Most massive binary star identified

  
NASA, ESA, D. Lennon en E. Sabbi (ESA/STScI)

By NOVA, Leiden

Published: April 19, 2013

Astronomers have observed a binary star that potentially weighed 300 to 400 solar masses at birth. The present day total mass of the two stars is between 200 and 300 times that of the Sun, depending on its evolutionary stage, which possibly makes it the most massive binary star known to date.

The massive binary star R144 is located in an outer area of the star-forming region 30 Doradus in the Large Magellanic Cloud. A number of particularly bright stars can be found in the center of that region with a characteristic pattern of spectral lines. The masses of these so-called Wolf-Rayet stars are up to 250 times the mass of the Sun. R144 is the visually brightest light source of this type in the star-forming region 30 Doradus and radiates strongly in X-rays. This was an indication that R144 is a binary star. Scientists have now confirmed this presumption thanks to the discovery of periodic (orbital) changes in the spectrum.

Astronomers obtained spectra of R144 with the X-shooter spectrograph on the European Southern Observatory’s Very Large Telescope. X-shooter is one of the most sensitive spectrographs on Earth and can observe light from the near-ultraviolet to the near-infrared in one shot. “The identification of this candidate would have been a great challenge without X-shooter. This spectrograph makes observations a lot easier and much more efficient, especially because less observation time is required to cover a large spectral range,” said Hugues Sana from the University of Amsterdam.

The spectrum forms the fingerprint of a star. From the changing shape and position of the spectral lines, it becomes clear that R144 is a binary star. The spectral lines also suggest that the binary system is formed by two hydrogen-rich Wolf-Rayet stars with similar masses, and a current total mass of 200 to 300 solar masses. NGC 3603-A1 was formerly known as the most massive binary star, with a total mass that is equal to 212 times the mass of the Sun.

“It is a mystery how extremely massive stars form,” said Frank Tramper from the University of Amsterdam. “According to the most widely accepted theories, stars of hundreds of solar masses can only form in massive star clusters. The fact that R144 lies far out from the central star cluster in 30 Doradus is possibly an indication that these systems can form in isolation.”

“There is an alternative scenario for the formation of R144,” said Alex de Koter, also from the University of Amsterdam, “namely that R144 was formed in the central star cluster, but that it was ejected by dynamical interactions with other massive stars.” The team is already working on follow-up observations to determine whether R144 is indeed a “runaway” star to definitively establish its mass and its other physical properties in order to decide whether R144 really is the most massive double star discovered so far.

Dying supergiant stars implicated in hours-long gamma-ray bursts

GRB 111209A exploded on December 9, 2011. The blast produced high-energy emission for an astonishing seven hours, earning a record as the longest-duration GRB ever observed. This false-color image shows the event as captured by the X-ray Telescope aboard NASA's Swift satellite. //NASA/Swift/B. Gendre (ASDC/INAF-OAR/ARTEMIS)

By NASA's Goddard Space Flight Center, Greenbelt, Maryland

Published: April 17, 2013

Three unusually long-lasting stellar explosions discovered by NASA’s Swift satellite represent a previously unrecognized class of gamma-ray bursts (GRBs). Two international teams of astronomers studying these events conclude that they likely arose from the catastrophic death of supergiant stars hundreds of times larger than the Sun.

GRBs are the most luminous and mysterious explosions in the universe. The blasts emit surges of gamma rays — the most powerful form of light — as well as X-rays, and they produce afterglows that are visible at optical and radio energies. Swift, Fermi, and other spacecraft detect an average of about one GRB each day.

“We have seen thousands of gamma-ray bursts over the past four decades, but only now are we seeing a clear picture of just how extreme these extraordinary events can be,” said Bruce Gendre, a researcher now associated with the French National Center for Scientific Research who led this study while at the Italian Space Agency’s Science Data Center in Frascati, Italy.

Prior to Swift’s launch in 2004, satellite instruments were much less sensitive to GRBs that unfolded over comparatively long timescales.

Traditionally, astronomers have recognized two GRB types, short and long, based on the duration of the gamma-ray signal. Short bursts last two seconds or less and are thought to represent a merger of compact objects in a binary system, with the most likely suspects being neutron stars and black holes. Long GRBs may last anywhere from several seconds to several minutes, with typical durations falling between 20 and 50 seconds. These events are thought to be associated with the collapse of a star many times the Sun’s mass and the resulting birth of a new black hole.

Both scenarios give rise to powerful jets that propel matter at nearly the speed of light in opposite directions. As they interact with matter in and around the star, the jets produce a spike of high-energy light.

