Astronomers have recently uncovered an important clue in the puzzle of how supermassive black holes were able to grow rapidly in the early universe, particularly through the discovery of a distant active galactic nucleus (AGN). This AGN, identified as a blazar, is so far away that its light has taken over 12.9 billion years to reach Earth. The significance of this discovery lies not only in the rarity of such distant objects but also in what it implies about the nature of black hole growth in the early universe.
Blazars are a specific type of AGN, which are the extremely bright centers of galaxies powered by supermassive black holes. The enormous energy emitted by AGN is generated as matter falls onto these black holes, a process known as accretion. Accretion is the most efficient known mechanism for releasing vast amounts of energy, which is why AGNs can outshine entire galaxies. This energy is primarily released in the form of light and other electromagnetic radiation. However, many AGNs also produce powerful particle jets, which shoot out in two opposite directions from the vicinity of the black hole, guided by magnetic fields.
In the case of a blazar, these jets must be pointed directly at Earth, which is a rare and unlikely alignment. When this happens, the AGN appears as an exceptionally bright object, much like a flashlight beam shining directly into your eyes. Moreover, blazars are known for their rapid brightness fluctuations, occurring over timescales as short as hours or even minutes. These fluctuations are due to the chaotic nature of the accretion disk—the rotating disk of gas falling into the black hole—and the instabilities that arise in the interaction between the magnetic fields and the charged particles in the jet.
The recent discovery is the result of a systematic search for AGNs in the early universe, led by Eduardo Bañados at the Max Planck Institute for Astronomy, who specializes in the study of the first billion years of cosmic history. The research team aimed to find AGNs that were so distant that their light was redshifted beyond the visible spectrum. This means that, due to the expansion of the universe, their light had been stretched to much longer wavelengths, which is why they would not have been visible in the usual visible-light surveys.
By using a radio survey (the 3 GHz VLASS survey), the team was able to identify a potential candidate, J0410–0139, which showed significant brightness fluctuations in the radio spectrum. This raised the possibility that it was a blazar. The researchers then conducted a series of observations using a wide array of telescopes, including ESO’s New Technology Telescope (NTT), the Very Large Telescope (VLT), Keck and Magellan telescopes, the XMM-Newton and Chandra space telescopes, as well as the ALMA and NOEMA millimeter-wave arrays, and the VLA radio telescopes. These observations confirmed that J0410–0139 was indeed an AGN, specifically a blazar, and that the light from this object had traveled 12.9 billion years to reach us, allowing astronomers to study the conditions of the universe as it was nearly 13 billion years ago.
The findings from this discovery have been published in two prominent scientific journals: Nature Astronomy and The Astrophysical Journal Letters. These publications underscore the importance of the discovery in advancing our understanding of cosmic evolution and the early growth of supermassive black holes.
The implications of this discovery go beyond the identification of a single distant blazar. According to Bañados, the discovery of one AGN with a jet pointed directly toward Earth provides a statistical marker for the existence of many more similar objects from that era. Much like finding one winner in a lottery implies the existence of many more participants who did not win the jackpot, discovering one AGN with a jet aimed at us suggests that there were many others with jets that were not pointed toward Earth. This insight allows astronomers to infer the existence of a larger population of AGNs from this period of cosmic history, which are likely to have emitted powerful particle jets.
The discovery of J0410–0139 is particularly important because it pushes back the timeline for the formation of such powerful AGNs. Prior to this discovery, the most distant known blazar had a redshift of z=6.1, which meant its light had taken 12.8 billion years to reach us. While this difference of about 100 million years might seem insignificant on cosmological timescales, it is actually crucial. In this short period, the universe was evolving rapidly, and it is believed that supermassive black holes could increase their mass by an order of magnitude during such a time. As a result, the number of AGNs is thought to have increased by a factor of five to ten during the additional 100 million years between z=6.1 and z=6.9964.
This finding has profound implications for our understanding of how supermassive black holes grew so quickly in the early universe. Black holes with jets are thought to have a distinct advantage in terms of growth. Normally, gas that falls toward a black hole tends to orbit it in a way that conserves angular momentum, much like the way planets orbit the sun. For the gas to actually fall into the black hole, it needs to lose angular momentum. This is where the jets come into play. The magnetic fields associated with the jets interact with the surrounding accretion disk, providing a braking mechanism that helps the gas lose angular momentum and fall into the black hole, thus allowing it to grow more quickly.
The discovery of J0410–0139, and the implication that there was a large population of similar objects at that time, provides a new building block for models of black hole growth. It suggests that black holes in the early universe could have grown more quickly than previously thought, due to the presence of jets and the associated magnetic fields that facilitated faster accretion of matter. This insight is important for refining our understanding of the early universe, where the conditions for galaxy and black hole formation were much different from today.
Moreover, the discovery highlights the importance of systematic surveys and the use of multiple observational tools in identifying such distant and rare objects. The use of radio, infrared, X-ray, and millimeter-wave telescopes, among others, allows astronomers to obtain a comprehensive view of distant AGNs and their properties, including the jets that make blazars so unique. As technology advances and more sensitive instruments become available, it is likely that more such objects will be discovered, offering new insights into the formation and evolution of black holes, galaxies, and the universe itself.