Energetic gamma rays spotted from ‘microquasar’

Material stolen from a young star (blue) forms a disc (red) around a black hole or neutron star in this illustration of the system Cygnus X-3. Strong flares occasionally erupt from this disc (Illustration: Walter Feimer/NASA Goddard Space Flight Center)

by Rachel Courtland

After decades of searching, astronomers have confirmed that a gluttonous stellar remnant that glows brightly in X-rays can create high-energy gamma rays as well. The tiny powerhouse could serve as a nearby laboratory to study how particles are accelerated in the universe’s biggest black holes.

Cygnus X-3, a pair of objects that sit some 30,000 light years from Earth, has long been a puzzle. The system is thought to contain the dense remnant of a star – either a black hole or a neutron star – that is feeding on a disc of material stolen from a companion star.

The pair orbit each other once every 4.8 hours, shining in X-rays and occasionally sending jets of material, or flares, outwards at close to the speed of light. Because of these flares, Cygnus X-3 has been dubbed a “microquasar”, since it resembles quasars, the flaring supermassive black holes at the centres of some galaxies.

Interest in Cygnus X-3 has grown since the flares were first discovered by radio telescopes in 1972. In the following decades, astronomers have found hints that gamma rays – the universe’s highest-energy photons – could be coming from Cygnus X-3 with energies as high as trillions or even quadrillions of electronvolts (eV).

But these detections remained tentative, in part because the flares, which occur every year or so, are unpredictable. Until now, no one has found gamma rays stemming from Cygnus X-3 that had energies higher than 300,000 eV, gamma rays that are only slightly more energetic than the highest-energy X-rays, says Marco Tavani of the Space Astrophysics and Cosmic Physics Institute in Rome, Italy.

“People claimed to have detected high-energy emission from Cygnus X-3 on many occasions, but these reports were never confirmed,” Tavani told New Scientist. “For many years, people thought it was a sort of damned object.”

Accelerated particles

Now, two orbiting telescopes, the Italian Space Agency’s AGILE telescope and NASA’s Fermi Gamma-ray Space Telescope, have detected gamma rays emanating from Cygnus X-3, some more than 1000 times more energetic than previous measurements.

It is not clear how these high-energy photons are produced, Tavani says. The gamma rays could be generated when charged particles are accelerated by strong magnetic fields around the stellar remnant. They could also be created when electrons travelling close to the speed of light collide with light streaming from the companion star.

These gamma rays must overcome significant obstacles to escape Cygnus X-3 and reach telescopes in orbit around Earth. That’s because the system is swaddled in a thick cloud of charged particles shed from the companion star, and these particles scatter photons. The gamma rays can also be stopped in their tracks if they collide with other photons to produce pairs of electrons and their antiparticles.

Quasars, writ small

Although the origin of the gamma rays is still being investigated, their discovery suggests the flaring behaviour of Cygnus X-3 is an even better analogue to that of quasars and other types of flaring galaxies known as “active galactic nuclei” (AGN) than previously thought.

“Something that will take millions of years to take place in AGN will take place over a matter of months in microquasars,” says Stéphane Corbel of the Denis Diderot University, Paris, and CEA Saclay, France, and a member of the Fermi team.

“It’s a new window into trying to figure out what’s happening in the jets of these black hole systems,” says Tod Strohmayer of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved with the studies.

Journal references: Nature, DOI: 10.1038/nature08578, Science, DOI: 10.1126/science1182174

http://www.newscientist.com/article/dn18202-energetic-gamma-rays-spotted-from-microquasar.html

Cassini Captures Ghostly Dance of Saturn’s Northern Lights

This still image from a video shows the tallest known auroras in the solar system, rippling high above Saturn. (Credit: NASA/JPL/Space Science Institute)

In the first video showing the auroras above the northern latitudes of Saturn, Cassini has spotted the tallest known “northern lights” in the solar system, flickering in shape and brightness high above the ringed planet.

The new video reveals changes in Saturn’s aurora every few minutes, in high resolution, with three dimensions. The images show a previously unseen vertical profile to the auroras, which ripple in the video like tall curtains. These curtains reach more than 1,200 kilometers (750 miles) above the edge of the planet’s northern hemisphere.

