31 new quasars have been discovered in the young universe, including two that emitted light when the universe was only about 670 million years old. The discovery deepens the mystery of how supermassive black holes managed to grow so rapidly so soon after the Big Bang.
The space telescope Euclid The European Space Agency's helped astronomers discover 31 Quasars From the earliest period in the history of the universe. Two of them are the oldest observed so far: their light was emitted when the universe was only about 670 million years old, less than five percent of its current age.
The new quasars were discovered in the Euclid Wide Survey data. 14 of them are inRedshift of 7 or higher, and the two oldest are at redshifts 7.69 and 7.77. The discovery more than doubles the number of quasars known from such an early period and provides astronomers with a larger population with which to study the growth of black holes and the first galaxies.
The findings were published in the journal Astronomy & Astrophysics by an international team led by Deming Yang, a doctoral student at Leiden University, and with the participation of Prof. Joseph Hanaway from the University of California, Santa Barbara and Leiden University.
Cosmic beacons powered by black holes
A quasar is an extremely active and bright core of a galaxy. Its energy source is not the black hole itself, from which light cannot escape, but the matter surrounding it.
Gas and dust drawn towards a supermassive black hole form an accretion disk. The material in the disk is heated to very high temperatures due to friction and magnetic processes, and emits radiation of enormous intensity. A quasar can shine with an intensity comparable to that of trillions of suns and be brighter than all the stars in the host galaxy combined.
This brightness allows quasars to be seen from vast cosmic distances. In fact, astronomers do not see them as they are today, but as they were when the light emerged from them more than 13 billion years ago.
"These objects provide the best clues to understanding how Supermassive black holes", said Hanawi. According to him, the very existence of black holes with hundreds of millions of solar masses at such an early time poses a challenge to the models that explain their development.
How did black holes grow so quickly?
Stellar black holes are usually formed after the collapse of massive stars. However, even if one of the first black holes began to swallow material shortly after the first stars appeared, the time it had available to the time when the new quasars were observed was very short in cosmic terms.
To reach hundreds of millions of solar masses in less than 700 million years, a black hole must start from a relatively massive "seed", accumulate material at a very rapid rate, merge with other black holes – or combine several of these processes.
One possibility is that early stars were extremely massive, and after their collapse left behind black holes larger than those formed today. Another possibility is that huge gas clouds collapsed directly into black holes of thousands or tens of thousands of solar masses, without first going through a prolonged phase of being a regular star.
Each additional ancient quasar allows scientists to test which of these scenarios fit the data. The older the quasar, the less time the black hole at its center has had to grow – and so the challenge for the models becomes more difficult.
Why are ancient quasars so hard to find?
Quasars from this period are very rare. The universe was still young, and few galaxies had time to grow and feed active, bright black holes.
In addition, distant quasars may appear in photographs very similar to nearby stars in the Milky Way galaxy, especially brown dwarfs. For every real ancient quasar, there are thousands of closer objects that may look like it in initial measurements.
The expansion of the universe adds another difficulty. Light emitted from quasars in the ultraviolet is stretched on its way to us and arrives at wavelengths in the near infrared. This process is called redshift. The higher the redshift, the more likely the light came from a more distant object and from an earlier time in the history of the universe.
At a redshift of 7, we see the universe as it was when it was about 750 million years old. The two new quasars, which have a redshift of close to 7.7, were observed from an even earlier time.
Observation from the ground is difficult because Earth's atmosphere itself glows in the infrared and obscures faint sources. Detecting rare quasars requires both a deep survey and wide-sky coverage—a combination that Euclid can provide from space.
Euclid's advantage: vast depth and sky area
Euclid was launched in 2023 to study dark matter, dark energy, and the evolution of the large-scale structure of the universe. Its broad survey is designed to cover more than a third of the night sky and image billions of galaxies in visible and near-infrared light.
This capability also made it a particularly effective tool for searching for ancient quasars. Before its operation, only a few of the brightest quasars from the early universe had been found. Euclid is able to scan vast areas with high sensitivity and detect even fainter sources.
