Hubble Finds Cause for Betelgeuse’s Mysterious Dimming – Is Aging Red Supergiant About to Supernova?

This four-panel graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020. In the first two panels, as seen in ultraviolet light with the Hubble Space Telescope, a bright, hot blob of plasma is ejected from the emergence of a huge convection cell on the star’s surface. In panel three, the outflowing, expelled gas rapidly expands outward. It cools to form an enormous cloud of obscuring dust grains. The final panel reveals the huge dust cloud blocking the light (as seen from Earth) from a quarter of the star’s surface. Credit: NASA, ESA, and E. Wheatley (STScI)

Hubble Finds That Betelgeuse’s Mysterious Dimming Is Due to a Traumatic Outburst

Observations by NASA’s Hubble Space Telescope are showing that the unexpected dimming of the supergiant star Betelgeuse was most likely caused by an immense amount of hot material ejected into space, forming a dust cloud that blocked starlight coming from Betelgeuse’s surface.

Hubble researchers suggest that the dust cloud formed when superhot plasma unleashed from an upwelling of a large convection cell on the star’s surface passed through the hot atmosphere to the colder outer layers, where it cooled and formed dust grains. The resulting dust cloud blocked light from about a quarter of the star’s surface, beginning in late 2019. By April 2020, the star returned to normal brightness.

Betelgeuse is an aging, red supergiant star that has swelled in size due to complex, evolving changes in its nuclear fusion furnace at the core. The star is so huge now that if it replaced the Sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter.

The unprecedented phenomenon for Betelgeuse’s great dimming, eventually noticeable to even the naked eye, started in October 2019. By mid-February 2020, the monster star had lost more than two-thirds of its brilliance.

This sudden dimming has mystified astronomers, who scrambled to develop several theories for the abrupt change. One idea was that a huge, cool, dark “star spot” covered a wide patch of the visible surface. But the Hubble observations, led by Andrea Dupree, associate director of the Center for Astrophysics | Harvard & Smithsonian (CfA), Cambridge, Massachusetts, suggest a dust cloud covering a portion of the star.

Several months of Hubble’s ultraviolet-light spectroscopic observations of Betelgeuse, beginning in January 2019, yield a timeline leading up to the darkening. These observations provide important new clues to the mechanism behind the dimming.

Hubble captured signs of dense, heated material moving through the star’s atmosphere in September, October, and November 2019. Then, in December, several ground-based telescopes observed the star decreasing in brightness in its southern hemisphere.

“With Hubble, we see the material as it left the star’s visible surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim,” Dupree said. “We could see the effect of a dense, hot region in the southeast part of the star moving outward.

“This material was two to four times more luminous than the star’s normal brightness,” she continued. “And then, about a month later, the south part of Betelgeuse dimmed conspicuously as the star grew fainter. We think it is possible that a dark cloud resulted from the outflow that Hubble detected. Only Hubble gives us this evidence that led up to the dimming.”

The team’s paper will appear online today (August 13, 2020) in The Astrophysical Journal.

Massive supergiant stars like Betelgeuse are important because they expel heavy elements such as carbon into space that become the building blocks of new generations of stars. Carbon is also a basic ingredient for life as we know it.

Tracing a Traumatic Outburst

Dupree’s team began using Hubble early last year to analyze the behemoth star. Their observations are part of a three-year Hubble study to monitor variations in the star’s outer atmosphere. Betelgeuse is a variable star that expands and contracts, brightening and dimming, on a 420-day cycle.

Hubble’s ultraviolet-light sensitivity allowed researchers to probe the layers above the star’s surface, which are so hot — more than 20,000 degrees Fahrenheit — they cannot be detected at visible wavelengths. These layers are heated partly by the star’s turbulent convection cells bubbling up to the surface.

Hubble spectra, taken in early and late 2019, and in 2020, probed the star’s outer atmosphere by measuring magnesium II (singly ionized magnesium) lines. In September through November 2019, the researchers measured material moving about 200,000 miles per hour passing from the star’s surface into its outer atmosphere.

This hot, dense material continued to travel beyond Betelgeuse’s visible surface, reaching millions of miles from the seething star. At that distance, the material cooled down enough to form dust, the researchers said.

This interpretation is consistent with Hubble ultraviolet-light observations in February 2020, which showed that the behavior of the star’s outer atmosphere returned to normal, even though visible-light images showed that it was still dimming.

Although Dupree does not know the outburst’s cause, she thinks it was aided by the star’s pulsation cycle, which continued normally though the event, as recorded by visible-light observations. The paper’s co-author, Klaus Strassmeier, of the Leibniz Institute for Astrophysics Potsdam, used the institute’s automated telescope called STELLar Activity (STELLA), to measure changes in the velocity of the gas on the star’s surface as it rose and fell during the pulsation cycle. The star was expanding in its cycle at the same time as the upwelling of the convective cell. The pulsation rippling outward from Betelgeuse may have helped propel the outflowing plasma through the atmosphere.

