Posted on by Fraser Cain

Enceladus is Creating one of Saturn’s Rings

Enceladus plume. Image credit: NASA/JPL/UA Click to enlarge
Cassini observations by several instruments have revealed the source of Saturn’s broadest and faintest ring. Recent observations show that tiny particles of frozen water ice are streaming outward into space from the south polar region of the moon Enceladus.

The source of geological activity on Enceladus is a mystery. “We’re amazed to see ice geysers on this little world that was thought to be cold and dead long ago,” commented Dr. Dale Cruikshank of NASA Ames Research center, a member of the visual and infrared mapping spectrometer team. “Some unexpected process is vigorously heating the interior of Enceladus, especially the south polar region, and causing the ejection of the plumes of ice particles.”

As the icy plumes jet out from the moon, the larger particles probably follow paths that mostly bring them back to the surface, while the smaller particles are nudged by sunlight into orbits around Saturn.

“Most of these small particles probably re-impact the moon, but the smallest ones eventually disperse as a result of radiation (light) pressure and interactions with Saturn’s magnetosphere to form the broad E ring,” said Dr. Mark Showalter of the SETI Institute, Mountain View, Calif. Thus, the E ring is currently being regenerated by some kind of geological activity in the interior of Enceladus.

During the Cassini spacecraft’s flyby on Nov. 26, the visual and infrared mapping spectrometer instrument measured the spectrum of the polar plumes of Enceladus. “We see a very clear signature of small ice particles in the plume data, in the form of a strong absorption band at 2.9 microns in an otherwise featureless spectrum,” said Dr. Phil Nicholson, professor of astronomy at Cornell University, Ithaca, N.Y. Nicholson is a member of the visual and infrared mapping spectrometer science team.

The visual and infrared mapping spectrometer images of Enceladus show not only the plume over the south pole, but also the dark side of the moon, silhouetted against a foggy background of light from the E Ring. Measurements of the spectrum show a very similar signature of small ice particles to that in the plumes, confirming earlier expectations that Enceladus is indeed the source of the E ring.

Preliminary analyses suggest that the average size of the particles in the plume is about 10 microns (1/100,000 of a meter), whereas the particles in the E ring are about three times smaller. The sunlit surface of Enceladus itself is also composed of water ice, but with a much larger grain size than the plume.

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

What’s Up This Week – December 19 – December 25, 2005

NGC 1300. Image credit: Hilary Mathis/NOAO/AURA/NSF. Click to enlarge.
Monday, December 19 – ‘Tis the season for freezin’, but you won’t be cold for long as you head towards the furnace of Fornax to discover one of the most awesome structured galaxies around – NGC 1300.

Located about a fistwidth north-northeast of Alpha Fornacis in the constellation of Eridanus, NGC 1300 is definitely one of the best barred spiral galaxies that can be viewed with the average telescope. Cataloged and studied by both Herschels, just the central bar in this 75 million light year distant beauty is larger in diameter than our own Milky Way – it spans an incredible 150,000 light years. As a topic of scientific study, the speed at which NGC 1300’s clouds of gas and stars rotate has been measured to help understand how this type of galaxy forms.

Easily reached by small telescopes, this 10th magnitude galactic giant will reveal its bright core area and the beginnings of resolution to larger aperture. No matter which hemisphere you observe from, this hot galaxy is definitely very “cool!”

Tuesday, December 20 – Tonight is the peak of Delta Arietid meteor shower. While most showers are best after midnight, this is a both hemispheres, early evening shower that must be viewed before the radiant sets. The fall rate is modest – about 12 per hour – but with early evening dark skies, your chance of success is good.

Today marks the founding of the Mt. Wilson Solar Observatory, which officially opened its doors in 1904. We also celebrate the birth of Walter S. Adams on this date. Born in 1876, Adams was an astronomer at Mt. Wilson who revealed the nature of Sirius B, the first known white dwarf star. Sirius B was first seen by Alvan Clark in 1862 abd hust recently, the Hubble Space Telescope precisely measured the mass of B for the first time.

