Discovery of the most distant galaxy in the cosmic dawn

In addition to finding the most distant galaxy, the team's research verified that the proportion of neutral hydrogen gas in the 750-million-year-old early universe was higher than it is today.

By NAOJ, Japan — Published: June 19, 2012

Color composite image of the Subaru XMM-Newton Deep Survey Field. Right panel: The red galaxy at the center of the image is the most distant galaxy, SXDF-NB1006-2. Left panels: Close-ups of the most distant galaxy. Credit: NAOJ A team of astronomers led by Takatoshi Shibuya from the Graduate University for Advanced Studies, Japan; Nobunari Kashikawa from the National Astronomical Observatory of Japan; Kazuaki Ota from Kyoto University, Japan; and Masanori Iye from the National Astronomical Observatory of Japan has used the Subaru and Keck telescopes to discover the most distant galaxy ever found, SXDF-NB1006-2, at a distance of 12.91 billion light-years from Earth. This galaxy is slightly farther away than GN-108036, which the Subaru Telescope discovered last year, and was the most distant galaxy discovered at the time. In addition, the team's research verified that the proportion of neutral hydrogen gas in the 750-million-year-old early universe was higher than it is today. These findings help scientists understand the nature of the early universe during the "cosmic dawn," when the light of ancient celestial objects and structures appeared from obscurity. Astronomers think that the universe began 13.7 billion years ago at the Big Bang. The exteme temperature and density of this fireball decreased rapidly as its volume increased. Hot cosmic plasma composed mainly of protons and electrons recombined to form neutral hydrogen atoms within 380,000 years after the Big Bang — this was the beginning of the cosmic "Dark Ages." From then on, the gas continued to cool and fluctuated in density. About 200 to 500 million years after the Big Bang, the dense parts of neutral hydrogen clouds contracted under their own gravity, and the first stars and galaxies formed. The radiation from this first generation of stars started to heat and reionize the hydrogen in nearby space, eventually leading to the reionization of the entire universe. This was the era of "cosmic reionization" or the "cosmic dawn." The current team focused their research on identifying the exact epoch of the cosmic dawn in an effort to answer major astronomical questions about the history of our universe. How did the team design research to explore such an ancient, extremely distant time? The group's first steps were to conduct a survey of distant galaxies and measure their number and brightness. Because light from the distant universe takes time to reach Earth, identification of more distant galaxies allows astronomers to trace farther back in time and locate the epoch of the cosmic dawn. However, neutral hydrogen in intergalactic space dimmed the light from galaxies before the cosmic dawn and made them more difficult to observe. Because the team needed to search a vast area for objects in the far distant universe, it used the prime focus camera mounted on the Subaru Telescope (Suprime-Cam) for its initial surveys. Suprime-Cam captures images of objects in a wide field of view from the large 8.2-meter primary mirror of the Subaru Telescope and is well-known for discovering faint, far distant galaxies and then measuring the amount of neutral hydrogen in the early universe. The use of Suprime-Cam was even more compelling with the 2008 installation of new detectors with a sensitivity about twice as high as their predecessors, particularly in the red wavelengths.  Armed with the most sensitive eyes in the world, the researchers could carry out surveys for extremely distant galaxies — beyond redshift 7, where the majority of energy output from galaxies is detected in red wavelengths. To fine-tune their survey even more, a team led by Iye constructed a new special filter named NB1006 through which they could selectively identify the light of distant galaxies at a redshift of nearly 7.3.  The team used Suprime-Cam, complete with its new highly sensitive detectors, and attached the NB1006 filter to observe two specifically designated regions of the sky for detailed study: the Subaru Deep Field and the Subaru XMM-Newton Deep Survey Field. After a total of 37 hours in seven nights of observations in these wide fields, the team carefully processed the images they had obtained. Shibuya measured the color of 58,733 objects in the images and identified four galaxy candidates at a redshift of 7.3. A careful investigation of the brightness variation of the objects allowed the team to narrow down the number of candidates to two.  Then it was necessary for the team to make spectroscopic observations to confirm the nature of these candidates. They observed the two galaxy candidates with two spectrographs — the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope and the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck Telescope — and identified one candidate for which a characteristic emission line of distant galaxies could be detected.  The current team found that the proportion of neutral hydrogen was increasing in the far distant universe. They concluded that about 80 percent of the hydrogen gas in the ancient universe, 12.91 billion years ago at a redshift of 7.2, was neutral. In sum, this careful research plan and procedures, including the appropriate removal of contaminations that could lead to false results, resulted in the successful discovery and confirmation of the most distant galaxy ever discovered: SXDF-NB1006-2. In addition, the findings gave the astronomers confidence that they were observing an object during the last phase of the cosmic dawn. Although finding just one galaxy at a critical epoch is exciting by itself, it is not a sufficient sample to characterize the entire epoch. Precise measurement of the number of galaxies during the cosmic dawn requires surveys of even wider fields. The scheduled 2012 installation of Subaru's new instrument, Hyper Suprime-Cam (HSC), will allow researchers to observe a field of view seven times greater than that of Suprime-Cam and open the door to a huge galaxy sample beyond redshift 7. Observations with HSC are steps in the direction of uncovering the dark periods of the universe and understanding the physical properties and formation of the first stars and galaxies. Shibuya summarized the team's future intent and hopes: "By conducting an extremely wide HSC survey for distant galaxies beyond redshift 7, we will find the mechanisms of the cosmic reionization in a variety of ways, not just by investigating their number and brightness."  "We have been pushing the limits of 8-10-meter-class telescopes to detect distant galaxies," said Iye. "The 30-meter mirror of the TMT will be able to gather up to 10 times more light than current large telescopes and detect faint light from galaxies up to a redshift of 14. The day is not so far off when the mysteries of the Dark Ages of the universe and the physical properties of the first galaxies will be revealed."

