The James Webb Space Telescope (JWST) has significantly advanced astronomers’ understanding of the universe’s infancy since it began transmitting data in the summer of 2022. Priced at $10 billion, this advanced telescope has unveiled supermassive black holes with masses millions of times that of the sun, dating back to when the universe was less than one billion years old. This groundbreaking discovery challenges existing theories about the growth timelines of such massive entities.
In the early cosmos, tiny red dots appear far more frequently than previously recognized populations of active galactic nuclei (AGNs), seen from Earth as quasars powered by supermassive black holes. These red dots, which are in fact galaxies, existed approximately 1.5 billion years following the Big Bang, representing an era when the universe was merely about 11% of its current age. Light from these galaxies has traveled for approximately 12.5 billion years to reach Earth, providing a window into the distant past.
Using data from JWST's second year "All the Little Things (ALT)" survey, researchers constructed a precise 3D map of galaxies in a specific sky region. This map enabled scientists to infer various properties of the faint AGN-hosting galaxies. Jorryt Matthee, leading the research team, noted that the discovery of these little red dot galaxies presents a puzzle. Scientists have previously estimated that it takes over a billion years for black holes to merge and grow progressively larger through mergers and feeding on surrounding matter.
"These objects became known as 'little red dots' because that's how they appear in JWST images."
Matthee suggested that supermassive black holes in the early universe must have formed and grown more efficiently than those observed in today's universe. The team discovered that these little red dots exist in environments akin to low-mass, young galaxies. This revelation could provide astronomers crucial insights into how supermassive black holes attained their enormous sizes rapidly in the universe's early stages.
The team's findings indicate that the mass of supermassive black holes was about 10% of the stellar mass within their host galaxies during the early universe. This starkly contrasts with the modern universe, where supermassive black holes typically possess masses around 0.01% of their host galaxy's stellar mass. This suggests a much higher ratio of stellar mass to supermassive black hole mass in the early universe compared to today.
"The little red dots also show some very remarkable properties, such as the faintness in X-ray emission, which is pretty unusual for AGNs, and the infrared emission is also unusual," said Jorryt Matthee.
"Due to these complications, we are struggling to interpret the light that we observe from the little red dots, which means that it is very difficult to study their properties," Matthee continued.
"The mass of these supermassive black holes is very high compared to the stellar mass of the galaxies that host them."
"At face value, our measurements imply that the supermassive black hole mass is 10% of the stellar mass in the galaxies we studied," Matthee explained.
"In the most extreme scenario, this would imply that the black holes are 1,000 times too heavy," he added.
Rather than viewing this discovery as troubling, Matthee considers it promising, suggesting a potential breakthrough in understanding cosmic phenomena.
"Rather than saying this discovery is 'troubling,' I would say it is 'promising,' as the large discrepancy suggests that we are about to learn something new," noted Matthee.
The JWST's role has been pivotal in this research for two primary reasons. First, it facilitated the discovery of faint AGN populations that were previously undetectable. Second, it enabled the creation of an accurate 3D map of galaxy distributions, allowing researchers to deduce properties of galaxies hosting these faint AGNs.
"The JWST has been important for two main reasons: Without it, we would not have discovered those populations of faint AGNs," Matthee acknowledged.
"Also, without the JWST, we would not have been able to make the accurate 3D map of galaxy distributions that we used to infer the properties of the galaxies hosting the faint AGNs."
Astronomers are now tasked with ensuring that their findings regarding the stellar mass-to-supermassive black hole mass ratio are not skewed by measurement inaccuracies or selection biases favoring more active and massive black holes.
