Posted on by Fraser Cain

NASA Needs Better Shuttle Pictures

Image credit: CAIB

The Columbia Accident Investigation Board released its fifth major finding today, which recommends that NASA improve the way it takes photographs of the shuttle launch. During the launch of Columbia, NASA cameras provided poor images from a critical point of view which would have showed foam falling from the external fuel tank more clearly. NASA is considering additional ground, aircraft, and even shuttle-mounted cameras to better document future launches. The final report is expected within a month.

The Columbia Accident Investigation Board today issued its fifth preliminary finding and recommendation to the National Aeronautics and Space Administration, in advance of its appearance in the final report.

Recommendation Five:

  • Provide a capability to obtain and downlink high-resolution images of the External Tank (ET) after ET separation. Modifying one of the two umbilical cameras to meet this requirement is acceptable.
  • Provide a capability to obtain and downlink high-resolution images of the underside of the orbiter leading edge system and forward section of both wings? Thermal Protection System (TPS).

Facts:

  • Imaging the Space Shuttle System during launch and ascent provides necessary engineering data including the ability to examine the Space Shuttle System for any unexpected debris or other anomalies during ascent.
  • The Shuttle has two on-board cameras that image the ET after separation, but the images from these cameras are available only post-flight.
  • Very little engineering quality, on-board imaging of the ET was available for STS-107.

Findings:

  • There is a requirement to obtain and downlink on-board engineering quality imaging from the vehicle during launch and ascent.

Background:

  • The Space Shuttle is still a developmental vehicle, and engineering data from each launch is essential to further understand the vehicle.
  • An ability to provide engineering quality imaging data of the ET after separation is important to determine if any debris from the ET was shed during ascent.
  • Since the total elimination of all sources of debris has not yet been achieved, a much better understanding of all the potential sources of debris is required.
  • Since the total elimination of all sources of debris has not yet been achieved, early detection of debris strikes against the forward underwing TPS of both wings will increase safety margins.
  • The CAIB is aware of the excellent preliminary work already in progress at NASA in this area.

Original Source: CAIB News Release

Posted on by Fraser Cain

Neutron Star Binaries are More Common in Clusters

Image credit: Chandra

Many of the stars that we see in globular star clusters are actually binary stars, formed when two stars get caught in each other’s gravity. But new research from the Chandra X-Ray Observatory shows that there are many more binary objects which are stars orbiting a neutron star or white dwarf. Chandra can detect the unique x-ray signature that a neutron star gives off, which is invisible in an optical telescope. The research seems to indicate that these neutron star binaries form much more commonly found in globular clusters than in other parts of a galaxy.

NASA’s Chandra X-ray Observatory has confirmed that close encounters between stars form X-ray emitting, double-star systems in dense globular star clusters. These X-ray binaries have a different birth process than their cousins outside globular clusters, and should have a profound influence on the cluster’s evolution.

A team of scientists led by David Pooley of the Massachusetts Institute of Technology in Cambridge took advantage of Chandra’s unique ability to precisely locate and resolve individual sources to determine the number of X-ray sources in 12 globular clusters in our Galaxy. Most of the sources are binary systems containing a collapsed star such as a neutron star or a white dwarf star that is pulling matter off a normal, Sun-like companion star.

“We found that the number of X-ray binaries is closely correlated with the rate of encounters between stars in the clusters,” said Pooley. “Our conclusion is that the binaries are formed as a consequence of these encounters. It is a case of nurture not nature.”

A similar study led by Craig Heinke of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. confirmed this conclusion, and showed that roughly 10 percent of these X-ray binary systems contain neutron stars. Most of these neutron stars are usually quiet, spending less than 10% of their time actively feeding from their companion.

A globular cluster is a spherical collection of hundreds of thousands or even millions of stars buzzing around each other in a gravitationally-bound stellar beehive that is about a hundred light years in diameter. The stars in a globular cluster are often only about a tenth of a light year apart. For comparison, the nearest star to the Sun, Proxima Centauri, is 4.2 light years away.

With so many stars moving so close together, interactions between stars occur frequently in globular clusters. The stars, while rarely colliding, do get close enough to form binary star systems or cause binary stars to exchange partners in intricate dances. The data suggest that X-ray binary systems are formed in dense clusters known as globular clusters about once a day somewhere in the universe.

Observations by NASA’s Uhuru X-ray satellite in the 1970’s showed that globular clusters seemed to contain a disproportionately large number of X-ray binary sources compared to the Galaxy as a whole. Normally only one in a billion stars is a member of an X-ray binary system containing a neutron star, whereas in globular clusters, the fraction is more like one in a million.

The present research confirms earlier suggestions that the chance of forming an X-ray binary system is dramatically increased by the congestion in a globular cluster. Under these conditions two processes, known as three-star exchange collisions, and tidal captures, can lead to a thousandfold increase in the number of X-ray sources in globular clusters.

In an exchange collision, a lone neutron star encounters a pair of ordinary stars. The intense gravity of the neutron star can induce the most massive ordinary star to “change partners,” and pair up with the neutron star while ejecting the lighter star.

A neutron star could also make a grazing collision with a single normal star, and the intense gravity of the neutron star could distort the gravity of the normal star in the process. The energy lost in the distortion, could prevent the normal star from escaping from the neutron star, leading to what is called tidal capture.

“In addition to solving a long-standing mystery, Chandra data offer an opportunity for a deeper understanding of globular cluster evolution,” said Heinke. “For example, the energy released in the formation of close binary systems could keep the central parts of the cluster from collapsing to form a massive black hole.”

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release

Posted on by Fraser Cain

Ion Drive Powered Spacecraft

Image credit: ESA

The European Space Agency’s SMART-1 mission will use a revolutionary ion engine to help it search for evidence that the Moon was formed after a violent collision of a smaller planet with the Earth. An ion engine works by accelerating ionized particles of gas in a constant stream for months or even years. Although the thrust is very low, it’s very efficient and requires a fraction of fuel that traditional rockets use.

Science fiction movie fans know that, if you want to travel short distances from your home planet, you would use a sublight ‘ion drive’. However, is such an ion drive science fiction, or science fact?

The answer lies somewhere in between. Ion engines date back to at least 1959. Two ion engines were even tested in 1964 on the American SERT 1 satellite – one was successful, the other was not.

The principle is simply conventional physics – you take a gas and you ionise it, which means that you give it an electrical charge. This creates positively charged ions of gas, along with electrons. The ionised gas passes through an electric field or screen at the back of the engine and the ions leave the engine, producing a thrust in the opposite direction.

Very fuel-efficient
Operating in the near vacuum of space, ion engines shoot out the propellant gas much faster than the jet of a chemical rocket. They therefore deliver about ten times as much thrust per kilogram of propellant used, making them very ‘fuel-efficient’.

Although they are efficient, ion engines are very low-thrust devices. The amount of push you get for the amount of propellant used is very good, but they do not push very strongly. For example, astronauts could never use them for taking off the surface of a planet. However, once in space, they could use them for manoeuvring around, if they are not in a hurry to accelerate quickly. Why? Ion drives can get up to high speeds in space, but they need a very long distance to build up to such speeds over time.

Leisurely advantage
Ion engines work their magic in a leisurely way. Electric guns accelerate the ions. If the power for this acceleration comes from the spacecraft’s solar panels, scientists call it ‘solar-electric propulsion’. Solar panels of the size typically used on current spacecraft can supply only a few kilowatts of power.

A solar-powered ion engine could therefore not compete with the large thrust of a chemical rocket. However, a typical chemical rocket burns for only a few minutes, whereas an ion engine can go on pushing gently for months or even years – as long as the Sun shines and the supply of propellant lasts.

