RSSArchive for January, 2011

Galaxy at the edge of time

Portion of the Hubble Ultra Deep Field

The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope. This is the deepest infrared image taken of the universe. Based on the object's colour, astronomers believe it is 13.2 billion light-years away.

  • Using Hubble data, team spots galaxy with redshift of 10.3
  • We’re seeing it as it was 13.2 billion years ago

Astronomers studying ultra-deep imaging data from the Hubble Space Telescope have found what may be the most distant galaxy ever seen, about 13.2 billion light-years away.

The study pushed the limits of Hubble’s capabilities, extending its reach back to about 480 million years after the Big Bang, when the universe was just 4 percent of its current age.

“We’re getting back very close to the first galaxies, which we think formed around 200 to 300 million years after the Big Bang,” said Garth Illingworth, professor of astronomy and astrophysics at the University of California, Santa Cruz.

Illingworth and UCSC astronomer Rychard Bouwens (now at Leiden University in the Netherlands) led the study, which has been published in the January 27 issue of Nature.

Rapid build-up of galaxies

Using infrared data gathered by Hubble’s Wide Field Planetary Camera 3 (WFC3), they were able to see dramatic changes in galaxies over a period from about 480 to 650 million years after the Big Bang.

The rate of star birth in the universe increased by ten times during this 170-million-year period, Illingworth said.

“This is an astonishing increase in such a short period, just 1 percent of the current age of the universe,” he said.

There were also striking changes in the numbers of galaxies detected.

“Our previous searches had found 47 galaxies at somewhat later times when the universe was about 650 million years old. However, we could only find one galaxy candidate just 170 million years earlier,” Illingworth said. “The universe was changing very quickly in a short amount of time.”

According to Bouwens, these findings are consistent with the hierarchical picture of galaxy formation, in which galaxies grew and merged under the gravitational influence of dark matter.

“We see a very rapid build-up of galaxies around this time,” he said. “For the first time now, we can make realistic statements about how the galaxy population changed during this period and provide meaningful constraints for models of galaxy formation.”

Here’s a NASA video with some comments from Garth Illingworth:

Remarkable redshift

Astronomers gauge the distance of an object from its redshift, a measure of how much the expansion of space has stretched the light from an object to longer (“redder”) wavelengths.

The newly detected galaxy has a likely redshift value (“z”) of 10.3, which corresponds to an object that emitted the light we now see 13.2 billion years ago, just 480 million years after the birth of the universe.

“This result is on the edge of our capabilities, but we spent months doing tests to confirm it, so we now feel pretty confident,” Illingworth said.

The galaxy, a faint smudge of starlight in the Hubble images, is tiny compared to the massive galaxies seen in the local universe. Our own Milky Way, for example, is more than 100 times larger.

The researchers also described three other galaxies with redshifts greater than 8.3. The study involved a thorough search of data collected from deep imaging of the Hubble Ultra Deep Field (HUDF), a small patch of sky about one-tenth the size of the Moon.

During two four-day stretches in summer 2009 and summer 2010, Hubble focused on one tiny spot in the HUDF for a total exposure of 87 hours with the WFC3 infrared camera.

Graph showing ability of different telescopes to look increasingly deeper back into time

Timeline of time: Over the years, improvements in technology have enabled astronomers to use their telescopes to peer further and further back into time. The forthcoming James Webb Space Telescope will be able to see even further.

Next step? Hubble’s successor

To go beyond redshift 10, astronomers will have to wait for Hubble’s successor, the James Webb Space Telescope (JWST), which NASA plans to launch later this decade. JWST will also be able to perform the spectroscopic measurements needed to confirm the reported galaxy at redshift 10.

“It’s going to take JWST to do more work at higher redshifts. This study at least tells us that there are objects around at redshift 10 and that the first galaxies must have formed earlier than that,” Illingworth said.