While Sirius is far too low at an early hour to study its white dwarf, we can have a look at a similar star when we view Omicron 2 Eridani located roughly a handspan west of Rigel. As the southernmost of the Omicron pair, it is sometimes known as 40 Eridani and you’ll find it to be an interesting multiple star system that’s very worthy of your time.
Discovered by William Herschel in 1783, this 16 light year distant system is the eighth nearest of the unaided visible stars. Well spaced from the primary, the companion star is also a double for high powers and will reveal a red dwarf discovered by Otto Struve. Now, look closely at the 9th magnitude B star. This is the only white dwarf that can be considered “easy” for the backyard telescope. Its diameter is only about twice the size of Earth and its mass is about that of our Sun. Power up and locate the 11th magnitude companion…for it’s one of the least massive stars known!

Wednesday, December 21 – Today marks the official beginning of winter for the northern hemisphere. For the USA at 1:35 p.m. EST, the Sun will stand directly over the Tropic of Capricorn and meet its most southern extension. This time of solstice is also a good time to create your own shadow marker, so you may follow as the Sun changes positions in the sky. Anything can be used as a marker – be it a fencepost or simply a stake driven into the ground. At local noon, measure the distance between your marker and the end of the shadow. Every so often, repeat the process and watch the changes in shadow length in the weeks ahead!

Tonight let’s have a look at an open cluster best suited to binoculars or telescopes at very low power – Collinder 62. Located about two fingerwidths south of Alpha Auriga – Capella – this scattered collection of mixed magnitude stars is often overlooked in favor of the Messier objects. While its small groupings of roughly 8th magnitude stars occupy an area about the size of the full Moon, it fares well under tonight’s darker skies. Be sure to look for its brightest member in a zig-zag formation of stars.

Thursday, December 22 – Up early? Fantastic! In the pre-dawn hours of this morning, we have a treat for you – the Ursid meteor shower. Cruising around the Sun about every thirteen and a half years, Comet 8P/Tuttle sheds a little skin. Although it never passes inside of Earth’s orbit, some six years later we pass through its debris stream. Not so unusual? Then think again, because it takes as much as six centuries before any one meteoroid’s orbit is affected enough by Jupiter’s gravitation to pass into our atmosphere.

With only a little interference from the Moon while watching this northern circumpolar meteor shower, the hours before dawn could see activity of up to 12 per hour. By keeping watch on the constellation of Ursa Major, you just might spot one of these slow moving, 600 year old travelers that make their path only halfway between us and Selene!
While you’re out, be sure to have a look at Jupiter and see if you can spot Mercury as well. You’ll find the swift inner planet around a handspan and a half further east along the ecliptic plane. Don’t confuse it with the lower Antares!

Friday, December 23 – This will be a morning worth getting up early for – as almost all of the North American continent will be treated to an event when the Moon occults Beta Virginis. Be sure to check this IOTA page for a listing of times and locations in your area. Best of luck!

After sunset tonight, be sure to have a look at the rapidly slimming crescent of Venus. At this time, its orbital track is carrying it past the Earth and it will begin its “retrograde” – or reverse – motion as it heads off on its journey around the Sun.

Today in 1672, astronomer Giovanni Cassini discovered Saturn’s moon Rhea. Around four hours after local sunset you’ll find Saturn rising along the ecliptic plane and becoming more accessible to view. While a small telescope can easily resolve the largest satellite Titan, you can also see Tethys, Rhea and Dione in aperture as small as 4″. The clue is to watch carefully along the boundaries of the ring system. These moons stay in close and with good conditions you can catch their “wink” easily!

Saturday, December 24 – ‘Twas the night before Christmas and all through the house, not a creature was stirring…except for the mouse with the telescope who wants to see a multiple star system! Why don’t we join him tonight and have a look at very nice, and easily resolved, Sigma Orionis.

This particular system is easily found without a map. By identifying the three “belt” stars of Orion, go to the easternmost – Alnitak. Sigma is the first star south of it. In the telescope you will find a beautiful combination of four stars. The 3.8 magnitude white primary commands attention. With a designation of “A/B,” this super-massive and extremely bright pair is far too close (about 100 AU apart) to be split with a small scope. Looking 11″ to the southwest, you will discover the 10th magnitude white “C” star and you will see the 7.2 magnitude red “D” star 13″ to the east. Further away yet at a distance of 42″ to the east-northeast is the 6.5 magnitude blue “E” star.
Sharp-eyed observers will also note another multiple system in the same field of view to the northwest. This is Struve 761. As an “all white” system of similar magnitudes, you will see two residing east/west of each other and the third companion to the north. What we are looking at is a system that is about 1,500 light years away from us in the rich, star-forming region of Orion. Give that mouse a piece of cheese!

