What Is Dark Energy? 'Beyond Einstein' Program Aims To Investigate

Source:

http://www.sciencedaily.com/releases/2007/09/070906140741.htm

Science Daily — NASA and the U.S. Department of Energy should pursue the Joint Dark Energy Mission (JDEM) as the first mission in the "Beyond Einstein" program, according to a new report from the National Research Council.

Beyond Einstein is NASA's research roadmap for five proposed mission areas to study the most compelling questions at the intersection of physics and astronomy.
The committee that wrote the report added that another proposed mission to detect gravitational waves using the Laser Interferometer Space Antenna (LISA) should eventually become the flagship mission of Beyond Einstein, given that it is likely to provide an entirely new way to observe the universe. However, LISA needs more testing before a launch can be planned, whereas the Joint Dark Energy Mission is ready now for a competitive selection of mission concept proposals.
Prompted by Congress and the Office of Science and Technology Policy, NASA and DOE asked the committee to assess the five proposed mission areas and recommend one for first development and launch. NASA's Beyond Einstein program, set to begin in 2009, is comprised of two astronomical observatories, Constellation-X and LISA, as well as a series of probes: the Inflation Probe (IP), the Black Hole Finder Probe (BHFP), and JDEM.
"All of the mission areas in the Beyond Einstein program have the potential to fundamentally alter our understanding of the universe," said committee co-chair Charles F. Kennel, distinguished professor and director of the Environment and Sustainability Initiative at the University of California, San Diego. "But JDEM will provide direct insight into a key Beyond Einstein science question, and is the most technically feasible option for immediate development."
Of particular interest to researchers is whether the acceleration of the expansion of the universe varies over time. So far, three specific mission plans have been studied in this area: the Supernova Acceleration Probe (SNAP), the Dark Energy Space Telescope (DESTINY), and the Advanced Dark Energy Physics Telescope (ADEPT), but the eventual JDEM could be any one of the three or be based on a different option altogether.
The committee found that the underlying technology for a dark energy mission is, for the most part, in the prototype phase, and will require less development than most of the other missions. The potential gains for JDEM also outweigh its scientific risks, such as the possibility that the mission may not provide substantial insight beyond that provided by telescopes on the ground. The report recommends that NASA and DOE proceed immediately with a competition for mission proposals that will investigate the nature of dark energy with high precision.
The committee also recommended that NASA invest additional Beyond Einstein funds in technology development of the LISA program. LISA, which is funded through a partnership between NASA and the European Space Agency (ESA), is designed to detect gravitational waves arising from, among other phenomena, the merging of black holes.
The committee found that LISA will open up new ways of observing the universe, but must await results from ESA's "LISA Pathfinder" mission first. Scheduled for launch in 2009, LISA Pathfinder will test many of the new technologies required for the LISA program. Yet, some critical technologies, such as extended use of micro-Newton thruster technology, will not be tested. The report recommends that the development of these technologies should be a high priority for the Beyond Einstein program.
The report indicates that the three elements of Beyond Einstein that are not being recommended for immediate implementation are still important endeavors that should receive continued support. The committee found that because the Constellation-X mission is a general-purpose x-ray observatory capable of broad contributions to astrophysics, it should be funded and assessed in a broader context than the Beyond Einstein program.
The Black Hole Finder Probe and Inflation Probe missions will also make important scientific contributions; however, because of scope and technical readiness issues, they fell behind JDEM and LISA. The committee recommended that Constellation-X, Black Hole Finder Probe, and Inflation Probe receive continued support to prepare them for the next decadal survey of astronomy and astrophysics.
The study was sponsored by the U.S. Department of Energy and NASA. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies.
Note: This story has been adapted from a news release issued by The National Academies.

Fausto Intilla

www.oloscience.com

Scientists Confirm Long-held Theory About Source Of Sunshine

Source:

http://www.sciencedaily.com/releases/2007/08/070820150232.htm

Science Daily — Scientists are a step closer to understanding sunshine. A monumental experiment buried deep beneath the mountains of Italy has provided Princeton physicists with a clearer understanding of the sun's heart -- and of a mysterious class of subatomic particles born there.

