Scientists have solved a six-decade-old mystery about the brightest and most powerful objects in the universe

One of the most mysterious objects in the universe just got a little less mysterious.

Astronomers have pondered what quasars are for sixty years since their first discovery. What we did know was this: they are among the brightest and most powerful objects in the entire universe. They are extremely distant from earth but can shimmer as bright as a trillion Stars as they cluster in a space as small as our solar system – that’s an extremely concentrated level of energy.

But until this week, astronomers weren’t quite sure what’s causing these extreme explosions in the first place.

The term quasar is a concatenation of quasi-stellar radio sources – so named because astronomers like Hong-Yee Chiu, who coined the term, were stunned by these strange interstellar objects when they were first identified. Their powerful gravity can create physical illusions known as gravitational lenses, in which light is distorted like cosmic magnifying glasses. Just a few decades ago, it was hard to know which direction that lens came from.

As we narrowed it down, we learned that quasars sit at the centers of galaxies, which are huge swirling discs of stars, gas, dust, and dark matter strung together by gravity. This may seem obvious, but galaxies must rotate something. Most galaxies, including ours, have a central supermassive black hole around which everything revolves — and so named because these dead stars can be anywhere from a hundred thousand to tens of billions of times more massive than our Sun. The Milky Way spirals around a supermassive black hole aptly named Sagittarius A*. We haven’t detected the merger of two supermassive black holes since humans had the telescopic technology to detect black hole mergers – which admittedly was not very long ago. If we do that, the explosion will be unpredictable.

But some galaxies have very different objects at their center, called the active galactic nucleus (AGN). These can be quite fleeting, such as blazars, which are AGN that eject jets of ionized matter traveling at nearly the speed of light. But quasars are AGN, which are even more intense. They are powered by supermassive black holes that sometimes eject waves of matter that can annihilate baby stars. As such, they have become an integral part of our understanding of the early evolution of the universe and galaxy.

Unfortunately, despite their importance and impressive destructive power, quasars are difficult to study due to their extreme distance and brightness. They also don’t have very long lifetimes compared to when their triggering events occur, and their brightness can change over time, further complicating observations and obscuring the data. All this has made their origin unclear.

A new study in the Monthly Notices of the Royal Astronomical Society sheds light on the question of quasars and essentially solves one of the central mysteries of quasar formation. The answer may lie in galactic collisions.

As the researchers explain, colliding galaxies appear to create the conditions for the birth of a quasar. In fact, these fierce entanglements may allow enough gas to flow toward the core’s supermassive black holes and initiate quasar activity before the two galaxies fully merge.

This theory has been proposed before, but direct evidence has never been so solid. The researchers, led by Jonathon Pierce, a post-doctoral fellow at the University of Hertfordshire, observed nearly 50 galaxies hosting quasars and compared them to more than 100 quasar-free galaxies. Similar comparisons have been made many times before, but this is the first time so many quasars have been imaged with such sensitivity. They used deep imaging observations from the Isaac Newton Telescope on La Palma, one of the Spanish colonies in the Canary Islands, and concluded that galaxies harboring quasars are about three times more likely to collide or interact with other galaxies .

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In the study, the authors said their images of quasars “provide strong evidence that galaxy interactions are the dominant triggering mechanism for quasars in the local Universe.” This, they said, is consistent with quasars of different “brightness,” that is, with different strengths of their radio emissions.

All quasars are extremely distant, meaning they are also in the distant past, since this distance correlates with earlier times when we look at distant objects. However, there could be a quasar nearby in a few billion years if you can wait that long. As the Milky Way collides with the Andromeda Galaxy in a protracted process that will take place in about five billion years, the consequence will likely produce a quasar.

“Quasars are one of the most extreme phenomena in the Universe, and what we’re seeing likely represents the future of our own Milky Way when it collides with the Andromeda Galaxy in about five billion years,” said Professor Clive Tadhunter of the University of Sheffield’s Department of Physics and Astronomy and one of the paper’s co-authors, said in a statement. “It’s exciting to watch these events and finally understand why they’re occurring — but thankfully, Earth won’t be anywhere near any of these apocalyptic episodes for quite a while.”

It has taken decades of work to get our understanding of quasars to where we are now, which is fundamental to shaping our theories of how the universe formed and where it is headed. As Pierce, the study’s lead author, explained in the same statement: “One of the main scientific motivations for NASA’s James Webb Space Telescope was to study the earliest galaxies in the universe, and Webb is capable of detecting light from even the most distant quasars to discover. were emitted nearly 13 billion years ago. Quasars play a key role in our understanding of the history of the Universe and possibly the future of the Milky Way.”