The Flash of a Star’s Death

The most violent single event in the universe is the death of a massive star, a supernova.  We have seen several different types, though the common element is a massive explosion, taking a star hiding amongst the background into an eruption that outshines it’s entire host galaxy.  We have seen the brightness grow and fade over the duration of a supernova event, but we have never seen one just as it’s starting.  Until now.

Explosive death of star KSN 2011d Credit: NASA, ESA, Armin Rest (STScI) and Peter Garnavich (University of Notre Dame)

Would you ever have thought that the Kepler space telescope, a planet hunter that continuously observes stars, could see supernovae?  The key is in the words ‘continuously observed.’  By keeping focused on stars likely to explode as a supernova, a team of international Astronomers has spied two stars right as they underwent the final step before a supernova explosion: core collapse.

Core collapse is the moment when a supernova becomes inevitable.  It’s when the fuel runs out and the star’s gravity overcomes it’s outward pressure, causing the core to collapse rapidly and send out a shockwave that obliterates anything in it’s path.  This is what we eventually see as a supernova.  When the shockwave first reaches the surface of the star, it produces a flash of light called a shock breakout.  When astronomers notice a new supernova in the sky, the shock breakout has already occurred and the star is exploding, but observing this key moment is considered critical to understanding the process of a supernova explosion.

By understanding that massive supergiant stars are likely to explode as supernovae in the cosmically near future, the researchers trained Kepler to 50 Trillion supergiant stars for a period of three years, hoping to see the shock breakout.  Even with a huge supply of data, it was very unlikely to catch even a single explosion, because the flash from the shock breakout lasts only about an hour.

But their efforts paid off, as two stars exploded in 2011 while researchers were watching.  They were both located in distant galaxies, and both were several hundred times the mass of the Sun.  These observations are important for our understanding of how supernovae explode.  These explosions are responsible for seeding the cosmos with the heavy elements needed for all life and everything rocky we see in the universe. None of this would exist if it weren’t for the explosion of supernovae.


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