Gendre and his colleagues made a detailed study of GRB 111209A, which erupted December 9, 2011, using gamma-ray data from the Konus instrument on NASA’s Wind spacecraft, X-ray observations from Swift and the European Space Agency’s XMM-Newton satellite, and optical data from the TAROT robotic observatory in La Silla, Chile. The burst continued to produce high-energy emission for an astonishing seven hours, making it by far the longest-duration GRB ever recorded.

Another event, GRB 101225A, exploded on Christmas Day in 2010 and produced high-energy emission for at least two hours. Subsequently nicknamed the “Christmas burst,” the event’s distance was unknown, which led two teams to arrive at radically different physical interpretations. One group concluded the blast was caused by an asteroid or comet falling onto a neutron star within our galaxy. Another team determined that the burst was the outcome of a merger event in an exotic binary system located some 3.5 billion light-years away.

“We now know that the Christmas burst occurred much farther off, more than halfway across the observable universe, and was consequently far more powerful than these researchers imagined,” said Andrew Levan from the University of Warwick in Coventry, England.

Using the Gemini North Telescope in Hawaii, Levan and his team obtained a spectrum of the faint galaxy that hosted the Christmas burst. This enabled the scientists to identify emission lines of oxygen and hydrogen and determine how much these lines were displaced to lower energies compared to their appearance in a laboratory. This difference, known to astronomers as a redshift, places the burst some 7 billion light-years away.

As a part of this study, Levan’s team also examined 111209A and the more recent burst 121027A, which exploded October 27, 2012. All show similar X-ray, ultraviolet, and optical emission and all arose from the central regions of compact galaxies that were actively forming stars. The astronomers conclude that all three GRBs constitute a hitherto unrecognized group of “ultralong” bursts.

To account for the normal class of long GRBs, astronomers envision a star similar to the Sun’s size but with many times its mass. The mass must be high enough for the star to undergo an energy crisis, with its core ultimately running out of fuel and collapsing under its own weight to form a black hole. Some of the matter falling onto the nascent black hole becomes redirected into powerful jets that drill through the star, creating the gamma-ray spike, but because this burst is short-lived, the star must be comparatively small.

“Wolf-Rayet stars fit these requirements,” said Levan. “They are born with more than 25 times the Sun’s mass, but they burn so hot that they drive away their deep, outermost layer of hydrogen as an outflow we call a stellar wind.” Stripping away the star’s atmosphere leaves an object massive enough to form a black hole but small enough for the particle jets to drill all the way through in times typical of long GRBs.

Because ultralong GRBs persist for periods up to 100 times greater than long GRBs, they require a stellar source of correspondingly greater physical size. Both groups suggest that the likely candidate is a supergiant, a star with about 20 times the Sun’s mass that still retains its deep hydrogen atmosphere, making it hundreds of times the Sun’s diameter.

Gendre’s team goes further, suggesting that GRB 111209A marked the death of a blue supergiant containing relatively modest amounts of elements heavier than helium, which astronomers call metals.

“The metal content of a massive star controls the strength of its stellar wind, which determines how much of the hydrogen atmosphere it retains as it grows older,” Gendre said. The star’s deep hydrogen envelope would take hours to complete its fall into the black hole, which would provide a long-lived fuel source to power an ultralong GRB jet.

Metal content also plays a strong role in the development of long GRBs, according to a detailed study presented by John Graham and Andrew Fruchter, both from the Space Telescope Science Institute in Baltimore, Maryland.

Stars make heavy elements throughout their energy-producing lives and during supernova explosions, and each generation of stars enriches interstellar gas with a greater proportion of them. While astronomers have noted that long GRBs occur much more frequently in metal-poor galaxies, a few of them have suggested that this pattern is not intrinsic to the stars and their environments.

To examine this possibility, Graham and Fruchter developed a novel method that allowed them to compare galaxies by their underlying rates of star formation. They then examined galaxies that served as hosts for long GRBs and various types of supernovae as well as a control sample of 20,000 typical galaxies in the Sloan Digital Sky Survey.

The astronomers found that 75 percent of long GRBs occurred among the 10 percent of star formation with the lowest metal content. While the study found a few long GRBs in environments with high-metal content, like our galaxy, these occur at only about 4 percent the rate seen in low-metal environments per unit of underlying star formation.

“Most stars form in metal-rich environments, and this has a side effect of decreasing the prevalence of long GRBs as the universe grows older,” Graham said. “And while a nearby long GRB would be catastrophic to life on Earth, our study shows that galaxies like our own are much less likely to produce them.”

