Astronomers Spot Three Active Black Holes in a Single Galaxy From the Early Universe

Light from the galaxy J0148-4214 has been traveling toward Earth for more than 12.5 billion years, showing the galaxy as it appeared roughly 1.2 billion years after the Big Bang. Inside that ancient galaxy, an international team led by the Max Planck Institute for Extraterrestrial Physics (MPE) has identified three actively accreting supermassive black holes, each drawing in matter from a surrounding disk. The distance was determined from the galaxy's redshift, a stretching of its light toward longer wavelengths caused by the universe's expansion.

"This is the first evidence of three active black holes in a single galaxy in the distant Universe," said Hannah Übler, research group leader at MPE and lead author of the study. Two of the black holes sit near the galactic center, separated by only 620 light-years, while the third lies roughly 5,500 light-years from the center. The researchers traced the black holes through distinctive spectral signatures produced by hydrogen atoms moving at high speed within their gravitational influence, since the central pair could not be resolved as separate points.

The resulting mass estimates were approximately 80 million, 0.6 million and 2 million times the mass of the Sun. Despite being the most massive, the 80-million-solar-mass black hole is feeding more slowly than its 0.6-million-solar-mass neighbor, which is accreting so rapidly that it exceeds the maximum rate predicted by basic models of black hole growth, known as the Eddington limit. The team also estimated the galaxy's total stellar mass at about 1.3 billion times the mass of the Sun, of which the black holes represent a significant fraction.

The two central black holes are expected to merge within the next few hundred million years. "These results are extremely exciting," said Roberto Maiolino, a University of Cambridge professor and study co-author. "They suggest that black hole merging may be an additional, fast route for their rapid growth in the early Universe." The third black hole, away from the galactic center, could be left over from an earlier merger displaced by a gravitational recoil kick, or it may currently be moving inward, the researchers said.