Illingworth’s team maintains the First Galaxies website, with information about the latest research on distant galaxies: http://firstgalaxies.org/

In addition to Bouwens and Illingworth, the co-authors of the Nature paper include Ivo Labbe of Carnegie Observatories; Pascal Oesch of UCSC and the Institute for Astronomy in Zurich; Michele Trenti of the University of Colorado; Marcella Carollo of the Institute for Astronomy; Pieter van Dokkum of Yale University; Marijn Franx of Leiden University; Massimo Stiavelli and Larry Bradley of the Space Telescope Science Institute; and Valentino Gonzalez and Daniel Magee of UC Santa Cruz.

The research was supported by NASA and the Swiss National Science Foundation.

Adapted from information issued by UCSC. Images credit: NASA, ESA, Garth Illingworth (UC Santa Cruz), Rychard Bouwens (UC Santa Cruz and Leiden University) and the HUDF09 Team / A. Feild (STScI).

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Recycled spacecraft to revisit comet

An artist's impression of Stardust NExT approaching comet Tempel 1.

The Stardust NExT spacecraft will fly past comet Tempel 1 on February 15 (Sydney time) at a distance of only 200 kilometres.

NASA’S STARDUST NEXT SPACECRAFT is nearing a celestial date with comet Tempel 1 at approximately 3:37pm on February 15, Sydney time (11:37pm US EST on Feb 14). The mission will enable scientists for the first time to look for changes on a comet’s surface that occurred following an orbit around the Sun.

The Stardust-NExT, or New Exploration of Tempel, spacecraft will take high-resolution images during the encounter, and attempt to measure the composition, distribution, and flux of dust emitted into the coma…the cloud of material surrounding the comet’s core.

Data from the mission will provide important new information on how certain types of comets evolved and formed.

The mission will expand the investigation of the comet initiated by NASA’s Deep Impact mission. In July 2005, the Deep Impact spacecraft sent an impactor into the surface of Tempel 1 to study its composition. The Stardust spacecraft may capture an image of the crater formed by the impactor. This would be a bonus to the huge amount of data that mission scientists expect to obtain.

Here’s a short video of the result of Deep Impact’s impactor hitting Tempel 1:

“Every day we are getting closer and closer and more and more excited about answering some fundamental questions about comets,” said Joe Veverka, Stardust-NExT principal investigator at Cornell University.

“Going back for another look at Tempel 1 will provide new insights on how comets work and how they were put together four-and-a-half billion years ago.”

Close encounter of the comet kind

At approximately 336 million kilometres away from Earth, Stardust-NExT will be almost on the exact opposite side of the Solar System at the time of the encounter. (As of January 20, the spacecraft was approximately 24.6 million kilometres away from its encounter.) During the flyby, the spacecraft will take 72 images and store them in an onboard computer.

Initial raw images from the flyby will be sent to Earth for processing that will begin at approximately 7:00pm Sydney time on February 15. Images are expected to be made public 90 minutes later.

Since 2007, Stardust-NExT executed eight flight path correction manoeuvres, logged four circuits around the Sun and used one Earth gravity assist to meet up with Tempel 1.

Tempel 1 impact blast

The blast produced when an impactor released by the Deep Impact spacecraft, hit comet Tempel 1 in 2005. Scientist's hope Stardust NExT will give them a close-up look at the blast crater.

Another three manoeuvres are planned to refine the spacecraft’s path to the comet. Tempel 1’s orbit takes it as close in to the Sun as the orbit of Mars and almost as far away as the orbit of Jupiter. The spacecraft is expected to fly past the nearly 6-kilometre-wide comet at a distance of approximately 200 kilometres.

Running on empty

In 2004, Stardust became the first mission to collect particles directly from comet Wild 2, as well as interstellar dust. Samples were returned in 2006 for study via a capsule that detached from the spacecraft and parachuted to the ground southwest of Salt Lake City.

Mission controllers placed the still viable Stardust spacecraft on a trajectory that could potentially reuse the system if a target of opportunity presented itself.

In January 2007, NASA re-christened the mission Stardust-NExT and began a four-and-a-half year journey to comet Tempel 1.

“You could say our spacecraft is a seasoned veteran of cometary campaigns,” said Tim Larson, project manager for Stardust-NExT at NASA’s Jet Propulsion Laboratory.

