The Star that everyone missed

photo: This image shows the nova V598 Puppis, which was accidentally discovered in the XMM-Newton slew survey. The X-ray contours, which indicate the position of the nova, are overlaid on an optical image taken from the Digitised Sky Survey. ESA/XMM-Newton/EPIC (adapted from A. Read et al.), Background: Digitised Sky Survey.

July 18, 2008

XMM-Newton has discovered an exploding star in the Milky Way. Usually that would be important in itself, but this time there is a special twist. Calculations show that the explosion must have been clearly visible to the unaided eye but was missed by the legions of star watchers around the planet.

On October 9, 2007, ESA's orbiting X-ray observatory XMM-Newton was turning from one target to another. As it did so, it passed across a bright source of X-rays that no one was expecting. The source was not listed in any previous X-ray catalogue, yet XMM-Newton was receiving some 50 X-rays every second from this mysterious object.

The only celestial object the XMM-Newton team could find at this location was a faint star, known only by its catalogue number USNO-A2.0 0450-03360039. Acting quickly, Andy Read of the University of Leicester and Richard Saxton of ESA's European Space Astronomy Centre (ESAC), Spain, arranged for an astronomical telegram to be circulated across the Internet, informing other astronomers of the newly-discovered X-ray source.Astronomers using the 6.5-meter Magellan-Clay telescope at Las Campanas Observatory in Chile, found that USNO-A2.0 0450-03360039 had dramatically brightened by more than 600 times. Analyzing the light from the source meant that they could classify the object as a nova.

Novae occur when a compact star, called a white dwarf, feeds off the gas of a nearby companion star. When sufficient gas builds up on the white dwarf, a nuclear reaction begins releasing large quantities of energy, prompting the white dwarf to shoot up in brightness.

But there was a puzzle. The incandescent explosion does not immediately release X-rays; the expanding cloud of debris created in the detonation temporarily masks them. As this clears, the X-rays shine through. So, for XMM-Newton to see this nova, the explosion must have taken place many days before. Yet, no one had reported seeing it.Usually, dedicated amateur and professional astronomers find novae by regularly sweeping the night sky for stars that suddenly brighten. This one, it seemed, had slipped the net. Saxton contacted the robotic survey project ASAS and asked them to check their data. They found the nova. It had taken place on June 5, 2007 and had been clearly visible, even to the unaided eye.

"Anyone who went outside that night and looked towards the constellation of Puppis would have seen it," says Saxton.

The nova is now officially designated V598 Puppis and is one of the brightest for almost a decade, doubling the irony that it was not spotted during its brilliant peak. As news of it spread, the global effort to track its fading light became intense. "Suddenly there was all this data being collected about the star. For variable star work like this, the contribution of the amateur community can be at least as important as that from the professionals," says Read.

Thanks to XXM-Newton, this story has a happy ending, but it does make astronomers wonder whether there are other discoveries going unnoticed too.

NASA confirms liquid lake on Saturn moon

photo:This artist concept shows a mirror-smooth lake on the surface of the smoggy moon Titan. Cassini scientists have concluded that at least one of the large lakes observed on Saturn’s moon Titan contains liquid hydrocarbons, and have positively identified ethane. This result makes Titan the only place in our solar system beyond Earth known to have liquid on its surface.

Date:July 31, 2008

Cassini spacecraft reveals a large body of liquid ethane, methane, other hydrocarbons, and nitrogen on Titan.NASA scientists have concluded that at least one of the large lakes observed on Saturn's moon Titan contains liquid hydrocarbons, and have positively identified the presence of ethane. This makes Titan the only body in our solar system beyond Earth known to have liquid on its surface.

Scientists made the discovery using data from an instrument aboard the Cassini spacecraft. The instrument identified chemically different materials based on the way they absorb and reflect infrared light. Before Cassini, scientists thought Titan would have global oceans of methane, ethane, and other light hydrocarbons. More than 40 close flybys of Titan by Cassini show no such global oceans exist, but hundreds of dark lake-like features are present. Until now, it was not known whether these features were liquid or simply dark, solid material.

"This is the first observation that really pins down that Titan has a surface lake filled with liquid," said Bob Brown of the University of Arizona, Tucson. Brown is the team leader of Cassini's visual and mapping instrument. The results will be published in the July 31 issue of the journal Nature.

Ethane and several other simple hydrocarbons have been identified in Titan's atmosphere, which consists of 95 percent nitrogen, with methane making up the other 5 percent. Ethane and other hydrocarbons are products from atmospheric chemistry caused by the breakdown of methane by sunlight.

Some of the hydrocarbons react further and form fine aerosol particles. All of these things in Titan's atmosphere make detecting and identifying materials on the surface difficult, because these particles form a ubiquitous hydrocarbon haze that hinders the view. Liquid ethane was identified using a technique that removed the interference from the atmospheric hydrocarbons.

The visual and mapping instrument observed a lake, Ontario Lacus, in Titan's south polar region during a close Cassini flyby in December 2007. The lake is roughly 7,800 square miles (20,200 square kilometers) in area, slightly larger than North America's Lake Ontario.

"Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan," said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey in Flagstaff, Arizona. "The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan's atmosphere, raises expectations for exciting future lake discoveries by our instrument."

The ethane is in a liquid solution with methane, other hydrocarbons and nitrogen. At Titan's surface temperatures, approximately -300° Fahrenheit (-185° Celsius), these substances can exist as both liquid and gas. Titan shows overwhelming evidence of evaporation, rain, and fluid-carved channels draining into what, in this case, is a liquid hydrocarbon lake.

Earth has a hydrological cycle based on water and Titan has a cycle based on methane. Scientists ruled out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus. The observations also suggest the lake is evaporating. It is ringed by a dark beach, where the black lake merges with the bright shoreline. Cassini also observed a shelf and beach being exposed as the lake evaporates.

"During the next few years, the vast array of lakes and seas on Titan's north pole mapped with Cassini's radar instrument will emerge from polar darkness into sunlight, giving the infrared instrument rich opportunities to watch for seasonal changes of Titan's lakes,"
Soderblom said.

Launched in October 1997, Cassini's 12 instruments have returned a daily stream of data from Saturn's system. The mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

Miniature black holes are no danger

photo: The LHC is the world’s most powerful particle accelerator. It is housed in a 17-mile tunnel that runs between Lake Geneva and the Jura mountain range. Maximilien Brice/CERN.By smashing together atomic nuclei at nearly the speed of light, scientists hope to find the particle responsible for mass.

The Large Hadron Collider (LHC), the largest and most expensive scientific instrument ever built in peacetime, begins operations this Wednesday, September 10 when a beam of high-speed protons begins shooting around the machine's 16-mile, 27-kilometer, circular tunnel beneath Geneva, Switzerland.

When the protons collide with each other inside the machine, one thing that scientists are certain won't happen is the production of miniature black holes that gobble up nearby matter. A new study shows that the continuing existence of old stars in the sky is evidence that small black holes can't swallow the Earth.

That is not to say that the new collider might not actually create mini-black holes, as no one knows for sure what will emerge from the debris of the LHC collisions. Black holes are thought to represent the ultimate state of compressed matter, with gravity so powerful that any bit of matter, and even light, would be sucked inexorably inwards with no chance for escape if it gets too close to the black hole's boundary.

That was the thinking about black holes before Stephen Hawking, the Cambridge University scientist, came forth with the idea that even black holes can lose energy. The density of energy inside a black hole is so huge that some of it can be converted into creating new particles, he said. If this conversion happens right at the edge of the black hole, Hawking argued, some of those new particles could escape, taking energy with them. In this way black holes can lose energy. They can "evaporate."

