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The periodic eruptions from a protostar is because of a companion object that is a failed star.
A protobinary system, similar to V347 Aurigae. (Image Credit: ALMA. ALMA / ESO / NRAO / NAOJ, Alves et al 2019).
New Delhi: Protostars are objects in the earliest stages of star formation, that are dense clumps in molecular clouds that have started accreting material under the influence of gravity. V347 Aurigae is a protostar that is just a few hundred thousand years old, much younger than our 4.5 billion year old Sun. For years, astronomers have been mystified by periodic bursts of light from the protostar, which makes it about 100 times brighter. Researchers have observed the protostar for three years with the Canada-France-Hawaii telescope on top of the Maunakea volcano in Hawaii, and discovered that V347 Aurigae is actually a binary system.
The luminous outbursts are because of a young companion of the protostar that is 10 times less massive. The object is a brown dwarf, or a failed star that contains about 30 masses of Jupiter. This brown dwarf is in orbit around V347 Aurigae. The brown dwarf was formed much in the same way as the protostar, but did not manage to accrete enough material to sustain nuclear fusion, which is why it is considered to be a failed star. This brown dwarf moves away from the porotostar about once every 155 days, triggering instabilities in the accretion disc surrounding the protostar.
Why V347 Aurigae erupts periodically
The brown dwarf is in an elliptical orbit around the protostar. When the brown dwarf reaches the most distant point of its orbit around the protostar, the destabilised material from the circumstellar disc falls into the star, causing it to flare up. The researchers were able to reconstruct the magnetic field of V347 Aurigae, as well as its temporal evolution, and were able to determine that this magnetic field also fluctuates every 155 days. The researchers have proposed the name of ‘pulsating dynamo’ to describe the mechanism. A paper describing the research has been published in the Monthly Notices of the Royal Astronomical Society.
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