Scientists may have solved a 60-year-old mystery by discovering these quasars — energetic objects powered by voracious supermasses black holes and can outshine trillions of stars together—formed when galaxies collide and merge.
The results suggest that the Milky Way could host its own quasar when it collides with neighboring Andromeda Galaxy in a few billion years.
Scientists have previously tracked the bright, energetic emissions from quasars in regions at the hearts of galaxies roughly the width of the Solar System — meaning quasars must have come from incredibly compact objects. The leading theory is that quasars are supermassive black holes that heat up vast amounts of surrounding gas, releasing enormous amounts of radiation before the material falls onto the black hole’s surface.
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Since their discovery six decades ago, quasars have puzzled scientists — mostly because it’s unclear how supermassive black holes can suck in enough raw material to power such powerful emissions. While supermassive black holes live at the centers of most galaxies, the gas needed to power quasars usually orbits at the fringes of galaxies. So there must be a delivery service that delivers gas to the hearts of the galaxies.
New research results have now been published in the journal Monthly Bulletins of the Royal Astronomical Society uses deep imaging observations from the Isaac Newton Telescope in Spain’s Canary Islands to finally solve this mystery.
“To understand how quasars are ignited, we need to determine how gas can fall into the center of the host galaxy at sufficiently high speeds,” said the study’s lead author Clive Tahunter, a professor at the Department of Physics and Astronomy at the University of Sheffield in the UK, told Live Science via email. “One idea is that the necessary radial dip is caused by collisions between galaxies, whose associated gravitational forces can disrupt the gas from its usual circular orbits.”
Comparing 48 nearby galaxies that host quasars to 100 galaxies that do not host quasars, the researchers discovered the presence of distorted structures at the edges of the galaxies that host quasars. These structures also indicate a past or ongoing collision and merger with another galaxy, Tadhunter said.
“We found a high rate of such structures in galaxies hosting quasars, three times that of a carefully matched control sample of non-quasar galaxies imaged using the same techniques,” Tadhunter said. “This is strong evidence that quasars are indeed triggered in galaxy collisions.”
The team’s research isn’t the first time galactic mergers have been linked to quasars. However, Tadhunter pointed out that attempts to test this hypothesis by looking for distorted structures on the outer parts of galaxies, characteristic of such collisions, had previously proved ambiguous.
“Some studies have found the expected structures, others have not,” he continued. “We believe that much of the previous ambiguity in this area is due to the fact that many of the previous imaging studies did not have sufficient depth to discern the sometimes faintly distorted structures in the outer parts of the galaxies that host the quasars.”
Quasars can have a major impact on the evolution of galaxies that host them; A better understanding of how quasars ignite could help scientists refine their models of galaxy evolution and the evolution of the Universe as a whole.
“It is important to understand how, when and where quasars are triggered because the tremendous radiative force produced by a quasar can have a large, damaging effect on the surrounding host galaxy,” Tadhunter said. “For example, the pressure of the radiation can drive out the remaining gas in the remnant galaxy system. Since gas is needed to form new stars, it will cut off any future star formation Activity, practically the death throes of the galaxy.”
Tadhunter also pointed out that understanding the connection between galactic collisions and quasars is crucial to determining the future of our own corner of the cosmos.
“The next large galaxy – the Andromeda spiral – is coming straight towards us at high speed and will collide with and merge with the Milky Way in about 5 billion years,” he said. “If that happens, a quasar is likely to be triggered as gas falls into the center of the rest of the system.”
The team intends to continue this research by examining other quasars, located at greater distances and detected using other methods, to see if they share the same features that link them to galactic collisions.
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