Another advantage of gentle thrust is that it allows very accurate spacecraft control, very useful for scientific missions that require highly precise target pointing.

Ensuring ESA’s place in space
Engineers tested an ion engine as a main propulsion system for the first time using NASA’s Deep Space 1 mission between 1998 and 2001. ESA’s SMART-1 mission, due for launch in late August 2003, will go to the Moon and demonstrate more subtle operations of the kind needed in future long-distance missions. These will combine solar-electric propulsion with manoeuvres using the gravity of planets and moons for the first time.

SMART-1 will ensure Europe’s independence in the use of ion propulsion. Other space science missions are expected to use ion engines for complex manoeuvres close to Earth’s orbit. For example, ESA’s mission LISA will detect gravitational waves coming from the distant Universe. ESA’s future missions to the planets will also use ion engines to send them on their way.

Now science fact
The present-day realities of solar-electric propulsion might not match the movie magic of sci-fi films with spacecraft flying around on our cinema screens. However, ESA’s work on SMART-1 and future missions is ensuring that ion drives are now more science fact than science fiction.

Original Source: ESA News Release

Posted on by Fraser Cain

Satellite Confirms Ozone Recovery

Image credit: NASA

Observations from three NASA satellites have confirmed that the rate of ozone depletion in the Earth’s upper atmosphere is decreasing. The observations were made by SAGE I, SAGE II, and HALOE satellites which scanned the upper stratosphere since 1997. Their observations are consistent with the decline of man-made chemicals in the atmosphere which contribute to ozone depletion. The ozone layer protects the Earth’s surface from sun’s harmful ultraviolet radiation.

NASA satellite observations have provided the first evidence the rate of ozone depletion in the Earth’s upper atmosphere is decreasing. This may indicate the first stage of ozone layer recovery.

From an analysis of ozone observations from NASA’s first and second Stratospheric Aerosol and Gas Experiment (SAGE) and the Halogen Occultation Experiment (HALOE) satellite instruments, scientists have found less ozone depletion in the upper stratosphere (22-28 miles altitude) after 1997. The American Geophysical Union Journal of Geophysical Research has accepted a paper for publication on these results.

This decrease in the rate of ozone depletion is consistent with the decline in the atmospheric abundance of man-made chorine and bromine-containing chemicals that have been documented by satellite, balloon, aircraft and ground based measurements.

Concerns about ozone depletion in the upper atmosphere or stratosphere led to ratification of the Montreal Protocol on Substances that Deplete the Ozone Layer by the international community in 1987. The protocol restricts the manufacture and use of human-made, ozone-depleting compounds, such as chlorofluorocarbons and halons.

“Ozone is still decreasing but just not as fast,” said Mike Newchurch, associate professor at the University of Alabama, Huntsville, Ala., and lead scientist on the study. “We are still decades away from total ozone recovery. There are a number of remaining uncertainties such as the effect of climate change on ozone recovery. Hence, there is a need to continue this precise long-term ozone data record,” he said.

“This finding would have been impossible had either SAGE II or HALOE not lasted so long past their normal mission lifetime,” said Joe Zawodny, scientist on the SAGE II satellite instrument science team at NASA’s Langley Research Center, Hampton, Va.

SAGE II is approaching the 19th anniversary of its launch, and HALOE has been returning data for 11 years. Scientists also used international ground networks to confirm these data from satellite results.

SAGE I was launched on the Applications Explorer Mission-B spacecraft in 1979; the Earth Radiation Budget Satellite carried SAGE II into orbit in 1984. The Space Shuttle Discovery carried HALOE into space on the Upper Atmosphere Research Satellite in 1991.

NASA’s Earth Science Enterprise funded this research in an effort to better understand and protect our home planet. The ozone layer protects the Earth’s surface from the sun’s harmful ultraviolet rays. Ultraviolet radiation can contribute to skin cancer and cataracts in humans and harm other animals and plants. Ozone depletion in the stratosphere also causes the ozone hole that occurs each spring over Antarctica.

Original Source: NASA News Release

Posted on by Fraser Cain

Mars is Close and Getting Closer

Image credit: Hubble

On August 27, 2003 the Planet Mars will be a mere 55.76 million kilometres away from the Earth – the closest it’s been in 50,000 years. Visible in the early morning, Mars is the brightest object in the sky, after the Moon and Venus, and almost any small telescope will be able to show details on the planet’s surface. Make sure you enjoy Mars’ close approach this summer, as it won’t make another visit this close for nearly 300 years.

Living too close to a neighbor may not be very appealing, but when Earth?s neighboring red planet moves closer than it?s been in 60,000 years, observers expect nothing but acclaim.

This August, scientists and amateur astronomers will benefit from the spectacular view of Mars as it appears bigger and brighter than ever before, revealing its reflective south polar cap and whirling dust clouds.

On August 27, 2003, the fourth rock from the sun will be less than 55.76 million kilometers (34.65 million miles) away from the Earth. In comparison to the space between your house and your neighbor?s yard, that may seem like a large distance, but Mars was about five times that distance from Earth only six months ago.

“Think of Earth and Mars as two race cars going around a track,” said Dr. Myles Standish, an astronomer from NASA?s Jet Propulsion Laboratory, Pasadena, Calif. “Earth is on a race track that is inside the track that Mars goes around, and neither track is perfectly circular. There is one place where the two race tracks are closest together. When Earth and Mars are at that place simultaneously, it is an unusually close approach, referred to as a ‘perihelic opposition’.”

Opposition is a term used when Earth and another planet are lined up in the same direction from the Sun. The term perihelic comes from perihelion, the point of orbit in which a celestial body is closest to the Sun. This August, Mars will reach its perihelion and be in line with Earth and the Sun at the same time.

The average opposition occurs about every two years, when Earth laps Mars on its orbit around the Sun. In 1995, the opposition brought Mars 101.1 million kilometers (62.8 million miles) from the Earth, twice as far as this most recent approach.

“It gets more complicated as the race tracks are changing shape and size and are rotating, changing their orientation,” Standish explains. “So this place where the two tracks are closest together constantly changes, changing the opposition closeness as well. This is why a ‘great’ approach, like the one this month, hasn?t happened in 60,000 years. But with the tracks closer together now, there will be even closer approaches in the relatively near future.”

Aside from visiting a local observatory, peering through a telescope is the best way to take advantage of this unique opportunity. Since June, Mars has been noticeably bright in the night?s sky, only outshined by Venus and the Moon. Observers in the Northern Hemisphere will see it glowing remarkably in the southern sky in the constellation Aquarius, best seen just before dawn.

“You’re not going to go outside and see some big red ball in the sky. It will look like a bright red star,” said Standish.

The word ‘planet’ is derived from the Greek expression for ?wanderer.? At such a close distance, Mars remains true to this expectation as it consistently wanders across the night?s sky. Tracking the “red star?s” movement from week to week is yet another way to appreciate the opposition as Mars appears to dart across the sky in comparison to more distant planets, such as Jupiter.

Although Mars will be closest on August 27, astronomers suggest viewing the planet earlier, as dust storm season is just beginning on the red planet and can obstruct a more detailed view.

Whether you are viewing through a telescope, glancing through a pair of binoculars, or star-gazing outside the city, be sure to take advantage of this once-in-a-lifetime opportunity, for Mars will not make another neighborly visit this close until 2287.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

New Satellite Image of the Aral Sea

Image credit: ESA

A new image taken by the European Space Agency’s Envisat satellite shows how much the Aral Sea has evaporated. Located in Central Asia, the Aral Sea used to be the fourth largest lake in the world, but rivers that feed the lake were diverted for cotton agriculture. It’s now half its former surface area and one-quarter its original volume and continuing to shrink. The picture was taken using the Medium Resolution Imaging Spectrometer (MERIS) instrument which has a resolution of 300 metres.

Earth?s youngest desert is shown in this July MERIS satellite image of the Aral Sea in Central Asia. Once the fourth largest lake in the world, over the last 40 years the Aral Sea has evaporated back to half its original surface area and a quarter its initial volume, leaving a 40,000 square kilometre zone of dry white-coloured salt terrain now called the Aralkum Desert.

As its water level has dropped 13 metres since the 1960s the Sea has actually split into two ? the larger horseshoe-shaped body of water and a smaller almost unconnected lake a little to its north. This Small Aral Sea is the focus of international preservation efforts, but the Large Aral Sea has been judged beyond saving (the shallowness of its eastern section is clear in the image). It is expected to dry out completely by 2020.

Towards the bottom right can be seen the sands of the Qyzylqum Desert. Already stretching across an area greater than Italy, this desert is set to extend further west in future, eventually merging with its younger Aralkum sibling. The distinctive darker area to the south of the Large Aral Sea is the delta of the Amu Darya river. Its waters support environmentally-unique tugai forests found only in Central Asia, along with land used for rice and cotton cultivation.

The grey area seen in the otherwise whitish zone between the two arms of the Large Aral Sea was once Vozrozhdeniye (‘Rebirth’) Island, the isolated site of biological warfare experimentation during the Cold War, now joined to the mainland and freely accessible by foot. In reaction to this development, a US-led international team last year moved in to destroy remaining anthrax stocks.

Located on the border between Uzbekistan and Kazakhstan, the Aral Sea shows what happens when the concept of sustainable development is disregarded. Starting in the 1960s, the waters of the two rivers feeding the Sea ? the Amu Darya, seen south, and the Syr Darya to the northwest ? were diverted by Soviet planners to irrigate thirsty cotton fields across the region. By the 1980s there was little water reaching the lake and it began to shrink.

For local people the results have been disastrous. The Aral Sea’s retreating shoreline has left ports landlocked and boats stranded on dry sand. Commercial fishing was forced to halt twenty years ago. The few remaining fishermen commute by car to the water’s edge. The waters that remain grow increasingly saline so only salt-resistant fish imported from elsewhere can endure them. Wildlife habitats have been destroyed and communities find themselves without clean water supplies.

The retreat of the waters has also altered the regional microclimate. Winters are colder and the summers hotter. Each year violent sandstorms pick up at least 150,000 tonnes of salt and sand from the dried-up lakebed and transport it across hundreds of kilometres.

The sandstorms are tainted with pesticide residue and have been linked to high regional rates of respiratory illnesses and certain types of cancer. The salty dust does harm to livestock pastures and has even been linked with melting glaciers up in the distant Pamir Mountains, on the Afghanistan border.

Back in the days of the USSR, planners spoke casually of diverting Siberian rivers to save the Aral Sea. Today that certainly will not happen. Instead Central Asian governments have come together to establish the International Fund for Saving the Aral Sea. But their economies are too dependent on cotton exports to end all irrigation.

The Small Aral Sea is still thought to be saveable, and several dikes have been constructed to cut it off from the Large Aral Sea ? preventing water loss and salt contamination – but shifting water levels have so far defeated these efforts. The channel connecting the two should soon dry up anyway, preserving the Small Aral Sea at least. Meanwhile researchers are studying the salty Aralkum Desert ? effectively the newest land surface on Earth ? to see how best to promote plant growth and stabilise the dusty dry lakebed.

Original Source: ESA News Release

Posted on by Fraser Cain

South African Observatory Nearing Completion

Image credit: SALT

The observatory that will house the largest optical telescope in the Southern hemisphere is nearing completion. The Southern African Large Telescope (SALT) is being built by a consortium of six countries at the southern edge of the Kalahari Desert in Africa. The 11-by-10 metre telescope is 18 months away from being done, but the structure of the observatory is nearly complete. The entire project will cost $18 million and be fully operational in late 2004.