There is a rule in physics that says that the smaller the black hole, the quicker the evaporation. For an LHC-style black hole, estimated to be only a billionth of a billionth of a meter across (an atto-meter) the black hole would exist for a bit more than a few billion-billion-billionths of a second. It wouldn't be around long enough to swallow any nearby matter and would pose no danger to ordinary matter.But what if Hawking is wrong? What if some black holes don't evaporate, but go on eating matter? What if scientists create some small, long-lasting black holes in Geneva, and they get loose? This possibility is addressed in a new report in the journal Physical Review D.

In their study of the matter, Steve Giddings of the University of California at Santa Barbara and Michelangelo Mangano of the European Organization for Nuclear Research (the parent laboratory where LHC operates) look at what happens if there existed a type of black hole, one we'd be concerned about, that could not only survive but would continue to grow to a macroscopic size in a time shorter than billions of years.

If such a type of black hole existed, it would grow even quicker inside super-compressed stars, such as white dwarfs and neutron stars, where the density of matter is billions or trillions of times greater then the density of rock on Earth. These celestial objects are created when an ordinary star runs out of fuel and starts to contract. There is no LHC on such stars but a black hole could presumably be spawned when a passing cosmic ray, a haphazard shooting particle that races around the cosmos, strikes and burrows inside the neutron star.

Since astronomers look out and see perfectly healthy and very old white dwarfs and neutron stars of the right types, Giddings concludes that quickly-growing black holes, the kind that voraciously eat their surroundings, can't exist. Such a dangerous black hole couldn't exist inside dense stars and couldn't exist on Earth.

Michael Peskin, a Stanford physicist who did not take part in the study, says that the continued existence of superdense stars act like the canaries that coal miners used to take underground — the idea being that the presence of deadly gas would more quickly overcome the canary, giving the miners warning of a dangerous condition. As long as those stars keep sending their light, Peskin says, the Earth is not in danger from black holes

If scientists don't know for sure what particles the LHC will produce, why build a massive, very expensive machine to smash particles together in the first place? The smashing is needed because to explore the interior of atoms and the power of the collisions of particles is directly related to how deep inside the researchers can see. Increasing the power of the proton beams used in the collisions requires increasing the size of the collider.

Why do the beams have to be so powerful? The answer is related to the idea that energy can be converted from one form into another. The protons at the LHC whiz around their long track at a speed of 99.999999 percent of the speed of light. Actually two beams circulate in the same underground tunnel in opposite directions, and when two protons hit each other head on, a lot of their immense energy of motion can, at the moment of collision, be transformed into new particles that weren't there a moment before.

When two automobiles hit head-on the results are always bad. But in the world of high-energy physics, instigating a violent smashup, with lots of debris spraying out, is exactly what researchers want. Among the debris can be particles that might have existed billions of years ago but which, because of their instability, long ago decayed away. Creating these rare particles again in a modern experiment is precisely the plan at LHC. The thinking here is that such formerly-extinct species of matter can tell us things about the forces of nature.

MESSENGER's second Mercury flyby

photo: The spectacular image shown here is one of the first to be returned and shows a WAC image of the departing planet taken about 90 minutes after the spacecraft’s closest approach to Mercury. NASA/JHU APL/Carnegie Institution of Washington.

When Mariner 10 flew past Mercury three times in 1974 and 1975, the probe imaged less than half the planet. In January, during MESSENGER's first flyby, its cameras returned images of about 20 percent of the planet's surface missed by Mariner 10. On October 6, at 4:40 a.m. EDT, MESSENGER successfully completed its second flyby of Mercury, and its cameras captured more than 1,200 high-resolution and color images of the planet — unveiling another 30 percent of Mercury's surface that had never before been seen by spacecraft.

"The MESSENGER team is extremely pleased by the superb performance of the spacecraft and the payload," said MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington. "We are now on the correct trajectory for eventual insertion into orbit around Mercury, and all of our instruments returned data as planned from the side of the planet opposite to the one we viewed during our first flyby. When these data have been digested and compared, we will have a global perspective of Mercury for the first time."

On October 7, at about 1:50 a.m. EDT, MESENGER turned to Earth and began transmitting data gathered during its second Mercury encounter. The spectacular image on the right — one of the first to be returned — was snapped by the Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS) instrument, about 90 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 17,000 miles (27,000 kilometers).

The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s. For most of the terrain east of Kuiper, toward the edge of the planet, the departing images are the first spacecraft views of that portion of Mercury's surface. A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper.

Thunderstorms can drive jet streams on all giant planets

photo: Moist convection produces jet streams resembling those observed on Jupiter, Saturn, Uranus, and Neptune. NASA/JPL.

DATE: October 13, 2008

Researchers account for the different number of jet streams on the gas giants based on the expected amount of water vapor found on each planet.Turbulence generated by thunderstorms can drive the multiple east-west jet streams on the giant planets — Jupiter, Saturn, Uranus, and Neptune — and explain a long-standing conundrum concerning the puzzling differences between the two innermost gas giants, Jupiter and Saturn, and the outermost two, Uranus and Neptune.

Scientists have been trying to understand the mechanisms that form the jet streams and control their structure since the Pioneer and Voyager spacecrafts returned the first high-resolution images of the giant planets in the 1970s and 1980s.

The jet streams are narrow rivers of air that flow east-west. On Earth, they are major component of our planet's global circulation and control much of the large-scale weather that the United States and other countries outside of the tropics experience. Analogous jet streams dominate the circulation of Jupiter, Saturn, Uranus, and Neptune, reaching up to 400 mph (600 km/h) on Jupiter and nearly 900 mph (1,500 km/h) on Saturn and Neptune. The question of what causes these jet streams and sets their structure remains one of the most important unsolved problems in the study of planetary atmospheres.

Yuan Lian and Adam Showman of the University of Arizona showed how storms can generate the jet streams during Division of Planetary Sciences of the American Astronomy Society meeting in Ithaca, New York. Lian is a graduate student and Showman is a professor at the university, which is based in Tucson, Arizona.

Lian and Showman performed state-of-the-art computer simulations showing how moist convection — essentially, thunderstorms — can produce patterns of jet streams resembling those on the four giant planets. In the simulations, water vapor condensation generates small hurricane-like storms that interact with each other to form global jet streams. The study is the first to self-consistently describe both the generation of these storms and their interaction with the global circulation.

"Thunderstorms have been known to exist on Jupiter and Saturn since the early 1980s, and it has repeatedly been proposed that they drive the jet streams on these planets, but before now this idea had never been adequately tested," Lian said. "We showed that such storms can indeed drive jet streams similar to those observed."

A long-standing puzzle is the dichotomy between sister planets Jupiter and Saturn on the one hand and Uranus and Neptune on the other. "Unlike Earth, Jupiter and Saturn have about 20 jet streams each, which are associated with the banded cloud patterns on those planets," Showman said. "In contrast, Uranus and Neptune have only three jet streams each. Another conundrum is that the jet stream on the equator flows eastward on Jupiter and Saturn but westward on Uranus and Neptune. Understanding that dichotomy has been a hard nut to crack."

The simulations successfully produced about 20 jet streams each for Jupiter and Saturn and three jet streams each for Uranus and Neptune, consistent with observations. Moreover, the simulations explained the direction of the equatorial winds on all four planets — eastward on Jupiter and Saturn but westward on Uranus and Neptune.

"Previous investigations generally predicted that the equatorial jet stream would have the same direction on all four planets, inconsistent with observations," Lian added. "Our study is among the first to provide an explanation for these differences."

In the simulations, the abundance of water vapor — which is modest on Jupiter and Saturn but expected to be large on Uranus and Neptune — controlled the differences.

The storms produced in the simulations also bear an encouraging resemblance to those observed on Jupiter and Saturn, Showman noted.

Lian cautioned that much work remains to be done. "Our study provides a mechanism that can generate the jets on the giant planets. However, the wind speeds in our computer simulations are generally too weak. Overcoming this discrepancy will require continued improvements in our models."