The new video and still images are online at: http://www.nasa.gov/cassini , http://saturn.jpl.nasa.gov and http://ciclops.org .

Auroras occur on Earth, Jupiter, Saturn and a few other planets, and the new images will help scientists better understand how they are generated.

“The auroras have put on a dazzling show, shape-shifting rapidly and exposing curtains that we suspected were there, but hadn’t seen on Saturn before,” said Andrew Ingersoll of the California Institute of Technology in Pasadena, who is a member of the Cassini imaging team that processed the new video. “Seeing these things on another planet helps us understand them a little better when we see them on Earth.”

Auroras appear mostly in the high latitudes near a planet’s magnetic poles. When charged particles from the magnetosphere — the magnetic bubble surrounding a planet — plunge into the planet’s upper atmosphere, they cause the atmosphere to glow. The curtain shapes show the paths that these charged particles take as they flow along the lines of the magnetic field between the magnetosphere and the uppermost part of the atmosphere.

The height of the curtains on Saturn exposes a key difference between Saturn’s atmosphere and our own, Ingersoll said. While Earth’s atmosphere has a lot of oxygen and nitrogen, Saturn’s atmosphere is composed primarily of hydrogen. Because hydrogen is very light, the atmosphere and auroras reach far out from Saturn. Earth’s auroras tend to flare only about 100 to 500 kilometers (60 to 300 miles) above the surface.

The speed of the auroral changes in the video is comparable to some of those on Earth, but scientists are still working to understand the processes that produce these rapid changes. The height will also help them learn how much energy is required to light up auroras.

“I was wowed when I saw these images and the curtain,” said Tamas Gombosi of the University of Michigan in Ann Arbor, who chairs Cassini’s magnetosphere and plasma science working group. “Put this together with the other data Cassini has collected on the auroras so far, and you really get a new science.”

Ultraviolet and infrared instruments on Cassini have captured images of and data from Saturn’s auroras before, but in these latest images, Cassini’s narrow-angle camera was able to capture the northern lights in the visible part of the light spectrum, in higher resolution. The movie was assembled from nearly 500 still pictures spanning 81 hours between Oct. 5 and Oct. 8, 2009. Each picture had an exposure time of two or three minutes. The camera shot pictures from the night side of Saturn.

The images were originally obtained in black and white, and the imaging team highlighted the auroras in false-color orange. The oxygen and nitrogen in Earth’s upper atmosphere contribute to the colorful flashes of green, red and even purple in our auroras. But scientists are still working to determine the true color of the auroras at Saturn, whose atmosphere lacks those chemicals.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for the Science Mission Directorate at NASA Headquarters in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

Story Source:

Adapted from materials provided by NASA/Jet Propulsion Laboratory.

http://www.sciencedaily.com/releases/2009/11/091125231252.htm

Dark power: Grand designs for interstellar travel

Traveling the universe on the back of black holes (Image:George Marks/Kauko Helavuo/Stone/Getty)

by Marcus Chown

SPACE is big,” wrote Douglas Adams in his book The Hitchhiker’s Guide to the Galaxy. “You just won’t believe how vastly, hugely, mind-bogglingly big it is.”

He wasn’t exaggerating. Even our nearest star Proxima Centauri is a staggering 4.2 light years away – more than 200,000 times the distance from the Earth to the sun. Or, if you like, the equivalent of 50 million trips to the moon and back.

Such vast distances would seem to put the stars far beyond the reach of human explorers. Suppose we had been able to hitch a ride on NASA’s Voyager 1 the fastest interstellar space probe built to date. Voyager 1 is now heading out of the solar system at about 17 kilometres per second. At this rate it would take 74,000 years to reach Promixa Centauri – safe to say we wouldn’t be around to enjoy the view.

So what would it take for humans to reach the stars within a lifetime? For a start, we would need a spacecraft that can rush through the cosmos at close to the speed of light. There has been no shortage of proposals: vehicles propelled by repeated blasts from hydrogen bombs, or from the annihilation of matter and antimatter. Others resemble vast sailing ships with giant reflective sails, pushed along by laser beams.

All these ambitious schemes have their shortcomings and it is doubtful they could really go the distance. Now there are two radical new possibilities on the table that might just enable us – or rather our distant descendants – to reach the stars.

