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IT Home, November 15 — Using the James Webb Space Telescope (JWST), astronomers have discovered the oldest observed pair of quasars powered by supermassive black holes. The discovery, however, presents a puzzle: under current theories, they should not have existed so early.
The closely spaced quasar pair was confirmed with the Gemini North telescope. Cataloged as J1602+4228AB, it has been nicknamed Nāpōwawāʻenakaulua, meaning “two celestial bodies in endless powerful darkness, reborn in heat and injecting energy into the universe.”
Astronomers are seeing the pair as it appeared about 900 million years after the Big Bang. The universe was still at an extremely early stage, when, according to current theories, supermassive black holes should not have had enough time to grow to such astonishing masses.
Nāpōwawāʻenakaulua is not only the oldest and most distant quasar pair discovered to date; its two supermassive black holes are also only about 18,100 light-years apart, roughly one-fifth the diameter of the Milky Way. Their masses are about 1.5 billion and 400 million times that of the Sun, respectively.
This makes Nāpōwawāʻenakaulua the closest pair of quasars discovered from the cosmic dawn. The cosmic dawn was the earliest stage of the universe, when the first stars, galaxies and black holes began to appear.
“There is currently no clear theory that can explain why a giant quasar like this already existed so early in the universe’s history, let alone two at the same time,” Silvia Onorato, the research team’s leader at the U.S. National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab), said in a statement.
“When we observe Nāpōwawāʻenakaulua, the universe is less than one-thirteenth its present age. Surprisingly, these two supermassive black holes have already reached masses comparable to those of black holes observed today.”
How did supermassive black holes at the cosmic dawn acquire so much matter?
According to IT Home, quasars are among the brightest objects in the universe. A quasar can form when a supermassive black hole at the center of a large galaxy is surrounded by a flattened, rotating cloud of gas and dust. This material is called an “accretion disk,” through which the black hole continually consumes matter.
A black hole’s powerful gravity causes material in the accretion disk to move at high speed and generate friction, releasing large amounts of heat. This makes the disk shine extremely brightly, potentially outshining all the stars in the surrounding galaxy combined. The intense light astronomers observe is a quasar.
Across the roughly 13.8 billion years since the universe began, finding a quasar is not particularly surprising. Finding two quasars so close together, however, remains extremely rare.
In fact, such paired systems should theoretically be fairly common. Galaxies frequently merge, gradually bringing the supermassive black holes at their centers closer together. This process should produce many quasar pairs separated by less than the size of a typical galaxy.
But astronomers face three major difficulties in finding them.
First, the period during which a supermassive black hole is active as a quasar is relatively brief on a cosmic scale. Second, even if two quasars are fairly close to each other, they appear very faint and are hard to detect from the ground when they lie in the extremely distant universe. Finally, when two supermassive black holes are close together and also extremely far away, telescopes have difficulty resolving them separately.
Even so, astronomers have continued to discover quasar pairs. Sometimes their timing and separation pose problems for researchers because they may challenge existing theories of black hole growth.
The problem concerns the period less than 1 billion years after the universe began. Under current models, black holes need at least 1 billion years to grow to millions or even billions of solar masses through continued accretion and mergers with one another.
Yet since it began operating in 2022, the Webb telescope has repeatedly found quasars powered by supermassive black holes, some appearing just about 400 million years after the Big Bang.
If those discoveries already challenged existing theories, Nāpōwawāʻenakaulua may put even more pressure on current models. It is the third quasar pair astronomers have discovered from the cosmic dawn.
The research team found the pair in data from the Webb telescope’s Aether survey, a project intended to conduct a systematic census of objects in the early universe.
Using the integral field unit of the Webb telescope’s Near-Infrared Spectrograph (NIRSpec), researchers have discovered about 200 quasars, slightly fewer than half the total number of early-universe quasars currently known.
While examining Aether project data, the researchers found that the quasar cataloged as J1602+4228A was not alone: it had a companion, J1602+4228B.
From ground-based telescopes, resolving the two quasars separately seemed almost impossible. Gemini North ultimately succeeded, however. The key was well-timed observing and excellent weather above Maunakea in Hawaii, the dormant volcano where the telescope is located.
Although how Nāpōwawāʻenakaulua formed remains a mystery, it may help scientists better understand how galaxies gradually gathered and merged at the cosmic dawn, and how structures formed in the early universe. This was a crucial stage in cosmic evolution.
“Nāpōwawāʻenakaulua is a very unique environment,” Onorato said. “It provides astronomers with a natural laboratory where we can study how the first massive galaxies and their central black holes gradually assembled through direct interactions between galaxies in the early universe.”
The research team published its findings in The Astrophysical Journal Letters on November 10.
References:
https://iopscience.iop.org/article/10.3847/2041-8213/aeb11f
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