Posted on by Fraser Cain

Astronomers Map Dark Matter Halo

Image credit: Hubble

Two Canadian and a US astronomer have created a detailed map of the halo of dark matter that seems to surround all galaxies. The mass of dark matter accounts for 50 times the mass and five times the size of the light-producing material in a galaxy. This flattened sphere-shaped halo was seen by measuring how the gravity from a closer galaxy bends the light from a distant object that passes behind it; a technique called gravity lensing.

Two U of T astronomers and a U.S. colleague have made the first-ever measurements of the size and shape of massive dark matter halos that surround galaxies.

“Our findings give us the clearest picture yet of a very mysterious part of our universe,” says principal investigator Henk Hoekstra, a
post-doctoral fellow at U of T’s Canadian Institute for Theoretical Astrophysics. “Using relatively simple physics, we can get our first direct glimpse of the size and shape of these halos which are more than fifty times more massive than the light-producing part of galaxies that we can see.” He and his team presented their findings July 25 at the 25th general assembly of the International Astronomical Union in Sydney, Australia.

Their research indicates that dark matter halos extend more than five times further than the visible stars in a galaxy, says Hoekstra. In the case of our Milky Way galaxy, he says, the halo extends to more than 500,000 light-years away and weighs approximately 880 billion times more than the sun. The findings also provide strong support for the popular “cold dark matter” model of the universe.

Dark matter emits no light and, therefore, cannot be seen directly,
Hoekstra explains. The only evidence for its existence comes from its gravitational pull on stars, gas and light rays. Dark matter is believed to account for approximately 25 per cent of the total mass in the universe, with the rest of the universe composed of normal matter (five per cent) and dark energy (70 per cent).

To date, most information about dark matter has come from measurements of the motion of gas and stars in the inner regions of galaxies. Other important data have come from computer simulations of the formation of the universe’s structure. However, scientists can explain their findings about dark matter only if it is true that galaxies are surrounded by massive, three-dimensional halos.

The majority of astronomers believe in the so-called cold dark matter theory of the universe, which suggests these halos are slightly flattened. Hoekstra’s findings corroborate this. Using the relatively new technique of weak gravitational lensing which allows astronomers to study the size and shape of dark matter, the team measured the shapes of more than 1.5 million distant galaxies using the Canada-France-Hawaii Telescope in Hawaii. “The small changes in the shapes of the galaxies offered a strong indication to us that the halos are flattened, like a rubber ball compressed to half its size,” Hoekstra says.

Their findings can also be applied to a larger scientific debate about the nature of the universe. Some scientists have developed theories about the universe using the assumption that dark matter does not exist and, as a result, they have proposed changes to the law of gravity. However, Hoekstra is confident that his team’s findings will refute these theories.

The research was conducted with Professor Howard Yee of U of T’s Department of Astronomy and Astrophysics and Michael Gladders, a former U of T graduate student now at the Observatories of the Carnegie Institution of Washington in Pasadena, Calif. It was funded by the Natural Sciences and Engineering Research Council of Canada and U of T.

Original Source: University of Toronto News Release

Posted on by Fraser Cain

Pluto Mission Will Fly on an Atlas V

Image credit: NASA/JHU

The first robotic mission to launch to the planet Pluto will be on board an Atlas V rocket, according to NASA. The New Horizons mission, built by NASA, the Southwest Research Institute and Johns Hopkins University is scheduled to take off in January 2006 and wouldn’t reach the planet until 2015. New Horizons will take the first high-resolution photographs of Pluto, and help to answer key questions about its surface, atmosphere, and environment.

NASA has chosen the Atlas V expendable launch vehicle provided by Lockheed Martin Commercial Launch Services, Inc. as the launch system for the proposed Pluto New Horizons mission. The mission is scheduled for launch to Pluto in January 2006. As proposed, the Pluto New Horizons mission is a scientific investigation to obtain the first reconnaissance of Pluto-Charon, a binary planet system.

This will be a firm fixed-price launch service task order awarded under the terms of the current NASA Launch Services contract. The prime contractor will be Lockheed Martin Commercial Launch Services, Inc.; a constituent company of International Launch Services and legal contracting entity for Atlas launch services, located in McLean, Va.