And even if that mouse just has a pair of binoculars, it’s in for another treat tonight as a great opportunity arises for binocular and small scope users to locate bright asteroid Vesta. Around 9:00 p.m. local time, look for the constellation of Gemini rising and identify bright Pollux – the southeastern of the pair. A little less than a fistwidth to the southwest of Pollux you will see Delta Geminorum at the “waist” of Gemini. Aim there and you will find Vesta very close to Delta! For accurate locator charts, be sure to visit Heavens-Above.

Today in 1968 Apollo 8 became the first manned spacecraft to orbit the Moon. If you should be out when the Moon rises, have a look at its beautiful cold surface for features we often see during the waxing phases – the fantastic Copernicus and the peaceful Sinus Iridum.

Sunday, December 25 – For a huge portion of the United States and Canada, this will be a Christmas morning to remember as the Moon will occult bright Spica in the hours before dawn! Please take the time to check this IOTA information page for the precise path locations and times in your area. May the morning bring you clear skies!

Like a present, Sir Isaac Newton was born on this day 1642 – Newton was the British “inventor” of calculus and a huge amount of what we now consider classical physics. Even young children are aware of his simple laws of motion and gravity. It wasn’t until the age of Einstein that things changed!

In keeping with the season, tonight’s astronomical object is a celebration of both starlight and asterism. Located 10 degrees east of Betelgeuse, NGC 2264 will be a challenging object. But thanks to the late rise of the Moon, the results will be quite worth it. Also known as “the Christmas Tree” cluster, this asterism of approximately 20 bright stars and over 100 fainter ones is embroiled in a faint nebula that will be lost to smaller scopes and binoculars, leaving only the delightful “Christmas Tree” shape adorned with stars.
The very brightest of these stars, S Monoceros, is fifth magnitude and will show clearly in the finderscope and as a double at magnification. Steady skies will reveal that the “star” at the top of our “tree” is also a visual double and home to the beautiful “Cone Nebula!” Many of the stars will also appear to have companions, as well as tints of silver and gold. The visual effect of this splendid open cluster is well worth the challenge it presents.

Thank you all for such a spectacular year. Here’s wishing everyone the most joyous of holiday seasons! Light speed… ~Tammy Plotner

Posted on by Fraser Cain

Moving the Newsletter to Feedblitz

For the 35,000 or so of you receiving Universe Today by email, things are going to seem a little strange for the next few days. I’m moving the mailing service from my webserver to a service called Feedblitz. What this does is take the last 24 hours worth of stories on Universe Today and mail them out to all the subscribers. If I’ve done everything right, the newsletter will look almost identical to the one you’ve been getting in the past; however, it will have new “unsubscribe” information down at the bottom. You’ll get an email today confirming that your address has been transfered, and future emails will be coming from [email protected], so update your address books, etc. As always, please let me know if you have any questions or comments, and I’ll help however I can. For some of you, this will be the first email you’ve received from me in a couple of months, which means I’ve figured out a solution to stop the newsletter from getting blocked.

Thanks!

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

1000 Year-Old Supernova Remnant

SN 1006. Image credit: NASA. Click to enlarge
This false-color Chandra image of a supernova remnant shows X-rays produced by high-energy particles (blue) and multimillion degree gas (red/green). In 1006 AD, what was thought to be a “new star” suddenly appeared in the sky and over the course of a few days became brighter than the planet Venus. The supernova of 1006, or SN 1006, may have been the brightest supernova on record.

We now know that SN 1006 heralded not the appearance of a new star, but the cataclysmic death of an old one located about 7,000 light years from Earth. It was likely a white dwarf star that had been pulling matter off an orbiting companion star. When the white dwarf mass exceeded the stability limit (known as the Chandrasekhar limit), it exploded.

The supernova ejected material at millions of miles per hour, generating a forward shock wave that raced ahead of the ejecta. Particles accelerated to extremely high energies by this shock wave produce the bright blue filaments seen in the upper left and lower right of the image. Why the bright filaments occur only in the observed locations and do not encircle the remnant is not understood. One possibility is that they are due to the orientation of the interstellar magnetic field which may be roughly perpendicular to the filaments.

