Alien residents of any planets circling the bright, visible star Rho Cassiopeiae had better pack their bags. An international team of astronomers using the Utrecht Echelle Spectrograph on the William Herschel Telescope has identified Rho Cassiopeiae as the best candidate to undergo a supernova explosion in the near future. Observations between 1993 and 2002 show the star’s temperature to have dropped from 7000 degrees to only 4000 degrees in less than a decade. Similar but less precisely measured periods of coolings have been observed in 1893 and 1945 as well. The conclusion is inescapable – like a sputtering car chugging to a stop on the side of the road, Rho Cassiopeiae is running out of the (nuclear) fuel needed to keep its (fusion) engine going. The end could come at any time – but then what?
Stars are an exquisite, delicate balance between gravity (which pulls inward, trying to crush the star) and heat (which pushes outward, trying to explode the star). When a star finally runs out of hydrogen gas fuel, the heat suddenly stops but the gravity relentlessly continues. The exploding force of heat vanishes and the crushing force of gravity suddenly takes over as the sole master of a star’s fate. In a gut-wrenching plunge far more dizzying than any roller-coaster drop, the star implodes inward, becoming much smaller and much more dense. If the ashes from its billions of years of burning are just the right mix and amount, an amazing thing can happen. At a level of compression incomprehensible to mere humans, those ashes can themselves become a nuclear fuel in a new reaction far more powerful than even the normal stellar energy of hydrogen fusion. The star is said to become a supernova with such a titanic level of energy output that it becomes visible not only throughout our galaxy but in other galaxies halfway across the universe as well. And in this malestrom of nuclear fury a true miracle occurs. The ashes of the now-consumed star – light gases like helium – are joined together in new ways to create carbon, and oxygen, and nitrogen and all the other elements up to iron. There is no other known source in the universe where this process occurs. The very stuff of life and the metals for civilization are born in dying stars like the one Rho Cassiopeiae is destined to become at any time.
And after – or instead of – a supernova? That way lies the birth of neutron stars and black holes and even stranger things – another story for another day.