- An international research team has imaged two large particle streams, or jets, in the core of a galaxy.
- It’s direct evidence of a pair of supermassive black holes orbiting each other closely. It’s also the first discovery of its kind.
- Astronomers believe the pair is in the final phase before merging. Until now, it was unclear whether this phenomenon could exist and whether it could be observed.
The Max Planck Institute for Radio Astronomy published this original story on April 7, 2026. Edits by EarthSky.
Close pair of supermassive black holes could merge in 100 years
Current findings suggest that a supermassive black hole lies at the center of almost every large galaxy. These supermassive black holes have masses millions or even billions of times greater than our sun. It’s still unclear exactly how they can reach such enormous masses. Gas collecting (or accreting) from the surrounding area alone would take too long. So it’s likely they have to merge with other massive black holes.
Astronomers have observed galaxy collisions throughout our universe. It is thus likely that the supermassive black holes at the centers of these colliding galaxies also merge. They would first orbit each other ever closer before ultimately coalescing into one.
On April 7, 2026, astronomers from the Max Planck Institute for Radio Astronomy (MPIfR) said they’ve detected the first close pair of supermassive black holes. At the center of a galaxy named Markarian 501, the astronomers found what appears to be not just one supermassive black hole, but two. And radio observations over several years suggest that the duo could merge in as short as 100 years.
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Telltale particle beam
Theoretical models cannot yet accurately describe the final phase of merging black holes. Complicating matters further, astronomers had not reliably detected a close pair of massive black holes. That’s despite collisions between galaxies being commonplace on cosmic timescales. But a new study of the galaxy Markarian 501 in the constellation Hercules has changed that.
Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn led an international team that found direct evidence of such a pair at the heart of Markarian 501. Their work has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society. It will appear in an upcoming issue.
The black hole at the center of Markarian 501 ejects a powerful jet of particles traveling at nearly the speed of light into space. For the study, the team analyzed high-resolution observations of the region. These observations cover various radio frequencies. Astronomers collected them on dozens of days over a period of approximately 23 years.
These long-term data reveal not only a single jet, but a second one as well. It is the first direct image of such a system at the center of a galaxy. And it’s a clear indication of the existence of a second supermassive black hole. Britzen said:
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.
Close dance of supermassive black holes
The first jet points toward Earth. That’s why it appears particularly bright to us and we’ve known about it for a long time. The second jet is oriented differently and was therefore more difficult to detect.
Over a period of just a few weeks, the astronomers observed significant changes: The second jet starts behind the larger black hole and moves counterclockwise around it. This process repeats itself. Britzen explained:
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.
On one observation day in June 2022, the radiation emitted by the system reached us on such a crooked path that it appeared ring-shaped. This was a so-called Einstein ring. The most likely explanation is that the system was perfectly aligned toward us. Gravitational lensing by the known black hole in front then shaped the light of the second jet behind it.
By analyzing the progression over time and recurring patterns in the brightness of the jets, the researchers were able to deduce that the two black holes orbit each other with a period of approximately 121 days. They are about 250 to 540 times farther apart than the distance between Earth and the sun. That’s tiny for such extreme objects with masses of between 100 million and a billion times that of the sun. Depending on their actual masses, the distance between them could decrease so rapidly that they could merge in as short as 100 years.
Countdown to the finale
Due to the great distance between Markarian 501 and Earth, even the most advanced observation methods cannot image the two black holes as separate objects. Not even the Event Horizon Telescope, which gave us the first images of black holes in 2019 and 2022, is powerful enough. So we won’t be able to observe the shrinking orbit of the pair. Nevertheless, scientists expect clear evidence of the ever-decreasing separation between the two black holes: The system should emit gravitational waves at very low frequencies, which could be detected using pulsar timing arrays.
Supermassive black hole binaries are already the favored explanation for the observed gravitational wave background. The European Pulsar Timing Array and others found evidence for them in 2023. Markarian 501 is now a prime candidate for attributing gravitational wave emission measured with pulsar timing arrays to a specific supermassive black hole binary. Co-author Héctor Olivares of Goethe University Frankfurt said:
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.
Bottom line: For the first time, astronomers have direct evidence of a close pair of supermassive black holes in a galaxy. These black holes could merge in as short a time as 100 years.
Source: Detection of a second jet within the nuclear core of Mrk 501
Via Max Planck Institute for Radio Astronomy