Violent wind collision zone between two stars seen for the first time

A team of international researchers, including Professor Stefan Kraus from the University of Exeter, have gained unique images of the chaotic region found between the two stars in the Eta Carinae binary system, found 7,500 light years from Earth.

Powerful stellar winds from the two stars – one of which is one of the largest and most luminous stars discovered and 100 times more massive than the sun – collide in the central region. The new observations, carried out with the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory, should provide a greater understanding of the enigmatic stellar giant stars and how they interact with each other.

Professor Kraus, an Associate Professor of Astrophysics at the University of Exeter said: “These new images will provide pivotal new information about these colossal stars. It is an incredible achievement to witness so clearly the way in which these high speed winds collide with each other, but we are also able to learn so much more about these stars, so far away in our galaxy.”

The more massive of the two stars in the Eta Carinae system, called the primary star, is five million times more luminous than our sun. In late phases of its evolution, such massive stars lose huge amounts of gas before they explode as a supernova. Studies of this dramatic mass-loss process are important to improve our understanding of stellar evolution.

Both stars of the Eta Carinae binary system are so bright that the powerful radiation they produce drives matter from their surfaces in the form of massive, fast stellar winds. These high-velocity stellar winds violently collide in the space between the two stars. Extreme physical processes occur in this innermost region, where the very fast stellar wind from the less massive but hotter companion star crashes into the dense primary star wind with a velocity of about 3000 km per second (more than 10 million km per hour).

In this collision region, temperatures reach many tens of millions of degrees, hot enough to emit X-rays. In the past, it was not possible to resolve this violent collision zone, because its extension is too small even for the largest telescopes.

The new research, led by Gerd Weigelt from the Max Planck Institute for Radio Astronomy in Bonn/Germany, obtained extremely sharp images of Eta Carinae by using a new imaging technique based on long-baseline interferometry – a technique that combines the light from three or more telescopes to obtain multi-telescope images called interferograms. From a large number of interferograms, extremely sharp images can be reconstructed using sophisticated image reconstruction techniques.

Gerd Weigelt, lead author of the study, said: “Our dreams have come true, because we can now get extremely sharp images in the infrared regime. The ESO VLTI provides us with a unique opportunity to improve our physical understanding of Eta Carinae and many other key objects.”

The technique used by the research team allowed, for the first time, both direct images of the stellar wind zone surrounding the primary star and the collision zone in the central region between the two stars to be seen. Co-author Karl-Heinz Hofmann (also from Bonn) added: “Our multi-wavelength image reconstruction method allowed us to discover unexpected structures in a wide velocity range. It is clear that infrared interferometry will revolutionise infrared astronomy.”