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Researchers estimate ice content of crater at Moon's south pole

In addition to the possible evidence of ice, the scientists' map of Shackleton revealed a remarkably preserved crater that has remained relatively unscathed since its formation more than 3 billion years ago.

By NASA Headquarters, Washington, D.C., NASA's Goddard Space Flight Center, Greenbelt, Maryland — Published: June 21, 2012

Elevation (left) and shaded relief (right) image of Shackleton, a 12.5-mile-diameter (20 kilometers) permanently shadowed crater adjacent to the lunar south pole. The structure of the crater's interior was revealed by a digital elevation model constructed from over 5 million elevation measurements from the Lunar Orbiter Laser Altimeter. Credit: NASA/Zuber, M.T. et al., Nature, 2012 NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft has returned data that indicate ice may make up as much as 22 percent of the surface material in a crater located on the Moon's south pole.  A team of NASA and university scientists using laser light from LRO's laser altimeter examined the floor of Shackleton Crater. They found that the crater's floor is brighter than those of other nearby craters, which is consistent with the presence of small amounts of ice. This information will help researchers understand crater formation and study other uncharted areas of the Moon.  "The brightness measurements have been puzzling us since two summers ago," said Gregory Neumann of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "While the distribution of brightness was not exactly what we had expected, practically every measurement related to ice and other volatile compounds on the Moon is surprising, given the cosmically cold temperatures inside its polar craters."  The spacecraft mapped Shackleton Crater with unprecedented detail, using a laser to illuminate the crater's interior and measure its albedo, or natural reflectance. The laser light measures to a depth comparable to its wavelength, or about a micron. That represents a millionth of a meter, or less than one ten-thousandth of an inch. The team also used the instrument to map the relief of the crater's terrain based on the time it took for laser light to bounce back from the Moon's surface. The longer it took, the lower the terrain's elevation. In addition to the possible evidence of ice, the group's map of Shackleton revealed a remarkably preserved crater that has remained relatively unscathed since its formation more than 3 billion years ago. The crater's floor is itself pocked with several small craters, which may have formed as part of the collision that created Shackleton. The crater, named after the Antarctic explorer Ernest Shackleton, is 2 miles (3 kilometers) deep and more than 12 miles (19 kilometers) wide. Like several craters at the Moon's south pole, the small tilt of the lunar spin axis means Shackleton Crater's interior is permanently dark, and therefore extremely cold.  "The crater's interior is extremely rugged," said Maria Zuber from the Massachusetts Institute of Technology in Cambridge. "It would not be easy to crawl around in there."  While the crater's floor was relatively bright, Zuber and her colleagues observed that its walls were even brighter. The finding was at first puzzling. Scientists had thought that if ice were anywhere in a crater, it would be on the floor where no direct sunlight penetrates. The upper walls of Shackleton Crater are occasionally illuminated, which could evaporate any ice that accumulates. A theory offered by the team to explain the puzzle is that "moonquakes"— seismic shaking brought on by meteorite impacts or gravitational tides from Earth — may have caused Shackleton's walls to slough off older darker soil, revealing newer, brighter soil underneath. Zuber's team's ultra-high-resolution map provides strong evidence for ice on both the crater's floor and walls.  "There may be multiple explanations for the observed brightness throughout the crater," said Zuber. "For example, newer material may be exposed along its walls, while ice may be mixed in with its floor."

