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Study reports evidence of second supermassive black hole in galaxy Mrk 501

ScienceDaily reports that radio observations of galaxy Mrk 501 suggest a black hole pair that could merge in as little as 100 years.

Updated Oct 18, 2026 · 14:06 UTC1 reports

The short version

  • A team led by Silke Britzen reports evidence of a second supermassive black hole at the center of galaxy Mrk 501.[ScienceDaily]
  • Radio observations over about 23 years suggest the pair orbits roughly every 121 days, an estimated 250 to 540 Earth-Sun distances apart.[ScienceDaily]
  • Depending on estimated masses of 100 million to a billion solar masses, the black holes could merge in as little as 100 years.[ScienceDaily]
  • Current instruments cannot separately resolve the pair, so researchers plan to search for merger signals in low-frequency gravitational waves.[ScienceDaily]

Key facts

  • Silke Britzen of the Max Planck Institute for Radio Astronomy led the international team that reported evidence of a second supermassive black hole at the center of Mrk 501.[ScienceDaily]
  • The analysis is based on radio observations collected at multiple frequencies over approximately 23 years.[ScienceDaily]
  • The team estimates that the black hole pair completes an orbit approximately every 121 days.[ScienceDaily]
  • The team estimates the separation between the two black holes at 250 to 540 times the Earth-Sun distance.[ScienceDaily]
  • The team estimates the black holes' masses at 100 million to a billion times the Sun's mass, which could allow a merger in as little as 100 years.[ScienceDaily]
  • Current instruments, including the Event Horizon Telescope, cannot resolve the two black holes as separate objects at Mrk 501's distance.[ScienceDaily]
  • Researchers plan to search for gravitational waves from the pair using pulsar timing arrays.[ScienceDaily]
  • The findings have been accepted for publication in Monthly Notices of the Royal Astronomical Society, with no issue date given.[ScienceDaily]

What remains uncertain

  • The existence of the pair rests on the team's interpretation of radio jet observations; the reporting provided does not describe independent confirmation.[ScienceDaily]
  • The orbital period, separation, masses and merger timescale are estimates, and the 100-year merger figure depends on masses that remain uncertain.[ScienceDaily]
  • Whether pulsar timing arrays will detect gravitational waves from the pair is unknown; the reporting describes detection only as a planned search.[ScienceDaily]

Sources

Outlet counts describe coverage, not independent confirmation. Reports may share a wire service or original source.