In August, physicist Jia Liu at New York University outlined his design for a spacecraft powered by dark matter (arxiv.org/abs/0908.1429v1). Soon afterwards, mathematicians Louis Crane and Shawn Westmoreland at Kansas State University in Manhattan proposed plans for a craft powered by an artificial black hole (arxiv.org/abs/0908.1803).

No one disputes that building a ship powered by black holes or dark matter would be a formidable task. Yet remarkably there seems to be nothing in our present understanding of physics to prevent us from making either of them. What’s more, Crane believes that feasibility studies like his touch on questions in cosmology that other research hasn’t considered.

Fuel as-you-go

Take Liu’s dark matter starship. Most astronomers are convinced of the existence of dark matter because of the way its gravity tugs on the stars and galaxies we see with our telescopes. Such observations suggest that dark matter outweighs the universe’s visible matter by a factor of about six – so a dark matter starship could have a plentiful supply of fuel.

Liu was inspired by an audacious spacecraft proposed by the American physicist Robert Bussard in 1960. Bussard’s “ramjet” design used magnetic fields generated by the craft to scoop up the tenuous gas of interstellar space. Instead of using conventional rockets, the craft would be propelled by forcing the hydrogen gas it collected to undergo nuclear fusion and ejecting the energetic by-products to provide thrust.

Because dark matter is so abundant throughout the universe, Liu envisages a rocket that need not carry its own fuel. This immediately overcomes one of the drawbacks of many other proposed starships, whose huge fuel supply greatly adds to their weight and hampers their ability to accelerate. “A dark matter rocket would pick up its fuel en route,” says Liu.

A huge fuel supply hampers a spacecraft’s ability to accelerate. Dark matter starships would avoid this

His plan is to drive the rocket using the energy released when dark matter particles annihilate each other. Here’s where Liu’s idea depends on more speculative physics. No one knows what dark matter is actually made of, though there are numerous theories of the subatomic world that contain potential dark matter candidates. One of the frontrunners posits that dark matter is made of neutralinos, particles which have no electric charge. Neutralinos are curious in that they are their own antiparticles: two neutralinos colliding under the right circumstances will annihilate each other.

If dark matter particles do annihilate in this way, they will convert all their mass into energy. A kilogram of the stuff will give out about 10¹⁷ joules, more than 10 billion times as much energy as a kilogram of dynamite, and plenty to propel the rocket forwards.

Even less certain is the detail of how a dark matter rocket might work. Liu imagines the engine as a “box” with a door that is open in the direction of the rocket’s motion (see diagram). As dark matter enters, the door is closed and the box is shrunk to compress the dark matter and boost its annihilation rate. Once the annihilation occurs, another door opens and the products rocket out. The whole cycle is repeated, over and over again.

Liu points out that the faster his dark matter rocket travels, the quicker it will scoop up dark matter and accelerate. Precisely how quickly it can accelerate depends on the density of the surrounding dark matter, the collecting area of the engine and the mass of the rocket. In his calculations, Liu assumes the starship weighs a mere 100 tonnes and has a collecting area of 100 square metres. “Such a rocket might be able to reach close to the speed of light within a few days,” he says. So the journey time to Proxima Centauri would be slashed from tens of thousands of years to just a few.

Article Continues – http://www.newscientist.com/article/mg20427361.000-dark-power-grand-designs-for-interstellar-travel.html

“Hypernovas” – The Most Violent Object in the Universe Confirmed

Most astronomers today believe that one of the most plausible reasons we have yet to detect intelligent life in the universe is due to the deadly effects of local supernova explosions that wipe out all life in a given region of a galaxy.

While there is, on average, only one supernova per galaxy per century, there is something on the order of 100 billion galaxies in the observable Universe. Taking 10 billion years for the age of the Universe (it’s actually 13.7 billion, but stars didn’t form for the first few hundred million), Dr. Richard Mushotzky of the NASA Goddard Space Flight Center, derived a figure of 1 billion supernovae per year, or 30 supernovae per second in the observable Universe!

Certain rare stars -real killers -type 11 stars, are core-collapse hypernova that generate deadly gamma ray bursts (GRBs). These long burst objects release 1000 times the non-neutrino energy release of an ordinary “core-collapse” supernova. Concrete proof of the core-collapse GRB model came in 2003.

