Betelgeuse is a super interesting star.
Not only does it have an incredible name, but it’s one of the closest red supergiants
to us, meaning that while it is cooler than the majority of star types, it has an enormous
diameter.
If it was the star in our Solar System, everything up until the asteroid belt would be contained
within it.
It’s about 700 ly away from us, a lot further away than most other visible stars, but because
it is so large, it’s the 10th brightest star to the naked eye in the sky, and brightest
in the near infrared.
It easily visible as the left shoulder of Orion.
If you do look for it in the night sky, it is also visibly redder than any of the surrounding
stars, and it does a lot of twinkling.
There’s something else very special about Betelgeuse.
It is likely to explode in a supernova at any moment, although I say that in astronomical
timescales, that means it could still take 100,000 years.
How do we know that?
Well, you see, large mass main sequence stars, or stars in the adulthood phase of their existence,
are powered by the nuclear fusion that goes on within their core, converting hydrogen
to helium.
This fusion creates an internal pressure, which combats the effects of gravity wanting
to compress the star into a smaller volume.
However, eventually the hydrogen fuel in the core will run out, having been converted to
helium, meaning the fusion process stops and the star’s core can’t overcome the effects
of gravity anymore.
The core compresses, but if the star is massive enough, the compression will trigger fusion
again, this time with the helium in the core into heavier elements like carbon, with this
process repeating for oxygen and neon.
With every new fusion cycle, the star’s internal pressure expands the diameter of
the star until it begins the red supergiant phase of its life, when the core is being
converted predominately into iron.
Red supergiants can’t fuse anything beyond iron, so once the fusion stops, the star collapses
completely into a supernova.
And that’s where we are at with Betelgeuse now, we are awaiting this final collapse.
Whenever it does explode, it will eject its atmosphere far into space, which will be visible
in our sky for a good 2-3 months before it dims again.
It is far enough away that no harm will befall us on Earth, but it will make quite the spectacle,
perhaps being as bright as a full moon so even visible during the day.
Now, something else very interesting has been going on with Betelgeuse.
It’s been in the news a lot, like in 2009 when it contracted in size by 15%.
You may have also heard this last year that Betelgeuse has been dimming, and scientists
didn’t really know why.
Speculations were running rampant that this could be a precursor to this promised supernova,
although perhaps sadly, this is likely not the case.
New data from the Hubble Space telescope has shown that the star itself may not really
be dimming, but rather that some dust which was ejected by the star may have cooled and
obscured the view.
In September 2019, Hubble saw heated material moving away from the star’s atmosphere.
Over the course of the next few months, this material was observed near the star.
By December, the star began dimming in its southern hemisphere.
It is theorised that heated carbon was in the outflow, and as it moved around the star,
it expanded which cooled it down.
When we lost sight of it, it didn’t move away from the star, but rather crossed over
our view of Betelgeuse.
At its peak, Betelgeuse was two-thirds dimmer than normal, however, since April 2020, Betelgeuse
has actually returned to its normal brightness, so this cloud has either moved out the way
or totally dispersed.
So maybe this wasn’t the exciting conclusion to this story you were looking for.
Probably no supernovas for a while yet.
But maybe that’s a good thing, because after the event, Betelgeuse will no longer be visible!
So, next time you have a clear night, find Orion in the sky, and have a new appreciation
for the red twinkly star of Betelgeuse.
Thanks for watching!
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