Tides have major impact on planet habitability

photo: New research shows that tides can play a major role in heating terrestrial planets and create extremely hot conditions on rocky alien worlds that otherwise might be livable. However, tidal heat can also create conditions favorable to life on planets that would otherwise be unlivable. ESO

October 14, 2008

Astronomers searching for rocky planets that could support life in other solar systems should look outside, as well as within, the so-called "habitable zone," University of Arizona planetary scientists say.

Planets too close to their stars are roasted. Planets too far from their stars are frozen. In between, research models show, there's a habitable zone where planet temperatures approximate Earth's. Any rocky planets in this just-right Goldilocks zone could be awash in liquid water, a requisite for life as we know it, theorists say.

New research by Brian Jackson, Rory Barnes, and Richard Greenberg of Arizona's Lunar and Planetary Laboratory shows that tides can play a major role in heating terrestrial planets, creating hellish conditions on rocky alien worlds that otherwise might be livable. And just the other way, tidal heat can also create conditions favorable to life on planets that would otherwise be unlivable.Our own solar system is something of an anomaly in that its planets move in relatively quiescent, circular orbits around the Sun. Most extrasolar planets found to date have highly elongated orbits. During each orbit, tides stretch the planet the most when the celestial body is near the host star, and less when the planet is farther from its star. The resulting friction generates the internal heat that drives the planet's geophysical processes.

If the recently discovered "super-Earths" — extrasolar planets only 2 to 10 times as massive as Earth — are indeed terrestrial, tidal heating may be great enough to melt them. At least, it could produce volcanism on par with Jupiter's moon Io, "dimming their prospects for habitability," Jackson said. So, some of the recently discovered super-Earths may be more like "super-Ios," he said. Io is the most volcanically active body in our solar system.

"Tidal heating scales with planet mass, so we expect that most easily detectable super-Earths will be dominated by volcanic activity," Jackson said. "That's one of our first conclusions from this work — that the first earthlike planets found are probably going to be strongly heated and have big volcanoes. Even if earthlike planets are found within the habitable zone, they may not be habitable because they will be overwhelmed by this tidal heating."

Tidal heating may also create habitable conditions on planets that otherwise are too small or too cold to support life, Jackson said. Tidal heating can enhance outgassing of volatiles that contribute or replenish a planet's atmosphere through volcanism. Tidal heating also can generate sub-surface liquid oceans on water-rich, rocky planets that would otherwise be frozen, just as tidal heating is believed to warm a sub-surface liquid water ocean on Jupiter's moon Europa.

Also, tidal heating can drive plate tectonics, a mechanism that checks excessive carbon dioxide from accumulating in a planetary atmosphere. This produces the kind of deadly greenhouse atmosphere found on Venus.

"Our study shows that tidal heating could produce enough heat to drive plate tectonics for billions of years, long enough for life to appear and flourish," Jackson said.

Doubles make bubbles

photo: The Hubble image of IC 418 is shown in a false-color. Red shows emission from ionized nitrogen (the coolest gas), green shows emission from hydrogen, and blue traces the emission from ionized oxygen (the hottest gas). AURA / STScI / NASA.

January 22, 2004

A favorite object of many backyard and professional astronomers alike, planetary nebulae are some of the most beautiful objects in the universe. Puffed out into wildly psychedelic shapes and colors, these shells of gas mark the spectacular final act of a lone dying star — at least this is what scientists thought was going on. Now, surprising new observations point to a more bizarre and complex birth for some of these cosmic bubbles, making astronomers see double.

Using the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5-meter telescope at the Kitt Peak National Observatory to peer into the hearts of nearly a dozen planetary nebulae, a team of American scientists has found convincing evidence that most of these gas clouds harbor binary stars in their centers. The radial velocity measurements for ten out of eleven central stars revealed the telltale wobble signifying the gravitational tug of an unseen companion star.



Photo: The Hubble Space Telescope captured Henize 3-401 on June 12, 1997. It's the first look at the central, dying star which has cast off its outer layers to produce the "bipolar" nebula. Astronomers aren't sure why the star's expelled gas is jutted into two long lobes, though. European Space Agency / Pedro García-Lario (ESA ISO Data Centre).

"If our current results are confirmed with further observations, we could be at the start of a revolution in the study of the origin of planetary nebulae," says team leader Howard Bond of the Space Telescope Science Institute. "If these nebulae arise from binary stars, it implies a very different origin for these systems than what most astronomers had thought."

It is widely acknowledged that Sun-like stars end their days by shedding most of their atmosphere into a gaseous cocoon — but Bond and his colleagues believe binary stars play a crucial role in planetary nebula formation. The team's unexpected results reveal double star systems may affect how stellar remnants are thrown out into space, leading to many of the more exotic morphologies.



photo: This Hubble Space Telescope image reveals Menzel 3's glowing lobes, which extend from a dying, sunlike star. This composite image of the planetary nebula is constructed from exposures taken by Hubble's Wide Field and Planetary Camera 2 in 1997 and 1998. NASA / ESA / The Hubble Heritage Team (STScI / AURA).

While planetary nebulae can thank bloated red-giant stars for their initial creation, the stars' spin rates and associated magnetic fields cannot account for the creation of some of the more complex shapes seen in nebulae. The Hubble Space Telescope's gallery of greatest images shows off a kaleidoscope of gas bubbles in all shapes and symmetries. Many of the more picturesque planetary nebulae often appear elliptical, with lobe-like structures attached to jet-like extensions. The enigmatic structures of these nebulae, however, have puzzled astronomers and challenged existing theories.



photo: This nebula, called NGC 2440, is rich in clouds of dust, some of which form long, dark streaks pointing away from the central star. In addition, the bright nebula is surrounded by a much larger cloud of cooler gas which is invisible in ordinary light but can be detected with infrared telescopes. AURA / STScI / NASA.

"The most direct way to spin up these vast, fluffy stars is by the action of an orbiting companion. In extreme cases, as a red giant star gradually increases in size, it may actually swallow a companion star, which would then spiral down inside the giant and eventually eject its outer layers," describes Orsola De Marco, an astronomer at the American Museum of Natural History in New York and coauthor of the study. "Despite this, the mainstream astronomical view remains rooted in single-star theories for the evolution of planetary nebulae, supported by the small percentage of planetary nebulae central stars that were previously known to be binaries. However, our new research threatens to turn this viewpoint on its head."

Reporting their results in the February 1 issue of The Astrophysical Journal Letters, the team hopes to find more candidate sources. In order to rule out the possibility of any physical sources that may be only mimicking the stellar wobble, they will attempt to pin down precise orbital periods for these binary stars. DeMarco adds: "We are reasonably sure that these variations are due to binarity, but determination of their precise periods is the only way to be sure."

A supernova survivor

photo: This artwork illustrates the scene of Supernova 1993J. The red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). ESA and Justyn R. Maund (University of Cambridge)

January 11, 2004

For the first time, astronomers uncover a companion star among a supernova's remains.Supernovae — the brilliant fireworks that signal the death of a star — are key in our understanding of the universe. They seed the cosmos with chemical elements cooked up in their fiery ovens and they serve as shining tracers of the expansion of space itself.

But while scientists have devised comprehensive models of the process of such an explosion, they've had little observational evidence to go on. That's because once the blaze of a supernova is spotted in the sky, the star has already blown itself to pieces, leaving scarcely a trace of its history amid the wreckage. Or so scientists thought. Recent observations of a supernova's glowing remains have uncovered pre-explosion details and have revealed, for the first time, a survivor.

Supernova 1993J was seen burning in the sky in spiral galaxy M81 back in the spring of 1993. After the star detonated, observers searched archived images of M81's stars to pinpoint which star had gone supernova. It appeared that a massive red supergiant had been the unfortunate progenitor, but something didn't make sense. Material ejected by the explosion was too rich in helium to have come from the supergiant alone. Moreover, the supernova's light showed a sharp, uncharacteristic peak in brightness that suggested something else was going on.

