First Close Supermassive Black Hole Pair Detected
Get the Health newsletter
Daily health & science — research, biotech, public health, the studies worth knowing. Free.
- Silke Britzen of the Max Planck Institute for Radio Astronomy led a team that found direct evidence of two supermassive black holes orbiting each other closely in galaxy Markarian 501, in the constellation Hercules — the first such close pair ever detected.
- The researchers identified a second particle jet from the galaxy's center by analyzing high-resolution radio observations spanning approximately 23 years and dozens of observing days, producing the first direct image of a two-black-hole system at a galactic core.
- The two black holes orbit each other with a period of approximately 121 days at a separation of 250 to 540 times the Earth–Sun distance, with individual masses estimated between 100 million and 1 billion times that of the Sun.
- On one observation day in June 2022, the system's geometry produced an Einstein ring — a ring-shaped image of the second jet's radiation shaped by gravitational lensing from the black hole in front of it.
- Depending on their actual masses, the pair's orbit could shrink fast enough for the black holes to merge in as little as 100 years; the system should emit low-frequency gravitational waves detectable by pulsar timing arrays (PTAs).
- Co-author Héctor Olivares noted that if gravitational waves are detected, their frequency should steadily rise as the two giants spiral inward, offering a rare chance to watch a supermassive black hole merger unfold.
- The findings were published by S. Britzen et al. in the Monthly Notices of the Royal Astronomical Society (2026), and Mrk 501 is now a prime candidate for attributing PTA-measured gravitational wave emission to a specific supermassive black hole binary.
Why it matters: Mrk 501 gives astronomers their first named, trackable target for a supermassive black hole merger — the system joins the diffuse 2023 gravitational-wave background (detected by the European Pulsar Timing Array and others) with a specific source, potentially allowing researchers to watch a 121-day orbital signal tighten in real time over the coming century.