High pressure behind the forward shock wave pushes back on the supernova ejecta, causing a reverse shock that heats the ejecta to millions of degrees. The fluffy red features seen throughout the interior of the remnant are from gas heated by the reverse shock. The X-ray spectrum of this gas indicates that it is enriched in oxygen and other elements synthesized by nuclear reactions during the stellar explosion.

Original Source: Chandra X-Ray Observatory

Posted on by Fraser Cain

Martian Bacteria Could Be Under the Ice

Martian surface. Image credit: NASA Click to enlarge
A University of California, Berkeley, study of methane-producing bacteria frozen at the bottom of Greenland’s two-mile thick ice sheet could help guide scientists searching for similar bacterial life on Mars.

Methane is a greenhouse gas present in the atmospheres of both Earth and Mars. If a class of ancient microbes called Archaea are the source of Mars’ methane, as some scientists have proposed, then unmanned probes to the Martian surface should look for them at depths where the temperature is about 10 degrees Celsius (18 degrees Fahrenheit) warmer than that found at the base of the Greenland ice sheet, according to UC Berkeley lead researcher P. Buford Price, a professor of physics.

This would be several hundred meters – some 1,000 feet – underground, where the temperature is slightly warmer than freezing and such microbes should average about one every cubic centimeter, or about 16 per cubic inch.

While Price is not expecting any time soon a mission to Mars to drill several hundred meters beneath the surface, methanogens (methane-generating Archaea) could just as easily be detected around meteor craters where rock has been thrown up from deep underground.

“Detecting this concentration of microbes is within the ability of state-of-the-art instruments, if they could be flown to Mars and if the lander could drop down at a place where Mars orbiters have found the methane concentration highest,” Price said. “There are oodles of craters on Mars from meteorites and small asteroids colliding with Mars and churning up material from a suitable depth, so if you looked around the rim of a crater and scooped up some dirt, you might find them if you land where the methane oozing out of the interior is highest.”

Price and his colleagues published their findings last week in the Early Online edition of the journal Proceedings of the National Academy of Sciences, and presented their results at last week’s meeting of the American Geophysical Union in San Francisco.

Variations in methane concentration in ice cores, such as the 3,053-meter-long (10,016-foot-long) core obtained by the Greenland Ice Sheet Project 2, have been used to gauge past climate. In that core, however, some segments within about 100 meters, or 300 feet, of the bottom registered levels of methane as much as 10 times higher than would be expected from trends over the past 110,000 years.

Price and his colleagues showed in their paper that these anomalous peaks can be explained by the presence in the ice of methanogens. Methanogens are common on Earth in places devoid of oxygen, such as in the rumens of cows, and could easily have been scraped up by ice flowing over the swampy subglacial soil and incorporated into some of the bottom layers of ice.

Price and his colleagues found these methanogens in the same foot-thick segments of the core where the excess methane was measured in otherwise clear ice at depths 17, 35 and 100 meters (56, 115 and 328 feet) above bedrock. They calculated that the measured amount of Archaea, frozen and barely active, could have produced the observed amount of excess methane in the ice.

“We found methanogens at precisely those depths where excess methane had been found, and nowhere else,” Price said. “I think everyone would agree that this is a smoking gun.”

Biologists at Pennsylvania State University had earlier analyzed ice several meters above bedrock that was dark gray in appearance because of its high silt content, and identified dozens of types of both aerobic (oxygen-loving) and anaerobic (oxygen-phobic) microbes. They estimated that 80 percent of the microbes were still alive.

Though methane has been detected in Mars’ atmosphere, ultraviolet light from the sun would have broken down the amount observed in about 300 years if some process was not replenishing the methane, Price noted. While interaction of carbon-bearing fluid with basaltic rock might be responsible, methanogens might instead take in subsurface hydrogen and carbon dioxide to make the methane, he said.

If methanogens are responsible, Price calculated that they would occur in a concentration of about one microbe per cubic centimeter at a depth of several hundred meters, where the temperature – about zero degrees Celsius (32 degrees Fahrenheit) or a bit warmer – would allow just enough metabolism for them to keep alive, just as the microbes in the Greenland ice sheet are doing.