The "Exoplanet" Venus

Observing the Transit of Venus won't be just a memorable experience. Astronomers hope the event will help them understand alien worlds around other stars, too. 


These days, most people don't think of sky events as scientific opportunities. Excuse for a star party, sure; reason to stop looking at your feet or your iPhone as you walk, maybe. But Venus's upcoming transit of the Sun isn't useful just for astronomy publicity: there are real science gains to be had, too. Among these is the chance to use our sister planet as an exoplanet proxy.

Venus's atmosphere appears strangely yellow and purple in this enhanced-color image, created by combining shots taken through ultraviolet, green, and near-infrared filters.

S&T: Sean Walker

The analog isn't 1-to-1. An Earth- or Venus-sized exoplanet seen passing in front of a Sun-like star would cause a roughly 0.008% drop in the star's brightness. That's less than one-tenth the magnitude of the drop Venus causes during its central passage as seen from Earth (0.1%). The difference is due to scale: Venus is much closer to us than the Sun, so it looks bigger compared to the Sun than it actually is. On the other hand, an exoplanet and its star are basically the same distance from us, so the amount of light blocked is more a matter of actual size than perspective.

But Venus's transit still has exoplanet merit. In particular, observations of sunlight passing through the planet's atmosphere during the transit might help astronomers out. Researchers hope to determine whether spectroscopic measurements of that sunlight — which tease apart the chemical composition of the atmosphere the light is passing through — are accurate enough to determine which elements enshroud faraway worlds.

Astronomers have already studied several exoplanet atmospheres anddetected hazes and elements such as water. But Venus will be a sanity check that's hard to come by for those observing planets no one can see with the naked eye.

The Hubble Space Telescope is jumping into this fun, too. Just like us, Hubble can't stare directly at the Sun without damaging its optics. Instead, Hubble operators will point the telescope at the Moon, using it as a (less-than-smooth) projection screen to watch changes in reflected sunlight during Venus's transit. The scope's Advanced Camera for Surveys, Wide Field Camera 3, and Space Telescope Imaging Spectrograph will observe the Moon in wavelengths ranging from ultraviolet to near-infrared. By closely studying the light from before, during, and after the transit, astronomers hope to pick out chemical signatures from Venus's atmosphere that match what they already know is there from direct measurements. 

Only 1/100,000th of the sunlight will filter through Venus's atmosphere and be reflected off the Moon, so this task is no mean feat.

Astronomers have also asked for Hubble time to watch a similar reflection off Jupiter on September 20th, when Venus transits the Sun as seen from the king of the planets. And at Saturn, NASA's Cassini spacecraft is already set to watch Venus transit from that system on December 21st. Unlike Hubble, Cassini can directly observe the Sun.

 

Para ler a notícia na íntegra clique no link: http://www.skyandtelescope.com/news/The-Exoplanet-Venus-155964305.html

 

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X-ray Telescope Launches Successfully

After 20 years of planning, the NuSTAR X-ray telescope launched today from an island in the Pacific. 

Artist's concept of NuSTAR in orbit. The 10-meter (30-foot) mast separates the optics modules with the nested mirrors (right) from the digital camera (left). The background image is a view of the Galactic Center as seen by the Chandra X-ray Observatory at lower X-ray energies.

NASA / JPL-Caltech

NuSTAR, the first telescope to focus very high-energy X-rays, launched successfully from Kwajalein Atoll at 9:00 a.m. Pacific time. NuSTAR will collect X-rays in the energy range of 6 to 79 keV, similar to the energy range of medical X-rays. Most X-ray astronomy has been done at lower energies, where X-rays are less difficult to focus. But rather than penetrate skin and muscle to look for broken bones, NuSTAR's X-rays penetrate dust and gas to reveal supernova remnants and the flicker of gas around feeding black holes, where high-energy processes abound 

To place NuSTAR in an equatorial, low-Earth orbit, one that will avoid interference from energetic charged particles trapped in Earth's magnetic field, the launch had to take an unusual form. An L-1011 Stargazer aircraft climbed to 40,000 feet before dropping a Pegasus XL rocket strapped to its belly. The rocket fell for 5 seconds before igniting the first of three stages to carry NuSTAR into orbit. Watch a video of a Stargazer-Pegasus launch here: 



NuSTAR was originally scheduled for launch in March, but a problem (now fixed) in the flight software delayed the launch by three months. For principal investigator Fiona Harrison (California Institute of Technology), three months was a drop in the bucket compared to the 20 years she has dedicated to this mission. 

