Tag Archives: betelgeuse

These images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprecedented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020 and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. (ESO/M. Montargès et al)

Astronomers Solve the Mystery of Betelgeuse’s ‘Great Dimming’

In late 2019 and early 2020 Betelgeuse, a red supergiant in the constellation of Orion, made headlines when it underwent a period of extreme dimming. This dip in brightness for the star, which is usually around the tenth brightest in the night sky over Earth, was so extreme it could even be seen with the naked eye.

Some scientists even speculated that the orange-hued supergiant may be about to go supernova, an event which would have been visible in daylight over Earth for months thanks to its power and relative proximity–700 light-years from Earth. Yet, that supernova didn’t happen and Betelgeuse returned to its normal brightness.

This left the ‘great dimming’ of Betelgeuse–something never seen in 150 years of studying the star–an open mystery for astronomers to investigate.

These images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprecedented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020, and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. (ESO/M. Montargès et al.)

Now, a team of astronomers led by Miguel Montargès, Observatoire de Paris, France, and KU Leuven, Belgium, and including Emily Cannon, KU Leuven, have found the cause of this dimming, thus finally solving this cosmic mystery. The researchers have discovered that the darkening of Betelgeuse was caused by a cloud of dust partially concealing the red supergiant.

“Our observations show that the Southern part of the star was hidden and that the whole disk of the star was fainter. The modelling is compatible with both a cool spot of the photosphere and a dusty clump in front of the star,” Montargès tells ZME Science. “Since both signatures have been detected by other observers, we conclude that the Great Dimming was caused by a cool patch of material that, due to its lower temperature, caused dust to form in gas cloud ejected by the star months to years before.”

The ‘great dimming’ of this massive star lasted a few months presented a unique opportunity for researchers to study the dimming of stars in real-time.

“The dimming of Betelgeuse was interesting to professional and amateur astronomers because not only was the appearance of the star changing in real time we could also see this change with the naked eye. Being able to resolve the surface of a star during an event like this is unprecedented.”

Emily Cannon, KU Leuven

The team’s research is published in the latest edition of the journal Nature.

A Unique Opportunity to Capture a Dimming Star

Montargès and his team first trained the Very Large Telescope (VLT)–an ESO operated telescope based in the Atacama Desert, Chile–on Betelgeuse when it began to dim in late 2019. The astronomers took advantage of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the VLT as well as data from the telescope’s GRAVITY instrument. This allowed them to create stunning images tracking the great dimming event allowing them to distinguish it from regular dips in brightness demonstrated by the supergiant stars.

Betelgeuse has been seen to decrease in brightness before as a result of its convection cycle, which causes material to rise and fall throughout the star’s layers based on its temperature. This convection cycle results in a semi-regular dimming cycle that lasts around 400 days.

When the ‘great dimming’ was first observed in October 2019 astronomers had assumed this was due to its natural dimming cycle. That assumption was dismissed by December that same year when the star became the darkest that it had been in a century. The star had returned to its normal brightness by April 2020.

“No other red supergiant star has been seen dimming that way, particularly to the naked eye. Even Betelgeuse that has been closely monitored for 150 years has not shown such behaviour.”

Miguel Montargès, Observatoire de Paris, France

Not only does this finding solve the mystery of this star’s dimming, but it also provides evidence of the cooling of a star causing the creation of stardust which goes on to obscure the star.

Even though Betelgeuse is much younger than the Sun–10 million years old compared to our star’s age of 4.6 billion years–it is much closer to the supernova explosion that will signal the end of its lifecycle. Astronomers had first assumed that dimming was a sign that the red supergiant was exhibiting its death throes ahead of schedule.

Thanks to the work of Montargès and his team, we now know this isn’t the case. The dimming is the result of a veil of stardust obscuring the star’s southern region.

“We have observed dust around red supergiant stars in the past,” Cannon explains. “However, this is the first time we have witnessed the formation of dust in real-time in the line of sight of a red supergiant star,”

This stardust will go on to form the building blocks of the next generation of stars and planets, and the observations made by Montargès, Cannon and the team represent the first time we have seen an ancient supergiant star ‘burping’ this precious material into the cosmos.

The Giant that Burped Stardust

The surface of Betelgeuse–which with its diameter of around 100 times that of the Sun would consume the orbits of the inner planets including Earth were it to sit in our solar system–is subject to regular changes as bubbles of gas move around it, change in size, and swell beneath it. Montargès, Cannon and their colleagues believe that sometime before the great dimming began the red supergiant ‘burped’ out a large bubble of gas.

This bubble moved away from the star leaving a cool patch on its surface. It was within this cool patch that material was able to solidify, creating a cloud of solid stardust. The team’s observations show for the first time that stardust can rapidly form on the surface of a star.

