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Thursday, July 18, 2024 | Back issues
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Scientists measure a pair of nearby black holes for the first time using novel technique

Astronomers have determined the mass and distance of the two super massive black holes nearest to Earth by looking at the ways their gravitational pull influences the stars around them.

(CN) — A team of astronomers has revealed two super massive black holes are closer to Earth than any previously discovered.

Using the European Observatory’s Very Large Telescope, or VLT, the scientists were able to measure the mass of the black holes by looking at how their gravity influenced the surrounding stars.

The team found that the two black holes located in NGC 7727, a neighboring galaxy about 90 million light years from Earth, were much closer together than any pair previously identified and predicted that in the future they will merge into a single, much larger black hole. The authors described the new discovery and the methods used to identify them in a study published Tuesday in the journal Astronomy & Astrophysics.

The larger of the two black holes has a mass nearly 154 million times that of the Earth’s sun, according to the authors, while the smaller of the two is 6.3 million solar masses. Thanks to their relatively close proximity to Earth, the team was able to determine the masses of the objects with gravitational observations taken from the Paranal Observatory in Chile using the Multi-Unit Spectroscopic Explorer, or MUSE, on the European Southern Observatory’s VLT. The team also used data from the Hubble Space Telescope to confirm their observations.

“We investigate whether the recently discovered two nuclei in NGC 7727 both host a super-massive black hole (SMBH),” said the authors in the study. “We use the high spatial resolution mode of the integral-field spectrograph MUSE on the VLT in adaptive optics mode to resolve the stellar kinematics within the sphere-of-influence of both putative black holes. We combine the kinematic data with an HST-based mass model and use Jeans models to measure their SMBH mass.”

It’s the first time the masses of a pair of supermassive black holes have been measured in this manner and it appears to bode well for the future of astronomy with new, more powerful telescopes coming online in the near future. The European Southern Observatory’s Extremely Large Telescope, or ELT, will mark a significant upgrade for these types of measurements and is set to begin operation toward the end of the decade in Chile’s Atacama Desert. The ELT is projected to cost just shy of $1.5 billion dollars and will add much needed capabilities for users tasked with charting the cosmos.

“This detection of a supermassive black hole pair is just the beginning,” said co-author Dr. Steffen Mieske, an astronomer at ESO in Chile and Head of ESO Paranal Science Operations. “With the HARMONI instrument on the ELT we will be able to make detections like this considerably further than currently possible. ESO’s ELT will be integral to understanding these objects.”

When galaxies merge, it’s believed that the supermassive black holes at their centers end up coalescing to form a much larger black hole. Astronomers were previously unable to confirm the black hole pair’s presence due to a lack of high-energy radiation emanating from its presumed location, which would normally be a tell-tale sign of a black hole, despite suspicions that the NGC7727 galaxy contained just such a pair. By employing this novel technique looking at the black holes’ gravitational pull on surrounding stars they were finally able to nail down the pair’s approximate location and size.

“Our finding implies that there might be many more of these relics of galaxy mergers out there and they may contain many hidden massive black holes that still wait to be found,” concluded Dr. Karina Voggel, a CNES fellow at the Strasbourg Observatory in France and author of the study. “It could increase the total number of supermassive black holes known in the local Universe by 30 percent.”

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