The Death of a Star - As beautiful a Star can be!

Stars are beautiful. But their explosions are even more beautiful. And the remnants of that, further more beautiful. Beautiful, beautifuller, beautifullest!

When a massive star collapses, it implodes. That's its death. A core collapse supernova. These explosions are extremely luminous and can outshine an entire galaxy. But long after this catastrophic death, the legacy of the star continues. The remnants of these explosions can be seen for another tens of thousands of years; telling the lore of the star to the generations yet to live. Shaping the rest of the universe, by cosmic rays, shocks and radiations. Research proves that even distant explosions have influenced the atmosphere on Earth (see article). 

What if the star wasn't massive? Then they end up as White Dwarfs. But these White Dwarfs may accrete more mass to it from its companion, and thus explode due to 'over-mass'.  This detonation is a Type Ia supernova. 

These explosions enrich the universe with light and heavy elements. In a star, fusion happens only until Iron. Any element heavier than Iron requires more input energy than output. But, the energy of a supernova explosion is so huge that this energy can synthesise further elements like Gold and Uranium. This process is the rapid neutron capture process, or in short, the r-process. Recent observations suggest that this is only one of the processes, and that there are more dominant processes for this synthesis.

The Beautiful Afterlife

After the glory and shine of the explosion, everything fades. But the beauty prevails. The gas expands, shocks propagate, and its so hot. This supernova remnant will remain here for quite long. 

At first it expands freely. And then it starts sweeping in matter from the interstellar medium as it expands. As it sweeps in gas and dust, we see structures form. And then it cools, radiating its energy away. Slowly, after a few tens of thousands of years, this too fades off, blending into the interstellar medium; merging off into a no-one after giving off its entirety into shaping the environment.

The Affair with Clouds

Suppose you see a supernova remnant so close to a molecular cloud - this is a common sight for a core-collapse supernovae. But, what are they doing? Are they interacting?  Ask a scientist and you will get a list of things to check, including shock signatures, broad absorption features, shock excited lines etc. Let me bring your attention to cosmic rays. These are particles accelerated as they cross the shock waves in clouds. Scientists call this diffusive shock acceleration. So if you see a molecular cloud and a supernova remnant close-by and want to investigate if they are interacting, look at the "smoking gun" - look if there are particles accelerated from this region. But detecting such high energies with good resolution is not easy. What is easier than this is radio observation. Which is, in contrast, on the low energy end. But, how can we see this in the radio wavelengths?

The 1720 MHz line of the hydroxyl molecule (OH). These emission features are the masers from the collisionally excited gas. And, how can the gas be collisionally excited here? Well, when a supernova shock passes through. 

The Growth with Siblings

Multiple supernova explosions can form a cavity in the medium, carved by their shocks combined. Such bubbles are expected from regions of active star formation where the shocks of different supernovae overlap in course of time. We are also in a superbubble - an old superbubble, whom we call, for obvious reasons, the local bubble.