PASADENA, Calif. -- A five-year survey of 200,000 galaxies, stretching back seven billion years in cosmic time, has led to one of the best independent confirmations that dark energy is driving our universe apart at accelerating speeds. The survey used data from NASA's space-based Galaxy Evolution Explorer and the Anglo-Australian Telescope on Siding Spring Mountain in Australia.
The findings offer new support for the favored theory of how dark energy works -- as a constant force, uniformly affecting the universe and propelling its runaway expansion. They contradict an alternate theory, where gravity, not dark energy, is the force pushing space apart. According to this alternate theory, with which the new survey results are not consistent, Albert Einstein's concept of gravity is wrong, and gravity becomes repulsive instead of attractive when acting at great distances.
"The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster," said Chris Blake of the Swinburne University of Technology in Melbourne, Australia. Blake is lead author of two papers describing the results that appeared in recent issues of the Monthly Notices of the Royal Astronomical Society. "The results tell us that dark energy is a cosmological constant, as Einstein proposed. If gravity were the culprit, then we wouldn't be seeing these constant effects of dark energy throughout time."
Dark energy is thought to dominate our universe, making up about 74 percent of it. Dark matter, a slightly less mysterious substance, accounts for 22 percent. So-called normal matter, anything with atoms, or the stuff that makes up living creatures, planets and stars, is only approximately four percent of the cosmos.
The idea of dark energy was proposed during the previous decade, based on studies of distant exploding stars called supernovae. Supernovae emit constant, measurable light, making them so-called "standard candles," which allows calculation of their distance from Earth. Observations revealed dark energy was flinging the objects out at accelerating speeds.
Dark energy is in a tug-of-war contest with gravity. In the early universe, gravity took the lead, dominating dark energy. At about 8 billion years after the Big Bang, as space expanded and matter became diluted, gravitational attractions weakened and dark energy gained the upper hand. Billions of years from now, dark energy will be even more dominant. Astronomers predict our universe will be a cosmic wasteland, with galaxies spread apart so far that any intelligent beings living inside them wouldn't be able to see other galaxies.
The new survey provides two separate methods for independently checking the supernovae results. This is the first time astronomers performed these checks across the whole cosmic timespan dominated by dark energy. The team began by assembling the largest three-dimensional map of galaxies in the distant universe, spotted by the Galaxy Evolution Explorer. The ultraviolet-sensing telescope has scanned about three-quarters of the sky, observing hundreds of millions of galaxies.
"The Galaxy Evolution Explorer helped identify bright, young galaxies, which are ideal for this type of study," said Christopher Martin, principal investigator for the mission at the California Institute of Technology in Pasadena. "It provided the scaffolding for this enormous 3-D map."
The astronomers acquired detailed information about the light for each galaxy using the Anglo-Australian Telescope and studied the pattern of distance between them. Sound waves from the very early universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years.
This "standard ruler" was used to determine the distance from the galaxy pairs to Earth -- the closer a galaxy pair is to us, the farther apart the galaxies will appear from each other on the sky. As with the supernovae studies, this distance data were combined with information about the speeds at which the pairs are moving away from us, revealing, yet again, the fabric of space is stretching apart faster and faster.
The team also used the galaxy map to study how clusters of galaxies grow over time like cities, eventually containing many thousands of galaxies. The clusters attract new galaxies through gravity, but dark energy tugs the clusters apart. It slows down the process, allowing scientists to measure dark energy's repulsive force.
"Observations by astronomers over the last 15 years have produced one of the most startling discoveries in physical science; the expansion of the universe, triggered by the Big Bang, is speeding up," said Jon Morse, astrophysics division director at NASA Headquarters in Washington. "Using entirely independent methods, data from the Galaxy Evolution Explorer have helped increase our confidence in the existence of dark energy."
Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory in Pasadena, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission. Caltech manages JPL for NASA
Saturday 31 March 2012
Gliese 581d: A Habitable Exoplanet?
Gliese 581d: A Habitable Exoplanet?