New Horizons would seek to answer key scientific questions regarding the surfaces, atmospheres, interiors, and space environments of Pluto and Charon using imaging, visible and infrared spectral mapping, ultraviolet spectroscopy, radio science, and in-situ plasma sensors. The Principal Investigator is Dr. Alan Stern of the Southwest Research Institute, Boulder, Colo. The implementing institution is the Applied Physics Laboratory of The Johns Hopkins University, Laurel, Md. The proposed mission would use a spacecraft supplied Star 48B based 3rd Stage, manufactured by The Boeing Company of Huntington Beach, Calif., to achieve the required mission performance.

Original Source: NASA News Release

Posted on by Fraser Cain

NASA Names the Next Crew for the Space Station

Image credit: NASA

NASA has named the next crew who will live on board the International Space Station. This time it’s going to be astronaut Michael Foale and Russian cosmonaut Alexander Kaleri; both have significant spaceflight experience. Expedition 8 will launch on board a Russian Soyuz rocket on October 18 and dock two days later. Spanish astronaut Pedro Duque will also make the journey to the ISS, but then return 10 days later with the current ISS crew: Yuri Malenchenko and Ed Lu. ISS will continue to be staffed by two people until the space shuttle returns to regular flights.

Veteran NASA astronaut Michael Foale and seasoned Russian cosmonaut Alexander Kaleri are set to be the eighth crew to live aboard the International Space Station. They’re scheduled to begin their mission in October, when they launch into space aboard a Russian Soyuz spacecraft.

Foale will serve as the Expedition 8 Commander and NASA/International Space Station Science Officer. Kaleri will be the Soyuz Commander and Space Station Flight Engineer.

Their mission is scheduled to begin October 18, when the Russian Soyuz TMA-3 launches from the Baikonur Cosmodrome in Kazakhstan. European Space Agency (ESA) astronaut Pedro Duque, from Spain, will make the outbound trip with Foale and Kaleri as Flight Engineer and return home 10 days later.

On October 20, the three will dock their Soyuz to the Station and begin an eight-day transfer process with the Expedition 7 crew, Commander and Russian cosmonaut Yuri Malenchenko and Ed Lu, NASA/International Space Station Science Officer.

On October 28, Malenchenko, Lu and Duque will return to Earth aboard the Soyuz currently docked to the Station. Malenchenko and Lu have been aboard the Station since late April.

The backup crew for Expedition 8 is veteran NASA astronaut Bill McArthur, a retired U.S. Army colonel; Russian veteran cosmonaut Valery Tokarev, a Russian Air Force colonel; and Duque’s backup is ESA astronaut Andre Kuipers from the Netherlands.

Until the NASA Space Shuttle, with its significant cargo capability, returns to flight, the International Space Station will be staffed with a crew of two instead of three. The smaller crew is big enough to maintain operations on board the Station and small enough to live on a reduced supply of water and other consumables. Foale and Kaleri are scheduled to spend approximately six months on board the Station.

Foale is a veteran of five space flights totaling more than 178 days in space, including more than four months on the Russian Mir Space Station. Kaleri has flown on three previous missions to the Mir and has logged 416 days in space. October’s mission will be Duque’s second space flight, following his mission on the Shuttle Discovery (STS-95) in 1998.

Original Source: NASA News Release

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Planet Hunting Instrument Proven to Work

Image credit: NASA/JPL

Engineers at NASA’s Jet Propulsion Lab have built an instrument so sensitive it can measure distances within 1/10th the thickness of a hydrogen atom. This instrument will serve as the heart of NASA’s Space Interferometry Mission, which will be able to detect the interactions between Earth-sized planets and the stars they orbit. Due to launch in 2009, the spacecraft will also measure the distance to stars at an accuracy several hundred times better than currently possible.

Even though astronomers have discovered more than 100 planets around stars other than the Sun in recent years, the “holy grail” of the search — an Earth-sized planet capable of supporting life — remains elusive. The main problem is that an Earthlike planet would be much smaller than any of the gas giants detected so far (see illustration at right).

Planets orbiting other stars are too dim to be observed directly, but scientists infer their presence by the tiny gravitational “wobble” they induce in their parent stars. Observed from tens of light years away (one light-year is 5.88 trillion miles), this movement becomes very tiny indeed. The smaller the planet, the less the star parent wobbles.

