A newly discovered cluster of quasars appears to stretch farther across the universe than scientists previously thought possible.
At a hard-to-grasp length of 4 billion light-years, the large quasar group, or LQG, is almost 4 times larger than the theoretical size limit predicted by the modern cosmological model, said lead researcher Roger Clowes.
“This structure is a few percent of the size of the observable universe,” Clowes told The Space Reporter in an exclusive interview. “Our cosmological model is based on the assumption that homogeneity applies. In the past when we’ve discovered large structures we haven’t had to worry too much because we’ve had lots of scope to increase the scale of homogeneity.”
“But with this new structure,” Clowes said, “we’re running out of room in which to maneuver in this way.”
To gain some perspective on the sheer enormity of the newly identified LQG, our own Milky Way galaxy is only 100,000 light-years across. Our nearest galactic neighbor, Andromeda, is about 2.5 million light-years away. By comparison, the new quasar cluster is 1,600 times larger than the distance between the Milky Way and Andromeda, and a whopping 40,000 times larger than our home galaxy.
A computer simulation of the cosmological model, performed in 2010 by Jaswant Yadav and colleagues for the Korea Institute for Advanced Study, produced the so-called concordance model. This predicts that no structure in the universe should exceed about 1 billion light-years in size, to support Einstein’s assumption that when viewed on a sufficiently large scale, the properties of the universe are the same for all observers.
So what are the implications for cosmology and Einstein’s theory in light of the recent discovery? “It’s not the theory that’s a problem – it’s the assumption of the cosmological principle,” Clowes explained. “The assumption makes the math a lot easier, but if it turns out we have to drop the assumption then we certainly don’t have to drop Einstein’s [theory of general relativity].”
Quasars, 73 of which combine to form the massive LQG, tend to form the nuclei of ancient galaxies. They are the brightest objects in the known universe, because of the massive amount of radiation they emit while sucking huge amounts of matter into the supermassive black holes at their cores. Astronomers have known for years that quasars tend to assemble in huge groups—some as wide as 700 million light years—but nothing on this scale was previously imagined to be physically possible.
Clowes and his team used open-source information able to identify the structure, which lies about 9 billion light years from Earth. “We used data from the Sloan Digital Sky Survey from the Apache Point observatory in New Mexico,” said Clowes. “It’s a great thing that the data is made publicly available for anyone in the world to use.”
The team then submitted the data to rigorous computer modeling to reach its conclusions on the LQG’s unfathomable size. “Our calculation of size is based on the concordance model … and then we go on to to question the model a little!” observed Clowes.
When asked about his personal reaction to the discovery, Clowes said, “Surprise! Of course. I remember sending the details to my colleague Luis Campusano in Chile and his response was “What is THAT?” – so “What is THAT” seems like the appropriate reaction.”
Despite the fresh mysteries it raises, the super-structure of quasars could help scientists to better understand the evolution of galaxies. Quasars are believed by many astronomers to represent an early stage in the life of most galaxies. While the exact nature of this connection is still not fully understood, one theory suggests that this type of colossal quasar collection may be a precursor to galaxy superclusters in the modern universe.
Gerard Williger, an astronomer at the University of Louisville in Kentucky, believes the discovery could hold some important clues. “This structure is bigger than we expect based on the shockwaves formed in the universe after the big bang,” Williger said.
“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.”
Clowes and his team will continue to investigate the implications of their discovery as things move forward. “We have a few more examples to follow up,” he said. “They’re not quite so extreme as the one we just published, but I think they’re going to be interesting too.”
The quasar study was published this week in the Monthly Notices of the Royal Astronomical Society.