To build NuSTAR, Harrison and colleagues had to develop several new technologies. "Focusing [high-energy] X-rays calls for a new way of doing business," says instrument manager William Craig (UC Berkeley). Unlike visible light, which comes to a focus when photon paths bend through a lens or bounce straight off a mirror, X-rays have too much energy, and too short a wavelength, to be directed in this way. If you send X-rays straight at a mirror, they'll pass right through. 

NuSTAR's two optics modules each contain 133 nested mirrors. This picture shows the first optics module midway through assembly with 82 nested mirrors.

www.nustar.caltech.edu

Instead, NuSTAR's mirrors will deflect the X-rays by bouncing them at a very low "grazing incidence" angle barely skimming the mirrors. This method has long been used in other X-ray telescopes, but NuSTAR's design is more extreme. With 133 mirrors nested inside one another in each of two optic units, NuSTAR can focus enough high-energy X-rays to make images ten times crisper and 100 times more sensitive than what is currently possible. Each image can be broken down into a spectrum with ten times the spectral resolution currently possible at these energies. 

"It's rare you get the chance of increasing a sensitivity factor by more than 100 times better than current methods," says Bill Craig (Lawrence Livermore National Laboratory). "This is really a game changer."

NuSTAR's mirrors came surprisingly cheap — only $20 per sheet — because the mirrors are made of the same glass used in laptop displays. Each mirror has a special reflective coating only a few atoms thick.

NuSTAR's mast will deploy to the length of a school bus, separating the camera from the mirrors so that X-rays can be brought to a focus. This image shows a mast deployment test done in August 2009.

www.nustar.caltech.edu

Because the X-rays bend so slightly when they graze off the nested mirrors, they come to a focus at a great distance. So the camera imaging has to be placed far from the mirrors. A lightweight, but incredibly stiff mast holds the cameras 10 meters (33 feet) from the mirrors. This mast is a scaled-down version of a longer mast used successfully in a previous radar topography mission. The full-length mast wouldn't fit in a Pegasus rocket, so it was folded up for launch. The whole telescope was no bigger than a refrigerator this morning. But roughly a week from today, scientists and engineers will be biting their nails as the mast deploys, each part unfolding and locking like a Tinkertoy set. See the simulation here: 



Three weeks after the mast is deployed, the telescope should be ready for science operations. The primary mission is set for two years, but NuSTAR's mission could potentially be extended several years beyond that. Among its many targets are spinning black holes, radioactive titanium shining in supernova remnants, and the Sun's atmosphere.

 

The ESA's Integral satellite took the fuzzy picture on the upper left, showing X-rays from galaxies far beyond our own. NuSTAR will be able to resolve the fuzzy image into distinct sources, as demonstrated by the simulation on the lower right.

ESA / NASA / JPL-Caltech

The launch of NuSTAR, a NASA Small Explorer mission, comes at an interesting time: even as X-ray astronomy celebrates its 50th anniversary, the next major X-ray observatory (the International X-ray Observatory) has been cancelled, and no major X-ray telescopes are planned for the near future. X-ray astronomers will depend on smaller satellites with shorter expected lifetimes, such as NuSTAR and the JapaneseASTRO-H (set to launch in 2014), as well as aging observatories, such as Chandra and XMM-Newton, to advance the field over the next decade or two.

 

Para ler a notícia na íntegra clique no link: http://www.skyandtelescope.com/news/Successful-Launch-of-X-ray-Telescope-158867225.html

 

 

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Lucimary Vargas
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Observatório Astronômico Monoceros
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All-Sky Survey Sees Millions of Stars

A collaboration between professional and amateur astronomers is producing a careful map of stellar brightnesses and colors across the entire night sky. 

When I flip through the press conference schedule for an American Astronomical Society meeting, I usually don't expect to see a presenter listed from a professional-amateur collaboration. So I was pleasantly surprised to find that Arne Henden, Director of the American Association of Variable Star Observers, was speaking at the AAS summer meeting this week in Anchorage, Alaska. 

This map shows the current coverage of the primary AAVSO All-Sky Photometric Survey, with two visits per field. The white spot over New Mexico is due to the July monsoon season and fires in the state. About 95% of the sky has been covered; the remainder has one visit.

AAVSO / E. Los

As Henden announced yesterday, the sixth interim release is out for the AAVSO Photometric All-Sky Survey, a pro-am collaboration that's taking careful color and brightness measurements, through five filters, of stars between 10th and 17th magnitude. This magnitude range has never before been systematically surveyed, although it does partly overlap with previous all-sky work in both photometry and astrometry (high-precision position measurements, such as those done by the ESA's Hipparcos satellite and the U.S. Naval Observatory's UCAC program).

