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Billion-pixel space camera

Artist's impression of Gaia

Gaia's billion-pixel digital camera will study a billion stars and other objects in our Milky Way galaxy and other galaxies.

  • Gaia mission set for launch in 2013
  • Will carry a billion-pixel digital camera
  • Will map 1 billion stars in the Milky Way

THE LARGEST DIGITAL CAMERA ever built for a space mission has been painstakingly pieced together from 106 separate electronic detectors. The resulting “billion-pixel array” will serve as the super-sensitive ‘eye’ of the European Space Agency’s (ESA) galaxy-mapping Gaia mission.

While the naked human eye can see several thousand stars on a clear night, Gaia will map a billion stars within our Milky Way galaxy and its neighbouring galaxies over the course of its five-year mission from 2013.

It will chart their brightnesses and spectral characteristics along with their three-dimensional positions and motions.

A key step

In order to detect distant stars up to a million times fainter than the eye can see, Gaia will carry 106 charge coupled devices (CCDs)—advanced versions of the chips found within standard digital cameras.

Developed for the mission by e2v Technologies of Chelmsford, UK, these rectangular detectors are a little smaller than a credit card, each one measuring 4.7 x 6cm but thinner than a human hair.

The 50 x 100cm mosaic has been assembled at the Toulouse facility of Gaia prime contractor, Astrium France.

Technicians working on Gaia’s focal plane

A total of 106 CCDs make up Gaia’s focal plane. Technicians from Astrium France are seen attaching and aligning the CCDs onto the support structure.

Technicians spent much of May carefully fitting together each CCD package on the support structure, leaving only a 1mm gap between them. Working in double shifts in strict cleanroom conditions, they added an average four CCDs per day, finally completing their task on June 1.

“The mounting and precise alignment of the 106 CCDs is a key step in the assembly of the flight model focal plane assembly,” said Philippe Garé, ESA’s Gaia payload manager.

A cool view

The completed array is arranged in seven rows of CCDs. The main part comprises 102 detectors dedicated to star detection, while four others will check the image quality of each telescope and the stability of the 106.5º angle between the two telescopes that Gaia will use to obtain stereo views of stars.

In order to increase the sensitivity of its detectors, the spacecraft will maintain their temperature at a chilly –110ºC. The following video shows how Gaia’s heatshield will unfurl to protect it from the Sun:

Gaia’s CCD support structure, like much of the rest of the spacecraft, is made of silicon carbide (SiC )—a ceramic-like material, extraordinarily resistant to deformation under temperature changes.

First synthesised as a diamond substitute, SiC has the advantage of low weight—the entire support structure with its detectors is only 20 kg.

Targets near and far

Scheduled for launch in 2013, Gaia’s three-dimensional star map will help to reveal the composition, formation and evolution of the Milky Way, sampling 1% of our galaxy’s stars.

Gaia will also study large numbers of other celestial bodies, from minor bodies in our own Solar System to more distant galaxies and quasars near the edge of the observable Universe.

Adapted from information issued by ESA. Images courtesy ESA / Astrium / C. Carreau.

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Star Aussie student wins astronomy prize

A nebula and stars

Dying stars return their gas into the interstellar environment, which then becomes the raw material for new generations of stars and planets.

UPDATED 24/05/2011: I’ve added a short Q&A with Barnaby Norris.

MUCH OF THE MATTER that forms new stars and planets—and even our own bodies—is produced in the last gasps of dying, giant stars.

A thesis produced by Barnaby Norris—an astronomy student based within the University of Sydney’s School of Physics—helps answer the longstanding mystery of how these dying stars eject their matter into the galaxy.

For his work, Barnaby has been awarded the 2011 Bok Prize for the Best Honours Thesis in astronomy across all Australian universities.

Barnaby Norris

The judges said Barnaby Norris' thesis was a "clear and deserving winner".

“I am interested in how old stars are recycled to make a new generation of stars, planets and all the matter that makes up the universe,” said Barnaby.

Barnaby, who is now a PhD student at the Sydney Institute for Astronomy based at the University of Sydney, said he was excited to have won the Bok Prize: “This came as a great surprise. Given all the amazing work done by Australian astronomers in this field I feel really honoured to be selected.”

The Bok Prize is awarded annually by the Astronomical Society of Australia to recognise outstanding research in astronomy by an honours student at an Australian university.

It was established to honour Dr Bart Jan Bok, the Director of Mount Stromlo Observatory from 1957 to 1966. Dr Bok energetically promoted the undergraduate and graduate study of astronomy in Australia and set up the Graduate School of Astronomy at the Australian National University.

