A binary star as a cosmic particle accelerator.

Using a specialized telescope in Namibia, a team of researchers led by DESY has demonstrated a certain type of binary star as a new type of very high-energy cosmic gamma radiation source. Eta Carinae is 7,500 light years away in the constellation Carina (the keel of the ship) in the southern sky and, according to the data collected, emits gamma rays with energies of up to 400 gigaelectronvolts (GeV), about 100 billion times more than the energy of visible light. The team led by Stefan Ohm, Eva Leser and Matthias Füßling of DESY present their findings, made at the High Stereocopic System (HESS) gamma-ray observatory, in the journal. Astronomy and astrophysics. An accompanying multimedia animation explains the phenomenon. “With such visualizations we want to make the fascination of research tangible,” emphasizes Christian Stegmann, Director of Astroparticle Physics at DESY.

Eta Carinae is a binary system of superlatives, consisting of two blue giants, one approximately 100 times, the other approximately 30 times the mass of our sun. The two stars orbit each other every 5.5 years in highly eccentric elliptical orbits, their separation varies approximately between the distance from our Sun to Mars and from the Sun to Uranus. Both gigantic stars throw dense supersonic stellar winds of charged particles into space. In the process, the larger of the two loses a mass equivalent to all of our Sun in just 5,000 years or so. The smallest produces a fast stellar wind that travels at speeds of around eleven million kilometers per hour (about one percent of the speed of light).

A huge shock front forms in the region where these two stellar winds collide, heating the material in the wind at extremely high temperatures. At around 50 million degrees Celsius, this matter radiates brilliantly in the X-ray range. However, the particles in the stellar wind are not hot enough to emit gamma radiation. “However, shock regions like this are typically sites where subatomic particles are accelerated by strong predominant electromagnetic fields,” explains Ohm, who is the head of the HESS group at DESY. When particles accelerate so fast, they can also emit gamma radiation. In fact, the “Fermi” satellites, operated by the US space agency NASA, and AGILE, belonging to the Italian space agency ASI, already detected energetic gamma rays of up to 10 GeV from Eta Carinae in 2009.

“Different models have been proposed to explain how this gamma radiation is produced,” reports Füßling. “It could be generated by accelerated electrons or by high-energy atomic nuclei.” It is crucial to determine which of these two scenarios is correct: The very energetic atomic nuclei represent the majority of the so-called Cosmic Rays, a subatomic cosmic hailstorm that strikes the Earth constantly from all directions. Despite intense research for over 100 years, the sources of the Cosmic Rays are not yet fully known. Since electrically charged atomic nuclei are deflected by cosmic magnetic fields as they travel through the universe, the direction from which they reach Earth no longer points to their origin. Cosmic gamma rays, on the other hand, do not drift. So if gamma rays emitted by a specific source can be shown to originate from high-energy atomic nuclei, one of the accelerators of cosmic particle radiation will have been identified.

“In the case of Eta Carinae, electrons find it particularly difficult to accelerate at high energies because the magnetic fields constantly deflect them during acceleration, causing them to lose energy again,” says Leser. “Very high energy gamma radiation begins above the 100 GeV range, which is difficult enough to explain at Eta Carinae to come from electron acceleration.” Satellite data has already indicated that Eta Carinae also emits gamma radiation beyond 100 GeV, and HESS has now managed to detect such radiation up to energies of 400 GeV at the time of the close encounter of the two blue giants in 2014 and 2015. This makes The binary star is the earliest known example of a source in which very high-energy gamma radiation is generated by collisions of stellar winds.

“Analysis of gamma radiation measurements taken by HESS and satellites shows that radiation can best be interpreted as the product of rapidly accelerated atomic nuclei,” says Ph.D. from DESY. student Ruslan Konno, who has published a follow-up study, together with scientists from the Max Planck Institute for Nuclear Physics in Heidelberg. “This would make the collision regions of colliding stellar winds a new type of natural particle accelerator for cosmic rays.” Named after cosmic ray discoverer Victor Franz Hess and the upcoming Cherenkov Telescope Array (CTA), the next-generation gamma-ray observatory currently being built in the Chilean highlands, scientists hope Investigate this phenomenon in greater detail and discover more sources of this type.

Thanks to detailed observations of Eta Carinae at all wavelengths, the properties of stars, their orbits, and stellar winds have been determined with relative precision. This has given astrophysicists a better picture of the binary star system and its history. To illustrate Eta Carinae’s new observations, DESY astrophysicists have produced an animation video together with animation specialists from the award-winning Science Communication Lab. Computer-generated images are close to reality because measured orbital, stellar, and wind parameters were used for this purpose. The internationally acclaimed multimedia artist Carsten Nicolai, who uses the pseudonym Alva Noto for his musical works, created the sound for the animation.

“I find science and scientific research to be extremely important,” says Nicolai, who sees close parallels in the creative work of artists and scientists. For him, the appeal of this work also lies in the artistic mediation of the results of scientific research: “particularly the fact that it is not a soundtrack for a film, but has a genuine reference to reality,” emphasizes the musician and artist. Along with exclusively composed sound, this unique collaboration of scientists, animation artists, and musicians has resulted in multimedia work that takes viewers on an extraordinary journey to a superlative double star some 7,500 light-years away.