Betelgeuse Is Dimmer Than We’ve Ever Seen It

Over the last weekend, astronomy Twitter started
noting that the red giant Betelgeuse, the prominent shoulder of Orion was looking visibly
dimmer in the sky, and I had a few people reach out to me and ask me if it was really
happening and if I knew what was going on. This is exciting, of course, because Betelgeuse
is living on borrowed time, and it could explode as a supernova any day now. Or, it might not detonate for another 100,000
years. We just don’t know. What’s Betelgeuse up to? Is this a sign that it’s about to explode? And what would it mean if it did? When it comes to stars, you couldn’t have
a star more different from our Sun than Betelgeuse. It’s located about 640 light-years away
from us in the constellation of Orion. There are many stars much closer than Betelgeuse,
but it’s still in the top 10 brightest stars because it’s so large, and pumping out so
much radiation. Ethan Siegel blew my mind with the fact that
if we could see all the radiation coming from Betelgeuse, and not just the visible light,
it would be the second brightest star in the sky after our Sun. If you dropped Betelgeuse into the Solar System,
its size would engulf the asteroid belt, reaching almost to Jupiter. It’s one of the few stars that astronomers
can actually reveal features on its surface. Astronomers estimate that Betelgeuse has 12
to 20 times the mass of the Sun, and like all stars with that much mass, they’re destined
to live very short lives, just a few million years before they explode as supernovae. When Betelgeuse does explode, it’ll actually
be the second brightest star in the sky, vastly outshining everything else except for the
Sun and the Moon. In fact, some estimates say that it might
even outshine even the full Moon. Bright enough to see during the daytime, blazing
away for an entire year until it finally fades away. Even the wreckage it leaves behind will be
a stunning deep-sky object, which will continue to enjoy for thousands of years as it fades
away. This is the Crab Nebula, the remnant from
a supernova that exploded back in 1054 and it’s roughly 6500 light-years away and has
a diameter of about 11 light-years across. The closest supernova in living memory is
SN 1987a, which exploded over 30 years ago in the Large Magellanic Cloud 170,000 light-years
away. It was visible to the unaided eye when it
went off, and astronomers still watch the expanding radiation shockwave as it expands
through the cloud of debris shed by the star as it was dying. And don’t worry, even though Betelgeuse
is closer than any supernova explosion on record, it’s still far enough away that
it doesn’t pose any risk at all to the Erth. So what’s going on? On December 8, 2019 the Astronomer’s Telegram
reported that Betelgeuse was getting fainter. According to astronomers from Villanova University
and the American Association of Variable Star Observers, Betelgeuse has been declining in
brightness since October 2019, reaching its modern all-time low of 1.12 magnitude of December
7th, 2019. Betelgeuse was already known to be a variable
star, changing in brightness every 420 days +/- 15 days. It also has a longer cycle of 5-6 years as
well as a shorter cycle of 100-180 days. But right now, it’s at its dimmest point
in 25 years of continuous monitoring and 50 years of other observations. So why is it changing in brightness? Astronomers know a few of the mechanisms that
make red supergiants variable stars. Just like our Sun, they have granules on the
surface, which are convection currents of warmer material rising up from the interior
and then releasing their heat. Think of the bubbles you see on a pot of boiling
water. These bubbles are big. They can be 60% the radius of the star. Not 60% the radius of the Sun, but 60% the
radius of Betelgeuse, which is almost 500x bigger than the Sun. Variable stars also pulsate in size and brightness. Stars are always a balance between gravity
pulling in and the light pressure pushing out. The interior of the star releases less radiation,
gravity pulls the star inward. Then the higher density and temperature creates
more radiation, so it expands out again. Betelgeuse is definitely dying. It’s nearing the end of its life, and that
means powerful solar winds are throwing its material out into the Universe. A red supergiant like Betelguese will blast
out about half the mass of our Sun in powerful solar winds. This material is constantly hurled out into
space for thousands of years, creating a bubble of material that gets illuminated by the shockwave
of radiation when it explodes. The brightness of the star can be affected
by the amount of dust that’s obscuring our view. There could even be new physics that astronomers
don’t understand yet. This is one of those situations where I’m
probably the bearer of bad news. There’s no reason to believe that Betelgeuse
is dimming because it’s getting set to explode. Betelgeuse is a variable star and it changes
in brightness all the time. The fact that it’s dimmed more than astronomers
have seen in 50 years is exciting, and it’s an opportunity to learn more about the star
and its longer dimmer cycles. There’ll probably be hundreds of stars that
explode in the Milky Way before Betelgeuse goes off. I wanted to do this video to manage your expectations. There are some pretty breathless articles
out there speculating that it’s going to explode, and you need to be very skeptical
about that. But is anyone working on a way to figure out
when a supernova is about to explode? Could we get at least a few hours warning? I’ll talk about that in a second, but first
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Today website for patrons, for life. Join our community at Is there a way to know, with more precision
when a supergiant star is going to explode? Maybe, thanks to neutrinos. When a star explodes as a supernova, it releases
99% of its energy in the form of neutrinos in just 10 seconds. These high-speed, low mass particles pass
easily through almost all the mass they encounter, but a tiny fraction are detectable in some
of our largest detectors, like the 1-km Icecube instrument in Antarctica. As a star is in the process of exploding as
a supernova, the neutrinos from the center escape into space faster than the light does,
which means that we should get a few hours warning from the neutrinos before the light
arrives. A worldwide network of detectors called the
Supernova Early Warning System is now online to give scientists an alert when a supernova
has gone off. The supernova has got to be close. A supernova that exploded in the galaxy M82
in 2014 didn’t result in any detections – it was 11.4 million light-years away. There’s a really cool idea that you could
detect the neutrinos from a massive star that’s about to go supernova by the amount of neutrinos
coming from it. In the last couple of hours, before it dies,
the star is fusing heavier and heavier elements on its way up to iron on the periodic table. The releases a kind of neutrino that should
be detectable above the background noise of the Universe. And in theory, detectors should be able to
find stars about to go supernova to a distance of about 100,000 light-years. In other words, we’d get about two hours
of notice of any star about to go supernova across the Milky Way. Betelgeuse, at only 650 light-years away would
be very detectable. Imagine a neutrino detector so powerful that
it could observe stars in the sky by the neutrinos they’re generating, and detect how they’re
shifting over to new elements in their cores. This is actually a tremendously difficult
challenge because the Sun’s neutrinos overwhelm our local environment. But still, a man can dream. So, is Betelguese about to explode? Probably not. This is an incredibly rare event, and it’s
only happened a handful of times in recorded history. The last time a supernova went off close enough
to be bright enough to see in the daytime was Kepler’s Supernova, observed by the
astronomer in 1604, and visible in the day for a few weeks. It’s unlikely that it’ll be us who see
it go off. And yet, it’s just a blink of the eye in
the age of the Universe. Hopefully, astronomers will still be here
in the next few tens of thousands of years when it does go off, capitalizing on the treasure
trove of astronomical secrets it reveals. But I really really want one of them to be
me. So come on Betelgeuse, explode already. What do you think? Let me know your thoughts in the comments. Here are the names of the Patrons who support
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Universe Today on iTunes, Spotify or wherever you get your podcasts. I’ll put a link in the show notes. We talked briefly about neutrinos in this
episode, but we did a whole video on them and the enormous Icecube Observatory embedded
in the ice in Antarctica. And you can watch that here while you’re
waiting for Betelgeuse to explode.