First discovered 60 years ago, quasars, which can shine as bright as a trillion stars, have long been a mystery as no one knew what could trigger such powerful activity. Until now.

An international scientific team discovered that quasars, some of the brightest and most energetic objects in the universe, are ignited primarily by mergers between galaxies.

The finding sheds new light, after years of controversy, on what is the cause of the emission of large amounts of energy in the most powerful active nuclei, details the Institute of Astrophysics of the Spanish Canary Islands archipelago (IAC) in a statement.

For the research, the results of which are published in the Monthly Notices of the Royal Astronomical Society, observations made with the Isaac Newton Telescope (INT) and the William Herschel Telescope (WHT) of the Roque de los Muchachos Observatory in La Palma (Spanish Atlantic) were used. ).

First discovered 60 years ago, quasars can be as bright as a trillion stars packed into a volume the size of Earth’s solar system.

Since its discovery, the origin of the processes that trigger such a powerful activity has been a mystery.

Consequence of the merger of galaxies
Now, new work led by scientists from the Universities of Sheffield and Hertfordshire (United Kingdom), together with three IAC researchers, reveals that they are the result of the merger of galaxies.

The high incidence of mergers in quasars was discovered when the research team observed, using the deep imaging capabilities of INT’s Large Field Camera and the WHT’s PF-QHY camera, the presence of distorted structures of low surface brightness in the outer regions of galaxies that host quasars.

Most galaxies have supermassive black holes at their centers. They also contain substantial amounts of gas, but most of the time this gas orbits at great distances from the centers of galaxies, out of the range of these black holes, the IAC explains in the statement.

The high incidence of mergers in quasars was discovered when the research team observed, using the deep imaging capabilities of INT’s Large Field Camera and the WHT’s PF-QHY camera, the presence of distorted structures of low surface brightness in the outer regions of galaxies that host quasars.

Most galaxies have supermassive black holes at their centers. They also contain substantial amounts of gas, but most of the time this gas orbits at great distances from the centers of galaxies, out of the range of these black holes, the IAC explains in the statement.

Extraordinary amounts of energy
When two galaxies merge, gravitational forces pull gas toward the center of the galactic system. Just before the gas is consumed by the black hole at its core, it releases extraordinary amounts of energy in the form of radiation, giving rise to the characteristic glow of quasars.

The ignition of a quasar can have dramatic consequences for entire galaxies: it can expel the rest of the galaxy’s gas, preventing the galaxy from forming new stars for billions of years.

It is the first time that a sample of obscured quasars of this size has been observed with such a high level of detail, thanks to the depth and quality of the images obtained at the Roque de Los Muchachos Observatory.

By comparing observations of 48 quasars and their host galaxies with images of more than 100 non-quasar galaxies, the science team concluded that quasar-hosting galaxies are about three times more likely to be interacting or colliding with other galaxies.

This implies that galaxy mergers are the main trigger mechanism for quasar-like activity, the researchers conclude.

Quasars, key to understanding the evolution of galaxies
Clive Tadhunter, a researcher at the University of Sheffield who co-leads the study, points out that “quasars are one of the most extreme phenomena in the universe and it is likely that what we see represents the future of the Milky Way when it collides with the Andromeda galaxy within about five billion years.”

Quasars are important to astrophysics because, because of their brightness, they stand out at great distances and thus “act like beacons showing the earliest epochs in the history of the Universe,” says Jonny Pierce, a postdoctoral researcher at the University of Hertfordshire and first author of the article.

“Finding out how quasars turn on is key to understanding the evolution of galaxies, since they have a very large impact on the gas and stars of the galaxies that host them”, highlights Cristina Ramos Almeida, a researcher at the IAC who leads the international project QSOFEED of which this study forms part and in which Patricia Bessiere and Giovanna Speranza, both IAC researchers and co-authors of the study, also participate.

source: https://academic.oup.com/mnras/article/522/2/1736/7035603?login=false