A neutrino (Italian pronunciation: [neuˈtriːno], meaning "small neutral one"; English pronunciation: /njuːˈtriːnoʊ/) is an elementary particle that usually travels close to the speed of light, is electrically neutral, and is able to pass through ordinary matter almost undisturbed. This makes neutrinos extremely difficult to detect. Neutrinos have a very small, but nonzero mass. They are denoted by the Greek letter ν (nu).
Neutrinos are created as a result of certain types of radioactive decay or nuclear reactions such as those that take place in the Sun, in nuclear reactors, or when cosmic rays hit atoms. There are three types, or "flavours", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos; each type also has a corresponding antiparticle, called antineutrinos. Electron neutrinos (or antineutrinos) are generated whenever protons change into neutrons (or vice versa), the two forms of beta decay. Interactions involving neutrinos are mediated by the weak interaction.
Most neutrinos passing through the Earth emanate from the Sun, and more than 50 trillion solar neutrinos pass through an average human body every second.
Friday, August 27, 2010
Dark Matter
In astronomy and cosmology, dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation. Its existence was hypothesized to account for discrepancies between measurements of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and measurements based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic media. According to observations of structures larger than galaxies, as well as Big Bang cosmology interpreted under the "Friedmann equations" and the "FLRW metric", dark matter accounts for 23% of the mass-energy density of the observable universe, while the ordinary matter accounts for only 4.6% (the remainder is attributed to dark energy). From these figures, dark matter constitutes 80% of the matter in the universe, while ordinary matter makes up only 20%.
Dark matter was postulated by Fritz Zwicky in 1934 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe, including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.
Dark matter plays a central role in state-of-the-art modeling of structure formation and galaxy evolution, and has measurable effects on the anisotropies observed in the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation. The largest part of dark matter, which does not interact with electromagnetic radiation, is not only "dark" but also, by definition, utterly transparent.
As important as dark matter is believed to be in the universe, direct evidence of its existence and a concrete understanding of its nature have remained elusive. Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws, and quantum gravitational laws.
Dark matter was postulated by Fritz Zwicky in 1934 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe, including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.
Dark matter plays a central role in state-of-the-art modeling of structure formation and galaxy evolution, and has measurable effects on the anisotropies observed in the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation. The largest part of dark matter, which does not interact with electromagnetic radiation, is not only "dark" but also, by definition, utterly transparent.
As important as dark matter is believed to be in the universe, direct evidence of its existence and a concrete understanding of its nature have remained elusive. Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws, and quantum gravitational laws.
Tuesday, August 24, 2010
Cassini-Huygens Trajectory
The initial gravitational-assist trajectory of Cassini–Huygens is the process whereby an insignificant mass approaches a significant mass "from behind" and "steals" some of its orbital momentum. The significant mass, usually a planet, loses a very small proportion of its orbital momentum to the insignificant mass, the space probe in this case. However, due to the space probe's small mass, this momentum transfer gives it a relatively large momentum increase in proportion to its initial momentum, speeding up its travel through outer space.
The Cassini–Huygens space probe performed two gravitational assist fly-bys at Venus, one more fly-by at the Earth, and a final fly-by at Jupiter.
Cassini-Huygens (Saturn orbiter)
http://www.nasa.gov/mission_pages/cassini/main/index.html
Cassini–Huygens is a joint NASA/ESA/ASI robotic spacecraft mission currently studying the planet Saturn and its many natural satellites. The spacecraft consists of two main elements: the NASA-designed and -constructed Cassini orbiter, named for the Italian-French astronomer Giovanni Domenico Cassini, and the ESA-developed Huygens probe, named for the Dutch astronomer, mathematician and physicist Christiaan Huygens. The complete Cassini space probe was launched on October 15, 1997, and after a long interplanetary voyage, it entered into orbit around Saturn on July 1, 2004. On December 25, 2004, the Huygens probe was separated from the orbiter at approximately 02:00 UTC. Then, it reached Saturn's moon Titan on January 14, 2005, when it made a descent into Titan's atmosphere, and downwards to the surface, radioing scientific information back to the Earth by telemetry. On April 18, 2008, NASA announced a two-year extension of the funding for ground operations of this mission, at which point it was renamed to Cassini Equinox Mission.[1] This was again extended in February 2010 and the mission may potentially continue until 2017. Cassini is the fourth space probe to visit Saturn and the first to enter orbit.