Astronomers soon realized that to account for 1993J's strange behavior, the red supergiant must have had a companion star, which may have perished in the blast.

That was over a decade ago. Now, as the explosion's embers are beginning to fade, a team of observers using both the Hubble Space Telescope's Advanced Camera for Surveys and the Keck Observatory in Hawaii has peered into the rubble and found a massive star at the exact position predicted for the supernova's companion.
"This is the first time such a companion star has been found," says University of Cambridge's Justyn Maund, a member of the discovery team. "We can say that the companion star survived the supernova explosion of its partner. Given that only two progenitor stars are known, this is an important step in understanding the progenitors of any supernova."

"It is like a detective story," says team member Rolf Kudritzki of the University of Hawaii. "Because of the new equipment, you are now able to track down new evidence [that] was impossible to do before. Astronomers had clear ideas about the scenarios that lead to supernova explosions, but no direct observational proofs. Now we have, for the first time, very detailed data so that we can understand the formation of these supernovae. This is an important step forward."

Not only can astronomers dig up the dirt on 1993J's past, but they also can keep an eye on the area to see what will develop in the near future. By continuing to observe the companion star, they may be able to witness either a neutron star or a black hole emerge from the remnants in "real time." Such an awesome event could take place within the next ten years.

"Supernovae produce all the elements heavier than hydrogen and helium," Maund explains. "These heavy elements are now seen in the latest generations of stars, and [they] form planets and life as we know it. Astronomers need to understand what is going on in an explosion to know how much of these heavy elements is produced and how [the elements] are spread around the galaxy to be recycled into new stars.

"In addition, supernovae are a useful distance measure — but to calibrate them, we need to understand the explosions," Maund adds. "Supernovae can then be used to map out the history of the universe."

Record-breaking cosmic mirage

photo: This picture, taken by the Subaru Telescope on the summit of Mauna Kea in Hawaii, shows four images of the same quasar (the four white dots in the center). The quasar is almost 10 billion light-years from us and its light has been split into four by the gravitational influence of a foreground cluster of galaxies 6.2 billion light-years from us. Some of the galaxies of the cluster appear as yellow dots in the image. Sloan Digital Sky Survey


January 1, 2004

A widely lensed quasar reveals the presence of dark matter.Having something block your view when taking a photo can be a real pain — except perhaps when studying cosmic mirages and dark matter.

Astronomers have discovered a gravitationally lensed quasar located more than 10 billion light-years away that is shedding new light on dark matter in the universe. Parked behind a massive cluster of galaxies, the quasar's feeble light has been bent and split into four distorted images that have the largest angular separation ever found. According to the discovery team, this wide-angle effect is evidence that invisible cold dark matter dominates the foreground cluster and is responsible for the record-breaking quadruple mirage.

Since 1979, more than 80 gravitationally lensed quasars have been cataloged, however none were found to have separations of more than 7 arcseconds. Despite theoretical models that predicted larger splitting of quasar images, numerous searches had come up empty — until now.

Mining the colossal database of over 30,000 quasars from the Sloan Digital Sky Survey (SDSS), an international team of astronomers led by Naoisha Inada and Masamune Oguri from the University of Tokyo pinpointed SDSS J1004+4112 in the constellation Leo Minor.Using the Subaru Telescope on the summit of Mauna Kea, Hawaii, the group managed to identify four individually split quasar images separated by 14.62 arcseconds — more than twice as large as the previous record-holding lensed quasar.



photo: This 2.5-meter telescope is the main workhorse of the Sloan Digital Sky Survey. Its box-shaped structure protects it against the wind. SDSS Collaboration.

"Additional observations obtained at the Subaru 8.2-meter Telescope and Keck Telescope confirmed that this system is indeed a gravitational lens," explains lead author Inada. "Quasars split this much by gravitational lensing are predicted to be very rare, and thus can only be discovered in very large surveys like the SDSS."

First predicted by Einstein more than six decades ago, gravitational lensing occurs when the gravity from a massive foreground object bends and amplifies the light from a more distant object, as seen from Earth. Astronomers have been using this giant magnifying-lens effect to bring into view quasars and galaxies that otherwise would be too faint to detect. Some lensed quasars produce multiple images including, in rare cases (if the alignment is perfect), rings around the lensing galaxies.In the December 18 edition of Nature, the team argues that the quadruple lensing effect at J1004+4112 is caused by the gravitational influence of a cluster of galaxies about 6.2 billion light-years away. They believe that because the visible mass of this cluster cannot account for the observed 14.62-arcsecond separation, high concentrations of intervening material in the form of unseen cold dark matter must be causing this unprecedented wide splitting.



photo: In a gravitational lens, a foreground galaxy (here shown as a red spiral) causes light (dashed lines) from a background quasar to bend. As a result, an observer may see multiple quasars instead of just one. In most cases the quasar images are only offset by an arcsecond, but occasionally, as is shown here, the offset is much larger. Astronomy.com: Pamela L. Gay

Oguri added: "Discovering one such wide gravitational lens out of over 30,000 SDSS quasars surveyed to date is perfectly consistent with theoretical expectations of models in which the universe is dominated by cold dark matter. This offers additional strong evidence for such models."

The authors expect many more such wide-angle lensed quasars will be encountered and that they will become powerful tools in the study of the distribution of dark matter in the universe. "The gravitational lens we have discovered will provide an ideal laboratory to explore the relation between visible objects and invisible dark matter in the universe," adds Oguri.

Fast jets shoot from a star

photo: Circinus X-1, the subject that influenced this illustration, is located about 20,000 light years from Earth in the constellation Circinus near the Southern Cross. NASA.

Date: January 29, 2004

A neutron star in a binary star system is spewing matter into space at nearly the speed of light.The recent discovery of a neutron star exhibiting behavior previously believed to be exclusive to black holes is challenging astronomers' understanding of the nature of some of the most extreme phenomena in the cosmos.

An international team of astronomers from the Netherlands, United Kingdom, and Australia used the Australia Telescope to study binary star system Circinus X-1 in radio waves during the past three years. Circinus X-1 consists of a star 3 to 5 times the mass of the Sun in a close orbital dance with a neutron star companion. The star system lies about 20,000 light-years away from Earth in our Milky Way Galaxy.

Since the 1970s, observers have noted Circinus X-1's emission of radio waves. Now, the team of astronomers, led by Rob Fender of the University of Amsterdam, has peered into the depths of the radio cloud and found something astonishing. Jets of matter are ejected out of the star system at 99.8 percent the speed of light.

These jets are the fastest ever observed shooting out of something other than a supermassive black hole in the center of a distant galaxy, and the fastest outflow ever observed originating within our own Milky Way.

The two stars circle each other once every 16.6 days, drawing tauntingly closer, then moving farther apart. As they dance, the neutron star — the end product of the violent explosion and collapse of a giant star — steals matter away from its stellar companion, forming an ever-growing accretion disk of hot gas in its outer atmosphere.

It seems that when the two stars get closest to one another, roughly every 17 days, hot matter from the accretion disk is spewed violently into interstellar space. The observation raises the question: What creates these enormously fast jets?

Astronomers previously attributed such speeding torrents to the environment characteristic of black holes, where space-time is warped beyond repair and gravity becomes infinitely potent. But if a neutron star can produce the same ultra-relativistic eruptions, then some more general set of circumstances must exist that accelerates matter to breakneck speeds.

"Whatever the physics underlying the production of ultra-relativistic jets — which are related to the jets of distant, massive galaxies and also probably gamma-ray bursts — it must be connected to the things that neutron stars and black holes have in common," says Fender.

He points to high densities, high pressures, and the build-up of magnetic fields as mutual characteristics and potential clues.

The observation is forcing astronomers to rethink their definitions of black holes and neutron stars, and to come to grips with the mechanism behind high-speed jets. It is at these most extreme conditions — where gravity contorts space and slows time — that fundamental physics comes to light.