The researchers, working as part of an international collaboration at the underground Gran Sasso National Laboratory near L'Aquila, Italy, have made the first real-time observation of low-energy solar neutrinos, which are fundamental particles created by nuclear reactions that stream in vast numbers from the sun's core.
"Our observations essentially confirm that we understand how the sun shines," said Frank Calaprice, a professor of physics and principal investigator of the Princeton team. "Physicists have had theories regarding the nuclear reactions within the sun for years, but direct observations have remained elusive. Now we understand these reactions much better."
The scientists' precise measurements of the neutrinos' energy provide long-sought proof of the theory regarding how these neutrinos are produced.
In stars the size of the sun, most solar energy is produced by a complex chain of nuclear reactions that converts hydrogen into helium. Beginning with protons from hydrogen's nucleus, the chain takes one of several routes that all end with the creation of a helium nucleus and the production of sunlight.
Steps along two of these routes require the presence of the element beryllium, and physicists have theorized that these steps are responsible for creating about 10 percent of the sun's neutrinos. But technological limitations had made the theory difficult to test until now.
The Gran Sasso lab's giant Borexino detector, located more than a kilometer below the Earth's surface, overcame these limitations, permitting the team to observe low-energy neutrinos, which interact extremely rarely with other forms of matter. Scientists have desired a way to detect them, because they emerge largely unchanged from their journey through the sun's interior to the Earth -- offering an unsullied glimpse into the processes that forged them.
Most particles that emerge from the sun take so long to escape the interior that they change drastically before scientists can study them, so it has been difficult to prove how the sun creates energy. Neutrinos provide a key because they escape before they have time to change.
"The findings show that science's understanding of the chain of nuclear processes that make the sun shine is essentially correct, as least as far as the part of the chain that involves beryllium is concerned," Calaprice said. "The reaction does not generate a large percentage of the sun's energy, but confirming that we understand it makes us more certain that we know how the other processes that create sunlight work."
The results address other longstanding questions as well. The highly sensitive detector has confirmed theories regarding why previous experiments had found fewer solar neutrinos than expected at higher energies, a problem that stemmed from the particles' odd capacity to oscillate from one form to another as they travel through space. While the sun only produces electron neutrinos, these can change into tau or muon neutrinos, which have proved more difficult to detect.
Observing lower-energy neutrinos may also help physicists understand other predicted effects of neutrino oscillation that have not yet been tested.
"This experiment is an important step along the way toward understanding the details of neutrino physics using neutrinos from the sun," said physicist Morgan Wascko, co-spokesman for SciBooNE neutrino experiment at Fermi National Accelerator Laboratory. "Using these particles to observe the sun is important because they give us a lot of information about the way the universe functions, because it's full of stars."
The Borexino experiment's entire research team, which includes more than 100 scientists from many institutions worldwide, will publish its findings in an upcoming edition of the scientific journal Physics Letters B. Calaprice's Princeton colleagues include Cristiano Galbiati, assistant professor of physics, and Jay Benziger, professor of chemical engineering.
The experiment is funded by the National Science Foundation.
Note: This story has been adapted from a news release issued by Princeton University.

Fausto Intilla

www.oloscience.com

Star Light, Star Bright: Duplicating Conditions Of Supernovas

Source:

http://www.sciencedaily.com/releases/2007/08/070814150620.htm

Science Daily — How is matter created? What happens when stars die? Is the universe shrinking, or is it expanding? For decades, scientists have been looking for answers to such "big picture" questions.For the past few months, members of the department of physics at Florida State University have begun using a groundbreaking new research facility to conduct experiments that may help provide answers to just such questions.

RESOLUT -- short for "REsonator SOLenoid with Upscale Transmission" -- is the name of the facility, which is located within the John D. Fox Superconducting Accelerator Laboratory on the FSU campus. Over the past few months, FSU researchers have begun using RESOLUT to create very rare, extremely short-lived radioactive particles similar to those that form inside exploding stars -- and then using the analytical data produced in the experiments as the basis for hypotheses about the behavior of matter and the physical properties governing the universe."We're doing experiments that replicate, in a very controlled manner, the explosions that take place in stars," said Ingo Wiedenhover, an associate professor of physics at FSU who heads up the RESOLUT team. "This helps us understand the nuclear processes that occur in stars, the origin of elements, and how stars explode."Getting to this point has been an arduous process that began in 2002."After five years of proposals, fundraising, designing, building and carefully testing RESOLUT, we are very excited that it has now come online for experiments," said Samuel L. Tabor, a professor of physics at FSU who directs the John D. Fox Superconducting Accelerator Laboratory. "To my knowledge, only one other university in the entire United States has a facility similar to RESOLUT, so our students have a pretty unique opportunity to receive hands-on experience that they can get almost nowhere else."Weighing some 16 tons and taking up more than 450 square feet of space along a wall inside the accelerator lab, RESOLUT enables researchers to fire a beam of atomic particles through a steel tube at speeds approaching 60 million miles per hour -- roughly one-tenth the speed of light -- and then to observe the nuclear reactions that occur."When the beam strikes a target, the collision produces very exotic nuclei that contain properties similar to those occurring in stars and star explosions," Wiedenhover said. "But perhaps RESOLUT's greatest value as a scientific instrument is its function as a mass spectrometer -- a device that allows us to identify and study the short-lived particles created during these miniature explosions."Wiedenhover currently is overseeing several experiments using RESOLUT that create, for a fraction of a second, a specific type of radioactive nuclei that are found only in a type of exploding star known as a Type Ia supernova."Type Ia supernovas result when a certain type of star known as a white dwarf reaches a critical mass and burns through its nuclear fuel so quickly that it suddenly explodes," Wiedenhover said. "What makes these explosions so useful for astrophysicists is that they always release the same amount of energy, so their peak brightness is virtually the same in all instances. This uniform level of brightness makes Type Ia supernovas useful as a 'standard candle' -- a gauge for measuring distances across the universe."Such standard candles also have helped scientists to determine in recent years that the universe is expanding, not shrinking -- and that the expansion is taking place at an ever-increasing rate."Observations of Type Ia supernovas have greatly increased science's understanding of the workings of the universe," Tabor said. "Now, with RESOLUT, we hope to learn even more about these gigantic nuclear explosions -- all from the safety of a lab in a basement on the FSU campus."

Note: This story has been adapted from a news release issued by Florida State University.

Fausto Intilla

www.oloscience.com