16 European countries and the United States make up the team responsible for designing, building, flying and collecting data from the Cassini orbiter and Huygens probe. The mission is managed by NASA’s Jet Propulsion Laboratory in the United States, where the orbiter was designed and assembled. Development of the Huygens Titan probe was managed by the European Space Research and Technology Centre, whose prime contractor for the probe was the Alcatel company in France. Equipment and instruments for the probe were supplied from many countries. The Italian Space Agency (ASI) provided the Cassini probe's high-gain radio antenna, and a compact and lightweight radar, which acts in multipurpose as a synthetic aperture radar, a radar altimeter, and a radiometer.
Cassini–Huygens is a joint NASA/ESA/ASI robotic spacecraft mission currently studying the planet Saturn and its many natural satellites. The spacecraft consists of two main elements: the NASA-designed and -constructed Cassini orbiter, named for the Italian-French astronomer Giovanni Domenico Cassini, and the ESA-developed Huygens probe, named for the Dutch astronomer, mathematician and physicist Christiaan Huygens. The complete Cassini space probe was launched on October 15, 1997, and after a long interplanetary voyage, it entered into orbit around Saturn on July 1, 2004. On December 25, 2004, the Huygens probe was separated from the orbiter at approximately 02:00 UTC. Then, it reached Saturn's moon Titan on January 14, 2005, when it made a descent into Titan's atmosphere, and downwards to the surface, radioing scientific information back to the Earth by telemetry. On April 18, 2008, NASA announced a two-year extension of the funding for ground operations of this mission, at which point it was renamed to Cassini Equinox Mission.[1] This was again extended in February 2010 and the mission may potentially continue until 2017. Cassini is the fourth space probe to visit Saturn and the first to enter orbit.
16 European countries and the United States make up the team responsible for designing, building, flying and collecting data from the Cassini orbiter and Huygens probe. The mission is managed by NASA’s Jet Propulsion Laboratory in the United States, where the orbiter was designed and assembled. Development of the Huygens Titan probe was managed by the European Space Research and Technology Centre, whose prime contractor for the probe was the Alcatel company in France. Equipment and instruments for the probe were supplied from many countries. The Italian Space Agency (ASI) provided the Cassini probe's high-gain radio antenna, and a compact and lightweight radar, which acts in multipurpose as a synthetic aperture radar, a radar altimeter, and a radiometer.
Evidence for the big bang
Evidence for the Big Bang
The CMB signal detected by Penzias and Wilson, a discovery for which they later won a Nobel Prize, is often described as the “echo” of the Big Bang. Because if the Universe had an origin, it would leave behind a signature of the event, just like an echo heard in a canyon represents a “signature” of the original sound. The difference is that instead of an audible echo, the Big Bang left behind a heat signature throughout all of space.
Another prediction of the Big Bang theory is that the Universe should be receding from us. Specifically, any direction we look out into space, we should see objects moving away from us with a velocity proportional to their distance away from us, a phenomenon known as the red shift.
http://scienceblogs.com/startswithabang/upload/2010/06/your_theory_doesnt_do_everythi/big-bang.jpg
The CMB signal detected by Penzias and Wilson, a discovery for which they later won a Nobel Prize, is often described as the “echo” of the Big Bang. Because if the Universe had an origin, it would leave behind a signature of the event, just like an echo heard in a canyon represents a “signature” of the original sound. The difference is that instead of an audible echo, the Big Bang left behind a heat signature throughout all of space.
Another prediction of the Big Bang theory is that the Universe should be receding from us. Specifically, any direction we look out into space, we should see objects moving away from us with a velocity proportional to their distance away from us, a phenomenon known as the red shift.
http://scienceblogs.com/startswithabang/upload/2010/06/your_theory_doesnt_do_everythi/big-bang.jpg
Monday, August 23, 2010
Sunday, August 22, 2010
Dark matter
The Alpha Magnetic Spectrometer (AMS), an experiment that will search for antimatter and dark matter in space, leaves CERN August 24 on the next leg of its journey to the International Space Station. The AMS detector is being transported from CERN to Geneva International Airport in preparation for its planned departure from Switzerland on 26 August, when it will be flown to the Kennedy Space Center in Florida on board a US Air Force Galaxy transport aircraft.
