This illustration gives you an idea of Betelgeuse’s enormity. Put in place of the sun, it would be nearly as large as the orbit of Saturn. The inset photo was taken by the Hubble Space Telescope. Credit: Tom Callen, Cosmonova, Swedish Museum of Natural History, Stockholm
It’s sad there’s so much distance between us and Betelgeuse, Orion’s second brightest star. To the eye, it’s a flickering pink spark and no more. In all but the most powerful professional telescopes Betelgeuse remains a pinpoint. But if we could dissolve the 640 light years that separate Earth and star, we’d be awestruck at the sight.
Hovering before us would be a bloated sphere of fiery gas almost 1000 times the size of the sun and 135,000 times brighter. Over time we’d be able to watch it’s atmosphere slowly pulsate, expanding and contracting like an enormous heart. Betelgeuse is a red supergiant star only 8.5 million years old, barely a teenager by stellar standards. Compare that to the sun, which is over four billion years old, and just now entering middle age.
The Hubble Space Telescope was the first to image the actual disk of Betelgeuse. The red "collar" is the star’s outer atmosphere. Credit: NASA/ESA
Betelgeuse, which has a variety of pronounciations –BEET-el-jooz and BET-el-jooz are the most common — is so large that it’s consuming its hydrogen fuel at a rapid rate. As stars "cook" hydrogen in their interiors, they convert it into energy (starshine) and heavier elements like helium, carbon, oxygen and so forth. Giant stars cook elements all the way up to iron. Once they hit the "iron wall", they run out of material to burn. Iron can’t be cooked to create heat and new materials. With no heat to counteract the ever-present pull of gravity, the star collapses, rebounds and tears itself apart in frighteningly powerful shock wave.
Such an event is called a supernova. I’ve been fortunate to track down several hundred of them in galaxies beyond the Milky Way over the past 25 years. While a supernova looks like an ordinary star, you’re watching one of the biggest bangs the universe has to offer. It always gives me a thrill.
No one’s seen a supernova in our galaxy for the past 400 years but Betelgeuse is a prime candidate to become one. It’s big enough to cook up iron and blow bigtime. When you ask? Scientists estimate Betelgeuse is within about 10,000 years of exploding. Will it be tonight, next week, the year 4209 AD? When it goes, it’ll be as bright as the half moon, visible in the daytime and cast crisp shadows at night. Even though Betelgeuse is many light years away, the explosion will send a pulse of ultraviolet light that could endanger future space travelers to the outer solar system. There’s even a remote possibility the blast wave could alter the Earth’s upper atmosphere.
Let’s pull back a safe distance from Betelgeuse again. The next clear night, gaze across the light years into its baleful red eye, and cross your fingers the big show will happen during our lifetimes.
(Star size comparison diagram above from NASA)