Highly energetic explosions in the sky are commonly attributed to gamma-ray bursts. We now understand that these bursts originate from either the merger of two neutron stars or the collapse of a massive star. In these scenarios, a newborn black hole is formed, emitting a jet that travels at nearly the speed of light. When these jets are directed toward Earth, we can observe them from vast distances - sometimes billions of light-years away - due to a relativistic effect known as Doppler boosting. Over the past decade, thousands of such gamma-ray bursts have been detected.
Since its launch in 2024, the Einstein Probe - an X-ray space telescope developed by the Chinese Academy of Sciences (CAS) in partnership with European Space Agency (ESA) and the Max Planck Institute for Extraterrestrial Physics - has been scanning the skies looking for energetic explosions, and in April the telescope observed an unusual event designated as EP240408A. Now an international team of astronomers, including Dheeraj Pasham from MIT, Igor Andreoni from University of North Carolina at Chapel Hill, and Brendan O'Connor from Carnegie Mellon University, and others have investigated this explosion using a slew of ground-based and space-based telescopes, including NuSTAR, Swift, Gemini, Keck, DECam, VLA, ATCA, and NICER, which was developed in collaboration with MIT.
An open-access report of their findings, published Jan. 27 in The Astrophysical Journal Letters , indicates that the characteristics of this explosion do not match those of typical gamma-ray bursts. Instead, it may represent a rare new class of powerful cosmic explosion - a jetted tidal disruption event, which occurs when a supermassive black hole tears apart a star.
"NICER's ability to steer to pretty much any part of the sky and monitor for weeks has been instrumental in our understanding of these unusual cosmic explosions," says Pasham, a research scientist at the MIT Kavli Institute for Astrophysics and Space Research.
While a jetted tidal disruption event is plausible, the researchers say the lack of radio emissions from this jet is puzzling. O'Connor surmises, "EP240408a ticks some of the boxes for several different kinds of phenomena, but it doesn't tick all the boxes for anything. In particular, the short duration and high luminosity are hard to explain in other scenarios. The alternative is that we are seeing something entirely new!"
According to Pasham, the Einstein Probe is just beginning to scratch the surface of what seems possible. "I'm excited to chase the next weird explosion from the Einstein Probe", he says, echoing astronomers worldwide who look forward to the prospect of discovering more unusual explosions from the farthest reaches of the cosmos.