AMS will examine fundamental issues about matter and the origin and structure of the Universe directly from space. Its main scientific target is the search for dark matter and antimatter, in a programme that is complementary to that of the Large Hadron Collider.
Last February the AMS detector travelled from CERN to the European Space Research and Technology Centre (ESTEC) in Noordwijk (Netherlands) for testing to certify its readiness for travel into space. Following the completion of the testing, the AMS collaboration decided to return the detector to CERN for final modifications. In particular, the detector's superconducting magnet was replaced by the permanent magnet from the AMS-01 prototype, which had already flown into space in 1998. The reason for the decision was that the operational lifetime of the superconducting magnet would have been limited to three years, because there is no way of refilling the magnet with liquid helium, necessary to maintain the magnet's superconductivity, on board the space station. The permanent magnet, on the other hand, will now allow the experiment to remain operational for the entire lifetime of the ISS.
Following its return to CERN, the AMS detector was therefore reconfigured with the permanent magnet before being tested with CERN particle beams. The tests were used to validate and calibrate the new configuration before the detector leaves Europe for the last time.
Upon arrival at the Kennedy Space Center, AMS will be installed in a clean room for a few more tests. A few weeks later, the detector will be moved to the space shuttle. NASA is planning the last flight of the space shuttle programme, which will carry AMS into space, for the end of February 2011.
Once docked to the ISS, AMS will search for antimatter and dark matter by measuring cosmic rays. Data collected in space by AMS will be transmitted to Houston (USA) and on to CERN's Prévessin site, where the detector control centre will be located, and to a number of regional physics analysis centres set up by the collaborating institutes.
AMS will examine fundamental issues about matter and the origin and structure of the Universe directly from space. Its main scientific target is the search for dark matter and antimatter, in a programme that is complementary to that of the Large Hadron Collider.
Last February the AMS detector travelled from CERN to the European Space Research and Technology Centre (ESTEC) in Noordwijk (Netherlands) for testing to certify its readiness for travel into space. Following the completion of the testing, the AMS collaboration decided to return the detector to CERN for final modifications. In particular, the detector's superconducting magnet was replaced by the permanent magnet from the AMS-01 prototype, which had already flown into space in 1998. The reason for the decision was that the operational lifetime of the superconducting magnet would have been limited to three years, because there is no way of refilling the magnet with liquid helium, necessary to maintain the magnet's superconductivity, on board the space station. The permanent magnet, on the other hand, will now allow the experiment to remain operational for the entire lifetime of the ISS.
Following its return to CERN, the AMS detector was therefore reconfigured with the permanent magnet before being tested with CERN particle beams. The tests were used to validate and calibrate the new configuration before the detector leaves Europe for the last time.
Upon arrival at the Kennedy Space Center, AMS will be installed in a clean room for a few more tests. A few weeks later, the detector will be moved to the space shuttle. NASA is planning the last flight of the space shuttle programme, which will carry AMS into space, for the end of February 2011.
Once docked to the ISS, AMS will search for antimatter and dark matter by measuring cosmic rays. Data collected in space by AMS will be transmitted to Houston (USA) and on to CERN's Prévessin site, where the detector control centre will be located, and to a number of regional physics analysis centres set up by the collaborating institutes.
News
Joint Dark Energy Mission a Top Priority for NASA, Says NRC
BERKELEY, CA — The National Research Council's Beyond Einstein Program Assessment Committee has recommended that the Joint Dark Energy Mission (JDEM), jointly supported by the National Aeronautics and Space Administration and the Department of Energy, be the first of NASA's Beyond Einstein cosmology missions to be developed and launched.
SNAP, the SuperNova/Acceleration Probe, is one of three concepts competing for NASA and DOE's Joint Dark Energy Mission (JDEM).
One of the three competing projects in the JDEM program is Lawrence Berkeley National Laboratory's SuperNova/Acceleration Probe, or SNAP, a versatile space-borne observatory with a powerful two-meter-class telescope and a half-billion pixel imager, designed to study dark energy by recording the distance and redshift of some 2,000 Type Ia supernovae a year and mapping the sky with unprecedented resolution. Dark energy is the name given to the mysterious entity which is causing the universe to expand ever more rapidly. It accounts for nearly three-quarters of all the energy in the universe.