To detect the stellar wobble caused by a planet as small as Earth, scientists need an instrument of almost unbelievable sensitivity. Let’s say there’s an astronaut standing on the moon, wiggling her pinky. You’d need an instrument sensitive enough to measure that movement from Earth, a quarter million miles away.

In order to do that, the instrument needs to be a “ruler” accurate to within just one-tenth the width of a hydrogen atom. That’s about 1 millionth of the width of the thickest human hair.

Is such precision possible? After a six-year struggle, engineers at the Jet Propulsion Laboratory recently proved that the answer is yes.

Such sub-atomic measurements were conducted for the first time ever within a vacuum-sealed chamber called the Microarcsecond Metrology Testbed.

By doing this, the engineers proved they can measure the movements of stars with an astonishing degree of accuracy never before achieved in human history.

The testbed, which resembles a shiny silver submarine, is jammed with mirrors, lasers, lenses and other optical components. Because even small air movements can interfere with the measurements, all air is pumped out of the chamber before each experiment is run. Laser beams, moving mirrors and a camera are used to help detect movements of an artificial star, which simulates the light that would be emitted by a real star.

The instrument that engineers have demonstrated in the laboratory will become the heart of a revolutionary new space telescope known as the Space Interferometry Mission.

“Six-and-a-half years ago, this technology was unproven and unsubstantiated,” said Brett Watterson, the mission’s deputy project manager. “It was just a remote possibility that we could do it. It was through ingenuity, insight, leadership and sheer perseverance that the team was able to overcome these difficult technological challenges.”

NASA recently gave the go-ahead for the second stage of development for the mission, which will not only be able to search for Earth-like planets around other stars, but will also measure cosmic distances several hundred times more accurately than currently possible. Scheduled to launch in 2009, it will scan the heavens for five years and provide astronomers with the first truly accurate road map of our Milky Way galaxy.

“This is a historical time that we’re intimately involved with,” Watterson said. “Unlike any other culture in history, we have the technological means, the budget, and the will to determine the occurrence of Earthlike planets orbiting other stars. Everyone on the team is aware of their role in this pivotal stage in the search for life elsewhere in the universe.”

The Space Interferometry Mission is managed by JPL as part of NASA’s Origins program.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Gravity Map Released

Image credit: NASA

The Gravity Recovery and Climate Experiment (Grace) mission has created the most accurate map of the Earth’s gravity field. The joint NASA-German Aerospace Center mission consists of two spacecraft connected by a cable which is able to measure fluctuations in the Earth’s gravity to a precision of a few centimetres. They found that the gravity field can fluctuate by as much as 200 metres around the world. This gravity map will give future water level measurements better accuracy, and help scientists better understand the slow redistribution of mass on the planet.

The joint NASA-German Aerospace Center Gravity Recovery and Climate Experiment (Grace) mission has released its first science product, the most accurate map yet of Earth’s gravity field. Grace is the newest tool for scientists working to unlock secrets of ocean circulation and its effects on climate.

Created from 111 days of selected Grace data, to help calibrate and validate the mission’s instruments, this preliminary model improves knowledge of the gravity field so much it is being released to oceanographers now, months in advance of the scheduled start of routine Grace science operations. The data are expected to significantly improve our ability to understand ocean circulation, which strongly influences weather and climate.

Dr. Byron Tapley, Grace principal investigator at UT’s Center for Space Research, called the new model a feast for oceanographers. “This initial model represents a major advancement in our knowledge of Earth’s gravity field. “Pre- Grace models contained such large errors many important features were obscured. Grace brings the true state of the oceans into much sharper focus, so we can better see ocean phenomena that have a strong impact on atmospheric weather patterns, fisheries and global climate change.”

Grace is accomplishing that goal by providing a more precise definition of Earth’s geoid, an imaginary surface defined only by Earth’s gravity field, upon which Earth’s ocean surfaces would lie if not disturbed by other forces such as ocean currents, winds and tides. The geoid height varies around the world by up to 200 meters (650 feet).

“I like to think of the geoid as science’s equivalent of a carpenter’s level, it tells us where horizontal is,” Tapley said. “Grace will tell us the geoid with centimeter-level precision.”

