Editor’s Note: Don Lincoln is a senior scientist at the Fermi National Accelerator Laboratory. He is the author of several science books for general audiences, including the best-selling audio book “The Theory of Everything: The Quest to Explain All Reality.” He also produces a series of science education videos. Follow him on Facebook. The opinions expressed in this commentary are solely his. View more opinion articles on CNN.
“My love for you is as eternal as the sun” might be a heartfelt line in a love letter written by a young man to his beloved. As poetic as the sentiment might be, it doesn’t mean quite what the young swain intended, for the sun, like all stars, was born and now lives in vibrant middle age, but it is destined to die one day. While that inevitable moment is billions of years in the sun’s future, a nearby star may be facing a more imminent demise.
Betelgeuse is a star in the constellation Orion and is one of the brightest stars in the heavens, prominently marching across the night sky every fall and spring. It has observably dimmed in recent months, a sign that some astronomers interpret as a warning that the star will explode in one of the most powerful and dramatic events in all of the cosmos – a supernova.
Betelgeuse is in a class of star called a red supergiant. The “red” means it is much cooler than the sun (e.g. a surface temperature of about 6000 degrees Fahrenheit, compared to about 10,000 F), and “supergiant” means both massive and with a large volume. (Those two things don’t necessarily have to go together, as a large thing like a hot air balloon doesn’t have to be massive. In the case of Betelgeuse, both apply.) Betelgeuse is approximately 12 times more massive than the sun and, if it were to be located in our solar system, it would be bigger than the orbit of the asteroid belt and perhaps even engulf Jupiter.
“Live fast and die young” might be the mantra of giant stars, and Betelgeuse is no exception. It is only about 10 million years old – compared to the sun’s 4.5 billion – but its days are numbered. Like all stars, Betelgeuse began its life by fusing hydrogen into helium, but its hydrogen supply has largely run out. It then began fusing helium into heavier elements. It is this transition to fusing helium that heated the core of the star and caused it to expand to its current enormous size.
Eventually stars run out of fuel and their cores are no longer hot enough to overcome the star’s gravity. Their cores collapse; their internal temperatures spike to incredible levels and the star then explodes. That is how a star goes supernova. Betelgeuse is approaching this phase.
Witnessing this process is rare for humans. Roughly speaking, astronomers expect two supernovae per century in the Milky Way. In fact, the last supernova observed in the Milky Way galaxy was in the 17th century and was recorded by Johannes Kepler. We’re overdue for another.
If Betelgeuse does go supernova, is there any danger to us here on Earth? The simple answer is no. The star is about 700 light-years away, which would attenuate the impact of the blast. High-energy light from the supernova will bathe the Earth’s ozone layer and it is possible that scientists will be able to see this effect, because a reduced ozone layer will result in increased ultraviolet radiation making it to the Earth’s surface.
If Betelgeuse does go supernova, it will be the brightest star in the sky for many months. (Except for the sun, of course.) It will even be visible during the day.
Of course, it is unlikely that the recent dimming of the star is the most immediate precursor of a supernova. Betelgeuse has varied its brightness for centuries and even perhaps has changed its color. Indeed, it is expected that a star in the last stages of using up all of its stellar fuel will undergo changes and the timescale for stellar evolution is much longer than human timescales. Astronomers predict that Betelgeuse will continue to burn through the last of its fuel for as many as 100,000 years. So, as exciting as the prospect of getting such a close view of a supernova is for astronomers, this outcome is improbable during our lifetime.
Still, it would be exciting to see in the world’s telescopes. Perhaps even more exciting is the prospect of seeing the explosion using other scientific instruments. The LIGO and Virgo detectors, located in the United States and Italy, respectively, are gravitational wave detectors that have seen the merging of pairs of black holes. They use powerful lasers and mirrors separated a kilometer apart to measure distances smaller than the size of a proton, and will also be able to record Betelgeuse’s death knell.
Another set of cosmic observatories are large neutrino detectors, including IceCube, a detector that uses a cubic kilometer of ice under Antarctica to study cosmic neutrinos from outer space. And, if Betelgeuse cooperates and waits for perhaps a decade to explode, two sophisticated neutrino detectors (DUNE, hosted by my own laboratory, Fermilab, and Hyper-K in Japan) are being built that will be able to study the outpouring of neutrinos that accompany a supernova.
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The last time terrestrial detectors monitored a supernova was in 1987, when a star in a smaller galaxy orbiting the Milky Way detonated. Betelgeuse’s proximity and more than 30 years of improvements in detector technology will give vastly improved measurements.
While the speculation of the impending death of Betelgeuse is probably premature, it is a captivating prospect to consider, both from a human and a scientific perspective. And, if we do see it, it might make young lovers reconsider their metaphors for permanent devotion as they compose their letters.