The recommendations of NRC's Beyond Einstein Program Assessment Committee (BEPAC), posted on the internet Sept. 5, follow nearly a year of intensive study of the five proposed missions in the Beyond Einstein program. Due to budget constraints and technological readiness only one such mission can be started at this time, so NASA and DOE requested in August, 2006 that the NRC, while assessing the program as a whole, recommend which mission should be developed and launched first.
"NASA and DOE have moved forward together since joining forces on the Joint Dark Energy Mission four years ago, including their support for Berkeley Lab's approach to the mission, SNAP," says Steven Chu, Director of the Department of Energy's Lawrence Berkeley National Laboratory. "By recommending that JDEM be the first Beyond Einstein mission to be launched, the National Research Council has assured that the two agencies will be partners in investigating one of the most pressing scientific questions of the 21st century. We look forward to the agencies' moving forward upon receiving the NRC Committee Report."
"It's wonderful to know that NASA will be moving forward with this exciting project as a result of the committee's recommendation that JDEM be the first mission to fly," says Saul Perlmutter, a member of Berkeley Lab's Physics Division and Professor of Physics at the University of California at Berkeley. "Each of the highly ranked Beyond Einstein projects will contribute greatly to our understanding of the universe, yet few questions are more fundamental or pressing than the mysterious nature of dark energy, which accounts for some three-quarters of the energy density of our universe — but about which we know almost nothing."
"It is not surprising that the BEPAC reaffirmed the importance of the exciting science that connects quarks with the Cosmos — the stunning scientific opportunities, from understanding how the Universe began to unraveling the mystery of the dark energy to probing black holes, speak for themselves," says Michael Turner, Professor of Physics and of Astronomy and Astrophysics at the University of Chicago, who led an NRC Quarks-to-the-Cosmos study which stimulated the Beyond Einstein program. However, says Turner, "Today's real milestone is the selection of the Joint Dark Energy Mission as the first of multiple missions in NASA's Beyond Einstein program.... JDEM will harness the powerful combination of two science agencies, DOE and NASA, and the scientists they support, to shed light on the most abundant and most mysterious stuff in the Universe. JDEM will set a high mark for the Beyond Einstein missions that follow."
The JDEM Mission to Explore Dark Energy
Three concepts for a JDEM mission have been proposed: the SuperNova/Acceleration Probe (SNAP), the Dark Energy Space Telescope (DESTINY), and the Advanced Dark Energy Physics Telescope (ADEPT).
SNAP is being developed by an international collaboration led by principal investigator Perlmutter and by co-principal investigator and project director Michael Levi, of Lawrence Berkeley National Laboratory's Physics Division and UC Berkeley's Space Sciences Laboratory. In addition to Berkeley Lab, partner institutions include the Space Sciences Laboratory; the French Space Agency, the Centre National D'Etudes Spatiales; and a number of U.S. and Canadian universities. DESTINY is led by Tod Lauer of the National Optical Astronomy Observatory, and ADEPT is led by Charles Bennett of Johns Hopkins University.
Dark energy, which accounts for about three-quarters of the energy density of the universe, was unknown before 1998. Early that year two international teams, the Supernova Cosmology Project based at Lawrence Berkeley National Laboratory and led by Perlmutter, and the High-Z Supernova Search Team led by Brian Schmidt of the Australian National University, independently announced their discovery that the expansion of the universe is not slowing from the contracting force of gravity but is in fact growing more and more rapidly. The cause of accelerating expansion was soon named dark energy.
Perlmutter and Schmidt and the members of their teams share the 2007 Gruber Cosmology Prize for their discovery. Perlmutter, Adam Riess of Johns Hopkins University, and Schmidt shared the 2006 Shaw Prize in Astronomy for this discovery. Perlmutter also received the 2006 International Antonio Feltrinelli Prize in the Physical and Mathematical Sciences, awarded once every five years, for his work leading to the discovery of dark energy.
"Evidence for dark energy came almost ten years ago," Michael Turner remarks, "and the mystery of this weird stuff with repulsive gravity which controls the expansion of the Universe and its destiny has captured the attention of physicists, astronomers and the public alike." Scientists still cannot say whether dark energy has a constant value or is changing over time — or even whether dark energy is an illusion, with the accelerating expansion of the universe a consequence of a failure of general relativity.