So why is knowing the geoid height so important? JPL’s Dr. Lee-Lueng Fu, scientist on Topex/Poseidon and Jason project said, “The ocean’s surface, while appearing flat, is actually covered with hills and valleys caused by currents, winds and tides, and also by variations in Earth’s gravity field. “Scientists want to separate out these gravitational effects, so they can improve the accuracy of satellite altimeters like Jason and Topex/Poseidon, which measure sea surface height, ocean heat storage and global ocean circulation. This will give us a better understanding of ocean circulation and how it affects climate.”

Dr. Michael Watkins, Grace project scientist at JPL, put improvements to Earth’s gravity model into perspective. “Scientists have studied Earth’s gravity for more than 30 years, using both satellite and ground measurements that were of uneven quality. “Using just a few months of our globally uniform quality Grace data, we’ve already improved the accuracy of Earth’s gravity model by a factor of between 10 and nearly 100, depending on the size of the gravity feature. In some locations, errors in geoid height based upon previous data were as much as 1 meter (3.3 feet). Now, we can reduce these errors to a centimeter (0.4 inches) in some instances. That’s progress.”

Dr. Christoph Reigber, Grace co-principal investigator at GeoForschungsZentrum Potsdam, said, “As we continue to assess and refine Grace’s instruments and subsystems, we’re confident future monthly gravity solutions will be even better than the map we’re releasing now. “Those solutions will allow us to investigate processes associated with slow redistribution of mass inside Earth and on its land, ocean and ice surfaces. Our initial attempts to identify such small gravity signals with Grace look very promising.”

Grace senses minute variations in gravitational pull from local changes in Earth’s mass by precisely measuring, to a tenth of the width of a human hair, changes in the separation of two identical spacecraft following the same orbit approximately 220 kilometers (137 miles) apart. Grace will map the variations from month to month, following changes imposed by the seasons, weather patterns and short-term climate change.

Original Source: University of Texas News Release

Posted on by Fraser Cain

Air Force Suspends Business With Boeing

Image credit: Boeing

The US Air Force announced its investigation findings today, that The Boeing Company had committed serious violation of federal law by using propriety documents from Lockheed Martin to win a series of launches during a 1998 contract competition. The Air Force said that Boeing will forfeit seven of its 19 launch contracts and several upcoming launch contracts will be awarded to Lockheed Martin instead of Boeing. All told, Boeing will lose $1 billion of Air Force launch business.

The Air Force announced today that it has determined that The Boeing Company has committed serious violations of federal law based on its review into allegations of wrongdoing by Boeing during the 1998 Evolved Expendable Launch Vehicle (EELV) source selection. As a result, the Air Force will suspend three Boeing Integrated Defense System business units and three former Boeing employees from eligibility for new government contracts. The suspensions are issued against The Boeing Company’s Launch Systems, Boeing Launch Services and Delta Program business units as they existed in the Boeing organizational structure as of July 21, 2003. This suspension will apply to these business units regardless of where they fall in any Boeing reorganization.

The individuals suspended are William David Erskine, former ground operations lead on Boeing’s EELV program; Kenneth V. Branch, former senior engineer/scientist on Boeing’s EELV program; and Larry Dean Satchell, a former member of Boeing’s EELV proposal team.

In addition, the Air Force will notify Boeing of its intent to reallocate launches under its existing EELV contract, which was awarded in October 1998 and is known as Buy I. Under this reallocation the Air Force will reduce the total number of Boeing Buy I Delta IV launches from 19 to 12. The Air Force will increase the total number of Lockheed Martin Buy I Atlas V launches from 7 to 14.

Further, the Air Force will permit Lockheed Martin to develop a west coast launch capability at Vandenberg AFB by upgrading an existing launch facility.

The Air Force also announced the results of its EELV Buy II decision. The Air Force disqualified Boeing from the award of three Buy II launches and plans to award Lockheed Martin three Buy II launches from Vandenberg AFB.

“Our inquiry into Boeing found that they were in possession of thousands of pages of Lockheed Martin proprietary EELV documents during the 1998 source selection,” said Under Secretary of the Air Force Peter B. Teets. “As a matter of policy we do not tolerate breaches of procurement integrity and we hold industry accountable for the actions of their employees. We believe the suspension is necessary and we hope all contractors will take note and strive to enforce the highest integrity standards in their organizations.”

