Astronomers find evidence of supermassive black hole pair

Galaxy Mrk 501 hosts a pair of black holes orbiting every 121 days, offering a rare preview of an imminent cosmic merger

By LineZotpaper

Published19 October 2026

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An international team of researchers led by the Max Planck Institute for Radio Astronomy has found compelling evidence of two supermassive black holes locked in a tight orbit at the centre of the galaxy Markarian 501. Analysing over two decades of radio observations revealed a hidden second jet and an Einstein ring, pointing to a binary system whose components are so close they could merge in as little as 100 years. If confirmed, this would be one of the closest known supermassive black hole binaries, offering an unprecedented window into their final growth stages.

Supermassive black holes, weighing millions to billions of times the mass of the Sun, are thought to exist at the centre of nearly all large galaxies. While they grow by consuming surrounding gas, the largest examples are expected to require mergers with other black holes to reach their size. When galaxies collide, their central black holes should spiral together, yet astronomers have struggled to find pairs in the final stages of this process.

The new study, led by Silke Britzen of the MPIfR and accepted for publication in Monthly Notices of the Royal Astronomical Society, provides what the team describes as the first direct imaging evidence of such a system. Detailed radio observations collected on dozens of days over approximately 23 years revealed a second jet alongside the familiar one at the centre of Mrk 501. "We searched for it for so long, and then it came as a complete surprise that we could not only see a second jet, but even track its movement," Britzen reported.

Over just a few weeks of observations, astronomers noticed dramatic changes in the second jet's position; it appeared to emerge from behind the larger black hole and sweep counterclockwise around it. "Evaluating the data felt like being on a ship. The entire jet system is in motion. A system of two black holes can explain this: The orbital plane sways," Britzen explained. In June 2022, the system produced an Einstein ring, where the gravity of a foreground object bent light from the jet behind it, acting as a natural lens.

The researchers calculated the two black holes complete an orbit around each other every 121 days, separated by 250 to 540 times the distance between Earth and the Sun. Given their masses, estimated at 100 million to one billion solar masses, this is an exceptionally compact orbit. The tight configuration suggests the pair could merge in just 100 years, a remarkably short countdown by astronomical standards.

While telescopes like the Event Horizon Telescope cannot resolve the black holes individually, the pair should radiate gravitational waves detectable by pulsar timing arrays. Co-author H\u00e9ctor Olivares noted: "If gravitational waves are detected, we may even see their frequency steadily rise as the two giants spiral toward collision, offering a rare chance to watch a supermassive black hole merger unfold."

Analysis

Why This Matters

The discovery provides the first direct imaging evidence of two supermassive black holes in a tight binary system, solving a long-standing puzzle in galaxy evolution.
Observing a system on the brink of merger offers an unparalleled test for theories of black hole growth and general relativity.
It creates a primary target for pulsar timing arrays to detect gravitational waves from a specific source, rather than just a background hum.

Background

Supermassive black holes are thought to exist at the centres of most large galaxies. Galaxy collisions are common, making it likely their central black holes eventually come together. However, the final stages of this process, known as the final parsec problem, have been difficult to confirm observationally. In 2023, the European Pulsar Timing Array and other collaborations reported evidence of a gravitational wave background, thought to arise from many distant supermassive black hole binaries across the universe. Mrk 501 may now provide a specific binary to anchor these observations.

Key Perspectives

[Research team (Silke Britzen et al.):] They interpret the second jet, its sweeping motion, and the 2022 Einstein ring as direct evidence of a supermassive black hole binary system. They argue the 121-day orbital period and potential 100-year merger timeline make this an extraordinary opportunity to study the final stages of black hole coalescence.

[Skeptical astronomers and peer reviewers]: The scientific community will seek to rule out alternative explanations for the second jet, such as instabilities in the accretion disk or interactions with surrounding gas, before fully accepting the binary model and the exceptionally short merger timescale.

[Gravitational wave astronomers (PTAs):] Mrk 501 is now a high-priority target. Confirming a binary here could connect the gravitational wave background to an individual source, allowing direct measurement of orbital decay predicted by general relativity.

What to Watch

Confirmation of the 121-day orbital period through continued monitoring of the jet motion.
Detection of gravitational waves from Mrk 501 by the European Pulsar Timing Array or NANOGrav.
Refinement of the black hole masses and merger timeline, which could extend from 100 years to significantly longer.
Further Einstein ring events, which could provide more precise geometric data on the system.

Sources

Two monster black holes could collide in just 100 years · Latest Science News -- ScienceDaily

Checked

12 claims in this story checked against 1 source: 9 supported.

Show each claim

SupportedAstronomers find evidence of supermassive black hole pairLatest Science News -- ScienceDaily: “An international research team ... has now uncovered direct observational evidence suggesting that such a pair exists at the center of the galaxy Mrk 501.”
SupportedGalaxy Mrk 501 hosts a pair of black holes orbiting every 121 daysLatest Science News -- ScienceDaily: “the two black holes appear to complete an orbit around each other approximately every 121 days.”
Supportedoffering a rare preview of an imminent cosmic mergerLatest Science News -- ScienceDaily: “offering a rare chance to watch a supermassive black hole merger unfold”
Not in the sourcesIf confirmed, this would be one of the closest known supermassive black hole binariesLatest Science News -- ScienceDaily
Partly supportedoffering an unprecedented window into their final growth stagesLatest Science News -- ScienceDaily: “offering a rare chance to watch a supermassive black hole merger unfold”
Supportedthe new study provides what the team describes as the first direct imaging evidence of such a systemLatest Science News -- ScienceDaily: “The observations provide what the researchers describe as the first direct imaging evidence of such a system”
Partly supportedIn June 2022, the system produced an Einstein ring, where the gravity of a foreground object bent light from the jet behind it, acting as a natural lens.Latest Science News -- ScienceDaily: “unusual event in June 2022, when radiation from the system appeared to form a ring... One possible explanation is that the two black holes and Earth were briefly aligned... gravity of the foreground black hole could have acted like a lens”
Supported"We searched for it for so long, and then it came as a complete surprise that we could not only see a second jet, but even track its movement," Britzen reported.Latest Science News -- ScienceDaily: “"We searched for it for so long, and then it came as a complete surprise that we could not only see a second jet, but even track its movement," reports Silke Britzen.”
Supported"Evaluating the data felt like being on a ship. The entire jet system is in motion. A system of two black holes can explain this: The orbital plane sways," Britzen explained.Latest Science News -- ScienceDaily: “"Evaluating the data felt like being on a ship. The entire jet system is in motion. A system of two black holes can explain this: The orbital plane sways," explains Silke Britzen.”
Supported"If gravitational waves are detected, we may even see their frequency steadily rise as the two giants spiral toward collision, offering a rare chance to watch a supermassive black hole merger unfold," notes co-author Héctor Olivares.Latest Science News -- ScienceDaily: “"If gravitational waves are detected, we may even see their frequency steadily rise as the two giants spiral toward collision, offering a rare chance to watch a supermassive black hole merger unfold," notes co-author Héctor Olivares.”
SupportedThe researchers calculated the two black holes complete an orbit around each other every 121 daysLatest Science News -- ScienceDaily: “the team calculated that the two black holes appear to complete an orbit around each other approximately every 121 days.”
Supportedseparated by 250 to 540 times the distance between Earth and the SunLatest Science News -- ScienceDaily: “Their estimated separation is just 250 to 540 times the distance between Earth and the Sun.”