The Cold Spot area resides in the constellation
Eridanus in the southern galactic hemisphere. The insets show the
environment of this anomalous patch of the sky as mapped by Szapudi’s
team using PS1 and WISE data and as observed in the cosmic microwave
background temperature data taken by the Planck satellite. The angular
diameter of the vast supervoid aligned with the Cold Spot, which exceeds
30 degrees, is marked by the white circles. Graphics by Gergő Kránicz.
Image credit: ESA Planck Collaboration. High-resolution version (6.6 Mb)
Synopsis: A very large cold spot that has been a mystery for over a decade can now be explained
In 2004, astronomers examining a map of the radiation leftover from
the Big Bang (the cosmic microwave background, or CMB) discovered the
Cold Spot, a larger-than-expected unusually cold area of the sky. The
physics surrounding the Big Bang theory predicts warmer and cooler spots
of various sizes in the infant universe, but a spot this large and this
cold was unexpected.
Now, a team of astronomers led by Dr. István
Szapudi of the Institute for Astronomy at the University of Hawaii at
Manoa may have found an explanation for the existence of the Cold Spot,
which Szapudi says may be “the largest individual structure ever
identified by humanity.”
If the Cold Spot originated from the Big Bang itself, it could be a
rare sign of exotic physics that the standard cosmology (basically, the
Big Bang theory and related physics) does not explain. If, however, it
is caused by a foreground structure between us and the CMB, it would be a
sign that there is an extremely rare large-scale structure in the mass
distribution of the universe.
Using data from Hawaii’s Pan-STARRS1 (PS1)
telescope located on Haleakala, Maui, and NASA’s Wide Field Survey
Explorer (WISE) satellite, Szapudi’s team discovered a large supervoid, a
vast region 1.8 billion light-years across, in which the density of
galaxies is much lower than usual in the known universe. This void was
found by combining observations taken by PS1 at optical wavelengths with
observations taken by WISE at infrared wavelengths to estimate the
distance to and position of each galaxy in that part of the sky.
Earlier studies, also done in Hawaii, observed a
much smaller area in the direction of the Cold Spot, but they could
establish only that no very distant structure is in that part of the
sky. Paradoxically, identifying nearby large structures is harder than
finding distant ones, since we must map larger portions of the sky to
see the closer structures. The large three-dimensional sky maps created
from PS1 and WISE by Dr. András Kovács (Eötvös Loránd University,
Budapest, Hungary) were thus essential for this study. The supervoid is
only about 3 billion light-years away from us, a relatively short
distance in the cosmic scheme of things.
Imagine there is a huge void with very little
matter between you (the observer) and the CMB. Now think of the void as a
hill. As the light enters the void, it must climb this hill. If the
universe were not undergoing accelerating expansion, then the void would
not evolve significantly, and light would descend the hill and regain
the energy it lost as it exits the void. But with the accelerating
expansion, the hill is measurably stretched as the light is traveling
over it. By the time the light descends the hill, the hill has gotten
flatter than when the light entered, so the light cannot pick up all the
energy it lost upon entering the void. The light exits the void with
less energy, and therefore at a longer wavelength, which corresponds to a
colder temperature.
Getting through a supervoid can take millions of
years, even at the speed of light, so this measurable effect, known as
the Integrated Sachs-Wolfe (ISW) effect, might provide the first
explanation one of the most significant anomalies found to date in the
CMB, first by a NASA satellite called the Wilkinson Microwave Anisotropy
Probe (WMAP), and more recently, by Planck, a satellite launched by the
European Space Agency.
While the existence of the supervoid and its
expected effect on the CMB do not fully explain the Cold Spot, it is
very unlikely that the supervoid and the Cold Spot at the same location
are a coincidence. The team will continue its work using improved data
from PS1 and from the Dark Energy Survey
being conducted with a telescope in Chile to study the Cold Spot and
supervoid, as well as another large void located near the constellation
Draco.
The study is being published online on April 20 in Monthly Notices of the Royal Astronomical Society
by the Oxford University Press. In addition to Szapudi and Kovács,
researchers who contributed to this study include UH Manoa alumnus
Benjamin Granett (now at the National Institute for Astrophysics,
Italy), Zsolt Frei (Eötvös Loránd), and Joseph Silk (Johns Hopkins).
Contacts:
Dr. István Szapudi+1 808 956-6196
szapudi@ifa.hawaii.edu
Dr. András Kovács
+34 93 176 3966
akovacs@ifae.es
Dr. Roy Gal
+1 808-956-6235
cell: +1 301-728-8637
rgal@ifa.hawaii.edu
Ms. Louise Good
Media Contact
+1 808-381-2939
good@ifa.hawaii.edu
Source: Institute for Astronomy - University of Hawaii
Note:
Note:
Founded in 1967, the Institute for Astronomy at the University of
Hawaii at Manoa conducts
research into galaxies, cosmology, stars, planets, and the
sun. Its faculty and staff are also involved in astronomy
education,
deep space missions, and in the development and management
of the observatories on Haleakala and Maunakea. The
Institute operates facilities on the islands of Oahu, Maui, and Hawaii.
The Pan-STARRS1 Surveys (PS1) have been made possible
through contributions by the Institute for Astronomy, the University of
Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its
participating institutes, the Max Planck Institute for Astronomy,
Heidelberg and the Max Planck Institute for Extraterrestrial Physics,
Garching, The Johns Hopkins University, Durham University, the
University of Edinburgh, the Queen's University Belfast, the
Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory
Global Telescope Network Incorporated, the National Central University
of Taiwan, the Space Telescope Science Institute, and the National
Aeronautics and Space Administration under Grant No. NNX08AR22G issued
through the Planetary Science Division of the NASA Science Mission
Directorate, the National Science Foundation Grant No. AST-1238877, the
University of Maryland, Eötvös Loránd University (ELTE), and the Los
Alamos National Laboratory.