascinating object. But I also like the poetic imagery: It’s a place which is transforming itself from a cloud into stars…and the metaphor to a tadpole is pretty obvious. Nicely played, Universe.