Supermassive black holes in the centers of galaxies do not always appear as quasars. They are much more likely to appear as blazars. A recent study of one of these objects has provided a better understanding of the evolution of the early Universe.
Active Galactic Nucleus and the Evolution of the Universe
Astronomers have discovered an important piece of the puzzle of how supermassive black holes could grow so fast in the early universe. It is a special kind of active galactic nucleus so distant that its light took more than 12.9 billion years to reach us. This so-called blazar serves as a statistical marker: its existence suggests a large but hidden population of similar objects, each of which should emit powerful jets of particles.
This is where the discovery becomes important for cosmic evolution: black holes with jets are thought to be able to grow much faster than those without jets. The findings are filed in a paper published in Nature Astronomy and another in The Astrophysical Journal Letters.
Active galactic nucleus (AGN) are the extremely bright centers of galaxies. The engines that provide their enormous energy are supermassive black holes. The fall of matter onto such black holes (accretion) is the most efficient mechanism known to physics when it comes to releasing massive amounts of energy. This unrivaled efficiency is the reason why black holes can produce more light than all the stars in hundreds, thousands, or even more galaxies combined, and in a volume of space smaller than our solar system.
At least 10% of all AGNs are thought to emit focused, high-energy beams of particles known as jets. These jets fly out of the immediate vicinity of the black hole in two opposite directions, supported and guided by magnetic fields in an “accretion disk” of matter, a disk formed by gas that swirls around the black hole and falls into it. For us to see a black hole as a flash, something very improbable would have to happen: the Earth, our observing base, would have to be in the right place for the AGN jet to be pointed directly at us.
Search for active galactic nucleus in the very early Universe
The new discovery is the result of a systematic search for an active galactic nucleus in the early universe by Eduardo Baniados, a group leader at the Max Planck Institute for Astronomy who specializes in the first billion years of cosmic history, and an international team of astronomers.
Because it takes time for light to reach us, we see distant objects as they were millions or even billions of years ago. For more distant objects, the so-called cosmological redshift caused by the expansion of space shifts their light to much longer wavelengths than those at which the light was emitted. Baniados and his team exploited this fact by systematically searching for objects whose redshift was so significant that they were not even visible in ordinary visible light (in this case as part of the Dark Energy Legacy Survey), but were bright sources in the radio survey (the 3 GHz VLASS survey).
Among the 20 candidates that met both criteria, only one, J0410-0139, met the additional criterion of significant brightness fluctuations in the radio mode, raising the possibility that it was a blazar.
The researchers then dug deeper using an extremely large battery of telescopes, including near-infrared observations with ESA’s New Technology Telescope (NTT), spectra from ESA’s Very Large Telescope (VLT), additional near-infrared spectra from the LBT, one of the Keck telescopes and the Magellan Telescope, X-ray images from ESA’s XMM-Newton and NASA’s Chandra space telescopes, millimeter-wave observations with the ALMA and NOEMA arrays, and more detailed radio observations with the US National Radio Astronomy Observatory’s VLA telescopes to confirm the object’s status as an AGN, specifically as a blazar.
The observations also allowed us to determine the distance to the supernova (by redshift) and even find traces of the parent galaxy in which the supernova is embedded. The light from this active galactic nucleus traveled to us for 12.9 billion years (z=6.9964), carrying information about the Universe as it was 12.9 billion years ago.
Where there’s one, there’s a hundred more
According to Baniados, the fact that J0410-0139 is a blazar, that is, a jet that happens to be aimed directly at Earth, has immediate statistical implications. As a real-life analogy, imagine reading about someone who won 100 million dollars in the lottery. Given how rare such a win is, you can immediately conclude that many more people participated in that lottery who did not win such an exorbitant amount.
Similarly, finding one AGN with a jet pointed directly at us means that at that period of cosmic history, there must have been many AGNs with jets that were not pointed at us.
According to Silvia Belladitta, co-author of this publication, where there is one, there are a hundred more.
Light from the previous record holder for the most distant flare took 100 million years less to reach us (z=6.1). The extra 100 million years may seem short in light of the fact that we are looking back more than 12 billion years, but it is crucial. This is a time when the Universe is changing rapidly. In those 100 million years, a supermassive black hole can increase its mass by an order of magnitude.
According to current models, the number of AGNs should have increased by a factor of five to ten over these 100 million years. The discovery that such a blazar existed 12.8 billion years ago would not be a surprise. It is quite another matter if it turns out that such a blazar existed 12.9 billion years ago, as in this case.
Helping black holes grow 12.9 billion years ago
The presence of an entire population of AGN with jets at that early period has important implications for cosmic history and the growth of supermassive black holes in the centers of galaxies in general. Black holes whose AGNs have jets can potentially gain mass faster than black holes without jets.
Contrary to popular belief, it is difficult for gas to enter a black hole. The gas naturally orbits around the black hole, similar to the way a planet orbits around the sun, with an increase in speed as the gas approaches the black hole. In order to fall inward, the gas must slow down and lose energy. Magnetic fields associated with a jet of particles that interact with the swirling disk of gas can provide such a “braking mechanism” and help the gas fall inward.
This means that the implications of the new discovery are likely to be a building block of any future model of black hole growth in the early universe: they suggest the existence of a large number of active galactic nucleus 12.9 billion years ago that had jets, and therefore associated magnetic fields, which may help black holes grow at a significant rate.
Provided by phys.org