“It’s been half-way to Jupiter, executed picture-perfect flybys of an asteroid and a comet, collected cometary material for return to Earth, then headed back out into the void again, where we asked it to go head-to-head with a second comet nucleus.”

The mission team expects this fly-by to write the final chapter of the spacecraft’s success-filled story. The spacecraft is nearly out of fuel as it approaches 12 years of space travel, logging almost 6 billion kilometres since launch in 1999.

This fly-by and planned post-encounter imaging are expected to consume the remaining fuel.

Adapted from information issued by NASA Jet Propulsion Laboratory.

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Moon’s core values

The Moon

New analysis of Apollo mission seismometer data has revealed similarities between the Earth and Moon's cores.

  • Moon long assumed to have a core, but its nature remained a mystery
  • New analysis of old Apollo-era seismic data reveals the core’s nature
  • Future space missions will provide even greater certainty

STATE-OF-THE-ART seismological techniques applied to Apollo-era data suggest our Moon has a core similar to Earth’s.

Uncovering details about the lunar core is critical for developing accurate models of the Moon’s formation. The data sheds light on the evolution of a lunar dynamo—a natural process by which our Moon may have generated and maintained its own strong magnetic field.

The team’s findings suggest the Moon possesses a solid, iron-rich inner core with a radius of nearly 240 kilometres and a fluid, primarily liquid-iron outer core with a radius of roughly 330 kilometres.

Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 480 kilometres.

The research indicates the core contains a small percentage of light elements such as sulphur, echoing new seismology research on Earth that suggests the presence of light element

Passive Seismic Experiment deployed on the Moon

A close-up view of the Passive Seismic Experiment, deployed on the Moon by the Apollo 14 astronauts.

s—such as sulphur and oxygen—in a layer around our own core.

New use for old data

The researchers used extensive data gathered during the Apollo-era Moon missions. The Apollo Passive Seismic Experiment consisted of four seismometers deployed between 1969 and 1972, which recorded continuous lunar seismic activity until late-1977.

“We applied tried and true methodologies from terrestrial seismology to this legacy data set to present the first-ever direct detection of the Moon’s core,” said Renee Weber, lead researcher and space scientist at NASA’s Marshall Space Flight Centre.

In addition to Weber, the team consisted of scientists from Marshall; Arizona State University; the University of California at Santa Cruz; and the Institut de Physique du Globe de Paris in France.

The team also analysed Apollo lunar seismograms using array processing, techniques that identify and distinguish signal sources of moonquakes and other seismic activity.

The researchers identified how and where seismic waves passed through or were reflected by elements of the Moon’s interior, signifying the composition and state of layer interfaces at varying depths.

Disagreements

Although sophisticated satellite imaging missions to the Moon made significant contributions to the study of its history and topography, the deep interior of Earth’s sole natural satellite remained a subject of speculation and conjecture since the Apollo era.

Artist's rendering of the lunar core

An artist's rendering of the lunar core, as identified in new findings by a NASA-led research team.

Researchers previously had inferred the existence of a core, based on indirect estimates of the Moon’s interior properties, but many disagreed about its radius, state and composition.

A primary limitation to past lunar seismic studies was the wash of “noise” caused by overlapping signals bouncing repeatedly off structures in the Moon’s fractionated crust.

To mitigate this challenge, Weber and the team employed an approach called seismogram stacking, or the digital partitioning of signals. Stacking improved the signal-to-noise ratio and enabled the researchers to more clearly track the path and behaviour of each unique signal as it passed through the lunar interior.

“We hope to continue working with the Apollo seismic data to further refine our estimates of core properties and characterise lunar signals as clearly as possible to aid in the interpretation of data returned from future missions,” Weber said.

Twin spacecraft to study Moon

Future NASA missions will help gather more detailed data. The Gravity Recovery and Interior Laboratory, or GRAIL, is a NASA Discovery-class mission set to launch this year. The mission consists of twin spacecraft that will enter tandem orbits around the Moon for several months to measure the gravity field in unprecedented detail.

The mission also will answer longstanding questions about the Moon and provide scientists a better understanding of the satellite from crust to core, revealing subsurface structures and, indirectly, its thermal history.

