NASA, ESA JOIN TOGETHER TO STUDY THE DARK SIDE

Astronomers using NASA's Hubble Space Telescope took advantage of a giant cosmic magnifying glass to create one of the sharpest and most detailed maps of dark matter in the universe. Dark matter is an invisible and unknown substance that makes up the bulk of the universe's mass. Credit: NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

FROM: NASA
NASA Joins ESA's 'Dark Universe' Mission

WASHINGTON -- NASA has joined the European Space Agency's (ESA's) Euclid mission, a space telescope designed to investigate the cosmological mysteries of dark matter and dark energy.

Euclid will launch in 2020 and spend six years mapping the locations and measuring the shapes of as many as 2 billion galaxies spread over more than one-third of the sky. It will study the evolution of our universe, and the dark matter and dark energy that influence its evolution in ways that still are poorly understood.

The telescope will launch to an orbit around the sun-Earth Lagrange point L2. The Lagrange point is a location where the gravitational pull of two large masses, the sun and Earth in this case, precisely equals the force required for a small object, such as the Euclid spacecraft, to maintain a relatively stationary position behind Earth as seen from the sun.

"NASA is very proud to contribute to ESA's mission to understand one of the greatest science mysteries of our time," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate at the agency's Headquarters in Washington.

NASA and ESA recently signed an agreement outlining NASA's role in the project. NASA will contribute 16 state-of-the-art infrared detectors and four spare detectors for one of two science instruments planned for Euclid.

"ESA’s Euclid mission is designed to probe one of the most fundamental questions in modern cosmology, and we welcome NASA’s contribution to this important endeavor, the most recent in a long history of cooperation in space science between our two agencies," said Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

In addition, NASA has nominated three U.S. science teams totaling 40 new members for the Euclid Consortium. This is in addition to 14 U.S. scientists already supporting the mission. The Euclid Consortium is an international body of 1,000 members who will oversee development of the instruments, manage science operations, and analyze data.

Euclid will map the dark matter in the universe. Matter as we know it -- the atoms that make up the human body, for example -- is a fraction of the total matter in the universe. The rest, about 85 percent, is dark matter consisting of particles of an unknown type. Dark matter first was postulated in 1932, but still has not been detected directly. It is called dark matter because it does not interact with light. Dark matter interacts with ordinary matter through gravity and binds galaxies together like an invisible glue.

While dark matter pulls matter together, dark energy pushes the universe apart at ever-increasing speeds. In terms of the total mass-energy content of the universe, dark energy dominates. Even less is known about dark energy than dark matter.

Euclid will use two techniques to study the dark universe, both involving precise measurements of galaxies billions of light-years away. The observations will yield the best measurements yet of how the acceleration of the universe has changed over time, providing new clues about the evolution and fate of the cosmos.

Euclid is an ESA mission with science instruments provided by a consortia of European institutes and with important participation from NASA. NASA's Euclid Project Office is based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. JPL will contribute the infrared flight detectors for the Euclid science instrument. NASA's Goddard Space Flight Center in Greenbelt, Md., will test the infrared flight detectors prior to delivery. Three U.S. science teams will contribute to science planning and data analysis.

SPACEDOCK

FROM:  NASA
Astronaut Ron Garan took this image during the spacewalk conducted on Tues., July 12, 2011. It shows the International Space Station with Space Shuttle Atlantis docked on the right and a Russian Soyuz on the far left. In the foreground is the Alpha Magnetic Spectrometer (AMS) experiment installed during the STS-134 mission.


AMS is a state-of-the-art particle physics detector designed to use the unique environment of space to advance knowledge of the universe and lead to the understanding of the universe's origin by searching for antimatter and dark matter, and measuring cosmic rays.

Image Credit: NASA

HISTORY OF UNDERSTANDING THE AGE OF THE UNIVERSE

FROM: NASA

Astronomers determine properties of the universe by fitting the WMAP data with models. Values for when the first stars appear, the amount of dark matter, the age of the universe etc. are adjusted in the model until the resulting background matches the WMAP observations. The model that best fits the data gives an age for the universe of 13.7 ± 0.2 billion years.
　

