Once Upon a Time…

Once Upon a Time…

Once Upon a Time…

Bad Astronomy
The entire universe in blog form
Nov. 15 2005 10:43 PM

Once Upon a Time…

I have a nursery tale to tell you. It's about newborn babies, gassy babies, babies getting so heated they destroy their nursery. But it has a happy ending.

Our story begins like so many children's tales: with a picture.

NGC 1333 in the Infrared
The chaotic glory of NGC 1333. Click to embiggen.

Photo by NASA/JPL-Caltech/R. A. Gutermuth (Harvard-Smithsonian CfA)

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OK, first, wow. That's a very pretty picture (click it for access to a vastly bigger copy). But what is it?

It won't really help you much if I tell you that it's named NGC 1333 (the 1333rd object in the New General Catalog of celestial objects, which was published in 1877, making it not terribly new anymore), but it might help more if I say that it's a region of gas, dust, and hot young stars (that phrase should up my Google ranking!) in the constellation of Perseus. It's about 1000 light years away, give or take. I've seen many images of it, but none quite like this. Why not? Because this one is in infrared.

Regular readers (both those who eat their bran and otherwise) know that looking in the infrared can tell you a lot more about an object than visible light alone can. In this case, infrared light is useful because it can travel through dust that would otherwise block the visible light. NGC 1333 is a beautiful object in visible light, but there doesn't appear to be many stars in it. If you look in the IR, though, the stars jump right out as they do in the Spitzer picture.

The very cool science thing about this is you can, using IR, sweep aside the curtain of dust veiling our view and peer deep into the heart of the dust complex (to mix a metaphor). It's been long known that stars are born in such clouds, but here we see clear evidence for it. Well, I do, at least, but I'm kinda used to looking at things like this. So let's take a closer look.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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A star is formed when a cloud of gas and dust collapses. Maybe it smacked into another cloud, or maybe a nearby star blew up and the blast wave slammed into the cloud. No one is quite sure what triggers cloud collapse, or at least what proportion of collapse is caused by what event. But either way, when the cloud starts to compress, it gets denser and heats up. The core gets pretty warm, and emits IR light. This leaks out of the cloud, so we expect star-forming clouds to pour out IR light. IR is invisible to "regular" telescopes; it takes an IR detector to see it, like the kind Spitzer has onboard. When Spitzer looks at NGC 1333, it sees lots of infrared light, supporting the idea this is a stellar nursery.

As the cloud collapses, random swirls and eddies get amplified because angular momentum is conserved (like when a figure skater draws her arms in during a spin and her rotation increases). The material starts to spin, and as it collapses the stuff on the outer edges flattens into a disk. In the center, the gas is getting very dense and hot. Eventually it forms the star itself. Any magnetic field in the gas gets amplified as the collapse continues, too. Due to some pretty complex physics (that, to be honest, is not entirely worked out) the gas near the center can be blown out as twin beams, like a light house. This is common in young stars, and again if you look at the Spitzer image you'll see several stars with these beams, or jets, coming out. So this is further evidence we're looking at stars in the very earliest stage of life.

If you've ever played with a top, you know that it can wobble as it spins. This is called precession. It's due to a force acting on the top, like friction from the floor. The Moon has gravity which tugs on the Earth, and the Earth precesses as it spins, too. So too with baby stars: a nearby star, or a planet that formed in the disk can tug on the disk itself, causing the entire system to wobble. So you might expect to see some of the jets from the young stars to bend, just like how the water sprayed from a sprinkler looks like it's bending when, in reality, the water drops are moving straight. The source is spinning, making it just look like the stream is bending.

Well, lookie here:

NGC 1333 in the Infrared
Detail from the picture above.

Photo by NASA/JPL-Caltech/R. A. Gutermuth (Harvard-Smithsonian CfA)

That's an incredible picture-- those jets are billions of miles long, tens of billions. But again, it's pretty much what you'd expect. See how the gas at the tips of the curved arms is green? In this image, green light (which is really IR and just colored green in the picture) represents warm gas that is hitting cooler gas; in this case, warm gas in the jet hitting the colder gas surrounding the star. Again, more evidence that this is a star in the throes of birth. It's indirect evidence of a planet in there as well.

NGC 1333 is gorgeous, but it won't always be. Eventually, as do we all, those stars will age, and reach maturity. Their solar winds will blow away the surrounding gas and dust, leaving behind a cluster of young stars, maybe like the Pleaides. Eventually that too will disburse, and the stars will roam the Galaxy alone. Some may travel in pairs, though. Hmmm... this anthropomorphism goes a long way.

I've said it many times, and I'll say it many times again: one of the reasons I love astronomy is not just because of the beautiful pictures, but because those pictures have such a deep and enthralling story to tell. And it's a story, a novel, whose plot hangs together, with no plotholes, no deux ex machina, no bad dialog, and no Hollywood ending. We understand so much of the Universe, and there is so much left to learn! That's why we'll keep on building telescopes like Hubble, and Spitzer, and Chandra, because so much of the book is still left to be read.