A team of researchers from the Hebrew University of Jerusalem (HUJI) led by Dr. Assaf Horesh has discovered the first evidence of radio flares emitted only long after a star is destroyed by a black hole. Published in the magazine Nature astronomy, the discovery relied on ultra-powerful radio telescopes to study these catastrophic cosmic events in distant galaxies called Tidal Disruption Events (TDE). While researchers knew that these events cause the release of radio flashes, this latest discovery saw those flashes emitted months or even years after the stellar disruption. The team was led by Dr. Horesh of the Racah Institute of Physics in Hebrew along with the director of NASA’s Swift Space Telescope, Professor Brad Cenko and Dr. Iair Arcavi of Tel-Aviv University.
“Based on existing theories about how these events occur, if no radio emission has been discovered immediately after the outage, there is no expectation that it will occur later,” says Dr. Horesh. “However, we decided to make a final radio observation six months after the star was destroyed and surprisingly we discovered a bright radio emission. Once we discovered this delayed radio flare, we continued to collect data for a year, during the which the radio emission faded away. In addition, we find a delayed second flash, four years after the initial discovery of stellar rupture. This is the first discovery of such delayed radio flashes from such events, when a star is interrupted by a hole. black “.
The flares are believed to be caused by a high-speed jet launched when the star is destroyed and sucked into the black hole or as a result of blasting out debris from the explosion.
Analysis of the delayed radio flares led the research team to several conclusions.
First, they now believe that new models must be developed to explain such a long delay in the emission of radio flares. Second, such delayed radio flashes may be a common phenomenon, but to find more of them, teams will need to stay focused on observations surrounding affected areas long after the initial outage. Third, it is possible that a substantial amount of the stellar debris eventually accumulates (gets into) the black hole, but only long after the star has been destroyed.
“What caused the delay and what is the exact physical process responsible for such a late release remain open questions,” says Dr. Horesh. “In light of this discovery, we are actively looking for more delayed radio flares in other tidal disruption events.”
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