Cosmic vortices discovered around a red giant

Gas spiral provides new insights into the formation of stardust

Observations of the ALMA telescope show an unexpected spiral structure in the material around the old star "R Sculptoris". © ALMA (ESO / NAOJ / NRAO)
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For the first time, astronomers have discovered a red giant surrounded by a huge spiral of released gas. The vortex was created when matter was blown out of the star into space by a thermal pulse. Through these observations fundamentally new insights are possible, as the wind of red giant stardust is transported into space and there contributes to the construction of matter. The researchers report in the journal "Nature".

The people and the whole world is ultimately stardust. The chemical elements that compose all matter are born by nuclear fusion inside stars. "They are then transported to the surface and blown out into space as gas and dust - in a wind from the surface of the star, which constantly loses mass, " reports first author Matthias Maercker, a scientist at the Argelander Institute for Astronomy at the University of Bonn and fellow of the European Southern Observatory (ESO).

A gigantic bubble of dust and gas

The new elements are formed when a "thermal pulse" occurs in the star. At the same time, much more matter is blown into space at a higher speed from the stellar surface in a short time than usual. However, such an event takes place only about every 50, 000 years and lasts only a few hundred years. "The extra matter and increased speed of the wind during the thermal pulse cause gas and dust to spread in the form of a gigantic, very thin bubble, which then inflates further and further around the star, " says Maercker. The survival time of these bubbles by thermal pulses is relatively short, which is why they have been discovered so far only about ten red giants.

The red giant "R Sculptoris" has known since the late 1980s that such a bubble surrounds him. A red giant is an old star of great size that shines particularly brightly. Pictures of R Sculptoris already supplied the Hubble Space Telescope. "Hubble, however, only shows the dust bubble around R Sculptoris, " says Maercker. "The ejected gases are not visible with the telescope. The scientists now used the new ALMA radio telescope in the Chilean Atacama Desert radio waves to investigate the bubble closer. ALMA took a close look at the carbon monoxide emitted by the red giant R Sculptoris.

A spiral of gas winds around the red giant

In doing so, the team unearthed surprising facts: The observations showed not only the expected bubble of gas, but also that the wind of the star forms a spiral like that of a galactic roundabout around the red giant. "We never thought that we could observe a bubble and a spiral at the same time, " says Maercker. The cause of this peculiar phenomenon is a companion star orbiting R Sculptoris. The gravity of the companion star focuses the wind around the red giant behind him. The movement of the companion star around R Sculptoris then suggests a spiral in the wind of gas and dust, reports the Bonn scientist. display

This makes the material between the bubble and the star visible in a unique way. The spiral comprises five turns. From this, the researchers concluded that since the thermal pulse R Sculptoris has circled the companion star a total of five times, thereby appropriately shaping the gases expelled from the star. The observations of ALMA show that the bubble is spreading at a speed of 14 kilometers per hour. Together with the size of the bladder, this results in an age of around 1800 years. This results in a round trip duration of the companion star of around 350 years, predicts Maercker.

The brightness of each turn makes it possible to determine the amount of matter that has been blown away from the star at any point in the last 1800 years. "This is the first time we have been able to observe how a star loses matter during and after a thermal pulse, " says Maercker. "The mass loss during a pulse is about 30 times greater than during the pulse-free times, " reports the astronomer. "That's about three times more than previously thought." (Nature, 2012; doi: 10.1038 / nature11511)

(Rheinische Friedrich-Wilhelms-University Bonn, 12.10.2012 - NPO)