A new observatory that promises to give Wisconsin astronomers unique access to the southern sky is now a prominent feature on a remote South African plateau.

The observatory that will house the largest optical telescope in the Southern Hemisphere, known as the Southern African Large Telescope (SALT), is now nearly complete, according to astronomers at UW-Madison. Although the telescope itself is still 18 months from completion, the mirror segments that will make up the 11-by-10-meter hexagonal primary mirror are starting to come together, says Matthew Bershady a UW-Madison professor of astronomy who is helping to oversee planning and construction of the new observatory.

“We are at a point where we have a structure that is nearly completed,” says Bershady of the observatory situated 220 miles from Cape Town on a mountain plateau at the southern end of the Kalahari Desert. “Now, we are starting to populate the (telescope) truss with glass.”

The $18 million SALT Observatory is being built by a consortium of government and academic institutions from six countries. In addition to UW-Madison, Rutgers and Carnegie Mellon universities, Germany’s University of Gottingen, the University of Canterbury in New Zealand, the United Kingdom Consortium, and the governments of Poland and South Africa are partners in the SALT consortium.

UW-Madison’s contribution is a $3 million imaging spectrograph that is being built under the direction of astronomy Professor Kenneth H. Nordsieck. A spectrograph is a device that breaks light down into its constituent wavelengths, each of which has a different story to tell about the star or galaxy from which the light is gathered.

“We’re past the design stage now,” says Nordsieck of the 500-kilogram instrument that will be at the heart of the new observatory. “We’re cutting metal and polishing glass.”

The Wisconsin spectrograph will be the telescope’s primary scientific instrument. Positioned high above the huge segmented mirror at the prime focus of the telescope, the device will be capable of capturing spectra at a rate of 10 times a second.

To explain the importance of spectroscopy to astronomy, one spectrum – in the words of one astronomer – is worth a thousand pictures.

The device, says Nordsieck, will sample light in the near ultraviolet part of the electromagnetic spectrum: “This is light that our eyes can’t see, but it still gets through the atmosphere. It’s the same kind of light that causes sunburn.”

In addition, the spectrograph will be capable of doing polarimetry, measuring how light waves are scattered as they bounce off objects in space and are pushed and pulled by the immense magnetic fields of interstellar space. Polarimetry, Nordsieck says, helps reveal geometric information, giving astronomers insight into how starlight interacts with the objects it encounters.

“We will also have one of the first large Fabry-Perot devices,” he adds. “It is basically a tunable filter” capable of imaging a large part of the sky.

Fittingly, among the system of lenses to be included in the spectrograph will be a set made of sodium chloride – or salt.

Together, the large, segmented primary mirror and the novel scientific instrumentation will position SALT to break plenty of new ground in the southern skies.

“One of the big things this telescope will be tuned for are the Magellanic Clouds,” says Bershady. “They are important because they are the galaxies nearest to our own, and they offer the best opportunity to study stars and galaxies outside of the Milky Way. It’s always a good thing to look outside of your own immediate environment to find out how unique you are, if at all.”

The SALT construction schedule is right on time, Bershady adds. “That we haven’t slipped at all is amazing,” he says. “Our hope is to stay on track for first light in late 2004.”

Original Source: SALT News Release

Posted on by Fraser Cain

Neutron Star Has Twin Tails

Image credit: ESA

Astronomers using the European Space Agency’s XMM-Newton space observatory have discovered a neutron star with two mysterious x-ray tails, stretching out almost a third of a light year. The neutron star is named Geminga, and it’s one of the closest known neutron stars, at a distance of only 500 light-years away. Unlike most neutron stars, Geminga is strangely quiet in the radio spectrum, but pulsates huge quantities of gamma radiation.

Astronomers using ESA?s X-ray observatory, XMM-Newton, have discovered a pair of X-ray tails, stretching 3 million million kilometres across the sky. They emanate from the mysterious neutron star known as Geminga. The discovery gives astronomers new insight into the extraordinary conditions around the neutron star.