It was made possible in part to a fortuitously “nearby” burst whose location was distributed to astronomers by the Gamma-ray Burst Coordinates Network (GCN). On March 29, 2003, a burst went off close enough that the follow-up observations were decisive in solving the gamma-ray burst mystery. The optical spectrum of the afterglow was nearly identical to that of supernova SN1998bw. In addition, observations from x-ray satellites showed the same characteristic signature of “shocked” and “heated” oxygen that’s also present in supernovae. Thus, astronomers were able to determine the “afterglow” light of a relatively close gamma-ray burst (located “just” 2 billion light years away) resembled a supernova.

It isn’t known if every hypernova is associated with a GRB. However, astronomers estimate only about one out of 100,000 supernovae produce a hypernova. This works out to about one gamma-ray burst per day, which is in fact what is observed.

What is almost certain is that the core of the star involved in a given hypernova is massive enough to collapse into a black hole (rather than a neutron star). So every GRB detected is also the “birth cry” of a new black hole.

Who ever said science is boring!

Casey Kazan.Adapted from NASAJPL materials.

http://imagine.gsfc.nasa.gov/docs/science/know_l1/why_hyper.html

http://www.dailygalaxy.com/my_weblog/2009/11/hypernovas-the-most-violent-object-in-the-universe-confirmed.html

SPACE PHOTOS THIS WEEK: Blue “Crab,” Sun Tsunami, More

Solar tsunamis are real, say astronomers who caught the first three-dimensional pictures of a giant wave rippling across the sun. Solar physicists first saw evidence for such waves in satellite pictures of the sun taken in 1996 (pictured), but many doubted that anything of the suggested scale could really exist.

Now the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft have captured an unprecedented view of a solar tsunami triggered by a sunspot explosion in February. The massive wave rose more than 62,000 miles (100,000 kilometers) high, raced outward at 560,000 miles (901,000 kilometers) an hour, and packed as much energy as 2,400 megatons of TNT.

—Image courtesy SOHO (ESA & NASA)

http://news.nationalgeographic.com/news/2009/11/photogalleries/091124-week-in-space-pictures-70/photo5.html

Plan for human mission to asteroid gains speed

An artist’s interpretation of a manned mission to a near Earth asteroid using NASA’s new Orion spacecraft.

Trips could build confidence in long-duration stints at the moon and Mars

By Leonard David

Space.com’s Space Insider columnist

updated 5:02 p.m. CT, Mon., Nov . 23, 2009//

BOULDER, Colo. – Call it Operation: Plymouth Rock. A plan to send a crew of astronauts to an asteroid is gaining momentum, both within NASA and industry circles.

Not only would the deep space sojourn shake out hardware, it would also build confidence in long-duration stints at the moon and Mars. At the same time, the trek would sharpen skills to deal with a future space rock found on a collision course with Earth.

In Lockheed Martin briefing charts, the mission has been dubbed “Plymouth Rock — An Early Human Asteroid Mission Using Orion.” Lockheed is the builder of NASA’s Orion spacecraft, the capsule-based replacement for the space shuttle.

Study teams are now readying high-level briefings for NASA leaders — perhaps as early as this week — on a pilgrimage to an asteroid, along with appraisals of anchoring large, astronaut-enabled telescopes far from Earth, a human precursor mission to the vicinity of Mars, as well as an initiative to power-beam energy from space to Earth.

The briefings have been spurred in response to the recent Review of U.S. Human Spaceflight Plans Committee and the option of a “Flexible Path” to human exploration beyond low-Earth orbit.

On this path, the committee suggested, humans would visit sites never visited before and extend U.S. savvy in how to operate in space — while traversing greater and greater distances from Earth.

Building momentum
The merits of a human mission to a Near Earth Object were detailed here Nov. 18 during a two-day meeting of the Small Bodies Assessment Group.

SBAG was established by NASA in 2008 to identify scientific priorities and opportunities for the exploration of asteroids, comets, interplanetary dust, small satellites and Trans-Neptunian Objects. The group also provides scientific input on the utility of asteroids and comets in support of human space activities.

The new studies are viewed as an iterative process — to be weighed both by NASA and the White House, said Paul Abell, a research scientist at the Planetary Science Institute detailed to the space agency’s Johnson Space Center in Houston, Texas and working in the Astromaterials Research and Exploration Science Directorate. “It’s going to take a bit of time. I don’t think there’s going to be a quick decision.”

