Researchers from MIT have made significant strides in understanding the ancient quasars that existed over 13 billion years ago. These distant celestial signals provide critical insights into the evolution of the universe’s earliest black holes and galaxies.
Quasars, or “quasi-stellar objects,” are the brilliant centers of active galaxies, where a supermassive black hole resides at the core. Every galaxy may contain a central black hole that intermittently consumes gas and stellar debris, creating a temporary burst of light. In contrast, quasars can consume vast amounts of matter over extensive periods, producing a residual glow so immense that they rank among the brightest entities in the cosmos.
Interestingly, while quasars outshine their host galaxies, the MIT team managed to capture the fainter starlight emanating from the host galaxies of three ancient quasars for the very first time.
By analyzing this faint stellar radiance, the researchers estimated the mass of each host galaxy and compared it to the mass of its respective supermassive black hole. They discovered that these ancient quasars have significantly more massive central black holes relative to their host galaxies than those seen today.
Published in the Astrophysical Journal, these findings may illuminate how supermassive black holes amassed their tremendous size within the early universe—a period of time that was both relatively brief and yet crucial for cosmic development. Specifically, it suggests that these early colossal black holes possibly originated from larger “seed” black holes than those currently observed.
“Following the universe’s inception, seed black holes rapidly consumed surrounding material, allowing them to grow quickly,” explains Minghao Yue, a postdoctoral researcher at MIT’s Kavli Institute for Astrophysics and Space Research. “One of our main inquiries is pinpointing how these massive black holes achieved such rapid growth.”
Study co-author Anna-Christina Eilers, an assistant professor of physics at MIT, adds, “These black holes possess masses billions of times greater than the sun, all during a time when the universe was still nascent. Our findings suggest that supermassive black holes may have accumulated their mass prior to their host galaxies developing, hinting that the initial black hole seeds could have been larger than those formed in more recent epochs.”
The team’s research incorporated contributions from several collaborators, including MIT Kavli Director Robert Simcoe, postdoctoral fellow Rohan Naidu, and associates from Switzerland, Austria, Japan, and North Carolina State University.
The Radiant Centers
The extraordinary brightness of quasars has been acknowledged since they were first discovered in the 1960s. Initially thought to stem from a singular stellar source, scientists later realized that their luminosity originates from the accretion of material by supermassive black holes at their cores, overshadowing the fainter stars of their host galaxies.
Separating the light from a quasar’s central black hole and the stars of its host galaxy is a daunting task. It’s akin to spotting a collection of fireflies illuminating a field beneath a powerful searchlight. Thanks to advancements in technology, particularly with the launch of NASA’s James Webb Space Telescope (JWST), astronomers can now probe deeper into the cosmic past with unprecedented resolution.
For this particular study, Yue and Eilers utilized dedicated time on the JWST to observe six ancient quasars from the fall of 2022 through spring of 2023. They accumulated more than 120 hours of observation data.
“Quasars greatly overpower the luminosity of their host galaxies. Previous images lacked the clarity to distinguish the faint stars surrounding them,” Yue noted. “For the first time, we could unveil the light from these stars by meticulously analyzing the sharper images provided by JWST.”
Balancing the Light
The research team examined the JWST imaging data of the six quasars, which were estimated to be around 13 billion years old. They analyzed the light captured across different wavelengths, distinguishing between the luminous emissions of a black hole’s accretion disk and the diffuse light from the stars in the surrounding galaxy.
This detailed modeling allowed the researchers to separate each quasar’s light into two key sources: the bright disk around the central black hole and the softer light from the host galaxy’s stars. Their findings revealed a mass ratio of approximately 1:10 between the central black hole and its host galaxy—starkly contrasting today’s ratio of 1:1,000, where modern black holes are significantly less massive relative to their host galaxies.
“This discovery raises important questions about growth dynamics: Does the black hole gain mass first while the galaxy catches up, or do galaxies grow while regulating black hole development?” Eilers asked. “Our observations imply that black holes in the early universe expanded faster than their host galaxies.”
“There must have been mechanisms enabling black holes to gain mass prior to their galaxies during those formative billion years,” Yue emphasized. “This discovery serves as pioneering evidence for that phenomenon, which is truly exciting.”
Photo credit & article inspired by: Massachusetts Institute of Technology
