New probe data sheds light on dark matter

The data allowed researchers to calculate a more precise estimate of the age of the universe, now thought to be 13.7 billion years old, with only a 120 million year margin of error, said physics professor Lyman Page, one of the team’s lead researchers. Page added that the satellite has also helped scientists determine what actual processes were going on when the universe was less than a billionth of a billionth of a second old.

“We can start to probe those earliest times with a new degree of confidence,” he said.

The pictures transmitted by the probe have also helped the researchers make important discoveries about the formation of the first stars.

“Currently the WMAP data is pretty much the only way to gain information as to when the universe was ionized by the first generation of stars,” said Eiichiro Komatsu, an astronomy professor at the University of Texas-Austin who worked on the WMAP project from 2001 to 2003, when he was a postdoctoral fellow at Princeton.

The data showed that the first stars must have formed during the first 500 million years after the Big Bang, astrophysics professor David Spergel ’82 said.

This discovery will have important implications for the James Webb Space Telescope, scheduled to be launched in 2013 by NASA, Komatsu said.

“One of [the Webb Telescope’s] prime science goals is to see the sources of ... the first generation of stars directly,” Komatsu said. “It is important to know when a significant fraction of these sources were around, so that we know where to look using this telescope.”

Discovering dark matter

The WMAP transmissions also provide the first evidence for the existence of the mysterious dark matter astrophysicists have long suspected composes much of the universe.

“[WMAP data] implies that atoms make up only 5% of the universe,” Spergel said in an e-mail. “The next roughly 20% is made up of ‘dark matter,’ most likely a new class of subatomic particles that interact[s] only extremely weakly with normal matter. The remaining 75% is made up of ‘dark energy’ associated with empty space.”

Many scientists have suspected that dark matter exists, specifically particles called neutrinos, but its existence was never before confirmed by evidence, said Charles Bennett, WMAP’s principal investigator and a physics and astronomy professor at Johns Hopkins.

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“Dark matter has never been detected directly in the laboratory; we’ve only inferred its existence from astronomical observations,” said Gary Hinshaw, an astrophysicist with the NASA Goddard Space Flight Center. “Neutrinos have been detected, but not this kind. These are produced shortly after the Big Bang.”

The cosmic neutrino background that the probe shows is only a small fraction of the total dark matter in the universe, Hinshaw added.

“[The neutrino background] has always been assumed to be there ... [The] challenge was to actually see it in the data,” Komatsu said. “Particle physicists are detecting neutrinos on the ground, but those neutrinos are from the atmosphere, sun, or nuclear reactors. The energy of the cosmic neutrino background is at least a million times smaller than their neutrinos, which means that it is extremely difficult to detect them ... with the current technology.”

The benefits of collaboration

The University’s involvement in the probe project began around 1991 and was led by David Wilkinson, a former University physics professor who passed away in 2002, Page said. The satellite was later named for Wilkinson.

“WMAP is very different from most astronomical satellites,” Spergel said. “Rather than take pictures of individual objects, it makes a precise measurement of fluctuations across the entire sky.”

The collaboration with NASA began around 1994, Page said, when the research group won a design competition for building a new satellite.

During the collaboration, University researchers focused on building the microwave instrument that detected radiation in space, Hinshaw said. The instrument was built at the University and then shipped to the Goddard Center in Maryland, where it was assembled into the satellite.

The satellite, launched in June 2001, orbits the sun at a distance of about one million miles from earth. The probe transmits temperature data back to earth, recording miniscule variations to about one millionth of a degree Kelvin. The data is received and analyzed by a joint NASA and Princeton team, Hinshaw said. The researchers submitted seven papers containing the new WMAP results to the Astrophysical Journal last week.

The project was also unique in that the science team had much more hands-on involvement than is usual for space missions, Bennett said.

“The scientists worked hand-in-hand with engineers, who often said things like, ‘I never knew that there were scientists who knew how to do practical things,’ ” Bennett said. “I am certain that this hands-on role of the science team was critical to the success of the mission.”

Bennett added that WMAP is the “most cost-effective” mission NASA has ever flown. “The number of high-impact scientific citations is very large, while the cost of the mission was among the least,” Bennett said. “The science output per dollar is unmatched.”

The satellite will likely continue to transmit data for another three years, Hinshaw said, and a new European probe, which is scheduled to be launched later this year, will complement the WMAP discoveries in the future. The European Planck satellite will be more sensitive and transmit higher-resolution images than the WMAP, Page said.

“It will be nice to have overlapping data for a short time to tie the data together and make sure we understand everything,” Hinshaw said.

The discoveries fueled by WMAP transmissions have been truly astronomical and have radically transformed the study of the universe, Komatsu said.

“WMAP definitely made our time the golden age in cosmology,” he said.