Betelgeuse has been dramatically dimming since
September of 2019. At first, astronomers thought it would eventually
return to normal brightness, but that hasn’t happened yet. Instead, it’s become even more faint. As of February 2020, Betelgeuse is just 38%
of its normal brightness. And if that weren’t weird enough, new images
from ESO’s Very Large Telescope show the star as it has never appeared before. Welcome back to Launch Pad, I’m Christian
Ready, your friendly neighborhood astronomer. And yeah, Betelgeuse is just getting more
and more weird. To recap, it’s been fading ever since it
became visible once again in September 2019. Initially, it wasn’t a huge surprise because
Betelgeuse is semi-variable star that fluctuates roughly every 420 days or so. But starting in November, it became much fainter
than in previous cycles and by the end of December it had lost nearly half its normal
brightness! Much of the work involving Betelgeuse has
been based on directly measuring its brightness and seeing how it changes in comparison to
nearby, non-variable stars. This is a technique called photometry and
nowadays it can be done by anyone with a telescope and the right camera and software. What’s a lot harder to do, however, is take
a direct image of Betelgeuse. Even though it’s relatively large on the
sky, imaging the star requires ideal observing conditions, ultra-sensitive detectors, and
sophisticated image processing. But in December, a team of astronomers led
by Miguel Montargès of KU Leuven in Belgium managed to image Betelgeuse, and the result
is incredible. I gotta admit, I’ve never seen anything
like this! Some news articles are claiming that Betelgeuse
has physically changed its shape. While that’s certainly possible, it's a
little hard to conclude from the just the press release image alone. However, it is clear that one part of the
star is very bright while the other is really, really dim. Even better, Montargès' team just happened
to image Betelgeuse in January 2019. The result is a stunning before and after
comparison. Both images were taken using the SPHERE instrument
mounted on the 8-meter Very Large Telescope in Chile. It’s hard to overstate just how difficult
these observations are. It’s like being able to resolve a quarter
from 100 km away! I love how these images show how radically
Betelgeuse has changed over the course of just a year. It’s clear that there’s much less light
coming from it in the December image. And that, of course, would explain the dimming. And yet, it’s not clear why Betelgeuse appears
so strange in the first place. Like our Sun, Betelgeuse carries energy from
its interior to its surface via convection. But supergiant stars like Betelgeuse are so
large, the convection is very uneven. Remember, if Betelgeuse were placed at the
center of our solar system, its outer edges would reach Jupiter’s orbit. So while our Sun is covered evenly with millions
of small convection cells, Betelgeuse’s distended envelope is just a handful of gigantic
blobs. It should look less like a star and more like
an angry cloud. The outer layers are so far from the star’s
interior the gravitational pull on the surface is very weak. If enough energy gets convected up from the
interior, a chunk of the surface can blow away, forming Betelgeuse’s powerful stellar
wind. If the gas in this wind is enriched with carbon,
it could condense into dust. In fact, another team led by Pierre Kervella
from the Observatory of Paris used the VISIR instrument, also on the Very Large Telescope
to reveal the dust environment surrounding Betelgeuse. The VISIR image was taken around the same
time as the SPHERE image. VISIR uses a disc to block out the star and
its immediate surroundings, which are both bright and must be masked to allow the fainter
dust plumes to be seen. The orange dot in the middle is the SPHERE
image of Betelgeuse’s surface, which, remember, reaches out to Jupiter’s orbit. The dust cloud is formed by Betelgeuse’s
stellar wind. Is it possible that Betelgeuse is fading due
to a clump obscuring dust? Maybe, but that would imply it’s somehow
only obscuring half the star’s surface. Perhaps a large clump of dust was expelled
from the star’s Southern Hemisphere or maybe there's a clump of orbiting dust just happened
to float past. However, Ed Guinan of Villanova University
and Rick Wasatonic have been monitoring Betelgeuse for the last 40 years using photometry. They were among the first to report on Betelgeuse’s
fading in a pair of Astronomical telegrams in December. In a follow-up telegram on February 1st, Guinan
reports that Betelgeuse has continued to fade since the December image was taken. Betelgeuse’s nominal magnitude is around
+0.5 in middle of the visible part of spectrum, called the V-band. By the end of December it had fallen to about
magnitude +1.5. Now Guinan and Wasatonic report that the star
may have faded further to magnitude +1.62. That would make it as faint as nearby Bellatrix
in the constellation Orion. In other words, it appears that the star has
lost at least 2.5 times its original brightness since September. However, the star doesn’t seem to be fading
as rapidly as it did before, and it may in fact be leveling off. And, in a private communication, Guinan tells
me it’s been holding relatively steady for the last week or so, and if that's the case
then it may - just may, mind you - be approaching the end of its 420-day pulsation cycle and
we may start to see it brighten again before the end of winter. Or it may just continue to fade and confound
us even more [chuckles]. Still, despite the headlines, there isn’t
any new evidence that Betelgeuse will go supernova anytime soon. I mean, sure, if its core becomes iron it
could supernova tonight, but the reality is that probably won’t happen for another 100,000
years...despite my wishes that it would happen sooner...like tonight...while it's clear,
and I'm outside looking at it...come on, Betelgeuse, you owe me a solid... I discuss why in my last video on Betelgeuse
so make sure you check that out when we’re done here. In the meantime, make sure you out outside
tonight and take a look at Betelgeuse in the shoulder of Orion. It’s remarkable how faint it’s become. Now if we can just figure out why… Thanks once again to my patrons, especially
Michael Dowling and Steven J Morgan for helping to make Launch Pad Astronomy possible. If you’d like to help out for the price
of a cup of coffee every month, check out my Patreon page. And if you’d like to join me on this journey
of this incredible Universe of ours, please make sure to subscribe and ring that notification
bell so you don’t miss out on any new videos. Until next time, stay curious my friends.