The astronomers suspect this pattern reflects a difference in how well a massive star manages to retain its rotation speed. Rising metal content means stronger stellar winds. As these winds push material off the star’s surface, the star’s rotation gradually decreases in much the same way as a spinning ice skater slows when she extends her arms. Stars with more rapid rotation may be more likely to produce a long GRB.

Graham and Fruchter hypothesize that the few long GRBs found in high-metal environments received an assist from the presence of a nearby companion star. By feeding mass — and with it, rotational energy — onto the star that explodes, a companion serves as the physical equivalent of someone pushing a slowly spinning ice skater back up to a higher rotational speed.

GRB 101225A, better known as the "Christmas burst," was an unusually long-lasting gamma-ray burst. Because its distance was not measured, astronomers came up with two radically different interpretations. In the first, a solitary neutron star in our  galaxy shredded and accreted an approaching comet-like body. In the second, a neutron star is engulfed by, spirals into, and merges with an evolved giant star in a distant galaxy. Now, thanks to a measurement of the Christmas burst’s host galaxy, astronomers have determined that it represented the collapse and explosion of a supergiant star hundreds of times larger than the Sun

Kepler discovers smallest "habitable zone" planets

Fig : The diagram compares the planets of the inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth in the constellation Lyra. The five planets of Kepler-62 orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the Sun and only one-fifth as bright. At 7 billion years old, the star is somewhat older than the Sun. The green areas mark each star's habitable zone. (NASA Ames/JPL-Caltech)

By NASA Headquarters, Washington, D.C., NASA's Ames Research Center in Moffett Field, California 

Published: April 19, 2013

NASA’s Kepler mission has discovered two new planetary systems that include three super-Earth-sized planets in the “habitable zone,” the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water.

The Kepler-62 system has five planets: 62b, 62c, 62d, 62e, and 62f. The Kepler-69 system has two planets: 69b and 69c. Kepler-62e, 62f, and 69c are the super-Earth-sized planets.

Two of the newly discovered planets orbit a star smaller and cooler than the Sun. Kepler-62f is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Kepler-62f is likely to have a rocky composition. Kepler-62e orbits on the inner edge of the habitable zone and is roughly 60 percent larger than Earth.

The third planet, Kepler-69c, is 70 percent larger than Earth and orbits in the habitable zone of a star similar to our Sun. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a Sun-like star resembles that of our neighboring planet Venus.

Scientists do not know whether life could exist on the newfound planets, but their discovery signals that astronomers are another step closer to finding a world similar to Earth around a star like our Sun.


“The Kepler spacecraft has certainly turned out to be a rock star of science,” said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, D.C. “The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity.”

The Kepler space telescope, which simultaneously and continuously measures the brightness of more than 150,000 stars, is NASA’s first mission capable of detecting Earth-sized planets around stars like our Sun.

Orbiting its star every 122 days, Kepler-62e was the first of these habitable zone planets identified. Kepler-62f, with an orbital period of 267 days, was later found by Eric Agol, associate professor of astronomy at the University of Washington.

The scientists have measure the size of Kepler-62f is now measured, but they have yet to determine its mass and composition. Based on previous studies of rocky exoplanets similar in size, however, astronomers are able to estimate its mass by association.

“The detection and confirmation of planets is an enormously collaborative effort of talent and resources, and requires expertise from across the scientific community to produce these tremendous results,” said William Borucki, Kepler science principal investigator at NASA’s Ames Research Center at Moffett Field, California. “Kepler has brought a resurgence of astronomical discoveries, and we are making excellent progress toward determining if planets like ours are the exception or the rule.”

The two habitable zone worlds orbiting Kepler-62 have three companions in orbits closer to their star, two larger than the size of Earth and one about the size of Mars. Kepler-62b, Kepler-62c, and Kepler-62d orbit every five, 12, and 18 days, respectively, making them very hot and inhospitable for life as we know it.

The five planets of the Kepler-62 system orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the Sun and only one-fifth as bright. At 7 billion years old, the star is somewhat older than the Sun. It is about 1,200 light-years from Earth in the constellation Lyra.

A companion to Kepler-69c, known as Kepler-69b, is more than twice the size of Earth and whizzes around its star every 13 days. The Kepler-69 planets’ host star belongs to the same class as our Sun, called G-type. It is 93 percent the size of the Sun and 80 percent as luminous; it's located approximately 2,700 light-years from Earth in the constellation Cygnus.