Early estimates of the Age of the Universe

In the 1920's Edwin Hubble discovered the expansion of the universe. He found that galaxies which are further away are moving at a higher speed following the law, v=Hd, where v is the velocity in km/s, d is the distance in Mpc, and H is the Hubble constant in km/s/Mpc. By independently measuring the velocity and distances to galaxies, the value of H could be determined. Astronomers further determined that the age of the universe is related to Hubble's constant, and that it is between 1/H and 2/3H depending on cosmological models adopted. The velocity could be determined via the redshift in the spectrum. The distance to the galaxy can be determined using observations of certain types of pulsating stars, called Cepheids, whose instrinsic brightness is related to the period of their brightness variation. However, the accuracy of the distance measurement was hampered by how faint ground based telescopes could see. Up until the 1990's, the best estimates for H were between 50 km/s/Mpc and 90 km/s/Mpc, giving a range on the age of the universe between 7 and 20 billion years.

Enter the Hubble Space Telescope

So in 1993, the orbiting Hubble Space Telescope began a "key project" to obtain distances to the Cepheids in 18 galaxies. Astronomers were able to obtain for the first time more precise distances, and a more accurate value of H. In 1999 after several years of observations with HST astronomers were able to estimate H to be 71 km/s/Mpc within 10% uncertainty, one of the greatest achievements of modern astronomy. Extrapolating back to the Big Bang, that value of H implied an age between 9 and 14 billion years old.

A New Approach using WMAP

In February 2003, the WMAP project released an all-sky map of the radiation emitted before there were any stars. This cosmic microwave background radiation (CMB) is the remnant heat from the Big-Bang and was predicted already in 1946 by George Gamow and Robert Dicke. Since then, astronomers have tried to detect and interpret the CMB. The first detection of the CMB was found in 1965 by chance by Arno Penzias and Robert Woodrow Wilson using a radiometer built to detect astronomical radio signals. They found an excess in their measurements which was later interpreted as the CMB, a 2.725 kelvin thermal spectrum of black body radiation that fills the universe. In 1992, the satellite Cosmic Background Explorer (COBE) which was designed to map the CMB showed for the first time large scale fluctuations in the CMB. These fluctuations were interpreted as evidences of what later formed clusters of galaxies and voids. However, only WMAP had the resolution and sensitivity to detect tiny fluctuations and constrain the age of the universe with high precision. The WMAP team's results are based on the underlying model used to fit their data. This model assumes that 70% of the energy of the present universe is in the form of dark energy, 26% of the energy is in the form of cold (not thermalized) dark matter, and the remaining 4% of the energy is in the atoms and photons. According to their estimates the universe is 13.7 billion years old with an uncertainty of 200 million years. The WMAP value of H is 71 ± 4 km/s/Mpc which is in agreement with the HST key project.

Another approach

Another way of obtaining the age of the universe is by dating stars. Some of the oldest stars live inside globular clusters and their ages have been extensively estimated in the past decade. For a while, astronomers were puzzled by the fact that those stars seemed to be a few billion years older than the age of the universe estimated from the Hubble constant. Is there a problem with H
or with the cluster's age? It turned out that age dating of globular clusters stars is very tricky and inaccurate distances to the clusters, as well caveats in stellar evolution, can solve the mystery. The age of clusters is proportional to one over the luminosity of the RR Lyra stars which are used to determine the distances to globular clusters. Therefore, accurate distances were needed and could only be obtained after the European Hipparcos satellite in the mid-90s. By using the new distance estimates, the age of the clusters fell from 15 billion years to 11.5 billion years with an uncertainty of about 1 billion year. These results agree with the age of the universe from both the Hubble constant and WMAP.
 
_{Publication Date: May 2006
NOTE: ABOVE "H" SHOULD BE "Ho."}

DARK MATTER IN GALAXY CLUSTER ABELL 383

The photo and following excerpt are from the NASA website: 
Two teams of astronomers have used data from NASA's Chandra X-ray Observatory and other telescopes to map the distribution of dark matter in a galaxy cluster known as Abell 383, which is located about 2.3 billion light years from Earth. Not only were the researchers able to find where the dark matter lies in the two dimensions across the sky, they were also able to determine how the dark matter is distributed along the line of sight.

Dark matter is invisible material that does not emit or absorb any type of light, but is detectable through its gravitational effects. Several lines of evidence indicate that there is about six times as much dark matter as "normal," or baryonic, matter in the Universe. Understanding the nature of this mysterious matter is one of the outstanding problems in astrophysics.

Galaxy clusters are the largest gravitationally-bound structures in the universe, and play an important role in research on dark matter and cosmology, the study of the structure and evolution of the universe. The use of clusters as dark matter and cosmological probes hinges on scientists' ability to use objects such as Abell 383 to accurately determine the three-dimensional structures and masses of clusters.

The recent work on Abell 383 provides one of the most detailed 3-D pictures yet taken of dark matter in a galaxy cluster. Both teams have found that the dark matter is stretched out like a gigantic football, rather than being spherical like a basketball, and that the point of the football is aligned close to the line of sight.

