Tour: Stellar Beads on a String

Astronomers have discovered one of the most powerful eruptions from a black hole ever recorded. This mega-explosion billions of years ago may help explain the formation of a striking pattern of star clusters around two massive galaxies, resembling ‘beads on a string.’

This discovery was made in the system known as SDSS J1531, which is located 3.8 billion light-years from Earth. Researchers used several telescopes for this study, including NASA’s Chandra X-ray Observatory, and the Low Frequency Array, or LOFAR, which is a network of radio telescopes in Europe.

SDSS J1531 is a massive galaxy cluster containing hundreds of individual galaxies and huge reservoirs of hot gas and dark matter. In the heart of SDSS J1531, two of the cluster’s largest galaxies are colliding with each other. Surrounding these merging giants is a set of 19 large clusters of stars, called superclusters, arranged in an ‘S’ formation that resembles beads on a string. A team of astronomers used X-ray, radio and optical data to unravel how this unusual chain of star clusters probably formed. The discovery of evidence for an ancient, titanic eruption in SDSS 1531 provided a vital clue. The eruption likely occurred when the supermassive black hole in the center of one of the large galaxies produced an extremely powerful jet. As the jet moved through space, it pushed the surrounding hot gas away from the black hole, creating a gigantic cavity.

The Chandra data revealed wing-like shaped X-ray emission tracing dense gas near the center of SDSS J1531. These wings are the edge of the cavity and the less dense gas in between is part of the cavity. LOFAR shows radio waves from the remains of the jet’s energetic particles filling in the giant cavity. Together, these data provide compelling signs of an ancient, massive explosion.

How did this giant eruption lead to the unusual pattern of 19 star clusters? The astronomers also found cold and warm gas located near the opening of the cavity using the Atacama Large Millimeter and submillimeter Array, ALMA, and the Gemini North Telescope in Hawaii. They argue that some of the hot gas pushed away from the black hole eventually cooled to form the cold and warm gas seen in the data.

The team thinks tidal effects from the two merging galaxies compressed this gas along curved paths, leading to the star clusters forming in the “beads on a string” pattern. Scientists have witnessed black holes doing many things over the years, but making a string of star clusters may be a first.