“We have directly witnessed the formation of so-called stardust,” says Montargès. “The dust expelled from cool evolved stars, such as the ejection we’ve just witnessed, could go on to become the building blocks of terrestrial planets and life.”

One explanation for why Betelgeuse went dark in 2019 is that the star ‘burped’ out a burst of gas and dust (illustrated, left), which condensed into a dark cloud and left a cool patch of stardust on the star’s surface. (right). (NASA, ESA, E. WHEATLEY/STSCI)

With regards to the future, the researchers point to the Extremely Large Telescope (ELT), currently under construction in the Atacama Desert as the ideal instrument to conduct further observations of Betelgeuse. “With the ability to reach unparalleled spatial resolutions, the ELT will enable us to directly image Betelgeuse in remarkable detail,” says Cannon. “It will also significantly expand the sample of red supergiants for which we can resolve the surface through direct imaging, further helping us to unravel the mysteries behind the winds of these massive stars.”

For Montargès solving this mystery and observing a phenomenon for the first time, solidifies a lifetime of fascination with Betelgeuse and points towards a deeper understanding of the stardust that is the building blocks of stars, planets, and us. “We have seen the production of star dust, materials we are ourselves made of. We have even seen a star temporarily change its behavior on a human time scale.”

Betelgeuse is getting dimmer — but will it explode soon?

This comparison image shows the star Betelgeuse before and after its unprecedented dimming. Credit: ESO/M. Montargès et al.

The 10-million-year-old star — a mere juvenile by stellar standards considering the Sun is 4.6 billion years old — is around 20 times more massive than the Sun and around 900 times larger. Virtually all red supergiants like Betelgeuse are destined to live fast and die young, eventually meeting their end in a supernova — the most powerful and luminous explosions known in astronomy.

Betelgeuse is a variable star, so it’s normal for it to get dimmer and brighter, but recent observations have been extremely surprising.

Astronomers operating ESO’s Very Large Telescope have found that since December of last year, Betelgeuse is now around 64% dimmer than its usual brightness.

On a normal day, Betelgeuse is the 11th brightest star in the sky, part of the Orion constellation. Today, it’s only the 24th brightest star.

These observations were made with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. This is one of the most advanced and exciting astronomical instruments equipped on an Earth-based observatory. SPHERE allows scientists to see the polarized infrared light emitted by newly forming planets (essentially just planetary disks at this point) orbiting around young stars. Apparently, it’s also sharp enough to capture extremely high-resolution pictures of Betelgeuse.

Because Betelgeuse is only 650 light-years away, and because it’s so large, astronomers were able to reveal certain features that would have otherwise been obscured, including convection cells, or granules. These are huge blobs of hot gas that have migrated from deep inside the core of the star to the surface.

The new images of Betelgeuse suggest that it has not only dimmed considerably, it also changed its shape.

Dimming red giants are believed to be a sign that they are about to imminently turn supernova.

If Betelgeuse truly was about to explode, it would be the brightest supernova ever observed in our galaxy. I’d be so brilliant that it would make it difficult to see other stars near it.

A direct-sky image of Betelgeuse. Credit: ESO/Digitized Sky Survey 2. Acknowledgment: Davide De Martin.

But while it’s possible that the star could explode anytime between this moment and 100,000 years from now, this dimming might not actually be a sign that it’s about to go supernova.

Artist’s impression of the supergiant star Betelgeuse. The scale in units of the radius of Betelgeuse, as well as a comparison with the Solar System, is also provided. Credit:
ESO/L. Calçada.

According to one theory, the red giant is currently undergoing a period of activity as it pulsates and as heat travels around its surface. Convection cells as big as 60% of the entire star’s size could be dimming Betelgeuse temporarily. Another explanation is that the star belched out a cloud of dust that has partially obscured our field of view.

“The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us,” said Miguel Montargès, an astronomer at KU Leuven in Belgium and the leader of the team responsible for the new observations. “Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen.”

So, the bottom line is that we don’t know if Betelgeuse is going to explode soon. Which is too bad — it would be quite the show if it happened during our lifetimes.

“The phrase ‘we are all made of stardust’ is one we hear a lot in popular astronomy, but where exactly does this dust come from?” says Emily Cannon, a PhD student at KU Leuven working with SPHERE images of red supergiants. “Over their lifetimes, red supergiants like Betelgeuse create and eject vast amounts of material even before they explode as supernovae. Modern technology has enabled us to study these objects, hundreds of light-years away, in unprecedented detail giving us the opportunity to unravel the mystery of what triggers their mass loss.”

Gravitational waves have scientists searching for answers

Gravitational waves were always going to pose more questions than answers — and that’s exactly what they’re doing.

