One of the most prominent stars in the night sky in the Northern Hemisphere during winter
is the red supergiant star Betelgeuse, the shoulder of the constellation Orion and one
of the few stars sufficiently bright that you can actually see its reddish orange color
with the naked eye.
Betelgeuse is usually the tenth brightest star in the night sky, but it’s always been
known to vary in brightness.
Part of the reason for this is that it is not a typical star due its immense size, if
it were in the solar system it would stretch out to the asteroid belt, and have a mass
20 times that of the sun.
Betelgeuse is young, about 8 to 10 million years old.
Supergiant stars like this don’t live long and burn rapidly through their nuclear fuel
and go supernova relatively quickly on geologic timescales.
This also means they evolve rapidly, and betelgeuse may actually have done that right before humanity’s
eyes.
The mystery of the star’s color begins around the second century BC, Chinese astronomers
noted that betelgeuse appeared distinctly yellow in color.
By about the middle of the 2nd century AD however, the Greco-Roman astronomer Ptolemy
described it as orangish, or ruddy as it appears today.
Medieval observers in the Middle East saw much the same.
There has been some debate over just how people in the past named colors, or perceived them,
but in this case it’s actually physically possible for Betelgeuse to have changed color
in a matter of a few centuries.
It’s possible that the Chinese astronomers may have been observing Betelgeuse at a time
when it was still in a yellow supergiant phase of its life, and over several centuries it
evolved into the red supergiant phase.
Given that humans, by our nature, are night sky watchers, you have to wonder how many
people across the globe that could see the star noticed the change but left no records.
After all, changes to a star like that probably came with all sorts of dimming and brightening
events that aren’t recorded.
Hey friend, didn’t that star used to be brighter?
And that’s exactly what’s been happening over the last few years.
Betelgeuse is a variable star, but it seems to conform to some cyclic behavior.
In 2019, it began to plummet in brightness, which was visibly noticeable with the naked
eye for those used to gazing at this star as I was.
It was not its normal self for 2019 and into early 2020.
Over time it recovered, and one theory was that some of these cycles had coincided making
for a particularly deep dip in brightness, but observations by the Hubble Space Telescope
seem to suggest that the star actually had ejected a titanic amount of hot material into
space, which cooled and formed a huge dust cloud that was blocking out a significant
portion of the star’s light from our perspective.
This was weird.
Betelgeuse went from a member of the ten brightest stars in the night sky, to less than the 20th
brightest.
It was actually strange to see it dimmer than nearby Aldebaran, which is the 14th brightest
star.
I’ve looked at those stars most of my life, and that was a little disconcerting, like
seeing an old friend that’s visibly unwell.
Thankfully Betelgeuse got better, but did not stop behaving strangely.
And this time, it’s in a state right now even stranger than a dimming.
Over the last few months Betelgeuse has dramatically brightened, currently to the tune of 50 percent
above normal.
This is rather disconcerting for this star.
Dimming events could simply mean it belched out some dust or some cycles coincided, or
it’s covered itself in particularly giant sunspots, but a dramatic brightening is an
entirely different phenomenon, but may be related.
When Betelgeuse ejected the material in the 2019 event, it may have severely disrupted
the normal flow of plasma inside the star, so we may be seeing a kind of aftershock of
the ejection.
But what’s ultimately causing the strange behavior of the star above and beyond its
normal variability?
One possibility that’s been floated a number of times is that the star is getting very
close to supernova.
More conservative numbers say that the star is within about a hundred thousand years of
going supernova, but the chances of it happening at any given time are rather low, or if you
will one in a hundred thousand for any given year.
Some work also suggested that it may be even further from a supernova than that, and it
might take hundreds of thousands of years.
Yet another recent paper suggests it might be closer, as in it could explode at any time.
In a paper by Hideyuki Saio and colleagues, link in the description below, they hypothesize
that betelgeuse may actually be further down the nuclear fusion line than was previously
thought.
Looking at the patterns of variability with Betelgeuse, they find four periodic changes
that happen ever 2200,420,230 and 185 days.
The longest period is of unknown origin, no one’s figured out what this periodic variability
is due to, but it could be that it’s the fundamental period, and the other shorter
ones are overtones.
The researchers state that they have a model where this is caused by Betelgeuse being in
a very late stage of carbon burning, meaning that it actually is about to explode and could
top the candidate list for the next expected supernova within the Milky Way.
Part of the problem of unraveling the mystery of what’s going on with this star is that
there are some contradictory observations regarding the ejection of materials and now
the recovery.
The consensus being that it was a mass ejection of material, not unknown for many types of
stars, the sun does this on a smaller scale in a different way.