The pro-am team behind the project also chose these magnitudes because they're the ones typically observed in backyard telescopes.

The APASS project uses two pairs of 8-inch astrographs, one in New Mexico and the other in Chile. Each pair sits on a Paramount ME mount and is operated remotely to point at the same position on the sky. One scope takes the blue filter exposures (Johnson B and Sloan g') and the other the redder exposures (Johnson V and Sloan r' and i'). Each image is 2.9° × 2.9° in size, a field of view that would encompass roughly 90 full moons. So far, the survey has covered roughly 95% of the sky twice and measured the color and brightness of 42 million stars.

"The 8-inch scopes are the right tool for the job," Henden said during the press conference. "They may look small, but they're doing frontline, state-of-the-art science." 

APASS uses solely commercial hardware and software, working thanks to private grants and equipment loans from vendors. Originally the project planned to have only one set of 8-inch scopes, using them first in New Mexico from October 2009 to summer 2010 and then moving them to Chile to observe the Southern Hemisphere. Although the team still moved the tried-and-true New Mexico scopes to Chile as planned, an additional grant from the Robert Martin Ayers Science Fund allowed the AAVSO to purchase a second pair of astrographs to put in New Mexico to continue observing the Northern Hemisphere.

Henden says they have already compared their observations against a number of standard fields and found APASS's photometric precision is about 3%. He expects that to go down to 1-2% by the final release of the catalog in 2014. 

Brian Skiff (Lowell Observatory), who's spent several years compiling a database of high-quality photometry, says he suspects that for the most crowded parts of the sky observers will still need to rely on photometric data taken with bigger telescopes. "But even within its limits, [APASS] should be a boon for observers — both professional and amateur — doing systematic observing of just about any sort," he adds. It's a big deal to have reliable magnitudes and colors for these stars done with a standard system: if you have high-precision photometry for stars across the whole sky, you can more accurately (and more quickly) determine brightnesses for variable stars or for new objects such as supernovae — without searching around the sky or your images for something you do have data for. "Folks have wanted a uniform survey like this for a long time."

 

Para ler a notícia na íntegra clique no link: http://www.skyandtelescope.com/news/All-Sky-Survey-Sees-Millions-of-Stars-158868375.html

 

The Universe’s Lost Lithium

The Universe's Lost Lithium

A decades-old clash between modern cosmology and stellar observations may have just gotten worse. 

A paper set to appear in Physical Review Letters later this month might add to a problem that's had astronomers baffled for 30 years: the universe doesn't have enough lithium.

An artist's highly symbolic representation of the Cygnus X-1 black hole and its X-ray-hot inner accretion disk. A new study suggests that jet-shooting, star-siphoning stellar mass black holes might make worse an already long-standing cosmochemical problem.

NASA / CXC / M.Weiss

As the third element in the periodic table, lithium is one of a few elements that have an abundance closely tied to processes just after the Big Bang. Detailed models of big bang nucleosynthesis predict certain levels of these elements, such as hydrogen and helium, and for the most part these models closely match what observers see in the cosmos. 

But 30 years ago, Monique and François Spite (Paris Observatory) reported that the isotope lithium-7 was far rarer in old, metal-poor stars in the Milky Way's halo than it should be. These stars formed in our galaxy's early days, back when its chemical makeup more or less matched what existed after the universe's birth. Relatively cool and with poor mixing between surface and interior, such stars should have lithium-7 levels in keeping with primordial abundances. 

Yet these stars have at most one-third the amount of lithium-7 predicted. Even lower levels are found in the most primitive stars — stars with very low levels of heavy elements, which weren't created by big bang nucleosynthesis. This upper limit became known as "the lithium problem." 

Astronomers have devised various solutions to explain the missing lithium, but nothing's really worked. Any process that could deplete the lithium would need to happen in stars of various temperatures and compositions and without messing up the abundances of the other elements, François Spite says. 

Now, Fabio Iocco (Oskar Klein Center for Cosmoparticle Physics, Sweden) and Miguel Pato (Munich Technical University, Germany) have added another potential hurdle: black holes.

Recent work suggests that in the early galaxy there may have been a fairnumber of "microquasars," stellar-mass black holes yanking material off a stellar companion and shooting jets of superhot plasma into space. Iocco and Pato looked at the conditions in the hot accretion disks around these black holes, where temperatures can reach tens to hundreds of billions kelvin. Such temperatures jump over those where lithium-7 is merely disrupted (around 2.5 million K) and up to the point where the helium reactions that create lithium happen, Iocco says.