Most of the laboratory work was performed by UC Berkeley undergraduate H. C. Tung of the Department of Environmental Science, Policy and Management. She is now a graduate student at UC Santa Cruz. Also coauthoring the paper was Nathan E. Bramall, a graduate student in the Department of Physics.

The work was supported by the National Science Foundation Office of Polar Programs.

Original Source: UC Berkeley News Release

Posted on by Fraser Cain

Perseus Spiral Arm is Closer Than Previously Thought

The locations of our solar system and of W3OH in our galaxy. Image credit: Max Planck Society Click to enlarge
The Perseus spiral arm, the nearest spiral arm in the Milky Way outside the Sun’s orbit, lies only half as far from Earth as some previous results had suggested. An international team of astronomers including scientists from the Max-Planck-Institut f??bf?r Radioastronomie (MPIfR) has recently achieved the most accurate distance measurement ever to the Perseus arm. This was done by use of a vast array of radio telescopes in the USA called the Very Long Baseline Array, observing very bright spots within clouds of gas that contain methyl alcohol in the placental material surrounding a newly formed star called W3OH.

Dr. Xu Ye, an astronomer at Shanghai Observatory now working at the Max-Planck-Institut f??bf?r Radioastronomie and one of the members of the international team who made the measurements, stated that “we measured distance by the simplest and most direct method in astronomy – essentially the technique used by surveyors called triangulation.” Specifically, the team used the changing vantage point of the Earth as it orbits the Sun to form one leg of a triangle. Measuring the change in apparent position of a source, they could calculate the source’s distance by simple trigonometry (resulting in 6357??bf?130 light years).

This result resolves the longstanding problem of the distance to this spiral arm. In thje past, different methods of measuring distance have disagreed by more than a factor of 2. Prof. Karl Menten, another member of the team, states that “this confirms distances based on the apparent luminosity of young stars but disagrees with distances based on a model of the rotation of the Milky Way. The reason for the discrepancy is that young stars in the Perseus spiral arm have unexpectedly large motions.”

The astronomers found that the young star is not moving in a circular orbit around the Milky Way, but deviates by 10% from circular. It is rotating more slowly and “falling” toward the center of the Milky Way. Team member Zheng Xing-Wu of Nanjing University points out that “the simplest explanation is that the cloud of gas out of which the star formed was gravitationally attracted by excess mass of material in the Perseus spiral arm.”

“Studies such as ours are the first steps to accurately map the Milky Way,” says Dr. Mark Reid, a member of the team from the Harvard-Smithsonian Center for Astrophysics. “We have established that the radio telescope we used, the Very Long Baseline Array, can measure distances with unprecedented accuracy–nearly a factor of 100 times better than previously accomplished.” To get a feeling for this measurement one may visualize a person standing on the moon, holding a torch in his stretched-out hand. Let her turn around herself like an ice scater, but only making a single turn in the course of one year. The VLBA measurement is equivalent to measuring the torch’s motion with an accuracy comparable to the torch’s size.

The technique used is Very Long Baseline Interferometry (VLBI), where observations made with many telescopes are combined to achieve the resolution of an extraordinarily large telescope nearly the size of the Earth. The VLBA telescopes stretch from Hawaii over the continental United States to the Virgin Island of St. Croix, producing the resolution of an 8000 km diameter telescope. While the VLBA has extremely high resolution, it requires extremely bright and very compact radio sources such as masers for such measurements (a maser is the microwave equivalent of a laser.) Along with water, methanol is the most widespread maser molecule found in star-forming regions. The methanol spectral line used for the present experiment was discovered in the course of Prof. Menten’s dissertation in the 1980s. In 1988, while working with Dr. Reid, they conducted the first VLBI observations of methanol masers; the target then was also W3OH. “Already then we dreamt of observations such as this one” says Menten.

In fact similar VLBA observations have also been made on water masers in W3OH. This effort, led by the MPIfR’s Kazuya Hachisuka, yielded a distance similar to the methanol masers. “A splendid confirmation!” says Hachisuka. His team also includes Reid and Menten and a number of Japanese scientists.