SNAP, the SuperNova/Acceleration Probe
It was in 1999, soon after the discovery of dark energy, that members of the Supernova Cosmology Project joined with their colleagues to devise a space-based experiment, SNAP, to reveal its nature. Intensive research and development efforts for SNAP have been vigorously supported by DOE's Office of Science since it was proposed, and by NASA since 2003, when it joined with DOE to pursue the Joint Dark Energy Mission.
In May, 2006, NASA, DOE, and NSF's Dark Energy Task Force reported that different techniques for measuring dark energy in combination "have substantially more statistical power, much more ability to discriminate among dark energy models, and more robustness to systematic errors than any single technique."
"SNAP will investigate dark energy using two independent and powerful techniques," says Perlmutter, SNAP's principal investigator. "The best proven and most powerful current technique is to determine changes in the universe's expansion rate by comparing the redshift and distance of Type Ia supernovae, of which SNAP will find some 2,000 a year. But we are also targeting the most promising complementary technique, called 'weak gravitational lensing.'"
Levi, SNAP's co-principal investigator, explains that "Weak gravitational lensing has been part of the SNAP concept since its beginning in 1999. SNAP will make a high-resolution map of the sky covering an area 2,000,000 times larger than the Hubble Deep Field. This map will be sensitive to the minute distortions of distant galaxy shapes when their light passes through uneven distributions of matter — a phenomenon called 'weak lensing.' Weak lensing promises a powerful way to measure the distribution of dark matter and to probe dark energy's effect on the growth structure of the universe. The huge survey map will also provide astronomers with an unparalleled wealth of high-resolution images never before seen."
NASA incorporated JDEM into the Beyond Einstein program when it was formulated by the agency's Astronomy and Physics Division in 2004. The program eventually focused on five such missions: to detect gravitational waves, provide a more powerful x-ray telescope, investigate models of cosmic inflation, find black holes, and study the nature of dark energy.
BERKELEY, CA — The National Research Council's Beyond Einstein Program Assessment Committee has recommended that the Joint Dark Energy Mission (JDEM), jointly supported by the National Aeronautics and Space Administration and the Department of Energy, be the first of NASA's Beyond Einstein cosmology missions to be developed and launched.
SNAP, the SuperNova/Acceleration Probe, is one of three concepts competing for NASA and DOE's Joint Dark Energy Mission (JDEM).
One of the three competing projects in the JDEM program is Lawrence Berkeley National Laboratory's SuperNova/Acceleration Probe, or SNAP, a versatile space-borne observatory with a powerful two-meter-class telescope and a half-billion pixel imager, designed to study dark energy by recording the distance and redshift of some 2,000 Type Ia supernovae a year and mapping the sky with unprecedented resolution. Dark energy is the name given to the mysterious entity which is causing the universe to expand ever more rapidly. It accounts for nearly three-quarters of all the energy in the universe.
The recommendations of NRC's Beyond Einstein Program Assessment Committee (BEPAC), posted on the internet Sept. 5, follow nearly a year of intensive study of the five proposed missions in the Beyond Einstein program. Due to budget constraints and technological readiness only one such mission can be started at this time, so NASA and DOE requested in August, 2006 that the NRC, while assessing the program as a whole, recommend which mission should be developed and launched first.
"NASA and DOE have moved forward together since joining forces on the Joint Dark Energy Mission four years ago, including their support for Berkeley Lab's approach to the mission, SNAP," says Steven Chu, Director of the Department of Energy's Lawrence Berkeley National Laboratory. "By recommending that JDEM be the first Beyond Einstein mission to be launched, the National Research Council has assured that the two agencies will be partners in investigating one of the most pressing scientific questions of the 21st century. We look forward to the agencies' moving forward upon receiving the NRC Committee Report."
"It's wonderful to know that NASA will be moving forward with this exciting project as a result of the committee's recommendation that JDEM be the first mission to fly," says Saul Perlmutter, a member of Berkeley Lab's Physics Division and Professor of Physics at the University of California at Berkeley. "Each of the highly ranked Beyond Einstein projects will contribute greatly to our understanding of the universe, yet few questions are more fundamental or pressing than the mysterious nature of dark energy, which accounts for some three-quarters of the energy density of our universe — but about which we know almost nothing."
