They discover a new type of nebula around binary stars thanks to the collaboration of amateur astronomers

Rummaging through digitized photographs from the 1980s, a group of amateur astronomers came across, not long ago, images of what looked like part of a nebula, a gaseous structure illuminated by radiation from nearby stars. They were hunting for unknown objects, so, intrigued, they decided to share their find with some professionals, including the Department of Astrophysics and Particle Physics at the University of Innsbruck, in Austria.

That first discovery by a group of French and German amateurs, combined with observations from the last 20 years obtained by several observatories, data from four satellites and the support of an international team, has led to a remarkable discovery that now it echoes Astrophysics and Astronomy: a new type of galactic nebulae.

Some very special ones, too. With the track provided by the amateurs, an international team led by Stefan Kimeswenger, from the center of Innsbruck, has detected a nebula around binary stars. The discovery is important both for the phenomenon it identifies and for its value in better understanding the evolution of stars. It also notes, highlights the University of Innsbruck, the tremendous potential of collaboration between professionals and amateurs.

An effort on an international scale

What exactly have they seen? Well, according to the model that experts have developed after their observations, it is a binary star system made up of a white dwarf star of 66,500 degrees and another normal one with a mass slightly less than that of the Sun, both orbiting each other at a distance of just 2.2 solar radii. What characterizes them is that both are surrounded by a large shared cladding, a common wrapping system (CE), formed by the outer material of the white dwarf, which was expelled about 500,000 years ago.

What highlights the University of Innsbruck, it is the first time that astronomers have obtained evidence of a fully developed layer of this type (CE). Star systems had been discovered on the verge of generating a similar envelope, but without appreciating galactic nebulae like the one they have now recorded. Why? Simple: because they are very difficult to catch.

“They are too big for the field of view of modern telescopes and at the same time they are very faint. What’s more, his life is quite short, at least when considered on a cosmic time scale. It’s only a few hundred thousand years,” says Kimeswenger.

Precisely for this reason, when the Innsbruck team received the warning from their amateur colleagues, they thought that they were surely looking at a planetary nebula caused by the remains of dying stars. Thanks to the help of Chile’s telescopes and spectrograph observations by US scientists were finally able to capture the vast expanse of the nebula.

“The diameter of the main cloud is 15.6 light years, almost a million times greater than the distance from the Earth to the Sun and much greater than the distance from our Sun to its nearest neighboring star. Fragments up to 39 light-years away have also been found.” Kimeswenger shouts. Its location, slightly above the Milky Way, has probably allowed the nebula to develop without being disturbed by other surrounding gas clouds.

As the Innsbruck researcher details, towards the end of their lives the stars inflate until they become red giant stars. In binary star systems the expanding outer part of a star merges as a common envelope around both stars. Within that layer, however, the cores of the two stars are practically unaltered and continue their evolution. Thanks to the analysis of its chemical and physical properties, scientists know that there are star systems that are the result of this process. Until now, however, they had not observed the fully developed envelope of that common system and their expulsion into interstellar space.

“They are of great importance for our understanding of the evolution of stars in their final phase. In addition, they help us understand how they enrich interstellar space with heavy elements, which in turn are important for the evolution of planetary systems, such as ours”, he clarifies.

Important unknowns remain on the astronomers’ table. The main one is that perhaps the images discovered by amateurs are not the first clues of these new nebulae. “It is even possible that this system is related to an observation of a nova made by Korean and Chinese astronomers in 1086. In any case, the positions of the historical observations coincide very well with those of our object described here”, slides the expert from Austria.

Cover image: Maicon Germiniani/ University of Innsbruck