Betelgeuse — the Star You Think You Know
A Dying Star Gives Up Its Secrets
Veteran stargazers are very familiar with the bright star Betelgeuse, the shoulder star in the constellation Orion, the Hunter. Northern hemisphere viewers begin to see Betelgeuse in the autumn; for folks in the southern hemisphere, this star is a familar spring sight.
Astronomers have known for years that Betelgeuse (also known as alpha Orionis because it’s the second-brightest star in Orion; Rigel is the first-brightest and is known as Beta Orionis) is a red supergiant star — that is, a star that is well advanced in old age. It’s also a variable star — which means that its brightness pulsates on a regular schedule.
Betelgeuse (alpha Orionis) as seen by the NASA/ESA Hubble Space Telescope. Courtesy Space Telescope Science Institute.
Betelgeuse isn’t a very old star in terms of stellar age — perhaps only a few million years old. The Sun, by comparison, is 4.5 billion years old. So, how can Betelgeuse be advanced in old age when it’s younger than the Sun?
It’s because Betelgeuse is a high-mass star — many many times more massive than the Sun. High-mass stars evolve very quickly — they burn through their nuclear fuel at prodigious rates, which brings them to the ends of their lives in a very short time in comparison to longer-lived, lower-mass stars.
What happens to massive stars when they get old? First they blow much of their outer atmosphers off to space in episodes of activity that astronomers call “mass loss.” At some point, what’s left of the star collapses and then rebounds out in a spectacular explosion called a supernova. The cataclysm rips the star apart and hurls its matter into space. The leftovers — a neutron star and an expanding cloud of debris — form some very haunting visions of destruction across the Milky Way Galaxy.
So, will Betelgeuse explode as a supernova? Very likely so — and possibly in the span of human civilization in the not-all-that-distant future. Perhaps our great-grandchildren or their great-grandchildren will see Betelgeuse become very bright in the night time sky and then fade out slowly over thousands of years. They will witness first-hand the fate of massive stars when Betelgeuse dies.
Scientists are now studying this star to understand just when it will face that fate — and what clues we see around it today that predict its ultimate demise. It’s relative easy to study because it’s only about 640 light-years from us. Recent images of Betelgeuse show that it has blown a great deal of its material out to space — a precursor to its death throes. In addition, its variability may also be a clue to its fate, and astronomers are studying the star to understand what’s causing it to slowly brighten and dim in a regular pulsation of luminosity.
Want to know more? Check out the December episode of The Astronomer’s Universe to see just what scientists are learning about Betelgeuse!