A star is being consumed by a nearby supermassive black hole, in a rare event that astronomers call a tidal disruption event (TDE). What makes this event, AT2022cmc, even more rare is that as the black hole ripped the star apart, jets of material moving at almost the speed of light were launched. AT2022cmc, depicted here in an artist’s impression, was the first jetted-TDE discovered in over a decade and the first since the launch of NuSTAR. The sensitive, broadband X-ray observation by NuSTAR provided critical data for understanding the event. Image credit: ESO/M.Kornmesser
NuSTAR unveiled crucial details for understanding one of the most energetic types of event in the universe. If a star comes too close to a supermassive black hole, it will be torn apart by the black hole’s tidal force. Fundamentally, the side of the star closer to the black hole feels a stronger gravitational pull than the far side of the star, much like people on Earth feel stronger gravity than an astronaut in the International Space Station. However, you’d have to imagine an astronaut so tall that their feet were on Earth while their head was in orbit. And the difference in gravitational field would also be much larger. When a star comes extremely close to the black hole, it becomes stretched and is pulled apart. The resulting stream of material loops around the black hole. Some stellar material is captured into orbit, creating an accretion disk around the black hole. This disk becomes quite bright. In a very rare subclass of events, a relativistic jet is also produced, creating another source of light. As the disk material is consumed by the black hole over the course of months to years, the event gradually fades.
Tidal disruption events, or TDEs for short, were first predicted in the 1970s, and first observed in the 1990s. Currently, approximately 100 TDEs are known, only four of which are of the rare jetted-TDE variety.
Just after midnight on February 11, 2022, the Zwicky Transient Facility at Palomar Observatory in Southern California detected a new transient source. Data obtained over the next two nights led to this new source, AT2022cmc, being flagged as unusual, rising and falling faster than a typical supernova. This inspired follow-up observations using telescopes around the planet and in space. Those data provided the distance and energetics of the system, ultimately classifying it as a jetted-TDE. This subclass of TDE is very bright at X-ray energies, and only four have been detected to date. The most recent jetted-TDE occurred more than a decade ago, prior to the launch of NuSTAR. NuSTAR is the first focusing high-energy, or hard X-ray telescope in orbit, providing two orders of magnitude improvement in sensitivity compared to previous instruments. NuSTAR significantly extends the range of X-ray energies that can be studied in detail for astrophysical phenomena. AT2022cmc provided the first opportunity to study this type of rare, X-ray bright, transient event and motivated three NuSTAR observations in the month after its discovery.
While the lower energy emission from jetted-TDEs is relatively well understood (e.g., at radio, optical, and UV energies), the location and mechanism producing the bright X-ray emission in jetted-TDEs is a topic of active debate. The most popular scenario is that the X-rays come from less energetic photons in the radio and optical bands being scattered by energetic relativistic electrons in the surrounding plasma up to X-ray energies. This scenario predicts that we should see the high-energy X-ray spectrum as a smooth extrapolation of the lower-energy X-ray spectrum. However, when NuSTAR observed AT2022cmc, it detected a pronounced break in the X-ray spectrum within the NuSTAR band. This break gives an important clue to the X-ray emission mechanisms of jetted-TDEs.
In a recent paper published in the Astrophysical Journal, Dr. Yuhan Yao of the University of California, Berkeley and her team report that the NuSTAR data and spectral break are consistent with a phenomenon known as synchrotron radiation, created as relativistic charged particles (i.e., electrons) move through a strong magnetic field. This is naturally expected from astrophysical jets, though the leading jetted-TDE models had predicted it to be subdominant to the up-scattered emission in jetted-TDEs. Modeling the X-ray data, Dr. Yao and her team were able to constrain the properties of the jet and determine what part of the jet is dominating its X-ray emission. They find that the jet is likely to be starved of protons, and instead is dominated by electrons moving in a highly magnetized jet.
AT2022cmc represents a significant leap in our understanding of relativistic jets in astrophysical phenomena. “The NuSTAR data challenge existing models and suggest that magnetic reconnection plays a key role in accelerating particles within these jets,” noted Dr. Yao. This result not only sheds light on the inner workings of TDEs but also has broader implications for understanding relativistic jets in other high-energy astrophysical sources, such as gamma-ray bursts. Dr. Yao explained, “overall, this work contributes to the ongoing quest to decipher the composition and acceleration mechanisms of relativistic jets in the Universe.”
Tidal disruption events, or TDEs for short, were first predicted in the 1970s, and first observed in the 1990s. Currently, approximately 100 TDEs are known, only four of which are of the rare jetted-TDE variety.
Just after midnight on February 11, 2022, the Zwicky Transient Facility at Palomar Observatory in Southern California detected a new transient source. Data obtained over the next two nights led to this new source, AT2022cmc, being flagged as unusual, rising and falling faster than a typical supernova. This inspired follow-up observations using telescopes around the planet and in space. Those data provided the distance and energetics of the system, ultimately classifying it as a jetted-TDE. This subclass of TDE is very bright at X-ray energies, and only four have been detected to date. The most recent jetted-TDE occurred more than a decade ago, prior to the launch of NuSTAR. NuSTAR is the first focusing high-energy, or hard X-ray telescope in orbit, providing two orders of magnitude improvement in sensitivity compared to previous instruments. NuSTAR significantly extends the range of X-ray energies that can be studied in detail for astrophysical phenomena. AT2022cmc provided the first opportunity to study this type of rare, X-ray bright, transient event and motivated three NuSTAR observations in the month after its discovery.
While the lower energy emission from jetted-TDEs is relatively well understood (e.g., at radio, optical, and UV energies), the location and mechanism producing the bright X-ray emission in jetted-TDEs is a topic of active debate. The most popular scenario is that the X-rays come from less energetic photons in the radio and optical bands being scattered by energetic relativistic electrons in the surrounding plasma up to X-ray energies. This scenario predicts that we should see the high-energy X-ray spectrum as a smooth extrapolation of the lower-energy X-ray spectrum. However, when NuSTAR observed AT2022cmc, it detected a pronounced break in the X-ray spectrum within the NuSTAR band. This break gives an important clue to the X-ray emission mechanisms of jetted-TDEs.
In a recent paper published in the Astrophysical Journal, Dr. Yuhan Yao of the University of California, Berkeley and her team report that the NuSTAR data and spectral break are consistent with a phenomenon known as synchrotron radiation, created as relativistic charged particles (i.e., electrons) move through a strong magnetic field. This is naturally expected from astrophysical jets, though the leading jetted-TDE models had predicted it to be subdominant to the up-scattered emission in jetted-TDEs. Modeling the X-ray data, Dr. Yao and her team were able to constrain the properties of the jet and determine what part of the jet is dominating its X-ray emission. They find that the jet is likely to be starved of protons, and instead is dominated by electrons moving in a highly magnetized jet.
AT2022cmc represents a significant leap in our understanding of relativistic jets in astrophysical phenomena. “The NuSTAR data challenge existing models and suggest that magnetic reconnection plays a key role in accelerating particles within these jets,” noted Dr. Yao. This result not only sheds light on the inner workings of TDEs but also has broader implications for understanding relativistic jets in other high-energy astrophysical sources, such as gamma-ray bursts. Dr. Yao explained, “overall, this work contributes to the ongoing quest to decipher the composition and acceleration mechanisms of relativistic jets in the Universe.”