The methanol observations are only the start of a very large-scale project that Reid and Menten have initiated. It will determine distances and motions of methanol masers all over the Milky Way. It has been granted a large block of VLBA observing time. In addition to the motions on the sky these observations also yield the star’s velocity toward or away from the observer by measuring the Doppler shift of the methanol lines. The resulting three dimensional motions will deliver unique constraints not only on the rotation of the Milky Way but also on the distribution of the unseen Dark Matter that is postulated to surround it.

While the method – simple trigonometry – sounds basic, the transformation into practical results requires a comprehensive understanding of VLBA and all aspects of the observations, including thorough modeling of the Earths’ atmosphere which affects the incoming radio waves. Dr. Reid has dedicated many years of his life to reach the point were programs such as this one can be performed.

Over the years this truly international effort was supported by a Research Prize granted to Dr. Reid by the Alexander von Humboldt Foundation. The cooperation with Shanghai Observatory is supported by a joint program of the Max Planck Society, the Chinese Academy of Sciences, and the Smithsonian Institution’s Visitor Program.

Original Source: Max Planck Society

Posted on by Fraser Cain

Prometheus and Pandora

Shepherd moons, Prometheus and Pandora. Image credit: NASA/JPL/SSI Click to enlarge
This spectacular image shows Prometheus (at left) and Pandora (at right), with their flock of icy ring particles (the F ring) between them. Pandora is exterior to the ring, and closer to the spacecraft here. Each of the shepherd satellites has an unusual shape, with a few craters clearly visible.

The effect of Prometheus (102 kilometers, or 63 miles across) on the F ring is visible as it pulls material out of the ring when it is farthest from Saturn in its orbit. Pandora is 84 kilometers (52 miles) across.

The image was taken in polarized green light with the Cassini spacecraft narrow-angle camera on Oct. 29, 2005, at a distance of approximately 459,000 kilometers (285,000 miles) from Pandora and 483,500 kilometers (300,500 miles) from Prometheus. The image scale is 3 kilometers (2 miles) per pixel on Pandora and 3 kilometers (2 miles) per pixel on Prometheus. The view was acquired from about a third of a degree below the ringplane.

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 NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Black Hole Gulps Down a Neutron Star

Gamma-Ray Burst GRB 050724. Image credit: ESO Click to enlarge
An international team of astronomers reports the discovery of a third short gamma-ray burst, associated with a nearby elliptical galaxy. The low level of star formation in such galaxies and the detection of a second long-lasting flare indicate that this gamma-ray burst is most likely the final scream of a neutron star as it is being devoured by a black hole.

Gamma-ray bursts (GRBs), the most powerful type of explosion known in the Universe, come in two different flavours, long and short ones. Over the past few years, international efforts have shown that long gamma-ray bursts are linked with the ultimate explosion of massive stars (hypernovae).

Very recently, the observations by different teams – including the GRACE and MISTICI collaborations that use ESO’s telescopes – of the afterglows of two short gamma-ray bursts provided the first conclusive evidence that this class of objects originates most likely from the collision of compact objects, neutron stars or black holes.

On July 24, 2005, the NASA/PPARC/ASI Swift satellite detected another short gamma-ray burst, GRB 050724. Subsequent observations, including some with the ESO Very Large Telescope, allowed astronomers to precisely pinpoint the position of the object, lying about 13,000 light-years away from the centre of an elliptical galaxy that is located 3,000 million light-years away (redshift 0.258).

“From its characteristics, we infer that this galaxy contains only very old stars,” says Guido Chincarini (INAF-Brera and Milan University, Italy), co-author of the paper presenting the results. “This is similar to the host galaxy of the previous short GRB which could be precisely localised, GRB 050509B, and very different from host galaxies of long bursts.”

These observations thereby confirm that the parent populations and consequently the mechanisms for short and long GRBs are different in significant ways. The most likely scenario for short GRBs is now the merger of two compact objects.

The observations also show this short burst has released between 100 and 1000 less energy than typical long GRBs. “The burst itself was followed after about 200-300 seconds by another, less-energetic flare,” says Sergio Campana (INAF-Brera), co-author of the paper. “It is unlikely that this can be produced by the merger of two neutron stars. We therefore conclude that the most probable scenario for the origin of this burst is the collision of a neutron star with a black hole.”

