From NASA Chandra: “Galaxies Hit Single; Doubles; and a Triple (Growing Black Holes)”

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NASA Chandra X-ray Space Telescope

From NASA Chandra

January 14, 2021

Media contacts:
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Molly Porter
Marshall Space Flight Center, Huntsville, Alabama

X-ray: NASA/CXC/Univ. of Michigan/A. Foord et al.; Optical: SDSS & NASA/STScI.

A new study looked at triple galaxy mergers to learn what happens to their supermassive black holes.

The results find a single, four doubles, a triple giant black hole remain in six of the seven mergers.

A team used several telescopes including Chandra plus specially-developed software to identify these growing black holes.

This helps astronomers better understand what role mergers play in how galaxies and their giant black holes grow.

A new study helps reveal what happens to supermassive black holes when three galaxies merge, as reported in our latest press release. This result, which used data from NASA’s Chandra X-ray Observatory and several other telescopes, tells astronomers more about how galaxies and the giant black holes in their centers grow over cosmic time.

While there have been previous studies of mergers between two galaxies, this is one of the first to systematically look at the consequences for supermassive black holes when three galaxies come together. This panel of images contains data from two of seven galactic collisions in the new study containing two supermassive black holes left growing after the collision. The pair of mergers are seen in X-rays from Chandra (left in purple) and optical data (right) from NASA’s Hubble Space Telescope and the Sloan Digital Sky Survey (SDSS). Circles in a labeled version of the Chandra image show X-rays from hot gas falling towards each black hole.

NASA/ESA Hubble Telescope.

SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft).

Apache Point Observatory, near Sunspot, New Mexico Altitude 2,788 meters (9,147 ft).

These triple galaxy mergers were first identified by sifting through data from the SDSS and NASA’s WISE mission and then comparing the results to X-ray data in the Chandra archive.


This method identified seven triple galaxy mergers located between 370 million and one billion light years from Earth.

Using specialized software, the team went through Chandra data targeting these systems to detect X-ray sources marking the location of growing supermassive black holes. As material falls toward a black hole, it gets heated to millions of degrees and produces X-rays. The combination of the new software and Chandra’s sharp X-ray vision enabled the researchers to identify the black holes despite their close proximity in the images.

Out of seven triple galaxy mergers, the results are: one with a single growing supermassive black hole, four with double growing supermassive black holes (two of which are shown in the main graphics), and one that is a triple. The final merger of three galaxies they studied seems to have no X-ray emission detected from the supermassive black holes. This means that none of the supermassive black holes were left rapidly pulling in matter. In the systems with multiple black holes, the separations between them range between about 10,000 and 30,000 light years.

Once they found evidence for bright X-ray sources as candidates for growing supermassive black holes in the Chandra data, the researchers incorporated archival data from other telescopes such as WISE mission, the Infrared Astronomical Satellite, and the Two Micron All Sky Telescope as another check in the process.

Caltech 2MASS Telescopes, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC) at Caltech, at the Whipple Observatory on Mt. Hopkins south of Tucson, AZ, Altitude 2,606 m (8,550 ft) and at the Cerro Tololo Inter-American Observatory at an altitude of 2200 meters near La Serena, Chile.

NASA/UK/NL Infrared Astronomical Survey IRAS spacecraft

Studies of triple mergers can help scientists understand whether pairs of supermassive black holes can approach so close to each other that they make ripples in spacetime called gravitational waves. The energy lost by these waves will inevitably cause the black holes to merge.

Adi Foord presented the new study, which she worked on as part of her Ph.D. at the University of Michigan, at the 237th meeting of the American Astronomical Society, which is being held virtually from January 11-15, 2021. Two papers describing this work have recently been accepted for publication in The Astrophysical Journal and preprints are available here and here.

A Quick Look at Triple Galaxy Mergers

See the full article here .


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NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.