The X-ray data (purple) from Chandra in the composite image show the hot gas, which is by far the dominant type of normal matter in the cluster. Galaxies are shown with the optical data from the Hubble Space Telescope (HST), the Very Large Telescope, and the Sloan Digital Sky Survey, colored in blue and white.

Both teams combined the X-ray observations of the "normal matter" in the cluster with gravitational lensing information determined from optical data. Gravitational lensing -- an effect predicted by Albert Einstein -- causes the material in the galaxy cluster, both normal and dark matter, to bend and distort the optical light from background galaxies. The distortion is severe in some parts of the image, producing an arc-like appearance for some of the galaxies. In other parts of the image the distortion is subtle and statistical analysis is used to study the distortion effects and probe the dark matter.

A considerable amount of effort has gone into studying the center of galaxy clusters, where the dark matter has the highest concentration and important clues about its behavior might be revealed. Both of the Abell 383 studies reported here continue that effort.

The team of Andrea Morandi from Tel Aviv University in Israel and Marceau Limousin from Université de Provence in France and University of Copenhagen in Denmark concluded that the increased concentration of the dark matter toward the center of the cluster is in agreement with most theoretical simulations. Their lensing data came from HST images.

The team led by Andrew Newman of the California Institute of Technology and Tommaso Treu of University of California, Santa Barbara (UCSB) used lensing data from HST and the Japanese telescope Subaru, but added Keck observations to measure the velocities of stars in the galaxy in the center of the cluster, allowing for a direct estimate of the amount of matter there. They found evidence that the amount of dark matter is not peaked as dramatically toward the center as the standard cold dark matter model predicts. Their paper describes this as being the "most robust case yet" made for such a discrepancy with theory.

The contrasting conclusions reached by the two teams most likely stem from differences in the data sets and the detailed mathematical modeling used. One important difference is that because the Newman et al. team used velocity information in the central galaxy, they were able to estimate the density of dark matter at distances that approached as close as only 6,500 light years from the center of the cluster. Morandi and Limousin did not use velocity data and their density estimates were unable to approach as close to the cluster's center, reaching to within 80,000 light years.

Another important difference is that Morandi and Limousin used a more detailed model for the 3-D map of dark matter in the cluster. For example, they were able to estimate the orientation of the dark matter "football" in space and show that it is mostly edge-on, although slightly tilted with respect to the line of sight.

As is often the case with cutting-edge and complex results, further work will be needed to resolve the discrepancy between the two teams. In view of the importance of resolving the dark matter mystery, there will undoubtedly be much more research into Abell 383 and other objects like it in the months and years to come.

If the relative lack of dark matter in the center of Abell 383 is confirmed, it may show that improvements need to be made in our understanding of how normal matter behaves in the center of galaxy clusters, or it may show that dark matter particles can interact with each other, contrary to the prevailing model.

The Newman et al. paper was published in the February 20, 2011 issue of the Astrophysical Journal Letter and the Morandi and Limousin paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society. Other members of the Newman et al. team were Richard Ellis from Caltech, and David Sand from Las Cumbres Global Telescope Network and UCSB.

Credits: X-ray: NASA/CXC/Caltech/A.Newman et al/Tel Aviv/A.Morandi & M.Limousin; Optical: NASA/STScI, ESO/VLT, SDSS

DARK MATTER CORE DEFIES EXPLANATION IN NASA HUBBLE IMAGE

The following excerpt is from the NASA website:

"WASHINGTON -- Astronomers using data from NASA's Hubble Telescope have
observed what appears to be a clump of dark matter left behind from a
wreck between massive clusters of galaxies. The result could
challenge current theories about dark matter that predict galaxies
should be anchored to the invisible substance even during the shock
of a collision.

Abell 520 is a gigantic merger of galaxy clusters located 2.4 billion
light-years away. Dark matter is not visible, although its presence
and distribution is found indirectly through its effects. Dark matter
can act like a magnifying glass, bending and distorting light from
galaxies and clusters behind it. Astronomers can use this effect,
called gravitational lensing, to infer the presence of dark matter in
massive galaxy clusters.

This technique revealed the dark matter in Abell 520 had collected
into a "dark core," containing far fewer galaxies than would be
expected if the dark matter and galaxies were anchored together. Most
of the galaxies apparently have sailed far away from the collision.
"This result is a puzzle," said astronomer James Jee of the University
of California in Davis, lead author of paper about the results
available online in The Astrophysical Journal. "Dark matter is not
behaving as predicted, and it's not obviously clear what is going on.
It is difficult to explain this Hubble observation with the current
theories of galaxy formation and dark matter."

