Black hole winds ain’t what they used to be

Artist’s impression of the surroundings of a supermassive black hole at the center of an active galaxy. Credit: ESO/M. Grain Knives

During the first billion years of the universe, the winds blown by supermassive black holes at the center of galaxies were much more frequent and stronger than those observed in galaxies today, some 13 billion years ago. later. Such winds were so powerful that they slowed the growth of the supermassive black holes from which they originated. These are the results of a study by three researchers from the Italian National Institute of Astrophysics (INAF) in Trieste, published today in the journal Nature.

The work is based on observations of 30 quasars observed with the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile. Quasars are extremely bright point sources at the heart of distant galaxies, whose emission comes from the intense activity of central supermassive black holes sucking in surrounding matter. The host galaxies of these quasars were observed around cosmic dawn, when the universe was between 500 million and 1 billion years old.

“For the first time, we have measured the fraction of quasars in the young universe exhibiting black hole winds,” explains Manuela Bischetti, researcher at INAF in Trieste and first author of the new study. “Contrary to what we observe in the universe closer to us, we have found that black hole winds in the young universe are very frequent, have high speeds of up to 17% of the speed of light and pump large amounts of energy into their host galaxy.”

About half of the quasars observed in this research show black hole winds, which are much more frequent and 20 times stronger than those known in quasars from the closer cosmos when the universe was around 4 billion years old.

“Observations of black holes in the young universe show that they grow much faster than their host galaxies, whereas in the local universe black holes and galaxies are known to co-evolve,” adds the co-author. Chiara Feruglio, INAF researcher in Trieste. “This implies that some mechanism must have acted at some point in the universe, slowing the growth of the black hole. Our observations allowed us to identify this mechanism in the black hole winds produced when the universe was between 0 .5 and 1 billion years.”

The energy injected by the winds could thus have stopped the accretion of matter on the black hole, slowed its growth and triggered a phase of “common evolution” between the black hole and its host galaxy. “This study allowed us to identify the epoch in the history of the universe when the impact of black hole winds began to be significant,” adds Bischetti. “This has a huge impact on our knowledge of the initial growth phases of black holes and their host galaxies, placing strong constraints on models that describe the formation of early galaxies.”

A totally unexpected discovery, it was made possible thanks to high-quality data from the Xshooter instrument installed on the VLT as part of an extensive ESO program with around 250 hours of observations.

“Quasars are among the brightest observable objects in the early universe, but due to their distance they are quite faint in terms of observed magnitude,” says co-author Valentina D’Odorico of INAF Trieste. , affiliated with the Scuola Normale Superiore of Pisa. and principal investigator of the observational program on which the study is based. “The large time investment in observing these objects and the unique capabilities of X-shooter in terms of efficiency, wavelength coverage and resolving power have allowed us to obtain spectra of very good quality which allowed this interesting result.”

“We’ve had indications for a few years that black holes 1 billion times more massive than the sun…could launch powerful winds that travel at 20% the speed of light through their surroundings,” adds Andrea Ferrara. , professor at the Scuola Normale Superiore (SNS) and co-author of the study. “Today we have confirmation of this thanks to data obtained with a European telescope by a team with a strong Italian footprint and leadership. The SNS has contributed on the theoretical interpretation side. The discovery of these spectacular galactic winds at times as far away could have had enormous and still unexplored implications for the birth and evolution of galaxies like ours. We will address these questions in the rest of this study.”

The program was not originally designed for this scientific purpose, but primarily to study intergalactic gas in the early universe. Based on information from closer quasars, such winds were considered rare. “Fortunately, we said, because these features complicate the reconstruction of the quasar’s intrinsic emission, they were not desired by the astronomers in our collaboration who study the intergalactic medium along the line of sight,” explains D ‘Odorico. “Unexpectedly, we found these very common winds in the young universe, which complicated our analysis but gave us the opportunity to discover a very important result.”

Simulated Webb images of the quasar and the quasar surrounding the galaxy

More information:
M. Bischetti et al, Suppression of black hole growth by strong exits at redshifts 5.8–6.6, Nature (2022). DOI: 10.1038/s41586-022-04608-1

Provided by the Italian National Institute of Astrophysics

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