How the White House will react to a human trek to an asteroid is beyond anybody’s crystal ball. However, undertaking the effort has garnered the attention of Lockheed Martin — builder of the space shuttle replacement — the Orion spacecraft.

Asteroid-bound Orion
The Plymouth Rock mission study began a couple years ago, said Josh Hopkins, in the advanced programs for human space flight division at Lockheed Martin Space Systems Company in Denver, Colo.

“We have been looking at what other interesting science missions could be done with Orion … and asteroids were one of the ideas that percolated to the top,” Hopkins told the SBAG attendees. He made it clear that the firm’s study was done using corporate funds and doesn’t imply that NASA has endorsed company results.

Initial looks at the NEO venture involve the coupling of two Orion spacecraft.

In this situation, a two-person Orion would link up with an unpiloted sister craft that’s loaded with extra fuel, food, water, and oxygen. It would be tossed into orbit — as well as an Earth departure stage — by NASA’s planned Ares V heavy-lift booster.

Bridging the moon and Mars
While detailed NASA and industry looks at the makings of a NEO mission are still in play — including use of inflatable modules to add crew volume — “it’s an attractive option,” Hopkins said. “It’s really a good middle-step between the moon and Mars.”

However, maximizing astronaut safety, dealing with such things as trash management, cosmic rays, sketching out abort scenarios must still be addressed, Hopkins noted. But given the core attributes already built into the Orion system “we think it does make sense for the human spaceflight program to be investigating this,” he said.

Between NASA and industry looks, the flight of astronauts to a NEO could occur in the 2020 to 2025 time period. The round-trip mission would take some six months.

There would be no landing on the asteroid. Rather, they would park in close proximity, then jet backpack onto the object. Once there, science gear would be deployed as samples of the space rock are gathered — on the order of a couple hundred pounds (100 kilograms).

“We assume staying at the asteroid for five days. They could stay a week or two. But staying for a month gets hard,” Hopkins explained. While on duty, astronauts would engage in gathering data useful to understand the internal makeup of the asteroid. That, in turn, is solidly helpful, he added, in dealing with harmful space rocks on a worrisome trajectory dangerous to Earth.

Today, there are a handful of candidate asteroids that could be visited a couple decades from now, said Clark Chapman, an asteroid expert at Southwest Research Institute here in Boulder. That number will grow as more ground and space-based instruments come on-line, surely increasing the discovery rate of NEOs, he stated.

“We’d really like a larger pool of candidate targets so that we could visit a NEO that has cool properties and would have the greatest scientific return,” Chapman told SPACE.com.

Profound impact
“Human exploration is for human purposes,” said Mark Sykes, chair of the Small Bodies Assessment Group. He is also director of the Planetary Science Institute in Tucson, Ariz .

Science by itself doesn’t drive human exploration, Sykes noted, “but we can benefit, scientifically, from this. We’ll take advantage of whatever opportunities come our way!”

Sykes said that he had briefed the committee that conducted the recent review of U.S. human spaceflight plans.

Specifically, Sykes said that he underscored the prospect that NEOs represent a location of resources that could have a profound impact on expanding sustainable human operations beyond low Earth orbit. They could be a well spring of water, he added, as well as useful for life support and radiation shielding.

If so, asteroids may well act as a lynch pin for people living, working and populating space, Sykes suggested. But are those resources recoverable in an economic way?

“It’s within the realm of consideration. Of course, a lot more homework needs to be done,” Sykes stressed.

© 2009 Space.com. All rights reserved. More from Space.com.

http://www.msnbc.msn.com/id/34116126/ns/technology_and_science-space/

Spitzer Telescope Observes Baby Brown Dwarf

This image shows two young brown dwarfs, objects that fall somewhere between planets and stars in terms of their temperature and mass. Image credit: (Credit: NASA/JPL-Caltech/Calar Alto Observatory/Caltech Submillimeter Observatory)

NASA’s Spitzer Space Telescope has contributed to the discovery of the youngest brown dwarf ever observed — a finding that, if confirmed, may solve an astronomical mystery about how these cosmic misfits are formed.