Source: CNRS press release
Alien Life
Posted: 05/20/11
Summary: A new computer model that simulates possible exoplanet climates indicates that the planet Gliese 581d might be warm enough to have oceans, clouds and rainfall. Gliese 581d is likely to be a rocky planet with a mass at least seven times that of Earth.
Schematic of the global climate model used to study Gliese 581d. Red / blue shading indicate hot / cold surface temperatures, while the arrows show wind velocities at 2 km height in the atmosphere. © LMD/CNRS Are there other planets inhabited like the Earth, or at least habitable? The discovery of the first habitable planet has become a quest for many astrophysicists who look for rocky planets in the “habitable zone” around stars, the range of distances in which planets are neither too cold nor too hot for life to flourish.
In this quest, the red dwarf star Gliese 581 has already received a huge amount of attention. In 2007, scientists reported the detection of two planets orbiting not far from the inner and outer edge of its habitable zone (Gliese 581d and Gliese 581c). While the more distant planet, Gliese 581d, was initially judged to be too cold for life, the closer-in planet, Gliese 581c, was thought to be potentially habitable by its discoverers. However, later analysis by atmospheric experts showed that if it had liquid oceans like Earth, they would rapidly evaporate in a 'runaway greenhouse' effect similar to that which gave Venus the hot, inhospitable climate it has today.
A new possibility emerged late in 2010, when a team of observers led by Steven Vogt at the University of California, Santa Cruz, announced that they had discovered a new planet, which they dubbed Gliese 581g, or 'Zarmina's World'. This planet, they claimed, had a mass similar to that of Earth and was close to the centre of the habitable zone. For several months, the discovery of the first potential Earth twin outside the Solar System seemed to have been achieved. Unfortunately, later analysis by independent teams has raised serious doubts on this extremely difficult detection. Many now believe that Gliese 581g may not exist at all. Instead, it may simply be a result of noise in the ultra-fine measurements of stellar 'wobble' needed to detect exoplanets in this system.
Surface temperature maps for simulations of Gliese 581d assuming an atmosphere of 20 bars of CO2 and varying rotation rates. It is currently unknown whether the planet rotates slowly or has permanent day and night sides. In all cases, the temperatures allow for the presence of liquid water on the surface. © LMD/CNRS It is Gliese 581g's big brother – the larger and more distant Gliese 581d - which has been shown to be the confirmed potentially habitable exoplanet by Robin Wordsworth, François Forget and co-workers from Laboratoire de Météorologie Dynamique (CNRS/UPMC/ENS/Ecole Polytechnique) at the Institute Pierre Simon Laplace in Paris, in collaboration with a researcher from the Laboratoire d'astrophysique de Bordeaux (CNRS/Université Bordeaux 1). Although it is likely to be a rocky planet, it has a mass at least seven times that of Earth, and is estimated to be about twice its size.
At first glance, Gliese 581d is a pretty poor candidate in the hunt for life: it receives less than a third of the stellar energy Earth does and may be tidally locked, with a permanent day and night side. After its discovery, it was generally believed that any atmosphere thick enough to keep the planet warm would become cold enough on the night side to freeze out entirely, ruining any prospects for a habitable climate.
To test whether this intuition was correct, Wordsworth and colleagues developed a new kind of computer model capable of accurately simulating possible exoplanet climates. The model simulates a planet's atmosphere and surface in three dimensions, rather like those used to study climate change on Earth. However, it is based on more fundamental physical principles, allowing the simulation of a much wider range of conditions than would otherwise be possible, including any atmospheric cocktail of gases, clouds and aerosols.
To their surprise, they found that with a dense carbon dioxide atmosphere - a likely scenario on such a large planet - the climate of Gliese 581d is not only stable against collapse, but warm enough to have oceans, clouds and rainfall. One of the key factors in their results was Rayleigh scattering, the phenomenon that makes the sky blue on Earth.
