Astronomers have discovered what may be the first example of a new class of radio galaxy, one where the central black hole has seemingly launched powerful jets four separate times. Using high-resolution data from the upgraded Giant Metrewave Radio Telescope (GMRT), along with observations from MeerKAT and the Very Large Array, researchers identified four pairs of radio structures arranged symmetrically around the galaxy's core. A paper describing this finding was posted on the arXiv preprint server on September 8. Radio galaxies are a type of active galactic nucleus where a supermassive black hole at the center launches powerful jets of particles, detectable in radio waves. The most energetic type, known as FR II galaxies, produce bright "hotspots" where the jets collide with surrounding gas, creating structures that can extend millions of light-years. In some FR II galaxies, the black hole appears to activate its jets multiple times over time, with each burst leaving its own pair of hotspots. Older episodes are farther from the galaxy's center, as they have had more time to travel outward, while newer ones are closer. Galaxies with two such episodes are called double-double radio galaxies, and about 192 are known. Triple-double galaxies, with three episodes, are rarer, with only seven confirmed or possible examples. Until now, no galaxy had been found with four confirmed jet episodes. The research team, led by Pavan Vijay Khadekar from the Indian Institute of Science Education and Research, Pune, studied a radio source called J023721.13−010528.5, located in a massive elliptical galaxy at a redshift of 0.372. By combining data from three powerful radio telescopes across multiple frequencies, they identified four distinct pairs of hotspots labeled N1–N4 and S1–S4, arranged in a sequence moving outward from the galaxy's core. They calculated the physical distance of each hotspot from the center and estimated the "kinematic ages" of each pair, assuming a typical jet speed. They also determined the "spectral ages" by analyzing how the radio "color" had changed over time. To ensure the hotspots were not just random "knots" in a continuously active jet, the team conducted additional tests. If the knots were part of a single jet, they should all be roughly the same age. However, if they represented separate jet episodes, the ages should increase with distance from the galaxy's core. The four pairs showed spectral ages ranging from 4.5 to 20.5 million years, with the age clearly increasing as the distance from the core grew. This pattern strongly supports the idea of four distinct, sequential jet episodes rather than random knots. The team also noted that the data quality was poorer on the southern side, leading to larger uncertainties there. Using a statistical symmetry test, they found the "four separate episodes" explanation was about 3 million times more likely than the "random knots" explanation. The researchers also observed that the axes of the hotspot pairs were rotating counterclockwise by increasing amounts: −7° for N2–S2, −16° for N3–S3, and −24° for N4–S4. This suggests the central black hole's spin axis is slowly "wobbling" over time. This wobbling, or "progressive rotation," aligns with the galaxy's jets displaying an S-shaped structure. The galaxy's radio emissions span about 3.9 million light-years, making it the second-largest S-shaped radio source known. Scientists suggest that such large, S-shaped radio galaxies may be the best places to search for more rare, multi-episode systems like this one.