October 9 – Supernova!

nPosted October 9, 2017

Key points

nThe largest explosions that take place in space are supernovas (also spelled supernovae).

nThese are not common events. Even though there are about 100 BILLION stars in the Milky Way Galaxy, a supernova occurs only once every 50 years or so.

nThere are two reasons for this. First, most stars are pretty long lived – they last (by continuously fusing hydrogen) for a few million years to 10 billion years. Second – even more important! – less than one percent of stars become supernovas!!

Would it surprise you to know that a star explodes into a supernova about once every second? I know you’re thinking, “Wait! I thought she said once every 50 years! Now she’s saying once a second?”

Well, the first number (once every 50 years, approximately) is for our galaxy alone. But there are a LOT of galaxies – probably about 100 billion galaxies in the observable universe!

nSo there are probably around 1,000,000,000,000,000,000,000,000 stars in the observable universe! One percent of such a huge number is still huge:

n10,000,000,000,000,000,000,000

nNo wonder supernovas occur every second!

This is a color-enhanced photo
of the remnant left over from the
1604 supernova.

nWhy are we talking about such far-away events TODAY? Well, October 9, 1604, was the date of the first appearance of the most recent Milky Way supernova that people could see “with the naked eye.”

nThis stellar eruption appeared in our skies in the constellation Ophiuchus, and it occurred in space only about 20,000 light years away from Earth.

nSuch a big explosion so nearby meant that this star became the brightest star in the night sky and was even visible during the day, for more than three weeks!

nAn Italian scholar was the first person to record his observation of the star. His name was Lodovico delle Colombe. The supernova was also recorded by Chinese and Korean astronomers / observers.

nAbout 8 days after the supernova was first spotted, the German astronomer Johannes Kepler began to observe it. He tracked the star for more than a year, and he wrote a book about it. The supernova is often referred to by its date, Supernova 1604, but it is also known as Kepler’s Supernova, Kepler’s Nova, or even Kepler’s Star.

nBy the way, although this supernova is the last one we are certain was in our galaxy that could be seen with the naked eye, we have been able to see supernovas in other nearby galaxies! (And when I say “nearby” – I mean near compared to most other galaxies! Trust me, these astronomical distances are mind-bogglingly far!)

nOne supernova that occurred during my lifetime is Supernova 1987A. It appeared in the Large Magellanic Cloud and was “easily visible” to the naked eye.

nBut the LMC is not visible from where I live in the Northern Hemisphere. Even worse, I live in Southern California, where the cities have conglomerated together into one big mega-city, and where the night sky is pretty darned polluted with light!

nThere aren’t very many galaxies visible to the naked eye, but supernovas are such HUGE explosions, they can outshine their entire galaxy for a short time. A supernova explosion can radiate more energy than our Sun will in its entire 10-billion-year lifetime.

nCrucially, supernovas are the main way in which heavy elements are created and spread out through the universe. If there were no supernovas, there would be no me to type these words, there would be no computer for me to type on, and there would be no you to read them!