“We only know of one star that hosts a planet with life — the Sun. Finding a planet in the habitable zone around a star like our Sun is a significant milestone toward finding truly Earth-like planets,” said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, California, and lead author of the Kepler-69 system discovery.

When a planet candidate transits, or passes in front of, the star from the spacecraft’s vantage point, a percentage of light from the star is blocked. The resulting dip in the brightness of the starlight reveals the transiting planet’s size relative to its star. Using the transit method, Kepler has detected 2,740 candidates. Using various analysis techniques, ground telescopes and other space assets, astronomers have confirmed 122 as planets.

Early in the mission, the Kepler telescope primarily found large gas giants in very close orbits of their stars. Known as “hot Jupiters,” these worlds are easier to detect due to their size and very short orbital periods. Earth would take three years to accomplish the three transits required to be accepted as a planet candidate. As Kepler continues to observe, transit signals of habitable zone planets the size of Earth orbiting stars like the Sun will begin to emerge.

 

Ice cloud over Titan's south pole

Fig :  The recently formed south polar vortex stands out in the color-swaddled atmosphere of Saturn's largest moon, Titan, in this natural color view from NASA's Cassini spacecraft. NASA/JPL-Caltech/Space Science Institute

By Jet Propulsion Laboratory, Pasadena, California, NASA's Goddard Space Flight Center, Greenbelt, Maryland

 Published: April 12, 2013

An ice cloud taking shape over Titan’s south pole is the latest sign that the change of seasons is setting off a cascade of radical changes in the atmosphere of Saturn’s largest moon. Made from an unknown ice, this type of cloud has long hung over Titan’s north pole, where it is now fading, according to observations made by the composite infrared spectrometer (CIRS) on NASA’s Cassini spacecraft.

“We associate this particular kind of ice cloud with winter weather on Titan, and this is the first time we have detected it anywhere but the north pole,” said Donald E. Jennings of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The southern ice cloud, which shows up in the far infrared part of the light spectrum, is evidence that an important pattern of global air circulation on Titan has reversed direction. When Cassini first observed the circulation pattern, warm air from the southern hemisphere was rising high in the atmosphere and was transported to the cold north pole. There, the air cooled and sank down to lower layers of the atmosphere and formed ice clouds. A similar pattern, called a Hadley cell, carries warm, moist air from Earth’s tropics to the cooler middle latitudes.

Based on modeling, scientists had long predicted a reversal of this circulation once Titan’s north pole began to warm and its south pole began to cool. The official transition from winter to spring at Titan’s north pole occurred in August 2009. But because each of the moon’s seasons lasts about 7.5 Earth years, researchers still did not know exactly when this reversal would happen or how long it would take.

The first signs of the reversal came in data acquired in early 2012, which came shortly after the start of southern fall on Titan, when Cassini images and visual and infrared mapping spectrometer data revealed the presence of a high-altitude “haze hood” and a swirling polar vortex at the south pole. Both features have long been associated with the cold north pole. Later, Cassini scientists reported that infrared observations of Titan’s winds and temperatures made by CIRS had provided definitive evidence of air sinking, rather than upwelling, at the south pole. By looking back through the data, the team narrowed down the change in circulation to within six months of the 2009 equinox.

Despite the new activity at the south pole, the southern ice cloud had not appeared yet. CIRS didn’t detect it until about July 2012, a few months after the haze and vortex were spotted in the south.

“This lag makes sense because first the new circulation pattern has to bring loads and loads of gases to the south pole. Then, the air has to sink. The ices have to condense. And the pole has to be under enough shadow to protect the vapors that condense to form those ices,” said Carrie Anderson from Goddard.

At first blush, the southern ice cloud seems to be building rapidly. The northern ice cloud, on the other hand, was present when Cassini first arrived and has been slowly fading the entire time the spacecraft has been observing it.

So far, the identity of the ice in these clouds has eluded scientists, though they have ruled out simple chemicals, such as methane, ethane and hydrogen cyanide, which are typically associated with Titan. One possibility is that “species X,” as some team members call the ice, could be a mixture of organic compounds.

“What’s happening at Titan’s poles has some analogy to Earth and to our ozone holes,” said F. Michael Flasar of Goddard. “And on Earth, the ices in the high polar clouds aren’t just window dressing: They play a role in releasing the chlorine that destroys ozone. How this affects Titan chemistry is still unknown. So it’s important to learn as much as we can about this phenomenon, wherever we find it.”