Understanding the cause of these jets, then, is crucial.

"They are the fastest moving phenomena in the universe and probably are responsible for, or at least associated with, the biggest explosions since the Big Bang," Fender says.

That's why the team plans to continue studying Circinus X-1, to home in on the details.

"Since the outbursts go off every 16.6 days," explains Fender, "we can uniquely time the observations from ground and space-based facilities to observe at the moment of jet formation, and to study the physics more closely. This year, we will continue to make radio observations and hope to have long observations with the European Integral orbiting gamma-ray observatory."

Galactic archaeology

Space telescopes spy ancient galaxy clusters in the young universe, shedding light on the years following the Big Bang.

photo: This galaxy cluster is shown as it existed when the universe was just 5 billion years old. The cluster is as massive as 300 trillion suns and is the most massive known cluster of its epoch. This image, which was taken between May and June 2002 with Hubble's Advanced Camera for Surveys Wide Field Camera, shows just the core of the cluster. Only about 50 galaxies are shown, but the cluster likely contains thousands. Dominating the core are a pair of large, reddish, elliptical galaxies (near the center of the image). Their red color indicates they hold a population of stars that are at least a billion years old. The red galaxies surrounding the central pair are also cluster members. Many of the other galaxies, including several blue galaxies, lie in the foreground. NASA / ESA / J.Blakeslee (JHU) / M. Postman (STScI) / P. Rosati (ESO)

January 5, 2004

In piecing together the story of the universe's history, scientists are hoping to figure out exactly how and when galaxies first formed. It's a crucial question because early structure formation carries the imprint of conditions in the newborn universe, which can help us understand our cosmic beginnings. Now, two key discoveries of early galaxy clusters are helping astronomers see the foundations of the universe's galactic architecture directly.

Using a powerful combination of NASA's Chandra X-ray Observatory and the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope, an international team of astronomers has found and studied two record-breaking ancient galaxy clusters.

The first is a cluster whose light is reaching us from 9 billion years ago, when the universe was a mere 5 billion years old. It's the most massive known cluster of that epoch, which means it must have been growing for quite some time already — a somewhat surprising result for such an early time in the universe's youth.

"We determined that the galaxies in this cluster were already about 3 billion years old," explains astronomer John Blakeslee of Johns Hopkins University, a member of the team. "Thus, these galaxies formed most of their stars about 2 billion years after the Big Bang."

The second finding is a proto-cluster of embryonic galaxies from a time when the universe was only about 1.5 billion years old. This is the most distant, and therefore earliest, proto-cluster ever found.



photo: Taken by Hubble's Advanced Camera for Surveys Wide Field Camera in July 2002, this image shows the embryonic cluster as it was when the universe was just 1.5 billion years old. This is the most distant proto-cluster known. It is dominated by a massive baby galaxy, seen as the green object near the center of this image. The galaxy is producing powerful radio emissions, and it is the brightest galaxy in the proto-cluster. The green color is indicative of glowing hydrogen gas. The galaxy's clumpy appearance suggests it is still developing. Smaller growing galaxies are scattered around the massive galaxy. The bright object in the upper part of the image is a foreground star. NASA / ESA / G. Miley and R. Overzier (Leiden Observatory)

"Given that this is a very dense region of the early universe with so many galaxies, it's quite reasonable to suggest that these galaxies are some of the oldest in the universe," Blakeslee says of this group. "More importantly, though, we are directly observing the galaxy-cluster formation epoch, and it is in clusters that the oldest galaxies tend to reside."



photo: This color composite image of the galaxy cluster RDCS 1252.9-2927 shows the X-ray (purple) light from 70-million-degree Celsius gas in the cluster, and the optical (red, yellow and green) light from the galaxies in the cluster. The X-ray data was taken by the Chandra X-ray Observatory, and the optical data is from European Southern Observatory's Very Large Telescope (VLT) in Chile.
X-ray data indicate that this cluster formed more than 8 billion years ago and has a mass at least 200 trillion times that of the Sun. It is the most massive cluster ever observed at such an early stage in the evolution of the universe. The width of the image spans 2 arcminutes. X-ray: NASA / CXC / ESO / P. Rosati et al.; Optical: ESO / VLT / P. Rosati et al.

Both findings are evidence that galaxies started forming soon after the Big Bang, as slightly denser regions in the primordial universe gravitationally coalesced. That process involved many cosmological factors: the pattern of initial density fluctuations in the universe, the nature of gravity, the expansion rate of the universe, the strength of dark energy, and the abundance of dark matter, to name a few.

Witnessing the sculpting of large-scale structure, then, allows scientists to probe these many mysteries and home in on some details of galaxy formation itself, a complicated process that is still not entirely understood. Having found such ancient clusters at various stages in the process certainly will be helpful in putting all the pieces of the puzzle together.

"It's part of the quest to understand our origins," Blakeslee says.

A Magnetic planet

photo: Astronomers have observed a spot on the star HD179949 that travels around the star's surface at the same rate as a close-orbiting planet circles the star. The astronomers believe the planet's magnetic field is transferring energy to the star's chromosphere, heating it and causing the blemish. The planet, which is at least 270 times as massive as Earth, orbits the planet once every 3.09 days. The star and planet lie 90 light-years from us in the constellation Sagittarius. Shane Erno / University of British Columbia.

Scientists discover an extrasolar planet's magnetic field is creating sunspots on its parent star.The study of planets circling distant stars is scarcely more than a decade old — the fantastic assumption that planetary systems exist outside our own was first confirmed in 1991 — and already it is making exciting progress. Over 110 extrasolar planets have been detected so far. Now, a team of Canadian astronomers has found that one such planet actually is heating its parent star and leaving a telltale imprint of its travels. The finding bolsters astronomers' theoretical understanding of planetary formation and offers a new method of detecting elusive yet intriguing worlds that dance unseen in the sky.

Astronomers Evgenya Shkolnik and Gordon Walker of the University of British Columbia and David Bohlender of the National Research Council of Canada/Herzberg Institute for Astrophysics used the 3.6-meter Canada-France-Hawaii Telescope in Hawaii to study the light streaming from star HD179949, a star much like our Sun but situated roughly 90 light-years away. In 2000, observers discovered a large planet nearly the size of Jupiter closely orbiting the star. Traveling 350,000 miles per hour, the planet laps the star every 3.09 days.

The team noticed that a bright spot on the outer gaseous layer of the star seemed to glide across its surface, keeping pace with the giant planet's orbit but staying just a few steps ahead. After tracing the path of this hot spot for over a year — for more than a hundred orbits — the astronomers confirmed that, indeed, its movement is tightly correlated with the planet's cycle.They realized the planet's own magnetic field must be transferring energy to the star's chromosphere, heating its already scorching 14,000° Fahrenheit temperature by an additional 750°. The extra heat shows up in ultraviolet wavelengths as a periodic glowing sunspot. While this phenomenon was predicted in 2000 by Steve Saar of the Harvard-Smithsonian Center for Astrophysics and by Manfred Cuntz of the University of Texas at Arlington, this is the first observation of a planet actually heating its parent star.

Astronomers believe all planets are surrounded by magnetic fields captured from interstellar space during each planet's formation and sustained by the rotation of its fluid metal interior. The spin of Earth's iron and nickel inner core within the liquid outer core, for example, creates a powerful magnetic field capable of defending us from the Sun's violent storms and showers of electrically charged particles.



photo: The structure of the CFHT is based on an equatorial mount design, with one of the axis of rotation set parallel to the axis of the Earth's rotation. The mirror cell (the white circular structure at the bottom of the telescope, seen just above the person at the bottom of the photograph) holds and protects the mirror. The world's largest digital imager, MegaPrime, is the black structure sitting atop the telescope. Canada-France-Hawaii Telescope (2003)

The existence of this extrasolar planet's magnetic armor, therefore, provides clues to the composition of the planet's core and may help account for the planet's very formation and survival. "The magnetic shielding could well have protected the planet from total ablation by the ionic wind from the parent star," Walker explains.

