A High Energy X-Ray Superbubble

A long, long time ago in a galaxy not that far away at all as a matter of fact, a cluster of stars formed inside a great cloud of gas and dust. Among them were giant stars whose masses may have been between 10-30 times the mass of our Sun. These behemoth stars lived fast, fusing their once hydrogen cores into heavier and heavier elements until one day they could no longer sustain themselves and they explodeed as supernovae.

Like TNT exploding in a mine, the supernovae sent out powerful shock waves that blew a giant bubble in the cloud 1,200 light-years across. Behold:

Massive stars exploded as supernovae, creating superbubbles in the surrounding gas. X-Ray (blue), Optical (yellow/green), Infrared (red) composite of N44 in the Large Magellanic Cloud. Click for the 864×690 version, or get the ridiculously  cool 3600×2874 version Credit: X-ray: NASA/CXC/U.Mich./S.Oey, IR: NASA/JPL, Optical: ESO/WFI/2.2-m

Holy Cosmic Cauldrons! This region is known as N44 and resides in the Large Magellanic Cloud, a satellite galaxy to our own Milky Way. It’s actually a composite of an image of N44 taken by the Chandra X-Ray Observatory, an optical image taken by the 2.2-meter Max-Planck-ESO telescope in Chile, and the Spitzer Space Telescope.

The colors correspond to different wavelengths imaged by the different observatories. Red stands in for infrared emission captured by Spitzer. This is cooler gas and dust and is relatively “intact” surrounding the bubble.

Yellow corresponds to imagery from the Max-Planck-ESO telescope and shows hot ionized gas. This gas is glowing from the ultraviolet radiation from hot, young stars, in much the same way that gas glows in a florescent light bulb.

Finally, we have the really high-energy stuff, the x-ray emission (shown here in blue), taken by the Chandra X-Ray Observatory. In fact, let’s take a look at just the Chandra X-Ray image:

Chandra X-Ray image of star cluster NGC 1929 inside N44.

Here’s where the story gets really interesting. For a long time, it was assumed that the bubbles were created by winds from the hot stars that eventually went supernova. That makes sense. After all, the more massive and hotter they are, the more mass they lose as stellar winds.

Well, the winds from these stars certainly did “blow” out the bubbles. However, it turns out there is a lot more x-ray radiation coming from inside the bubbles than was expected from just the winds alone.

So where is this extra x-ray radiation coming from? Dr. Anne  Jaskot from the University of Michigan and her team used Chandra to find out. It turns out that there are two extra sources of x-ray radiation: the supernova shock waves striking the walls of the cavities, and hot material evaporating from the cavity walls. In fact, if you compare the two images above, you can actually see the X-ray radiation coming off the walls of the bubbles. Cool!

In other words, the supernova explosions themselves generated a lot of high-energy x-ray radiation by slamming into the walls of the bubble making the walls so hot they give off x-rays as the shock waves passed through.

Moreover, these shockwaves, created in the supernovae of these massive stars, compressed the surrounding gas. This in turn triggered the formation of even more stars.

And there it is, the cycle of stellar life: the ashes of stars are blown along the expanding wave of a cosmic bubble, and seed the next generation of stars.

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