14 DAY TRIAL // Investigators announce that AX Persei, which is a symbiotic variable star system, shows signs of increased activity, which means that it could be on its way towards a new eruption.
This star has been under monitoring for years, because it goes through cycles of calm periods and times of massive eruptions, and astronomers want to keep an eye on these rare cosmic phenomena.
Recently, scientists at the Asiago Novae and Symbiotic Stars collaboration – who were looking at the variable star – discovered a series of changes on Ax Persei, which means that the object may be on its way to yet another eruption.
The last one that astronomers kept tabs on took place between 1988 and 1992. Since then, the star has kept quiet until the spring of 2009, when it showed the first signs of activity in 17 years.
At the time, it only emitted a short outburst of material, but many are now convinced that the event was a sign of a much larger eruption that could take place soon. Some stars indeed act like volcanoes in this regard, increasing their activity shortly before erupting.
One of the reasons why watching such eruption is so interesting stems from the very nature of the variable stars, which are a special class of binary systems, Universe Today reports.
They are made up of a rather cool and giant central star, which is orbited by a very hot and compact white dwarf, the helium-burning core of a former Sun-sized star that reached the end of its burning cycle.
Generally, members of symbiotic variables orbit around each other once every 100 to 2,000 days, as viewed from our vantage point. Unlike other binary systems, stars in these ones do not exchange matter directly.
The two components are relatively far away from each other, which means that the white dwarf does not siphon mass of the cool giant directly, or through an accretion disk.
The exchange is in turn made as the red giant blows strong stellar winds away from its surface, which slam into the white dwarf. This phenomenon produces a gas/dust shroud called the common envelope.
In symbiotic variable systems, the behavior of stars is unpredictable, and eruptions can take place at any time. They are generally caused by abrupt changes in the accretion flow of gas onto the primary star.
Alternatively, they can also be produced as the excess mass accumulating on the surface of the white dwarf spontaneously triggers thermonuclear fusion. The star then detonates, shedding the excess material that makes it unstable.
Other types of binary systems feature the same type of behavior, the difference being the way in which the extra gas is accreted, and what types of stars are in the system.