"It is not surprising that the BEPAC reaffirmed the importance of the exciting science that connects quarks with the Cosmos — the stunning scientific opportunities, from understanding how the Universe began to unraveling the mystery of the dark energy to probing black holes, speak for themselves," says Michael Turner, Professor of Physics and of Astronomy and Astrophysics at the University of Chicago, who led an NRC Quarks-to-the-Cosmos study which stimulated the Beyond Einstein program. However, says Turner, "Today's real milestone is the selection of the Joint Dark Energy Mission as the first of multiple missions in NASA's Beyond Einstein program.... JDEM will harness the powerful combination of two science agencies, DOE and NASA, and the scientists they support, to shed light on the most abundant and most mysterious stuff in the Universe. JDEM will set a high mark for the Beyond Einstein missions that follow."
The JDEM Mission to Explore Dark Energy
Three concepts for a JDEM mission have been proposed: the SuperNova/Acceleration Probe (SNAP), the Dark Energy Space Telescope (DESTINY), and the Advanced Dark Energy Physics Telescope (ADEPT).
SNAP is being developed by an international collaboration led by principal investigator Perlmutter and by co-principal investigator and project director Michael Levi, of Lawrence Berkeley National Laboratory's Physics Division and UC Berkeley's Space Sciences Laboratory. In addition to Berkeley Lab, partner institutions include the Space Sciences Laboratory; the French Space Agency, the Centre National D'Etudes Spatiales; and a number of U.S. and Canadian universities. DESTINY is led by Tod Lauer of the National Optical Astronomy Observatory, and ADEPT is led by Charles Bennett of Johns Hopkins University.
Dark energy, which accounts for about three-quarters of the energy density of the universe, was unknown before 1998. Early that year two international teams, the Supernova Cosmology Project based at Lawrence Berkeley National Laboratory and led by Perlmutter, and the High-Z Supernova Search Team led by Brian Schmidt of the Australian National University, independently announced their discovery that the expansion of the universe is not slowing from the contracting force of gravity but is in fact growing more and more rapidly. The cause of accelerating expansion was soon named dark energy.
Perlmutter and Schmidt and the members of their teams share the 2007 Gruber Cosmology Prize for their discovery. Perlmutter, Adam Riess of Johns Hopkins University, and Schmidt shared the 2006 Shaw Prize in Astronomy for this discovery. Perlmutter also received the 2006 International Antonio Feltrinelli Prize in the Physical and Mathematical Sciences, awarded once every five years, for his work leading to the discovery of dark energy.
"Evidence for dark energy came almost ten years ago," Michael Turner remarks, "and the mystery of this weird stuff with repulsive gravity which controls the expansion of the Universe and its destiny has captured the attention of physicists, astronomers and the public alike." Scientists still cannot say whether dark energy has a constant value or is changing over time — or even whether dark energy is an illusion, with the accelerating expansion of the universe a consequence of a failure of general relativity.
SNAP, the SuperNova/Acceleration Probe
It was in 1999, soon after the discovery of dark energy, that members of the Supernova Cosmology Project joined with their colleagues to devise a space-based experiment, SNAP, to reveal its nature. Intensive research and development efforts for SNAP have been vigorously supported by DOE's Office of Science since it was proposed, and by NASA since 2003, when it joined with DOE to pursue the Joint Dark Energy Mission.
In May, 2006, NASA, DOE, and NSF's Dark Energy Task Force reported that different techniques for measuring dark energy in combination "have substantially more statistical power, much more ability to discriminate among dark energy models, and more robustness to systematic errors than any single technique."
"SNAP will investigate dark energy using two independent and powerful techniques," says Perlmutter, SNAP's principal investigator. "The best proven and most powerful current technique is to determine changes in the universe's expansion rate by comparing the redshift and distance of Type Ia supernovae, of which SNAP will find some 2,000 a year. But we are also targeting the most promising complementary technique, called 'weak gravitational lensing.'"
Levi, SNAP's co-principal investigator, explains that "Weak gravitational lensing has been part of the SNAP concept since its beginning in 1999. SNAP will make a high-resolution map of the sky covering an area 2,000,000 times larger than the Hubble Deep Field. This map will be sensitive to the minute distortions of distant galaxy shapes when their light passes through uneven distributions of matter — a phenomenon called 'weak lensing.' Weak lensing promises a powerful way to measure the distribution of dark matter and to probe dark energy's effect on the growth structure of the universe. The huge survey map will also provide astronomers with an unparalleled wealth of high-resolution images never before seen."