In the Solar System, Rayleigh scattering limits the amount of sunlight a thick atmosphere can absorb, because a large portion of the scattered blue light is immediately reflected back to space. However, as the starlight from Gliese 581 is red, it is almost unaffected. This means that it can penetrate much deeper into the atmosphere, where it heats the planet effectively due to the greenhouse effect of the CO2 atmosphere, combined with that of the carbon dioxide ice clouds predicted to form at high altitudes. Furthermore, the 3D circulation simulations showed that the daylight heating was efficiently redistributed across the planet by the atmosphere, preventing atmospheric collapse on the night side or at the poles.
This artist's concept illustrates a young, red dwarf star surrounded by three planets. Such stars are dimmer and smaller than yellow stars like our sun. Credit: NASA/JPL-Caltech Scientists are particularly excited by the fact that at 20 light years from Earth, Gliese 581d is one of our closest galactic neighbours. For now, this is of limited use for budding interstellar colonists – the furthest-travelled man-made spacecraft, Voyager 1, would still take over 300,000 years to arrive there. However, it does mean that in the future telescopes will be able to detect the planet's atmosphere directly.
While Gliese 581d may be habitable there are other possibilities; it could have kept some atmospheric hydrogen, like Uranus and Neptune, or the fierce wind from its star during its infancy could even have torn its atmosphere away entirely. To distinguish between these different scenarios, Wordsworth and co-workers came up with several simple tests that observers will be able to perform in future with a sufficiently powerful telescope.
If Gliese 581d does turn out to be habitable, it would still be a pretty strange place to visit – the denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth. But the diversity of planetary climates in the galaxy is likely to be far wider than the few examples we are used to from the Solar System. In the long run, the most important implication of these results may be the idea that life-supporting planets do not in fact need to be particularly like the Earth at all.
Source: CNRS press release
Alien Life
Posted: 05/20/11
Summary: A new computer model that simulates possible exoplanet climates indicates that the planet Gliese 581d might be warm enough to have oceans, clouds and rainfall. Gliese 581d is likely to be a rocky planet with a mass at least seven times that of Earth.
Schematic of the global climate model used to study Gliese 581d. Red / blue shading indicate hot / cold surface temperatures, while the arrows show wind velocities at 2 km height in the atmosphere. © LMD/CNRS Are there other planets inhabited like the Earth, or at least habitable? The discovery of the first habitable planet has become a quest for many astrophysicists who look for rocky planets in the “habitable zone” around stars, the range of distances in which planets are neither too cold nor too hot for life to flourish.
In this quest, the red dwarf star Gliese 581 has already received a huge amount of attention. In 2007, scientists reported the detection of two planets orbiting not far from the inner and outer edge of its habitable zone (Gliese 581d and Gliese 581c). While the more distant planet, Gliese 581d, was initially judged to be too cold for life, the closer-in planet, Gliese 581c, was thought to be potentially habitable by its discoverers. However, later analysis by atmospheric experts showed that if it had liquid oceans like Earth, they would rapidly evaporate in a 'runaway greenhouse' effect similar to that which gave Venus the hot, inhospitable climate it has today.
A new possibility emerged late in 2010, when a team of observers led by Steven Vogt at the University of California, Santa Cruz, announced that they had discovered a new planet, which they dubbed Gliese 581g, or 'Zarmina's World'. This planet, they claimed, had a mass similar to that of Earth and was close to the centre of the habitable zone. For several months, the discovery of the first potential Earth twin outside the Solar System seemed to have been achieved. Unfortunately, later analysis by independent teams has raised serious doubts on this extremely difficult detection. Many now believe that Gliese 581g may not exist at all. Instead, it may simply be a result of noise in the ultra-fine measurements of stellar 'wobble' needed to detect exoplanets in this system.
