Astronomers are witnessing an unusually prolonged and energetic outburst from a supermassive black hole, offering a rare glimpse into the chaotic aftermath of a stellar disruption event. The black hole, located approximately 665 million light-years from Earth, is continuing to eject material at high speeds years after consuming a star that ventured too close.
The observations, primarily conducted using radio telescopes in New Mexico and South Africa, reveal a jet of material that began to emerge a full two years after the star was initially torn apart by the black hole’s immense gravitational forces. What sets this event apart is not just the delay, but the sustained intensity of the outflow, which has now persisted for six years and continues to brighten. This duration is significantly longer than previously observed in similar events.
“The exponential rise in the luminosity of this source is unprecedented,” says Yvette Cendes, an astrophysicist at the University of Oregon and lead author of the study published in the issue of the Astrophysical Journal. “It’s now about 50 times brighter than when it was first discovered, and is now incredibly bright for an object in radio waves. This has been going on for years now, and no sign of stopping. That is super unusual.”
Black holes, by their very nature, are regions of spacetime with gravity so intense that nothing, not even light, can escape. Supermassive black holes reside at the centers of most galaxies, including our own Milky Way. When a star wanders too close to such a behemoth, the tidal forces become overwhelming, stretching and ultimately shredding the star in a process known as a tidal disruption event (TDE). While TDEs are not uncommon, the subsequent behavior of the black hole and the ejected material can vary significantly.
Typically, after a star is disrupted, a surge of radiation is observed as the stellar debris heats up and falls towards the black hole, forming an accretion disk. This disk emits light across the electromagnetic spectrum, including radio waves. However, the emission usually peaks relatively quickly and then fades over weeks or months. This particular black hole is defying that pattern.
The prolonged and intensifying jet suggests a more complex interaction between the black hole and the remaining stellar material than previously understood. One possible explanation, according to researchers, involves shock waves within the ejected material. As the initial outflow collides with surrounding gas, it creates shock fronts that accelerate particles to extremely high energies, boosting the radio emission. The continued brightening could indicate that these shock waves are still propagating outwards, continually energizing the jet.
The delay between the disruption event and the onset of the radio emission is also puzzling. It’s possible that a significant portion of the stellar debris initially formed a dense, opaque cloud around the black hole, obscuring the radio signals. Over time, this cloud dissipated, allowing the jet to become visible. Alternatively, the black hole may have been in a relatively quiescent state immediately after the disruption, gradually ramping up its activity as more material fell into the accretion disk.
Understanding these processes is crucial for refining our models of black hole accretion and jet formation. Jets are a common feature of active galactic nuclei (AGN), which are powered by supermassive black holes. These jets can extend for millions of light-years and have a profound impact on the surrounding environment, influencing star formation and the evolution of galaxies.
The observations highlight the dynamic and often unpredictable nature of black holes. While they are often described as “cosmic vacuum cleaners,” relentlessly consuming everything in their path, the reality is far more nuanced. The way a black hole interacts with its surroundings depends on a complex interplay of factors, including its mass, spin, and the properties of the infalling material.
Further observations, particularly at multiple wavelengths, will be essential to unravel the mysteries surrounding this unusual black hole. Astronomers plan to continue monitoring the source with radio telescopes, as well as with optical and X-ray observatories, to track the evolution of the jet and gain a deeper understanding of the underlying physical processes. The ongoing study promises to provide valuable insights into the extreme environments around supermassive black holes and the fate of stars that venture too close.
The sheer distance to this black hole – 665 million light-years – underscores the power of modern astronomical instruments to probe the distant universe and witness events that occurred billions of years ago. Each photon of radio energy detected by these telescopes has traveled for an immense amount of time, carrying with it a message from a cataclysmic event in a faraway galaxy.
