Bell Labs Astrophysicists Map Large-Scale Distribution of Cosmic Dark Matter.

Business & High-Tech Editors

MURRAY HILL, N.J.--(BUSINESS WIRE)--May 11, 2000

Astrophysicists at Bell Labs, the research and development arm of Lucent Technologies (NYSE: LU), have detected the long-sought large-scale distribution of an invisible form of matter that pervades the universe.

Known as "dark matter," this invisible matter makes its presence felt through its gravity and constitutes more than 90 percent of the mass in the universe. Since it cannot be seen by telescopes, its nature and distribution have puzzled astronomers for decades, making the quest to understand it one of the biggest challenges of science. This is the first time its distribution has been mapped over significant regions of the sky that were thought to be devoid of clumps of matter.

To obtain the dark matter distribution, David Wittman, Anthony Tyson and David Kirkman of Bell Labs, along with two collaborators, Ian Dell'Antonio of both the National Optical Astronomy Observatory as well as Brown University and Gary Bernstein of the University of Michigan at Ann Arbor, used a method known as weak gravitational lensing, in which they analyzed the light from 145,000 very distant galaxies for evidence of distortions produced by dark matter that lay in its path. Einstein's general theory of relativity predicts that gravity bends light; in weak gravitational lensing, dark matter in the foreground produces a distortion or "shear" in the shapes of background galaxies. By analyzing the cosmic shear produced in these thousands of galaxies, the researchers were able to obtain the distribution of dark matter over large regions of the sky. They are reporting their results in the May 11 issue of the journal Nature.

"The cosmic shear measures the structure of dark matter in the universe in a way that no other observational measurement can," Tyson said. "We now have a powerful tool to test the foundations of cosmology."

The cosmic shear measurement allowed the astrophysicists to test current predictions of the ultimate fate of the universe. According to models favored by cosmologists, the amount of cosmic dark matter will determine whether the universe will continue to expand forever, slow down to a halt, or one day collapse on itself. Based on their analysis, Wittman and his colleagues were able to rule out a well-known cosmological scenario known as the standard cold dark matter model, in which there is enough ordinary matter and dark matter in the universe to eventually stop its expansion. Instead, their observations support an alternative universe, which contains a certain amount of vacuum energy that causes it to expand more rapidly over time.

The technique

The astrophysicists used a camera they designed and built expressly to measure cosmic shear to take images of 145,000 distant galaxies using the 4-meter Blanco telescope at the National Science Foundation's Cerro Tololo Interamerican Observatory in Chile. They figured out a way to control imaging errors - a problem introduced when the light from distant sources passes through the Earth's atmosphere as well as a telescope's optics - by using thousands of foreground stars to correct these errors.

Cosmic shear introduces certain similarities in the images of background galaxies that appear close together on the sky. Light from such galaxies passes through similar intervening volumes of dark matter and gets bent by the dark matter's gravity. Encoded in the distorted light is information about the dark matter distribution.

The researchers were able to set up an automated data processing pipeline to analyze the thousands of galaxy images and decode the dark matter distribution. Since galaxies are typically football-shaped, detecting any additional stretching of background galaxies is difficult and many thousands of galaxies had to be averaged to conclusively detect cosmic shear.

"This technique is maturing rapidly," Tyson said. "In the future, similar studies will use tens of millions of distant galaxies to see how the distribution of mass in the universe evolved with time."

Further measurements of cosmic shear planned by Tyson and his colleagues, when combined with observations of the cosmic microwave background - a diffuse radiation that is a remnant of the Big Bang explosion that created the universe and is present everywhere - will enable them to compare the dark matter distribution in the universe today with what it was when the universe was a lot younger. When they succeed, they will cast light on one of cosmology's most intractable problems.

"The future is bright for dark matter," Tyson joked.

Bell Labs is celebrating its 75th anniversary this year. One of the most innovative R&D entities in the world, Bell Labs has generated more than 40,000 inventions since 1925. It has played a pivotal role in inventing or perfecting key communications technologies for most of the 20th century, including transistors, digital networking and signal processing, lasers and fiber-optic communications systems, communications satellites, cellular telephony, electronic switching of calls, touch-tone dialing, and modems.

It was at Bell Labs that Karl Jansky first detected radio signals coming from the center of the Milky Way. In the 1960s, using a Bell Labs radio antenna, Arno Penzias and Robert Wilson detected the cosmic microwave background radiation, the strongest observational proof for the Big Bang scenario of the universe's creation.

Today, Bell Labs continues to draw some of the best scientific minds. With more than 30,000 employees located in 25 countries, it is the largest R&D organization in the world dedicated to communications and the world's leading source of new communications technologies. In a recent report, Technology Review magazine said Bell Labs patents had the greatest impact on telecommunications for 1999.

Lucent Technologies, headquartered in Murray Hill, N.J., U.S.A., designs and delivers the systems, software, silicon and services for next-generation communications networks for service providers and enterprises. Backed by the research and development of Bell Labs, Lucent focuses on high-growth areas such as optical and wireless networks; Internet infrastructure; communications software; communications semiconductors and optoelectronics; Web-based enterprise solutions that link private and public networks; and professional network design and consulting services. For more information on Lucent Technologies and Bell Labs, visit the company's Web site at http://www.lucent.com or the Bell Labs Web site at http://www.bell-labs.com.