The Sciences

Hubble’s 17th: Chaos, birth, and near-death

Bad AstronomyBy Phil PlaitApr 24, 2007 3:32 PM


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Update (April 26, 2007): I somehow missed the fact that the release of this image is also available at the Space Telescope Science Institute itself. Duh! Sorry about the oversight.

Today is the 17th anniversary of Hubble's launch on April 24, 1990. Oh, I remember it. There has been so much knowledge gained since then, and so much of it due to that observatory! And it's changed the way the public looks at astronomy, too. I remember when Hubble was the butt of jokes from magazines to late-night talk shows -- it was a colossally expensive endeavor, and it was launched with a flawed mirror. We've come a long way.

To celebrate 6209 days in space, the European arm of the Hubble science community has released the extraordinary image above. It's of the Carina nebula, a vast complex of gas, dust, stars, forces, and energy sitting 7500 light years away. The image is a mosaic of 50 frames from the Advanced Camera for Surveys onboard Hubble. It shows a region only 50 light years wide... and yet there is so much to see! That picture I posted above does not do the original justice at all. I've extracted some highlights below, but you should really do yourself a favor and grab the high-res version of the image and scan across it. If your machine can hack it, try the 200 Mb version. If you happen to have a Cray lying around, then why waste your time with the kid's stuff? Grab the 500 Mb image! Or, better, you can take a look at a copy safely stored on a computer in Europe, and zoom, pan, and scan to your heart's delight.

Honestly, 7500 light years distant isn't enough buffer for my taste. Sitting inside that nebula are a dozen stars with more than 50 times the Sun's mass, stars guaranteed to explode some day as titanic supernovae. One star, Eta Carinae, is in its death throes, violently expelling gas in eruptive events that are only a hair's breadth shy of a supernova themselves. The last such, in 1843, expelled two vast lobes of gas -- seen in the image above as an elongation in the gas surrounding the star -- brightening Eta so much it became the second brightest star in the sky, and it's nearly 1000 farther away than the first brightest! While those other stars in the Carina nebula will explode in the next million years or so, Eta has far less time, maybe thousands of years... or it may blow tonight. We don't know. It's far enough away that it poses no immediate threat to us, but when it does go, it'll be one of the brightest objects in the sky once again.

Despite the brutal and violent forces tossed around inside the nebula, there are also regions of ethereal and delicate beauty. As gas from a star or a cluster of stars expands, it rams the other gas around it, forming a shock wave. Like the water displaced by the front of a moving boat, the gas shock forms a bow shape. In this case, it's difficult to tell from where the gas is coming. I see no star at the focus of the arc, no tell-tale signs of a source. Maybe it's from a long-dead supernova, the original star having torn itself literally to shreds. All that's left is this ghostly wave of gas, slowly mingling with and mixing into the nebula itself. As it compresses the surrounding gas, it may cause the nebula to collapse locally, forming more stars, and setting the cycle going once again.

There's plenty of evidence that's still going on in the Carina nebula. This part of the image shows a dense cluster of newborn stars, shining like beacons amidst the strewn gas and dust. These are most likely young stars, fiercely hot, and like many of their brethren in the nebula, doomed to explode someday. The smudges you see are not image defects: those are extremely dense globules of dust and gas. These are star forming factories in miniature: maybe only a few stars are forming in its core. Maybe only one. It looks like its sitting right in the cluster, but it may be many light years in front of or behind it: one of the maddening aspects of image analysis is the lack of depth. I doubt it's in the cluster; the violent winds and flood of ultraviolet light would make quick work of such a delicate cocoon. How do I know? Well, look at this:

This may be my favorite part of this huge image. This is a relatively dense section of the nebula, located above and to the right of the star cluster. See how there appear to be lower-left to upper-right series of alignments in it? Those all point more or less toward the cluster. This knot of gas is definitely being modified by the powerful winds and light from those nascent stars. If you look at a higher resolution image you can see shocks and rammed gas, and outflow all pouring off the dense knots like a snowball being blasted by a blowtorch. This clump of matter may not last more than a few thousand years before being literally blown away by that cluster. What a place, the Carina nebula! Hundreds of light years across; hundreds of thousands of solar masses of material; stars of all sizes, masses, temperatures, and brightnesses forming; gas and dust blown into all manners of shapes; stars dying, caught in the act. It's construction and deconstruction on a mind-numbing scale, and it's all laid out for us to see, thanks to telescopes like Hubble and others on the ground and in space. In 17 years, Hubble has taken a half million images of 25,000 astronomical objects, producing 30 terabytes of data in the process. If everything goes as planned, NASA will service this magnificent instrument yet again in 2008, and it will have many more years of service. What other images will it take, inviting us to peer farther into the Universe and add even more to our already considerable knowledge? Or will the Universe itself have something to say about our hubris?

I don't believe in signs... but I do believe in humor, and if the Universe has a sense of one, it has a funny way of showing it. But you can find everything in that nebula. Even an attitude.

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