A system of two almost touching stars discovered in the centre of a planetary nebula
Astronomers have discovered a binary system in the centre of the planetary nebula M3-1. The stars are so close together that they can not be separated during observations from Earth and they can explode as a nova.
Planetary nebulae are glowing gas and dust clouds formed from the outer layers of stars like our Sun, which have been ejected at the final stage of their evolution.
International team of astronomers, led by David Jones (IAC, Spain) with the participation of Paulina Sowicka - a PhD student from the Nicholas Copernicus Astronomical Center PAS (CAMK), discovered a binary system in the centre of the planetary nebula M 3-1, located in the constellation of Canis Major. This nebula was a strong candidate for having a binary system in the centre, due to its structure with jets and fibres, which is typical for interactions in a binary system.
It turns out that the central system of the M 3-1 nebula has one of the shortest orbital periods of such systems known to date, only slightly over three hours. The observations carried out using ESO telescopes also show that these two stars, most likely a white dwarf and a low-mass main sequence companion, are almost touching each other.
As a result, this tight binary system is likely to undergo a so-called nova eruption, in a thermonuclear explosion following the flow of matter to a white dwarf, reads the release sent to PAP. This is an unexpected phenomenon in the context of the current understanding of the evolution of binary stars. According to the theory, stars in a binary system should be well separated after the planetary nebula has formed. A lot of time should pass before they start interacting with each other again and events such as a nova explosion become possible.
In 2007, astronomers observed another nova explosion, also in the centre of a planetary nebula, known as Nova Vul 2007. That event was extremely difficult to explain. By the time the two stars are close enough for a nova, the material in the planetary nebula should have expanded and dissipated so much that it`s no longer visible. The central stars of M3-1 are another candidate for a similar nova eruption in the relatively near future.
Using the telescopes of the European Southern Observatory (ESO) in Chile, David Jones`s team looked at M3-1 over a period of several years. The two stars are so close to each other that they cannot be resolved from the ground, so instead the presence of the second star is inferred from the variation of their observed combined brightness - particularly the periodic eclipses of one star by the other which produce marked drops in the brightness, the Nicholas Copernicus Astronomical Center PAS informs.
The team now hope to continue to study the nebula and others like it, helping to shed light on the physical processes and origins of novae and supernovae, some of the most spectacular and violent phenomena in the Universe.
The results of the above research have been published in the prestigious Monthly Notices of the Royal Astronomical Society: Letter 482, L75 https://doi.org/10.1093/mnrasl/sly142
PAP - Science in Poland
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