NASA incorporated JDEM into the Beyond Einstein program when it was formulated by the agency's Astronomy and Physics Division in 2004. The program eventually focused on five such missions: to detect gravitational waves, provide a more powerful x-ray telescope, investigate models of cosmic inflation, find black holes, and study the nature of dark energy.
Galaxy formation
The formation of galaxies is still one of the most active research areas in astrophysics; and, to some extent, this is also true for galaxy evolution.
Some ideas, however, are now widely accepted.
After the Big Bang, the universe had a period when it was remarkably homogeneous, as can be observed in the Cosmic Microwave Background, the fluctuations of which are less than one part in one hundred thousand.
The most accepted view today is that all the structure we observe today was formed as a consequence of the growth of primordial fluctuations.
The primordial fluctuations caused gas to be attracted to areas of denser material, and star clusters and stars.
One consequence of this model is that the location of galaxies indicates areas of higher density of the early universe.
Hence the distribution of galaxies is closely related to the physics of the early universe..
Some ideas, however, are now widely accepted.
After the Big Bang, the universe had a period when it was remarkably homogeneous, as can be observed in the Cosmic Microwave Background, the fluctuations of which are less than one part in one hundred thousand.
The most accepted view today is that all the structure we observe today was formed as a consequence of the growth of primordial fluctuations.
The primordial fluctuations caused gas to be attracted to areas of denser material, and star clusters and stars.
One consequence of this model is that the location of galaxies indicates areas of higher density of the early universe.
Hence the distribution of galaxies is closely related to the physics of the early universe..
Recent discoveries
The first stars in our universe are long gone, but their light still shines, giving us a peek at what the universe looked like in its early years.
Astrophysicists believe they've spotted a faint glow from stars born at the beginning of time. Harvey Moseley, Ph.D., an astrophysicist at the NASA Goddard Space Flight Center in Greenbelt, Maryland, says, "The reason they're faint is just because they're very, very far away, they're over at the far edge of the universe."
After the big bang, the universe stayed dark for about 200 million years. Now, new pictures reveal the first light from objects 13 billion light years away, the infants of our universe. "So, we're seeing what sometimes people call the first light in the universe, which formed after the big bang," Dr. Moseley explains.
Using pictures taken with the Spitzer Space Telescope, scientists first removed light from closer stars and galaxies. The light areas left in the background are believed to be the first objects in space. Alexander Kashlinsky, Ph.D., astrophysicist at the NASA Goddard Space Flight Center, says, "The early universe was a very hot place in this sense, like it was filled with objects that have been emitting light much more furiously than today."
Researchers say the objects are either stars, hundreds of times more massive than our own sun, or enormous black holes. Either way, the pictures bring us one step closer to learning how the universe was born. NASA's planned James Webb Space Telescope will be able to identify the nature of the newfound clusters and determine if they are stars or black holes.
BACKGROUND: Using a telescope as a time machine, scientists at NASA's Goddard Space Flight Center are closer to identifying the first objects of the universe. The latest observations from the Spitzer Space Telescope suggest that infrared light detected in a prior study comes from clusters of bright objects that lived within the first billion years after the Big Bang.
THE DARK AGE: According to current science, space, time and matter originated 13.7 billion years ago in a tremendous explosion called the Big Bang. A few hundred million years later, the first stars formed, ending the "dark age" of the universe. Astronomers believe the objects observed by the Spitzer telescope are either the first stars -- hundreds of times more massive than our sun -- or voracious black holes that are consuming gas and spilling out tons of energy. If they turn out to be stars, then the clusters might be the first mini-galaxies. Our own Milky Way was probably created when mini-galaxies like these merged.
IN THE INFRARED: The Spitzer scientists were looking specifically at the cosmic infrared background of the universe, a diffuse light from the early epoch when structure first emerged in the cosmos. A prior study reported in 2005 detected infrared light, suggesting that it originated from clumps of the very first objects in the universe. This second analysis indicates that this patchy light is scattered across the entire sky and comes from clusters of bright, monstrous objects more than 13 billion light-years away. Although that light began its journey as ultraviolet or visible light, by the time it reached earth, its wavelengths had been stretched into the infrared by the growing space-time that causes the universe's expansion. Based on the strength of the infrared light signal, they concluded that the total amount of energy produced by the objects was so large, only very large stars or black holes consuming a lot of matter would be capable of emitting it. Other parts of the cosmic infrared background are from distant starlight absorbed by dust and re-emitted as infrared light.
