Newswise — The Big Bang theory is still the best way to describe the earliest days of the universe, but evidence from nearby galaxies suggests that the theory may be due for some tweaks, according to a Technion-Israel Institute of Technology researcher and colleagues.
Technion cosmologist Prof. Adi Nusser and Princeton University’s P.J.E. Peebles say that old stars in large galaxies, cosmic voids ringed by large galaxies and other tantalizing clues might mean that galaxies and groups of galaxies were built earlier in the course of the expanding universe than predicted by the standard Big Bang theory.
“We do not anticipate that this debate will lead to a substantial departure from the present standard picture of cosmic evolution in the hot Big Bang, because the picture passes a tight network of tests,” they write in the 3 June issue of the journal Nature. “But there is considerable room for adjustment of details, including the galaxies.”
John Kormendy, an astronomer at the University of Texas at Austin and an expert on the evolution of galaxies, praised the researchers for bringing together the latest observational data with theoretical cosmology.
The standard model has been “articulated in enormous detail and works very well,” Kormendy said. “But in various places, including what goes on in individual galaxies, lots of very messy physics come into play, and Peebles and Nusser have highlighted some of those problems.”
“A huge amount of observations have become available and computers have become so powerful that implications of the standard model could be studied in great detail,” said Nusser, of the Technion Physics Department. “The standard model was perceived long ago before these huge data sets became available.”
For instance, the standard model predicts that the largest and most luminous galaxies will form within massive dark matter halos, where gravity has collected matter into highly dense regions. But observations show that there are an unexpected number of large galaxies at the edge of a region called the Local Void, one of the least densely-populated places in our galactic neighborhood, the researchers noted.
It’s a problem that could be resolved if galactic structures grew more rapidly than predicted by the standard theory, “more completely emptying the Local Void and piling up matter on its outskirts,” Nusser and Peebles said.
The standard model also predicts a long and steady rain of cosmic debris—from stars and plasma and even smaller “satellite” galaxies—on to other larger galaxies. But astronomers have shown that the largest and brightest galaxies are not filled with young stars, as would be expected from constant collisions, but are instead populated by some of the oldest stars.
Kormendy’s own work has turned up few signs of major merging in a surprising number of galaxies in our local universe. For many of the biggest galaxies like the Milky Way, he said, “we have no idea right now within our standard picture how galaxies can grow so big without showing products of these mergers.”
“The fossil record in the stars in our home galaxies, the Milky Way, shows our galaxy is a tranquil place that has not been disturbed by in-falling cosmic debris for a long time,” Nusser noted. “The same is true of about half the other large nearby galaxies that can be observed in greatest detail.”
The presence of pure disk galaxies, where stars stream out in a flat plane unanchored by a bulging center, are another indication that the rain of debris ceased before there was time to build up a central bulge of stars, the researchers said.
Adjusting the standard theory to accommodate faster galactic evolution may break a fundamental rule of physics—at least at the level of very large cosmic objects, Nusser said.
For ordinary, visible matter, the acceleration of objects due to gravity depends only on the mass of the objects. That’s why a “feather will fall at the same rate as a ball of iron if let go from the same height,” said Nusser. But he and Peebles propose adding a force between dark matter particles only, as a way to build some speed into the early evolution of galaxies.
“This means that the acceleration of an object will depend on its composition,” Nusser explained. “If a small, so-called satellite galaxy is falling into the Milky Way, then the satellite galaxy will fall at a higher rate if it contains dark matter.”
Nusser said the shift from the current paradigm would not alter what the model predicts about how galaxies are distributed over large distances, such as the distance between galactic clusters. But the adjustments would “allow new physics operating on the scale of galaxies,” he said.
The Technion-Israel Institute of Technology is Israel's leading science and technology university. Home to the country’s winners of the Nobel Prize in science, it commands a worldwide reputation for its pioneering work in nanotechnology, computer science, biotechnology, water-resource management, materials engineering, aerospace and medicine. The majority of the founders and managers of Israel's high-tech companies are alumni. Based in New York City, the American Technion Society (ATS) is the leading American organization supporting higher education in Israel, with offices around the country.
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Nature (June 3, 2010)