Brown dwarfs are misfits because they fall somewhere between planets and stars in terms of their temperature and mass. They are cooler and more lightweight than stars and more massive (and normally warmer) than planets. This has generated a debate among astronomers: Do brown dwarfs form like planets or like stars?

Brown dwarfs are born of the same dense, dusty clouds that spawn stars and planets. But while they may share the same galactic nursery, brown dwarfs are often called “failed” stars because they lack the mass of their hotter, brighter stellar siblings. Without that mass, the gas at their core does not get hot enough to trigger the nuclear fusion that burns hydrogen — the main component of these molecular clouds — into helium. Unable to ignite as stars, brown dwarfs end up as cooler, less luminous objects that are more difficult to detect — a challenge that was overcome in this case by Spitzer’s heat-sensitive infrared vision.

To complicate matters, young brown dwarfs evolve rapidly, making it difficult to catch them when they are first born. The first brown dwarf was discovered in 1995 and, while hundreds have been found since, astronomers had not been able to unambiguously find them in their earliest stages of formation until now. In this study, an international team of astronomers found a so-called “proto brown dwarf” while it was still hidden in its natal star-forming region. Guided by Spitzer data collected in 2005, they focused their search in the dark cloud Barnard 213, a region of the Taurus-Auriga complex well known to astronomers as a hunting ground for young objects.

“We decided to go several steps back in the process when (brown dwarfs) are really hidden,” said David Barrado of the Centro de Astrobiología in Madrid, Spain, lead author of the paper on the discovery in the Astronomy & Astrophysics journal. “During this step they would have an (opaque) envelope, a cocoon, and they would be easier to identify due to their strong infrared excesses. We have used this property to identify them. This is where Spitzer plays an important role because Spitzer can have a look inside these clouds. Without it this wouldn’t have been possible.”

Spitzer’s longer-wavelength infrared camera penetrated the dusty natal cloud to observe a baby brown dwarf named SSTB213 J041757. The data, confirmed with near-infrared imaging from Calar Alto Observatory in Spain, revealed not one but two of what would potentially prove to be the faintest and coolest brown dwarfs ever observed.

Barrado and his team embarked on an international quest for more information about the two objects. Their overarching scientific objective was to observe and characterize the presence of this dusty envelope — proof of the celestial womb of sorts that would indicate that these brown dwarfs were, in fact, in their earliest evolutionary stages.

The twins were observed from around the globe, and their properties were measured and analyzed using a host of powerful astronomical tools. One of the astronomers’ stops was the Caltech Submillimeter Observatory in Hawaii, which captured the presence of the envelope around the young objects. That information, coupled with what they had from Spitzer, enabled the astronomers to build a spectral energy distribution — a diagram that shows the amount of energy that is emitted by the objects in each wavelength.

From Hawaii, the astronomers made additional stops at observatories in Spain (Calar Alto Observatory), Chile (Very Large Telescopes) and New Mexico (Very Large Array). They also pulled decade-old data from the Canadian Astronomy Data Centre archives that allowed them to comparatively measure how the two objects were moving in the sky. After more than a year of observations, they drew their conclusions.

“We were able to estimate that these two objects are the faintest and coolest discovered so far,” Barrado said. Barrado said the findings potentially solve the mystery about whether brown dwarfs form more like stars or planets. The answer? They form like low-mass stars. This theory is bolstered because the change in brightness of the objects at various wavelengths matches that of other very young, low-mass stars.

While further study will confirm whether these two celestial objects are in fact proto brown dwarfs, they are the best candidates so far, Barrado said. He said the journey to their discovery, while difficult, was fun. “It is a story that has been unfolding piece by piece. Sometimes nature takes its time to give up its secrets.”

These observations were made before Spitzer ran out of its liquid coolant in May 2009, beginning its “warm” mission.