SEEING IS BELIEVING: When we peer into space with a telescope, we are actually looking back in time. Telescopes detect emitted light, and the light that reaches us from the closest galaxy, Andromeda, for instance, has taken two million years to reach us. The Spitzer telescope looked at the first brilliant objects to exist in our universe. The Spitzer telescope scanned five areas of the sky for about 25 hours per region, collecting light even from the faintest of objects. Then astronomers meticulously subtracted light from things that were in the way, such as foreground galaxies and dust in our solar system, or in interstellar clouds. When all that was left was the most ancient light, the scientists studied fluctuations in the intensity of the infrared brightness, revealing a clustering of objects to produce the observed light pattern.
The American Astronomical Society contributed to the information contained in the video portion of this report.
Astrophysicists believe they've spotted a faint glow from stars born at the beginning of time. Harvey Moseley, Ph.D., an astrophysicist at the NASA Goddard Space Flight Center in Greenbelt, Maryland, says, "The reason they're faint is just because they're very, very far away, they're over at the far edge of the universe."
After the big bang, the universe stayed dark for about 200 million years. Now, new pictures reveal the first light from objects 13 billion light years away, the infants of our universe. "So, we're seeing what sometimes people call the first light in the universe, which formed after the big bang," Dr. Moseley explains.
Using pictures taken with the Spitzer Space Telescope, scientists first removed light from closer stars and galaxies. The light areas left in the background are believed to be the first objects in space. Alexander Kashlinsky, Ph.D., astrophysicist at the NASA Goddard Space Flight Center, says, "The early universe was a very hot place in this sense, like it was filled with objects that have been emitting light much more furiously than today."
Researchers say the objects are either stars, hundreds of times more massive than our own sun, or enormous black holes. Either way, the pictures bring us one step closer to learning how the universe was born. NASA's planned James Webb Space Telescope will be able to identify the nature of the newfound clusters and determine if they are stars or black holes.
BACKGROUND: Using a telescope as a time machine, scientists at NASA's Goddard Space Flight Center are closer to identifying the first objects of the universe. The latest observations from the Spitzer Space Telescope suggest that infrared light detected in a prior study comes from clusters of bright objects that lived within the first billion years after the Big Bang.
THE DARK AGE: According to current science, space, time and matter originated 13.7 billion years ago in a tremendous explosion called the Big Bang. A few hundred million years later, the first stars formed, ending the "dark age" of the universe. Astronomers believe the objects observed by the Spitzer telescope are either the first stars -- hundreds of times more massive than our sun -- or voracious black holes that are consuming gas and spilling out tons of energy. If they turn out to be stars, then the clusters might be the first mini-galaxies. Our own Milky Way was probably created when mini-galaxies like these merged.
IN THE INFRARED: The Spitzer scientists were looking specifically at the cosmic infrared background of the universe, a diffuse light from the early epoch when structure first emerged in the cosmos. A prior study reported in 2005 detected infrared light, suggesting that it originated from clumps of the very first objects in the universe. This second analysis indicates that this patchy light is scattered across the entire sky and comes from clusters of bright, monstrous objects more than 13 billion light-years away. Although that light began its journey as ultraviolet or visible light, by the time it reached earth, its wavelengths had been stretched into the infrared by the growing space-time that causes the universe's expansion. Based on the strength of the infrared light signal, they concluded that the total amount of energy produced by the objects was so large, only very large stars or black holes consuming a lot of matter would be capable of emitting it. Other parts of the cosmic infrared background are from distant starlight absorbed by dust and re-emitted as infrared light.
SEEING IS BELIEVING: When we peer into space with a telescope, we are actually looking back in time. Telescopes detect emitted light, and the light that reaches us from the closest galaxy, Andromeda, for instance, has taken two million years to reach us. The Spitzer telescope looked at the first brilliant objects to exist in our universe. The Spitzer telescope scanned five areas of the sky for about 25 hours per region, collecting light even from the faintest of objects. Then astronomers meticulously subtracted light from things that were in the way, such as foreground galaxies and dust in our solar system, or in interstellar clouds. When all that was left was the most ancient light, the scientists studied fluctuations in the intensity of the infrared brightness, revealing a clustering of objects to produce the observed light pattern.
The American Astronomical Society contributed to the information contained in the video portion of this report.
Intro
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions
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