What could have caused the new source of gravitational waves? Astronomers aren’t sure. (IMAGE: Shutterstock)

On January 14, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer picked up a split-second burst of gravitational waves, which are distortions in space-time. So far, it’s not known where the bursts were emitted from.

Generally, such waves are caused by the collision of immensely massive objects such as two black holes or two neutron stars — this is what happened in 2017 and again in April 2019.

However, these collisions generally last longer, whereas the new signals are short and they appear to come in a series from a very localized portion of the universe.

LIGO picked up the signals coming from the constellation Orion, which has some believing that an explosion of the red supergiant Betelgeuse might be forthcoming. Since October, the star — seen as the shoulder on the left side of Orion — has dimmed by a factor of two, something that has never been documented prior. This has some scientists believing that it could occur soonish (sometime between tomorrow or a 100,000 years from now). If it does occur, the star could leave us in spectacular fashion in the form of a supernova, where the glow could be as bright as the moon.

However, some don’t believe that to be the case. The burst “seems a little too short for what we expect from the collapse of a massive star,” Andy Howell, a scientist at Los Cumbres Observatory Global Telescope Network and an adjunct faculty member in physics at the University of California, Santa Barbara, told Live Science. Howell said that another reason he doesn’t believe this to be the case is that there were no neutrinos detected. Neutrinos are small subatomic particles supernovas are known to release which do not carry a charge.

Another possibility could be noise from LIGO itself, however, the fact that the burst was found by all three LIGO detectors (in Hanford, Washington; Livington, Louisiana; and Piso, Italy) essentially rules this out as well.

So that leaves astronomers scratching their heads as to what the latest burst could be. At least for now.

“The universe always surprises us,” Howell says. “There could be totally new astronomical events out there that produce gravitational waves that we haven’t really thought about.”

We were expecting gravitational waves to answer questions about the nature of the universe. That they did — but they are also posing pressing questions, for which there seems to be no answer yet.

Betelgeuse to turn supernova and become second Sun? No, not really

There’s been a whole lot of fuss lately, and you guys have also been writing a lot of emails about Betelgeuse turning supernova. I wrote about Betelgeuse and the odds of it going supernova, as well as the damage it would do a while ago, but there’s no harm in doing it again.

We are talking about one of the top 10 brightest stars, and one which will go supernova for sure – anytime in the next 100.000 years. The next year is just as good as any other one in the following 100.000, so we’re talking about a one in one hundred thousand chance; and for the next two years it’s 2 in 100.000, so 1 in 50.000. If we’re talking the next 100 years, it’s still 1 in 1000. It is possible, yes, but you shouldn’t bet your last penny on it.

“But what’s all this fuss about the star exploding by 2012? That’s complete garbage,” writes Discovery News’ Ian O’Neill. “There is absolutely no indication that the star will explode in the next year or so. Even the most advanced telescopes and sophisticated computer models cannot predict an exploding star with that precision!”

But even if it went boom tomorrow, what would really happen ? It wouldn’t be the major disaster most of the press has talked about. It would be bright, very bright, but it wouldn’t cook us, and as a matter of fact, it wouldn’t even be hot. Considering the distance, it would be about 1/100,000 as bright as the Sun. Basically, we would be able to see it as another full moon, but nothing more. Betelgeuse does pack a significant stellar power, but it’s 640 light-years away ! So there’s nothing to make you lose any sleep from this point of view.

No people, Betelgeuse is not going supernova

First of all, I have no idea how this rumour started, but a number of people signaled this already; the rumour sounded something like this:

I was talking to my son last week (he works on Mauna Kea), and he mentioned some new observations (that will no doubt get published eventually) of “Beetlejuice”; it’s no longer round. This is a huge star, and when it goes, it will be at least as bright as that 1054 supernova…except that this one is 520 light years away, not 6,300

Yep, it's this big

Yep, it's this big

Betelgeuse is about 100.000 times bigger than the sun, and “just” 600 light years away, so if it would have gone supernova, it would have been a big deal; although it probably wouldn’t hurt us, it would be an astronomical bonanza like no other ever seen in our history.

I don’t know where this rumour first popped out, but by the I read it, it sounded really vague and not quite trustworthy; sounded like something somebody heard from somebody who sort of heard it. It’s also not true, at least according to the man who runs the observatory on Mauna Kea. According to him:

Betelgeuse will go supernova within the next 100,000 years, so the odds against it doing so in the next year are 100,000-to-1. We have no information about “recent” observations of Betelgeuse collapsing. It’s actually quite unlikely that Betelgeuse would have been targeted for observation in the last month or so, as it’s not unfavorably close to the Sun and therefore difficult to observe.