Is Betelgeuse Going to Blow?

Short answer, not yet. Maybe not yet, but it will sometime, maybe soon, maybe not.  What’s going on with Betelgeuse?

Betelgeuse is a Red Super-giant Star, with a mass somewhere between 8 and 40 times that of the Sun.  That is a very broad range eh? Betelgeuse, like most red super-giant stars is variable in heat output and luminosity.  This makes determining an accurate mass difficult.

A Red super-giant star usually starts out as a white (class O) or blue (class B) giant star, fusing hydrogen like crazy during its brief stay on the main sequence of stellar evolution.  Expected lifespan is in the millions of years vs. 10 billion years for stars like our Sun.

The end of a brief childhood (maybe 5 million years) comes when helium overtakes hydrogen in its core (the result of hydrogen fusion).  The core cools, and this star starts fusing hydrogen in layers outside its core.  Without fusion producing outward pressure the core begins to contract, gravity taking control, and the lighter outer layers begin to expand outward via hydrogen fusion.  This is called the mirror effect. Cooling as it expands, the star turns from white/blue to red/orange.

As the star’s core contracts it gets hot, hotter than when fusing hydrogen, 100 million degrees Kelvin (K) vs about 20 million K.  The core’s helium begins to fuse, and the core expands, pushing those cooler, hydrogen fusing outer layers further outward.  Our star is growing up, becoming a red super-giant.

Fusing helium into carbon is more chaotic than hydrogen fusing into helium.  As carbon ash collects from helium fusion it damps fusion, resulting in sporadic outbursts where dust is blown away from the star.  These outbursts might account for red super-giant star’s variable luminosity and heat.  This will go on for a few million years, until the star has a mostly carbon core.  Maybe you guessed, the core contracts, heats up immensely, and carbon fusion starts.  All the while, hydrogen fusion goes on slowly and steadily in those outer layers.  But this star is nearing its end. Depending on its mass it could eventually blow as a type II supernova and become a neutron star, or possibly collapse directly into a black hole.

Astronomers think Betelgeuse is near the end of its helium fusing stage.

Between October and December 2019 Betelgeuse dimmed dramatically and unexpectedly.  After many months of study by several groups, the reason has not been definitively established.  Some think a larger than usual belch of carbon dust caused it.  Others think a large, lower temperature surface cell formed, resulting in a drop of luminosity.  It’s back to normal now so a blowout is not soon expected.

But it would be amazing to see!

What’s in the Sky?

03/20; 4:37am CDT: It’s the Vernal Equinox.

03/24; 6am CDT; South:  Jupiter’s moon Io transits Jupiter’s face, preceded by Io’s shadow.

West:  The Moon is north of open cluster M44 (Beehive) in Cancer