Euclid spots dozens of quasars in the early universe
The Euclid space telescope has discovered 31 extremely distant quasars, breaking the distance record for this type of bright galactic nucleus. Powered by colossal black holes, two of the discovered galactic nuclei were shining when the universe was only 670 million years old. That is just five per cent of the universe’s current age.
Quasars can shine with the brightness of a quadrillion stars (a 1 followed by 12 zeros) and are therefore the brightest objects in the universe. They form when a supermassive black hole at the centre of a galaxy draws in large amounts of matter in a spiral motion. As the matter heats up, a vast amount of energy is released.
Quasars can be seen throughout virtually the entire observable universe, and scientists have been searching for the most distant examples for decades. These objects reveal what happened in the early universe when the first supermassive black holes and galaxies were forming. However, quasars from this era are difficult to find. They are rare, and due to the vast distances involved, their light is faint and easily confused with that of closer stars.
The Euclid space telescope has now discovered 31 quasars that were shining when the universe was only five per cent of its current age. ‘These quasars date from the infancy of the universe,’ says Daming Yang, PhD candidate at Leiden Observatory and lead author of the scientific paper. ‘By studying them, we can better understand how such enormous systems formed and grew so rapidly. For the time being, this remains a major question in astrophysics.’
Record quasar
The discovery adds 12 new examples to the collection of quasars with a so-called redshift – a measure of distance – of 7 or higher. This means that these quasars were shining when the universe was at most 770 million years old. Until now, nine such quasars were known.
Two of the newly discovered quasars, EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3, have redshifts of 7.77 and 7.69 respectively, setting a record for the most distant examples ever found. Both are located more than 13 billion light-years away and formed during the first 670 million years of the universe.
The second-furthest quasar discovered by Daming and his colleagues has recently been studied in greater detail by Silvia Belladitta’s team. The observations show that the quasar is embedded in a gas- and dust-filled galaxy that is rapidly forming new stars. The results thus provide an insight into what the ‘host galaxy’ of an early supermassive black hole might look like.
Quasars as time machines
The quasars existed at a time in cosmic history known as the so-called reionisation era. This was the moment when the first stars began to shine. The radiation from these early stars transformed the universe from a cold and dark place into a cosmos in which matter in space – particularly hydrogen gas – became ionised and ‘transparent’ to ultraviolet radiation. The quasars can provide crucial information about how this reionisation took place, for example regarding the extent and speed with which the first galaxies influenced their surroundings.
Because so few quasars are known at this high redshift, questions of this kind about the early universe and the galaxies within it are still difficult to answer, according to Yang. ‘The only way to do so is to find more objects at this distance.’
Compared to its predecessors, Euclid is capable of detecting quasars that are 10 to 100 times fainter. ‘This result demonstrates the power of Euclid’s near-infrared observations. During the mission’s preparations, it was already clear that it would be an excellent tool for searching for distant quasars,’ says Henk Hoekstra, a professor at Leiden Observatory who is involved in the research. ‘Now we have that confirmation. Based on these initial data, I expect many more discoveries, especially as we further improve our data processing.’
The limits of what is technically possible
After one year, the Euclid data cover 1,900 square degrees of the sky, an area roughly the size of 10,000 full moons. The full six-year survey is expected to yield hundreds more distant quasars, including the first quasars with a redshift of more than 8. These galaxies existed when the universe was no more than 640 million years old.
‘This puts us at the very limits of what is observationally possible,’ says Huub Röttgering, professor at Leiden Observatory and one of the authors of the scientific paper. ‘Euclid shows us just how many quasars there actually are in the early universe. Our current models struggle to explain how galaxies and black holes could have become so massive so quickly in the universe. This will enable us to start finding a solution.’
Scientific article
This press release originally appeared on astronomie.nl.