Surface temperature maps for simulations of Gliese 581d assuming an atmosphere of 20 bars of CO2 and varying rotation rates. It is currently unknown whether the planet rotates slowly or has permanent day and night sides. In all cases, the temperatures allow for the presence of liquid water on the surface. © LMD/CNRS It is Gliese 581g's big brother – the larger and more distant Gliese 581d - which has been shown to be the confirmed potentially habitable exoplanet by Robin Wordsworth, François Forget and co-workers from Laboratoire de Météorologie Dynamique (CNRS/UPMC/ENS/Ecole Polytechnique) at the Institute Pierre Simon Laplace in Paris, in collaboration with a researcher from the Laboratoire d'astrophysique de Bordeaux (CNRS/Université Bordeaux 1). Although it is likely to be a rocky planet, it has a mass at least seven times that of Earth, and is estimated to be about twice its size.
At first glance, Gliese 581d is a pretty poor candidate in the hunt for life: it receives less than a third of the stellar energy Earth does and may be tidally locked, with a permanent day and night side. After its discovery, it was generally believed that any atmosphere thick enough to keep the planet warm would become cold enough on the night side to freeze out entirely, ruining any prospects for a habitable climate.
To test whether this intuition was correct, Wordsworth and colleagues developed a new kind of computer model capable of accurately simulating possible exoplanet climates. The model simulates a planet's atmosphere and surface in three dimensions, rather like those used to study climate change on Earth. However, it is based on more fundamental physical principles, allowing the simulation of a much wider range of conditions than would otherwise be possible, including any atmospheric cocktail of gases, clouds and aerosols.
To their surprise, they found that with a dense carbon dioxide atmosphere - a likely scenario on such a large planet - the climate of Gliese 581d is not only stable against collapse, but warm enough to have oceans, clouds and rainfall. One of the key factors in their results was Rayleigh scattering, the phenomenon that makes the sky blue on Earth.
In the Solar System, Rayleigh scattering limits the amount of sunlight a thick atmosphere can absorb, because a large portion of the scattered blue light is immediately reflected back to space. However, as the starlight from Gliese 581 is red, it is almost unaffected. This means that it can penetrate much deeper into the atmosphere, where it heats the planet effectively due to the greenhouse effect of the CO2 atmosphere, combined with that of the carbon dioxide ice clouds predicted to form at high altitudes. Furthermore, the 3D circulation simulations showed that the daylight heating was efficiently redistributed across the planet by the atmosphere, preventing atmospheric collapse on the night side or at the poles.
This artist's concept illustrates a young, red dwarf star surrounded by three planets. Such stars are dimmer and smaller than yellow stars like our sun. Credit: NASA/JPL-Caltech Scientists are particularly excited by the fact that at 20 light years from Earth, Gliese 581d is one of our closest galactic neighbours. For now, this is of limited use for budding interstellar colonists – the furthest-travelled man-made spacecraft, Voyager 1, would still take over 300,000 years to arrive there. However, it does mean that in the future telescopes will be able to detect the planet's atmosphere directly.
While Gliese 581d may be habitable there are other possibilities; it could have kept some atmospheric hydrogen, like Uranus and Neptune, or the fierce wind from its star during its infancy could even have torn its atmosphere away entirely. To distinguish between these different scenarios, Wordsworth and co-workers came up with several simple tests that observers will be able to perform in future with a sufficiently powerful telescope.
If Gliese 581d does turn out to be habitable, it would still be a pretty strange place to visit – the denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth. But the diversity of planetary climates in the galaxy is likely to be far wider than the few examples we are used to from the Solar System. In the long run, the most important implication of these results may be the idea that life-supporting planets do not in fact need to be particularly like the Earth at all.
Local Scientists Produce First Aerogel in Space
First Space-Produced Aerogel Made on Space Sciences Laboratory Rocket Flight
June 19, 1996: Aerogel is the lightest solid known to mankind, with only three times the density of air. A block the size of a human weighs less than a pound. Because of its amazing insulating properties, an inch-thick slab can safely shield the human hand from the heat of a blowtorch. A sugar-cubed size portion of the material has the internal surface area of a basketball court. As the only known transparent insulator, Aerogel is a supercritically dried gel sometimes referred to as "frozen smoke".