Now that scientists know large planets that orbit close to their stars can produce detectable star-spots, they are privy to a new method of hunting for planets that might otherwise go unnoticed. "The detection of periodic hot spots might point to the presence of smaller magnetized planets around other stars," says Walker. As stars shine helpful hints our way, the search for far-off worlds continues.

Two Black Holes Teach Astronomers a Lesson

photo: GX 339-4, illustrated here, is a typical microquasar. A black hole orbits an evolved star, which donates matter to it. How the black hole manages to eject some of this gas in tight jets remains unknown.

Credit: ESO/Poshak Gandhi

Observations of two different systems -- both containing stellar-mass black holes -- are showing astronomers how much they have yet to learn. Coordinated observations of these systems using the European Southern Observatory's Very Large Telescope and NASA's Rossi X-ray Timing Explorer reveal surprising dips in optical brightness moments before high-energy flares erupt.

The systems are Swift J1753.5-0127 -- discovered by NASA's Swift satellite -- and GX 339-4. In them, a black hole and a normal star orbit a few million miles apart. That's less than 10 percent of the distance between Mercury and our sun.

Because the normal stars in these systems have evolved into bloated giants, a stream of matter spills toward the black hole and forms a disk of hot gas around it. As matter collides in this so-called accretion disk, it heats up to millions of degrees. Near the black hole, intense magnetic fields in the disk accelerate material into tight jets that flow in opposite directions away from the hole.

If that sounds familiar, it should. A similar process occurs in active galaxies and quasars, where black holes weighing millions of suns gobble up matter. Jets from active galaxies may extend tens of thousands of light-years. Because the process is thought to be the same despite the black hole's size, astronomers class systems like Swift J1753.5-0127 and GX 339-4 as "microquasars."

Astronomers don't fully understand how black holes create these jets, so they study nearby microquasars for a detailed look at the process in miniature. "Microquasars are not only closer, but they change more rapidly," says Richard Mushotzky at NASA's Goddard Space Flight Center in Greenbelt, Md. "Changes that may take a year to see in a quasar occur in these systems over a minute or less."

"The orbital period of Swift J1753.5-0127 -- just 3.2 hours -- is the fastest found for a likely black hole," says team member Martin Durant at the Institute of Astrophysics of the Canary Islands. The orbital period of GX 339-4, by contrast, is about 1.7 days. "Yet the two systems are similar in their X-ray properties," he notes.Astronomers had thought that the cooler visible-light emission comes from so far out in a black hole's accretion disk that it reflects little of the main action. "We were wrong, and these systems prove it," Durant says. "The optical and X-ray emissions are intrinsically linked, probably by the same immense magnetic fields that can hurl material into light-years-long jets."

To study the systems, an international team led by Poshak Gandhi of Japan's RIKEN Institute of Physical and Chemical Research watched them simultaneously using two different instruments, one on the ground and one in space. A high-speed camera called ULTRACAM on the European Southern Observatory's Very Large telescope captured visible light changes. ULTRACAM recorded up to 20 images a second.

NASA's Rossi X-ray Timing Explorer captured the X-ray variations. The satellite can record changes in X-ray output that occur in millionths of a second. "Being able to take readings at high speed and coordinate between NASA's satellite and the ESO's biggest telescopes gives us a unique opportunity to seeing what's going on in the systems," Durant says.

The data show that the light output typically drops just before the X-ray output undergoes a large spike, which mean the two emissions are strongly connected. "The rapid variations in the X-ray and visible light output must have some common origin, and one very close to the black hole itself," Gandhi concludes. "The cool thing about discovering such patterns that stand out amidst chaotic fluctuations of light is that they give us a new handle on understanding the underlying physics."

“Strong magnetic fields represent the best candidate for the dominant physical process,” says team member Jon Miller at the University of Michigan. Magnetic fields can soak up energy liberated close to the black hole and store it. This energy is released either as multi-million-degree, X-ray-emitting gas or as streams of charged particles traveling near the speed of light. How the black holes divide the energy between these two forms determines the characteristic pattern of X-ray and optical changes astronomers observe.

"These kinds of studies are mapping the accretion disks around black holes," says Mushotzky. "Right now, astronomers aren't sure what's happening where."

Date: October 15, 2008

Ice Cold Sunrise on Mars

Date: August 26, 2008

From the location of NASA's Phoenix Mars Lander, above the Martian arctic circle, the sun does not set during the peak of the Martian summer.

This period of maximum solar energy is past -- on Sol 86, the 86th Martian day after the Phoenix landing, the sun fully set behind a slight rise to the north for about half an hour.

This red-filter image taken by the lander's Surface Stereo Imager, shows the sun rising on the morning of sol 90, Aug. 25, 2008, the last day of the Phoenix nominal mission.

The image was taken at 51 minutes past midnight local solar time during the slow sunrise that followed a 75 minute "night." The skylight in the image is light scattered off atmospheric dust particles and ice crystals.

The setting sun does not mean the end of the mission. In late July, the Phoenix Mission was extended through September, rather than the 90-sol duration originally planned as the prime mission.

The mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

Frost on Mars

This image shows bluish-white frost seen on the Martian surface near NASA's Phoenix Mars Lander. The image was taken by the lander's Surface Stereo Imager on the 131st Martian day, or sol, of the mission (Oct. 7, 2008). Frost is expected to continue to appear in images as fall, then winter approach Mars' northern plains.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

Date: October 8, 2008

Phoenix Lander Digs and Analyzes Soil as Darkness Gathers

This false color image, taken by NASA's Phoenix Mars Lander's Surface Stereo Imager, was taken on the 131st Martian day, or sol, of the mission (Oct. 7, 2008). The image shows color variations of the trench, informally named "La Mancha," and reveals the ice layer beneath the soil surface. The trench's depth is about 5 centimeters deep.

The color outline of the shadow at the bottom of the image is a result of sun movement with the combined use of infrared, green, and blue filters.

Date: October 8, 2008

As fall approaches Mars' northern plains, NASA's Phoenix Lander is busy digging into the Red Planet's soil and scooping it into its onboard science laboratories for analysis.

Over the past two weeks, Phoenix's nearly 2.4-meter-long (8 feet) arm moved a rock, nicknamed "Headless," about 0.4 meters (16 inches), and snapped an image of the rock with its camera. Then, the robotic arm scraped the soil underneath the rock and delivered a few teaspoonfuls of soil onto the lander's optical and atomic-force microscopes. These microscopes are part of Phoenix's Microscopy, Electrochemistry and Conductivity Analyzer (MECA).

Scientists are conducting preliminary analysis of this soil, nicknamed "Galloping Hessian." The soil piqued their interest because it may contain a high concentration of salts, said Diana Blaney, a scientist on the Phoenix mission with NASA's Jet Propulsion Laboratory, Pasadena, Calif.

As water evaporates in arctic and arid environments on Earth, it leaves behind salt, which can be found under or around rocks, Blaney said. "That's why we wanted to look under ‘Headless,' to see if there's a higher concentration of salts there."

More digging is underway. Phoenix scientists want to analyze a hard, icy layer beneath the Martian soil surface, and excavating to that icy layer underneath a rock might give scientists clues about processes affecting the ice.

So the robotic arm has dug into a trench called "La Mancha," in part to see how deep the Martian ice table is. The Phoenix team also plans to dig a trench laterally across some of the existing trenches in hopes of revealing a cross section, or profile, of the soil's icy layer.

"We'd like to see how the ice table varies around the workspace with the different topography and varying surface characteristics such as different rocks and soils," said Phoenix co-investigator Mike Mellon of the University of Colorado, Boulder. "We hope to learn more about how the ice depth is controlled by physical processes, and by looking at how the ice depth varies, we can pin down how it got there."