The Boeing Delta IV and Lockheed Martin’s Atlas V are the two families of EELVs developed with the Air Force to modernize and reduce the cost of the nation’s spacelift operation while providing the United States with assured access to space.

Original Source: Air Force News Release

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Unlocking the Secrets of Dwarf Galaxies

Image credit: UCSC

A team of astronomers from the University of Cambridge have been researching a rare group of galaxies, known as dwarf spheroidal galaxies, which seem to have few stars but massive amounts of “dark matter”. The team analyzed one such galaxy and found that the stars in the outer edges were moving so quickly that the galaxy could only stay together if it had 100 times more dark matter than the mass of the stars alone. This research will help astronomers understand how galaxies are formed and how dark matter plays into their composition.

New research on dwarf spheroidal galaxies by a team of astronomers at the University of Cambridge promises a real astronomical first: detection, for the first time, of the true outer limits of a galaxy.

The team is presenting today (23 July 2003) at the 25th General Assembly of the International Astronomical Union (IAUXXV) in Sydney, Australia. The research could provide the key to understanding how larger galaxies were formed, including our own Milky Way galaxy.

The rare dwarf spheroidal galaxies display few stars but contain massive amounts of ‘dark matter’ or matter that does not emit radiation that can be observed by astronomers. The team studied these galaxies in detail using some of the largest optical telescopes on earth in order to probe their dark secrets. Dwarf spheroidal galaxies are widely believed to be the building blocks from which galaxies were formed.

By studying the motion of many stars the scientists have created a picture of how the mass of the galaxy is arranged. Surprisingly, when the Cambridge team looked at the stars at the edge of one such galaxy, Draco, they found that the outer stars were moving so quickly that the galaxy could only stay together if it contained 100 times more dark matter than the mass of the stars alone. Using detailed models of the motions of stars in a galaxy containing large quantities of dark matter, the group was able to demonstrate their observations could only be understood if the galaxy was surrounded by a large halo of dark matter.

Observations of the Ursa Minor dwarf spheroidal galaxy presented a new complication in the study. The team found an unexpected clump of slow-moving stars interpreted as the dead remains of one of the pure star systems, a globular cluster. The cluster should have been scattered across the galaxy, but it was still held together. The team realised this was only possible if the dark matter were arranged in a manner very differently from standard galaxies.

In May 2003, further research into Ursa Minor showed the stars in the very outermost parts are not moving quickly like the stars at the edge of Draco. Several theories are being investigated including dark matter from edge of Ursa Minor has been snatched away from the galaxy by its massive parent, the Milky Way, allowing some stars to wander gently away from their parent. Or they could be stars which wandered too close to other stars in the centre of the galaxy and were slung out to the edge of the galaxy as a result.

Whatever the explanation, the findings promise a real astronomical first: detection, for the first time, of the true outer limits of a galaxy.

Gerry Gilmore, Professor of Experimental Philosophy at the Institute of Astronomy at the University of Cambridge, said:

“This research, utilising some of the largest optical telescopes on earth, has provided us with insight to the makeup of these rare dwarf galaxies. This research helps astronomers better understand how galaxies were formed, and help take into account dark matter in all galaxies.”

Original Source: Cambridge University News Release

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Board Reveals Why the X-43A Failed

Image credit: NASA

A NASA investigation board released its findings on Wednesday that revealed why the X-34A Hyper-X prototype failed during a test on June 2, 2001. The investigators found that various miscalculations built into the prototype collectively caused the mishap. The X-34A is an experimental program to develop an air breathing hypersonic aircraft that could eventually fly up to 10 times the speed of sound. The X-34A was attached to the front of a Pegasus rocket and launched from a modified B-52 bomber. Only 13 seconds into its flight the aircraft went out of control, and was destroyed.

The NASA mishap investigation board, charged to review the loss of the X-43A Hyper-X program research vehicle during its June 2, 2001 launch, concluded no single factor or potential contributing factor caused the mishap. The flight failed because the vehicle’s control system design was deficient in several analytical modeling areas, which overestimated the system’s margins.

NASA’s Hyper-X program is developing “air breathing” engine technologies that promise performance benefits for future hypersonic aircraft and reusable space launch vehicles. In the X-43A test program, three, 12-foot long, unpiloted vehicles were planned to fly up to 10 times the speed of sound to demonstrate scramjet, or supersonic-combustion ramjet, technologies. The mishap occurred on the first of three planned flights.