NASA and other space agencies have been studying concepts to establish an International Lunar Network—a robotic set of geophysical monitoring stations on the Moon—as part of efforts to co-ordinate international missions during the coming decade.

Adapted from information issued by NASA / MSFC / JSC / Renee Weber.

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Mars’ moon seen close-up

Mars Express image of Phobos

The larger of Mars' two moons, Phobos, as seen in a newly returned image from Europe's Mars Express spacecraft. The image has been enhanced to illuminate darker areas. The resolution is 4.1 metres per pixel.

MARS EXPRESS HAS RETURNED images from its close fly-by of one of Mars’ moons, Phobos, on January 9, 2011. The European Space Agency (ESA) spacecraft zipped past the moon at a distance of only 100 kilometres.

Phobos is the larger and closer of the two moons of Mars, the other being Deimos. Both moons were discovered in 1877. With a mean radius of 11.1 km, Phobos is 7.24 times as massive as Deimos. It is named after the Greek god Phobos (which means “fear”), a son of Ares (Mars).

A small, irregularly shaped body, Phobos orbits about 9,377 km from the centre of Mars, closer to its planet than any other known planetary moon. It orbits so close to the planet that it moves around Mars faster than Mars itself rotates. As a result, from the surface of Mars it appears to rise in the west, move rapidly across the sky (in 4 h 15 min or less) and set in the east.

Phobos’ orbital radius is decreasing, and it will eventually either impact the surface of Mars or break up into a planetary ring.

Phobos is one of the least-reflective bodies in the Solar System, and features a large impact crater, Stickney crater.

Here’s a video of Phobos compiled from images taken by Mars Express and NASA’s Viking spacecraft.

Keeping an eye on Mars

Mars Express is Europe’s first planetary mission. At launch, the mission consisted of an orbiter carrying seven instruments for remote sensing observations of the planet, and a lander (Beagle 2) for on-the-spot measurements of Martian rock and soil.

While approaching Mars on 19 December 2003, Beagle 2 was released and started its 6-day journey to the planet’s surface. However, the attempts to communicate with it on 25 December 2003, the date of its expected touchdown, were not successful. The Beagle 2 mission was declared lost on 6 February 2004. In contrast, the Mars Express orbiter started science observations as planned in January 2004, and since then it has been delivering an incredible amount of scientific results.

The ‘Express’ part of the name highlights the fact that the spacecraft was built more quickly than any other comparable planetary mission. In fact, it took only five years from mission approval to launch.

In addition to global studies of the surface, subsurface and atmosphere of Mars with unprecedented spatial and spectral resolution, the unifying theme of the Mars Express mission from orbit is the search for water in its various states, everywhere on the planet by all its seven instruments using different techniques.

Artist's concept of the Fobos-Grunt mission

Artist's concept of the Russian Fobos-Grunt mission, due for launch later this year.

The mission was originally planned for one Martian year (687 days). It has already been extended three times, and is now funded for operations until the end of 2012.

Russia to try again with Mars mission

Fobos-Grunt (meaning “Phobos Ground”) is a planned unmanned Russian “sample return” mission to Phobos. (The Chinese Mars orbiter Yinghuo-1 will be piggyback with the mission.) Scheduled for launch late 2011 or early 2012, Fobos-Grunt will be the first Russian interplanetary mission since the failed Mars 96 mission.

If successful, this will be the first large extraterrestrial sample from a planetary body brought back to Earth since the last sample return mission by Luna 24 in 1976. (The Japanese Hayabusa probe has returned with a sample from 25143 Itokawa in June 2010, but the sample only consisted of some particles of dust.)

Fobos-Grunt will also study Mars from orbit, including its atmosphere and dust storms, plasma and radiation. It is currently scheduled to be launched in November 201.

The journey to Mars is scheduled to take about ten months. The spacecraft will then spend several months studying the planet and its moons from orbit, before landing on Phobos. The current timeline is for arrival in October 2012 and landing in February 2013.

Immediately after the touchdown, the lander will load a soil sample into a return rocket. In case of a breakdown of communications with mission control, it can enter an emergency mode to collect samples and still send them home in the return rocket. Normal collection could last from two days to a week.