Over the weekend, on the 128th Martian day, or sol, Phoenix engineers successfully directed the robotic arm to dig in a trench called "Snow White" in the eastern portion of the lander's digging area. The robotic arm then delivered the material to an oven screen on Phoenix's Thermal and Evolved-Gas Analyzer.

The Phoenix team will try to shake the oven screen so the soil can break into smaller lumps and fall through for analysis.

The Phoenix lander, originally planned for a three-month mission on Mars, is now in its fifth month. As fall approaches, the lander's weather instruments detect diffuse clouds above northern Mars, and temperatures are getting colder as the daylight hours wane.

Consequently, Phoenix faces an increasing drop in solar energy as the sun falls below the Martian horizon. Mission engineers and scientists expect this power decline to curtail activities in the coming weeks. As darkness deepens, Phoenix will primarily become a weather station and will likely cease all activity by the end of the year.

The Phoenix mission is led by Principal Investigator Peter Smith at the University of Arizona. Project management is the responsibility of JPL, with development partnership by Lockheed Martin in Denver. International contributions come from the Canadian Space Agency; the University of Neuchatel, Switzerland; the universities of Copenhagen and Aarhus, Denmark; the Max Planck Institute, Germany; and the Finnish Meteorological Institute.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

Story of the Doomed

This moon is doomed. Mars, named for the Roman god of war, has two tiny moons--Phobos and Deimos--whose names are derived from the Greek for fear and panic. These Martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the solar system.

The larger moon, Phobos, is a cratered, asteroid-like object in this stunning color image from the Mars Reconnaissance Orbiter. Phobos orbits so close to Mars that gravitational tidal forces are dragging it down. In 100 million years or so, Phobos likely will be shattered by stress caused by the relentless tidal forces, the debris forming a decaying ring around Mars.

Image Credit: NASA

NASA'S Fermi Telescope Discovers First Gamma-Ray-Only Pulsar

photo: Clouds of charged particles move along the pulsar's magnetic field lines (blue) and create a lighthouse-like beam of gamma rays (purple) in this illustration.

Credit: NASA

Date: October 16, 2008

WASHINGTON -- About three times a second, a 10,000-year-old stellar corpse sweeps a beam of gamma-rays toward Earth. Discovered by NASA's Fermi Gamma-ray Space Telescope, the object, called a pulsar, is the first one known that only "blinks" in gamma rays.

"This is the first example of a new class of pulsars that will give us fundamental insights into how these collapsed stars work," said Stanford University's Peter Michelson, principal investigator for Fermi's Large Area Telescope in Palo Alto, Calif.

The gamma-ray-only pulsar lies within a supernova remnant known as CTA 1, which is located about 4,600 light-years away in the constellation Cepheus. Its lighthouse-like beam sweeps Earth's way every 316.86 milliseconds. The pulsar, which formed about 10,000 years ago, emits 1,000 times the energy of our sun.

A pulsar is a rapidly spinning neutron star, the crushed core left behind when a massive sun explodes. Astronomers have cataloged nearly 1,800 pulsars. Although most were found through their pulses at radio wavelengths, some of these objects also beam energy in other forms, including visible light and X-rays. However, the source in CTA 1 only pulses at gamma-ray energies."We think the region that emits the pulsed gamma rays is broader than that responsible for pulses of lower-energy radiation," explained team member Alice Harding at NASA's Goddard Space Flight Center in Greenbelt, Md. "The radio beam probably never swings toward Earth, so we never see it. But the wider gamma-ray beam does sweep our way."

Scientists think CTA 1 is only the first of a large population of similar objects.

"The Large Area Telescope provides us with a unique probe of the galaxy's pulsar population, revealing objects we would not otherwise even know exist," says Fermi project scientist Steve Ritz, also at Goddard.

The pulsar in CTA 1 is not located at the center of the remnant's expanding gaseous shell. Supernova explosions can be asymmetrical, often imparting a "kick" that sends the neutron star careening through space. Based on the remnant's age and the pulsar's distance from its center, astronomers believe the neutron star is moving at about a million miles per hour -- a typical speed.

Fermi's Large Area Telescope scans the entire sky every three hours and detects photons with energies ranging from 20 million to more than 300 billion times the energy of visible light. The instrument sees about one gamma ray every minute from CTA 1, enough for scientists to piece together the neutron star's pulsing behavior, its rotation period, and the rate at which it is slowing down.A pulsar's beams arise because neutron stars possess intense magnetic fields and rotate rapidly. Charged particles stream outward from the star's magnetic poles at nearly the speed of light to create the gamma-ray beams Fermi sees. Because the beams are powered by the neutron star's rotation, they gradually slow the pulsar's spin. In the case of CTA 1, the rotation period is increasing by about one second every 87,000 years.

"This observation shows the power of the Large Area Telescope," Michelson said. "It is so sensitive that we can now discover new types of objects just by observing their gamma-ray emissions."

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the U.S.

Big Galaxy Collisions Can Stunt Star Formation

Credit: Tomer Tal and Jeffrey Kenney/
Yale University and NOAO/AURA/NSF

Wednesday, October 08, 2008

A deep new image of the Virgo cluster has revealed monumental tendrils of ionized hydrogen gas 400,000 light-years long connecting the elliptical galaxy M86 and the disturbed spiral galaxy NGC 4438.

Taken with the wide-field Mosaic imager on the National Science Foundation’s Mayall 4-meter telescope at Kitt Peak National Observatory, this Hydrogen-alpha image and related spectroscopic measurements of the filament provide striking evidence of a previously unsuspected high-speed collision between the two galaxies.

“Our data show that this system represents the nearest recent collision between a large elliptical galaxy and a large spiral,” said Jeffrey Kenney of Yale University, lead author of a paper to be published in a November 2008 issue of Astrophysical Journal Letters. “This discovery provides some of the clearest evidence yet for high-speed collisions between large galaxies, and it suggests that the consequences of such collisions are a plausible alternative to black holes in trying to explain the mystery of what process turns off star formation in the biggest galaxies.”

The Virgo cluster is located approximately 50 million light-years from Earth. Previous studies had noticed disturbed H-alpha gas around each of the two galaxies, but no connection from the two had been inferred. Indeed, some results have suggested that NGC 4438 collided with the small lenticular galaxy NGC 4435, but NGC 4435 has a much higher line-of-sight velocity as seen from Earth and appears undisturbed.

Spectroscopy of selected regions along the filament between M86 and NGC 4438, obtained with the Sparsepak Integral Field Unit instrument on the WIYN 3.5-meter telescope on Kitt Peak, shows a fairly smooth velocity gradient between the galaxies, supporting the collision scenario. There are no obvious stars in the filaments.

“The image shows what you can find if you look deep and wide, and we needed to do both to see the M86-NGC4438 complex,” Kenney explains.

As in most elliptical galaxies, most of the gas within M86 is extremely hot, and therefore radiates X-rays. The X-ray distribution in M86 is irregular and sports a long plume, which had previously been interpreted as a tail of gas which is being stripped by ram pressure as M86 falls into the intracluster medium of the Virgo cluster. The new H-alpha image from Kitt Peak suggests that most of the disturbances to the interstellar medium in M86 are instead due to the collision with NGC 4438.

A current mystery in astronomy is what causes the biggest galaxies in the Universe—which are primarily ellipticals, like M86—to stop forming stars. “Something needs to heat up the gas so it doesn’t cool and form stars,” Kenney says. “A number of recent studies suggest that energy from active galactic nuclei associated with supermassive black holes may do this, but our new study shows that gravitational interactions may also do the trick.”

Low-velocity collisions, especially between small- to medium-sized galaxies, often cause an increase in the local star formation rate, as the collisions tend to cause gas to concentrate in the galaxy centers. But in high velocity collisions (which happen naturally between large galaxies, since their large gravity pulls mass inward much faster), the kinetic energy of the collision can cause the gas to heat up so much that it cannot easily cool and form stars.

