New Map of the “Nearby” Universe Reveals Large-Scale Structure of Galaxies
PASADENA, Calif. — Astronomers presented a new view of the “nearby”
universe, probing the way that galaxies cluster together over distances of
hundreds of millions of light years, at today’s meeting of the American
Astronomical Society being held in Pasadena, Calif. The new map for the
first time covers the whole sky, including the large portion ordinarily
hidden by our own galaxy, the Milky Way, and reveals a complicated network
of galaxies surrounding us. Galaxies do not uniformly dot the sky, explained
University of Massachusetts astronomer Stephen Schneider, who headed up the
project. Rather, gravitational forces spur them to form clusters and groups
of clusters, called superclusters. The findings offer scientists clues about
the conditions that existed during the early days of the universe.
The work is based on the recently completed infrared survey of the entire
sky called 2MASS (for 2-Micron All Sky Survey) carried out principally
by astronomers at the University of Massachusetts and NASA’s Infrared
Processing and Analysis Center. “Infrared light penetrates through the
dusty interstellar clouds in galaxies, allowing us to see more clearly out
of our own galaxy and to better see other galaxies,” said Schneider. “At
visual wavelengths very few galaxies are visible in a wide band called the
‘Zone of Avoidance’ girdling the sky because of the dusty disk of the galaxy
we live in.”
The team of astronomers selected one small region of the survey to carry out
more detailed studies of the galaxies’ distribution in space. They targeted
a cluster of galaxies called Abell 262, which is part of the Pisces-Perseus
supercluster, one of the major concentrations of galaxies in the local
universe. Parts of this supercluster were hidden by dust clouds in the Milky
Way. “In the new 2MASS map, the supercluster resembles large clumps with
long, threadlike filaments strung between them in a spiderweb pattern of
galaxies,” said Schneider. To determine how far away a galaxy is, scientists
rely on a phenonmenon called “redshift.” The expansion of the universe
implies that the farther away an object is, the faster it is moving away
from us, and its emissions are shifted to longer wavelengths of light.
The targeted study presented a small surprise. “We thought we were examining
galaxies in Abell 262, about 200 million light-years away, but found instead
that most of the galaxies lay in a background supercluster about 1 billion
light-years distant,” said Schneider. “We’re seeing layer upon layer of
structure in the way galaxies cluster. 2MASS is helping us to understand
how matter coagulated and collapsed to form structures after the Big Bang,
and how those structures are joined together.”
The research was conducted using 2Mass, twin infrared telescopes that see
wavelengths beyond red light in the rainbow of visible colors. Infrared
light enables astronomers to peer past interstellar dust. The 2Mass
telescopes are located at Mount Hopkins, Ariz., and Cerro Tololo, Chile.
Principal collaborators on the project were Michael Skrutskie of UMass;
Thomas Jarrett and Thomas Chester, both of IPAC; and John Huchra, of the
Harvard-Smithsonian Center for Astrophysics.
2MASS, the most extensive infrared astronomical survey to date, began
operations in 1997, and concluded observations earlier this year. The
release of nearly half of the all-sky survey, made available just a few
months ago, enabled amateur stargazers and high-level astronomers alike to
view a half-million galaxies and 162 million stars on their home computers.
The completion of the survey has allowed scientists to explore the entire
sky, including the “Zone of Avoidance.”
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Note: Stephen Schneider will be in attendance at the AAS meeting in Pasadena
this week. He can be reached via email, at schneider@astro.umass.edu. His
office phone number at UMass is 413-545-2076.
IMAGE CAPTION:
[http://www.umass.edu/newsoffice/archive/2001/0605012mass.html]
An all-sky map of galaxies within about 500 million light years of Earth
made with the infrared-sensitive 2MASS telescopes. Each dot represents a
single galaxy. The disk of the Milky Way runs along the horizontal axis
of the map, and external galaxies are hidden here at visual wavelengths.
Two of the major concentrations of galaxies in the local universe, the
so-called Great Attractor region and the Pisces-Perseus supercluster are
partially hidden from us at visual wavelengths because of dust inthe Milky
Way.