On April 3, 1996, the first space-produced samples of aerogels were produced by NASA on a flight of a starfire rocket. The production of such materials in space is interesting because of the strong influence of gravity on how a gel is formed. Comparison of gels manufactured in space and on the ground have shown large differences, and the production of gels in space can provide a higher-quality product with a more uniform structure.
Chemical Engineering Progress (June 1995, p 14) described "the holy grail of aerogel applications has been developing invisible insulation for use between window panes." The production of insulating and transparent windows through aerogel manufacturing in space can develop into a substantial market for residential and commercial applications. The excellent thermal properties and transparent nature of silica aerogel make it an obvious choice for super-insulating windows, skylights, solar collector covers, and specialty windows.
June 19, 1996: Aerogel is the lightest solid known to mankind, with only three times the density of air. A block the size of a human weighs less than a pound. Because of its amazing insulating properties, an inch-thick slab can safely shield the human hand from the heat of a blowtorch. A sugar-cubed size portion of the material has the internal surface area of a basketball court. As the only known transparent insulator, Aerogel is a supercritically dried gel sometimes referred to as "frozen smoke".
On April 3, 1996, the first space-produced samples of aerogels were produced by NASA on a flight of a starfire rocket. The production of such materials in space is interesting because of the strong influence of gravity on how a gel is formed. Comparison of gels manufactured in space and on the ground have shown large differences, and the production of gels in space can provide a higher-quality product with a more uniform structure.
Chemical Engineering Progress (June 1995, p 14) described "the holy grail of aerogel applications has been developing invisible insulation for use between window panes." The production of insulating and transparent windows through aerogel manufacturing in space can develop into a substantial market for residential and commercial applications. The excellent thermal properties and transparent nature of silica aerogel make it an obvious choice for super-insulating windows, skylights, solar collector covers, and specialty windows.
Space Sciences Laboratory Hosts Bill Nye, the Science Guy
October 16, 1996
This week, the Marshall Space Flight Center and the Space Sciences Laboratory are hosting Bill Nye, The Science Guy, as their crew from Seattle films for an upcoming episode of the PBS television series. Taping in SSL will occur on Wednesday, October 16 and Thursday, October 17.
Areas of science from the laboratory that will be featured on an upcoming episode of Bill Nye include Aerogel, "cool telescopes" such as BATSE and the AXAF Calibration Facility, the SSL Solar Vector Magnetograph, and the 105-meter drop tube for microgravity experimentation.
The program will also feature a dive in the Marshall Neutral Buoyancy Simulator, the large tank in which the Hubble Space Telescope repair missions are rehearsed by astronauts, as well as a visit to the Space Station Assembly facility.
This week, the Marshall Space Flight Center and the Space Sciences Laboratory are hosting Bill Nye, The Science Guy, as their crew from Seattle films for an upcoming episode of the PBS television series. Taping in SSL will occur on Wednesday, October 16 and Thursday, October 17.
Areas of science from the laboratory that will be featured on an upcoming episode of Bill Nye include Aerogel, "cool telescopes" such as BATSE and the AXAF Calibration Facility, the SSL Solar Vector Magnetograph, and the 105-meter drop tube for microgravity experimentation.
The program will also feature a dive in the Marshall Neutral Buoyancy Simulator, the large tank in which the Hubble Space Telescope repair missions are rehearsed by astronauts, as well as a visit to the Space Station Assembly facility.
First Space-Produced Aerogel Made on Space Sciences Laboratory Rocket Flight
October 8, 1996: Results are now beginning to become available from the April 3, 1996 rocket flight to produce the first space-made Aerogel. As described in the June 19, 1996 Aerogel Headline , Aerogel is the lightest solid known to mankind, with only three times the density of air. Aerogel, because of its appearence is sometimes referred to as "frozen smoke". Aerogel produced on the ground typically displays a blue haze or has a slight cloudiness to its appearence. This feature is believed to be caused by impurities and variations in the size of small pores in the Aerogel material. Scientists are trying to eliminate this haze so that the insulator might be used in window panes and other applications where transparency is important.
