Wednesday, February 12, 2020

Yes, Size Does Matter

     In this case, the sizes of supergiant stars and the Milky Way Galaxy:

     Supergiant star Betelgeuse has been getting dimmer at an unprecedented pace over the past few months, leading some astronomers to wonder if it might be in the process of the collapse that precedes a supernova explosion. But there are other possible explanations, and we should have a better idea of what's happening to the massive star by the end of the month.

     Veteran Villanova University astronomer Edward Guinan has been watching Betelgeuse for decades and reported earlier this month that the star appears to be "the least luminous and coolest yet measured from our 25 years of photometry."

     It's well known Betelgeuse has no more than about 100,000 years left to burn and could start its death throes just about anytime between now and then. When it does go supernova, it's expected to result in a dramatic light show that could be visible in daylight and appear brighter than the full moon for a few weeks. The last time humans were treated to such a sight was the 17th century.

     Betelgeuse is enormous. Its diameter is very nearly the same as that of Jupiter’s orbit. As a class M star, it’s expected to have relatively few years remaining before it...does what?

     Well, it might gutter out. Or it might go supernova. Both deteriorations are possible, supported by models of stellar physics that have not yet been disproved and might never be. But those observing Betelgeuse are rooting for a supernova. Why? Because the last known supernova occurred before the development of astronomical instruments capable of appreciating the event!

     The last supernova on record was observed in 1604: Kepler’s Star, which was about 20,000 light years distant from Earth. It was very bright for a while, peaking at a visual magnitude of -2.5 and fading to invisibility only after three weeks.

     Now, you might be thinking “Bring on the fireworks!” You might be thinking that if Betelgeuse is observed to go supernova, we’ll have ourselves a few weeks’ light show, and the astrophysics community will get a chance to confirm a few things and disprove a few others, and that’s about it. But there are a few possibilities physicists dislike to discuss out loud. Some of them pertain to a supernova that occurs relatively close to Earth, which Kepler’s Star was not.

     A supernova is highly exoenergetic. Its emissions include both matter and electromagnetic radiation. The radiation covers a very wide portion of the electromagnetic spectrum. And radiation can travel a very long distance. Especially ultra-short-wavelength radiation of the sort that’s dangerous to living creatures.

     Now, I did say “a supernova that’s relatively close to Earth.” How close is that? Well, it would have to be closer than Kepler’s Star at 20,000 light years...but Betelgeuse, a supergiant star 700 light years away estimated to be about twenty times the mass of our Sun, might be close enough to qualify.

     Now, there’s no cause for alarm. I mean, no power on earth could do anything to prevent Betelgeuse from going supernova. (Don’t bother writing to your Congressman.) Besides, it’s already happened...if it happened at all.

     Light, the fastest moving phenomenon of which we know, moves at...the speed of light! And that speed light-year per year! So if astronomers in this Year of Our Lord 2020 do get to observe a supernova at Betelgeuse, it will be because it happened 700 years ago.

     What’s done, as they say, is done. No point wringing our hands about it.

     But the physics of stellar collapse is largely a matter of theory that needs confirming data. Astrophysicists think they know what happens in a nova or supernova. However, we lack enough observational data to have high confidence in the models. Moreover, some of the data we really need could only be amassed from rather close to an exploding star...a place I, for one, would not care to be.

     But there is at least one certainty available to us: a certainty that recent events have “nailed to the wall” so tightly that no one, be he astrophysicist or layman, can doubt it for a moment. Whether you regard it as an occasion for laughter or tears, it’s as certain as the Sun rising in the East. And it is only this:

     Whatever happens, the Democrats will blame Trump.

No comments: