domingo, 2 de março de 2008

Secuencia Eclipse Total de Luna - 20/21 FEB 2008

Secuencia fotográfica del eclipse tomada por Jorge Coghlan (CODE-LIADA) con cámara fijada sobre trípode Olympus OM10 Teleobjetivo Zuiko 1:4 f=200mm acoplado a Teleconverter automático2x Vivitar, película Kodak Color de 100 DIN.
Haz clic para ampliar la secuencia de fotos

Posted by Lucimary Vargas

El eclipse desde el Sur de Mendoza

Estimados amigos,

Queremos compartir nuestra humilde y bella experiencia con el Eclipse lunar del pasado 20/21 de febrero, en el Instituto Copérnico:

Un fuerte abrazo a todos

Jaime y Rodolfo

Lunar eclipse photos - February 20/21, 2008

A beautiful lunar eclipse Wednesday night turned the moon a deep red. These images of the eclipse were taken from Central Florida.
Photo credit: Chris Miller/Spaceflight Now
Click to enlarge images

Credit: Chris Miller/Spaceflight Now

Aliens Might Be Moving Stars to Communicate With Us

Written by Fraser Cain
Rosette Nebula. Image credit: CFHT
You've got to love the audacity of this idea. In a recent article at Discover Magazine, virtual reality pioneer Jaron Lanier (you know, the guy with the dreadlocks) proposes that we get working on repositioning nearby stars to form geometric patterns - or at least start looking for places that it's already been done by aliens.

Move stars around into patterns? That's pretty crazy stuff. Sure, but there isn't any physical reason why it isn't possible; it happens all the time when galaxies collide. Of course, a spray of stars hurled into intergalactic space at random is different from a great big peace sign.
In order to actually move a star requires a gravitational tractor, and engineers are already planning this kind of a mission for a threat closer to home: asteroids. By flying a spacecraft near an asteroid, and fighting against the gravity pulling it down, you can actually pull the asteroid off course. Over a long period of time, you can move the asteroid enough in its orbit to prevent it from striking the Earth.
So scale that idea up. Send out a fleet of these spacecraft to tinker with the orbits of Kuiper Belt objects. These objects could rain into the inner Solar System and prod the Sun's motion through the galaxy. Over a long period of time (a really really long period of time), you could impart enough of a velocity change to drive your star anywhere you wanted it to go.
With this technique, and a few million years to time to kill, you could line up stars into a formation that shows an intelligence was behind it. The more stars you put into formation, the better your message will be.
One interesting suggestion, made to Lanier by Piet Hut at the Institute for Advanced Study is a multiply nested binary system. Imagine binary systems, orbiting binary systems, orbiting binary systems. With 16 stars in formation, you'd have a shape that mother nature would never arrange on her own, but would be stable for long periods of time. From long distances, astronomers wouldn't be able to resolve the individual stars, but they'd definitely know something strange was going on.
The advantage to this, of course, is that stars are visible for tremendous distances. Why bother sending out puny radio signals when you can harness the energy of an entire star.
Physicists predict that civilizations will eventually advance to the point that they master all the energy of their home planet, their star system, and eventually their entire galaxy. And if you're harnessing every watt of energy pouring out of every star in the galaxy, who'd miss a little extra energy being used for communications.
So, uh… let's get on that.
Original Source: Discover Magazine

Follow the water

Mars rovers sharpen questions about living conditions on the Red Planet.
Provided by JPL
This view from NASA's Mars Exploration Rover Opportunity shows bedrock within a stratigraphic layer informally named "Lyell," which is the lowermost of three layers the rover has examined at a bright band around the inside of Victoria Crater. NASA/JPL-Caltech/Cornell University [View Larger Image]
February 18, 2008
Like salt used as a preservative, high concentrations of dissolved minerals in the wet, early-Mars environment known from discoveries by NASA's Opportunity rover may have thwarted any microbes from developing or surviving.

"Not all water is fit to drink," says Andrew Knoll, a member of the rover science team who is a biologist at Harvard University.

Opportunity and its twin, Spirit, began their fifth year on Mars last month, far surpassing their prime missions of three months. At a meeting of the American Association for the Advancement of Science in Boston, scientists and engineers discussed on Friday new observations by the rovers, recent analysis of some earlier discoveries, and perspectives on which lessons from these rovers' successes apply to upcoming missions to Mars.

"The engineering efforts that have enabled the rovers' longevity have tremendously magnified the science return," says Steve Squyres of Cornell University, principal investigator for the rovers' science payload. "All of Spirit's most important findings, such as evidence for hot springs or steam vents, came after the prime mission."

Opportunity spent recent months examining a bright band of rocks around the inner wall of a crater. Scientists previously hypothesized this material might preserve a record of the ground surface from just before the impact that excavated the crater. Inspection suggests that, instead, it was at the top of an underground water table, Squyres reports.

Experiments with simulated Martian conditions and computer modeling are helping researchers refine earlier assessments of whether the long-ago conditions in the Meridiani area studied by Opportunity would have been hospitable to microbes. Chances look slimmer. "At first, we focused on acidity, because the environment would have been very acidic," Knoll says. "Now, we also appreciate the high salinity of the water when it left behind the minerals Opportunity found. This tightens the noose on the possibility of life."

Conditions may have been more hospitable earlier, with water less briny, but later conditions at Meridiani and elsewhere on the surface of Mars appear to have been less hospitable, Knoll says. "Life at the Martian surface would have been very challenging for the last 4 billion years. The best hopes for a story of life on Mars are at environments we haven't studied yet, older ones, subsurface ones," he says.

NASA's current rovers and orbiters at Mars pursue the agency's "follow the water" theme for Mars exploration. They decipher the roles and fate of water on a planet whose most striking difference from Earth is a scarcity of water. "Our next missions, Phoenix and Mars Science Laboratory, mark a transition from water to habitability, assessing whether sites where there's been water have had conditions suited to life," says Charles Elachi, director of NASA's Jet Propulsion Laboratory. "Where conditions were habitable, later missions may look for evidence of life."

Elachi cited the achievements of Spirit and Opportunity. "They have worked 16 times longer than planned, driven 20 times farther than planned, and, most important, found diverse geological records of the effects of water in ancient Martian environments," he says. "We must not let these successes lull us into thinking this type of exploration is easy. Fifty years into the Space Age, we are still in the golden age of robotic exploration of our solar system, when each mission is unprecedented in some way as we push the limits of what is possible. Each mission presents new challenges."

The Phoenix lander, on course to reach Mars on May 25, will assess habitability of a shallow subsurface environment of icy soil farther north than any earlier mission has landed. It revives technology from missions launched before Spirit and Opportunity. The following mission, the Mars Science Laboratory rover, will incorporate many lessons from the current rovers, says that project's manager, Richard Cook of JPL. "The next rover will be much bigger to carry the instruments necessary for meeting its goals, but it would be laughable to consider doing Mars Science Laboratory without the experience gained from doing the Mars Exploration Rovers," he says.

The Mars Science Laboratory rover will weigh about four times as much as Spirit or Opportunity. "There's no way we could use an airbag landing," says JPL's Rob Manning, chief engineer for the future rover. Instead, a rocket-powered hovering stage will lower it to the surface on a tether. Lessons from Spirit and Opportunity will come into play when it starts driving, though. "With the current rovers, we've learned we can trust the autonomous navigation technology to a level we never expected, so now we can include that as a capability in our mission design for Mars Science Laboratory," Manning says.


Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil

Galaxies found around galaxies

Hubble discovers 67 gravitationally lensed galaxies in the distant universe.
Provided by the Hubble ESA Information Centre
The positions of 67 newly found gravitational lenses are shown in this image. NASA/ESA/C. Faure/J.P. Kneib [View Larger Image]
February 20, 2008
Astronomers using the NASA/ESA Hubble Space Telescope have compiled a large catalog of gravitational lenses in the distant universe. The catalog contains a staggering 67 new gravitationally lensed galaxy images found around massive elliptical and lenticular-shaped galaxies. This sample demonstrates the rich diversity of strong gravitational lenses. If this sample is representative, there would be nearly half a million similar gravitational lenses in total over the whole sky.

The lenses come from a recently completed, large set of observations as part of a huge project to survey a single 1.6 square degree field of sky (nine times the area of the full Moon) with several space-based and Earth-based observatories. The COSMOS project, led by Nick Scoville at the California Institute of Technology, used observations from several observatories including the Hubble Space Telescope, as well as the Spitzer Space Telescope, the XMM-Newton spacecraft, the Chandra X-Ray Observatory, the Very Large Telescope (VLT), the Subaru Telescope and CFHT.
This is a triple gravitational lens, an example of the rich diversity of the 67 strong gravitational lenses found in the COSMOS survey. NASA/ESA/C. Faure/J.P. Kneib [View Larger Image]
A team of European astronomers led by Jean-Paul Kneib (Laboratoire d'Astrophysique de Marseille) and Cecile Faure (Zentrum für Astronomie, University of Heidelberg) analyzed the results from Hubble's Advanced Camera for Surveys (ACS). From ACS high-resolution images, complemented by the extensive ground-based follow-up observations, astronomers have identified 67 strong gravitationally lensed galaxies. These were found around very massive galaxies that are usually elliptical or lenticular in shape and often exhibit a paucity of gas and dust without spiral arms or discs. The strong lensing produced by massive galaxies is much more common than the usual giant "arc" gravitationally lensed galaxies that Hubble has previously observed; but they are generally more difficult to find as they extend over a smaller area and have a wide variety of shapes.

Gravitational lensing occurs when light traveling towards us from a distant galaxy is magnified and distorted as it encounters a massive object between the galaxy and us. These gravitational lenses often allow astronomers to peer much further back into the early universe than they would normally be able to.

The massive objects that create the lenses are usually huge clusters of massive galaxies. "We typically see the gravitational lens create a series of bright arcs or spots around a galaxy cluster. What we are observing here is a similar effect but on much smaller scale, happening only around a single but very massive galaxy," says Kneib.
An Einstein ring can be seen in this image from the COSMOS project. An Einstein ring is a complete circle image of a background galaxy, which is formed when the background galaxy, a massive, foreground galaxy, and the Hubble Space Telescope are all aligned perfectly. NASA/ESA/C. Faure/J.P. Kneib [View Larger Image]
Of the 67 gravitational lenses identified in the COSMOS survey, the most impressive lenses show the distorted and warped light of one or two background galaxies. At least four of the lenses give rise to Einstein rings, a complete circular image of a background galaxy, which is formed when the background galaxy, a massive foreground galaxy and the Hubble Space Telescope are all aligned perfectly.

Hubble astronomers went through a unique process to identify these incredible natural lenses. First, possible galaxies were identified from a galaxy catalog, comprising more than two million galaxies. "We then had to look through each individual COSMOS image by eye and identify any potential strong gravitational lenses," says Faure. Finally, checks were made to see if the foreground galaxy and the lensed galaxy were really different or just one galaxy with an odd shape. "With this sample of gravitational systems identified by the human eye, we now plan use the sample of lenses to train robot software to find more of these lenses across the entire Hubble image archive, and we may find even more strong lensing systems in the COSMOS field," adds Kneib.

The new results confirm that the universe is filled with gravitational lensing systems. Extrapolating these new findings to the whole sky, predicts no less than half a million similar lenses in total. The future prospects for finding more of these systems are thus excellent.

The study of these gravitational lenses will give astronomers a first-rate opportunity to probe the dark matter distribution around galactic lenses. Once astronomers find even larger numbers of these smaller, stronger lenses they can be used to create a census of galaxy masses in the universe to test the predictions of cosmological models.

Time to Observe Saturn

Written by Tammy Plotner
Saturn - courtesy of NASA
Are you ready to take a closer look at the real "Lord of the Rings"? Then say hello to Saturn as it reaches opposition tomorrow night. With the yellow planet rising around sunset, highest in the south around midnight, and setting around sunrise, now is the time for observers and photographers to enjoy Saturn the most!
Right now Saturn is positioned in Leo about 5 degrees east of the constellation's Alpha star - Regulus. Look for the asterism of a backwards question mark rising after sunset and the brightest "star" in the group will be Saturn! For observers who use only your eyes try comparing the distances by holding your hand at arm's length. Saturn and Regulus will be separated by about 3 fingerwidths. Look less than a fistwidth further north and you'll see a dimmer star - Gamma Leonis. Keep an eye on this trio in the days to come and you'll easily see Saturn's movement against the background stars!
For observers with binoculars, it's possible to see elongations on either side of Saturn which are the beginnings of its ring system trying to resolve. Before you complain about not getting a good enough view, remember what you're seeing is very much like what Galileo saw when he discovered Saturn in 1610. Saturn on Saturday? Why not! Saturn was named for the Roman god of agriculture and the day Saturday is also named after him.
While you're watching, think on this… Saturn is the second biggest planet, but it's also the lightest planet. If there was a bathtub big enough to hold Saturn, it would float in the water! Its diameter is approximately 75,000 miles (120,000 km) and more than 9 Earths could line up across it. It's composed of 97% hydrogen gas, about 3% helium gas and about 0.05% methane, plus ammonia. One of the reasons it appears slightly flattened is because it is! Saturn rotates in 10 hours, 39 minutes in Earth time and this fast pace is what gives it a unique shape. It takes Saturn almost 30 years to complete an orbit around the Sun!
Now on to observing with a small telescope…

What's that you say? You can barely see Saturn's rings? You're right. At the moment Saturn's rings are only tilted about 8 degrees from our line of sight. Earth's equator is tilted 23 degrees and this tilt gives our planet its four seasons. Each year as we orbit around the Sun, our tilt causes different parts of the planet to spend more time in sunlight. Days become longer… nights become shorter! Saturn's equator is tilted very similar to ours at 27 degrees. This gives Saturn the same seasonal changes as we here on Earth experience. Because of the tilt of Saturn and the thinness of the rings, every 14 years the rings look like they've disappeared when viewed through a small or medium sized telescope.
For larger telescopes, it's easier to see Saturn has a thin multiple ring system. The rings are made of chunks of rock and ice — some just tiny pieces of dust, some more than half a mile (one km) across. Observing Saturn at opposition is important because it will give you an opportunity to witness the Seeliger Effect. Only at opposition will you notice a distinct brightening of the ring system caused by backscattering of sunlight off the icy particles. While we're "lined up", keep an eye out for this unusual property as well as the shadow of the rings on the planet and the shadow of the planet on the rings.
And don't forget those moons… Titan is easy visible to even small telescopes!

Many nearby sun-like stars may form rocky planets

Posted: February 21, 2008

Astronomers have discovered that terrestrial planets might form around many, if not most, of the nearby sun-like stars in our galaxy. These new results suggest that worlds with potential for life might be more common than we thought.

This artist's concept illustrates the idea that rocky, terrestrial worlds like the inner planets in our solar system, may be plentiful and diverse in the universe. Credit: NASA/JPL-Caltech
University of Arizona, Tucson, astronomer Michael Meyer and his colleagues used NASA's Spitzer Space Telescope to determine whether planetary systems like ours are common or rare in our Milky Way galaxy. They found that at least 20 percent, and possibly as many as 60 percent, of stars similar to the sun are candidates for forming rocky planets.

Meyer is presenting the findings at the annual meeting of the American Association for the Advancement of Science in Boston. The results appear in the Feb. 1 issue of Astrophysical Journal Letters.

The astronomers used Spitzer to survey six sets of stars, grouped depending on their age, with masses comparable to our sun. The sun is about 4.6 billion years old. "We wanted to study the evolution of the gas and dust around stars similar to the sun and compare the results with what we think the solar system looked like at earlier stages during its evolution," Meyer said.

The Spitzer telescope does not detect planets directly. Instead it detects dust ­ the rubble left over from collisions as planets form ­ at a range of infrared wavelengths. The hottest dust is detected at the shortest wavelengths, between 3.6 microns and 8 microns. Cool dust is detected at the longest wavelengths, between 70 microns and 160 microns. Warm dust can be traced at 24-micron wavelengths. Because dust closer to the star is hotter than dust farther from the star, the "warm" dust likely traces material orbiting the star at distances comparable to the distance between Earth and Jupiter.

"We found that about 10 to 20 percent of the stars in each of the four youngest age groups shows 24-micron emission due to dust," Meyer said. "But we don't often see warm dust around stars older than 300 million years. The frequency just drops off.

"That's comparable to the time scales thought to span the formation and dynamical evolution of our own solar system," he added. "Theoretical models and meteoritic data suggest that Earth formed over 10 to 50 million years from collisions between smaller bodies."

In a separate study, Thayne Currie and Scott Kenyon of the Smithsonian Astrophysical Observatory, Cambridge, Mass., and their colleagues also found evidence of dust from terrestrial planet formation around stars from 10 to 30 million years old. "These observations suggest that whatever led to the formation of Earth could be occurring around many stars between three million and 300 million years old," Meyer said.

Kenyon and Ben Bromley of the University of Utah, Salt Lake City, have developed planet formation models that provide a plausible scenario. Their models predict warm dust would be detected at 24-micron wavelengths as small rocky bodies collide and merge. "Our work suggests that the warm dust Meyer and colleagues detect is a natural outcome of rocky planet formation. We predict a higher frequency of dust emission for the younger stars, just as Spitzer observes," said Kenyon.

The numbers on how many stars form planets are ambiguous because there's more than one way to interpret the Spitzer data, Meyer said. The warm-dust emission that Spitzer observed around 20 percent of the youngest cohort of stars could persist as the stars age. That is, the warm dust generated by collisions around stars three to 10 million years old could carry over and show up as warm dust emission seen around stars in the 10- to 30- million-year-old range and so on. Interpreting the data this way, about one out of five sun-like stars is potentially planet-forming, Meyer said.

There's another way to interpret the data. "An optimistic scenario would suggest that the biggest, most massive disks would undergo the runaway collision process first and assemble their planets quickly. That's what we could be seeing in the youngest stars. Their disks live hard and die young, shining brightly early on, then fading," Meyer said. "However, smaller, less massive disks will light up later. Planet formation in this case is delayed because there are fewer particles to collide with each other."

If this is correct and the most massive disks form their planets first and the wimpiest disks take 10 to 100 times longer, then up to 62 percent of the surveyed stars have formed, or may be forming, planets. "The correct answer probably lies somewhere between the pessimistic case of less than 20 percent and optimistic case of more than 60 percent," Meyer said.

The next critical test of the assertion that terrestrial planets like Earth could be common around stars like the sun will come next year with the launch of NASA's Kepler mission.

Meyer's 13 co-authors include John Carpenter of the California Institute of Technology in Pasadena. NASA's Jet Propulsion Laboratory in Pasadena 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.




Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil

EuroNews looks at comets and asteroids

22 February 2008
The menacing mass of a rolling asteroid flying past Earth at more than 10 km/s is tracked by the giant telescope of Arecibo in Puerto Rico as well as the powerful radar of Wachtberg in Germany. At ESA, these celestial bodies are studied with passion, in preparation for a possible, hazardous impact.
EuroNews is a key medium for delivering international information with a European point of view and in a choice of 7 languages. Broadcast in 121 countries worldwide, EuroNews reaches 190 million households in Europe, the Middle East, Africa, Central Asia and North and Latin America via cable, digital satellite and through terrestrial channels.
Broadcast times
Mon Tues Wed Thur Fri Sat Sun
8:45 9:15 9:15 9:15 8:45
13:45 13:45 * 12:45 12:45
18:15 18:15 18:15 18:15 17:45 19:15
20:45 20:45
22:45 22:45
00:45 23:45
* first airing: Friday 13:45

Ulysses mission coming to a natural end


22 February 2008
Ulysses, the mission to study the Sun's poles and the influence of our star on surrounding space is coming to an end. After more than 17 years in space – almost four times its expected lifetime – the mission is finally succumbing to its harsh environment and is likely to finish sometime in the next month or two.
Ulysses is a joint mission between ESA and NASA. It was launched in 1990 from a space shuttle and was the first mission to study the environment of space above and below the poles of the Sun. Originally designed for a lifetime of five years, the mission has surpassed all expectations. The reams of data Ulysses has returned have forever changed the way scientists view the Sun and its effect on the space surrounding it.

Ulysses is in a six-year orbit around the Sun. Its long path through space carries it out to Jupiter's orbit and back again. The further it ventures from the Sun, the colder the spacecraft becomes. If it drops to 2ºC, the spacecraft's hydrazine fuel will freeze.

This has not been a problem in the past because Ulysses carries heaters to maintain a workable on-board temperature. The spacecraft is powered by the decay of a radioactive isotope and over the 17-plus years, the power it has been supplying has been steadily dropping. Now, the spacecraft no longer has enough power to run all of its communications, heating and scientific equipment simultaneously.

'We expect certain parts of the spacecraft to reach 2ºC pretty soon," says Richard Marsden, ESA's Ulysses Project Scientist and Mission Manager. This will block the fuel pipes, making the spacecraft impossible to manoeuvre.
Ulysses mission artist view
Ulysses passing Jupiter
In an attempt to solve this problem, the ESA-NASA project team approved a plan to temporarily shut off the main spacecraft transmitter. This would release 60 watts of power that could be channelled to the science instruments and the heater. When data was to be transmitted back to Earth, the team planned to turn the transmitter back on. Unfortunately, during the first test of this method in January, the power supply to the radio transmitter failed to turn back on.

"The decision to switch the transmitter off was not taken lightly. It was the only way to continue the science mission," says Marsden, who is a 30-year veteran of the project, having worked on it for 12 years before the spacecraft was launched.

After many attempts, the Ulysses project team now consider it highly unlikely that the X-band transmitter will be recovered. They believe the fault can be traced to the power supply, meaning that the extra energy they hoped to gain cannot be routed to the heater and science instruments after all.

So, the spacecraft has lost its ability to send large quantities of scientific data back to Earth and is facing the gradual freezing of its fuel lines. This spells the end of this highly successful mission. "Ulysses is a terrific old workhorse. It has produced great science and lasted much longer than we ever thought it would," says Marsden. "This was going to happen in the next year or two, it has just taken place a little sooner than we hoped."

The team plan to continue operating the spacecraft in its reduced capacity for as long as they can over the next few weeks. "We will squeeze the very last drops of science out of it," says Marsden.
For more information:
Richard Marsden, ESA Ulysses Project Scientist and Mission Manager
Email: Richard.Marsden @

Debris from destroyed spy satellite falling back to Earth


Posted: February 21, 2008

A missile fired from a Navy cruiser struck a wayward U.S. spy satellite late Wednesday, likely obliterating its load of toxic propellant that could have posed a threat to people on Earth, senior military officials said.

"We're very confident that we hit the satellite," said Marine Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff. "We also have a high degree of confidence that we got the tank."

The SM-3 tactical missile, a modified component of the Aegis sea-based missile defense system, was aiming for a fuel tank embedded inside the craft's structure to release an estimated 1,000 pounds of corrosive hydrazine propellant.

Cartwright said he's about 80 to 90 percent sure the missile hit the fuel tank, based on data from a suite of optical, infrared and radar sensors derived from the national missile defense system.

A tracking camera aboard an aircraft flying over the Pacific captured dramatic images of the intercept, showing the moment of impact and a cloud of debris left behind after the collision.

"We have a fireball, and given that there's no fuel, that would indicate that that's the hydrazine fire. We have a vapor cloud that formed. That again would be likely to be the hydrazine. We also have some spectral analysis from airborne platforms that indicate the presence of hydrazine after the intercept. So again that would indicate to us that the hydrazine vented overboard in some quantity and we're starting to see that in space," Cartwright said.

Detailed results of the unprecedented strike must be confirmed through additional analysis before military officials will draw any more conclusions. That analysis is expected to take a day or two to complete.

"We're trying to pull all these pieces together and make sure that we're not stringing facts together erroneously," Cartwright said.

The SM-3 missile launched from the USS Lake Erie stationed northwest of Hawaii at 10:26 p.m. EST Wednesday. High seas in the Pacific Ocean threatened to preclude an attempt early in the day, but Navy ships reported acceptable conditions once they arrived at the launch site.

Based on recommendations from senior military commanders, Defense Secretary Robert Gates ordered the Navy to take advantage of the Wednesday's opportunity. An incoming weather system could have thwarted launch attempts in subsequent days.

A control center at Vandenberg Air Force Base in California confirmed the missile successfully crashed into the orbiting spacecraft at an altitude of 153 miles, Pentagon officials said.

Lacking a warhead, the interceptor relied on hitting the satellite with a combined relative velocity of about 22,000 miles per hour. The energy of the impact was enough to destroy the spacecraft, which was lost almost immediately after its December 2006 launch.

"This was uncharted territory," Cartwright said. "The technical degree of difficulty was significant here."

Initial radar data indicates the dead satellite broke into fragments no larger than a football, Cartwright reported.

"At the point of intercept last night, there were a few cheers from people who have spent many days working on this project," he said.

Infrared sensors detected numerous objects streaking through the atmosphere, but no sizable pieces of debris have reached the ground. Officials expected a large percentage of the debris to re-enter within the first few hours after the satellite's destruction.

A group of amateur astronomers in Prince George, British Columbia, observed more than a dozen visible debris trails crossing the sky less than 15 minutes after the impact, according to message distributed by the Royal Astronomical Society of Canada.

The targeted satellite's orbit would have taken it northeast across the Pacific Ocean and over Canada in the minutes following the strike.

The mission took only a few minutes to complete but more than a month to plan, according to senior military personnel.

The 5,000-pound satellite – called USA 193 in the military's spacecraft naming system – was about the size of a school bus, defense officials say. USA 193 was operated by the National Reconnaissance Office, the federal agency responsible for fielding spy satellites.

Officials don't know why the experimental satellite died because engineers are not able to communicate with it.

"A smoking gun on exactly why (the satellite failed) is something that has eluded us to date, just because we can't get any diagnostics to tell us what's going on," Cartwright said. "It didn't respond to us."

Because the craft failed so soon after launch, nearly all of its hydrazine maneuvering fuel remained on-board. The corrosive propellant had likely frozen during its 14-month stay in space, and military officials say the frozen tank would have survived a fiery uncontrolled entry into the atmosphere and made it to the ground.

Without control of the satellite, military leaders watched as drag from the thin outer reaches of the atmosphere gradually lowered the craft's orbit. The satellite's orbit fell by an average of more than 60 miles between its launch and this month, a rate that would have led to its natural decay by sometime next month, according to analysis by international hobbyists that observe spacecraft orbiting the planet.

Aerospace industry analysts predicted the hydrazine could be dispersed in an area about the size of two football fields, although the tank would have most likely landed in the ocean or an unpopulated area.

But hydrazine could be deadly to humans if they are exposed to heavy concentrations of the rocket fuel.

"You have to treat this as if it's going to hurt someone," Cartwright said. "If you can mitigate the threat, then you should take action if you have the opportunity."

Engineers estimated up to 2,800 pounds of debris could have made it to Earth if left intact. The satellite also carried sensitive experimental reconnaissance equipment, according to reports.

Some experts said the Pentagon's actions could be driven by the potential of classified technology falling into the wrong hands should the spacecraft come down on land.

"The hydrazine was unique here, not the size of the mass, not the reentry, not the classified nature," Cartwright said. "It was the hydrazine that drove this."

Officials began planning a possible strike in January, and President Bush gave the go-ahead to shoot down the satellite earlier this month.

"You want to reach out to each one of those people that probably gave up their weekends and nights to get this done in 30 days and put it together," Cartwright said.

The Missile Defense Agency added special instrumentation to beam telemetry from the missile to control centers, giving engineers additional insight into the mission. Other changes included tweaking software to allow the interceptor, originally designed to fend off short- and medium-range missiles, to reach a satellite in orbit.

"It's not something that we would be entering into the service in some standard way," Cartwright said. "This is a one-time type of event."

The launch also used a network of sensors used by the missile defense system to detect incoming ballistic missiles. The sensors included airborne detectors, ground radars and telescopes in Hawaii, tracking stations on ships, and satellite-based infrared instruments on the military's early warning satellites, a senior military official said on background.

The use of multiple tiers of the missile defense system in Wednesday's space shot proves it works, Secretary Gates said.

"Completely a side benefit of yesterday's action was to underscore the money that the Congress has been voting for this has resulted in a very real capability," Gates said.

Wednesday's intercept was the first time the U.S. military destroyed an orbiting satellite since 1985, when an air-launched missile struck a beleaguered solar observatory. China garnered international criticism last year when it conducted an unannounced test of an anti-satellite, or ASAT, weapon against one of its own weather satellites.

Military leaders drew distinctions between that test and Wednesday's mission. The concern that compelled the Pentagon's decision was public safety, Cartwright said.

"We did that in the 1980s. We understand ASAT. There's no reason to go back and reprove what we've already done," he said.

Government officials also informed foreign governments a week before the test. The Pentagon worked closely with the State Department to begin diplomatic efforts, according to Ambassador James Jeffrey, President Bush's deputy national security advisor.

Agencies are following a U.N. treaty that calls for member states to inform other countries about space activities of potential concern, Jeffrey said.

"What we've tried to do from the beginning was be as open as possible about the intention," said Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff.

Senior military leaders say the strike can serve as a model of openness to China and other countries conducting similar operations.

"The Chinese did not do that when they launched their anti-satellite test," said Navy Adm. Timothy Keating, commander of U.S. Pacific Command. "We hope there are some lessons that become apparent to them."

China's test last year created more than 2,000 pieces of space junk, most of which is still in orbit and could pose a risk to other spacecraft.

"The Chinese ASAT test was conducted against a satellite in a circular orbit at around 850 kilometers of altitude," said Mike Griffin, NASA administrator, during a press conference last week. "So the debris that was generated could go (through) a very large swath of Earth orbital space and will be up for decades."

Most of the chunks generated from Wednesday's intercept were expected to be down within hours and days.

"That's an enormous difference to spacefaring nations," Griffin said.

Giant ropes of dark matter found in new sky survey

Over time, matter pulls together into a web-like structure along a scaffolding of dark matter (Illustration: Center for Cosmological Physics/U Chicago)
Over time, matter pulls together into a web-like structure along a scaffolding of dark matter (Illustration: Center for Cosmological Physics/U Chicago)
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A star with an attitude

Powerful explosions suggest a neutron star is the missing link.
Provided by the Goddard Space Flight Center
This Chandra image shows the supernova Kes 75. The pulsar is in the center of the blue area at the top. NASA/CXC/M. Gonzalez/F. Gavriil/P. Slane [View Larger Image]
February 21, 2008
Observations from NASA's Rossi X-ray Timing Explorer (RXTE) have revealed that the youngest known pulsing neutron star has thrown a temper tantrum. The collapsed star occasionally unleashes powerful bursts of X-rays, which are forcing astronomers to rethink the life cycle of neutron stars.

"We are watching one type of neutron star literally change into another right before our very eyes. This is a long-sought missing link between different types of pulsars," says Fotis Gavriil of NASA's Goddard Space Flight Center and the lead author of the paper.

A neutron star forms when a massive star explodes as a supernova, leaving behind an ultradense core. Most known neutron stars emit regular pulsations that are powered by rapid spins. Astronomers have found nearly 1,800 of these so-called pulsars in our galaxy. Pulsars have incredibly strong magnetic fields by Earthly standards, but a dozen of them. Slow rotators known as magnetars actually derive their energy from incredibly powerful magnetic fields, the strongest known in the universe. These fields can stress the neutron star's solid crust past the breaking point, triggering starquakes that snap magnetic-field lines, producing violent and sporadic X-ray bursts.

But what is the evolutionary relationship between pulsars and magnetars? Astronomers would like to know if magnetars represent a rare class of pulsars, or if some or all pulsars go through a magnetar phase during their life cycles.

Gavriil and his colleagues have found an important clue by examining archival RXTE data of a young neutron star, known as PSR J1846-0258 for its sky coordinates in the constellation Aquila. Previously, astronomers had classified PSR J1846 as a normal pulsar because of its fast spin (3.1 times per second) and pulsar-like spectrum. But RXTE caught four magnetar-like X-ray bursts on May 31, 2006, and another on July 27, 2006. Although none of these events lasted longer than 0.14 second, they all packed the wallop of at least 75,000 Suns.
These images from NASA's Chandra X-ray Observatory show the pulsar in Kes 75 in October 2000 (left) and June 2006 (right). The pulsar clearly brightened in X-rays after giving off powerful outbursts earlier in 2006. NASA/CXC/M. Gonzalez/F. Gavriil/P. Slane [View Larger Image]
"Never before has a regular pulsar been observed to produce magnetar bursts," says Gavriil.

"Young, fast-spinning pulsars were not thought to have enough magnetic energy to generate such powerful bursts," says coauthor Marjorie Gonzalez, who worked on this paper at McGill University in Montreal, Canada. "Here's a normal pulsar that's acting like a magnetar."

Observations from NASA's Chandra X-ray Observatory also provided key information. Chandra observed the neutron star in October 2000 and again in June 2006, around the time of the bursts. Chandra showed the object had brightened in X-rays, confirming that the bursts were from the pulsar, and that its spectrum had changed to become more magnetar-like.

Astronomers know that PSR J1846 is very young for several reasons. First, it resides inside a supernova remnant known as Kes 75, an indicator that it hasn't had time to wander from its birthplace. Second, based on the rapidity that its spin rate is slowing down, astronomers calculate that it can be no older than 884 years, an infant on the cosmic timescale. Magnetars are thought to be about 10,000 years old, whereas most pulsars are thought to be considerably older.

The fact that PSR J1846's spin rate is slowing down relatively fast also means that it has a strong magnetic field that is breaking the rotation. The implied magnetic field is trillions of times stronger than Earth's field, but it's 10 to 100 times weaker than typical magnetar field strengths. Coauthor Victoria Kaspi of McGill University notes, "PSR J1846's actual magnetic field could be much stronger than the measured amount, suggesting that many young neutron stars classified as pulsars might actually be magnetars in disguise, and that the true strength of their magnetic field only reveals itself over thousands of years as they ramp up in activity."

Space Debris May be Catastrophic to Future Missions (and Google Earth is Watching…)

Written by Ian O'Neill
3D view of junk in low Earth orbit.
Kessler Syndrome could be a frightening situation for space travel. No, it's not a health risk to the human body in zero-G and it's not a psychological disorder for astronauts spending too much time from home. Kessler Syndrome is the point at which space travel becomes impossible without hitting into a piece of space junk, jeopardizing missions and risking lives. In extreme predictions, space debris from our constant littering of low Earth orbit, collisions between bits of rubbish may become more and more frequent, causing a catastrophic cascade of debris multiplying exponentially, falling through the atmosphere and making space impassable.
In the meanwhile, space mission controllers must be acutely aware that there could be an odd bolt or piece of old satellite flying toward their spaceship at velocities faster than the fastest rifle shot. Spare a thought for the space debris trackers as they try to keep a record of the 9,000+ pieces of junk currently orbiting our planet… but wait a minute, Google Earth can give us a ringside seat!

Strict international civil aviation-style laws may need to be imposed on the worlds space agencies if future generations of the human race are going to make it in space. This stark warning comes from Tommaso Sgobba, Director of the International Association for the Advancement of Space Safety, who will be presenting his case to the United Nations in April. Sgobba's main argument comes from the danger associated with the escalating accumulation of space debris in Earth orbit, should these high speed bits of junk hit a spaceship, satellite or an astronaut, death and disaster may ensue. It may get worse than this, possibly paralysing the Earth from having access to space at all.
"Failure to act now to regulate space to protect property and human life would be pure folly." - Tommaso Sgobba.
Other scientists agree with Sgobba, recommending that future missions in to space abide by some strict codes of practice (possibly more strict than those imposed on international civil aviation) to drastically cut the rate of orbital littering by the 20 countries currently able to send stuff into space.
Even the most tightly controlled missions, such as the International Space Station, are expected to shed bits and pieces over the course of their lifetimes. Space junk comes in all shapes and sizes and can be anything from a small screw to entire dead satellites. Recorded examples of space junk include an old glove lost by Ed White during the first ever US space walk in 1965 (during the Gemini-4 mission), a camera that Michael Collins let slip in space in 1966 (during the Gemini-8 mission) and a pair of pliers that International Space Station astronaut Scott Parazynski dropped during an EVA last year.
Some space debris near misses include:
  • Space Shuttle dodge: Space Shuttle Atlantis had to avoid collision with a piece of a Russian satellite by carrying out a seven second burn of its engines in 1991.
  • Aircraft scare: Bits of an Russian ex-spy satellite fell through the atmosphere coming very close to a Latin American Airbus, carrying 270 passengers in 2006.
  • Personal injury: fortunately there is only one documented account of someone being hit by a piece of debris on the ground. In 1997 a woman from Oklahoma was hit on the shoulder by a piece of a fuel tank from a Delta II rocket. She was unhurt and lived to tell the tail.
It is hoped that tighter controls on the rockets, satellites and spacecraft will slow the rate of junk increase, but the problem is already pretty worrying for long-term missions in orbit around the Earth. The two critical regions filling with debris are in low Earth and geosynchronous orbits, a few hundred and 22,300 miles high respectively. Low Earth orbit will cause problems for spacecraft to actually leave the atmosphere and geosynchronous orbit may hinder future communication satellite insertions.
To safeguard our access into space, and avoid an increase in debris-related incidents, action will need to be taken.
Google Earth-watch
Two screenshots. Looking up toward the constellation of Leo. One screen with and one without the positions of space debris.
During the research on this article, I came across some work being funded by Ministry of Culture of the Republic of Slovenia, Municipality of Ljubljana, where researchers are making debris location data available to the public via a plugin for the Google Earth application. According to the groups blog, the data is taken from a U.S. government-owned space observatory so known space debris (or as the blog calls it "pollution", which it really is) can be tracked.
On experimenting with the new space debris folder, it really did strike home as to what a problem space junk is becoming. For starters, there is an impossibly thick near-Earth layer and a distinct ring representing the geosynchronous debris. Plus, each item can be selected and information on the individual bits of debris can be found out… see the screenshots to find out what I mean…
3D view of junk in low Earth orbit.
Get the space junk plugin for Google Earth (read Google Earth documentation to learn how to use this plugin).
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Watch Out For The Zodiacal Light!

Written by Tammy Plotner
Zodical Light courtesy of NASA
For northern hemisphere SkyWatchers, the next week or so (until the Moon returns in the early evening) is prime time to spot the Zodiacal Lights. No, it's not a visitor from outer space but the interplanetary dust from within our own solar system!
Now that the Moon has departed from the early evening sky, this is a good time in the northern hemisphere to watch the western skyline for the evening Zodiacal Lights. If you live in an area where light and air pollution isn't heavy, you stand a very good chance of seeing the interplanetary dust in the plane of our own solar system lit by the setting Sun. At this time of year in the northern hemisphere, the ecliptic plane extends upright from the western horizon. (If you live in the southern hemisphere, you need to watch the eastern horizon before dawn after New Moon.) When the Sun is just below the horizon, we can see a ghostly glowing pyramid. But, what is it?
Sunlight is back-scattered off small interplanetary dust particles, perhaps some of them from the very formation of our solar system itself. However, a lot of these tiny, millimeter sized splinters are from asteroids - or debris ejected from comets. Some of these particles are initially distributed in the trails that cause meteor showers, but whole lot of the dust eventually gathers along the ecliptic plane. Why?
For the ultra-tiny particles, the radiation and solar wind disperses them beyond the confines of our solar system. The larger particles spiral inwards, pulled towards the Sun by gravity and form a flattened disc - a very low density cloud of dust, coincident with the plane of the solar system. Sunlight absorbed by the particles is re-emitted as invisible infrared radiation. This re-radiation causes the particles to spiral slowly into Sun, thus requiring continuous regeneration of the dust particles composing this cloud. The reflective particle disc makes its home in the same path the planets take around the Sun - the ecliptic. This imaginary path across the sky is where we here on Earth see the Sun and Moon, and it's also home to the constellations of the zodiac!
Using the same celestial mechanics that give us times of solstice, equinox, lunar and solar eclipses, it only stands to reason there comes a time when the ecliptic plane appears nearly vertical from a certain vantage point. For the northern hemisphere it's west in the spring and east in the fall. For the southern hemisphere it's just the opposite! When the plane is near vertical, the thick air near the horizon doesn't block out relatively bright reflecting dust and we see the Zodiacal Light!
Head out to an open horizon area where you're away from man-made light pollution. As the skies grow dark, look for a faint pyramid of light spread out over a very large area of the sky. It won't be as dramatic as photos show it. Near its base at the horizon it can measures as broad 40 degrees (two handspans), and stretch up as high as 60-80 degrees under good conditions. The spectrum of the zodiacal light is the same as the solar spectrum, reinforcing the deduction that it is merely sunlight reflected by dust in the plane of the planets. If you think you see a ghostly glow, you're probably right!
Best of luck… And share your photos and stories!

Record Breaking "Dark Matter Web" Structures Observed Spanning 270 Million Light Years Across

Written by Ian O'Neill
The distribution of dark matter obtained from a large numerical simulation (credit: Max-Planck Institute for Astrophysics)
It is well documented that dark matter makes up the majority of the mass in our universe. The big problem comes when trying to prove dark matter really is out there. It is dark, and therefore cannot be seen. Dark matter may come in many shapes and sizes (from the massive black hole, to the tiny neutrino), but regardless of size, no light is emitted and therefore it cannot be observed directly. Astronomers have many tricks up their sleeves and are now able to indirectly observe massive black holes (by observing the gravitational, or lensing, effect on light passing by). Now, large-scale structures have been observed by analyzing how light from distant galaxies changes as it passes through the cosmic web of dark matter hundreds of millions of light years across…

Dark matter is believed to hold over 80% of the Universe's total mass, leaving the remaining 20% for "normal" matter we know, understand and observe. Although we can observe billions of stars throughout space, this is only the tip of the iceberg for the total cosmic mass.
Using the influence of gravity on space-time as a tool, astronomers have observed halos of distant stars and galaxies, as their light is bent around invisible, but massive objects (such as black holes) between us and the distant light sources. Gravitational lensing has most famously been observed in the Hubble Space Telescope (HST) images where arcs of light from young and distant galaxies are warped around older galaxies in the foreground. This technique now has a use when indirectly observing the large-scale structure of dark matter intertwining its way between galaxies and clusters.
Astronomers from the University of British Columbia (UBC) in Canada have observed the largest structures ever seen of a web of dark matter stretching 270 million light years across, or 2000 times the size of the Milky Way. If we could see the web in the night sky, it would be eight times the area of the Moons disk.
This impressive observation was made possible by using dark matter gravity to signal its presence. Like the HST gravitational lensing, a similar method is employed. Called "weak gravitational lensing", the method takes a portion of the sky and plots the distortion of the observed light from each distant galaxy. The results are then mapped to build a picture of the dark matter structure between us and the galaxies.
The team uses the Canada-France-Hawaii-Telescope (CFHT) for the observations and their technique has been developed over the last few years. The CFHT is a non-profit project that runs a 3.6 meter telescope on top of Mauna Kia in Hawaii.
Understanding the structure of dark matter as it stretches across the cosmos is essential for us to understand how the Universe was formed, how dark matter influences stars and galaxies, and will help us determine how the Universe will develop in the future.
"This new knowledge is crucial for us to understand the history and evolution of the cosmos […] Such a tool will also enable us to glimpse a little more of the nature of dark matter." - Ludovic Van Waerbeke, Assistant Professor, Department of Physics and Astronomy, UBC
Source: UBC Press Release

Milky Way is Twice as Thick as Previously Believed

Written by Fraser Cain
Galaxy NGC 5866, seen edge on. Image credit: Hubble
Imagine suddenly realizing that your house was twice as big as you originally thought. Okay, maybe that's a little out there, but astronomers from Australia have calculated that the Milky Way is actually twice as thick as previously believed - doubling from the originally estimated 6,000 light-years to 12,000 light-years.

The calculation was made by a couple of astronomers from the University of Sydney. They were working with the accepted numbers for the dimensions of our home galaxy (6,000 light years thick, and 100,000 light-years wide) when they thought it might make sense to double check those basic assumptions.
They used an accepted technique for calculating distance; measuring the light from pulsars. When light from distant pulsars moves through the background material of the Milky Way (known as the Warm Ionised Medium), it slows down. The redder pulses of light actually slow down more than the bluer pulses.
By measuring the change in light from the pulsar, astronomers can determine how much material the light has traveled through.
When they used the old calculations for 40 different pulsars inside and above it, they got the old numbers. But when they just looked at 17 pulsars which are above and below the galactic disk they got a new, more accurate, estimate.
"Of the thousands of pulsars known in and around our Galaxy, only about 60 have really well known distances," said Professor Bryan Gaensler. "But to measure the thickness of the Milky Way we need to focus only on those that are sitting above or below the main part of the Galaxy; it turns out that pulsars embedded in the main disk of the Milky Way don't give us useful information."
Their results were presented in January at the annual meeting of the American Astronomical Society in Austin, Texas. Some of Dr. Gaensler's colleagues appreciated the revised calculations, while others… not so pleased at the implications for their own research.
Original Source: University of Sydney

Could Primordial Black Holes Deflect Asteriods on a Collision Course with Earth?

Written by Ian O'Neill
An artists impression of an asteroid belt (credit: NASA)
Primordial black holes (PBHs) are getting mischievous again. These artefacts from the Big Bang could be responsible for hiding inside planets or stars, they may even punch a neat, radioactive hole through the Earth. Now, they might start playing interplanetary billiards with asteroids in our solar system.
Knocking around lumps of rock may not sound very threatening when compared with the small black holes' other accolades, but what if a large asteroid was knocked off course and sent in our direction? This could be one of the most catastrophic events yet to come from a PBH passing through our cosmic neighborhood…

As a race, we are constantly worried about the threat of asteroids hitting Earth. What if another large asteroid - like the one that possibly killed the dinosaurs around 65 million BC or the one that blew up over Tunguska in 1908 - were to come hurtling through space and smash into the Earth? The damage caused by such an impact could devastate whole nations, or plunge the world as we know it to the brink of extinction.
But help is at hand. From the combined efforts by groups such as NASAs Near Earth Object Program and international initiatives, governments and institutions are beginning to take this threat seriously. Tracking threatening Near Earth Asteroids is a science in itself, and for now at least, we can relax. There are no massive lumps of rock coming our way (that we know of). The last scare was a comparatively small asteroid called "2008 CT1" which came within 135,000 km of the Earth (about a third of the distance to the Moon) on February 5th, but there are no others forecast for some time.
So, we now have NEO monitoring down to a fine art - we are able to track and calculate the trajectory of observed asteroids throughout the solar system to a very high degree of accuracy. But what would happen if an asteroid should suddenly change direction? This shouldn't happen right? Think again.
A researcher from the Astro Space Center of the P. N. Lebedev Physics Institute in Moscow has published works focusing on the possibility of asteroids veering off course. And the cause? Primordial black holes. There seems to be many publications out there at the moment musing what would happen should these black holes exist. If they do exist (and there is a high theoretical possibility that they do), there's likely to be lots of them. So Alexander Shatskiy has gotten to the task of working out the probability of a PBH passing through the solar systems asteroid belts, possibly kicking an asteroid or two across Earths orbit.
Shatskiy finds that PBHs of certain masses are able to significantly change an asteroids orbit. There are estimates of just how big these PBHs can be, the lower limit is set by black hole radiation parameters (as theorized by Stephen Hawking), having little gravitational effect, and the upper limit is estimated to be as massive as the Earth (with an event horizon radius of an inch or so - golf ball size!). Naturally, the gravitational influence by the latter will be massive, greatly affecting any piece of rock as it passes by.
Real-time map of the distribution of thousands of known asteroids around the inner solar system. Red and yellow dots represent high risk NEOs (credit: Armagh Observatory)
Should PBHs exist, the probability of finding one passing though the solar system will actually be quite high. But what is the probability of the PBH gravitationally scattering asteroids as it passes? If one assumes a PBH with a mass corresponding to the upper mass estimate (i.e. the mass of the Earth), the effect of local space would be huge. As can be seen from an asteroid map (pictured), there is a lot of rocky debris out there! So something with the mass of the Earth barrelling through and scattering an asteroid belt could have severe consequences for planets nearby.
Although this research seems pretty far-fetched, one of the calculations estimate the average periodicity of a large gravitationally disturbed asteroids falling to Earth should occur every 190 million years. According to geological studies, this estimate is approximately the same.
Shatskiy concludes that should small black holes cause deflection of asteroid orbits, perhaps our method of tracking asteroids may be outdated:
"If the hypothesis analyzed in this paper is correct, modern methods aimed at averting the asteroid danger appear to be inefficient. This is related to the fact that their main idea is revealing big meteors and asteroids with dangerous orbits and, then, monitoring these bodies. However, if the main danger consists in abrupt changes of asteroidal orbits (because of scattering on a PBH), revealing potentially dangerous bodies is hardly possible."

Chasing a Supernova Progenitor

The Type Ia supernova 2007on (with red tick) blew up last November in the outskirts of the galaxy NGC 1404, located 65 million light-years away in Fornax.
For the first time ever, astronomers may have found the progenitor of a Type Ia supernova. Or, frustratingly, maybe not.

This matters. The astronomers hoped their discovery would finally settle the nature of these exploding white-dwarf stars, which have become a critical tool for cosmology in the last ten years. But, as happens so often, a definitive answer isn't coming easily.

In old data archived from NASA's Chandra X-ray Observatory, Rasmus Voss (Max Planck Institute for Extraterrestrial Physics, Germany) and Gijs Nelemans (Radboud University, the Netherlands) found an X-ray source at the location where a Type Ia supernova, SN 2007on, later blew up. The supernova was discovered on November 5, 2007, in the outer edge of NGC 1404, an elliptical galaxy some 65 million light-years away in the southern constellation Fornax.

If the X-ray source was indeed the supernova's progenitor, notes Nelemans, this would support the theory that Type Ia explosions occur in binary-star systems where matter from a normal star streams onto a white-dwarf companion. The nuclear fusion of the freshly arrived material on the dwarf's surface would produce strong X-rays.

If such a feasting white dwarf grows heftier than 1.39 solar masses (the "Chandrasekhar limit"), it can't hold itself up against its own gravity anymore, and it starts to collapse inward. Within moments the temperature and pressure at its center become so great that the entire star explodes in a runaway thermonuclear reaction — as a distinctive, Type Ia supernova.

Because all white dwarfs have the same mass when they reach this tipping point, astrophysicists expect all Type Ia's (of a given subtype) to have the same luminosity. Therefore, cosmologists believe they can use Type Ia's as accurate "standard candles" to measure the distances of remote galaxies independently of redshift. By comparing the supernova distances to the redshifts of the host galaxies, astronomers can chart the history of the universe's changing expansion rate. In 1998 such studies led to the discovery that the expansion is speeding up, presumably due to some kind of "dark energy" pervading space.

Two Ways to Collapse

But no one knows for sure whether Type Ia supernovas really arise from a white dwarf accreting matter slowly from a normal star. Another possibility is that the blasts result from the merger of two white dwarfs in a close binary system spiraling together. A better understanding of the nature of Type Ia progenitors might help firm up the cosmological supernova data.

There's a key difference between the two scenarios. In the slow-accretion version, matter falling onto the white dwarf makes it shine brightly in X-rays. In the two-white-dwarfs version, no matter is exchanged beforehand and the system is essentially X-ray dark.

Pinpointing the Site. . . Maybe

Voss and Nelemans published their discovery of the possible X-ray progenitor of SN 2007on in the February 14th issue of Nature. It seemed to settle the question in favor of the standard, slow-accretion model.

However, after their paper was accepted for publication in mid-December, nagging doubts about the apparent association have surfaced.

In particular, more precise measurements of the supernova's position with telescopes run by the European Southern Observatory in Chile, including the Very Large Telescope at Cerro Paranal, reveal a small offset from the Chandra X-ray source's position. The discrepancy is barely more than one arcsecond, but that's enough to mean the X-ray source and the supernova had nothing whatever to do with each other — if in fact the X-ray position is as accurate as Chandra's operators believed.

Probably it is. Only a few X-ray photons were detected in the four-year-old Chandra observation, but that's enough that the probability of the X-ray source really being the supernova progenitor is now estimated to be no more than 1 percent, says Nelemans.

On the other hand, given the rarity of similar X-ray sources, the probability of a chance alignment is also less than 1 percent! "One way or the other, we have come across a very improbable event," says Nelemans.

Future observations should settle the issue. If the X-ray source was indeed what blew up later, it should now be gone. Voss and Nelemans are applying for Chandra time later this year to check.

Meanwhile, they are on the hunt for X-ray progenitors of other Type Ia events.



Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil


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