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Astronomers have discovered a surprising cosmic anomaly — a supermassive black hole in the galaxy NGC 5084 that appears to be completely tilted relative to its galaxy's structure. The discovery, hidden for years in archival data, was only revealed using advanced image analysis techniques.
The mystery of the black hole is revealed
NASA researchers have identified a strange black hole in the galaxy NGC 5084 — one that appears to be “flipped,” rotating at an unusual angle relative to the rest of the galaxy. Although NGC 5084 has been studied for years, the black hole’s unexpected orientation had remained hidden in old data archives. The breakthrough came when scientists at NASA’s Ames Research Center in Silicon Valley, California, used new image analysis techniques to re-examine archival data from the Chandra X-ray Observatory.
Using these advanced techniques, the Ames astronomers have discovered a surprising feature: four long plumes of plasma—hot, charged gas—emanating from the galaxy. One pair of plumes extends above and below the plane of the galaxy, which is typical in some galaxies. However, the second pair, which is located in the plane of the galaxy and forms an “X” shape with the first, is very unusual. Galaxies typically exhibit only one or two such plumes, which makes this discovery even more impressive.
New methods reveal the unexpected
The method that reveals these unexpected features of NGC 5084 was developed by Alejandro Serrano Borlaff, a research scientist at the Bay Area Institute for Environmental Research in Ames, and his colleagues to detect low-luminosity X-rays in data from the world's most powerful X-ray telescope. What they saw in the Chandra data seemed so strange that they immediately began looking for confirmation, digging into archives of data from other telescopes and requesting new observations from two powerful ground-based observatories.
The unexpected second set of plumes was a strong hint that the galaxy contained a supermassive black hole, but there could be other explanations. Archival data from the Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed another feature of NGC 5084: a small, dusty inner disk orbiting the galaxy's center. This also suggested the presence of a black hole, and, surprisingly, it was rotating at a 90-degree angle to the galaxy's overall rotation; the disk and the black hole were, in a sense, lying on their sides.
Assembling a galactic puzzle
Further analysis of NGC 5084 allowed researchers to study the same galaxy using a wide band of the electromagnetic spectrum – from visible light seen by Hubble to longer wavelengths observed by ALMA and the National Radio Astronomy Observatory's Expanded Very Large Array near Socorro, New Mexico.
"It was like seeing a crime scene with different types of light," said Borlaff, who is also the first author of the paper reporting the discovery. "Combining all the images showed that NGC 5084 has changed a lot in the recent past."
“It was like seeing a crime scene with different types of light.” Alejandro Serrano Borlaff, NASA researcher
"The discovery of two pairs of X-ray plumes in the same galaxy is exceptional," added Pamela Marcum, an astrophysicist at Ames and co-author of the discovery. "The combination of their unusual cross-shaped structure and the 'flipped' dust disk gives us unique insight into the history of this galaxy."
The history of the space revolution
Typically, astronomers expect the X-ray energy emitted by large galaxies to be distributed evenly in a generally spherical shape. When this is not the case, such as when they are concentrated in a set of X-ray plumes, they know that a major event has disrupted the galaxy at some point. Possible dramatic moments in its history that could explain NGC 5084's ejected black hole and double set of plumes include a collision with another galaxy and the formation of a chimney of superheated gas erupting from the upper and lower parts of the galactic plane.
More research will be needed to determine what event or events led to the galaxy's current bizarre structure. But it is already clear that the never-before-seen architecture of NGC 5084 was only revealed through archival data—some of it nearly three decades old—combined with new analysis techniques. The paper presenting the research was published in The Astrophysical Journal.
