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Study Points to Tight Supermassive Black Hole Binary in Markarian 501

Decades of radio imaging reveal a faint second jet consistent with a close pair now modeled on a 121-day orbit.

Overview

  • Researchers analyzed 23 years of high-resolution radio data and tracked a second, fainter jet moving around the bright core in work accepted by Monthly Notices of the Royal Astronomical Society.
  • An Einstein-ring pattern seen in June 2022 matches gravitational lensing of the faint jet by the black hole in front, strengthening the two-object reading.
  • The model fits a roughly 121-day orbital period, a separation of about 250 to 540 times Earth’s distance from the Sun, and masses near 100 million to 1 billion Suns.
  • The team says the pair could merge within about a century, which could let pulsar timing arrays detect very low-frequency gravitational waves from the system.
  • The case remains indirect because telescopes cannot resolve two accretion disks at this distance, so the evidence comes from jet behavior, cycles in brightness, and lensing.