Astronomers find the farthest merging quasar pair ever recorded

Astronomers have discovered a pair of merging quasars observed just 900 million years after the Big Bang. Not only is this the most distant pair of merging quasars ever found, but it’s also the first pair identified during a period in the history of the universe known as the “cosmic dawn.”

The dawn of the universe lasted from about 50 million to 1 billion years after the Big Bang.

During this period the first stars and galaxies began to appear and the dark universe was filled with light for the first time.

The appearance of the first stars and galaxies marked the beginning of a new era in the formation of the universe, known as the Reionization Epoch.

The epoch of reionization that occurred during the cosmic dawn was a period of cosmic transition.

About 400 million years after the Big Bang, ultraviolet light from the first stars, galaxies, and quasars spread throughout the universe, interacting with intergalactic matter and beginning a process called ionization, which stripped electrons from the universe’s primordial hydrogen atoms.

The reionization epoch is a crucial period in the history of the universe, marking the end of the cosmic dark ages and sowing the seeds of the large structures we observe in the local universe today.

To understand exactly what role quasars played during the reionization period, astronomers are interested in discovering and studying quasars that existed during this earlier, distant era.

“The statistical properties of quasars during the reionization stage can tell us a lot, including the progress and origin of reionization, the formation of supermassive black holes at the dawn of the universe, and the earliest evolution of the quasars’ host galaxies,” said Dr Yoshiki Matsuoka, an astronomer at Ehime University.

About 300 quasars have been discovered during the reionization period, but none have been found in pairs.

But as Dr. Matsuoka and his team were reviewing images taken with the Subaru Telescope’s HyperSupreme-Cam, a faint red spot caught their eye.

“While screening images for potential quasars, we noticed two similar, very red sources next to each other. This discovery was pure coincidence,” Dr Matsuoka said.

The distant quasar candidates are contaminated by many other sources, including foreground stars and galaxies and gravitational lensing, so the authors were unsure whether they were quasar pairs.

To confirm the nature of these objects, named HSC J121503.42-014858.7 and HSC J121503.55-014859.3, the team carried out follow-up spectroscopic measurements using the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope and the Gemini Near-Infrared Spectrograph (GNIRS) on the Gemini North Telescope.

The spectra obtained by GNIRS resolved the light emitted by the source into its constituent wavelengths and were crucial for characterizing the properties of the quasar pair and its host galaxy.

“GNIRS observations have shown that quasars are too faint to be detected in near-infrared light, even with the largest ground-based telescopes,” said Dr Matsuoka.

This allowed astronomers to deduce that some of the light detected in the visible wavelength range comes not from the quasar itself, but from ongoing star formation in its host galaxy.

The two black holes were also found to be enormous, with masses 100 million times that of the Sun.

This, combined with the presence of a bridge of gas extending between the two quasars, suggests that the two quasars and their host galaxies are undergoing a major merger.

“The existence of merging quasars during the reionization period has long been predicted, but this has now been confirmed for the first time,” said Dr Matsuoka.

This discovery paper In Astrophysical Journal Letters.

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Yoshiki Matsuoka others2024. Discovery of twin quasars merging at z = 6.05. Apu JL 965, L4; doi: 10.3847/2041-8213/ad35c7