The Aerogel made aboard the flight of the Starfire Rocket in April has indicated that gravity effects in samples of the material made on the ground may be responsible for the adverse pore sizes and thus account for the lack of transparency. Both the diameter and volume of the pores in the space-made Aerogel appear to be between 4 and 5 times better than otherwise identically formulated ground samples. Because Aerogels are the only known transparent insulator, with typical heat conduction properties that are five times better than the next best alternative, a number of novel applications are foreseen in high performance Aerogels.
The Aerogel made aboard the flight of the Starfire Rocket in April has indicated that gravity effects in samples of the material made on the ground may be responsible for the adverse pore sizes and thus account for the lack of transparency. Both the diameter and volume of the pores in the space-made Aerogel appear to be between 4 and 5 times better than otherwise identically formulated ground samples. Because Aerogels are the only known transparent insulator, with typical heat conduction properties that are five times better than the next best alternative, a number of novel applications are foreseen in high performance Aerogels.
Fall Science Meeting Highlights Tethered Satellite Results
October 15, 1996
Scientists attending the Fall 1996 meeting of the American Geophysical Union will be treated to three special sessions covering scientific results obtained from the reflight of the Tethered Satellite System (TSS-1R). The conference will take place on December 18 and 19 in San Francisco, California.
The TSS-1R science mission was conducted on space shuttle flight STS-75 at the end of February 1996. During the flight, the Tethered Satellite was deployed to a distance of 12.3 miles (19.7 km) and science data was collected aboard the satellite, the space-shuttle orbiter, and from a network of ground stations monitoring the earth's ionosphere.
Five hours of tethered operation yielded a rich scientific data set. These data include tether current and voltage measurements, plasma particle and wave measurements, and visual observations for a variety of pre-planned science objectives. During the flight the conducting tether connecting the Orbiter to the satellite was severed, and large currents were observed to be flowing between the satellite and the Orbiter during the break event.
Further scientific data were obtained from the instruments on the satellite after the break, when the science and NASA support teams were able to capture telemetry from the satellite during the overflight of NASA tracking stations.
One important finding from TSS-1R has been the high level of current collected by the satellite at relatively low voltage throughout the deployed phase of the mission. Surprisingly large currents were also observed during the tether break and gas releases, indicating important new physics at play. The three Tethered Satellite sessions at the AGU meeting will cover the results of data analysis from the mission, important supporting physics insights from laboratory experiments, theoretical and numerical modeling of current collection during the mission, and the conclusions of recent studies on the future use of tethers for science in space.
Scientists attending the Fall 1996 meeting of the American Geophysical Union will be treated to three special sessions covering scientific results obtained from the reflight of the Tethered Satellite System (TSS-1R). The conference will take place on December 18 and 19 in San Francisco, California.
The TSS-1R science mission was conducted on space shuttle flight STS-75 at the end of February 1996. During the flight, the Tethered Satellite was deployed to a distance of 12.3 miles (19.7 km) and science data was collected aboard the satellite, the space-shuttle orbiter, and from a network of ground stations monitoring the earth's ionosphere.
Five hours of tethered operation yielded a rich scientific data set. These data include tether current and voltage measurements, plasma particle and wave measurements, and visual observations for a variety of pre-planned science objectives. During the flight the conducting tether connecting the Orbiter to the satellite was severed, and large currents were observed to be flowing between the satellite and the Orbiter during the break event.
Further scientific data were obtained from the instruments on the satellite after the break, when the science and NASA support teams were able to capture telemetry from the satellite during the overflight of NASA tracking stations.
One important finding from TSS-1R has been the high level of current collected by the satellite at relatively low voltage throughout the deployed phase of the mission. Surprisingly large currents were also observed during the tether break and gas releases, indicating important new physics at play. The three Tethered Satellite sessions at the AGU meeting will cover the results of data analysis from the mission, important supporting physics insights from laboratory experiments, theoretical and numerical modeling of current collection during the mission, and the conclusions of recent studies on the future use of tethers for science in space.