For the launch, the X-43A was attached to the nose of a modified Pegasus launch vehicle, which was carried by NASA’s modified B-52 bomber. Seventy-five minutes after takeoff, at an altitude of approximately 24,000 ft., the Pegasus was released. Its solid rocket motor ignited 5.2 seconds later sending the launch vehicle and research vehicle payload on its test flight. Eight seconds later, the vehicle began its planned pitch up maneuver, which was expected to take it to an altitude of approximately 95,000 ft.

Shortly thereafter, the X-43A began to experience a control anomaly characterized by a roll oscillation. At 13.5 seconds after release and at an altitude of approximately 22,000 ft., structural overload of the starboard elevon occurred. The severe loss of control caused the X-43A to deviate significantly from its planned trajectory, and as a result, it was destroyed by range safety 48.6 seconds after release.

The mishap board found the major contributors to the mishap were modeling inaccuracies in the fin actuation system, modeling inaccuracies in the aerodynamics, and insufficient variations of modeling parameters. The flight mishap could only be reproduced when all of the modeling inaccuracies with uncertainty variations were incorporated in the analysis.

“I want to thank the Mishap Investigation Board for their comprehensive and thorough evaluation,” said Dr. Victor Lebacqz, acting Associate Administrator for NASA’s Office of Aerospace Technology. “The findings and recommendations of the board greatly enhance our opportunity for a successful second flight,” he said.

Original Source: NASA News Release

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100 Days Until Chinese Space Launch?

The Chinese attempt to launch humans into space might only be 100 days away according to industry insiders. Rumors say that space officials have chosen which astronaut will pilot the mission, Shenzhou-5, but his identity hasn’t been revealed to the public yet. Fourteen astronauts have been in training at the Beijing Aerospace city for many months, but so far all of their identities have been kept secret. The Chinese Space Agency is notorious for secrecy, waiting until after spacecraft have launched before revealing details to the public.

Posted on by Fraser Cain

Further Evidence Found for Dark Energy

Image credit: SDSS

Since the discovery several years ago of a mysterious force, called dark energy, which seems to be accelerating the Universe, astronomers have been searching for additional evidence to either support or discount this theory. Astronomers from the Sloan Digital Sky Survey have found fluctuations in cosmic background radiation that match the repulsive influence of dark energy.

Scientists from the Sloan Digital Sky Survey announced the discovery of independent physical evidence for the existence of dark energy.

The researchers found an imprint of dark energy by correlating millions of galaxies in the Sloan Digital Sky Survey (SDSS) and cosmic microwave background temperature maps from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP). The researchers found dark energy’s “shadow” on the ancient cosmic radiation, a relic of cooled radiation from the Big Bang.

With the combination of results from these two large sky surveys, this discovery provides physical evidence for the existence of dark energy; a result that complements earlier work on the acceleration of the universe as measured from distant supernovae. Observations from the Balloon Observations of Millimetric Extragalactic Radiation and Geophysics (BOOMERANG) of Cosmic Microwave Background (CMB) were also part of the earlier findings.

Dark energy, a major component of the universe and one of the greatest conundrums in science, is gravitationally repulsive rather than attractive. This causes the universe’s expansion to accelerate, in contrast to the attraction of ordinary (and dark) matter, which would make it decelerate.

“In a flat universe the effect we’re observing only occurs if you have a universe with dark energy,” explained lead researcher Dr. Ryan Scranton of the University of Pittsburgh’s Physics and Astronomy department. “If the universe was just composed of matter and still flat, this effect wouldn’t exist.”

“As photons from the cosmic microwave background (CMB) travel to us from 380,000 years after the Big Bang, they can experience a number of physical processes, including the Integrated Sachs-Wolfe effect. This effect is an imprint or shadow of dark energy on microwaves. The effect also measures the changes in temperature of cosmic microwave background due to the effects of gravity on the energy of photons”, added Scranton.

The discovery is “a physical detection of dark energy, and highly complementary to other detections of dark energy” added Dr. Bob Nichol, an SDSS collaborator and associate professor of physics at Carnegie Mellon University in Pittsburgh. Nichol likened the Integrated Sachs-Wolfe effect to looking at a person standing in front of a sunny window: “You just see their outline and can recognize them from just this information. Likewise the signal we see has the right outline (or shadow) that we’d expect for dark energy,” said Nichol.

