An international team of astronomers, led by the researcher of the Institute of Astrophysics of the Canary Islands (IAC) and the University of La Laguna (ULL) David Jones, has discovered a binary system with an orbital period of little more than three hours. The discovery, which has required several years of observations, is not only surprising because it is binary stars with one of the shortest orbital periods within a planetary nebula never observed, but also reveals the possibility that, due to its proximity, the system may experience a nova explosion before the nebula dissipates.
The results of the research have just been published in the prestigious journal Monthly Notices of the Royal Astronomical Society (MNRAS).
Planetary nebulae are envelopes of gas and dust that stars similar to our Sun expel at the end of their lives. "In many cases we see that this expulsion originates from an interaction between the progenitor star and a close companion, and that is why they form nebulae with such elaborate structures," explains Jones. In the research the planetary nebula M3-1 has been studied, a firm candidate to have been created by a binary system due to its jets of material, very common in interactions between two nearby stars.
According to Brent Miszalski, a researcher at the SALT Telescope in South Africa and co-author of the study, "it had to be a binary star, so we decided to observe it to try to understand the relationship between the stars and the nebula that they have formed."
The observations immediately confirmed the suspicions. "When we began to observe it, we immediately saw that it was a binary system and that its brightness changed rapidly, so it could mean that it had a very short orbital period," says Henri Boffin, researcher at the European Southern Observatory (ESO). ) in Germany. In fact, the calculated separation between the two stars is approximately 160,000 kilometers, that is, less than half the distance between Earth and the Moon.
After several observation campaigns in Chile with the Very Large Telescope (VLT) and New Technology Telescope (NTT) telescopes, the researchers managed to gather enough data to begin to understand the properties of the stars, such as their mass, temperature and size. "To our surprise we discovered that the stars were large and that, being so close, it is very likely that, within a few thousand years, we may see another type of binary interaction in the form of a nova explosion," adds Paulina Sowicka, student of the Nicolas Copernicus Center in Poland.
The result of the observations contradicts the current theories of evolution of binaries that maintain that, once formed the planetary nebula, the stars remain separated during a long time before getting to interact again. When this happens, the nebula should have already dispersed so that it would not be observed. However, an explosion of nova observed in 2007, known as Nova Vul 2007, within another planetary nebula, challenged the model. "In the case of M3-1, we see another candidate who may experience a similar evolution, as the stars are almost touching, it should not take long to interact again and, perhaps, produce a nova within a planetary nebula", concludes Jones.