Goodbye Betelgeuse?

About five nights ago, I stepped outside, to take a look. That is, up. It's a habit, formed, long ago as a young, budding astronomer (and, 'Rock Star' Drummer...well, never mind about the 'rock-star' drummer part), but - any time that the night sky is clear of clouds - and I know about it - I do a "status" check; just, making sure that, "everything's there - and, things are the way they're supposed to be". Kind of like looking in on your kids, long after they've gone to bed...

While I'm out there, I do a sub-conscious, magnitude comparison, between the stars of the constellation, 'Orion' - a relative, close, loosely-grouped gathering of red and blue, 'super-giant' stars, out here at our 'end' of the galaxy. Throughout my entire life - the stars, "Betelguese", and "Rigel"; the 'right shoulder', and 'left foot', respectively; of the Hunter, Orion - have always appeared to be close in brightness, with the blue, Rigel, out-shining the red, and somewhat variable, Betelguese - by just a few "points". Every night. Every year. Always the same - my whole, life-long, life...

...but on the night of 21 DEC 2019 - something was, very, very different. Indeed -- things were NOT, the way, they were supposed to be.

Betelgeuse is generally the eleventh-brightest star in the night sky and the second-brightest in the constellation of Orion. Image by Muir Evenden on Insight Observatory's 16" f/3.7 astrograph reflector (ATEO-1).

The 'ancient's', had understood the stars to be, 'immovable', 'invariable', and 'eternal' objects. No one could blame them; the distances to the stars - any star, even the very closest - is an unfathomable number of miles away from 'us'. (24,900,000,000,000 - to be exact). Any motion through 3-dimensional space goes undetected; although the stars, *are* moving through space, in their long trip around the galactic core of the Milky Way galaxy (that's ours), they are so distant that their motion is not perceptible to us, here on Earth - and, not to the ancient's, either. Compared with the rest of the universe - we just live at a 'fleeting' pace, but the truth is - the stars do move. And change; sometimes, catastrophically.

The stars of the Orion group are, in fact, a relatively, loosely-grouped, 'open cluster', in which, the grouping is moving through space, together, as a whole, around the galaxy. The group is between, about, 500 to 900 light-years (LY) distant. That's pretty close, by cosmological standards, and accounts for their relative brightnesses, being so high, compared with most other stars. These blue-white beauties are some of the brightest stars that can be seen from Earth - just a bit dimmer, than the brightest star, 'Sirius', which happens to lie very nearby. In fact, if you walk outside, on any, clear, winter night - the brightest stars that you will see will be those of the Orion group.

Astronomers have learned much about the 'Orion group', also known as the 'Orion OB-1 Association', over the decades. They are, distinctly, set apart from the other stars in our, somewhat, limited field of view, in that, quite a few of them are extremely large, bright stars, of a type of star, called a 'super-giant'.

Well, 'So what!?'

OK, well - *here's*, "what": beginning with a 3-star asterism that most people are acquainted with - "Orion's Belt", those three stars are part of the Orion OB-1 Association. The left-most star in the belt, 'Alnitak', is a blue type, supergiant, at 800 LY distant - Alnitak shines in at a monstrous - 100,000 times - brighter than the sun! That's because it is 40 times the diameter of the sun!

The next star, the 'center' star of Orion's 'belt', 'Alnilam', another, blue supergiant, is 375,000 times as bright as the sun. That's because it is 84 times the sun's diameter. The last, or 'right-most' star in the belt, 'Mintaka', is 36 times the diameter of the sun, and blares in at 90,000 times the output of the sun. Another blue supergiant.

The constellation Orion the Hunter - Illustration Credit: Earth Sky and The Atacama Large Millimeter/submillimeter Array (ALMA) captured this image of Betelgeuse, revealing its lopsided shape and a huge bright spot. ALMA (ESO / NAOJ / NRAO) / E. O’Gorman / P. Kervella

Most of the stars that you see, up there, in the dusky grey (it is not black anymore, where I live), are older, dimmer, and somewhat redder stars than these 'Mavericks' of Orion. Supergiant stars are stars that are on their way out. They have near the end of their time on the main sequence, drifting toward oblivion, but, one star out of this group, has aged much faster than the others. And it is, now, visually, very obvious.

The red supergiant, "Betelguese", is now, about ten times, less bright than I remember it as a kid. And it's dimmer, now, than it was, the last time I saw it, just over a year ago. The great, red, supergiant is now at the end of its lifespan. The constellation, "Orion", has changed.

The once, bright, red star, has begun to shrink, inward, toward a collapsing core. Having burned through all of its original hydrogen mass - and its converted, helium mass, it is in the process of fusing its remaining elemental composition, all the way down to iron. Once it has reached this stage, its thermal, expansion energy will no longer counter the energy of gravity, and it will collapse - blowing itself, in a crescendo of blazing light, metals, and x-rays -- to smithereens. It will leave behind, a cold, dead, neutronic core.

Betelguese, is now, ready to do just that.*

*It is difficult to know, exactly, when a star is going to actually go supernova. That could happen, anywhere, from - tonight - to a few more, thousand years. But, it could be - tonight!

Dale Alan Bryant
Senior Contributing Science Writer