Astronomers have recently made a fascinating discovery, spotting a massive black hole in the early universe that is in a state of dormancy, or “napping.” This black hole, located just 800 million years after the Big Bang, weighs in at an astonishing 400 million times the mass of our sun, making it one of the largest black holes ever observed by the James Webb Space Telescope (JWST). What makes this black hole particularly intriguing, however, is that it is no longer rapidly growing. Despite its immense size, the black hole is accreting, or consuming, matter at an extraordinarily low rate—about 100 times below the expected maximum. This behavior challenges conventional models of black hole formation and growth, presenting a puzzle for astronomers.
The discovery was made by an international team of astronomers, led by the University of Cambridge, who utilized the cutting-edge capabilities of the JWST to study black holes in the early universe. Black holes, which are regions of space where gravity is so strong that not even light can escape, are typically detected by the glow of hot, accreting gas swirling around their edges. These glowing accretion disks are formed as the black hole pulls in surrounding matter, causing the gas to heat up and radiate energy, often in the ultraviolet range.
What stands out in this case is the size of the black hole. While most black holes in the local universe constitute only about 0.1% of the total mass of their host galaxies, this one makes up roughly 40% of the mass of its host galaxy. The sheer mass of this black hole is consistent with a period of rapid growth, which is typical for black holes in the early universe. However, instead of continuing to grow at the expected rate, this black hole appears to have entered a dormant phase. It’s as though the black hole has overeaten, like a bear gorging itself on food before hibernating for the winter. Once it has consumed all the matter it could, it is now lying dormant, waiting to resume its growth later.
This finding presents a significant challenge to existing models of black hole formation. Traditionally, black holes are thought to form from the remnants of massive stars that collapse under their own gravity. After forming, they accrete matter until they reach a theoretical limit known as the Eddington limit, where the outward pressure from radiation balances the gravitational pull, preventing further growth. However, this newly discovered black hole appears to have surpassed that limit, defying our current understanding of how black holes should behave.
The most likely explanation, according to the researchers, is that black holes undergo brief periods of rapid growth, followed by long periods of dormancy. This hypothesis suggests that the black hole could have experienced a phase of hyperactivity, during which it grew very quickly, before entering a long period of inactivity. During these dormant phases, black holes are less luminous and more difficult to detect, especially with instruments like the JWST, which are designed to observe faint objects. However, because this particular black hole is so massive, it was still detectable, even in its dormant state.
Lead author Ignas Juodžbalis from the University of Cambridge’s Kavli Institute for Cosmology explained that while black holes are notoriously hard to detect, their immense size made this one stand out. Despite its current dormancy, the size of the black hole allowed astronomers to study not only its mass but also the properties of the galaxy hosting it. This discovery highlights that the early universe was capable of producing exceptionally massive black holes, even in relatively small galaxies.
Professor Roberto Maiolino, co-author of the study, further expanded on the findings, noting that one possible explanation for the size of this black hole is that it may have been “born big.” According to this theory, black holes could form with an unusually large mass right from the outset, bypassing the usual stages of slow growth. Alternatively, black holes could experience periods of rapid growth, followed by long stretches of dormancy, as suggested by the team’s computer simulations.
The computer models created by the research team indicate that black holes can exceed the Eddington limit for short bursts, enabling them to grow quickly in a relatively short time—perhaps five to 10 million years. Following these bursts, the black holes would then enter long periods of dormancy, sometimes lasting up to 100 million years. This pattern of rapid growth followed by extended inactivity would explain why dormant black holes are harder to detect and why the majority of black holes in the early universe might be in a similar state.
The implications of this discovery are far-reaching. If the majority of black holes in the early universe spend most of their time in a dormant state, this could mean that many more such black holes remain hidden, waiting to be uncovered. The fact that astronomers were able to detect this one is an exciting prospect, suggesting that there are likely many more massive, dormant black holes lurking in the universe, waiting for the right conditions to be observed. The researchers also note that this discovery is just the beginning, and there could be many more hidden black holes to be found with further observations using the JWST and other advanced telescopes.
Understanding how black holes form and grow is not just a theoretical exercise. It has profound implications for our understanding of the universe as a whole. Black holes play a crucial role in shaping galaxies, influencing the formation of stars, and driving the dynamics of cosmic evolution. The discovery of such a massive black hole in the early universe forces scientists to re-evaluate their models of galaxy formation and the processes that govern the evolution of the cosmos.
Moreover, the existence of dormant black holes challenges our assumptions about how cosmic growth unfolds. If black holes can go through rapid growth phases followed by long periods of inactivity, this could change our understanding of the timescales involved in galaxy evolution. It might also explain some of the anomalies observed in the early universe, where galaxies and their central black holes seem to evolve at different rates than expected.
As astronomers continue to probe deeper into the universe with the help of the James Webb Space Telescope, they are likely to uncover more black holes in various stages of dormancy. These discoveries will provide critical insights into the early universe and the mechanisms behind the formation and growth of black holes. The team’s findings not only shed light on the nature of black holes but also offer a glimpse into the dynamic processes that shaped the universe in its infancy.
The research was published in the journal Nature on December 18, 2024.
Source: University of Cambridge