A neutron star measures only 20-30 kilometres across and is the dense remnant of an exploded star. Geminga is one of the closest to Earth, at a distance of about 500 light-years. Most neutron stars emit radio emissions, appearing to pulsate like a lighthouse, but Geminga is ‘radio-quiet’. It does, however, emit huge quantities of pulsating gamma rays making it one of the brightest gamma-ray sources in the sky. Geminga is the only example of a successfully identified gamma-ray source from which astronomers have gained significant knowledge.

It is 350 000 years old and ploughs through space at 120 kilometres per second. Its route creates a shockwave that compresses the gas of the interstellar medium and its naturally embedded magnetic field by a factor of four.

Patrizia Caraveo, Instituto di Astrofisica Spaziale e Fisica Cosmica, Milano, Italy, and her colleagues (at CESR, France, ESO and MPE, Germany) have calculated that the tails are produced because highly energetic electrons become trapped in this enhanced magnetic field. As the electrons spiral inside the magnetic field, they emit the X-rays seen by XMM-Newton.

The electrons themselves are created close to the neutron star. Geminga?s breathless rotation rate ? once every quarter of a second ? creates an extraordinary environment in which electrons and positrons, their antimatter counterparts, can be accelerated to extraordinarily high energies. At such energies, they become powerful high-energy gamma-ray producers. Astronomers had assumed that all the electrons would be converted into gamma rays. However, the discovery of the tails proves that some do find escape routes from the maelstrom.

?It is astonishing that such energetic electrons succeed in escaping to create these tails,? says Caraveo, ?The tail electrons have an energy very near to the maximum energy achievable in the environment of Geminga.?

The tails themselves are the bright edges of the three-dimensional shockwave sculpted by Geminga. Such shockwaves are a bit like the wake of a ship travelling across the ocean. Using a computer model, the team has estimated that Geminga is travelling almost directly across our line of sight.

Studies of Geminga could not be more important. The majority of known gamma-ray sources in the Universe have yet to be identified with known classes of celestial objects. Some astronomers believe that a sizeable fraction of them may be Geminga-like radio-quiet neutron stars. Certainly, the family of radio-quiet neutron stars, discovered through their X-ray emission, is continuously growing. Currently, about a dozen objects are known but only Geminga has a pair of tails!

Original Source: ESA News Release

Posted on by Fraser Cain

Galaxy Evolution Explorer Delivers First Images

Image credit: NASA/JPL

Launched in April, 2003, NASA’s Galaxy Evolution Explorer has sent back its first images of star formation in hundreds of galaxies. The goal of the mission is to map the sky in the ultraviolet spectrum and help determine the evolution of star formation over the last 10 billion years – this singles out galaxies that contain young, hot stars which produce a lot of energy in the ultraviolet spectrum. The mission is expected to last 28 months.

NASA?s Galaxy Evolution Explorer has beamed back revealing images of hundreds of galaxies to expectant astronomers, providing the first batch of data on star formation that they had hoped for.

The recent ultraviolet color images from the orbiting space telescope were taken between June 7 and June 23, 2003 and are available online at http://www.galex.caltech.edu and http://photojournal.jpl.nasa.gov/mission/galex.

“The images clearly show active star formation in nearby galaxies, and large numbers of distant ultraviolet galaxies undergoing starbursts,” said Dr. Christopher Martin, the mission’s principal investigator and an astrophysics professor at the California Institute of Technology in Pasadena, which leads the mission. “This demonstrates that the Galaxy Evolution Explorer will be a powerful tool for studying star formation in galaxies near and far.”

“These stunning images provide us with valuable information needed to advance our knowledge of how galaxies, like our own Milky Way, evolve and transform,” said Dr. James Fanson, Galaxy Evolution Explorer project manager at NASA?s Jet Propulsion Laboratory, Pasadena, Calif. “Pictures of the ultraviolet sky reveal objects we could never have seen with visible light alone.”

