The beating heart of W5

The beating heart of W5

The beating heart of W5

Bad Astronomy
The entire universe in blog form
Aug. 22 2008 12:00 PM

The beating heart of W5

Spizter image of nebula W5

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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(Click to hugely embiggen)

W5 is a nebula, a giant cloud of gas roughly 6000 light years away in the constellation of Cassiopeia. It's enormous, spanning about 2 x 1.5 degrees of the sky (15 times the size of the full Moon on the sky), and is actively cranking out stars. The valentine-shape is actually an enormous cavern, a hollow carved out of the gas by the winds and fierce ultraviolet light flooding out from massive young stars in its... well, its heart. It's like these stars are blowing a vast bubble in the middle of the cloud.

The stars doing the work can be seen in the image; the bright blue ones are the culprits. Mind you, this is an infrared false-color image; blue is not really blue, it's actually light at 3.6 microns, more than four times the wavelength of visible light.

There's another way to find those stars: look at the edges of the bubble. See the triangular or finger-like extensions of material pointing into the bubble? Those are light years-long towers of gas being eaten away by the winds and UV light from the hot massive stars, so the fingers point right to those stars. Sometimes nature is kind to us, and literally points the way.

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There are stars in those towers, less massive stars (in this case, more like the Sun) being formed even as we watch. In fact, that's what makes this image so exciting scientifically (aside from its sheer awesome beauty); it appears that we're seeing triggered star formation. It's not perfectly clear yet just how massive clouds collapse to form stars. Sometimes it's from cloud collisions -- cosmic fender-benders or even head-on ramming that crunch up the clouds, triggering collapse and star formation. Sometimes it might be from nearby supernovae compressing the material. Or maybe it's from massive stars forming and then blowing bubbles in the cloud itself. That last one is the tricky bit. See how the material appears to be brighter along the edge of the bubble? That's due to compression from the more massive stars' sculpturing -- compressed material tends to glow brighter.

If that's true, we're seeing the first generation of stars born in that cloud directly causing the birth of the second. From studying the light from these stars, astronomers have found that the ages of the stars get younger as you move out from the middle, supporting the idea that the massive stars in the center (which form rapidly) are aiding star formation in the outer regions. As their winds and light move outward, they leave behind a wake of stellar birth.

I have spent the past year researching all the ways the Earth can end from cosmic catastrophes for my book, Death from the Skies! Being near a young, massive star is a good way to do this: they flood out fierce light while they are alive, and they tend to explode when they die. But here we see the exact opposite: these stars are the Johnny Appleseeds of the Universe, the lifegivers, sowing the galaxy with the conditions needed for more stars to form.

In the real world, life and death are inexorably intertwined, sometimes so tightly bound that they are nearly indistinguishable. And here we see it on a scale hundred of trillions of kilometers across, so large it appears majestic and calm, yet so finely detailed we can study the processes at work and learn how the basic building blocks of the Universe came to be.

Image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA