Using the James Webb Space Telescope, astronomers have 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 supermassive black hole is feeding on the surrounding matter, powering a quasar so bright that the James Webb Space Telescope sees it as it was less than a billion years after the Big Bang. The quasar, called PJ308-21, is located in an active galactic nucleus (AGN) in a galaxy 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 2 billion suns, they also found that both the quasar and the galaxies involved in the merger are highly evolved, a surprise given that they existed when the 13.8-year-old universe was just a baby.
The merger of these three galaxies will likely deliver massive amounts of gas and dust to the supermassive black hole, facilitating its growth and allowing it to continue powering PJ308-21.
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Our study reveals that both black holes at the center of high redshift [early and distant] “Quasars and the galaxies that host them undergo an extremely active and turbulent growth already in the first billion years of the Universe’s history, aided by the rich galactic environment in which these sources form,” says team leader Roberto DeCarli, a researcher at the National Institute of Astrophysics in Italy (INAF). He said in a statement:.
The data were collected in September 2022 by JWST’s Near-Infrared Spectrometer (NIRSpec) instrument as part of Program 1554, which aims to observe the merger between the galaxy hosting PJ308-21 and two of its satellite galaxies.
The work represents a real “emotional journey” for the team, DeCarli added, as they developed innovative solutions to overcome the initial difficulties in data reduction and produce images with an uncertainty of less than 1% per pixel.
Quasars are born when huge amounts of gas and dust surround supermassive black holes, millions or billions of times the mass of the Sun, at the heart of galaxies. This material forms a flattened cloud called an accretion disk that orbits the black hole and gradually feeds it.
The black hole’s immense gravitational forces generate powerful tidal forces in this accretion disk, heating the gas and dust to 120,000 degrees Fahrenheit (67,000 degrees Celsius). This causes light to be emitted from the accretion disk across the electromagnetic spectrum. This emission is often 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 do not have properties that can be used to determine how far they have evolved, their accretion disks (and thus quasars) do. In fact, galaxies can be “aged” in the same way.
The early universe was filled with hydrogen, the lightest and simplest element, and a small amount of helium. This formed the basis for the first stars and galaxies, but as these stellar bodies lived, 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 spread throughout their galaxies and became the building blocks for the next generation of stars. This process led to the stars, and through them the galaxies, becoming progressively “metal-rich.”
The team found that, like most active galactic nuclei, the active core of PJ308-21 is rich in metals, and that the surrounding gas and dust are undergoing “photoionization.” This is the process by which light particles, called photons, provide the energy needed for electrons 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 electromagnetic radiation from the quasar.
Photoionization also occurs in the second satellite galaxy, but in this case it is caused by a bout of rapid star formation. This second galaxy also differs from the first galaxy and the active galaxy in that it appears to be metal-poor.
“Thanks to NIRSpec, we can for the first time study the optical spectrum, which is 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,” says team member and astrophysicist at the National Institute of Astrophysics Federica Loiacono. “We can see, for example, the emission of hydrogen atoms and compare it with the emission of chemical elements produced by stars to determine how rich the gas is in metals.”
Although the light from this early-universe quasar radiates across a wide range of the electromagnetic spectrum, including optical light and X-rays, the only way to observe it is in infrared light.
This is because the light has traveled more than 12 billion years to reach the James Webb Telescope, causing its wavelengths to be “stretched” significantly. This “shifts” the light toward the “red end” of the electromagnetic spectrum, a phenomenon astronomers call “redshift,” which is represented by the letter “z.”
The James Webb Telescope has a superior ability to see “high redshift” or “high-shift” objects and events like PJ308-21 because of its sensitivity to infrared light.
“Thanks to the sensitivity of the James Webb Telescope in the near and mid-infrared, it has become possible to study the spectra of quasars and companion galaxies with unprecedented precision in the distant Universe. These observations can only be guaranteed by the excellent ‘view’ provided by the James Webb Telescope,” Loiacono concluded.
The team’s research has been accepted for publication in the June 2024 journal Astronomy and Astrophysics.
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