Astronomers have made a remarkable discovery: two active black holes merging at their farthest distance ever, just 900 million years after the Big Bang. This is the first time that two luminous supermassive black holes have been spotted during cosmic dawn, the period encompassing the first billion years of the universe. Cosmic dawn is a pivotal time, marked by the Epoch of Reionization, which began roughly 400 million years after the Big Bang. During this era, light from nascent stars stripped hydrogen atoms of their electrons, leading to a fundamental transformation of the universe.
The existence of merging quasars during this epoch has been a long-anticipated phenomenon. “It has now been confirmed for the first time,” said study lead author Yoshiki Matsuoka, an astronomer at Ehime University in Japan. The researchers published their findings in the journal Nature on April 5th.
Black holes are formed from the collapse of giant stars and grow by continuously consuming gas, dust, stars, and other black holes within the star-forming galaxies that host them. As these black holes grow, friction heats up the material spiraling into their cores, transforming them into quasars. Quasars are exceptionally luminous objects, emitting light up to a trillion times brighter than the brightest stars, shedding their gaseous cocoons in powerful bursts of light.
The farther scientists peer into the universe, the more distant light they capture, allowing them to observe events from the past. This is because light travels at a fixed speed through the vacuum of space. Past simulations of the cosmic dawn suggested that billowing clouds of cold gas might have collapsed rapidly, creating black holes. As the universe expanded, these early black holes likely merged with others, seeding the formation of even larger supermassive black holes throughout the cosmos.
Roughly 300 quasars have been previously discovered in the Epoch of Reionization, but these newly identified quasars are the first to be found as a pair. The researchers located them using the Subaru Telescope’s Hyper Suprime-Cam, where they appeared as two faint red smudges against a dazzling background of galaxies and stars. Further spectroscopic imaging confirmed that the light source was a pair of spiraling quasars.
The researchers believe their discovery will be instrumental in understanding how quasars’ powerful beams of light shaped the structures of the universe we observe today. “The statistical properties of quasars in the Epoch of Reionization tell us many things, such as the progress and origin of the reionization, the formation of supermassive black holes during Cosmic Dawn, and the earliest evolution of the quasar host galaxies,” said Matsuoka.