Next Door Earth Like Planets

This artist’s conception shows a hypothetical habitable planet with two moons orbiting a red dwarf star. Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away. // David A. Aguilar (CfA)

By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts

Published: February 6, 2013
 
Using publicly available data from NASA’s Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, have found that 6 percent of red dwarf stars have habitable Earth-sized planets. Since red dwarfs are the most common stars in our galaxy, the closest Earth-like planet could be just 13 light-years away.

“We thought we would have to search vast distances to find an Earth-like planet. Now, we realize another Earth is probably in our own backyard waiting to be spotted,” said Courtney Dressing from CfA.

Red dwarf stars are smaller, cooler, and fainter than our Sun. An average red dwarf is only one-third as large and one-thousandth as bright as the Sun. From Earth, no red dwarf is visible to the naked eye.

Despite their dimness, these stars are good places to look for Earth-like planets. Red dwarfs make up three out of every four stars in our galaxy for a total of at least 75 billion. The signal of a transiting planet is larger since the star itself is smaller, so an Earth-sized world blocks more of the star’s disk. And since a planet has to orbit a cool star closer in order to be in the habitable zone, it’s more likely to transit from our point of view.

Dressing culled the Kepler catalog of 158,000 target stars to identify all the red dwarfs. She then reanalyzed those stars to calculate more accurate sizes and temperatures. She found that almost all of those stars were smaller and cooler than previously thought.

Since the size of a transiting planet is determined relative to the star size, based on how much of the star’s disk the planet covers, shrinking the star shrinks the planet. And a cooler star will have a tighter habitable zone.

Dressing identified 95 planetary candidates orbiting red dwarf stars. This implied that at least 60 percent of such stars have planets smaller than Neptune. However, most weren’t quite the right size or temperature to be considered truly Earth-like. Three planetary candidates were both warm and approximately Earth-sized. Statistically, this means that 6 percent of all red dwarf stars should have an Earth-like planet.

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said David Charbonneau from CfA. “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

Locating nearby Earth-like worlds may require a dedicated small space telescope or a large network of ground-based telescopes. Follow-up studies with instruments like the Giant Magellan Telescope and James Webb Space Telescope could tell scientists whether any warm, transiting planets have an atmosphere and further probe its chemistry.

Such a world would be different from our own. Orbiting so close to its star, the planet would probably be tidally locked. However, that doesn’t prohibit life since a reasonably thick atmosphere or deep ocean could transport heat around the planet. And while young red dwarf stars emit strong flares of ultraviolet light, an atmosphere could protect life on the planet’s surface. In fact, such stresses could help life evolve. “You don’t need an Earth clone to have life,” said Dressing.

Since red dwarf stars live much longer than Sun-like stars, this discovery raises the interesting possibility that life on such a planet would be much older and more evolved than life on Earth. “We might find an Earth that’s 10 billion years old,” said Charbonneau.

The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5700° and 5900° Fahrenheit (3100° and 3300° Celsius). For comparison, our Sun’s surface is 10000° F (5500° C).

New Secrets of Super-Earths

Fig : A diagram comparing Earth, at left, to a cross-section of a super-Earth on the right. The super-Earth has a relatively small rocky core, an atmosphere of methane, water, and hydrogen, and an extended hydrogen envelope. // Credit: H. Lammer

By Royal Astronomical Society, United Kingdom


Published: February 4, 2013

In the past two decades, astronomers have found hundreds of planets in orbit around other stars. One type of these so-called “exoplanets” is the super-Earths that are thought to have a high proportion of rock but at the same time are significantly bigger than our world. Now, a new study led by Helmut Lammer of the Space Research Institute (IWF) of the Austrian Academy of Sciences suggests that these planets are actually surrounded by extended hydrogen-rich envelopes and that they are unlikely to ever become Earth-like. Rather than being super-Earths, these worlds are more like mini-Neptunes.

Super-Earths follow a different evolutionary track from the planets found in our solar system, but the question is whether they can evolve to become rocky bodies like the terrestrial planets Mercury, Venus, Earth, and Mars. To try to answer this, Lammer and his team looked at the impact of radiation on the upper atmospheres of super-Earths orbiting the stars Kepler-11, Gliese 1214, and 55 Cancri.

These planets are each a few times more massive and slightly larger than Earth and orbit close to their respective stars. The way in which the mass of planets scales with their sizes suggests that they have solid cores surrounded by hydrogen or hydrogen-rich atmospheres, probably captured from the clouds of gas and dust — nebulae — from which the planets formed.

