Theres a well-known star that I am positive you have seen within the sky. Its identify is Betelgeuse, and you will discover it within the Orion constellation, the place it marks Orion’s proper shoulder. If you wish to name it “Beetlejuice,” I am high-quality with that as long as you do not say it 3 times.
However one thing is happening up there. This pink supergiant has dimmed repeatedly up to now few years, which may imply that it is able to go full supernova fairly quickly—and by “quickly” we imply inside the subsequent 10,000 years. Really, because it’s some 500 light-years away, it is potential that it already exploded and we simply do not know it but. It may present up tomorrow.
One factor’s for positive: If Betelgeuse does blow, will probably be the brightest supernova ever witnessed by people. Simply how brilliant are we speaking? Might you see it throughout the day? Wouldn’t it be harmful? I’ll present you how one can determine all this out with just a few very primary physics.
What Is a Supernova?
In most stars, the core consists of hydrogen and helium, the 2 lightest components—however solely the positively charged nuclei of these atoms, because it’s too scorching for the electrons to remain put. Below immense gravity and temperatures, these nuclei can fuse into heavier components, releasing large quantities of vitality within the course of. (This nuclear fusion is the place our solar will get its vitality.)
For a steady star like our solar, there is a stability between two opposing forces. The mass of all of the matter within the star produces a gravitational power that tends to break down the star. Nevertheless, that is countered by the outward-pushing power from the core, so the star stays pretty fixed in measurement, though it is not a stable object like a planet.
However as a star ages, it steadily makes use of up its hydrogen and helium and begins producing heavier components like carbon, oxygen, silicon, and eventually iron. And that is so far as it goes—fusing components heavier than iron takes vitality as an alternative of making it, so the star basically runs out of gasoline and collapses in on itself.
In some circumstances, this collapse may be very extreme—so extreme that it quickly will increase the strain and temperature within the core of the star. The star then goes increase. Big boom. Effectively, large silent increase, since explosions make no sound within the vacuum of area.
However this produces A LOT of sunshine vitality. For comparability, our solar has a luminosity, or power output, of 3.8 x 1026 watts. A supernova that was observed in 2015 (ASASSN-15h) had a peak luminosity of round 2 x 1038 watts. That is extra energy output than 500 billion suns. It is loopy. Oh, you did not see that one? Yeah, as a result of it was in a distinct galaxy. Betelgeuse is in our again yard, astronomically talking.
Brightness and Luminosity
A very long time in the past, a Greek thinker named Hipparchus categorized the celebs into six teams, based mostly on how brilliant they appeared within the evening sky. From that, we now have developed a classification scheme for “obvious magnitude,” such {that a} star of magnitude 1 appears to be like very brilliant, when you in all probability cannot even see a magnitude 6 star via mild air pollution. Betelgeuse is within the first group.
To be clear, this is not the precise luminosity of a star—it is how brilliant it seems from Earth, which is dependent upon (1) how a lot mild it produces and (2) how far-off it’s. Oh, additionally (3), magnitude relies on how the human eye sees objects, and it is not linear. A magnitude 1 object has a light-weight depth (in watts per sq. meter) that’s 100 instances larger than a magnitude 6 object.
