Quasars are the brightest and most distant objects that can be observed in the cosmos. In these active galaxy nuclei sit supermassive black holes that devour matter at high speed. Now astronomers have discovered the most distant quasar to date, which has a particle jet that is “loud” in the radio range. Its light traveled to us for 13 billion years, so we see it as it was only 780 million years after the Big Bang. The quasar is thus the most distant known source of radio emissions, and its black hole has one of the highest known “feeding rates” to date.
Quasars are among the brightest objects in the cosmos: some of them shine as brightly as hundreds of trillion suns and emit enormous amounts of high-energy radiation. The origin of this radiation are the particularly active supermassive black holes in these distant galaxies: They devour large amounts of the surrounding gas and are surrounded by a vortex of rapidly rotating, hot plasma. Shortly before it falls into the black hole, it releases energy in the form of radiation. Their luminosity enables astronomers to observe quasars billions of light years away. The oldest active galaxy nuclei found to date come from a time only around 670 million years after the Big Bang. They therefore reflect the conditions in the early days of the cosmos.
Most distant “radio loud” quasar
Astronomers working with Eduardo Bañados from the Max Planck Institute for Astronomy in Heidelberg have now discovered a special representative of these distant quasars. To do this, they investigated the origin of a previously discovered strong radio source in the distant cosmos with a number of other telescopes, including the Very Large Telescope of the European Southern Observatory ESO and the Magellan Telescope at the Las Campanas Observatory in Chile. With the help of spectroscopic measurements, they were able to prove that there is a so-called “radio-loud” quasar behind this radio emission. These quasars generate strong radiation and particle currents that extend far into space and also emit a lot of radiation in the radio wave range. “Of the approximately 200 previously documented quasars with a redshift of more than 6, only three are known as radio-loud quasars,” the researchers report.
The discovery of a distant quasar with this radio emission is therefore already a rarity per se. But the radio-loud quasar with the name P172 + 18 is so far away that its light was around 13 billion years before it reached us. It already existed at a time when the universe was just about 780 million years old. This makes P172 + 18 the most distant known source of radio emissions and the most distant radio-loud quasar: “As soon as we got the data, we inspected it with the eye and we knew immediately that we had discovered the most distant radio-loud quasar known to date,” says Bañados.
(Video: ESO)
Extremely high accretion rate
Closer analysis revealed that the quasar’s black hole is about 300 million times more massive than our sun. It is not one of the largest gravitational giants of the early cosmos, but P172 + 18 could provide valuable information on how extremely massive black holes could be formed so shortly after the Big Bang. “The black holes in many of these very distant quasars challenge our notion of how fast such objects could grow so early in the history of the universe,” said co-author Emmanuel Momjian of the National Radio Astronomy Observatory (NRAO). In the case of P172 + 18, he and his colleagues found that this black hole is consuming the surrounding gas at breathtaking speed. “The black hole absorbs matter very quickly and its mass is growing at one of the highest rates ever observed,” explains co-author Chiara Mazzucchelli from the European Southern Observatory (ESO).
One possible reason for this is the powerful radio jets of the quasar P172 + 18. The astronomers suspect that these jets are able to perturb the material around the black hole. This, in turn, could result in the agitated gas being drawn into the black hole at a faster than usual rate. Therefore, studying radio-loud quasars can provide important insights into how black holes in the early Universe grew so quickly to their supermassive dimensions after the Big Bang. “Jets also play a role in the regulation of star formation and the growth of their galaxies, so this discovery is valuable for understanding these processes in the early universe,” says co-author Chris Carilli from the NRAO. Astronomers are confident that they will be able to track down even more, possibly more distant radio-loud quasars from the early cosmos in the future. “This discovery makes me optimistic and I believe – and hope – that the distance record will soon be broken,” says Bañados.
Source: Eduardo Bañados (Max Planck Institute for Astronomy, Heidelberg) et al., The Astrophysical Journal