Dr. Christopher Kochanek, Ohio State University – Visible Supernovae

Dec 26, 2013

In today’s Academic Minute, Dr. Christopher Kochanek of Ohio State University calculates the odds of a visible supernova occurring in the coming decades.

Christopher Kochanek is a professor of astronomy at Ohio State and the Ohio Eminent Scholar in Observational Cosmology. His research interests include cosmology and gravitational lensing. His astronomic research has been widely published and he holds a Ph.D. from the California Institute of Technology.

About Dr. Kochanek

Dr. Christopher Kochanek – Visible Supernovae

Fortunately for us, our Sun is a boring, long-lived middle weight star.  Bigger stars live faster and die younger, some even explode and for a month or so, these supernova explosions can outshine the entire galaxy of stars in which they live. 

We can see the remnants of supernovae for thousands of years as enormous clouds of hot, expanding gas.  Their numbers say that there should be a supernova in our galaxy every 50 to 100 years, but the last time anyone looked up in the sky to see one was in the year 1604.   We easily see the belt of stars that is our Milky Way galaxy, so how can we be missing explosions that are brighter than all those stars combined?

The answer lies in what astronomer's call "dust", “dust” is like the soot particles you see belching out of a diesel truck. In certain phases of their lives, stars do the same, blowing sooty particles out to pollute the gas that lies between the stars.  When we try to look through our galaxy, we have to look through all this soot, and just like that black cloud of exhaust, it obscures our view.   And this is why we can have one or two supernovae a century and yet not have seen one for four hundred years.

Our understanding of the distribution of this soot has improved considerably since the last time astronomers calculated how easily we could see a supernova in our Galaxy. In our study, we set out to update all these estimates and discuss them in the context of modern astronomical methods.

The bottom line is that everything is consistent. Our Galaxy contains so much soot, that only about one in 10 supernovae should be easily visible to the human eye, and that last supernova in 1604 was only seen by the naked eye.  The first telescope was only invented four years later in 1608. Today, with four hundred years of improvements, we find that our next supernova will be visible even to many amateur astronomers. 

We would also like to have measured the properties of the star before it exploded.  We’ve found that this can be challenging even with the world’s largest telescopes. However, infra-red light, like that used in a television remote control, passes through the soot. We find that existing surveys of our galaxy in this light already contain a picture of that next exploding star. Unfortunately, it is still a once in a lifetime experiences and so we must all still wait to find out which one.  

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.