Astronomers have concluded that the bright red supergiant star Betelgeuse literally blew its top in 2019, losing a significant portion of its visible surface and producing a massive Surface Mass Ejection (SME) after analyzing data from NASA’s Hubble Space Telescope and several other observatories. This is something never before seen in a normal star’s behavior.
In an event known as a Coronal Mass Ejection (CME), our Sun routinely blows off parts of its tenuous outer atmosphere, the corona. However, the Betelgeuse SME ejected 400 billion times the mass of a typical CME!
The monster star
is still struggling to recover from the effects of the catastrophic upheaval. “Betelgeuse continues doing some very unusual things right now; the interior is sort of bouncing,” said Andrea Dupree of the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts.
These new findings shed light on how red stars lose mass as their nuclear fusion furnaces burn out before exploding as supernovae. The amount of mass lost has a significant impact on their fate. Betelgeuse’s surprisingly petulant behavior, on the other hand, is not evidence that the star is about to explode anytime soon. As a result, the mass loss event is not always indicative of an impending explosion.
Dupree is now piecing together 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.
“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.”
A convective plume more than a million miles across,
bubbling up from deep within the star, may have caused the 2019 titanic outburst. It generated shocks and pulsations that blasted the chunk of photosphere away, leaving the star with a large cool surface area beneath the dust cloud created by the cooling piece of photosphere. Betelgeuse is currently recovering from this injury.
The fractured piece of photosphere, which weighed roughly several times as much as our Moon, sped off into space and cooled to form a dust cloud, which blocked light from the star as seen by Earth observers. The dimming, which began in late 2019 and lasted a few months, was easily visible even by backyard observers watching the star’s brightness change. Betelgeuse, one of the brightest stars in the sky, can be found in the right shoulder of the constellation Orion.
Even more incredible,
the supergiant’s 400-day pulsation rate has gone, at least temporarily. For nearly 200 years, astronomers have observed this rhythm in variations in Betelgeuse’s brightness and surface motions. Its disruption attests to the ferocity of the blowout.
According to Dupree, the star’s interior convection cells, which drive the regular pulsation, may be sloshing around like an unbalanced washing machine tub. The TRES and Hubble spectra indicate that the outer layers have returned to normal, but the surface is still bouncing like a plate of gelatin dessert as the photosphere rebuilds.
Even though our Sun has coronal mass ejections
that blow off small pieces of its outer atmosphere, astronomers have never seen such a large portion of a star’s visible surface blasted into space. As a result, surface mass ejections and coronal mass ejections could be distinct events.
Betelgeuse has grown so large that if it replaced the Sun at the center of our solar system, its outer surface would extend beyond Jupiter’s orbit. In 1996, Dupree used Hubble to resolve hot spots on the star’s surface. This was the first direct image of a star other than the Sun.
The ejected material may be detectable in infrared light by NASA’s Webb Space Telescope as it moves away from the star.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). The telescope is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations.
Illustration Credit: NASA, ESA, Elizabeth Wheatley (STScI)