It is a safe bet that most people who hear the name Betelgeuse think first of the 1988 fantasy horror comedy Beetlejuice, directed by Tim Burton and starring Michael (The Best Batman) Keaton as the obnoxious "bio-exorcist" from the Netherworld. That Beetlejuice was known to blow his top at the tiniest of annoyances. This week, another Betelgeuse blew its top (or possibly its bottom) – the famous star in the Orion constellation has been mysteriously dimming and astronomers suspect it is dying, but this enormous explosion blew off a huge chunk of its mass the likes of which astronomers have never seen before. This Betelgeuse is no longer dimming and the surface mass ejection may explain where it is at in its death cycle or it may not – astronomers say the star’s pulse’ has quickened. Will this Betelgeuse become the Michael Keaton of stars?
“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.”
Andrea Dupree of the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, gives full credit to the Hubble Space Telescope, which is definitely not in its dying days as the James Webb Space Telescope goes operational and gets all of the media attention, for the ability to watch Betelgeuse go through what appears to be its inevitable demise. In a NASA press release, she points out that the bright star of the Orion constellation, positioned on the right shoulder of Orion the hunter, caught everyone’s attention in October 2019 when its naked-eye brightness mysteriously began to dim. Just four months later in February 2020, its brightness had diminished by a factor of three. And then, as unexpectedly as it began to dim, Betelgeuse began to brighten again. Dupree is the lead author of a pre-print study entitled “The Great Dimming of Betelgeuse: a Surface Mass Ejection (SME) and its Consequences” where she attempts to make sense of these new actions of Betelgeuse.
"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."
By 2019, astronomers knew that Betelgeuse was an aging red star whose nuclear fusion center was burning out on its way to exploding in a supernova death. The dimming that year was at first assumed to be part of its regular increasing and decreasing brightness cycle due to size and temperature changes that contributed to its pulsating appearance. As it got dimmer than usual, astronomers theorized an eruption of gas or dust may have caused this particular severe reduction in brightness. Dupree led a team that used the Hubble, the Fred L. Whipple Observatory's Tillinghast Reflector Echelle Spectrograph (TRES), NASA's Solar Terrestrial Relations Observatory spacecraft (STEREO-A), and the American Association of Variable Star Observers (AAVSO) to study Betelgeuse age to the bottom of the dimming. Surprisingly, that’s where it came from – its bottom.
“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 the chunk of the photosphere leaving the star with a large cool surface area under the dust cloud that was produced by the cooling piece of photosphere.”
That “chunk” of the photosphere or solar atmosphere weighed several times as much as the Moon and shot far into space before cooling into a thick cloud of dust – the cloud that caused the dimming of Betelgeuse as observed by us Earthlings even without telescopes. A blast of that magnitude, causing the loss of such a huge piece of a star, should have hastened the death of Betelgeuse. But it mysteriously didn’t. After just a few months, the dimming stopped and the brightness quickly returned as the cloud of dust continued to move away from the star. Astronomers are hoping that the new kid on the block – James Webb – can be trained on Betelgeuse to detect and track the movement of the infrared light of the cloud. In the meantime, astronomers are looking for answers as to why Betelgeuse is looking somewhat healthier than before.
“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.”
In a description that could have come from a teen describing a massive belch and its aftermath, Dupree says “The star's interior convection cells, which drive the regular pulsation may be sloshing around like an imbalanced washing machine tub” and “the surface is still bouncing like a plate of gelatin dessert as the photosphere rebuilds itself.” And even after losing such a massive chunk of weight, Betelgeuse is growing again.
“Betelgeuse is now 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.”
That size makes comparisons between the slow dying of Betelgeuse and our Sun (in comparison) nearly useless. Not only had astronomers never seen a massive star blow so much of its surface into space, it has many thinking that surface mass ejections and coronal mass ejections may be completely different events. That could be good news for us – even though our Sun isn’t scheduled to die for a while.
If anyone should have an attachment to Betelgeuse – and an ache in their heart at the thought of its eventual supernova death – it is Andrea Dupree. She was the first astronomer to resolve hot spots on the star's surface in 1996 which was the result of the first direct image of a star other than the Sun ever by an astronomer. And the telescope she used? The Hubble … which means Dupree probably feels the same way about the eventual demise of the Hubble as James Watt and other new telescopes take over.
Who knew that astronomy was such an emotional profession?