Mars Express image of Phobos

Image of Phobos with a resolution of 8.2 metres per pixel. The ellipses mark the spots previously planned (red) and currently considered (blue) as landing sites for the Russian Fobos-Grunt mission.

The robotic arm can collect rocks up to about half an inch in diameter. It ends in a pipe-shaped tool that splits to form a claw. This encloses a piston that will push the soil sample into an artillery-shell-shaped container. A light-sensitive photo-diode in the claw will help scientists confirm that the device did scoop material. They hope also to see images of trenches the claw leaves on the surface. The manipulator should perform 15 to 20 scoops yielding a total of 85 to 160 g of soil.

The return rocket will sit atop the spacecraft, and will need to rise at 35 km/h to escape Phobos’ gravity on the return journey. To protect experiments remaining on the lander, springs will vault the rocket to a safe height, at which its engines will fire and begin manoeuvres for the eventual trip to Earth.

The lander’s experiments will continue in-situ on Phobos’ surface for a year.

Adapted from information issued by ESA / DLR / FU Berlin (G. Neukum) / http://en.wikipedia.org/wiki/Phobos-Grunt.

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Uranus fly-by – 25 years ago today

True- and false-colour images of Uranus

Two views of Uranus—one in true colour (left) and the other in false colour—were compiled from images returned Jan. 17, 1986, by the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million kilometres from the planet, and several days from closest approach.

AS NASA’S VOYAGER 2 spacecraft made the only close approach to date of our mysterious seventh planet Uranus 25 years ago, Project Scientist Ed Stone and the Voyager team gathered at NASA’s Jet Propulsion Laboratory, Pasadena, California, to pore over the data coming in.

Images of the small, icy Uranus moon Miranda were particularly surprising. Since small moons tend to cool and freeze over rapidly after their formation, scientists had expected a boring, ancient surface, pockmarked by crater-upon-weathered-crater.

Instead they saw grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda’s surface in the past.

Surface of Miranda

A section of the surface of Miranda, innermost of Uranus' large satellites, as seen by Voyager 2 from 36,000 kilometres away. A complex topography of high and low terrain, craters and scarps can be seen.

The scientists were also shocked by data showing that Uranus’s magnetic north and south poles were not closely aligned with the north-south axis of the planet’s rotation. Instead, the planet’s magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet’s interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.

“Voyager 2’s visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the solar system with Earth,” said Stone, who is based at the California Institute of Technology in Pasadena. “Even though similar in many ways, the worlds we encounter can still surprise us.”

Here’s NASA’s pre-encounter video from the 1980s, showing how Voyager 2 sped past the planet while collecting its data:

A host of new discoveries

Voyager 2 was launched on August 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometres away from the Sun. Voyager 2 made its closest approach—within 81,500 kilometres of the Uranian cloud tops—on January 24, 1986.

Before Voyager 2’s visit, scientists had to learn about Uranus by using Earth-based and airborne telescopes. By observing dips in starlight as a star passed behind Uranus, scientists knew Uranus had nine narrow rings.

But it wasn’t until the Voyager 2 flyby that scientists were able to capture for the first time images of the rings and the tiny shepherding moons that sculpted them. Unlike Saturn’s icy rings, they found Uranus’ rings to be dark grey, reflecting only a few percent of the incident sunlight.

Voyager image of Uranus' rings and two moons

Voyager 2 discovered two "shepherd" moons associated with Uranus' thin rings.

Scientists had also determined an average temperature for Uranus—minus 214 degrees Celsius—before this encounter, but the distribution of that temperature came as a surprise. Voyager showed there was heat transport from pole to pole in Uranus’ atmosphere that maintained the same temperature at both poles, even though the Sun was shining directly for decades on one pole and not the other.

By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.

Interstellar mission

Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometres away from the Sun.

Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometres away from the Sun.

“The Uranus encounter was one of a kind,” said Suzanne Dodd, Voyager project manager, based at JPL. “Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune.”

“Currently both Voyager spacecraft are on the cusp of leaving the Sun’s sphere of influence and once again blazing a trail of scientific discovery.”

