Space | 18. March 2020 | posted by Alessandra Roy Dörte Mehlert

SOFIA observes the star Betelgeuse

Credit: ESO/M. Montargès et al.
Betelgeuse in January and December 2019, captured by the European Southern Observatory (ESO) Very Large Telescope (VLT)

Curiosity is high, a lot has been said and written, but nobody knows what is really happening with the star Betelgeuse. Its luminosity has decreased drastically over the last five months. Now, there is speculation that the star could soon become a supernova – the explosion at the end of a large celestial body's life. A team led by Miguel Montargès of KU Leuven in Belgium has compared two images of Betelgeuse acquired by the European Southern Observatory's (ESO) Very Large Telescope (VLT) in January and December 2019 and has discovered something surprising – it is not only Betelgeuse's brightness that has changed, but also its shape.##markend##

Betelgeuse was previously one of the 10 brightest stars in the winter night sky over Europe. It is located in the constellation of Orion and is approximately 700 light years away from Earth. The star is a red supergiant. These stars are much larger, more massive and brighter than the Sun, but have relatively short life spans. Red supergiants are nearing the end of their lives, and they 'die' in a spectacular fashion – they become supernovae. The star explodes and the energy released is roughly equivalent to the typical energy generated by billions of normal stars. When this happens to Betelgeuse, it will appear as bright as the full Moon. But when will this happen? We do not know. It could occur within the next 100,000 years, or it could have already happened but not yet be observable due to how far it is from Earth. What we do know is that Betelgeuse’s current behaviour is atypical.

Credit: Betelgeuse image: ESA/Herschel/PACS/L. Decin. Orion image: Akira Fujii
Betelgeuse is a star in the constellation of Orion, in 'Orion's shoulder'

By February 2020, its luminosity had already dropped to just under 40 percent of its average value and it did not even make it into the top 20 brightest stars in the sky. Montargès and his team nevertheless do not expect an imminent end for Betelgeuse. They rather suspect that the observed phenomena are either caused by unusual activities in the star's interior or are due to the darkening being caused by matter ejected from the star in the direction of Earth. This matter would begin to glow in the mid- and far-infrared regions of the electromagnetic spectrum.

Astronomers are currently observing Betelgeuse with a number of telescopes, and the Stratospheric Observatory for Infrared Astronomy (SOFIA) is one of them. "We will be able to observe the part of the infrared spectrum that is otherwise invisible from the ground," explains Heinz Hammes, SOFIA Project Manager at the DLR Space Administration. "This will complement the other observations that have been made in recent months."

SOFIA is currently carrying out an extensive observation campaign to uncover the reason for the anomalous changes in brightness observed for Betelgeuse. These observations will reveal any changes in the star's chemical composition as well as study its infrared brightness. This is not the first time that SOFIA has observed Betelgeuse. Astronomers will therefore have the opportunity to compare the data obtained in this campaign with those recorded previously. This time, SOFIA observations are being performed with four instruments. Each instrument covers a specific part of the spectrum, from mid- to far-infrared, in order to study different phenomena. Once the observation campaign has been completed, these SOFIA data will immediately be made available to the scientific community and will also be compared with data from other observatories.

Three of the instruments on board SOFIA have completed their observations and their data are currently being analysed – the US instrument EXES (Echelon Cross-Echelle Spectrograph), the University of Stuttgart's imaging spectrometer FIFI-LS  (Field-Imaging Far- Infrared Line Spectrometer), and the GREAT (German Receiver for Astronomy at Terahertz Frequencies) instrument from the Max Planck Institute for Radio Astronomy in Bonn. "The data are very promising," reports Christian Fischer, of the German SOFIA Institute (DSI), who was on board the aircraft during the FIFI-LS observation as Instrument Engineer.

The US-American instrument FORCAST (Faint Object infraRed CAmera for the SOFIA Telescope) will be deployed in March and will collect further data from Betelgeuse in the mid-infrared region.

We are all looking forward to the SOFIA results and will report again as soon as there is any news.


About the author

Alessandra Roy studied astronomy at the University of Bologna (Italy). She received her doctorate from geodesy at the University of Bonn. She worked for almost 16 years at the University of Bonn and at the Max Plank Institute for Radio Astronomy. to authorpage

About the author

Dr. Dörte Mehlert hat an der Universität Hamburg Physik studiert und im Bereich Astronomie zum Thema "Elliptische Galaxien in hoher Umgebungsdichte: Der Coma-Galaxienhaufen" an der Ludwig-Maximilians-Universität München (LMU) promoviert. to authorpage