The team estimates the binary’s mass to be a whopping 28 billion times that of the Sun, qualifying the pair as the heaviest black hole binary ever measured

Astronomers have encountered a couple at an unexpected location—in space. Researchers discovered the heaviest pair of supermassive black holes ever measured. These large phenomena have a combined mass that’s 28 billion times larger than our sun. This combined mass makes it more fascinating. 

The merging of two supermassive black holes has long been theorized but never directly observed. It is almost akin to spotting a rare unicorn. The theory suggests that when two galaxies merge, their resident black holes engage with each other and eventually merge into a single entity. The expectation is that these pairs will release powerful gravitational waves.

To tackle this theory, a team of astronomers began analyzing data from the Gemini North telescope in Hawai’i. Their mission? To dissect a supermassive black hole binary in the elliptical galaxy B2 0402+379 and, in doing so, unveil the cosmic secrets behind the seemingly stagnant dance of these heavyweights.

The Gemini North telescope is one-half of the International Gemini Observatory operated by NSF’s NOIRLab, and allowed scientists to scrutinize this black hole duo.

However, the binary black hole within B2 0402+379 defied expectations. The team saw that it maintained a mere 24 light-years separation for over three billion years.

24 light-years of separation over 3 billion years
To go deeper, the team dove into archival data from Gemini North’s Gemini Multi-Object Spectrograph (GMOS), a device with sensitivity so keen it could map the speeding stars around the black holes. 

Roger Romani, a physics professor from Stanford University, explains, “The excellent sensitivity of GMOS allowed us to map the stars’ increasing velocities as one looks closer to the galaxy’s center.”

The key revelation of their research showed that the black hole binary’s mass acts as a gravitational roadblock. This prevents the long-anticipated merging of the two black holes. They are able to take the final step due to an invisible force field.

Furthermore, the team uncovered clues hinting at the binary’s origin story, suggesting it formed through multiple galactic mergers. B2 0402+379, a “fossil cluster,” results from an entire galaxy cluster’s worth of stars and gas merging into a large single galaxy.

Limbo or merge?
The presence of two supermassive black holes is born from the merger of smaller black holes from various galaxies. In the aftermath of galactic mergers, supermassive black holes spiral closer until gravitational radiation takes over, and they merge. 

However, in this heavyweight duo, their sheer large size has flung out nearly all surrounding matter, creating a gravitational void. “Since this pair is so heavy, it required lots of stars and gas to get the job done,” Romani pointed out.

The burning question is whether this black hole duo will remain in limbo indefinitely or overcome their gravitational radiation and merge. The potential ripple effect from the gravitational waves resulting from the merger could be a hundred million times more powerful than those from typical black hole mergers.

“We’re looking forward to follow-up investigations. This should give us more insight into whether the supermassive black holes can eventually merge or if they will stay stranded as a binary,” said Tirth Surti, Stanford undergraduate and lead author of the study.

The team’s findings are detailed in The Astrophysical Journal.

Study Abstract

We report on integral field unit (IFU) measurements of the host of the radio source 4C+37.11. This massive elliptical contains the only resolved double compact nucleus at parsec-scale separation, likely a bound supermassive black hole binary (SMBHB). i-band photometry and GMOS-N IFU spectroscopy show that the galaxy has a large rb = 1farcs5 core and that the stellar velocity dispersion increases inside of a radius of influence rSOI ≈ 1farcs3. Jeans Anisotropic Modeling analysis of the core infers a total SMBHB mass of 2.8 (+/- 0.8) x 10^10M, making this one of the most massive black hole systems known. Our data indicate that there has been significant scouring of the central kiloparsec of the host galaxy.