
As far as raw explosive power goes, no other cataclysm in the Universe is both as common and as destructive as a core-collapse supernova. In one brief event lasting only seconds, a runaway reaction causes a star to give off as much energy as our Sun will emit over its entire 10-12 billion year lifetime. While many supernovae have been observed both historically and since the invention of the telescope, humanity has never witnessed one up close.
Recently, the nearby red supergiant star, Betelgeuse, has started exhibiting interesting signs of dimming, leading some to suspect that it might be on the verge of going supernova. While our Sun isn’t massive enough to experience that same fate, it’s a fun and macabre thought experiment to imagine what would happen if it did. Yes, we’d all die in short order, but not from either the blast wave or from radiation. Instead, the neutrinos would get us first. Here’s how.
![An animation sequence of the 17th century supernova in the constellation of Cassiopeia. This... [+] explosion, despite occurring in the Milky Way and about 60-70 years after 1604, could not be seen with the naked eye due to the intervening dust. Surrounding material plus continued emission of EM radiation both play a role in the remnant's continued illumination. A supernova is the typical fate for a star greater than about 10 solar masses, although there are some exceptions.](https://i0.wp.com/onlinemarketingscoops.com/wp-content/uploads/2019/12/https3A2F2Fblogs-images.forbes.com2Fstartswithabang2Ffiles2F20162F122F12184961_1211042665579032_2558520137167044102_o-1200x621-1.jpg?resize=763%2C395&ssl=1)
An animation sequence of the 17th century supernova in the constellation of Cassiopeia. This… [+]
NASA, ESA, and the Hubble Heritage STScI/AURA)-ESA/Hubble Collaboration. Acknowledgement: Robert A. Fesen (Dartmouth College, USA) and James Long (ESA/Hubble)
A supernova — specifically, a core-collapse supernova — can only occur when a star many times more massive than our Sun runs out of nuclear fuel to burn in its core. All stars start off doing what our Sun does: fusing the most common element in the Universe, hydrogen, into helium through a series of chain reactions. During this part of a star’s life, it’s the radiation pressure from these nuclear fusion reactions that prevent the star’s interior from collapsing due to the enormous force of gravitation.
So what happens, then, when the star burns through all the hydrogen in its core? The radiation pressure drops and gravity starts to win in this titanic struggle, causing the core to contract. As it contracts, it heats up, and if the temperature can pass a certain critical threshold, the star will start fusing the next-lightest element in line, helium, to produce carbon.
![This cutaway showcases the various regions of the surface and interior of the Sun, including the... [+] core, which is where nuclear fusion occurs. As time goes on, the helium-containing region in the core expands and the maximum temperature increases, causing the Sun's energy output to increase. When our Sun runs out of hydrogen fuel in the core, it will contract and heat up to a sufficient degree that helium fusion can begin.](https://i0.wp.com/onlinemarketingscoops.com/wp-content/uploads/2019/12/https3A2F2Fblogs-images.forbes.com2Fstartswithabang2Ffiles2F20172F092FSun_poster.svg_.jpg?resize=840%2C420&ssl=1)
This cutaway showcases the various regions of the surface and interior of the Sun, including the… [+]
Wikimedia Commons user Kelvinsong
This will occur in our own Sun some 5-to-7 billion years in the future, causing it to swell into a red giant. Our parent star will expand so much that Mercury, Venus, and possibly even Earth will be engulfed, but let’s instead imagine that we come up some clever plan to migrate our planet to a safe orbit, while mitigating the increased luminosity to prevent our planet from getting fried. This helium burning will last for hundreds of millions of years before our Sun runs out of helium and the core contracts and heats up once again.
For our Sun, that’s the end of the line, as we don’t have enough mass to move to the next stage and begin carbon fusion. In a star far more massive than our Sun, however, hydrogen-burning only takes millions of years to complete, and the helium-burning phase lasts merely hundreds of thousands of years. After that, the core’s contraction will enable carbon fusion to proceed, and things will move very quickly after that.
![As it nears the end of its evolution, heavy elements produced by nuclear fusion inside the star are... [+] concentrated toward the center of the star. When the star explodes, the vast majority of the outer layers absorb neutrons rapidly, climbing the periodic table, and also get expelled back into the Universe where they participate in the next generation of star and planet formation.](https://i0.wp.com/onlinemarketingscoops.com/wp-content/uploads/2019/12/https3A2F2Fblogs-images.forbes.com2Fstartswithabang2Ffiles2F20172F122Fcasa_life_presupernova.jpg?resize=840%2C818&ssl=1)
As it nears the end of its evolution, heavy elements produced by nuclear fusion inside the star are… [+]
NASA / CXC / S. Lee
Carbon fusion can produce elements such as oxygen, neon, and magnesium, but only takes hundreds of years to complete. When carbon becomes scarce in the core, it again contracts and heats up, leading to neon fusion (which lasts about a year), followed by oxygen fusion (lasting for a few months), and then silicon fusion (which lasts less than a day). In that final phase of silicon-burning, core temperatures can reach ~3 billion K, some 200 times the hottest temperatures currently found at the center of the Sun.
And then the critical moment occurs: the core runs out of silicon. Again, the pressure drops, but this time there’s nowhere to go. The elements that are produced from silicon fusion — elements like cobalt, nickel and iron — are more stable than the heavier elements that they’d conceivably fuse into. Instead, nothing there is capable of resisting gravitational collapse, and the core implodes.
![Artist's illustration (left) of the interior of a massive star in the final stages, pre-supernova,... [+] of silicon-burning. (Silicon-burning is where iron, nickel, and cobalt form in the core.) A Chandra image (right) of the Cassiopeia A supernova remnant today shows elements like Iron (in blue), sulphur (green), and magnesium (red). We do not know whether all core-collapse supernovae follow the same pathway or not.](https://i0.wp.com/onlinemarketingscoops.com/wp-content/uploads/2019/12/https3A2F2Fblogs-images.forbes.com2Fstartswithabang2Ffiles2F20172F082Fcasa_lg-1200x576-1.jpg?resize=757%2C364&ssl=1)
Artist’s illustration (left) of the interior of a massive star in the final stages, pre-supernova,… [+]
NASA/CXC/M.Weiss; X-ray: NASA/CXC/GSFC/U.Hwang & J.Laming