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SYFY WIRE Bad Astronomy

The Tarantula Nebula is very, very big

By Phil Plait
vlt_tarantula_heroThe hugely sprawling Tarantula Nebula, a vast star-forming complex in a nearby satellite galaxy of the Milky Way. Credit: ESO

If you leave our Milky Way galaxy and back away from it — and even at the speed of light this will take, oh, two or three hundred thousand years, so pack a lunch — you’ll see we’re surrounded by dozens of much smaller galaxies. Two stand out, though: the Large and Small Magellanic Clouds, the biggest of the bunch, though still tiny compared to the mighty Milky Way.

The LMC (as those of us in the know call the bigger one) lies about 160,000 light-years from Earth, and is a smeared-out splotch of stars that nearly, but not quite, has a discernible shape. It’s classified as an irregular galaxy, though some astronomers argue it may be a nascent spiral.

Despite its relatively small stature, the LMC hosts what may be the single biggest star-forming nebula in the entire Local Group of 50 or so galaxies. It’s so big and has so many substructures that it goes by a host of names, but most astronomers know it as the Tarantula Nebula.

It’s so big and sprawling that words fall short of describing it in any way it deserves. The main nebula is something like 300 light-years across — compare that to the famous Orion Nebula, which is “only” a dozen or so light-years in size. At its heart is a cluster so massive — it contains stars that add up to half a million times the mass of the Sun — that they may actually be forming a globular cluster!

I could go on and on, but of course a picture is worth 1 kilowords. So here, gaze upon this, and have your sense of scale crushed into dust:

vlt_taThe hugely sprawling Tarantula Nebula, a vast star-forming complex in a nearby satellite galaxy of the Milky Way. Credit: ESOrantula_2500

OK, now let’s talk about this for a sec. This image was taken by the Omegacam on the VLT Survey Telescope (or VST; the VLT stands for Very Large Telescope, making for a confusingly redundant nested acronym). OmegaCam is a 256 megapixel detector (!!), and the telescope is a 2.6 meter beast, the largest telescope currently existing on Earth dedicated to doing surveys of the sky (as opposed to pointing at specific targets).

What you see here is nowhere near the full resolution image available; I had to download a smaller version (a mere 4,000 x 4,000 10 Mb version), and even then I had to crop it and save it at lower res to make sure the servers didn’t gag on it (I also rotated it 90° clockwise for aesthetic reasons).

If you want the full res version, you can get it here. Mind you, it’s 16,655 x 16,719 pixels and tips the scale at 157 Mb!

The Tarantula part of the nebula is the roundish region to the right. Here it is at higher resolution (though I still had to shrink it by 30% or so to get everything in it to fit here):

Detail of the Tarantula Nebula showing newly formed massive stars blasting away. Credit: ESO

The bright clutch of stars to the right is R136, that phenomenal cluster I mentioned above. You can see how chaotic this entire region is. Any civilization evolving on a planet anywhere near there will have a substantially different view of the cosmos than we do.

I wonder what their mythology would be like?

You can read more about this nebula at the European Southern Observatory site, or in any of the numerous articles I’ve written about the Tarantula. But there’s something else I want to point out in this image.

Let your eyes just wander over it, looking at medium scale features, not the smaller stuff. If you do this, you’ll notice there are a lot of loops and arcs of gas in it. And wherever you see these, you’ll notice a cluster of stars at its center. Here’s one for you:

Detail of the Tarantula Nebula of a cluster of stars plowing up gas around them into a thin shell. Credit: ESO

This is a small part of the big image (taken from just above and to the right of center). It’s pretty obvious here! The gas forms a complete circle around a decent collection of bright stars.

That’s no coincidence. When stars form en masse in a nebula, especially by the thousands, a few of them are going to be massive. When they turn on after they form, becoming true stars, they blast out a ridiculously fierce wave of both light and wind (like the solar wind, composed of subatomic particles, but far, far stronger). These carve out a cavity in the gas around them, and also push the gas like a snowplow driving through snow. The effect is roughly symmetric around the cluster, so you get a spherical shell of gas around it. When we view it off to the side, we see it as a thin circle of light, like a soap bubble.

And they’re all over this image! That’s a clear sign of ongoing star birth in the nebula. And that’s why it’s so bright; those hot, luminous stars light up the nebula, zapping it with ultraviolet light and causing it to glow. It’s a cosmic birth announcement, written across a card more than three quadrillion kilometers end to end.

Sometimes astronomy is subtle, with faint, small, distant objects barely detectable against the darkness of eternal night, a puzzle that hints at the science and grandeur behind it.

And sometimes it’s a sledgehammer pounding your eyes and brain with ostentationess and zest. I’m good with that too.