The duo found that, even if only 1% of the Milky Way's microquasars produced temperatures hot enough to create lithium-7, the amount created would rival that expected from the universe's first few hours.

So, the question remains: where is all the lithium?

 

Para ler a notícia na íntegra clique no link: http://www.skyandtelescope.com/news/Universes-Lost-Lithium-159192855.html

 

 

Titan's Tropical "Oases"

Based on infrared images from the Cassini orbiter, small areas in the equatorial regions of Titan appear to contain lakes of liquid methane. 

This infrared image from Cassini is looking toward the dark region of Titan called Shangri-La, east of the landing site of the Huygens probe. Saturn's rings lie in the distance.

NASA / JPL / Space Science Inst.

My vote for "Coolest Moon in the Solar System" goes to Saturn's Titan. A bit larger than Mercury, Titan has a crust of rock-hard water ice and an atmosphere denser than Earth's. The "air" around Titan is 95% nitrogen, but that's where any similarity to what we breathe ends. Almost all the rest is methane (CH₄).

Sunlight is very good at transforming methane into ethane(C₂H₆) and a host of other hydrocarbon compounds, a.k.a. smog. (That explains why this moon's surface is masked from our view, at least in visible light.) Not so long ago, astronomers assumed that enough ethane has been cooked up in in Titan's atmosphere to create a global ocean at least 3 miles (5 km) deep. 

But that's not the case at all! As first glimpsed by radar in the 1990, then later by infrared imaging, and most recently by NASA's Cassini orbiter, the surface of Titan is mostly dry land, er, ice. The spacecraft did find a cluster of hydrocarbon lakes at its poles, but the moon's midsection appeared to consist of vast tracts of dune fields. There must be someliquid methane near the equator — in 2005 the Huygens landed splutted onto a methane-moistened patch at latitude 10° south — but theorists have reasoned that any tropical methane should be quickly whisked toward the cooler poles and dumped into the reservoirs there.

Titan's atmospheric haze is transparent at the near-infrared wavelength of 1.3 microns, which allowed the Cassini spacecraft to record surface reflectivity (here color coded from black to red) in the vicinity of the Huygens landing site. This view is about 600 miles (900 km) wide.

C. Griffith & others / Nature

Now researchers led by Caitlin Griffith (University of Arizona) have found evidence of puddled methane in Titan's equatorial region. As they describe in theJune 14th issue of Nature, the suspect areas appear in views taken at several infrared wavelengths during close flybys between 2004 and 2008.

One oval feature, about 40 miles (60 km) long, lies about 500 miles (750 km) from the Huygens landing site. It's too dark to be a solid surface, which would reflect at least some infrared energy, or even solid particles floating atop liquid. The team concludes that it must be an exposure of liquid methane, one that's lacking the spectroscopic signature of liquid ethane seen the much larger Ontario Lacus near Titan's south pole.

Other features appear somewhat brighter in the infrared, suggesting that they're patches dampened by liquid methane a few inches deep. One of these is unusual in that it lies within a dune field. This hadn't been expected, though hollows sometimes become wet on similarly shaped sand dunes on Earth. "In essence," Griffith notes in a NASA press release, "Titan may have oases."

The existence of these tropical lakes has only deepened the mystery of where and how Titan generates its methane. They have to be replenished somehow, and hydrocarbons haven't rained down from the Titanian sky often enough to supply it. In fact, earlier studies show that the moon needs to generate some 50 million tons of methane each year to keep its atmosphere enriched at present-day levels. As Griffith and her colleagues conclude, "More observations are needed to determine whether this 4.5-billion-year-old moon is undergoing a specific recent flourish of geological activity."

Fortunately, NASA managers have agreed to fund the Cassini mission through at least September 2017, a few months after the next summer solstice in Saturn's northern hemisphere. The spacecraft just concluded a close brush Titan on June 6th, utilizing its radar imager while passing just 596 miles (959 km) away, and more close flybys have been scheduled in July, September, and November (twice).

 

Para ler a notícia na íntegra clique no link: http://www.skyandtelescope.com/news/Titans-Tropical-Oases-159586515.html

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Lucimary Vargas
Presidente
Observatório Astronômico Monoceros
Planetário Além Paraíba
Estação Meteorológica 083/MG-5ºDISME-INMET
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A Windy Early Universe

Winds in the early universe could make radio observations of the first stars and galaxies a little easier.

