For the first time ever rapid gas flares have been observed from a white dwarf binary star system.
Scientists from Oxford University detected the gas flare in SS Cyg, which suggests they do not yet have a complete understanding of star habits and capabilities.
Rapid flares are extremely powerful, fast variations in brightness that occur when a star suddenly releases a significant amount of energy.
A similar activity is seen in the Sun when magnetic energy is released over a short time-span in solar flares. This process involves less energetic activity than with the binary star.
The Oxford scientists observed the unusual active at radio wavelengths in SS Cyg—one of the brightest variable stars in the constellation of Cygnus, defying the current understanding of gas accretion and the production of flares in binary stars.
Dwarf novae—SS Cyg-like objects that contain a sun-like star orbiting a white dwarf star—are known for their repeated, low-level, bursting behavior.
However, they have never been observed exhibiting behavior on anything like the scale of rapid flares before.
While outbursts have previously been seen in white dwarfs, neutron stars and black holes residing in different galaxies, such stars mainly feed on gas from their companion stars through accretion—the process where a large amount of gas is accumulated and builds up through gravitational force.
These stars occasionally throw up some of the gas in the form of jets—powerful overflows of gas restricted to a single, narrow, cone-like flow.
Initial observations of the SS Cyg activity last February was considered an atypical outburst.
Later telescopic analysis showed that the rapid flares after the most unexpected behavior was observed at radio wavelengths towards the end of the outburst.
The flare lasted less than 15 minutes with energy more than a million times the strongest solar flares and an energy level never seen in dwarf nova systems and more consistent with that expected from a jet.
Kunal Mooley, Ph.D., astrophysics research fellow at Oxford University, who led the research, said the discovery may lead to further research.
“Many of astrophysics’ most compelling studies have been based on studying SS Cyg,” Mooley said in a statement. “The latest, a detection of a rapid, radio flare—especially a fast, bright flare towards the end of the outburst, is highly unusual and demonstrates that there may even be some new physics at play.
“We expected to see slow variation flares but found fast, rapid, cone-like spikes of activity and observed an enormous amount of energy being released in a time-span as short as ten minutes,” he added. “Nothing like this has ever been seen before in a dwarf nova system.”
Mooley explained what the next step will be.
“Moving forward, theorists should work with observers to find the answer to why these rapid flares occurred in SS Cyg,” Mooley said. “To really understand the process of gas accretion and gas expulsion in white dwarf systems—especially dwarf novae, similar studies should be carried out on other astrophysical systems.”
SS Cyg was first discovered more than 100 years ago and has provided new insights into the physical processes associated with white dwarf binary systems.
The Oxford science team will now conduct further analysis and work towards building a body of conclusive events about dwarf nova behaviors and establish if they are capable of launching powerful jets.
The study was published in the Monthly Notices of the Royal Astronomical Society.