Have any stars died during my lifetime that I could see ‘burn out’ in the sky?

Short answer: Yes, but I suppose it depends how old you are.

Long answer: Normal main sequence stars, similar to our sun, tend to ‘burn out’ in one of two ways, depending on their mass. Stars that are less massive than 8x the sun will burn hydrogen for several billion years, before swelling into a giant phase. As a giant, it sheds much of its outer envelope of gas, producing a spectacular nebula.

 

By NASA/JPL-Caltech/ J. Hora (Harvard-Smithsonian CfA) [Public domain], via Wikimedia Commons

When I woke up this morning I didn’t actually expect the universe to stare into my soul, but here we are.

That’s the Helix Nebula up there. It’s one of my favorites, and it’s a cloud that was produced when that little dot in the middle pooped off its outer layers. What’s left is doomed to become a white dwarf, which is a ball of matter close to the mass of the sun but about the size of the earth. No longer sustaining fusion to keep themselves hot and active, they spend the rest of time contracting and cooling, which is a multi-billion year process. Since the timescale for this part of the evolution is quite long compared to the lifespan of a human on earth, I don’t think it’s fair to say that it died during your lifetime, but rather that it was dying during your lifetime.

On the other hand, stars more than about 8x the mass of the sun tend to die in core collapse supernova. They look similar to planetary nebula. This, for example, is the Crab Nebula

By NASA, ESA, J. Hester and A. Loll (Arizona State University) (HubbleSite: gallery, release.) [Public domain], via Wikimedia Commons

A better name for it would be the “It looks nothing like a crab” Nebula

It exploded in 1054 and was observed by Chinese astronomers. It was visible for a few months and it would have been the brightest thing in the night sky except for the moon. In fact, the Chinese called it a “guest star” because it appeared where none was seen before, and it was so bright it was even been visible during the day for about one month. Indeed, if there was a supernova close enough to the earth, you could expect to cast two shadows during the day.

When a supernova goes off it’s generally over in seconds, so I think it’s fair to say that a star can die by a supernova during your lifetime, and astronomers observe plenty of them a year with telescopes. In fact, the average galaxy has about 1 supernova per century, and with about 100 billion to 1 trillion galaxies in the observable universe, that means a supernova goes off almost every 30 milliseconds! Of course, most of them are too far away to be visible with the naked eye, but once in a while we get lucky and see them in our neighborhood of the Milky Way, like the Crab in 1054.

So if you were lucky enough to be alive in 1987, you could have observed a supernova in the Large Magellanic Cloud, which is a nearby satellite galaxy to the Milky Way. That supernova is called SN1987A, and is one of our best data points for how supernova go off, and for how neutrinos behave. It was visible to the naked eye, just like SN 1054 observed by the Chinese, and would have similarly grown in brightness for a short time before fading from view. Although even if you were around in 1987 you might have missed it – the Large Magellanic Cloud is only visible from the southern hemisphere.

I wasn’t around to see this one, but I’ve been hoping for a galactic supernova during my lifetime. They’re great objects for doing physics- they’re the only known system where all four fundamental forces play a comparably important role in the evolution. Unfortunately, no matter how important it might be for physics, we can’t seem to convince the funding agencies to give us one.

 

 


 

 

asked by /u/Anivair
image credit: Wikimedia Commons

 


 

 

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