An artist imagines the adolescent universe, some 250 million years to 1 billion years after the Big Bang. The first stars and galaxies have already formed, burning holes in the surrounding hydrogen gas. Current generation telescopes are beginning to investigate this era, but new simulations suggest that information can be gleaned from earlier in the universe's evolution as well.

SKA Organisation/Swinburne Astronomy Productions

The early universe was a vastly different place from the one we see today. No stars burned in faraway galaxies — there weren't any galaxies. Instead, photons were trapped in a dance with the hot plasma of protons and electrons that suffused the universe. Sound waves rang out across this primordial soup, sloshing gas and photons into waves of higher and lower density. Only after about 300,000 years did the universe expand and cool enough for protons and electrons to begin to combine into hydrogen atoms. That set the photons free to travel across the universe, giving us the cosmic microwave background. 

Meanwhile, the hydrogen atoms fell together into gravity wells created by clumps of dark matter, starting the building process for proto-stars and proto-galaxies. But there's a catch. The sound waves ringing through the dense primordial soup gave some hydrogen atoms a bulk motion. That created a "wind" of ordinary matter that simply swept past the smaller of the dark matter clumps. 

The existence of that wind might have important consequences for the formation of structure in the early universe, researchers found in 2010. Now, an international team reports this week in the journal Nature the first simulated 3D maps that take this wind effect into account. 

Eli Visbal (Harvard University) and his colleagues mixed various physical considerations together to create the new maps, which show how the first stars might have been distributed in the young cosmos. When the universe is only 70 million years old, the stars already form a webby structure like that seen in today's universe, with clumps and voids roughly 20 million light-years across, large enough to be important for radio observations.

"You no longer have the old picture of dark matter and gas both quietly evolving," says Jonathan Pritchard (Imperial College London), who was not involved with the study. "Instead, you have supersonic winds of gas that could blow the gas out of dark matter gravity wells." 

In a windy early universe, galaxies would have been harder to form: only larger matter clumps would have successfully retained gas. But that's good news for radio telescopes looking back in time at the first structures in the early universe, because it means those first structures were larger (and, therefore, more obvious) than previously thought. 

Seeing the First Stars

The Murchison Widefield Array in Australia is a low-frequency radio telescope with an eye toward the evolving universe after the first stars and galaxies formed. A prototype has already been built, and construction has begun on the MWA, with science operations to begin in late 2012.

Photo courtesy of the MWA project

Individual stars and galaxies are too far away to be seen directly. Astronomers take an indirect approach, looking for where neutral hydrogen atoms don'texist. That's because, as the first stars formed, they heated their surroundings, blowing out bubbles of ionized hydrogen sort of like the holes in Swiss cheese, explains Abraham Loeb (Harvard University). 

Looking for the first stars is therefore a search for holes in hydrogen emission. In the lonely depths of space, neutral hydrogen atoms undergo a rare energy transition, emitting a radio signal with a specific wavelength of about 21 cm. This signal can be seen by radio telescopes and is often used to map galaxies' extended disks. 

Low-frequency radio telescopes such as the Murchison Widefield Array, the Low-Frequency Array (LOFAR), and the Precision Array to Probe the Epoch of Re-ionization (PAPER), already use the 21 cm signal to investigate the adolescent universe at an age of 250 million to 1 billion years after the Big Bang. At that point, stars and galaxies had already formed. Astronomers are planning the next generation of radio telescopes to go even further, looking back to the formation of the very first galaxies. (MWA and LOFAR do extend to low frequencies, but not at high enough sensitivity to test the predictions made by the simulations.)

An artist's illustration of the field of telescopes that will be part of the planned Square Kilometer Array.

SKA Organisation/TDP/DRAO/Swinburne Astronomy Productions

Simulations like those in the new study are crucial for planning future projects such as the Square Kilometer Array, Pritchard says. With powerful enough radio telescopes, astronomers could potentially see the 21 cm signal from a universe only 10 million years old, but researchers need to know whether it's even worth building instruments to look that far back. The new results suggest that the earliest Swiss-cheese hydrogen holes should be detectable around 50 to 150 million years after the Big Bang, at a time that (before now) it wasn't clear there was anything to see. That could help plans are already being proposed to extend SKA's frequency range to lower bands where such early times would be observable. 

