Cowabunga and the Star of Bethlehem

After centuries of study and careful observation, we still don’t have a good understanding of what the Star of Bethlehem was.  Most astronomers would bet on a supernova which is the final explosion of a dying star, because such events are extremely bright and last from a few weeks to a month or more.  

Way back, when dinosaurs ruled the earth, between the Jurassic and Triassic eras, 200 million years ago, an unremarkable star on the outskirts of a small galaxy, collapsed.  These are the death throes of every star.  They literally run out of fuel to support continuous nuclear fusion, so the fusion reactions slow down and stop.  Then there is no outward pressure of the constant fusion explosions.  Then all that hot matter begins to collapse under its own gravitational attraction. 

It collapses so fast and so tightly that it becomes super-hot so that other types of fusion reactions can begin to ignite.  Then you get an explosion of the outermost layers.  This is the supernova shining with the brightness of five billion of our own sun.  A supernova can outshine all the stars in its own galaxy.   The observable supernova carries on from a few days to a couple of months.  Then it fades away leaving behind a “compact object” which is either a neutron star or a black hole.  In the summer of 2018, the light from the supernova AT2018cow was observed.  The name refers to the telescope of first observation (The ATLAS or Asteroid Terrestrial-impact Last Alert telescope), the year (2018) and three random letters.  In this case, the star became known as the “cow.”  At only 200 million light-years away, cow is considered to be close to us and easily observable.   While supernovae are relatively common, observing one from the runup to the explosion to its dark days, has given astronomers an unprecedented opportunity to observe this object as it forms a new, compact object which will be either a super-dense neutron star or a black hole.   There is an unappreciated violence and dangerous potential in the seemingly far-away events.  In addition to the intense light shining in all directions from a supernova, along the polar axis of rotation, a highly collimated beam (think of a laser) of hard X-rays shines out for a few days.  Any planet with life on it and unlucky enough to be in the path of that X-ray emission, up to 100 million light years away, would be instantly fried by the X-rays.  Even microscopic life deep down in the rocks and soil of the planet would not be spared.   Our life is so precious and precarious that we are connected to stars that were shining when dinosaurs walked the earth.  In many respects, we are just plain lucky to have not been in the light path of one of those cosmic deep-fryers.  Makes you want to ponder the idea of “There but for the grace of God go we.”   Or in this case, we might just say, “Holy cow.”