The Brightest Objects in the Universe: Astronomers Finally Resolve a 60-Year-Old Mystery

After sixty years of puzzlement, one of the universe’s most enigmatic entities has been partially demystified. Quasars, which are known for their unparalleled luminosity and power, have long perplexed astronomers due to their extraordinary distance from Earth and concentrated energy output that rivals that of a trillion stars in a space as tiny as our solar system. However, until recently, scientists remained uncertain about the cause of these explosive phenomena.

The term “quasar” originated from the concatenation of quasi-stellar radio source. Astronomers like Hong-Yee Chiu, who coined the term, were perplexed by these peculiar interstellar objects. Their high gravity can cause gravitational lensing, creating optical illusions that bend light like a magnifying glass in space. Decades ago, it was difficult to discern the direction of this lensing phenomenon.

We now know that quasars reside at the center of galaxies, which are colossal rotating discs of gas, dust, stars, and dark matter held together by gravity. Although it may seem apparent, galaxies require a central pivot point. Most galaxies, including our own Milky Way, have supermassive black holes at their core, named for their mass, which ranges from a hundred thousand to ten billion times that of our Sun. The Milky Way rotates around a supermassive black hole dubbed Sagittarius A*. Despite having telescope technology that can detect black hole mergers, we have yet to observe the collision of two supermassive black holes. When this does occur, the explosion will be unimaginable.

This artist’s concept shows the brilliant glare of two quasars residing in the cores of two galaxies that are in the chaotic process of merging. (NASA, ESA, Joseph Olmsted (STScI))

At the center of certain galaxies lies an active galactic nucleus (AGN), which differs significantly from the central supermassive black holes present in most galaxies. AGNs like blazars can be unstable and emit ionized matter jets that travel close to the speed of light. However, quasars, which are also AGNs, are even more extreme. They are fueled by supermassive black holes that sometimes expel surges of matter, which can extinguish young stars. Therefore, they have emerged as a crucial element in our comprehension of the initial cosmos and the evolution of galaxies.

Despite their significance and remarkable destructive capability, quasars pose difficulties in terms of research due to their extreme distance and luminosity. Additionally, their lifespans are relatively short compared to the time at which their triggering events take place, and their brightness can change over time, making observations more challenging and data interpretation more complicated. Consequently, their origins have remained unclear.

A recent study published in the Monthly Notices of the Royal Astronomical Society has shed light on the elusive origins of quasars. The study offers a solution to one of the central mysteries surrounding the formation of these objects, suggesting that they may be created during galactic collisions.

According to the researchers, when galaxies collide, they create the necessary conditions for quasar formation. These violent encounters can cause gas to flow towards the central supermassive black holes, triggering quasar activity even before the galaxies merge completely.

While this theory has been proposed before, there was no concrete evidence to support it until now. Led by Jonathon Pierce, a postdoctoral research fellow at the University of Hertfordshire, the researchers observed almost 50 galaxies hosting quasars and compared them to over 100 quasar-free galaxies. This is the first time such a large number of quasars has been studied with such sensitivity, using deep imaging observations from the Isaac Newton Telescope in La Palma, one of Spain’s Canary Island colonies. The researchers concluded that galaxies with quasars are about three times more likely to be colliding or interacting with other galaxies than those without quasars.

The recent study published in the journal Monthly Notices of the Royal Astronomical Society suggests that galaxy interactions are the primary cause of quasar formation in the local universe. According to the researchers, their high-resolution images of quasars provide compelling evidence that colliding galaxies create the necessary conditions for quasars to emerge. This conclusion is consistent across a range of quasar brightness levels.

Since quasars are typically located at great distances from Earth, observing them allows us to study the early universe. However, the study suggests that there may be a quasar nearby in a few billion years as a result of the ongoing collision between the Milky Way and the Andromeda galaxy, which is likely to produce a quasar in its aftermath.

In a statement, Professor Clive Tadhunter, a co-author of the study and a member of the Department of Physics and Astronomy at the University of Sheffield, emphasized the significance of quasars as one of the most extreme events in the universe, and how they offer a glimpse into what the future holds for the Milky Way galaxy when it eventually collides with Andromeda in approximately five billion years. Although observing these events is exciting and offers insight into how they occur, Tadhunter reassures us that we won’t be anywhere near one of these events for quite some time.

It has taken years of research to develop our current understanding of quasars, and this knowledge is essential in shaping our understanding of how the universe came to be and its future. According to Jonathon Pierce, the lead author of the study, NASA’s James Webb Space Telescope was primarily created to study the earliest galaxies in the universe, and it is capable of detecting light emitted from even the most distant quasars, which were emitted nearly 13 billion years ago. Pierce asserts that quasars play a crucial role in our comprehension of the universe’s history and may provide insight into the future of the Milky Way.

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