Betelgeuse is recovering from blowing its top

Four images of a mottled orange globe with light and dark clouds bursting out from one point.
Do you remember when Betelgeuse suddenly got dimmer in 2019 and 2020? Scientists are watching the star slowly recover from an outburst that darkened its light. Image via NASA/ ESA/ Elizabeth Wheatley (STScI).

NASA originally published this article on August 11, 2022. You can read the original here. Edits by EarthSky.

Betelgeuse literally blew its top in 2019

Analyzing data from NASA’s Hubble Space Telescope and several other observatories, astronomers have concluded that the bright red supergiant star Betelgeuse quite literally blew its top in 2019. Betelgeuse lost a substantial part of its visible surface and produced a gigantic Surface Mass Ejection (SME). This is something never before seen in a normal star’s behavior.

Our sun routinely blows off parts of its tenuous outer atmosphere, the corona, in an event known as a Coronal Mass Ejection (CME). But the Betelgeuse SME blasted off 400 billion times as much mass as a typical CME!

Betelgeuse is slowly recovering

The monster star is still slowly recovering from this catastrophic upheaval. Andrea Dupree of the Center for Astrophysics, Harvard & Smithsonian in Cambridge, Massachusetts, said:

Betelgeuse continues doing some very unusual things right now; the interior is sort of bouncing.

These new observations yield clues on how red supergiant stars lose mass late in their lives as their nuclear fusion furnaces burn out, before exploding as supernovae. The amount of mass loss significantly affects their fate. However, Betelgeuse’s surprisingly petulant behavior is not evidence the star is about to blow up anytime soon. So the mass loss event is not necessarily the signal of an imminent explosion.

Studying Betelgeuse before, during and after the SME

Dupree is now pulling together all the puzzle pieces of the star’s petulant behavior before, after and during the eruption into a coherent story of a never-before-seen titanic convulsion in an aging star.

This includes new spectroscopic and imaging data from the STELLA robotic observatory, the Fred L. Whipple Observatory’s Tillinghast Reflector Echelle Spectrograph (TRES), NASA’s Solar Terrestrial Relations Observatory spacecraft (STEREO-A), NASA’s Hubble Space Telescope, and the American Association of Variable Star Observers (AAVSO). Dupree emphasizes that the Hubble data was pivotal to helping sort out the mystery. She explained:

We’ve never before seen a huge mass ejection of the surface of a star. We are left with something going on that we don’t completely understand. It’s a totally new phenomenon that we can observe directly and resolve surface details with Hubble. We’re watching stellar evolution in real time.

The titanic outburst in 2019 was possibly caused by a convective plume, more than a million miles across, bubbling up from deep inside the star. It produced shocks and pulsations that blasted off a chunk of the photosphere. This left the star with a large, cool surface area under the dust cloud that was produced by the cooling piece of photosphere. Betelgeuse is now struggling to recover from this injury.

Dust cloud from the ejection blocked Betelgeuse’s light

Weighing roughly several times as much as our moon, the fractured piece of photosphere sped off into space and cooled to form a dust cloud. That’s what blocked light from the star as seen from Earth. The dimming, which began in late 2019 and lasted for a few months, was easily noticeable by backyard observers watching the star change brightness. One of the brightest stars in the sky, you can easily find Betelgeuse in the right shoulder of the constellation Orion.

Even more fantastic, the supergiant’s 400-day pulsation rate is now gone, perhaps at least temporarily. For almost 200 years astronomers have measured this rhythm as evident in changes in Betelgeuse’s brightness variations and surface motions. Its disruption attests to the ferocity of the blowout.

Betelgeuse: 4 panels of outbursts on star and graph with sine wave and also irregular wave.
View larger. | The 4 illustrations at top show Betelgeuse ejecting mass from January 2019 to March 2020. At the bottom is a graph that plots the star’s change in brightness over time. The escaping material cooled to form a cloud of dust that temporarily made the star look dimmer from Earth. This unprecedented stellar convulsion disrupted the monster star’s 400-day-long oscillation period that astronomers had measured for more than 200 years. The interior may now be jiggling like a plate of gelatin. Image via NASA/ ESA/ Elizabeth Wheatley (STScI).

An interior like gelatin

Dupree suggests the star’s interior convection cells, which drive the regular pulsation, may be sloshing around like an imbalanced washing machine. TRES and Hubble spectra imply that the outer layers may be back to normal, but the surface is still bouncing like a plate of gelatin as the photosphere rebuilds itself.

Though our sun has coronal mass ejections that blow off small pieces of the outer atmosphere, astronomers have never witnessed such a large amount of a star’s visible surface blasted into space. Therefore, surface mass ejections and coronal mass ejections may be different events.

Betelgeuse is now so huge that if it replaced the sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter. Dupree used Hubble to resolve hot spots on the surface of Betelgeuse in 1996. This was the first direct image of a star other than the sun. NASA’s Webb Space Telescope may be able to detect the ejected material in infrared light as it continues moving away from the star.

Big red fuzzy, blobby star, with white near center fading to deep red on edges.
Betelgeuse imaged in ultraviolet light by the Hubble Space Telescope, and subsequently enhanced by NASA. The bright white spot is likely one of this star’s poles. Image via Andrea Dupree/ Ronald Gilliland/ NASA/ ESA/

Bottom line: Astronomers concluded that the bright red supergiant star Betelgeuse literally blew its top in 2019. Betelgeuse lost a substantial part of its visible surface, causing a dust cloud to form and dimming the star as seen from Earth. Betelgeuse is still recovering from that outburst.


August 11, 2022

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