Hot Stars Blow a Superbubble

By Phil Plait

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Posted Tuesday, Jan. 29, 2013, at 8:00 AM ET

Some stars are more carefree than others. How else would you explain a bunch of them getting together and blowing a superbubble?

Gamma rays made the Hulk a superhero, but X-rays are coming from this superbubble. Click to enroentgenate.
Image credit: X-ray: NASA/CXC/Univ of Michigan/A.E.Jaskot, Optical: NOAO/CTIO/MCELS

This is combination of an X-ray image from the Chandra X-Ray observatory and an optical image from the University of Michigan (my alma mater!) 0.9 meter telescope in Chile. What you’re seeing is N186 (also called DEM L50), a nebula about 160,000 light years away in the Small Magellanic Cloud, a companion galaxy to our Milky Way. N186 is several hundred light years across, so it’s pretty big.

Inside N186 are lots and lots of young stars. They probably formed only a few million years ago, which sounds like a lot until you remember our own Sun is middle aged at 4.5 billion years old. So these guys in N186 are whippersnappers.

A lot of those stars are probably like the Sun, with many even smaller and cooler. But a few are more massive, which makes them hotter. That means they blast out fierce winds of subatomic particles, like the solar wind but far, far stronger. These winds expand out from the stars, combining their forces and screaming into space at hundreds of kilometers per second. Surrounding the stars is the gas leftover from their own formation, and as those winds expand outward they sweep up material around them, blowing this ridiculously big superbubble. They also compress that gas, creating vast and powerful shock waves. These heat the gas inside to a temperature of a million degrees, which then glows in X-rays.

In the picture, you can see the twisted, compressed gas as a series of tangled orange filaments. See how it’s in a shell around the center? That’s the edge of the bubble, emitting visible light, the kind we see with our eyes. Inside the bubble is the superheated gas, glowing in X-rays (colored pink so you can see it). Not only that, but the pink swoosh at the top is the hot gas from a supernova, a star that exploded. It’s not clear if it’s related to N186 or just happens to be aligned with it in the sky.

Either way, it won’t be alone for long. Massive stars have an alarming tendency to explode, and there are plenty of hefty stars inside N186. Over the next few million years those things will pop off like firecrackers, their debris expanding outwards fast enough to eventually catch up with and slam into the bubble’s edge. When they do, they’ll blast the bubble from the inside out, shredding it. As the shrapnel expands it will eventually merge and mix with the gas between the stars, seeding it with the heavy elements forged in the hearts of the all those supernovae. These will eventually become the building blocks of other stars and planets.

Who knows? In a few billion years they may also become the seeds of life on those worlds. It’s weird to think that all that chaos can result in the amazing complexity and order of life, but that’s the way the Universe works.