This concept of 3-paneled artists illustrates new research, and explains why the bright red supergiant star Betelgeuse became fuller in late 2019 and early 2020 for several months. In panel 1, a bright, warm blob of plasma is emitted from the star. In panel 2, effluent gas expands outward and cools to form an enormous cloud of hidden dust. In panel 3, the enormous dust cloud partially blocks the light of Betelgeuse. Image via NASA / ESA / E. Wheatley (STScI) / CfA.
For our skywatchers, it was a lot of fun – and totally shocking – when the famous bright star Betelgeuse unexpectedly deepened in late 2019 and early 2020. Betelgeuse has such a solid face in our night life (and some of us) in the night sky have been for a while), shone with a red light on the shoulder of the easily visible constellation Orion the Hunter. The dimming of Betelgeuse was even more exciting, as it is a known fact that this star will one day explode. Was the sudden dimming of Betelgeuse a sign that it would soon explode? Speculation raged for weeks, when we looked at a fierce Betelgeuse than we had ever seen before. The star did not explode. In fact, the end of February began to clear again. Then last week – on August 13, 2020 – scientists released a new study suggesting that the sudden dimming of Betelgeuse was likely caused by the emission and cooling of dense hot gases. In the meantime, as I write this, it appears that Betelgeuse is dimming once more, about a year earlier than expected.
A statement from the Harvard & Smithsonian Center for Astrophysics (CfA) stated:
Between October and November 2019, Hubble Space Telescope observed dense, heated material orbiting through the star’s extended atmosphere at 200,000 miles per hour. The following month, several telescopes on the ground saw a decrease in brightness in the southern hemisphere of Betelgeuse, as if blocking some light in this region of the star. By February 2020, the star had lost more than two-thirds of its luster, a dimness visible even to the unaided eye, causing buzz that the star might go supernova. Continuous ultraviolet light spectroscopic observations with Hubble provided a timeline for researchers to follow, such as break rumors that lead through time to determine the source of the mysterious dimming.
Andrea Dupree is associate director of the Harvard & Smithsonian Center for Astrophysics and lead author of the study, which was published Aug. 13 in the peer-reviewed The Astrophysical Journal. She said in the statement of the scientists:
With Hubble, we have previously observed hot convection cells on the surface of Betelgeuse and in the fall of 2019, we discovered a large amount of dense hot gas moving outward through the expanded atmosphere of Betelgeuse. We think this gas cools millions of miles outside the star to form the dust that exposed the southern part of the star in January and February.
The material was two to four times brighter than the normal brightness of the star. And then, about a month later, the southern part of Bethelgeuse suddenly collapsed as the star grew brighter. We think it is possible that a dark cloud resulted from the outflow that Hubble discovered. Only Hubble gives us this evidence that led to the dimming.
Read more: Will the star Betelgeuse ever explode?
This spectral plot is based on observations from Hubble Space Telescope from March 2019 to February 2020. Hubble recorded a surprise eruption in the atmosphere of the nearby red supergiant star Betelgeuse. Measurements of magnesium II emission were used to detect movement in the pulsating atmosphere of the star. Hubble’s Space Telescope Imaging Spectrograph captured a dramatic increase in the brightness of magnesium emission in October 2019, in the southeastern region of the star, as indicated by the white circle. (Betelgeuse is close enough and large enough for Hubble to resolve the star’s enormous disk.) This traumatic event was different from what is normally seen during the star’s 420-day pulsation period. At the same time in October, the star began to dim abruptly. This fading continued until February 2020, by which time the Hubble ultraviolet spectral data were back to normal. It is suspected that he emitted a cloud of hot plasma that cooled to form dust that emitted a significant portion of the star’s light for a few months. Hubble’s long line of surveillance on the star helped bring the puzzle pieces together. Image via NASA / ESA / A. Dupree (CfA) / E. Wheatley (STScI) / CfA.
Models of scientists had suggested that – in this situation – the plasma would be emitted from the star’s poles of rotation. The Hubble observations showed that it was not, however. Dupree said:
Hubble observations suggest that material may be removed from any part of the stellar surface.
Dupree added that recent activity on Betelgeuse was not normal for this star. Dupree notes that Betelgeuse loses mass at a rate 30 million times higher than the Sun, but that recent activity has resulted in a loss of about twice the normal amount of material from the southern hemisphere of the star alone. She said:
All stars lose material to the interstellar medium, and we do not know how this material is lost. Is it a smooth wind that blows all the time? Or does it fit and start? Maybe with an event like we discovered on Betelgeuse? We know that other hot, bright stars lose material and it soon turns to dust which makes the star appear much weaker.
But in more than a century and a half, this has not happened to Betelgeuse. It is very unique.
An image from NASA’s STEREO spacecraft shows the star Betelgeuse, round. For several weeks in 2020, STEREO was the only observatory that made measurements of Betelgeuse because of the unique position of the spacecraft. Between late June and early August 2020, STEREO observed Betelgeuse on five separate days, and measured the relative brightness of the star compared to other stars. Image via NASA / STEREO.
The star Betelgeuse, and its constellation Orion, are behind the Sun as seen from Earth in the early summer of the Northern Hemisphere. They always return to our early morning skies in late July and early August. While Betelgeuse was hidden behind the sun for terrestrial observers, scientists turned to NASA’s Solar TErrestrial RElations Observatory – STEREO – to check the brightness of the star. Those observations revealed another surprise, scientists said: more unexpected dimming.
Between late June and early August 2020, STEREO observed Betelgeuse on five separate days, and measured the relative brightness of the star compared to other stars. Dupree said:
Our observations of Betelgeuse with STEREO confirm that the star is dimming again.
Betelgeuse is a variable star, although the rise and fall in brightness is not noticeable to casual observers. It usually goes through brightness cycles that last about 420 days.
Since the previous minimum occurred in February 2020, this new dimming is more than a year early, the scientists commented.
Dupree said she plans to re-observe Betelgeuse with STEREO next year, during the maximum of the star, to check for unexpected eruptions.
Sa #Betelgeuse is getting brighter again ?!
“Photometry of Betelgeuse with the STEREO Mission While in the Glory of the Earth’s Sun” https://t.co/0Uf9mY7oqI
“This summer, thanks to the STEREO mission, Betelgeuse cannot hide in the glare of the sun.”
Cool! pic.twitter.com/DKGHL0N5nq
– ASAS-SN (@SuperASASSN) 28 July 2020
People always want to know if Betelgeuse will explode. It’s an old star and a redundant star, and so the answer to that question is definitely yes. When Betelgeuse dimmed so markedly in late 2019 and early 2020, some scientists agreed that it could be a sign that the star was about to go into supernova. These scientists responded in their statement:
Betelgeuse is a bright star in our galaxy near the end of its life, which is likely to become a supernova. When the star became very weak in February 2020, this was the worst it has ever been since measurements began more than 150 years ago. The dimming was obvious to everyone as they looked at the constellation Orion; it was very strange, Betelgeuse almost missed.
At 725 light-years away, Betelgeuse’s light – and dimming – left the star on Earth today in the year 1300. Dupree said:
No one knows how a star behaved in the weeks before it exploded, and there were some unholy predictions that Betelgeuse was ready to become a supernova.
Chances are, though, that it will not explode in our lives, but who knows?
Bottom line: An explanation for the mysterious dimming of Betelgeuse in late 2019 and early 2020.
Source: Spatially Solved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
Via Harvard & Smithsonian Center for Astrophysics
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