While not many galaxies suffer such extreme collisions as M86, most galaxies experience minor mergers and gas accretion events, and these may play a significant role in heating the galaxy’s gas. These more common but modest events are very hard to study, since their observational signatures are weak.

“The same physical processes occur in both strong and weak encounters, and by studying the observable effects in extreme cases like M86 we can learn about the role of gravity in the heating of galaxy gas, which appears to be quite significant,” Kenney adds.

Astronomers get best view yet of infant stars at feeding time

photo: Tracing gas emission close to young stellar objects (Artist view)

Friday, October 10, 2008

Astronomers have used ESO's Very Large Telescope Interferometer to conduct the first high resolution survey that combines spectroscopy and interferometry on intermediate-mass infant stars. They obtained a very precise view of the processes acting in the discs that feed stars as they form. These mechanisms include material infalling onto the star as well as gas being ejected, probably as a wind from the disc.

Infant stars form from a disc of gas and dust that surrounds the new star and, later, may also provide the material for a planetary system. Because the closest star-forming regions to us are about 500 light-years away, these discs appear very small on the sky, and their study requires special techniques to be able to probe the finer details.

This is best done with interferometry, a technique that combines the light of two or more telescopes so that the level of detail revealed corresponds to that which would be seen by a telescope with a diameter equal to the separation between the interferometer elements, typically 40 to 200 metres. ESO's Very Large Telescope Interferometer (VLTI) has allowed astronomers to reach a resolution of about a milli-arcsecond, an angle equivalent to the size of the full stop at the end of this sentence seen from a distance of about 50 kilometres.

"So far interferometry has mostly been used to probe the dust that closely surrounds young stars," says Eric Tatulli from Grenoble (France), who co-led this international project. "But dust is only one percent of the total mass of the discs. Their main component is gas, and its distribution may define the final architecture of planetary systems that are still forming."

The ability of the VLTI and the AMBER instrument to take spectra while probing objects at milli-arcsecond resolution has allowed astronomers to map the gas. Astronomers studied the inner gaseous environments of six young stars belonging to the family of Herbig Ae/Be objects. These objects have masses a few times that of our Sun and are still forming, increasing in mass by swallowing material from the surrounding disc.

The team used these observations to show that gas emission processes can be used to trace the physical processes acting close to the star.

"The origin of gas emissions from these young stars has been under debate until now, because in most earlier investigations of the gas component, the spatial resolution was not high enough to study the distribution of the gas close to the star," says co-leader Stefan Kraus from Bonn in Germany. "Astronomers had very different ideas about the physical processes that have been traced by the gas. By combining spectroscopy and interferometry, the VLTI has given us the opportunity to distinguish between the physical mechanisms responsible for the observed gas emission."

Astronomers have found evidence for matter falling into the star for two cases, and for mass outflow in four other stars, either in an extended stellar wind or in a disc wind.

It also seems that, for one of the stars, dust may be present closer to the star than had been generally expected. The dust is so close that the temperature should be high enough for it to evaporate, but since this is not observed, it must mean that gas shields the dust from the star's light.

These new observations demonstrate that it is now possible to study gas in the discs around young stars. This opens new perspectives for understanding this important phase in the life of a star.

"Future observations using VLTI spectro-interferometry will allow us to determine both the spatial distribution and motion of the gas, and might reveal whether the observed line emission is caused by a jet launched from the disc or by a stellar wind", concludes Stefan Kraus.

Giant Cyclones at Saturn's Poles Create a Swirl of Mystery

Infrared Images of Saturn’s Poles
Credit: NASA/JPL/University of Arizona

New images from NASA’s Cassini spacecraft reveal a giant cyclone at Saturn’s north pole, and show that a similarly monstrous cyclone churning at Saturn’s south pole is powered by Earth-like storm patterns.

The new-found cyclone at Saturn’s north pole is only visible in the near-infrared wavelengths because the north pole is in winter, thus in darkness to visible-light cameras. At these wavelengths, about seven times greater than light seen by the human eye, the clouds deep inside Saturn’s atmosphere are seen in silhouette against the background glow of Saturn’s internal heat.



Saturn's South Polar Region Revealed
Credit: NASA/JPL/University of Arizona

The entire north pole of Saturn is now mapped in detail in infrared, with features as small as 120 kilometers (75 miles) visible in the images. Time-lapse movies of the clouds circling the north pole show the whirlpool-like cyclone there is rotating at 530 kilometers per hour (325 miles per hour), more than twice as fast as the highest winds measured in cyclonic features on Earth. This cyclone is surrounded by an odd, honeycombed-shaped hexagon, which itself does not seem to move while the clouds within it whip around at high speeds, also greater than 500 kilometers per hour (300 miles per hour). Oddly, neither the fast-moving clouds inside the hexagon nor this new cyclone seem to disrupt the six-sided hexagon.

New Cassini imagery of Saturn’s south pole shows complementary aspects of the region through the eyes of two different instruments. Near-infrared images from the visual and infrared mapping spectrometer instrument show the whole region is pockmarked with storms, while the imaging cameras show close-up details.



Convection in Saturn's Southern Vortex
Credit: NASA/JPL/Space Science Institute

Unlike Earth-bound hurricanes, powered by the ocean’s heat and water, Saturn's cyclones have no body of water at their bases, yet the eye-walls of Saturn’s and Earth’s storms look strikingly similar. Saturn's hurricanes are locked to the planet's poles, whereas terrestrial hurricanes drift across the ocean.

"These are truly massive cyclones, hundreds of times stronger than the most giant hurricanes on Earth," said Kevin Baines, Cassini scientist on the visual and infrared mapping spectrometer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Dozens of puffy, convectively formed cumulus clouds swirl around both poles, betraying the presence of giant thunderstorms lurking beneath. Thunderstorms are the likely engine for these giant weather systems," said Baines.

Just as condensing water in clouds on Earth powers hurricane vortices, the heat released from the condensing water in Saturnian thunderstorms deep down in the atmosphere may be the primary power source energizing the vortex.



The Yet Yawning Gulf
Credit: NASA/JPL/Space Science Institute

In the south, the new infrared images of the pole, under the daylight conditions of southern summer, show the entire region is marked by hundreds of dark cloud spots. The clouds, like those at the north pole, are likely a manifestation of convective, thunderstorm-like processes extending some 100 kilometers (62 miles) below the clouds. They are likely composed of ammonium hydrosulfide with possibly a mixture of materials dredged up from the depths. By contrast, most of the hazes and clouds seen on Saturn are thought to be composed of ammonia, which condenses at high, visible altitudes.

Complementary images of the south pole from Cassini’s imaging cameras, obtained in mid-July, are 10 times more detailed than any seen before. "What looked like puffy clouds in lower resolution images are turning out to be deep convective structures seen through the atmospheric haze," said Cassini imaging team member Tony DelGenio of NASA’s Goddard Institute for Space Studies in New York. "One of them has punched through to a higher altitude and created its own little vortex."

The "eye" of the vortex is surrounded by an outer ring of high clouds. The new images also hint at an inner ring of clouds about half the diameter of the main ring, and so the actual clear "eye" region is smaller than it appears in earlier low-resolution images.

"It’s like seeing into the eye of a hurricane," said Andrew Ingersoll, a member of Cassini's imaging team at the California Institute of Technology, Pasadena. "It’s surprising. Convection is an important part of the planet’s energy budget because the warm upwelling air carries heat from the interior. In a terrestrial hurricane, the convection occurs in the eyewall; the eye is a region of downwelling. Here convection seems to occur in the eye as well."

Further observations are planned to see how the features at both poles evolve as the seasons change from southern summer to fall in August 2009.

Tuesday, October 14, 2008