Unique telescope to open the X(-ray) Files
Artist's concept of AXAF in orbit., The nested mirrors are at center behind the dotted circles.
The finest set of mirrors ever built for X-ray astronomy has arrived at NASA's Marshall Space Flight Center for several weeks of calibration before being assembled into a telescope for launch in late 1998.
The High-Resolution Mirror Assembly (HRMA), as it is known, will be the heart of the Advanced X-ray Astrophysics Facility (AXAF) which is managed by Marshall Space Flight Center. HRMA was built by Eastman Kodak and Hughes Danbury Optical Systems. In 1997-98, they will be assembled by TRW Defense and Space Systems into the AXAF spacecraft. AXAF is designed to give astronomers as clear a view of the universe in X-rays as they now have in visible light through the Hubble Space Telescope.
Indeed, one of the Hubble's recent discoveries may move near the top of the list of things to do for AXAF. Hubble recently discovered that some quasars reside within quite ordinary galaxies. Quasars (quasi-stellar objects) are unusually energetic objects which emit up to 1,000 times as much energy as an entire galaxy, but from a volume about the size of our solar system.
More clues to what is happening inside quasars may lie in the X-rays emitted by the most violent forces in the universe.
Before AXAF can embark on that mission, though, its mirrors must be measured with great precision so astronomers will know the exact shape and quality of the mirrors. Then, once the telescope is in space, they will be able to tell when they discover unusual objects, and be able to measure exactly how unusual.
These measurements will be done in Marshall's X-ray Calibration Facility, the world's largest, over the next few weeks.
AXAF will use four sets of mirrors, each set nested inside the other, to focus X-rays by grazing incidence reflection, the same principle that makes sunlight glare off clear windshields. AXAF's smallest mirror - 63 cm (24.8 in.) in diameter - is larger than the biggest - 58 cm (22.8 in.) flown on the Einstein observatory (HEAO-2) in 1978-81.
Mapping the details of the mirror will start with an X-ray source pretty much like what a dentist uses to check your teeth. But that's next week's story.
The finest set of mirrors ever built for X-ray astronomy has arrived at NASA's Marshall Space Flight Center for several weeks of calibration before being assembled into a telescope for launch in late 1998.
The High-Resolution Mirror Assembly (HRMA), as it is known, will be the heart of the Advanced X-ray Astrophysics Facility (AXAF) which is managed by Marshall Space Flight Center. HRMA was built by Eastman Kodak and Hughes Danbury Optical Systems. In 1997-98, they will be assembled by TRW Defense and Space Systems into the AXAF spacecraft. AXAF is designed to give astronomers as clear a view of the universe in X-rays as they now have in visible light through the Hubble Space Telescope.
Indeed, one of the Hubble's recent discoveries may move near the top of the list of things to do for AXAF. Hubble recently discovered that some quasars reside within quite ordinary galaxies. Quasars (quasi-stellar objects) are unusually energetic objects which emit up to 1,000 times as much energy as an entire galaxy, but from a volume about the size of our solar system.
More clues to what is happening inside quasars may lie in the X-rays emitted by the most violent forces in the universe.
Before AXAF can embark on that mission, though, its mirrors must be measured with great precision so astronomers will know the exact shape and quality of the mirrors. Then, once the telescope is in space, they will be able to tell when they discover unusual objects, and be able to measure exactly how unusual.
These measurements will be done in Marshall's X-ray Calibration Facility, the world's largest, over the next few weeks.
AXAF will use four sets of mirrors, each set nested inside the other, to focus X-rays by grazing incidence reflection, the same principle that makes sunlight glare off clear windshields. AXAF's smallest mirror - 63 cm (24.8 in.) in diameter - is larger than the biggest - 58 cm (22.8 in.) flown on the Einstein observatory (HEAO-2) in 1978-81.
Mapping the details of the mirror will start with an X-ray source pretty much like what a dentist uses to check your teeth. But that's next week's story.
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