The new model suggests that the short wavelength of extreme ultraviolet light — much bluer than the blue light we see with our eyes — of the host stars heats up the gaseous envelopes of these worlds so that they expand to several times the radius of each planet, and gas escapes from them fairly quickly. Nonetheless, most of the atmosphere remains in place over the whole lifetime of the stars that they orbit.

“Our results indicate that although material in the atmosphere of these planets escapes at a high rate, unlike lower-mass Earth-like planets, many of these super-Earths may not get rid of their nebula-captured hydrogen-rich atmospheres,” said Lammer.

Rather than becoming more like Earth, the super-Earths may more closely resemble Neptune, which together with Uranus is a smaller “gas giant” in our solar system. If the scientists’ results are right, then super-Earths farther out from their stars in the “habitable zone,” where the temperature would allow liquid water to exist, would hold on to their atmospheres even more effectively. If that happens, they would be much less likely to be habitable.
 

Glowing Titan in the Dark

Figure : This set of images from NASA's Cassini spacecraft shows Saturn's moon Titan glowing in the dark. Titan was behind Saturn at the time, in eclipse from the sun. The image on the left is a calibrated, but unprocessed image from Cassini's imaging camera. The image on the right was processed to exclude reflected light off Saturn, and it is clear that even where Titan did not receive any Saturnshine, it is still emitting light. Some light appears to be emanating from high in the atmosphere (noted by the outer dashed line at about 625 miles [1,000 kilometers] in altitude). But more surprisingly, most of it is diffusing up from lower down in the moon's haze, from about 190 miles (300km) above the surface. //Credit: NASA/JPL-Caltech/SSI

By Cassini Imaging Central Lab, Boulder, Colorado, Jet Propulsion Laboratory, 
Pasadena, California

Published: November 6, 2012
A literal shot in the dark by imaging cameras on NASA’s Cassini spacecraft has yielded an image of a visible glow from Titan, emanating not just from the top of Titan’s atmosphere, but also from deep in the atmosphere through the moon’s haze. A person in a balloon in Titan’s haze layer wouldn’t see the glow because it’s too faint — something like a millionth of a watt. Scientists were able to detect it with Cassini because the spacecraft’s cameras are able to take long-exposure images.

“It turns out that Titan glows in the dark, though very dimly,” said Robert West at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “It’s a little like a neon sign, where electrons generated by electrical power bang into neon atoms and cause them to glow. Here we’re looking at light emitted when charged particles bang into nitrogen molecules in Titan’s atmosphere.”

Scientists are interested in studying the input of energy from the Sun and charged particles into Titan’s atmosphere because it is at the heart of the natural organic chemistry factory that exists in Titan’s atmosphere.

“Scientists want to know what galvanizes the chemical reactions forming the heavy molecules that develop into Titan’s thick haze of organic chemicals,” said Linda Spilker, also from JPL. “This kind of work helps us understand what kind of organic chemistry could have existed on an early Earth.” The light, known as airglow, is produced when atoms and molecules are excited by ultraviolet sunlight or electrically charged particles. Cassini scientists already have seen an airglow from Titan’s nitrogen molecules caused by X-rays and ultraviolet radiation from the Sun when Titan was illuminated by our star. During 2009, Titan passed through Saturn’s shadow, offering a unique opportunity for Cassini instruments to observe any luminescence from Titan while in darkness. Cassini’s imaging cameras could see in very dim light by using exposure times of 560 seconds.

Scientists expected to see a glow in the high atmosphere (above 400 miles [700 kilometers] in altitude) where charged particles from the magnetic bubble around Saturn strip electrons off atmospheric molecules at Titan. Although an extremely weak emission was seen in that region, they were surprised to see Titan’s dark face glow in visible wavelengths of light from deeper in the atmosphere (at about 190 miles [300km] above the surface), as though illuminated by moonshine from nearby satellites.

The scientists took into account sunlight reflected off Saturn. There was still a glow from the part of Titan that was dark. The luminescence was diffusing up from too deep for charged particles from the Sun to be exciting atmospheric particles. The area also was not affected by the shooting of charged particles into the magnetic fields, which is what causes aurorae.

Scientists’ best guess is that the glow is being caused by deeper-penetrating cosmic rays or by light emitted due to some kind of chemical reaction deep in the atmosphere.

“This is exciting because we’ve never seen this at Titan before,” West said. “It tells us that we don’t know all there is to know about Titan and makes it even more mysterious.”