The paper’s other authors are M. Morales-Calderon, Centro de Astrobiología and Spitzer Science Center; A. Palau and A. Bayo, Centro de Astrobiología; I. de Gregorio-Monsalvo, European Southern Observatory; C. Eiroa, Universidad Autónoma de Madrid; N. Huelamo, Centro de Astrobiología; H. Bouy, Instituto de Astrofísica de Canarias and European Space Agency; O. Morata, Institute of Astronomy and Astrophysics and National Taiwan Normal University; and L. Schmidtobreick, European Southern Observatory. More information on the Spitzer Space Telescope is online at http://spitzer.caltech.edu and http://www.nasa.gov/spitzer .

http://www.sciencedaily.com/releases/2009/11/091123173540.htm

Spiral Galaxies: Exploring the Baffling Boxy Bulge

Still an astrophysical mystery, the evolution of the bulges in spiral galaxies led astronomers to the edge-on galaxy NGC 4710. When staring directly at the centre of the galaxy, one can detect a faint, ethereal “X”-shaped structure. Such a feature, which astronomers call a “boxy” or “peanut-shaped” bulge, is due to the vertical motions of the stars in the galaxy’s bar and is only evident when the galaxy is seen edge-on. This curiously shaped puff is often observed in spiral galaxies with small bulges and open arms, but is less common in spirals with arms tightly wrapped around a more prominent bulge, such as NGC 4710. (Credit: NASA and ESA)

When targeting spiral galaxy bulges, astronomers often seek edge-on galaxies, as their bulges are more easily distinguishable from the disc. This exceptionally detailed edge-on view of NGC 4710 taken by the Advanced Camera for Surveys (ACS) aboard Hubble reveals the galaxy’s bulge in the brightly coloured centre. The luminous, elongated white plane that runs through the bulge is the galaxy disc. The disc and bulge are surrounded by eerie-looking dust lanes.

When staring directly at the centre of the galaxy, one can detect a faint, ethereal “X”-shaped structure. Such a feature, which astronomers call a “boxy” or “peanut-shaped” bulge, is due to the vertical motions of the stars in the galaxy’s bar and is only evident when the galaxy is seen edge-on. This curiously shaped puff is often observed in spiral galaxies with small bulges and open arms, but is less common in spirals with arms tightly wrapped around a more prominent bulge, such as NGC 4710.

NGC 4710 is a member of the giant Virgo Cluster of galaxies and lies in the northern constellation of Coma Berenices (the Hair of Queen Berenice). It is not one of the brightest members of the cluster, but can easily be seen as a dim elongated smudge on a dark night with a medium-sized amateur telescope. In the 1780s, William Herschel discovered the galaxy and noted it simply as a “faint nebula.” It lies about 60 million light-years from the Earth and is an example of a lenticular or S0-type galaxy — a type that seems to have some characteristics of both spiral and elliptical galaxies.

Astronomers are scrutinising these systems to determine how many globular clusters they host. Globular clusters are thought to represent an indication of the processes that can build bulges. Two quite different processes are believed to be at play regarding the formation of bulges in spiral galaxies: either they formed rather rapidly in the early Universe, before the spiral disc and arms formed; or they built up from material accumulating from the disc during a slow and long evolution. In this case of NGC 4710, researchers have spotted very few globular clusters associated with the bulge, indicating that its assembly mainly involved relatively slow processes.

Story Source:

Adapted from materials provided by ESA/Hubble Information Centre.

http://www.sciencedaily.com/releases/2009/11/091118072049.htm

Cassini Flyby Shows Enceladus Venting

Credit: NASA/JPL/SSI; Mosaic: Emily Lakdawalla

Explanation: What’s happening on the surface of Saturn’s moon Enceladus? Enormous ice jets are erupting. Giant plumes of ice have been photographed in dramatic fashion by the robotic Cassini spacecraft during this past weekend’s flyby of Saturn’s moon Enceladus. Pictured above, numerous plumes are seen rising from long tiger-stripe canyons across Enceladus’ craggy surface. Several ice jets are even visible in the shadowed region of crescent Enceladus as they reach high enough to scatter sunlight. Other plumes, near the top of the above image, appear visible just over the moon’s sunlit edge. That Enceladus vents fountains of ice was first discovered on Cassini images in 2005, and has been under close study ever since. Continued study of the ice plumes may yield further clues as to whether underground oceans, candidates for containing life, exist on this distant ice world.

http://antwrp.gsfc.nasa.gov/apod/image/0911/enceladus12_cassini_big.png

Extensive Valley Network on Mars Adds to Evidence for Ancient Martian Ocean

This is a global map depicting the dissection density of valley networks on Mars, in relation to the hypothesized northern ocean. Two candidate sea levels are shown: contact 1 with mean elevation at -1,680 meters and contact 2 with mean elevation of -3,760 meters. (Credit: Wei Luo, Northern Illinois University)

New research adds to the growing body of evidence suggesting the Red Planet once had an ocean.

