Astronomy Department Blow up, blow up, giant star … By Wladimir Lyra | New Mexico State University - BE BOLD. Shape the Future.
Skip to main content

Blow up, blow up, giant star … By Wladimir Lyra

(Originally published in the Las Cruces Sun News on February 9, 2020 – link)

… how I wonder what you’re doing.

Betelgeuse (pronounced “beetle juice”), the red star northwest of Orion’s belt, one of the brightest stars in the sky, has been dimming inexplicably. Without rhyme or reason, Betelgeuse has gotten fainter and fainter, dropping from the rank of 10th brightest star to the unremarkable 30th position – and falling. The once easily recognizable star has become just another face in the crowd. Astronomers are scratching their heads, at a loss to what is happening.

Coincidence or not, Betelgeuse has long been known to be nearing death. The crimson star will go out with a bang, in an apotheotic explosion known as supernova. When it happens, Betelgeuse will become brighter than the Moon, and visible at daytime. On a cold November evening in 1572, walking back home after dinner, the famed Danish astronomer Tycho Brahe witnessed this impressive event, and left a vivid account: “Amazed, and as if astonished and stupefied, I stood still, gazing. I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes.”

The name Tycho gave to the phenomenon, “nova” (meaning “new”, in Latin), stuck with astronomers. He studied the “new star” until it faded away from view, without having a good idea of what he was observing. Modern science has learned a lot since. Stars shine by smashing lighter atoms together and building heavier ones, releasing energy in the process. Behind their incandescent beauty lies a tug-of-war between the pull of gravity, trying to crush the star, and the outward push from the sizzling energy below. When the star’s nuclear fuel is exhausted, gravity wins and the star implodes. Ironically, the swift collapse of the star releases immense amounts of energy, way more than the star can handle, reversing the implosion and making the star explode.

Heavyweight stars like Betelgeuse, ten times heavier than the Sun, need to put out a lot of energy to push against the gravity of their own weight. They shine furiously, live fast, and die young. At 10 million years old, Betelgeuse is young enough that it did not exist when dinosaurs roamed the Earth. Yet, it is at the end of its life: in terms of lifespan, Betelgeuse is to the Sun what a butterfly is to us.

Betelgeuse is about to die, but we cannot pinpoint the exact moment of its last breath – it can happen anytime between tomorrow and the next one hundred thousand years. There is in fact much we don’t know about how exactly a star explodes. The last supernova in our galaxy was in 1604, long before modern science. We never could measure one up close with modern instruments to know exactly what the script is right before the supernova. Could Betelgeuse’s dimming be the prelude to the cataclysm? 650 light years away, Betelgeuse will be the closest supernova ever recorded. Far enough to not be harmful to life on Earth, and close enough for us to learn a lot from it.

Yet, as intriguing as Betelgeuse’s behavior is, an imminent supernova is wishful thinking. A more pedestrian explanation for the strange faintness is far more likely. Like the Sun has sunspots and solar winds, stars have starspots and stellar winds. Did Betelgeuse develop a lot of starspots? Or perhaps winds spread dust around the star, blocking the light from below. We don’t know.

Betelgeuse has been humanity’s companion. It was born from a cloud of gas 10 million years  ago, when the common ancestor among humans and the other great apes roamed the Earth. As a newborn star, it shone above the first primates learning to walk on two feet. It was a bright blue star to the gaze of Lucy, the famed australopithecus, and to the Homo Habilis sharpening their stone tools. As a giant ruby star it glanced over cro-magnons and Neanderthals. It has seen our feats and our follies as a species. Soon it will take over the night sky, attempt to compete with the Sun as a morning star; then slowly lose luster, and shine no more.

Will it give us this dazzling spectacle of astronomical proportions? Perhaps. Will it outlive humanity? Perhaps. What is sure is that one way or another the bright red star of Orion keeps inviting us to look up and stare in humility and wonder. At her. At us. Like stars do.