The prize consists of the Bok Medal together with an award of $500. The recipient is invited to present a paper on their research at the Annual Scientific Meeting of the Astronomical Society of Australia, where the prize will be presented.

SpaceInfo spoke with Barnaby Norris, and asked him about his research:

Can you give us more detail about your research into how stars are ‘recycled’?

I’m studying stars that undergo big pulsations over a year or so, during which they expel a lot of material in the form of a ‘stellar wind’.

Along with supernovae (exploding stars), the gas and dust expelled by these stars is the raw material that goes on to form the next generation of stars. But there has been a big mystery as to how exactly this loss of mass occurs.

It’s known that the mass loss is related to a shell of dust that forms around the star. But it’s incredibly hard to directly observe the dust shells—you’re trying to see this relatively faint detail around a star that is perhaps only 40 milli-arcseconds across (less than a millionth the width of the full Moon).

The research I did was one of the first times these shells of dust have been directly imaged. This led to measurements of the size of the shells and the size of the dust particles that make them up, which can be used in computer models to better understand the mass-loss process.

Bok globule

'Bok globules' are dense clouds of gas and dust, the raw material for a new generation of stars and planets. Courtesy NASA, ESA, and The Hubble Heritage Team STScI/AURA). Acknowledgment: P. McCullough (STScI).

What observations did you do, and what astronomical facilities did you use?

Due to the tiny angular size and high contrast involved, you can’t see the dust shells using regular astronomical imaging—it’s like standing in Sydney looking at a streetlight in Perth, and trying to figure out the species of moth flying around it!

I used a new technique based on a type of interferometry called aperture masking, combined with measurement of the polarisation of the light.

Aperture masking effectively turns a large telescope into lots of smaller telescopes. Combining the images helps you to see fine detail.

The observations were all done using the 8-metre telescope at the Very Large Telescope in Chile. I carried out some of the observations last year, and I also used some data taken by my supervisor and others the previous year.

My supervisors—Peter Tuthill (University of Sydney) and Michael Ireland (Macquarie University)—really pioneered the techniques I used in this study, and contributed immensely to the project.

Bart Bok, after whom the prize is named, was an astronomer who researched dark interstellar clouds (‘Bok globules’) that are involved in star birth and rebirth. Is it a nice touch that your work is in a closely related field?

Yes that is a nice touch. The whole cyclical nature of stellar evolution, from the death of old stars to the birth of new ones, such as in Bok globules, is really fascinating to me.

Finally, what got you into astronomy, and where would you like to go in this field?

I’ve always been fascinated by astronomy, and science in general, but I also love good nerdy stuff like building gadgets and writing computer programs. I could never be a theorist. I love the type of astronomy where you can get your hands dirty—bolt together an instrument in a lab, write some code, and then use it to find out something new!

Adapted from information issued by the University of Sydney. Portrait image courtesy University of Sydney. Hubble image courtesy NASA, ESA, R. O’Connell (University of Virginia), F. Paresce (National Institute for Astrophysics, Bologna, Italy), E. Young (Universities Space Research Association/Ames Research Centre), the WFC3 Science Oversight Committee, and the Hubble Heritage Team (STScI/AURA).

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Aussie astronomers find stellar heavyweights

  • Many huge stars in the Milky Way cannot be seen because of intervening dust
  • University of Sydney team develops method to spot them using X-ray data
  • These giant stars live fast and die young, often in violent explosions

AN ASTRONOMY TEAM at the University of Sydney has used the bright X-ray glow from our galaxy’s most massive stars to find where they are hiding.

There are over 400 million stars in the Milky Way but only a few are truly massive. These stars emits ‘winds’ that flash outwards at over 1,000 kilometres per second and at temperatures of up to 100 million degrees.

The search project—known as “ChIcAGO” (Chasing the Identification of ASCA Galactic Objects)—is lead by Gemma Anderson from the School of Physics.

“ChIcAGO was designed to explore the unidentified X-ray sources detected with the Advanced Satellite for Cosmology and Astrophysics (ASCA), an older generation orbital X-ray telescope,” says Anderson.

Ms Anderson says the massive stars they found can be 50 times heavier than our Sun. But they have very short life spans, and may end in a supernova explosion that produces enough light to outshine the entire galaxy.

“We asked how do we find these rare and distant supernova progenitors, hidden deep in the Milky Way?

