stickmaker | JOHT 85: More Things Change (Reply)

The Joy of High Tech

Rodford Edmiston

Being the occasionally interesting ramblings of a major-league technophile.

Please note that while I am an engineer (BSCE) and do my research, I am not a professional in this field. Do not take anything here as gospel; check the facts I give. If you find a mistake, please let me know about it.

More Things Change

Revisiting a frequent theme for the JOHT columns, but with a somewhat different emphasis this time.

Betelgeuse is dying. Though long known as a variable star, in recent years (in historical terms) it has been undergoing a rapid decline in brightness. This has many people watching the star very closely. We know that some of the dimming comes from gas and dust around the star, but not all of it.

The origin of the star's name is a bit confused. The traditional explanation is that "Betelgeuse" is derived from similar Arabic phrases meaning either "the armpit of Orion", or "the hand of Orion." Both are quite understandable, since the star is in the constellation of Orion. In English there are four common pronunciations of the star's name, the most common of these being popularized for sounding just like "beetle-juice." More formally, α Orionis (or Alpha Orionis) is the star's designation as given by Johann Bayer in 1603. One possible reason for the confusion about the Arabic name is that Betelgeuse is moving very rapidly with respect to the other stars in Orion and may eventually leave the constellation completely. Maybe it was recorded at different times in the past as being in different parts of the constellation.

For centuries Betelgeuse was one of the brightest stars in the sky, generally being ranked eleventh. In the infrared it was actually the brightest star as seen from Earth. For about the past century astronomers have been able to measure stellar brightness with purpose-built instruments, instead of using a Mark-1 Calibrated Eyeball. Even before that, however, it was known that the brightness of the star varied, with multiple overlapping cycles of brightening and dimming.

Betelgeuse is a red supergiant. The more massive a star is the faster it ages, and Betelgeuse is currently something like 12 - 20 times the mass of our Sun. This after ejecting huge amounts of matter in the recent (on an astronomical scale) past. Even though it is only about nine million years old, Betelgeuse is a star in a late stage of its life. It has therefore expanded to an enormous size, as senior stars tend to do. It is also very unsettled, which means bubbles of hot material from deep in the star to occasionally come to the surface and sink back. This changing mix of hotter and cooler stuff on the star’s surface makes Betelgeuse appear brighter and fainter over time. However, in the past few years it has fallen a huge amount in overall visible brightness. By mid-December of 2019, it had dropped to 23rd brightest (as seen from Earth) in the visible range. Some studies seem to show the star is also shrinking.

For stars of this type, the next stage is a supernova.

When it blows, Betelgeuse as seen from Earth will appear to be about half as bright as the full Moon. Though it is too far away to cause serious problems here on Earth - given the type of supernova it will produce - at the brightest it will be visible during the day, and may be a distraction for creatures which use moonlight for navigation. However, that event may be more than a hundred thousand years in the future. Or it could have already happened. (See below.)

By cosmic coincidence, there has not been an observable (from Earth) supernova in our galaxy since just before the first uses of the telescope to examine the heavens. Though supernovae have been observed in other galaxies since then, modern astronomers have never had one close enough to have a good view of what the star does during the preliminaries. If Betelgeuse blows soon (keep in mind that it is about 650 - 700 light years away (current estimates put the star considerably further away from us than did most previous ones) so it could have already popped and the light of that event be on the way to us) we should learn a great deal about supernovae.

Now, let's talk about Eta Carinae (aka η Carinae). Yes, it's another supergiant star about to go supernova. Actually, it is a star system, containing at least two stars. These have a combined luminosity greater than five million times that of the Sun. The system is located around 7,500 - 7800 light-years away from the Earth, in the constellation of Carina. In 1837 it attracted attention from astronomers by suddenly brightening in an event known as the Great Eruption. It went from a 4th magnitude star to the second brightest star in the sky. For a while some thought it was an actual supernova. However, it's rapid rise in brightness, short period of peak brightness and rapid decline to much dimmer than it had been before led to the understanding that what had happened was actually much smaller than a true supernova. In 1892 it had a lesser eruption. Starting in 1940 it began a sustained rise in brightness, until today is is about as bright as it was before the Great Eruption.