The Voyagers were built by NASA’s Jet Propulsion Laboratory in Pasadena, California, which continues to operate both spacecraft.

Link: More information about the Voyager spacecraft

Adapted from information issued by NASA Jet Propulsion Laboratory.

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Make your own planet!

Screenshot from NASA's Extreme Planet Makeover site

Screenshot from NASA's Extreme Planet Makeover site

The new “Extreme Planet Makeover” page on the NASA/JPL PlanetQuest site lets you roll up your sleeves and create your very own planet.

Balance five factors to create an Earth-like habitable world, or get wild and make your own extreme exoplanet. Use the Image Gallery feature to compare your creation with those of other Earthlings. Once you’ve finished creating the exoplanet of your dreams, download a picture of your custom world for posterity.

Link: Extreme Planet Makeover

New view of Orion

Orion Nebula

A new image of the Orion Nebula, a huge gas cloud in which new stars are being born.

THIS ETHERAL-LOOKING IMAGE of the Orion Nebula was captured using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile.

This nebula is much more than just a pretty face, offering astronomers a close-up view of a massive star-forming region to help advance our understanding of stellar birth and evolution.

The Orion Nebula, also known as Messier 42, is one of the most easily recognisable and best-studied celestial objects. It is a huge complex of gas and dust where massive stars are forming and is the closest such region to the Earth.

The glowing gas is so bright that it can be seen with the unaided eye and is a fascinating sight through a telescope.

Despite its familiarity and closeness, there is still much to learn about the Orion Nebula. It was only in 2007, for instance, that it was shown to be closer to us than previously thought—1,350 light-years, rather than about 1,500 light-years.

See a wallpaper-size version of the image here.

ESO 2.2m telescope

The MPG/ESO 2.2-metre telescope

A winning image

The data used to produce the image were selected by Igor Chekalin from Russia, who participated in ESO’s Hidden Treasures 2010 astrophotography competition.

Igor’s composition of the Orion Nebula was the seventh highest ranked entry in the competition, although another of Igor’s images was the eventual overall winner.

The Hidden Treasures competition gave amateur astronomers the opportunity to search through ESO’s vast archives of astronomical data, hoping to find a well-hidden gem that needed “polishing”.

Participants submitted nearly 100 entries and ten skilled people were awarded some extremely attractive prizes, including an all-expenses-paid trip for the overall winner to ESO’s Very Large Telescope (VLT) on Cerro Paranal in Chile.

Igor searched through ESO’s archive and identified datasets that he used to compose the image of Messier 42.

He also was awarded the first prize of the competition for his composition of Messier 78, and he also submitted an image of NGC3169, NGC3166 and SN 2003cg, which was ranked second highest.

Igor’s Orion Nebula image is a composite of several exposures taken through a total of five different filters. Light that passed through a red filter as well as light from a filter that shows the glowing hydrogen gas, were coloured red. Light in the yellow–green part of the spectrum is coloured green, blue light is coloured blue and light that passed through an ultraviolet filter has been coloured purple. The exposure times were about 52 minutes through each filter.

Adapted from information issued by ESO and Igor Chekalin.

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Birth and death in Andromeda

M31 Andromeda galaxy

The Andromeda Galaxy, seen at several wavelengths to reveal different stages of the stellar life cycle. Infrared shows reservoirs of gas in which stars are forming. Optical shows adult stars. X-rays show the violent endpoints of stellar evolution, in which individual stars explode or pairs of stars pull each other to pieces.

  • Andromeda Galaxy is the nearest large spiral galaxy
  • Contains a strange dust ring 75,000 light-years wide
  • Infrared and X-ray views show stars forming and dying

TWO SPACE TELESCOPES have combined forces to show the Andromeda Galaxy in a new light.

Using data from the European Space Agency’s (ESA) Herschel and XMM-Newton telescopes, the image shows the light of newborn stars and X-ray emission from dying stars.

Andromeda, also known as M31, is the nearest large spiral galaxy and is similar to our own Milky Way. Both contain several hundred billion stars.

Herschel was used to produce the most detailed far-infrared image of Andromeda ever taken, showing clearly that more stars are being added to the galaxy.

