Astronomers have discovered a structure in the distant reaches of the universe that dwarfs any previously known- a clump of quasars 4 billion light years across.
The Milky Way galaxy, in which our solar system resides, is so big that it can be a challenge to conceptualize. It takes 100,000 years for light to travel from one end to the other. The distance between us and our nearest galactic neighbor, Andromeda, is even more staggering– about 2.5 million light-years.
The newly discovered large quasar group, or LQG, is 1,600 times larger than the distance between the Milky Way and Andromeda, and 40,000 times larger than our galaxy.
“While it is difficult to fathom the scale of this LQG, we can say quite definitely it is the largest structure ever seen in the entire universe,” says Roger Clowes, leader of the research team at Britain’s University of Central Lancashire that made the discovery. “This is hugely exciting – not least because it runs counter to our current understanding of the scale of the universe.”
The sheer size of the structure challenges Albert Einstein’s Cosmological Principle, which states that when viewed on a sufficiently large scale, the properties of the Universe are the same for all observers. Calculations based on the principle, which underlies contemporary cosmological modeling, suggest that structures larger than about 1.2 billion light-years should not exist. The 4 billion light-year wide LQG, comprising 73 quasars and lying about 9 billion light years from Earth, blatantly defies this logic.
“It could mean that our mathematical description of the universe has been oversimplified-and that would represent a serious difficulty and a serious increase in complexity,” Clowes said.
Quasars are the nuclei of ancient galaxies, and emit so much radiation in the process of sucking huge amounts of matter into the supermassive black holes at their core that they are the brightest objects in the universe. For years astronomers have known that quasars tend to assemble in huge groups, some as wide as 700 million light years. But nothing on this scale was previously imagined, let alone observed.
“This represents a challenge to our current understanding and now creates a mystery—rather than solves one,” Clowes said.
Despite its brazen challenge to the cosmological status quo, the newly discovered structure could help scientists to decode early-galaxy evolution. Born in the Universe’s younger days, before it had let itself go quite so much (research suggests it is expanding at an accelerating rate), quasars are thought to represent an early stage in the evolution of most galaxies.
The exact nature of the connection between quasars and galaxies remains a mystery, but one theory contends that this type of colossal quasar collection may be a precursor to galaxy superclusters in the modern universe.
“This structure is bigger than we expect based on the shockwaves formed in the universe after the big bang,” said Gerard Williger, an astronomer at the University of Louisville in Kentucky.
“There is very likely some mechanism that is turning on quasars over a large scale like this—and in a short time—which could relate to some condition in the early universe.”
So how can we observe an ancient relic of the early universe in the present day? The massive distance separating us from the LQG means that we are essentially looking back in time through the 9 billion years that it has taken the quasars’ light to reach our humble planet.
The structure still needs to be mapped out more thoroughly with telescopes, and the data submitted to rigorous computer modeling both to verify the LQG’s dimensions and to better understand its implications. As things stand now, and as is the case with every great discovery, science suddenly has a bit of catching up to do.
The quasar study was published this week in the Monthly Notices of the Royal Astronomical Society.