A quasar — among the universe's most luminous and energetic objects — is a supermassive black hole caught in the act of guzzling matter at the heart of a galaxy. Scientists have now found quasars dating to so early in cosmic history that they are baffled as to how they already existed at that primordial time.
Using the European Space Agency's Euclid space telescope, researchers said they have identified 31 ancient quasars, observations that add to the mystery of how the universe was far more advanced in its earliest stages than previously believed.
These included the two earliest quasars known, dating to a bit more than 13.1 billion years ago when the universe was 5% of its current age, about 670 million years after the inceptive Big Bang event. They both shine with a brightness about a trillion times greater than the sun's.
Quasars like these are powered by black holes hundreds of millions to billions of times the sun's mass, though the masses of these two have yet to be precisely measured.
"A quasar is the blazing core of a galaxy," said Daming Yang, a doctoral student in astrophysics at Leiden University's Leiden Observatory in the Netherlands and lead author of the study published in the journal Astronomy & Astrophysics.
"At the center sits a giant black hole. Black holes themselves are dark, but the black hole's gravity pulls in gas and dust, which spiral toward it like water going down a drain. As this happens, the gas gets incredibly hot and shines brighter than the entire galaxy around it," Yang said.
The two earliest ones described in the study date to a chapter in the universe's history that scientists call the "epoch of reionization," or cosmic dawn.
"The universe back then was much smaller and denser, and filled with a fog of neutral hydrogen. It was also a time of rapid change: the first stars, galaxies and black holes were lighting up and burning away that fog, transforming the universe into the transparent one we see today," Yang said.
During this time, hydrogen atoms were stripped of their electrons and put into the state in which most hydrogen in intergalactic space remains today.
A DEEPENING MYSTERY
Scientists in recent years, through observations by the James Webb Space Telescope and Euclid among others, have gained a greater understanding of the universe's earliest stages. It possessed mature galaxies and, as the new study illustrates, hungry and huge supermassive black holes inside them.
"Everything was packed into a much smaller volume since the universe has expanded roughly eightfold in linear scale since then," said astrophysicist and study co-author Joseph Hennawi of the University of California, Santa Barbara, and Leiden University.
"The most important thing these distant quasars tell us is that these supermassive black holes were already present in the extremely early cosmic times. This does not provide very much time to grow these objects, because the universe is simply too young. This is a major unsolved problem in astrophysics," Hennawi said.
Having early supermassive black holes of this scale pushes the current understanding of black hole growth to its limits.
"Either the first black holes were born already massive through some exotic channel, or they grew much faster than we thought possible. Every step further back in time makes that puzzle harder," Yang said. "That is precisely the core mystery of these objects. And honestly, this study deepens it rather than solving it."
The earliest galaxies differed from the grand spiral and giant elliptical structures seen today. They were comparatively smaller, though richer in the gas that drove star formation.
As is still the case today, at the center of each of those galaxies sits a supermassive black hole. Our own Milky Way galaxy has one at its core, called Sagittarius A*, though it is in a quiescent phase.
Euclid was launched in 2023 mainly to investigate the mysterious cosmic components called dark energy and dark matter, but it has observed quasars, providing a scientific bonus.
"Before Euclid, decades of searching by the whole astronomical community had yielded only a handful of quasars from the early era, limited mainly by the telescopes available.
"With this sample, we are entering a new era: studying these earliest supermassive black holes as a population, and finally addressing how they were born and grew so quickly when the universe was very young," Yang said.