It is now known that Eta Carinae is actually two stars, which orbit each other with a period of about 5.54 years. The primary is a peculiar star similar to a luminous blue variable (LBV) but generally classified as an O. It is thought to have originally been 150–250 Solar masses (anything over about 120 solar masses are considered over the Eddington Limit and unstable). It is now believed to have lost at least 30 solar masses, much of that going into the cloud of gas and dust known as the Homunculus Nebula, which is inside the much larger Carina Nebula. (The Carina Nebula contains many giant stars and smaller nebulae. It is likely the result of multiple outbursts from several stars.) Eta Carinae is expected to explode as a supernova in the near future (in astronomical time). When it does, it should be about as bright as Venus. Depending on how it goes supernova the gamma radiation produced could have a minor impact on the ozone layer and be a slight threat to satellites and humans in space, but both of these situations are very unlikely. The Carinae system is too far away and turned the wrong direction to send much gamma towards us, even if the supernova produces a large amount.

Eta Carinae A is very strange in many ways. As one example, it is the only star known to produce ultraviolet laser emissions. (In this case meaning UV emissions with wavelengths in phase, as with a laser.) The secondary star in this system - Eta Carinae B - is also hot and highly luminous. It is probably also of spectral class O, and is around 30–80 times the mass of the Sun.

Exactly what caused the two recorded eruptions - similar events have happened to other stars, and are known as supernova imposter events - is unknown. One of the more adventurous hypotheses for the Great Eruption is that this was previously a triple star system, and Eta Carinae A absorbed the other member.

Because of the distance and the obscuring nebulae, learning details of this twin-star system is difficult. We don't know exactly the age or metallicity of either current member, or what stage of fusion burning either star is at. This makes predicting when either will go supernova very difficult. It even provides confusion as to exactly what type either supernova would be! The fact that these two stars are relatively close complicates predicting when either would pop. It is thought that they are slowly spiraling together, but a merger would take at least many thousands of years. Even if one goes supernova before that, the effect on such a close neighbor is a matter of speculation. If both are close to going supernova, one exploding could even trigger the other!

There is a small chance one or both stars have already gone supernova, and the light simply hasn't reached us yet. Though that is thought to be much less likely than with Betelgeuse.

The study of stars close to going supernova is a fascinating topic. I recommend that anyone interested look up more information on both of the stars (or star systems in one case) briefly described here. Especially Eta Carinae. As well as the information on the general topic.

I have written before in these columns about how changes in nature - particularly in the supposedly eternal, immutable and perfect heavens - drove some people to look beyond the dogmatic explanations of scholars and churches to objectively investigate what was actually happening. Astronomical observers no longer have to settle for "Well, your eyes must be wrong, because those star charts were made by the ancient Greeks, and they were never wrong!" It was the realization that the ancient Greeks often were right, and that the heavens had changed since those ancient star charts were made which helped drive the rise to the modern understanding of the universe. Not only positions and brightnesses but even the colors of some stars have changed over the previous few thousand years. Betelgeuse may actually have been yellow within historic times.

This is the advantage of the scientific method. When done right, it provides an objective view of the universe, correcting erroneous ideas through testing and evaluation. Science therefore trumps politics (though sometimes politicians override scientists). When Albert Abraham Michelson and Edward W. Morley asked of the Universe "Which way is the Earth moving through the luminiferous ether?" the response of the universe was essentially "Huh?!". Because there is no luminiferous ether. Therefore, the results they obtained were nonsense when analyzed from the viewpoint of the assumption that there was. Trying to figure out why the speed of light was the same in every direction regardless of the movement of the Earth is one of the things which led to the Theory of Relativity. This process continues to today.

So, in the words of the movies and the books, Keep Watching the Skies! Even if Betelgeuse or Eta Carinae don't go Boom! in our lifetimes, the heavens have always been interesting.