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Tour: NASA's Chandra Discovers Giant Black Holes on Collision Course

Astronomers have discovered the first evidence for giant black holes in dwarf galaxies on a collision course. This result from NASA’s Chandra X-ray Observatory has important ramifications for understanding how the first wave of black holes and galaxies grew in the early universe.

Collisions between the pairs of dwarf galaxies have pulled gas towards the giant black holes they each contain, causing the black holes to grow. Eventually the likely collision of the black holes will cause them to merge into much larger black holes. The pairs of galaxies will also merge into one.

Scientists think the universe was awash with small galaxies, known as “dwarf galaxies,” several hundred million years after the Big Bang. Most merged with others in the crowded, smaller volume of the early universe, setting in motion the building of larger and larger galaxies now seen around the local universe.

Dwarf galaxies by definition contain stars with a total mass less than about 3 billion times that of the Sun, compared to a total mass of about 60 billion Suns estimated for the Milky Way.

The earliest dwarf galaxies are impossible to observe with current technology because they are extraordinarily faint at their large distances. Astronomers have been able to observe two in the process of merging at much closer distances to Earth, but without signs of black holes in both galaxies.

Astronomers have found many examples of black holes on collision courses in large galaxies that are relatively close by, but searches for them in dwarf galaxies are much more challenging and until now had failed.

The new study overcame these challenges by implementing a systematic survey of deep Chandra X-ray observations and comparing them with infrared data from NASA’s Wide Infrared Survey Explorer, or WISE, telescope and optical data from the Canada-France-Hawaii Telescope.

Using this technique, a group of researchers identified two pairs of merging dwarf galaxies in separate galaxy clusters. The first is Abell 133, which is located about 760 million light-years away. The second is the galaxy cluster Abell 1758S, which is about 3.2 billion light-years from Earth.

Astronomers will use these systems as analogs for ones in the early universe, so they can drill down into questions about the first galaxies, their black holes, and star formation the collisions caused many billions of years ago.

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