Using the James Webb Space Telescope (JWST), astronomers have observed the spectacular “dance” between a supermassive black hole and two satellite galaxies. These observations could help scientists better understand how galaxies and supermassive black holes developed in the early universe.
This particular supermassive black hole is feeding on surrounding matter and powering a bright quasar that is so distant that JWST sees it as it was less than a billion years after the Big Bang. The quasar, designated PJ308-21, is located in an active galactic nucleus (AGN) in a galaxy that is merging with two massive satellite galaxies.
The team not only determined that the black hole had a mass equivalent to two billion suns, but they also discovered that the quasar and galaxies involved in this merger are highly evolved, a surprise given that they existed when the 13.8-year-old cosmos was just an infant.
The merger of these three galaxies will likely provide the supermassive black hole with vast amounts of gas and dust, which will facilitate its growth and allow it to continue feeding PJ308-21.
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“Our study reveals that black holes at the centers of high-redshift quasars (primitive and distant) and the galaxies that host them undergo extremely efficient and tumultuous growth from the first billion years of cosmic history, aided by the rich galactic environment in which these sources form,” team leader Roberto Decarli, a researcher at the Italian National Institute of Astrophysics (INAF), said in a statement.
The data were collected in September 2022 by JWST’s Near InfraRed Spectrograph (NIRSpec) instrument as part of the 1554 program, which aims to observe the merger between the galaxy hosting PJ308-21 and two of its satellite galaxies.
Decarli added that the work represented a real “emotional roller coaster” for the team, which developed innovative solutions to overcome initial data reduction difficulties and produce images with an uncertainty of less than 1% per pixel.
Quasars are born when supermassive black holes with masses several million or billion times that of the Sun, located at the heart of galaxies, are surrounded by a large amount of gas and dust. This material forms a flattened cloud called an accretion disk that swirls around the black hole and gradually feeds it.
The black hole’s immense gravitational forces generate powerful tidal forces in this accretion disk, which elevate gas and dust to temperatures of up to 67,000 degrees Celsius. The accretion disk then emits light across the entire electromagnetic spectrum. This emission can often be brighter than the combined light of all the stars in the surrounding galaxy, making quasars like PJ308-21 some of the brightest objects in the cosmos.
Black holes do not have any characteristics that can determine their degree of evolution, but their accretion disks (and therefore quasars) do. In fact, galaxies can age in the same way.
The early universe was filled with hydrogen, the lightest and simplest element, and a little helium. This formed the basis of the first stars and galaxies, but over the course of their lives, these stellar bodies forged elements heavier than hydrogen and helium, which astronomers call “metals.”
When these stars ended their lives in massive supernova explosions, these metals scattered throughout their galaxies and became the building blocks of the next generation of stars. This process saw the stars, and through them the galaxies, gradually become “metal-rich”.
The team found that, like most AGNs, PJ308-21’s active core is rich in metals, and the gas and dust surrounding it are “photoionized.” This is the process by which particles of light, called photons, provide the energy electrons need to escape from atoms, creating electrically charged ions.
One of the galaxies merging with the host galaxy PJ308-21 is also rich in metals, and its material is also partially photoionized by the quasar’s electromagnetic radiation.
Photoionization also occurs in the second satellite galaxy, but in this case it is caused by a period of rapid star formation. This second galaxy also differs from the first and the AGN in that it appears to be poor in metals.
“Thanks to NIRSpec, we can for the first time study, in the PJ308-21 system, the optical band rich in valuable diagnostic data on the properties of the gas near the black hole in the galaxy hosting the quasar and in the surrounding galaxies,” said team member and INAF astrophysicist Federica Loiacono. “We can observe, for example, the emission of hydrogen atoms and compare it with that of the chemical elements produced by stars to establish the richness of the gas in metals.”
Although light leaves this quasar in the early universe across the broad range of the electromagnetic spectrum, including optical light and X-rays, the only way to observe it is in the infrared.
Indeed, as light traveled over 12 billion years to reach the JWST, the expansion of the universe has significantly “stretched” its wavelengths. This “shifts” the light toward the “red end” of the electromagnetic spectrum, a phenomenon aptly called “redshift,” which astronomers refer to as “z.”
The JWST is able to detect “high redshift” or “high z” objects and events like PJ308-21 due to its sensitivity to infrared light.
“Thanks to the sensitivity of the JWST in the near and mid-infrared, it has been possible to study the spectra of quasars and their accompanying galaxies with unprecedented precision in the distant universe,” concludes Loiacono. “Only the excellent ‘view’ offered by the JWST is able to guarantee these observations.”
The team’s research has been accepted for publication in June 2024 in the journal Astronomy & Astrophysics.