"Euclid is a game changer," said Young. "Previously, we could only find a handful of the brightest early quasars, but Euclid allows us to search more efficiently across vast swaths of the sky and capture much fainter light."
The candidates detected in the Euclid data were subjected to spectroscopic observations to ensure that they were indeed distant quasars and not nearby stars. About two-thirds of the new quasars, including the three most distant, were confirmed using Telescopic Keck In Hawaii.
Machine learning found needles in a cosmic haystack
Alongside observations from space, the researchers used computational methods and machine learning to filter through tens of millions of light sources and locate the most likely candidates.
The algorithms compare the brightness of each object at different wavelengths and try to distinguish between the signature of a distant quasar and that of a closer star, brown dwarf, or galaxy.
Without such filtering, expensive follow-up observations would have to be made on thousands of similar-looking objects. Machine learning does not replace spectroscopy, but it does allow us to narrow down the list of candidates that can be tested with large telescopes.
A window into the Renaissance period
The new quasars existed during theReionization, a crucial stage in the history of the universe.
After the Big Bang, the universe cooled and neutral hydrogen formed. For hundreds of millions of years, this gas filled space and absorbed much of the ultraviolet radiation. Later, the first stars, galaxies, and active black holes began to emit radiation that reionized the hydrogen atoms—that is, separated the electrons from the nuclei.
The reionization process gradually made the universe more transparent to radiation, preparing the conditions for the universe we see today. The light from quasars passed through the intergalactic gas during this period, so their spectra carry information about the state of the hydrogen and the rate of reionization.
One of the earliest quasars in the group has already been studied in detail and is located within a galaxy rich in gas and dust, where a rapid rate of star formation was occurring. This may provide a glimpse into the environment in which the first supermassive black holes grew.
James Webb and ALMA will examine black holes
The researchers were given observation time on the James Webb Space Telescope to study some of the new quasars. The observations were designed to measure the masses of the black holes, examine the chemical composition of the gas around them, and examine how the quasars' light was affected by the intergalactic medium during the reionization period.
Radio Telescope Array ALMA In Chile, it will be possible to observe the radiation emitted from the dust and cold gas in the host galaxies, thereby measuring the rate of star formation and the reserves of material available to feed the black hole.
The team's next goal is to find a quasar at a redshift higher than 8 – an object whose light was emitted when the universe was less than 630 million years old.
According to Hanavi, the broad vision is to connect the various observations into a consistent timeline: "a chronicle of quasars in the first billion years."
Questions and Answers
What is a quasar?
A quasar is an extremely bright and active core of a galaxy, powered by material falling into a supermassive black hole. The material heats up in the accretion disk and emits enormous amounts of radiation.
How old are the earliest quasars discovered?
The light from the two most distant quasars was emitted when the universe was about 670 million years old. The light has been traveling toward us for more than 13 billion years.
What is redshift?
Redshift is the stretching of the wavelengths of light due to the expansion of the universe. The further away an object is, the more its light is generally shifted toward red and infrared wavelengths.
Why is the discovery of quasars surprising?
Quasars are powered by black holes with hundreds of millions of solar masses. It is unclear how black holes managed to accumulate so much mass in less than 700 million years after the Big Bang.
What is the contribution of the Euclid Telescope?
Euclid also images vast areas of the sky in the near infrared, above atmospheric disturbances. This allows it to detect rare and faint objects that are not easily accessible to ground-based surveys.
Did Euclid photograph the black holes themselves?
No. Black holes do not emit light directly. Euclid discovered the intense radiation from the material heating up around them and the light from the host galaxies.
The scientific article
10.1051 / 0004-6361 / 202658883
2 תגובות
An active core of a galaxy is one in which the black hole continues to swallow stars and dust from its surroundings. An inactive core means a quiet black hole – one that has finished everything it could swallow.
Hello
The explanation of what a quasar is used the term "active nucleus".
As someone who occasionally reads these articles, I have no general knowledge. Can you also explain what the term "active nucleus" means in this field?
Thanks