Dupree estimates that about two times the normal amount of material from the southern hemisphere was lost over the three months of the outburst. Betelgeuse, like all stars, is losing mass all the time, in this case at a rate 30 million times higher than the Sun.

Betelgeuse is so close to Earth, and so large, that Hubble has been able to resolve surface features – making it the only such star, except for our Sun, where surface detail can be seen.

Hubble images taken by Dupree in 1995 first revealed a mottled surface containing massive convection cells that shrink and swell, which cause them to darken and brighten.

A Supernova Precursor?

The red supergiant is destined to end its life in a supernova blast. Some astronomers think the sudden dimming may be a pre-supernova event. The star is relatively nearby, about 725 light-years away, which means the dimming would have happened around the year 1300. But its light is just reaching Earth now.

“No one knows what a star does right before it goes supernova, because it’s never been observed,” Dupree explained. “Astronomers have sampled stars maybe a year ahead of them going supernova, but not within days or weeks before it happened. But the chance of the star going supernova anytime soon is pretty small.”

Dupree will get another chance to observe the star with Hubble in late August or early September. Right now, Betelgeuse is in the daytime sky, too close to the Sun for Hubble observations. But NASA’s Solar Terrestrial Relations Observatory (STEREO) has taken images of the monster star from its location in space. Those observations show that Betelgeuse dimmed again from mid-May to mid-July, although not as dramatically as earlier in the year.

Dupree hopes to use STEREO for more follow-up observations to monitor Betelgeuse’s brightness. Her plan is to observe Betelgeuse again next year with STEREO when the star has expanded outward again in its cycle to see if it unleashes another petulant outburst.

Reference: “Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse” by Andrea K. Dupree, Klaus G. Strassmeier, Lynn D. Matthews, Han Uitenbroek, Thomas Calderwood, Thomas Granzer, Edward F. Guinan, Reimar Leike, Miguel Montargès, Anita M. S. Richards, Richard Wasatonic and Michael Weber, 13 August 2020, The Astrophysical Journal.
DOI: 10.3847/1538-4357/aba516

AstronomyHubble Space TelescopeNASANASA Goddard Space Flight CenterPopularStars
Comments ( 40 )
Add Comment
  • Peter Webster

    At the end of one’s life all is dust

  • Tomtom

    Too bad this story came out a few months ago. A little behind are we.

    • Tired of ID10ts

      What story are you referring to? Betelgeuse dimming? Yes that was months ago. This particular paper is just coming out, and it is providing a hypothesis as to what caused the dimming. See the reference right at the bottom of the article – it was published on 13 August.

  • Rob

    Technically, it probably happened a long time ago, but because of the immense distance, the visual spectacle hasn’t reached Earth yet.

  • Sybille Stahl

    Wouldn’t it be great if we got to see Betelgeuse go supernova!

    • Tired of ID10ts

      Yes! I was hoping it would go supernova. Being able to see that in my own lifetime would have been awesome. Come on 2020, for all the crap you’ve brought us, you owe us this!

  • Adam Colbenson

    Betelgeuse, Betelgeuse,Betelgeuse!

  • Jim__H

    Well that was certainly an interesting read

  • Link

    Why is it that NASA and Hubble always give us a graphic or artist rendition fake stuff they say they see in space

    • Tired of ID10ts

      Because this is a news article for the general public. The actual images are not easy to interpret unless you are an experienced astrophysicist. The actual images are available on the net.

  • H Munster

    Why do we only get graphic illustration and no actual image from Hubble?

    • Tired of ID10ts

      Because if you were given ultraviolet spectroscopy images from Hubble you wouldn’t be able to distinguish it from that mole on your girlfriend’s left buttock (ok, don’t ask me how I know).

  • Bob Jarvis

    @AdamColbenson – It’s…showtime!

    But that’s why I won’t do two shows a night. Just won’t do it!

  • Donnie

    No. They’re just having some electrical problems.

  • Donnie

    An Earth that is made into a garden and a sun is bound to have problems from time to time. We’re only human.

    • Tired of ID10ts

      If snails had wings, then woolly rhinos are bound to fart rainbows from time to time. Humans are only us.

  • Kosiiq

    There are multiple photos taken of Betelguese all over the internet for those with just a little bit of a sense of how Google works. There are also photos of the actual dimming too.

  • solar godzilla

    If the star goes supernova in my lifetime, it hope that it goes when it is visible in the night sky. We could use a little cheap entertainment and education.

  • Sam Starr

    Possibly recurrent micronovae when transitioning into more electrified galactic current sheet every 12k years. Stars across the galaxy are ejecting plasma, planets their atmosphere. The timeline is important. 600 years for Betelguese but a lot less for Pluto. Atmospheric rivers indicative of more electrified atmosphere (surface water attracted to ambiant current) here on earth. Electrical earth discharges happening with more frequency, (more surface to sky lightening.) Profound changes afoot. Thanks mad scientists in Wuhan for your epic timing. Time to go underground where possible. SuspiciousObservers on YT spells it all out.