Original Source: ESO News Release

Posted on by Fraser Cain

Debris Disk Could Be Forming Rocky Planets

An artist’s concept of a debris disk forming planets. Image credit: NASA/JPL Click to enlarge
Astronomers have found a debris disk around a sun-like star that may be forming or has formed its terrestrial planets. The disk – a probable analog to our asteroid belt – may have begun a solar-system-scale demolition derby, where the rocky remains of failed planets collide chaotically.

“This is one of a very rare class of objects that may give us a glimpse into what our solar system may have looked like during the formation of our terrestrial planets,” said Dean C. Hines of the Space Science Institute, a leader of the team that discovered the rare objects with NASA’s Spitzer Space Telescope.

“The target is essentially a star similar to our sun, seen at a time when the terrestrial planets in our solar system were thought to have formed,” Hines said. “We see evidence that this star might have an asteroid belt, roughly at the distance Jupiter is from our sun.”

“This object is very unusual in the context of all the others we’ve looked at,” said University of Arizona assistant astronomy Professor Michael R. Meyer, a colleague in the discovery. Meyer directs a Spitzer Legacy project to study solar system formation and evolution in a sample of 328 young sun-like stars in the Milky Way. The project turned up the unusual system.

“This is the only such debris disk among the 33 sun-like stars we’ve studied in our project so far, and one of only five such objects known,” Meyer said.

The star, named HD 12039, is about 30 million years old, or the age of the sun when the terrestrial planets are thought to have been 80 percent complete and the Earth-moon system formed, the astronomers said. It is roughly 137 light years away, or the distance light travels in 137 years.

HD 12039 is a “G” type star like our sun, a yellow star with surface temperatures between 5,000 and 7,000 degrees Fahrenheit. It hasn’t yet settled into the “main sequence,” or mature nuclear-burning phase as our sun has. It’s eight percent brighter, just slightly cooler and a little more massive than our sun, or 1.02 solar masses.

The Spitzer team discovered that the star’s debris disk temperature is 110 degrees Kelvin, or minus 262 degrees Fahrenheit. That’s warmer than temperatures of the frigid outer debris disks that Meyer’s Spitzer team commonly finds around sun-like stars. They’ve found that between 10 and 20 percent of the sun-like stars in their sample so far — whether young, middle-aged or old — have outer disks like our Kuiper Belt beyond Neptune.

“The temperature of the dust in HD 12039’s strange, narrow debris ring puts it between four and six astronomical units from the star — smack dab where Jupiter is in our solar system,” Meyer said. (An astronomical unit, or AU, is the mean distance between Earth and the sun.)

“What’s curious about this disk is that there’s little if any dust inside four AU and beyond six AU. It’s a narrowly confined ring that could be similar in some ways to the outer rings we see around Saturn,” Meyer said.

Just as small moons shepherd the ice grains orbiting Saturn into discrete rings, and just as Jupiter tends the outer edge of our solar system’s asteroid belt, an unseen giant planet may be nudging dust into the narrow debris ring around this star, the astronomers said.

“We think this is a tight, narrow ring of rocky objects similar to those in our asteroid belt, except this ring is five AU from its star, instead of two-to-three AU, the distance between our asteroid belt and the sun,” Meyer said.

“At 30 million years, the material we see in this star likely has to come from ground-up rocks in a zone where terrestrial planets could form,” Hines said.

NASA earlier this year announced a Spitzer telescope discovery of another of these alien asteroid belts. It orbits a two-billion-year-old sun-like star 35 light years away, at a distance comparable to that between Venus and the sun.

Based on Spitzer Telescope results to date, only one percent to three percent of the young, sun-like stars in our Milky Way have massive terrestrial debris disks, Meyer said.

“We could be witnessing a common, short-lived event through which all systems pass, or we could be seeing a rare example of a massive warm debris disk surrounding an unusual, sun-like star,” Meyer said.

The astronomers describe their work in an article to be published in The Astrophysical Journal.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA. For information on the Spitzer Space Telescope visit:
http://www.spitzer.caltech.edu/spitzer

The Space Science Institute is a nonprofit organization that carries out world-class research in space and Earth science, together with innovative science education programs that inspire and deepen the public’s understanding of planet Earth and its place in the grander universe. The institute’s integrated research and education programs span planetary science, space physics, astrophysics, astrobiology and Earth science.

Original Source: UA News Release