Sensitive to far-infrared light, Herschel sees the clouds of cool dust and gas where stars can form. Inside these clouds are many dusty cocoons containing still-forming stars, each one pulling itself together in a slow gravitational process that can last for hundreds of millions of years.

Once a star reaches a high enough density, it will begin to shine at optical wavelengths, whereupon it will become visible to normal telescopes.

Andromeda is interesting because it shows a large ring of dust about 75,000 light-years wide encircling the centre of the galaxy. Some astronomers speculate that this ring might be a “scar” that formed after a recent collision with another galaxy.

Herschel space telescope

Artist's impression of the Herschel space telescope

The new Herschel image reveals yet more intricate details, with at least five concentric rings of star-forming dust apparent.

X-rays of stellar corpses

Superimposed on the infrared image is an X-ray view taken almost simultaneously by XMM-Newton. Whereas infrared shows the beginnings of star formation, X-rays usually show the endpoints of stellar evolution.

XMM-Newton highlights hundreds of X-ray sources within Andromeda, many of them clustered around the centre, where stars are more crowded together.

Some of the X-ray sources reveal shockwaves rolling through space from exploded stars. Others indicate pairs of stars locked in a gravitational fight to the death.

In the latter case, one star has already died and is pulling gas from its still-living companion. As the gas falls through space, it heats up and gives off X-rays.

The living star will eventually be greatly depleted, having had much of its mass torn from it by the stronger gravity of its denser partner. As the stellar corpse wraps itself in this stolen gas, it could explode.

Both the infrared and X-ray images show information that is impossible to collect from the ground because these wavelengths are absorbed by Earth’s atmosphere.

Adapted from information issued by ESA. Image credits: Infrared, ESA / Herschel / PACS / SPIRE /J. Fritz, U. Gent; X-rays, ESA / XMM-Newton / EPIC / W. Pietsch, MPE; optical, R. Gendler.

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Crab’s candle starts to flicker

  • Crab Nebula is 6,500 light-years from Earth
  • It is the remains of an exploded star (a supernova)
  • Now shown to unexpectedly vary its energy output

DATA FROM SEVERAL NASA satellites has astonished astronomers by revealing unexpected changes in X-ray emission from the Crab Nebula, once thought to be the steadiest high-energy source in the sky.

“For 40 years, most astronomers regarded the Crab as a standard candle,” said Colleen Wilson-Hodge, an astrophysicist at NASA’s Marshall Space Flight Centre, who presented the findings recently at the American Astronomical Society meeting in Seattle.

“Now, for the first time, we’re clearly seeing how much our candle flickers.”

The Crab Nebula is the wreckage of an exploded star whose light reached Earth in 1054. Located 6,500 light-years away, it is one of the most studied objects in the sky.

At the heart of the expanding gas cloud lies what’s left of the original star’s core, a superdense neutron star that spins 30 times a second. All of the Crab’s high-energy emissions are thought to be the result of physical processes that tap into this rapid spin.

For decades, astronomers have regarded the Crab’s X-ray emissions as so stable that they’ve used it to calibrate space-borne instruments. They also customarily describe the emissions of other high-energy sources in “millicrabs,” a unit derived from the nebula’s output.

Crab Nebula

This view of the Crab Nebula comes from the Hubble Space Telescope and spans 12 light-years. The supernova remnant, located 6,500 light-years away, is among the best-studied objects in the sky. Image courtesy NASA / ESA / ASU / J. Hester.

“The Crab Nebula is a cornerstone of high-energy astrophysics,” said team member Mike Cherry at Louisiana State University (LSU), “and this study shows us that our foundation is slightly askew.”

Satellite tag teams

The story unfolded when Cherry and Gary Case, also at LSU, first noticed the Crab’s dimming in observations by the Gamma-ray Burst Monitor (GBM) aboard NASA’s Fermi Gamma-ray Space Telescope.

The team then analysed GBM observations of the object from August 2008 to July 2010 and found an unexpected but steady decline of several percent at four different “hard” X-ray energies.

With the Crab’s apparent constancy well established, the scientists needed to prove that the fadeout was real and was not an instrumental problem associated with the GBM.

