Betelgeuse — the star with the funny name. Maybe you know it from the 1988 movie Beetlejuice, about the eponymous poltergeist-for-hire. Or maybe you’ve heard the name in the news recently, in some overhyped speculation on the star’s imminent demise. As of this writing, Betelgeuse has not yet exploded, but the possibility that it will gives us all a chance to learn about supernovas.
It is not hard to find Betelgeuse in the night sky. After dark, head outside and find a location with a clear view to the south. Look for the constellation Orion (refer to last month’s column for details on how to find it). Then look for the red star that marks Orion’s right shoulder — that’s Betelgeuse.
The name Betelgeuse comes to us from medieval Arab astronomers. They called it bat al-jawzā, which means the giant’s shoulder. Later European astronomers adopted the name, and it eventually evolved into Betelgeuse. Yes, you can pronounce it “beetle-juice,” though some astronomers prefer “bettle-juice,” the first syllables rhyming with kettle.
In astronomical terms, Betelgeuse is in our near galactic neighborhood, about 600 light years away. That means that its light, traveling at 186,000 miles per second, takes 600 years to reach us. We see Betelgeuse as it was when the Inca civilization was at its height, and Zhu Di began construction of the Forbidden City, and Gutenberg invented the printing press.
Betelgeuse began its life as a blue-white star, hotter, brighter, and 10 to 25 times bigger than our Sun. As stars age, their internal chemistry changes; consequently, their size and color change. Now near the end of its life, Betelgeuse has evolved into what astronomers call a red supergiant, cooler and redder than our Sun, and swollen to 1,000 times the Sun’s size.
Betelgeuse is also unstable. Red supergiants have exhausted the hydrogen in their cores. That’s what stars burn in thermonuclear reactions, releasing energy — what makes them hot and bright. That energy also prevents stars from imploding from the force of their own gravity. Once the hydrogen is gone, red supergiants burn other elements for a couple of million years, keeping themselves intact. But sooner or later, the star exhausts all possible fuels; energy output falls below a critical threshold, and the delicate balance of forces collapses. The outer layers implode, then rebound off the core in a huge explosion called a supernova. Much of the star’s matter is blown off into space. What’s left is either a neutron star or the darling of science fiction, a black hole.
How close is Betelgeuse to exploding? Very close — in astronomy time. It could happen tonight, next week, or 100,000 years from now. Astronomers detected a dip in Betelgeuse’s brightness beginning in October 2019, and it continues to dim as of this writing. For those familiar with Betelgeuse and the other stars in Orion, the dimming is noticeable to the naked eye. Some have speculated that the dimming means impending explosion, and this made its way into the news. But many astronomers disagree and think that this dip is a normal fluctuation. No one is certain.
When Betelgeuse does explode, it will outshine the full moon for a time. It will be visible during the day. Then its brightness will fade, leaving behind a ghostly expanding shell, visible only via telescopes. Fortunately for us, Betelgeuse is distant enough that the huge flux of radiation and high-energy particles released by its explosion won’t affect life on Earth. But its death will affect Orion, leaving him forever changed.
Betelgeuse is a winter star, not as easily seen in summer. I encourage you to brave the cold and see Betelgeuse this winter — it might be your last chance to do so.
Editor’s note: Our astronomy columnist, who regularly sets up his telescope in New York City’s Fort Tryon Park, appeared in this week’s edition of the New York Times “Metropolitan Diary.” He moved a city bus for the sake of the night sky. Nice work, Justin.