Posted By Monica Young, June 20, 2012

 

Para ler a notícia na íntegra clique no link: http://www.skyandtelescope.com/news/A-Windy-Early-Universe-159762715.html

Fonte: AstronomyNews

Study Finds Ancient Warming Greened Antarctica

 

News release: 2012-179                                                                     June 17, 2012 Study Finds Ancient Warming Greened Antarctica The full version of this story with accompanying images is at: http://www.jpl.nasa.gov/news/news.cfm?release=2012-179&cid=release_2012-179 PASADENA, Calif. -- A new university-led study with NASA participation finds ancient Antarctica was much warmer and wetter than previously suspected. The climate was suitable to support substantial vegetation -- including stunted trees -- along the edges of the frozen continent. The team of scientists involved in the study, published online June 17 in Nature Geoscience, was led by Sarah J. Feakins of the University of Southern California in Los Angeles, and included researchers from NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Louisiana State University in Baton Rouge. By examining plant leaf wax remnants in sediment core samples taken from beneath the Ross Ice Shelf, the research team found summer temperatures along the Antarctic coast 15 to 20 million years ago were 20 degrees Fahrenheit (11 degrees Celsius) warmer than today, with temperatures reaching as high as 45 degrees Fahrenheit (7 degrees Celsius). Precipitation levels also were found to be several times higher than today. "The ultimate goal of the study was to better understand what the future of climate change may look like," said Feakins, an assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences. "Just as history has a lot to teach us about the future, so does past climate. This record shows us how much warmer and wetter it can get around the Antarctic ice sheet as the climate system heats up. This is some of the first evidence of just how much warmer it was." Scientists began to suspect that high-latitude temperatures during the middle Miocene epoch were warmer than previously believed when co-author Sophie Warny, assistant professor at LSU, discovered large quantities of pollen and algae in sediment cores taken around Antarctica. Fossils of plant life in Antarctica are difficult to come by because the movement of the massive ice sheets covering the landmass grinds and scrapes away the evidence. "Marine sediment cores are ideal to look for clues of past vegetation, as the fossils deposited are protected from ice sheet advances, but these are technically very difficult to acquire in the Antarctic and require international collaboration," said Warny. Tipped off by the tiny pollen samples, Feakins opted to look at the remnants of leaf wax taken from sediment cores for clues. Leaf wax acts as a record of climate change by documenting the hydrogen isotope ratios of the water the plant took up while it was alive. "Ice cores can only go back about one million years," Feakins said. "Sediment cores allow us to go into 'deep time.'" Based upon a model originally developed to analyze hydrogen isotope ratios in atmospheric water vapor data from NASA's Aura spacecraft, co-author and JPL scientist Jung-Eun Lee created experiments to find out just how much warmer and wetter climate may have been. "When the planet heats up, the biggest changes are seen toward the poles," Lee said. "The southward movement of rain bands associated with a warmer climate in the high-latitude southern hemisphere made the margins of Antarctica less like a polar desert, and more like present-day Iceland." The peak of this Antarctic greening occurred during the middle Miocene period, between 16.4 and 15.7 million years ago. This was well after the age of the dinosaurs, which became extinct 64 million years ago. During the Miocene epoch, mostly modern-looking animals roamed Earth, such as three-toed horses, deer, camel and various species of apes. Modern humans did not appear until 200,000 years ago. Warm conditions during the middle Miocene are thought to be associated with carbon dioxide levels of around 400 to 600 parts per million (ppm). In 2012, carbon dioxide levels have climbed to 393 ppm, the highest they've been in the past several million years. At the current rate of increase, atmospheric carbon dioxide levels are on track to reach middle Miocene levels by the end of this century. High carbon dioxide levels during the middle Miocene epoch have been documented in other studies through multiple lines of evidence, including the number of microscopic pores on the surface of plant leaves and geochemical evidence from soils and marine organisms. While none of these 'proxies' is as reliable as the bubbles of gas trapped in ice cores, they are the best evidence available this far back in time. While scientists do not yet know precisely why carbon dioxide was at these levels during the middle Miocene, high carbon dioxide, together with the global warmth documented from many parts of the world and now also from the Antarctic region, appear to coincide during this period in Earth's history. This research was funded by the U.S. National Science Foundation with additional support from NASA. The California Institute of Technology in Pasadena manages JPL for NASA. For more information about NASA programs and projects, visit: http://www.nasa.gov/ . Alan Buis 818-354-0474 Jet Propulsion Laboratory, Pasadena, Calif. alan.d.buis@jpl.nasa.gov J. D. Harrington 202-358-5241 NASA Headquarters, Washington j.d.harrington@nasa.gov Robert Perkins 213-740-9226 University of Southern California, Los Angeles perkinsr@usc.edu Zac Lemoine 225-578-1399 Louisiana State University, Baton Rouge jlemo26@lsu.edu - end -