Scientists have previously reported that the night side of Venus’ atmosphere also produces a glow, called the ashen light. Some have suggested that lightning on Venus is responsible, although that explanation is not universally accepted. While Cassini’s radio-wave instrument has detected lightning at Saturn, it has not detected lightning at Titan. Scientists plan to keep looking for clues as Cassini continues to make its way around the Saturn system for another season.

Planets can form in the galactic center (Near a Black Hole)

Fig : In this artist's conception, a protoplanetary disk of gas and dust (red) is being shredded by the powerful gravitational tides of our galaxy's central black hole. // Credit: David A. Aguilar (CfA)
  
By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts

  
Published: September 12, 2012
 
At first glance, the center of the Milky Way seems like a very inhospitable place to try to form a planet. Stars crowd each other as they whiz through space like cars on a rush-hour freeway. Supernova explosions blast out shock waves and bathe the region in intense radiation. Powerful gravitational forces from a supermassive black hole twist and warp the fabric of space itself.

Yet new research by astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) shows that planets still can form in this cosmic maelstrom. For proof, they point to the recent discovery of a cloud of hydrogen and helium plunging toward the galactic center. They argue that this cloud represents the shredded remains of a planet-forming disk orbiting an unseen star.

“This unfortunate star got tossed toward the central black hole. Now it’s on the ride of its life, and while it will survive the encounter, its protoplanetary disk won’t be so lucky,” said Ruth Murray-Clay of the CfA.

Last year, a team of astronomers discovered the cloud in question using the Very Large Telescope in Chile. The group speculated that it formed when gas streaming from two nearby stars collided, like windblown sand gathering into a dune.

Murray-Clay and colleague Avi Loeb propose a different explanation. Newborn stars retain a surrounding disk of gas and dust for millions of years. If one such star dived toward our galaxy’s central black hole, radiation and gravitational tides would rip apart its disk in a matter of years.

They also identify the likely source of the stray star — a ring of stars known to orbit the galactic center at a distance of about one-tenth of a light-year. Astronomers have detected dozens of young, bright O-type stars in this ring, which suggests that hundreds of fainter Sun-like stars also exist there. Interactions between the stars could fling one inward along with its accompanying disk.

Although this protoplanetary disk is being destroyed, the stars that remain in the ring can hold onto their disks. Therefore, they may form planets despite their hostile surroundings.

As the star continues its plunge over the next year, more and more of the disk’s outer material will be torn away, leaving only a dense core. The stripped gas will swirl down into the maw of the black hole. Friction will heat it to high enough temperatures that it will glow in X-rays.

“It’s fascinating to think about planets forming so close to a black hole,” said Loeb. “If our civilization inhabited such a planet, we could have tested Einstein’s theory of gravity much better, and we could have harvested clean energy from throwing our waste into the black hole.”

Dark matter near the Sun

Fig: The high-resolution simulation of the Milky Way used to test the mass-measuring technique. Image credit: Dr. A. Hobbs

By Royal Astronomical Society, United Kingdom

Published: August 9, 2012

 Astronomers have found large amounts of invisible dark matter near the Sun. Their results are consistent with the theory that the Milky Way Galaxy is surrounded by a massive “halo” of dark matter, but this is the first study of its kind to use a method rigorously tested against mock data from high-quality simulations. The scientists also have found tantalizing hints of a new dark matter component in our galaxy.

Swiss astronomer Fritz Zwicky first proposed dark matter in the 1930s. He found that clusters of galaxies were filled with a mysterious dark matter that kept them from flying apart. At nearly the same time, Jan Oort in the Netherlands discovered that the density of matter near the Sun was nearly twice what could be explained by the presence of stars and gas alone.

In the intervening decades, astronomers developed a theory of dark matter and structure formation that explains the properties of clusters and galaxies in the universe, but the amount of dark matter in the solar neighborhood has remained more mysterious. For decades after Oort’s measurement, studies found three to six times more dark matter than expected. Then last year new data and a new method claimed far less than expected. The community was left puzzled, generally believing that the observations and analyzes simply weren’t sensitive enough to perform a reliable measurement.

In this latest study, the astronomers are more confident in their measurement and its uncertainties. This is because they used a state-of-the-art simulation of our galaxy to test their mass-measuring technique before applying it to real data. This threw up a number of surprises. They found that standard techniques used over the past 20 years were biased, always tending to underestimate the amount of dark matter. They then devised a new unbiased technique that recovered the correct answer from the simulated data. Applying their technique to the positions and velocities of thousands of orange K dwarf stars near the Sun, they obtained a new measure of the local dark matter density.

