Unprecedented Gamma Flash Challenges Understanding of Stellar Cataclysms
A gamma-ray burst,designated GRB 250702B,has been observed lasting approximately a day – 100 to 1000 times longer than typical gamma flashes. This unusual event, initially detected on July 2 by NASA’s Fermi Gamma-Ray Space Telescope, revealed three distinct eruptions within a few hours, with preceding activity identified through data from teh Chinese Academy of Sciences’ einstein Probe in collaboration with ESA and the Max-Planck Institut Für Extraterrestrial Physik.
Gamma-ray bursts are generally understood to be the result of catastrophic stellar events and are not expected to repeat. Initial estimations placed the source within the Milky Way, but observations from the European Southern Observatory’s Very large Telescope (VLT), utilizing the HAWK-I camera, indicated a location outside our galaxy. This was later confirmed by the NASA/ESA Hubble Space Telescope.
The source galaxy is estimated to be several billion light-years away, though precise distance calculations are ongoing. Researchers, including Andrew Levan of Radboud university and the University of Warwick, are investigating the cause of this prolonged burst.
“Until these observations, the astronomical community assumed that the gamma flashes had taken place within this galaxy, but the VLT has thoroughly changed this image,” said Levan.
Possible explanations include the implosion of an exceptionally massive star, or the disruption of a star by an unusual black hole. “If it is a heavy star, then it was a collapse as we have never seen it before,” Levan explained, noting that typical stellar collapses produce gamma flashes lasting only seconds. alternatively, a day-long burst could result from a star torn apart by a black hole, requiring “an abnormal star…destroyed by an even more abnormal black hole” to account for the observed characteristics.
Further investigation is underway using instruments such as the VLT’s X-shooter spectrographer and the NASA/ESA/Canadian Space Agency’s Webb Space Telescope.”We still don’t know for sure what this has caused, but with this research we have taken a step forward in understanding this extremely unusual object,” Levan concluded.