Astronomers have known of V745 Sco – a very irregular nova – for decades, but only now have they been able to work out exactly what’s going on. An international team of researchers were finally able to produce detailed observations of the object and work out what’s going on.
V745 Sco is actually a binary system, where a large red giant star is orbited by a white dwarf. The dwarf’s gravitational pull removes layers of material from the red giant and, once enough material has accumulated, it triggers a thermonuclear explosion and becomes a nova. Suddenly, the star becomes thousands of times brighter.
The nova has been observed bursting in 1937 and in 1989, but only in 2014 were researchers ready to catch it. They used NASA’s X-ray telescope Chandra, and reported their findings in the Monthly Notices of the Royal Astronomical Society.
Thanks to these observations, the team from INAF-Osservatorio Astronomico di Palermo, the University of Palermo, and the Harvard-Smithsonian Center for Astrophysics built a 3D computer model. This allowed them to discover that most of the material was moving away from the nova in a north-south axis point in our direction.
The best reconstruction shows that the outburst had to interact with a large disk of cool gas located around the equator of the binary. The disk likely formed due to the gravitational interaction between the two stars. The energy necessary to release this material is quite extraordinary, equivalent to 10 million trillion hydrogen bombs, or over 80 times the energy released by the Sun in a single year.
And yet, according to the team, only a tiny fraction of the stolen material was expelled in the explosion and most of it remains on the white dwarf. This is quite the omen for the white dwarf. The dwarf will continue to accumulate material until it goes full supernova, ejecting its companion star. Although it might go supernova, there’s nothing to worry about as it’s over 25,000 light-years away.
The team was also able to estimate the composition of the white dwarf based on the expelled material. The analysis suggests it’s made of carbon and oxygen, common components of evolved stars.