“We are 99 percent confident that there is dark matter near the Sun,” said Silvia Garbari from the University of Zürich. “In fact, our favored dark matter density is a little high. There is a 10 percent chance that this is merely a statistical fluke. But with 90 percent confidence, we find more dark matter than expected. If future data confirms this high value, the implications are exciting. It could be the first evidence for a disk of dark matter in our galaxy, as recently predicted by theory and numerical simulations of galaxy formation. Or it could be that the dark matter halo of our galaxy is squashed, boosting the local dark matter density.”

Many physicists are placing their bets on dark matter being a new fundamental particle that interacts only weakly with normal matter — but strongly enough to be detected in experiments deep underground where confusing cosmic-ray events are screened by over a mile of solid rock.

An accurate measure of the local dark matter density is vital for such experiments. “If dark matter is a fundamental particle, billions of these particles will have passed through your body by the time you finish reading this article,” said George Lake from ETH Zürich. “Experimental physicists hope to capture just a few of these particles each year in experiments like XENON and CDMS currently in operation. Knowing the local properties of dark matter is the key to revealing just what kind of particle it consists of.”

NASA's New Mars Rover Sends Higher-Resolution Image

This is one of the first images taken by NASA's Curiosity rover, which landed on Mars the evening of Aug. 5 PDT (morning of Aug. 6 EDT). It was taken through a "fisheye" wide-angle lens on the left "eye" of a stereo pair of Hazard-Avoidance cameras on the left-rear side of the rover. The image is one-half of full resolution. The clear dust cover that protected the camera during landing has been sprung open. Part of the spring that released the dust cover can be seen at the bottom right, near the rover's wheel.

On the top left, part of the rover's power supply is visible.

Some dust appears on the lens even with the dust cover off.

The cameras are looking directly into the sun, so the top of the image is saturated. Looking straight into the sun does not harm the cameras. The lines across the top are an artifact called "blooming" that occurs in the camera's detector because of the saturation.

As planned, the rover's early engineering images are lower resolution. Larger color images from other cameras are expected later in the week when the rover's mast, carrying high-resolution cameras, is deployed.

Image Credit: NASA/JPL-Caltech 

By NASA Jet Propulsion Laboratory, CalTech
Published on : 6th August, 2012

About two hours after landing on Mars and beaming back its first image, NASA's Curiosity rover transmitted a higher-resolution image of its new Martian home, Gale Crater. Mission Control at NASA's Jet Propulsion Laboratory in Pasadena, Calif., received the image, taken by one of the vehicle's lower-fidelity, black-and-white Hazard Avoidance Cameras - or Hazcams.
The black-and-white, 512 by 512 pixel image, taken by Curiosity's rear-left Hazcam, can be found at: http://www.nasa.gov/mission_pages/msl/multimedia/msl5.html .

"Curiosity's landing site is beginning to come into focus," said John Grotzinger, project manager of NASA's Mars Science Laboratory mission, at the California Institute of Technology in Pasadena. "In the image, we are looking to the northwest. What you see on the horizon is the rim of Gale Crater. In the foreground, you can see a gravel field. The question is, where does this gravel come from? It is the first of what will be many scientific questions to come from our new home on Mars."

While the image is twice as big in pixel size as the first images beamed down from the rover, they are only half the size of full-resolution Hazcam images. During future mission operations, these images will be used by the mission's navigators and rover drivers to help plan the vehicle's next drive. Other cameras aboard Curiosity, with color capability and much higher resolution, are expected to be sent back to Earth over the next several days.

Curiosity landed at 10:32 p.m. Aug. 5, PDT, (1:32 a.m. EDT, Aug. 6) near the foot of a mountain three miles (about five kilometers) tall inside Gale Crater, 96 miles (nearly 155 kilometers) 7in diameter. During a nearly two-year prime mission, the rover will investigate whether the region has ever offered conditions favorable for microbial life, including the chemical ingredients for life.

The mission is managed by JPL for NASA's Science Mission Directorate in Washington. The rover was designed, developed and assembled at JPL, a division of Caltech.
For more information on the mission, visit:
http://www.nasa.gov/mars and http://marsprogram.jpl.nasa.gov/msl .
Follow the mission on Facebook and Twitter at
http://www.facebook.com/marscuriosity and http://www.twitter.com/marscuriosity
2012-231

Guy Webster / D.C. Agle 818-354-6278 / 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster@jpl.nasa.gov / agle@jpl.nasa.gov

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov