Betelgeuse - Red Supergiant

Betelgeuse - Red Supergiant
Betelgeuse is the star that represent's Orion's right shoulder. It's also one apex of the Winter Triangle and marks the center of the Winter Hexagon. Very bright, distinctly red, and part of the hunter's commanding presence, you can find it easily in the winter sky.

Ptolemy's Almagest, a second century astronomical work, listed the constellation Orion. Betelguese was unnamed, merely described as “the bright, reddish star on the right shoulder”. Later on, Arabic astronomers named the star. And over the centuries we ended up with something daunting to pronounce.

I usually hear the name pronounced BET.uhl.jooz. Yet I've found seven different pronunciations, not counting Beetlejuice which became popular after the movie of that name. But properly speaking, it should be variations on “Yetelgeuse”, as apparently medieval scholars translating the Arabic misread a 'y' as a 'b'.

Possibly the best strategy is just to adopt the pronunciation of people around you.

Bright but inconstant
It may be tricky to pronounce, but Betelgeuse is easy to see. Not only is it the tenth brightest star in the entire night sky, it's one of seven bright stars in Orion. Six of them are blue, with Betelgeuse the odd one out, a red supergiant with a noticeably reddish hue. The grouping of bright stars is so prominent that it's part of the skylore of civilizations around the globe.

Although Betelgeuse is always bright, its brightness varies. English astronomer John Herschel first described the variation in 1836, continuing to observe it for a number of years. Rigel is usually the brightest star in Orion, but Herschel saw Betelgeuse outshine it.

Herschel was the first western astronomer to describe Betelgeuse's variability, but he wasn't the first person to notice it. It was known by the aboriginal people of the Australian Great Victoria Desert and incorporated into their sky traditions. The hunter Nyeeruna [Orion] pursues the sisters of the Yugarilya [Pleiades] with lecherous intent. But he's stopped by the eldest sister Kambugudha [Hyades]. Betelgeuse is Nyeeruna's club, and with it he commanded fire magic. Ha! It has no effect on Kambugudha who has fire magic of her own to dim the fire in Betelgeuse.

Big and bright, but not so hot
The best measurements currently available suggest that if Betelgeuse were where the Sun is, it could fill the space out to about the orbit of Jupiter. It's thousands of times more luminous than the Sun, but the tremendous energy output is due to Betelgeuse's great size, not its temperature. Its temperature is only about sixty percent as hot as the Sun.

Young, but not youthful
Betelgeuse is a young star, less than ten million years old. That sounds ancient, but our Sun is 4.6 billion years old and scarcely halfway through its lifetime. Betelgeuse is some fifteen times more massive than the Sun, but has already completed over 90% of its lifetime.

It might seem that a massive star, having more fuel, should last longer. But it doesn't work like that. A star's size depends on the balance between the inward pull of gravity on its mass and the outward push of the energy released by nuclear fusion. A greater mass creates the conditions that accelerate nuclear fusion. First hydrogen is fused to helium, and then helium fusion occurs, releasing more energy and causing the star to expand. Heavier and heavier elements are fused until the star's core is iron.

Fusing iron doesn't release energy, it uses it, so fusion stops abruptly. With no outward pressure from fusion, the core collapses suddenly. A rebound produces a mammoth explosion — a supernova.

Astronomers say Betelgeuse will run out of nuclear fuel “soon”. This isn't a next week or even a few decades from now sort of “soon”. It's an astronomical “soon”, meaning more like a 100,000 years or even half a million. But when it happens, Betelgeuse's stardom will end in a supernova as bright as a whole galaxy. What will be left is a neutron star at the center of a gas cloud, creating a shockwave it expands.

What will happen to Earth when Betelgeuse becomes a supernova?
But if soon should turn out to mean in our lifetime, will we be in danger?

A supernova is no nice neighbor. It's emitting extremely dangerous high energy radiation in the form of gamma rays. A supernova within 30 light years of Earth would have a disastrous effect would have a disastrous effect on Earth's atmosphere and oceanic food chains. Depending on the energy output of the supernova, even up to 100 light years away, our protective ozone layer could be destroyed and large amounts of smoglike nitrous oxide produced. There would be a noticeable increase in the incidence of genetic mutations.

But the time to panic is never. How far away is Betelgeuse? Astronomers aren't certain. However using data from the best recent measurements, the distance is put at 600-900 light years. The European Space Agency (ESA) Gaia mission may soon provide an even more precise figure. Nonetheless you can see that we're well out of the danger zone.

What would happen is a spectacular event in the night sky that will probably also be bright enough to see during the day for a time.

(1) Leaman & Hamacher,
Aboriginal Astronomical Traditions from Ooldea, South Australia, arXiv:1403.7849 [physics.hist-ph]
(2) Harper et al,
An Updated 2017 Astrometric Solution for Betelgeuse, arXiv:1706.06020 [astro-ph.SR]

You Should Also Read:
Orion the Hunter
Death of a Massive Star
Winter Hexagon

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