But that’s not fully settled.
And, at the same time, supernovae happen, in 1987 we saw one cook off in a satellite
galaxy of the Milky Way, so it’s entirely possible that the estimates for when Betelgeuse
could explode might have been wrong, but at the same time don’t plan a vacation around
it.
Right now betelgeuse is difficult to observe, Betelgeuse has moved behind the sun and won’t
be observable again until at least August, so we don’t really know what the star is
doing at the the moment.
And It’s difficult to know what it will look like when it is viewable again.
What we do know is that it’s brightening against its cycles.
One interesting aspect about this however is that betelgeuse is so huge, and relatively
close thought to be around 600 light years distant, that it’s one of the few stars
that we can actually resolve a disk for.
Most stars are too distant to do this, they just appear as points of light.
But betelgeuse you can actually see a disk, and you can pick out direct variations in
its light output photographically, so not only do we have a supernova candidate, we
have one we can get all sorts of data on including pictures, fuzzy though they are.
So, the question is, what happens if Betelgeuse goes supernova?
Firstly, it will be spectacular and safe.
The star is too distant to cause any problems for earth.
And whenever it does go supernova, it won’t be the brightest object in the sky, the moon
will still outdo it significantly, and the sun goes without saying.
But it would be enough to cast shadows on its own at night, and would be visible in
the daytime for as long as a year.
The supernova would be visible at night for several years, but then would fade entirely,
presumably with a short period where it would be at its former brightness again.
But only for a time, it would continue to fade until there would no longer be a shoulder
star in the constellation Orion.
While the supernova will be safe, only very close ones within a few tens of lightyears
pose a threat and there isn’t anything close to earth right now and there won’t be for
at least hundreds of thousands or more years, it may actually confuse some things.
Some animals react and use moonlight for example for things like navigation, and with a second
bright light in the sky casting shadows that may mess some of them up.
It would also strangely enough complicate astronomy, as astronomical observations from
the surface of the earth are not idea during times when the moon is shining brightly.
This would also be an issue for a very bright supernova, though in fairness no small number
of those telescopes are likely to be more interested in the supernova than anything
else.
At the same time though, observing very bright objects can be a problem in itself for very
sensitive or large telescopes, they’d have to be stopped down to do meaningful observations.
And there would be foreshocks to the supernova to act as a warning to get the telescopes
ready in the form of neutrino and gravitational wave detections as much as a day before the
actual visible explosion.
We’d actually know enough to warn everyone to head out and watch it in real time with
the naked eye.
Scientifically watching it unfold, even if it takes thousands of years, will allow us
to collect a profile of data on a star nearing the end of its life and going supernova right
before our eyes and instruments.
But after the explosion has dimmed and disappeared, there will be much to observe with the aftermath
of the supernova.
This is the crab nebula, a supernova remnant that exploded in the 11th century and was
observed by humans.
If you’d have had a telescope a thousand years ago, you would not have seen this nebula
as it is today, it is still visible forming and expanding out from the explosion point.
What’s left over other than a huge expanding cloud of gas and dust depends on just how
much material the Type II supernova that will end Betegeuse’s life as a stellar fusion
furnace leaves behind.
It could go either way and collapse into a neutron star, or if enough is there it could
collapse into a black hole.
This is actually rare either way due to its proximity.
If it ends up as a neutron star, it would be among the closest known to earth.
If it collapses into a black hole, then it would be by far the closest one to earth for
quite a long while.
If a far future humanity needed access to a large black hole for whatever reason, it
could very well be Betelgeuse.
Still, traveling the 600 or 700 light years to get to it is quite a task.
There’s no guarantee that Betelgeuse is about to go supernova.
The surface of the star does not reveal that actual carbon burning of the interior is occurring,
nor does it reveal what stage its in.
We just know that it’s particularly unstable right now, but it could go back into its normal
cycles and remain that way for tens of years, or even centuries even if it’s close to
a supernova.
Or other models may be right, and we won’t see it explode for tens of thousands of years.
Only time will tell, but it does remind us that the night sky is not static, the stars
are not forever, though some of them will last unbelievable amounts of time, and that
the universe simply changes on both short and long time scales.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently eyeing Antares suspiciously.
It’s a lot like betelgeuse and will go supernova at some point, though probably not for a timeframe
closer to around a million years, but as betelgeuse showed those numbers can change.
Very questionable, red supergiants and be sure to check out my books at your favorite
online book retailer and subscribe to my channels for regular, in-depth explorations into the
interesting, weird and unknown aspects of this amazing universe in which we live.