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Analyzing data from NASA’s Hubble Space Telescope and several observatories, astronomers have concluded that the bright red supergiant star Betelgeuse literally blew its top in 2019, losing a substantial portion of its visible surface and producing a gigantic surface mass ejection (SME). This is something never seen before in the behavior of a normal star.
Our Sun routinely ejects parts of its tenuous outer atmosphere, the corona, in an event known as a coronal mass ejection (CME). But the Betelgeuse SME shot out 400 billion times more mass than a typical CME!
The monster star is still slowly recovering from this catastrophic upset. “Betelgeuse is still doing very unusual things right now; the interior is bouncing around,” said Andrea Dupree of the Center for Astrophysics | Harvard and Smithsonian in Cambridge, Massachusetts.
These new observations provide clues about how red stars lose mass at the end of their lives as their nuclear fusion furnaces burn out, before exploding as supernovae. The amount of mass loss significantly affects its fate. However, Betelgeuse’s surprisingly petulant behavior is not evidence that the star is about to explode anytime soon. Therefore, the mass loss event is not necessarily the signal of an imminent explosion.
Dupree is now piecing 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 imaging and spectroscopic data from the STELLA robotic observatory, the Fred L. Whipple Observatory’s Tillinghast Reflector Echelle Spectrograph (TRES), the Solar Earth Relations Observatory (STEREO-A) spacecraft, the NASA Hubble Space Telescope and the American Variable Association. Star Observers (AAVSO). Dupree stresses that the Hubble data was instrumental in helping to solve the mystery.
“We’ve never seen such a massive ejection from the surface of a star before. We’re left with something we don’t fully understand. It’s a brand new phenomenon that we can observe directly and resolve the surface details with Hubble. We’re seeing the evolution stellar in real time.”
The 2019 titanic explosion was possibly caused by a convective plume, more than a million miles in diameter, that rose from deep within the star. It produced shocks and pulsations that blew off the photosphere piece leaving the star with a large cool surface beneath the dust cloud that was produced by the cooled piece of the photosphere. Betelgeuse is now struggling to recover from this injury.
Weighing roughly several times that of our Moon, the fractured piece of photosphere drifted off into space and cooled to form a dust cloud that blocked the star’s light as seen by observers of the Earth The dimming, which began in late 2019 and lasted several months, was easily noticeable even by backyard observers who saw the star change in brightness. One of the brightest stars in the sky, Betelgeuse sits easily on the right shoulder of the constellation Orion.
Even more fantastic, the supergiant’s 400-day pulse rate is gone, at least temporarily. For nearly 200 years, astronomers have measured this rhythm as evident in changes in Betelgeuse’s brightness variations and surface motions. Its interruption attests to the ferocity of the explosion.
Dupree suggests that the star’s inner convection cells, which drive the regular pulsation, can move like an unbalanced washing machine tub. The TRES and Hubble spectra imply that the outer layers may be returning to normal, but the surface is still bouncing like a jello dessert plate as the photosphere rebuilds.
Although our Sun has coronal mass ejections that eject small pieces of the outer atmosphere, astronomers have never witnessed such a large amount of a star’s visible surface sink into space. Therefore, surface mass ejections and coronal mass ejections may be different events.
Betelgeuse is now so large that if it were to replace the Sun at the center of our solar system, its outer surface would extend beyond the orbit of Jupiter. Dupree used Hubble to resolve hot spots on the star’s surface 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 to move away from the star.
The Hubble Space Telescope is an international cooperation project between NASA and the ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, DC
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