Initial detections of dark matter in the cluster, made in 2007, were
so unusual that astronomers shrugged them off as unreal, because of
poor data. New results from NASA's Hubble Space Telescope confirm
that dark matter and galaxies separated in Abell 520.

One way to study the overall properties of dark matter is by analyzing
collisions between galaxy clusters, the largest structures in the
universe. When galaxy clusters crash, astronomers expect galaxies to
tag along with the dark matter, like a dog on a leash. Clouds of hot,
X-ray emitting intergalactic gas, however, plow into one another,
slow down, and lag behind the impact.

That theory was supported by visible-light and X-ray observations of a
colossal collision between two galaxy clusters called the Bullet
Cluster. The galactic grouping has become an example of how dark
matter should behave.

Studies of Abell 520 showed that dark matter's behavior may not be so
simple. Using the original observations, astronomers found the
system's core was rich in dark matter and hot gas, but contained no
luminous galaxies, which normally would be seen in the same location
as the dark matter. NASA's Chandra X-ray Observatory was used to
detect the hot gas. Astronomers used the Canada-France-Hawaii
Telescope and Subaru Telescope atop Mauna Kea to infer the location
of dark matter by measuring the gravitationally lensed light from
more distant background galaxies.

The astronomers then turned to the Hubble's Wide Field Planetary
Camera 2, which can detect subtle distortions in the images of
background galaxies and use this information to map dark matter. To
astronomers' surprise, the Hubble observations helped confirm the
2007 findings.

"We know of maybe six examples of high-speed galaxy cluster collisions
where the dark matter has been mapped," Jee said. "But the Bullet
Cluster and Abell 520 are the two that show the clearest evidence of
recent mergers, and they are inconsistent with each other. No single
theory explains the different behavior of dark matter in those two
collisions. We need more examples."

The team proposed numerous explanations for the findings, but each is
unsettling for astronomers. In one scenario, which would have
staggering implications, some dark matter may be what astronomers
call "sticky." Like two snowballs smashing together, normal matter
slams together during a collision and slows down. However, dark
matter blobs are thought to pass through each other during an
encounter without slowing down. This scenario proposes that some dark
matter interacts with itself and stays behind during an encounter.

Another possible explanation for the discrepancy is that Abell 520 has
resulted from a more complicated interaction than the Bullet Cluster
encounter. Abell 520 may have formed from a collision between three
galaxy clusters, instead of just two colliding systems in the case of
the Bullet Cluster.

A third possibility is that the core contained many galaxies, but they
were too dim to be seen, even by Hubble. Those galaxies would have to
have formed dramatically fewer stars than other normal galaxies.
Armed with the Hubble data, the group will try to create a computer
simulation to reconstruct the collision and see if it yields some
answers to dark matter's weird behavior.

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. NASA's Goddard Space
Flight Center in Greenbelt, Md., manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore, Md., conducts
Hubble science operations. STScI is operated by the Association of
Universities for Research in Astronomy, Inc., in Washington, D.C."

COMPOSITE PICTURE SHOWS DARK MATTER DISTRIBUTION ACROSS GALAXIES

The following excerpt and picture are from the NASA:


"This composite image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520, formed from a violent collision of massive galaxy clusters. The natural-color image of the galaxies was taken with NASA's Hubble Space Telescope and with the Canada-France-Hawaii Telescope in Hawaii. Superimposed on the image are "false-colored" maps showing the concentration of starlight, hot gas, and dark matter in the cluster. Starlight from galaxies, derived from observations by the Canada-France-Hawaii Telescope, is colored orange. The green-tinted regions show hot gas, as detected by NASA's Chandra X-ray Observatory. The gas is evidence that a collision took place. The blue-colored areas pinpoint the location of most of the mass in the cluster, which is dominated by dark matter. Dark matter is an invisible substance that makes up most of the universe's mass. The dark-matter map was derived from the Hubble Wide Field Planetary Camera 2 observations by detecting how light from distant objects is distorted by the cluster of galaxies, an effect called gravitational lensing. The blend of blue and green in the center of the image reveals that a clump of dark matter resides near most of the hot gas, where very few galaxies are found. This finding confirms previous observations of a dark-matter core in the cluster. The result could present a challenge to basic theories of dark matter, which predict that galaxies should be anchored to dark matter, even during the shock of a collision. Abell 520 resides 2.4 billion light-years away. Image Credit: NASA, ESA, CFHT, CXO, M.J. Jee (University of California, Davis), and A. Mahdavi (San Francisco State University)"