Supermassive black hole growth mystery solved

(ORDO NEWS) — An international team of astronomers has discovered that in the early universe, supermassive black holes in quasars generated very powerful stellar winds at record speeds not seen in more modern galaxies.

The results of the study, published in the journal Nature, solve the mystery of why supermassive black holes at some point stopped the phase of unusually rapid growth and began to increase mass gradually.

Although the mechanism for the emergence of supermassive black holes, which were already in the first billion years of the existence of the Universe, has not been precisely established, it is known that these objects went through a phase of rapid growth, which explains their huge mass at that time.

At some point, this growth was suppressed and came into line with the growth rates of the host galaxies. The mechanism of such suppression is still not well understood, but it was assumed that the driving force is the influence of the black hole itself on the galactic medium.

Astronomers have observed 30 quasars with the Very Large Telescope (VLT) in Chile. The redshift of quasars was in the range from 5.8 to 6.6, which corresponds to the travel time of light from them, equal to 12.6-12.8 billion years, or the accompanying distance (taking into account Hubble’s law in an expanding universe) of 27-28 billion light years.

Quasars are active and very bright nuclei of ancient galaxies, powered by the energy of a supermassive black hole that absorbs the surrounding matter. The oldest quasars have been observed at distances corresponding to the epoch of reionization, that is, the age of the Universe is 0.5-1 billion years.

The researchers noticed that the spectra of about half of the studied quasars showed signs of powerful stellar winds, whose speed reached a record 17 percent of the speed of light. Such winds are characteristic of more distant (and therefore earlier) quasars, whose redshift exceeds 5.8.

This means that more than 12.6 billion years ago, quasars dissipated a huge amount of kinetic energy into the interstellar medium and suppressed the accretion of matter, pushing it away from the black hole.

According to calculations, this energy was 20 times higher than the values ​​for later quasars with a redshift of 2-3 (the age of the Universe is about four billion years). As a result, the growth of the supermassive black hole was slowed down.

Powerful stellar winds are explained by the fact that around the same time, the host galaxies begin to grow rapidly, and the star formation rate reaches thousands of solar masses per year.

The interstellar medium became denser, accretion grew and at some point exceeded the Eddington limit, that is, the radiation pressure of the absorbed matter became so high that it pushed the matter away from the accretion disk.

From that time on, the growth of the black hole ceased to dominate the growth of the parent galaxy, and both processes became symbiotic, that is, the phase of general evolution began.

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