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The night sky might look like it never changes, but, if you look close enough, there's always something happening out there. Back in February, we told you about some strange observations astronomers had made of our neighboring star Betelgeuse.

As a red supergiant, Betelgeuse is basically a giant bomb waiting to go off, so it definitely got scientists' attention when its brightness started suddenly changing in late 2019. Over the course of a few months, the star's brightness dropped by a factor of three—and the southern half seemed to darken more dramatically than the north. It had lots of people wondering if it was getting ready to explode.

Then, in April, things just… returned to normal. Now, thanks to the Hubble Space Telescope, we finally have an idea what might have happened. In work published last week in The Astrophysical Journal, an international research team described observations that suggest the culprit might have been a cloud of dust that launched from the star itself.

A few months before Betelgeuse started acting up, the team began using Hubble to make regular observations of the star as part of a long-term study on variability in its outer layers. And starting in September 2019—just weeks before the star dimmed dramatically—this team detected a pulse of material moving outwards through the southern half of Betelgeuse's atmosphere. Throughout October and November, observations showed it continuing to move through the star's layers.

The pulse was made of hot, dense plasma, and at first, it actually made the star brighter in the ultraviolet part of the spectrum used by Hubble. Then, around December, the material left Betelgeuse behind and entered space. There, it quickly began to cool, forming a dense cloud of dust.

In their paper, the authors concluded that, around that time, the dust started blocking the star's visible light—which triggered that steep drop in brightness that got everybody's attention. So, it wasn't a sign that Betelgeuse was on the brink of explosion, and it definitely wasn't a sign that the energy beings that control our universe had had a glitch—it was just a cloudy few months for this star. Now, no one's entirely sure where this plume came from in the first place, but the authors speculate that it was the result of two physical processes lining up just right:.

For one, the material was likely caught in the updraft of what's called a convection cell. Convection is the circular motion of matter in the outer layers of a star that plays a big part in transporting the star's heat from its core to the surface. At the same time, the material likely got a boost from the star's natural expansion.

See, Betelgeuse goes through cycles of pulsation on time scales of around a year. It just happened to be expanding in late 2019, so, between that and a powerful convection updraft, the material just may have gotten the oomph it needed to break through the star's surface and into outer space. Then, after a few months of dimming the star, the cloud seems to have drifted out of our view, or maybe just dissipated.

Either way, we're seeing Betelgeuse bright and clear again. It's a subtle story that would have been really hard to tease apart without Hubble's help, so we're lucky the telescope just happened to be pointed the right way at the right time! Speaking of major observatories, last week we also got some unfortunate news from the.

Arecibo Observatory in Puerto Rico. In the early morning of August 10th, a massive steel support cable snapped, damaging the telescope and knocking its instruments offline. The cable was one of several supporting a giant steerable antenna called the Gregorian dome.

When it fell, the cable slashed into the metal structure of the dish, damaging about 250 of its nearly 40 thousand panels and leaving a hole more than 30 meters long. The cable was expected to last for decades longer than it did, so the observatory is currently investigating how it could have failed and what it will take to get the telescope up and running again. In the meantime, it's a big loss for astronomers.

Arecibo holds a unique place in the history of astronomy, and there's no scientific facility on Earth like it. It's a gigantic radio telescope that was built by the U. S. government in 1963.

And at 305 meters wide, it's so big that they built the dish into the Earth, using a natural sinkhole for support. Above its surface, a 900-ton platform is suspended in the air, with instruments that can not only listen to radio signals from across the universe, but also send them. Arecibo's planetary radar system can send a million watts of power into space—enough to bounce radio waves off objects like planets and asteroids in our solar system.

And in the last 60 years, it's been involved in discoveries that have transformed our understanding of the universe, including the discovery of the first pulsar and the first exoplanet. It's also a key tool in the search for asteroids that might hit Earth. In 1974, astronomers even used it to send our first message in search of extraterrestrial life, aiming a powerful radio transmission at a nearby star cluster.

But, more recently, the future of this aging observatory has become uncertain. In the last decade, the National Science Foundation, which provided most of the telescope's funding, began looking to move on. And in 2017, the facility was damaged when Hurricane Maria struck Puerto Rico.

The following year, a group led by the University of Central Florida stepped up to take over control of the observatory, but the damage caused by this latest problem won't make it any easier to keep the telescope online. Arecibo still has a lot to offer astronomy, though, and research depends on tools like it. So keep your fingers crossed for a speedy recovery.

Thanks for watching this episode of SciShow Space News! And a special thank you to this month's President of Space, Harrison Mills, for making this video possible. It takes a lot of people to make a SciShow video, and we could not do it without the support of our patrons.

If you're not yet a patron but want to join the amazing community helping us make science education free on the internet, you can find out how to support at patreon.com/SciShow. [ ♫ outro].