Using the James Webb Space Telescope (JWST), astronomers have observed the dramatic “dance” between a supermassive black hole and two satellite galaxies. The observations could help scientists better understand how galaxies and supermassive black holes grew in the early universe.
This supermassive black hole is feeding on the surrounding matter and powering a bright quasar that is so distant that JWST sees it as 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 in the process of merging with two massive satellite galaxies.
Not only did the team determine that the black hole has a mass equal to two billion suns, but they also found that the quasar and galaxies involved in this merger are highly evolved, a surprise considering they existed when the 13.8-year-old cosmos it was just a baby.
The merger of these three galaxies is likely to give the supermassive black hole large amounts of gas and dust, which will facilitate its growth and allow it to continue powering PJ308-21.
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“Our study reveals that both black holes are at high redshift [early and distant] quasars and the galaxies that host them undergo extremely efficient and turbulent growth already in the first billion years of cosmic history, aided by the rich galactic environment in which these sources formed,” team leader Roberto Decarli, a researcher at The National Institute of Astrophysics of Italy (INAF), says in a statement.
The data were collected in September 2022 by JWST’s Near InfraRed Spectrograph (NIRSpec) instrument as part of Program 1554, which aims to observe the merger between the host galaxy PJ308-21 and two of its satellite galaxies.
Decarli added that the work represented a real “emotional roller coaster” for the team, who developed innovative solutions to overcome initial difficulties in data reduction and produce images with an uncertainty of less than 1% per pixel.
Quasars are born when supermassive black holes, millions or billions of times the mass of the Sun, at the heart of galaxies, are surrounded by a large amount of gas and dust. This matter forms a flattened cloud called an accretion disk that orbits the black hole and gradually feeds it.
The black hole’s infinite gravitational forces generate powerful tidal forces in this accretion disk, which heat this gas and dust to temperatures of up to 120,000 degrees Fahrenheit (67,000 degrees Celsius). This causes the accretion disk to emit light across the electromagnetic spectrum. This emission can often be brighter than the combined light of every star in the surrounding galaxy, making quasars like PJ308-21 some of the brightest objects in the cosmos.
While black holes have no characteristics that can be used to determine how evolved they are, their accretion disks (and thus quasars) do. In fact, galaxies can “age” in the same way.
The early universe was filled with hydrogen, the lightest and simplest element, and some helium. This formed the basis of the first stars and galaxies, but during the lifetime of these stellar bodies, they forged elements heavier than hydrogen and helium, which astronomers call “metals”.
When these stars ended their lives in massive supernova explosions, these metals were scattered throughout their galaxies and continued to be the building blocks of the next generation of stars. This process saw stars, and through them galaxies, becoming progressively “metal-rich”.
The team found that, like most AGNs, PJ308-21’s active core is metal-rich, and the gas and dust around it is being “photoionized”. This is the process by which light particles, called photons, provide energy. that electrons must escape from atoms, creating electrically charged ions.
One of the galaxies merging with the host galaxy PJ308-21 is also metal-rich, and its material is being partially photoionized by electromagnetic radiation from the quasar.
Photoionization is also occurring in the second satellite galaxy, but in that case, it is being caused by a period of rapid star formation. This second galaxy also differs from the first and the AGN, as it appears to be metal-poor.
“Thanks to NIRSpec, for the first time, we can study, in the PJ308-21 system, the optical band rich with 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, for example, look at the emission of hydrogen atoms and compare that to that of the chemical elements produced by stars to determine how rich the gas is in metals.”
Although this early universe quasar emits light across the broad spectrum of the electromagnetic spectrum, including optical light and X-rays, the only way to observe it is in the infrared.
That’s because, as light traveled for more than 12 billion years to reach JWST, the expansion of the universe has “stretched” its wavelengths considerably. This “shifts” the light towards the “red end” of the electromagnetic spectrum, a phenomenon aptly called “redshift”, denoted as “z” by astronomers.
JWST is capable of seeing high-red or high-z objects and events like PJ308-21 because of its sensitivity to infrared light.
“Thanks to JWST’s near- and mid-infrared sensitivity, it was possible to study the spectrum of the quasar and its companion galaxies with unprecedented precision in the distant universe,” Loiacono concluded. “Only the excellent ‘view’ provided by JWST is able to provide these observations.”
The team’s research was accepted for publication in June 2024 in the journal Astronomy & Astrophysics.