Red supergiant spits matter

The sharpest images of the star Beteigeuze show huge gas currents and swaths

Betelgeuse with gas streams and gas cloud as illustration © ESO
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The star Beteigeuze is nearing the end of its life cycle. The harshest footage ever made by the red supergiant reveals that it has already ejected a massive, asymmetric gas cloud. Large-scale gas flows in the star atmosphere seem to be the trigger for this. An international research team reports now in two publications in the journal "Astronomy and Astrophysics".

Betelgeuse, also called Betelgeuse in English, is easily recognizable in the night sky, as it is the second brightest star of the constellation Orion. The red giant star forms one of the two "shoulder stars" of the mythical hunter. Almost thousand times larger than our sun, Beteigeuze is one of the biggest known stars. Although he is only a few million years old, he is rapidly approaching the end of his stellar life cycle, a supernova. Only held loose by the gravity of the core, expand the outer gas pockets and begin to dissolve.

Riddle of mass ejection

However, when Betelgeuse becomes a supernova, whether in a thousand or a hundred thousand years, is unclear. It is also unclear how the red migrations can emit so much material within a relatively short time. In the case of the Betelgeuse, after all, within only 10, 000 years, it is a mass comparable to that of the sun. To get to the bottom of it, an international team of astronomers from the European Southern Observatory is using the optical instrument "NACO" of the Very Large Telescope (VLT) at the Paranal in Chile.

The constellation Orion with the shoulder star Betelgeuse, a picture of the Betelgeuse and the sharpest achieved with the NACO-Insturment resolution. © ESO

Image combination produces hitherto sharpest resolution

NACO uses the so-called "lucky imaging" technique to compensate for the distortions and blurring caused by turbulence in the Earth's atmosphere. It chooses only the sharpest of the numerous shots and then combines them into a single combination image. This process produces images that are much sharper than a single, longer exposed one. They reach almost the theoretical limit of an eight-meter telescope: a resolution of 37 millibose seconds - the size of a tennis ball lying on the ground, seen from aboard the International Space Station.

"Thanks to these extraordinary shots, we have discovered a great swath of gas that extends from the surface of the Betelgeuse into space, " explains Pierre Kervella of the Paris Observatory, Director of the ESO team. The extent of the gas wave is at least six times the diameter of the star, which is comparable to the distance between the sun and the planet Neptune. "This is a clear indication that the entire outer shell of the star does not disperse its matter in all directions, " said the researcher. display

Polkappen or convection?

Theoretically, there are two mechanisms that could explain this asymmetric material output. The one assumes that the mass loss due to the rotation happens above all over the polar caps of the star. On the other hand, large-diameter gas convolutions are the star of the exciters for regional outbreaks. Such Umw lzstr mungen, called convection, arise in similar form in boiling water.

But what mechanism was responsible for the gas flow? To find out, Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn used the method of interferometry. With this method, several instruments can virtually interconnect, so that the resolution is increased. The AMBER instrument on the VLT combines the data from three 1.8-meter auxiliary telescopes from the ESO to produce resolutions equivalent to those of a 48-meter virtual telescope.

Up and down of the gases

In this extremely high resolution, the astronomers were able to recognize the finest details and thus also came to an answer to the question of the mechanism: It turned out that the gas in the atmosphere of Beteigeuze violent in bubbles moved up and down. These gas bubbles are as large as the entire star and indicate that convection triggered the emission of the gas silt.

We observed how the gas moved in different regions of the Betelgeuse surface. This is the first time that such a thing has ever been made for a star other than the Sun, "explains Ohnaka.

(ESO, 30.07.2009 - NPO)