“In particular the color of the signal is the same as the color of the cosmic microwave background, proving it is cosmological in origin and not some annoying contamination,” added Nichol.

“This work provides physical confirmation that one needs dark energy to simultaneously explain both the CMB and SDSS data, independent of the supernovae work. Such cross-checks are vital in science,” added Jim Gunn, Project Scientist of the SDSS and Professor of Astronomy at Princeton University.

Dr. Andrew Connolly of the University of Pittsburgh explained that photons streaming from the cosmic microwave background pass through many concentrations of galaxies and dark matter. As they fall into a gravitational well they gain energy (just like a ball rolling down a hill). As they come out they lose energy (again like a ball rolling up a hill). Photographic images of the microwaves become more blue (i.e. more energetic) as they fall in toward these supercluster concentrations and then become more red (i.e. less energetic) as they climb away from them.

“In a universe consisting mostly of normal matter one would expect that the net effect of the red and blue shifts would cancel. However in recent years we are finding that most of the stuff in our universe is abnormal in that it is gravitationally repulsive rather than gravitationally attractive,” explained Albert Stebbins, a scientist at the NASA/Fermilab Astrophysics Center Fermi National Accelerator Laboratory, an SDSS collaborating institution. “This abnormal stuff we call dark energy.”

SDSS collaborator Connolly said if the depth of the gravitational well decreases while the photon travels through it then the photon would exit with slightly more energy. “If this were true then we would expect to see that the cosmic microwave background temperature is slightly hotter in regions with more galaxies. This is exactly what we found.”

Stebbins added that the net energy change expected from a single concentration of mass is less than one part in a million and researchers had to look at a large number of galaxies before they could expect to see the effect. He said that the results confirm that dark energy exists in relatively small mass concentrations: only 100 million light years across where the previously observed effects dark energy were on a scale of 10 billion light years across. A unique aspect of the SDSS data is its ability to accurately measure the distances to all galaxies from photographic analysis of their photometric redshifts. “Therefore, we can watch the imprint of this effect on the CMB grow as a function of the age of the universe,” Connolly said. “Eventually we might be able to determine the nature of the dark energy from measurements like these, though that is a bit in the future.”

“To make the conclusion that dark energy exists we only have to assume that the universe is not curved. After the Wilkinson Microwave Anisotropy Probe results came in (in February, 2003), that’s a well-accepted assumption,” Scranton explained. “This is extremely exciting. We didn’t know if we could get a signal so we spent a lot of time testing the data against contamination from our galaxy or other sources. Having the results come out as strongly as they did was extremely satisfying.”

The discoveries were made in 3,400 square degrees of the sky surveyed by the SDSS.

“This combination of space-based microwave and ground-based optical data gave us this new window into the properties of dark energy,” said David Spergel, a Princeton University cosmologist and a member of the WMAP science team. “By combining WMAP and SDSS data, Scranton and his collaborators have shown that dark energy, whatever it is, is something that is not attracted by gravity even on the large scales probed by the Sloan Digital Sky Survey.

“This is an important hint for physicists trying to understand the mysterious dark energy,” Spergel added.

In addition to principal investigators Scranton, Connolly, Nichol and Stebbins, Istavan Szapudi of the University of Hawaii contributed to the research. Others involved in the analysis include Niayesh Afshordi of Princeton University, Max Tegmark of the University of Pennsylvania and Daniel Eisenstein of the University of Arizona.

ABOUT THE SLOAN DIGITAL SKY SURVEY (SDSS)
The Sloan Digital Sky Survey (sdss.org) will map in detail one-quarter of the entire sky, determining the positions and absolute brightness of 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars. The Astrophysical Research Consortium (ARC) operates Apache Point Observatory, site of the SDSS telescopes.

SDSS is a joint project of The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.

Funding for the project has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho and the Max Planck Society.

The WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) is a NASA mission built in partnership with Princeton University and the Goddard Space Flight Center to measure the temperature of the cosmic background radiation, the remnant heat from the Big Bang. The WMAP mission reveals conditions as they existed in the early universe by measuring the properties of the cosmic microwave background radiation over the full sky. (http://map.gsfc.nasa.gov)

Original Source: SDSS News Release