The Galaxy Evolution Explorer launched on April 28, 2003. Its goal is to map the celestial sky in the ultraviolet and determine the history of star formation in the universe over the last 10 billion years.

From its orbit high above Earth, the spacecraft will sweep the skies for up to 28 months using state-of-the-art ultraviolet detectors. Looking in the ultraviolet singles out galaxies dominated by young, hot, short-lived stars that give off a great deal energy at that wavelength. These galaxies are actively creating stars, therefore providing a window into the history and causes of galactic star formation.

In addition to leading the mission, Caltech is also responsible for science operations and data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and led the science instrument development. The mission is part of NASA’s Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission’s international partners are France and South Korea.

Original Source: NASA News Release

Posted on by Fraser Cain

Astronomers Map Dark Matter Halo

Image credit: Hubble

Two Canadian and a US astronomer have created a detailed map of the halo of dark matter that seems to surround all galaxies. The mass of dark matter accounts for 50 times the mass and five times the size of the light-producing material in a galaxy. This flattened sphere-shaped halo was seen by measuring how the gravity from a closer galaxy bends the light from a distant object that passes behind it; a technique called gravity lensing.

Two U of T astronomers and a U.S. colleague have made the first-ever measurements of the size and shape of massive dark matter halos that surround galaxies.

“Our findings give us the clearest picture yet of a very mysterious part of our universe,” says principal investigator Henk Hoekstra, a
post-doctoral fellow at U of T’s Canadian Institute for Theoretical Astrophysics. “Using relatively simple physics, we can get our first direct glimpse of the size and shape of these halos which are more than fifty times more massive than the light-producing part of galaxies that we can see.” He and his team presented their findings July 25 at the 25th general assembly of the International Astronomical Union in Sydney, Australia.

Their research indicates that dark matter halos extend more than five times further than the visible stars in a galaxy, says Hoekstra. In the case of our Milky Way galaxy, he says, the halo extends to more than 500,000 light-years away and weighs approximately 880 billion times more than the sun. The findings also provide strong support for the popular “cold dark matter” model of the universe.

Dark matter emits no light and, therefore, cannot be seen directly,
Hoekstra explains. The only evidence for its existence comes from its gravitational pull on stars, gas and light rays. Dark matter is believed to account for approximately 25 per cent of the total mass in the universe, with the rest of the universe composed of normal matter (five per cent) and dark energy (70 per cent).

To date, most information about dark matter has come from measurements of the motion of gas and stars in the inner regions of galaxies. Other important data have come from computer simulations of the formation of the universe’s structure. However, scientists can explain their findings about dark matter only if it is true that galaxies are surrounded by massive, three-dimensional halos.

The majority of astronomers believe in the so-called cold dark matter theory of the universe, which suggests these halos are slightly flattened. Hoekstra’s findings corroborate this. Using the relatively new technique of weak gravitational lensing which allows astronomers to study the size and shape of dark matter, the team measured the shapes of more than 1.5 million distant galaxies using the Canada-France-Hawaii Telescope in Hawaii. “The small changes in the shapes of the galaxies offered a strong indication to us that the halos are flattened, like a rubber ball compressed to half its size,” Hoekstra says.

Their findings can also be applied to a larger scientific debate about the nature of the universe. Some scientists have developed theories about the universe using the assumption that dark matter does not exist and, as a result, they have proposed changes to the law of gravity. However, Hoekstra is confident that his team’s findings will refute these theories.

The research was conducted with Professor Howard Yee of U of T’s Department of Astronomy and Astrophysics and Michael Gladders, a former U of T graduate student now at the Observatories of the Carnegie Institution of Washington in Pasadena, Calif. It was funded by the Natural Sciences and Engineering Research Council of Canada and U of T.

Original Source: University of Toronto News Release