A ‘Vampire Star’ Caught While Devouring its Companion

People might think of something beautiful when talking about stars, but in reality, they can be some pretty vicious pricks. Researchers have discovered a particularly brutal instance in a binary star located 3,000 light-years away, in which a small dead star repeatedly and over a period of time ate the binary mate’s gas.

This kind of engagement is known as cataclysmic variable star,’ but more commonly as a vampire star. These are binary systems where the smaller object, typically a white dwarf, sips material off the larger star.

However, in the case of this setting, the behavior is even more peculiar. The binary companion is a brown dwarf, a cosmic body that started to shape the way a star does, but could not gather sufficient mass to trigger hydrogen fusion in the nucleus. Such objects are usually called ‘failed stars,’ having a mass between massive gas planets and small stars.

This particular brown dwarf was about ten times smaller than the white dwarf in the system.

Caught in the Act

The occurrence was discovered in archived data gathered by the Kepler space telescope back in 2016. The instrument had spotted the star brightening immensely, but the data had been archived without the event being identified.

An automated program set to look through the data searching for changes in stars, also known as ‘transient events,’ discovered it.

“The rare event we found was a super-outburst from the dwarf nova, which can be thought of as a vampire star system,” explained astronomer Ryan Ridden-Harper from Australian National University.

“The incredible data from Kepler reveal a 30-day period during which the dwarf nova rapidly became 1,600 times brighter before dimming quickly and gradually returning to its normal brightness.”

That glow was generated by material rotating around the white dwarf in an accretion disc, the same event that happens on a wider level around supermassive black holes. The rotating disc produces such powerful heat through friction that it beams.

In exchange, this generates the star’s transient events. Due to the fact that the star is not eating in a constant manner, it dims and glows. A prior Kepler observation program in 2014 also contained the star, which was not feeding back then, therefore, offering the automated project with a foundation.

It Has a Peculiar Behavior

Ridden-Harper said: “The discovery of this dwarf nova was unexpected since it wasn’t what we were searching for, but it provided excellent data and new insights into these vampire star systems.”

The program has also found something pretty odd. The increase in brightness was not consistent in behavior observed in other dwarf-nova-super-outbursts, which suggests that there are new physics laws behind these outbursts that researchers known nothing about.

“The next steps for this project are to comb through all Kepler data and extend it to data from the Transiting Exoplanet Survey Satellite, which is known as TESS,” Ridden-Harper said. “This will give us the best understanding of the most rapid explosions in the Universe. Along the way, we might discover some rare events that no other telescope could find.”

The study has been published in the Monthly Notices of the Royal Astronomical Society.

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