NuSTAR Reveals Key Insights into Extreme Stellar Disruption by Black Holes.

A star is being torn apart by a supermassive black hole in a rare tidal disruption event (TDE) called AT2022cmc. What makes it even rarer is the launch of high-speed jets as the black hole consumes the star. This is the first jetted-TDE discovered in over a decade and the first since the launch of NuSTAR, whose X-ray observations provided critical data

NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) has unveiled crucial details about one of the universe’s most violent phenomena: tidal disruption events (TDEs). These occur when a star ventures too close to a supermassive black hole and is torn apart by its immense tidal forces. Just as an astronaut aboard the International Space Station experiences weaker gravity than people on Earth, the side of the star closest to the black hole feels a much stronger pull, stretching the star apart in a cosmic “spaghettification” process. This results in a stream of material that orbits the black hole, forming an accretion disk that glows brightly. In rare instances, this event also generates a relativistic jet, producing another source of light. Over time, the event fades as the black hole consumes the stellar debris.

First predicted in the 1970s and observed in the 1990s, TDEs have become a key area of study. There are about 100 known TDEs, with only four being of the rare jetted variety, where jets are formed and emit powerful X-rays. These jetted-TDEs are exceedingly bright in the X-ray spectrum, yet the mechanisms behind their X-ray emission remain an open question.

On February 11, 2022, the Zwicky Transient Facility detected an unusual transient event, AT2022cmc, in Southern California. This event rose and fell much more rapidly than typical supernovae, prompting an array of follow-up observations from telescopes worldwide. The data revealed that AT2022cmc was, in fact, a jetted-TDE, the first such event observed since the launch of NuSTAR. As the first focusing high-energy X-ray telescope in orbit, NuSTAR’s advanced sensitivity provided the ideal tool to study this rare, X-ray-bright transient.

Although much is known about the lower-energy emissions from jetted-TDEs—such as those observed in radio, optical, and ultraviolet wavelengths—the precise source of their high-energy X-rays has remained debated. The most widely accepted theory posits that the X-rays originate from lower-energy photons (in the radio and optical bands) being scattered by relativistic electrons in the surrounding plasma. This theory suggests a smooth continuation of the X-ray spectrum from lower energies. However, when NuSTAR observed AT2022cmc, it detected an unexpected break in the X-ray spectrum. This break provided a critical clue, indicating a different mechanism at play.

In a paper recently published in the Astrophysical Journal, Dr. Yuhan Yao from the University of California, Berkeley, and her team analyzed the NuSTAR data and proposed that the X-rays were produced by synchrotron radiation. This occurs when high-energy electrons move through strong magnetic fields, as seen in astrophysical jets. This finding challenges previous models, which had anticipated the synchrotron emission to be less significant than up-scattered emissions. By modeling the X-ray data, Dr. Yao’s team also determined that the jet in AT2022cmc is likely lacking protons, with the X-ray emission dominated by electrons in a highly magnetized environment.

This discovery marks a significant advancement in our understanding of relativistic jets. “The NuSTAR data challenge existing models and suggest that magnetic reconnection plays a key role in accelerating particles within these jets,” said Dr. Yao. The implications extend beyond TDEs, offering new insights into the nature of jets in other high-energy astrophysical phenomena, such as gamma-ray bursts.

Dr. Yao concluded, “This work contributes to the ongoing quest to decipher the composition and acceleration mechanisms of relativistic jets in the Universe.”