“If only one satellite instrument had reported this, no one would have believed it,” Wilson-Hodge said.

Graph showing multi-wavelength observations of the Crab Nebula

Data from four satellites show that the Crab Nebula's energy output has varied. Powerful gamma-ray flares (pink vertical lines) have been detected as well. Graph courtesy NASA Goddard Space Flight Centre.

So the team amassed data from the fleet of sensitive X-ray observatories now in orbit—NASA’s Rossi X-Ray Timing Explorer (RXTE) and Swift satellites and the European Space Agency’s International Gamma-Ray Astrophysics Laboratory (INTEGRAL).

The results confirm a real intensity decline of about 7 percent at certain energy ranges. They also show that the Crab has brightened and faded by as much as 3.5 percent a year since 1999.

The scientists say that astronomers will need to find new ways to calibrate instruments in flight and to explore the possible effects of the inconstant Crab on past findings.

Showing some flare

Fermi’s other instrument, the Large Area Telescope, has detected unprecedented gamma-ray flares from the Crab, showing that it is also surprisingly variable at much higher energies.

The nebula’s power comes from the central neutron star, which is also a pulsar that emits fast, regular radio and X-ray pulses. This pulsed emission exhibits no changes associated with the decline, so it cannot be the source.

Instead, researchers suspect that the long-term changes probably occur in the nebula’s central light-year, but observations with future telescopes will be needed to know for sure.

Adapted from information issued by NASA MSFC.

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Space museum for Australia

Advanced Instrumentation and Technology Centre

Mount Stromlo's Advanced Instrumentation and Technology Centre (AITC), one of the new facilities built in the wake of the 2003 bushfires. It will soon be joined by a new space and astronomy museum built in partnership with the Smithsonian Institution. Image courtesy ANU.

THE SIGNING OF AN AGREEMENT overnight in Washington DC between the Smithsonian’s National Air and Space Museum and The Australian National University represents a giant leap forward for efforts to build a national astronomy and space science museum at Mount Stromlo.

ANU Vice-Chancellor Professor Ian Chubb AC and National Air and Space Museum Director General John ‘Jack’ Dailey signed the agreement. It sets out the first steps for co-operation that will support the development of a museum to tell the story of Australia’s contribution to space science and space technologies, and celebrate the special role Australian astronomers have played in the exploration of the cosmos.

The signing comes as the University prepares to celebrate the 100th anniversary of the iconic Mount Stromlo Observatory and will see a number of key curatorial staff from Washington come to Canberra in coming months to take part in a planning conference for the proposed museum.

“The National Air and Space Museum in Washington DC is one of the great science museums of the world. We want to build a museum that will inspire our young people, melding science, art, culture and history—and growing our already close relationship with the Smithsonian Institution will ensure that we create something wonderful for Australia,” Professor Chubb said.

Mount Stromlo bushfires

An aerial view of part of Mount Stromlo on fire during the 2003 bushfires. Image by Ray Brown.

Mount Stromlo Observatory was almost completely destroyed by the terrible 2003 bushfires that ravaged Canberra and surrounding regions. The ANU has been rebuilding the facility.

Professor Chubb said the museum would draw on the long history of co-operation between the United States and Australia in astronomy and space science, and the Smithsonian Institution has always been part of that cooperation.

“The Smithsonian Institution has been linked to Canberra since 1907, when Smithsonian Secretary Walcott provided expert advice on the establishment of the Commonwealth Solar Observatory at Mount Stromlo. The observatory was designed so that it would complement the research of Smithsonian astronomers in the Northern Hemisphere,” Professor Chubb said.

“In the 1990s a joint ANU-Harvard-Smithsonian Centre for Astrophysics (CfA) research team discovered the acceleration of the universal expansion of the Universe, one of the major mysteries of modern science. And both the ANU and the Smithsonian are foundation partners in the billion-dollar Giant Magellan Telescope, which will push the boundaries of science.”

“A museum on Mount Stromlo, which is an active hub of leading edge international astronomy and space research, will ensure that we inspire future generations of young Australians to look to the skies.”

Adapted from information issued by ANU.

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