Using the James Webb Space Telescope (JWST), astronomers observed a 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 particular supermassive black hole feeds on the surrounding matter and powers 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 equivalent to two billion suns, but they also found that both the quasar and the galaxies involved in the merger are highly evolved, which is surprising given that they existed when it was 13.8 years old old. the cosmos was just an infant.
The merger of these three galaxies is likely to supply the supermassive black hole with enormous amounts of gas and dust, facilitating its growth and allowing it to continue to power 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 have been undergoing extraordinarily efficient and turbulent growth already in the first billion years of cosmic history, aided by the rich galactic environment in which these sources form,” said team leader Roberto Decarli, a researcher at Italy’s National Institute for 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 a merger between the host galaxy PJ308-21 and two of its satellite galaxies.
Decarli added that the work was a real “emotional rollercoaster” for the team, who developed an innovative solution to overcome initial data reduction difficulties and produce images with an uncertainty of less than 1% per pixel.
A very metallic quasar
Quasars are born when supermassive black holes, millions or billions of times the mass of the Sun, that reside at the heart of galaxies are surrounded by masses of gas and dust. This matter forms a flattened cloud called an accretion disk, which swirls around the black hole and gradually feeds it.
The enormous gravitational forces of the black hole generate powerful tidal forces in this accretion disk, heating 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 universe.
While black holes have no properties that can be used to determine how they evolved, 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 formed 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 became the building blocks of the next generation of stars. This process has seen stars, and through them galaxies, gradually become “metal-rich”.
The team found that, like most AGNs, the active heart of PJ308-21 is metal-rich, and the gas and dust around it are “photoionized”. This is the process by which particles of light, called photons, provide energy. that electrons need to escape atoms to form electrically charged ions.
One of the galaxies merging with the host galaxy PJ308-21 is also metal-rich, and its mass is also partially photoionized by electromagnetic radiation from the quasar.
Photoionization also occurs in the second satellite galaxy, but in that case it is caused by a bout of rapid star formation. This second galaxy also differs from the first and the AGN in that it appears to be metal-poor.
“With NIRSpec, for the first time in the PJ308-21 system, we can study an optical band rich in valuable diagnostic data about the properties of the gas near the black hole in the quasar host galaxy and in the surrounding galaxies. ” said team member and INAF astrophysicist Federica Loiacono. “We can see the emission of hydrogen atoms, for example, and compare it to the emission of chemical elements produced by stars to see how metal-rich the gas is.”
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Although light leaves this quasar of the early universe in a wide range of the electromagnetic spectrum, including optical light and X-rays, the only way to observe it is in the infrared.
This is because as the light traveled over 12 billion years to reach JWST, the expansion of the Universe greatly “lengthened” its wavelengths. This ‘shifts’ the light towards the ‘red end’ of the electromagnetic spectrum, a phenomenon understandably called ‘redshift’, which astronomers refer to as ‘z’.
Due to its sensitivity to infrared light, JWST is adept at observing “high redshift” or “high z” objects and events like PJ308-21.
“JWST’s near- and mid-infrared sensitivity has made it possible to study the spectrum of quasars and companion galaxies with unprecedented precision in the distant universe,” concluded Loiacono. “Only the excellent ‘view’ offered by JWST is able to provide these observations.”
The team’s research has been accepted for publication in June 2024 in the journal Astronomy & Astrophysics.