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A star far away

Thursday, 22 April 2021, Universität, Forschen

Astrophysicists from the University of Graz detect coronal mass ejections on neighbouring suns

They are hundreds of light years away. Stars that eject matter into space, just the way our Sun does. Could these eruptions be a threat to distant planets orbiting these stars? A team led by Astrid Veronig, an astrophysicist at the University of Graz, has developed a new method to find this out. As can be read in the renowned professional journal Nature Astronomy, they were able to detect 21 coronal mass ejections on stars and determine their strength.

Our Sun is the source of energetic eruptions in which plasma is ejected into space together with an embedded magnetic field. These coronal mass ejections vary in strength and move through our solar system at speeds of millions of kilometres per hour. The strongest eruptions can even trigger power cuts on Earth and paralyse electronic systems on satellites. However, they are also responsible for spectacular auroras. “The ejections are tracked with the help of coronagraphs, which block out the strong direct sunlight and thereby create a kind of artificial solar eclipse,” explains Astrid Veronig, who uses satellite-based telescopes for this purpose and works together with the space organisations ESA and NASA.

Dimmings in the aureole
While the Sun is a frequent subject of scientific research, so far not many coronal mass ejections have been observed on stars. Veronig: “The spatial resolution is too low and the radiation of the ejections too weak for us to be able to do coronagraphic measurements like those of the Sun.” The researchers therefore turned the tables and studied the Sun like they would study a star. The result was a novel method of detection. “We observe the Sun in the light of ultraviolet and X-ray radiation, where the million-degree hot corona emits the most radiation,” explains the astrophysicist. “When mass ejections occur, i.e. huge clouds of plasma are ejected from the corona, dimmings remain in this aureole and we are able to detect these.”

The scientists have now been able to apply these findings and methodology successfully to other stars. They discovered that such sudden dimmings in X-ray light curves can also be found there. Petra Odert, researcher at the Institute of Physics at the University of Graz and co-author of the study, confirms that “we infer from this that there are also coronal mass ejections on these other stars”. Using this technique, the scientists have discovered a total of 21 coronal mass ejections on other stars. During the CME, considerable parts of the corona can be ejected. Odert: “These high-energy plasma clouds are a threat to exoplanets orbiting the star, as they can erode their atmospheres completely.” However, it depends on the dose, as is so often the case. At the same time, a lower intensity could enable conditions that are just as liveable as those in our planetary system.

This research, supported by the Austrian Space Applications Programme of the Austrian Research Promotion Agency (FFG) and the Austrian Science Fund (FWF), was published in the journal Nature Astronomy.

Astrid M. Veronig, Petra Odert, Martin Leitzinger, Karin Dissauer, Nikolaus C. Fleck, Hugh S. Hudson, Indications of stellar coronal mass ejections through coronal dimmings, >> Nature Astronomy

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