    • Tired of ID10ts

      This kind of article never fails to bring out the loonies.

  • Squanch master

    I hope it unexpectedly goes SuperNova, but could that effect or atmosphere?

    • Tired of ID10ts

      No. Betelgeus is close enough to put on a spectacular show, but far enough not to have adverse effects on Earth. That’s the best kind of supernova to have.

  • RLM

    You will never see the super nova. You missed the part that the events seen now by Hubble happened 1300 years ago. I don’t think your social security checks will last that long.

    • Tired of ID10ts

      If Betelgeus went supernova 1300 years and 1 day ago, you would see it in the sky tomorrow. Maybe you are confused about something.

  • Squanch master

    Nvm I was thinking Pulsar pointed in our direction

  • Squanch master

    Yeah about 725;lightyears away from 🌎 so we’re just seeing it now

  • Ishstarr1

    If there are billions of stars in our galaxy and billions and billions of galaxies in the universe why dont we see a supernova every night in the night sky.surely it must be a common occurrence in the universe

  • Richard Wainio

    I like how they named this star after Lori Lightfoot! So stunning and so brave!

    • Tired of ID10ts

      Yep, there’s always that moron with a political statement in a science article comments section. You sir, win the moronet award for this post.

  • John Wilson

    Spoiler Alert: Betelgeuse already went supernova on May 30, 1431 (complete conjecture on my part). So, there’s still approx. 135 years until “we” see it.

  • Dawn

    I worked as a Technical Writer at Lockheed Missiles & Space (now Lockheed Martin) in Sunnyvale, Calif in the late 1980s. We built the Hubble Space Telescope there in a four or five story clean room. I remember when it was completed there was a day when I was invited to actually go over to that building to see it. It was very exciting. I took the elevator up to the top floor, got off and walked down this hallway where there was a huge window to the middle atrium. I looked out the window and down and there it was! I’ll never forget the big round silver Hubble. Down below on the ground floor I could see staff walking around fully covered in white suits and masks to protect it from dust, etc… Up where I was they had a big table set up with champagne and glasses. I got a glass and stayed there staring at th he Hubble through the window like it was a newborn baby at the hospital. There were many scientist from around the world there chatting in different languages and crying. I’ll never forget two French scientists hugging and crying. On the Hubble they had the logos of the various companies who had contributed to building it including LMSC. I imagine those logos are still there. They said the silver foil covering the Hubble was as thin as household aluminum foil! Waylon Jennings, his wife and son (who was a young boy then) visited LMSC and saw the Hubble. The Hubble equaled magic. And my goodness 30 years later it’s still out there producing its’ magic.

    • Cauldron Of Stardust

      @Dawn So you saw Hubble before it went into space. Certainly you would’ve been able to see that the Perkin-Elmer mirror was overbuffed by one-50th the length of a human hair thickness. Why didn’t you say anything!? lol, Just kidding. Great story. That’s awesome that you saw Hubble before it went up into Earth orbit & began doing its thing (that thing it does, of course, is being the most awesome thing ever!). The recollection of the seeing the French scientists crying with happiness was an nice detail to really convey just how deeply it touched all those involved with its creation. 🙂

  • Dawn

    They said from outer space the Hubble could zoom in on a dime laying on a sidewalk and photograph it. I still have a Hubble Space Telescope sticker that I got that day I viewed it. They flew it to Florida from Moffett Field Naval Air Station located next door to Lockheed. Now Google leases (or owns) that landing strip for all there private jets. The Navy Base is gone. Lockheed is still there in several buildings.

    For a while sometime in the 1990s I worked at Loral Space Systems in Mountain View, Calif and they were building satellites for China! WHY?

  • Robert Smith

    When it goes, it’ll be brighter than the Moon in the night sky

  • Tired of tired

    I wouldn’t want the betelgeuse to disappear, so how could Orion go hunting without one arm?
    The whole sky wouldn’t make sense then.

  • James

    I have Betelgeuse all over my windshield. It must have went supernova already. It went supernova about the time Columbus discovered America.

  • Patrick Hansen

    I’m more conserned about what effect it may have on the ort clowd. How much pressure would it take to create a shooting gallery?

  • Tesla the poor

    Even if it had a pressure wave srrong enough to effect it last time a star came close to oir solar system didsturbed ort cloud bout 30k years ago. Takes about 150k years for anything to make it here from ort cloud.

  • Jric107

    It is my belief that this the birth formation of a planetary mass. Much like I believe our own planets were formed. That is why planets hover around their host stars. It’s only logical to understand the recent discovery of hundreds of exoplanets. Hovering about their primary host stars as well

  • Clyde Turner Bain

    ‘We are stardust, we are golden, and we’ve got to get ourselves back to the garden’