Hubble reveals that Betelgeuse’s mysterious pain is due to a traumatic explosion
Observations from NASA‘s Hubble Space Telescope are showing that the sudden fading of the supergiant star Betelgeuse is likely to be caused by an extraordinary amount of hot material expelled into space, forming a cloud of dust that blocked the rays of stars coming from the surface of Betelgeuse.
Hubble researchers suggest that dust clouds form when superhot is made plasma released by the rise of a large convection cell on the surface of the star passed through the hot atmosphere to the colder outer layers, where it cooled and formed grains of dust. The resulting dust cloud blocked light from about a quarter of the star’s surface, beginning in late 2019. By April 2020, the star had returned to normal brightness.
Betelgeuse is an old, red supergiant star that has grown in size due to complications, evolving the changes in its nuclear fusion furnace in essence. The star is so large now that if it were to replace the Sun at the center of our solar system, its outer surface would extend beyond its orbit. Jupiter.
The unprecedented phenomenon for the Betelgeuse darkening, eventually visible even to the naked eye, began in October 2019. By mid-February 2020, the monster star had lost more than two-thirds of its luster.
This sudden eclipse has mystified astronomers, who tried to develop several theories for sudden change. One idea was that a large, cool, dark “star spot” covered a large part of the visible surface. But Hubble observations, led by Andrea Dupree, associate director of the Center for Astrophysics | Harvard & Smithsonian (CFA), Cambridge, Massachusetts, suggest a cloud of dust covering part of the star.
Several months of Betelgeuse Hubble spectroscopic ultraviolet light observations, starting in January 2019, provide a timeline that leads to obscuration. These observations provide important new data for the mechanism after dark.
Hubble captured signs of dense, hot material moving through the star’s atmosphere in September, October, and November 2019. Then, in December, several ground-based telescopes observed the star, shrinking in brightness in its southern hemisphere.
“With Hubble, we see the material as they leave the visible surface of the star and move through the atmosphere, before the dust formed that caused the star to fade,” Dupree said. “We can see the effect of a dense and hot region in the southeastern part of the star moving out.
“This material was two to four times brighter than the star’s normal brightness,” she continued. “And then, about a month later, the southern part of the Betelgeuse faded noticeably as the star became weaker. We think it is possible that a dark cloud will result from the leak that Hubble discovered. Only Hubble us gives this proof that led to darkness. “
The team newspaper will appear online today (August 13, 2020) at Astrophysical Magazine.
Massive supergiant stars like Betelgeuse are important because they expel heavy elements like carbon into space that become the building blocks of new generations of stars. Carbon is also an essential ingredient for life as we know it.
Tracing a traumatic outburst
The Dupree team began using Hubble early last year to analyze the behemoth star. Their observations are part of a three-year Hubble study to monitor changes in the star’s outer atmosphere. Betelgeuse is a variable star that expands and contracts, glowing and darkening, in a 420-day cycle.
Hubble’s sensitivity to ultraviolet light allowed researchers to investigate layers above the star’s surface that are so hot – more than 20,000 degrees degrees Fahrenheit – they can not be detected at visible wavelengths. These layers are partially heated by turbulent convection cells of the star that ignite to the surface.
Hubble spectra, taken in early and late 2019, and in 2020, investigated the star’s outer atmosphere by measuring the lines of magnesium II (the only ionizing magnesium). In September to November 2019, researchers measured the material by moving about 200,000 miles per hour passing from the star’s surface to its outer atmosphere.
This hot, dense material continued to travel beyond the visible surface of the Betelgeuse, reaching millions of miles from the star it caught. At that distance, the material cooled enough to form dust, the researchers said.
This interpretation is consistent with Hubble-light ultraviolet observations in February 2020, which showed that the star’s outer atmosphere behavior returned to normal, although visible light images showed that it was still obscuring.
Although Dupree does not know the cause of the explosion, she thinks it was helped by the star’s pulsation cycle, which continued normally even though the event, as recorded by observations with visible light. The paper’s co-author, Klaus Strassmeier, of the Leibniz Institute for Astrophysics in Potsdam, used the institute’s automated telescope called the STELLar Activity (STELLA) to measure changes in gas velocity at 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 convective cell was rising. The pulse coming out of the Betelgeuse may have helped push the plasma flowing through the atmosphere.
Dupree estimates that about twice the normal amount of material from the southern hemisphere was lost during the three months of the eruption. 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 managed to solve the features of the surface – making it the only such star, other than our Sun, where surface details can be seen.
Hubble images taken by Dupree in 1995 first revealed a smooth surface containing massive convection cells that shrink and swell, causing them to darken and glow.
A Supernova Forerunner?
The red superstar is destined to end his life in a supernova explosion. Some astronomers think the sudden eclipse may be a pre-supernova event. The star is relatively close, about 725 light-years away, which means that the eclipse would have occurred around 1300. But its light is now reaching Earth.
“No one knows what a star does before it goes to supernovae because it has never been observed,” Dupree explained. “Astronomers have examined stars, maybe a year before them, going to supernovae, but not within days or weeks before it happened. But the chance that the star will go to supernovaes anytime soon is very small.”
Dupree will get another chance to observe the star with Hubble in late August or early September. Now, Betelgeuse is in the sky during the day, very close to the Sun for Hubble observations. But NASA’s Solar Earth Observatory (STEREO) has taken pictures of the monster star from its location in space. These observations show that Betelgeuse faded again from mid-May to mid-July, though not as dramatically as at the beginning of the year.
Dupree hopes to use STEREO for more follow-up observations to monitor Betelgeuse brightness. Her plan is to observe Betelgeuse again next year with STEREO when the star has expanded back out into its cycle to see if it launches another petulant explosion.
Reference: “Betelgeuse excellent spatially resolved ultraviolet spectroscopy” by Andrea K. Dupree, Klaus G. Strassmeier, Lynn D. Matthews, Han Whitenbroek, Thomas Calderwood, Thomas Granzer, Edward F. Guinan, Reimar Leike, Miguel Montargè , etc. Anita MS Richards, Richard Wasatonic and Michael Weber, 13 August 2020, Astrophysical Magazine.
DOI: 10.3847 / 1538-4357 / aba516