Astronomers detect first confirmed close pair of supermassive black holes nearing merger

Tuesday 07 April 2026 - 16:20

By: Dakir Madiha

Astronomers detect first confirmed close pair of supermassive black holes nearing merger

Astronomers have discovered what appears to be the first reliably detected pair of supermassive black holes orbiting each other at close range at the center of the galaxy Markarian 501. The finding, announced Monday by the Max Planck Institute for Radio Astronomy in Bonn, opens a rare window into one of the least understood phases of galaxy evolution: the final moments before two colossal black holes collide.

An international team led by Silke Britzen of the Max Planck Institute for Radio Astronomy analyzed high-resolution radio observations of Markarian 501 collected over approximately 23 years across multiple frequencies. The long-term data revealed not one but two particle jets propelled at near-light speed, each powered by its own supermassive black hole. The two could merge in as little as 100 years, according to the institute.

The research has been accepted for publication in Monthly Notices of the Royal Astronomical Society. While theoretical models have long predicted that supermassive black holes should merge when their host galaxies collide, no close pair had been reliably observed until now. Even the Event Horizon Telescope, which produced the first direct images of black holes in 2019 and 2022, lacks sufficient resolution to distinguish the two objects within Markarian 501.

The system is now considered a prime candidate for detection by pulsar timing arrays, which measure minute variations in the arrival times of pulsar signals to detect low-frequency gravitational waves. Co-author Héctor Olivares noted that if gravitational waves are detected, it may become possible to observe their frequency gradually increase as the two giants spiral toward collision, offering a rare opportunity to witness a supermassive black hole merger in real time.

Separately, a series of studies published in The Astrophysical Journal Letters used the James Webb Space Telescope to examine small galaxies in the Virgo Cluster, approximately 55 million light-years away. Researchers found that the compact elliptical galaxy NGC 4486B hosts a black hole with a mass of roughly 360 million solar masses, accounting for up to 13% of the galaxy's total stellar mass. A companion study revealed that the ultra-compact dwarf galaxy UCD736 also contains an oversized black hole representing approximately 8% of its system's mass.

A third study found that the off-center black hole and double nucleus of NGC 4486B may be the aftermath of a recent black hole merger, with modeling suggesting the merged object received a gravitational recoil that displaced it from the galaxy's center.

Monica Valluri, research professor of astronomy at the University of Michigan and lead author of the studies, said the findings point to a wide diversity of black holes in dwarf galaxies, particularly those evolving in the dense environment of the Virgo Cluster.