In a new study, scientists from Northern Illinois University and the Lunar and Planetary Institute in Houston used an innovative computer program to produce a new and more detailed global map of the valley networks on Mars. The findings indicate the networks are more than twice as extensive (2.3 times longer in total length) as had been previously depicted in the only other planet-wide map of the valleys.

Further, regions that are most densely dissected by the valley networks roughly form a belt around the planet between the equator and mid-southern latitudes, consistent with a past climate scenario that included precipitation and the presence of an ocean covering a large portion of Mars’ northern hemisphere.

Scientists have previously hypothesized that a single ocean existed on ancient Mars, but the issue has been hotly debated.

“All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars,” NIU Geography Professor Wei Luo said. “It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet’s surface.”

Luo and Tomasz Stepinski, a staff scientist at the Lunar and Planetary Institute, publish their findings in the current issue of the Journal of Geophysical Research — Planets.

“The presence of more valleys indicates that it most likely rained on ancient Mars, while the global pattern showing this belt of valleys could be explained if there was a big northern ocean,” Stepinski said.

Valley networks on Mars exhibit some resemblance to river systems on Earth, suggesting the Red Planet was once warmer and wetter than present.

But, since the networks were discovered in 1971 by the Mariner 9 spacecraft, scientists have debated whether they were created by erosion from surface water, which would point to a climate with rainfall, or through a process of erosion known as groundwater sapping. Groundwater sapping can occur in cold, dry conditions.

The large disparity between river-network densities on Mars and Earth had provided a major argument against the idea that runoff erosion formed the valley networks. But the new mapping study reduces the disparity, indicating some regions of Mars had valley network densities more comparable to those found on Earth.

“It is now difficult to argue against runoff erosion as the major mechanism of Martian valley network formation,” Luo said.

“When you look at the entire planet, the density of valley dissection on Mars is significantly lower than on Earth,” he said. “However, the most densely dissected regions of Mars have densities comparable to terrestrial values.

“The relatively high values over extended regions indicate the valleys originated by means of precipitation-fed runoff erosion — the same process that is responsible for formation of the bulk of valleys on our planet,” he added.

The researchers created an updated planet-wide map of the valley networks by using a computer algorithm that parses topographic data from NASA satellites and recognizes valleys by their U-shaped topographic signature. The computer-generated map was visually inspected and edited with help from NIU graduate students Yi Qi and Bartosz Grudzinski to produce the final updated map.

“The only other global map of the valley networks was produced in the 1990s by looking at images and drawing on top of them, so it was fairly incomplete and it was not correctly registered with current datum,” Stepinski said. “Our map was created semi-automatically, with the computer algorithm working from topographical data to extract the valley networks. It is more complete, and shows many more valley networks.”

Stepinski developed the algorithms used in the mapping.

“The basic idea behind our method is to flag landforms having a U-shaped structure that is characteristic of the valleys,” Stepinski added. “The valleys are mapped only where they are seen by the algorithm.”

The Martian surface is characterized by lowlands located mostly in the northern hemisphere and highlands located mostly in the southern hemisphere. Given this topography, water would accumulate in the northern hemisphere, where surface elevations are lower than the rest of the planet, thus forming an ocean, the researchers said.

“Such a single-ocean planet would have an arid continental-type climate over most of its land surfaces,” Luo said.

The northern-ocean scenario meshes with a number of other characteristics of the valley networks.

“A single ocean in the northern hemisphere would explain why there is a southern limit to the presence of valley networks,” Luo added. “The southernmost regions of Mars, located farthest from the water reservoir, would get little rainfall and would develop no valleys. This would also explain why the valleys become shallower as you go from north to south, which is the case.

“Rain would be mostly restricted to the area over the ocean and to the land surfaces in the immediate vicinity, which correlates with the belt-like pattern of valley dissection seen in our new map,” Luo said.

The research was funded by NASA.

Story Source:

Adapted from materials provided by Northern Illinois University.

http://www.sciencedaily.com/releases/2009/11/091123094122.htm