If Betelgeuse Explodes, Just How Bright Will It Get?

Theres a celebrated prima that I'm definite you've seen successful the sky. Its sanction is Betelgeuse, and you tin find it successful the Orion constellation, wherever it marks Orion's close shoulder. If you privation to telephone it “Beetlejuice,” I'm good with that truthful agelong arsenic you don't accidental it 3 times.

But thing is going connected up there. This reddish supergiant has dimmed repeatedly successful the past fewer years, which could mean that it's acceptable to spell afloat supernova rather soon—and by “soon” we mean wrong the adjacent 10,000 years. Actually, since it's immoderate 500 light-years away, it's imaginable that it already exploded and we conscionable don't cognize it yet. It could amusement up tomorrow.

One thing's for sure: If Betelgeuse does blow, it volition beryllium the brightest supernova ever witnessed by humans. Just however agleam are we talking? Could you spot it during the day? Would it beryllium dangerous? I'm going to amusement you however to fig each this retired with conscionable immoderate precise basal physics.

What Is a Supernova?

In astir stars, the halfway is composed of hydrogen and helium, the 2 lightest elements—but lone the positively charged nuclei of those atoms, since it's excessively blistery for the electrons to enactment put. Under immense gravity and temperatures, these nuclei tin fuse into heavier elements, releasing monolithic amounts of vigor successful the process. (This atomic fusion is wherever our prima gets its energy.)

For a unchangeable prima similar our sun, there's a equilibrium betwixt 2 opposing forces. The wide of each the substance successful the prima produces a gravitational unit that tends to illness the star. However, this is countered by the outward-pushing unit from the core, truthful the prima remains reasonably changeless successful size, adjacent though it's not a coagulated entity similar a planet.

But arsenic a prima ages, it gradually uses up its hydrogen and helium and starts producing heavier elements similar carbon, oxygen, silicon, and yet iron. And that's arsenic acold arsenic it goes—fusing elements heavier than robust takes vigor alternatively of creating it, truthful the prima fundamentally runs retired of substance and collapses successful connected itself.

In immoderate cases, this illness tin beryllium precise severe—so terrible that it rapidly increases the unit and somesthesia successful the halfway of the star. The prima past goes boom. Big boom. Well, large silent boom, since explosions marque nary dependable successful the vacuum of space.

But this produces A LOT of airy energy. For comparison, our prima has a luminosity, oregon powerfulness output, of 3.8 x 10²⁶ watts. A supernova that was observed successful 2015 (ASASSN-15h) had a highest luminosity of astir 2 x 10³⁸ watts. That's much powerfulness output than 500 billion suns. It's crazy. Oh, you didn't spot that one? Yeah, due to the fact that it was successful a antithetic galaxy. Betelgeuse is successful our backmost yard, astronomically speaking.

Brightness and Luminosity

A agelong clip ago, a Greek philosopher named Hipparchus categorized the stars into six groups, based connected however agleam they appeared successful the nighttime sky. From that, we person developed a classification strategy for “apparent magnitude,” specified that a prima of magnitude 1 looks precise bright, portion you astir apt can't adjacent spot a magnitude 6 prima done airy pollution. Betelgeuse is successful the archetypal group.

To beryllium clear, this isn't the existent luminosity of a star—it's however agleam it appears from Earth, which depends connected (1) however overmuch airy it produces and (2) however acold distant it is. Oh, besides (3), magnitude is based connected however the quality oculus sees objects, and it's not linear. A magnitude 1 entity has a airy strength (in watts per quadrate meter) that is 100 times greater than a magnitude 6 object.