“These stars are nearly invisible to traditional optical telescopes, because the dust in … our galaxy absorbs their light,” Anderson explains.

Recent observations with NASA’s Chandra X-ray Observatory have discovered that these massive stars can be some of the brightest sources of X-ray radiation, easily shining through the galactic dust.

The ASCA satellite

The team used data from the ASCA satellite observatory.

Shocking discovery

Taking it a step further, the ChIcAGO project asked what possible process could cause a star to produce such high-energy radiation?

Anderson explains: “When X-ray radiation is detected from an astronomical object it means that [the object is] extremely hot and that particles are being accelerated to speeds near the speed of light.”

In this case the massive stars have winds that blow over 1,000 kilometres per second and are often found in binary star pairs.

“Such systems are known as colliding-wind binaries as the strong winds from these stars collide, creating extremely strong shocks that heat the stellar material to temperatures up to 100 million degrees, resulting it the production of bright and powerful X-rays,” added Anderson.

“The collisions in colliding-wind binaries are some of the most violent in our universe, only surpassed by extreme events like the death of one of these massive stars in a supernova.”

The detection of their X-ray emission is a new way of discovering massive stars that previously eluded discovery in extensive infrared and optical surveys of our galaxy.

“By searching for such high energy X-rays with Chandra we have devised an efficient way of finding the most massive stars in our galaxy,” Anderson says.

In the future, the ChIcAGO project is aiming to discover the identity of other massive stars in colliding-wind binaries, as well as their supernova remnants, allowing us the explore the life, death and evolution of these stellar giants in the Milky Way.

Other involved in the work include Bryan Gaensler (University of Sydney), David Kaplan (University of Wisconsin, Milwaukee), Bettina Posselt, Patrick Slane and Stephen Murray (Harvard-Smithsonian Center for Astrophysics, or CfA), Jon Mauerhan (California Institute of Technology), Robert Benjamin (University of Wisconsin, Whitewater), Crystal Brogan (National Radio Astronomy Observatory), Deepto Chakrabarty (Massachusetts Institute of Technology), Jeremy Drake (CfA), Janet Drew (University of Hertfordshire), Jonathan Grindlay and Jaesub Hong (CfA), Joseph Lazio (Naval Research Laboratory), Julia Lee (CfA), Danny Steeghs (University of Warwick), and Marten van Kerkwijk (University of Toronto).

The results have been published in The Astrophysical Journal.

Adapted from information issued by the University of Sydney. Images courtesy NASA / ESA.

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New way to find alien planets

Artist's concept of a red dwarf star and three planets

This artist's concept shows a young, red dwarf star circled by three planets. Such small, dim stars could be ideal targets for astronomers wishing to take images of exoplanets.

  • Planets circling bright stars are hard to see because of the stars’ glare
  • Those that circle dimmer stars could be much easier to image
  • So the hunt is on to find candidate nearby, small, dim stars

ASTRONOMERS HAVE A NEW WAY to identify close, faint stars with NASA’s Galaxy Evolution Explorer satellite.

The technique should help in the hunt for planets that lie beyond our Solar System, because nearby, hard-to-see stars could very well be home to the easiest-to-see alien planets.

The glare of bright, shining stars has frustrated most efforts at visualising distant worlds. So far, only a handful of distant planets, or exoplanets, have been directly imaged.

Small, newborn stars are less blinding, making potential orbiting planets easier to see, but the fact that these stars are dim means they are hard to find in the first place.

Fortunately, young stars emit more ultraviolet light than their older counterparts, which makes them conspicuous to the ultraviolet-detecting Galaxy Evolution Explorer.

“We’ve discovered a new technique of using ultraviolet light to search for young, low-mass stars near the Earth,” said David Rodriguez, a graduate student of astronomy at UCLA, and lead author of a recent study. “These young stars make excellent targets for future direct imaging of exoplanets.”

Artist's impression of GALEX

NASA's Galaxy Evolution Explorer could be pressed into service to find faint stars that are home to planets.

Tantrum-throwing baby stars

Young stars, like human children, tend to be a bit unruly — they spout a greater proportion of energetic X-rays and ultraviolet light than more mature stars.

In some cases, X-ray surveys can pick out these youngsters due to the “racket” they cause.

However, many smaller, less “noisy” baby stars perfect for exoplanet imaging studies have gone undetected except in the most detailed X-ray surveys. To date, such surveys have covered only a small percentage of the sky.

Rodriguez and his team figured the Galaxy Evolution Explorer, which has scanned about three- quarters of the sky in ultraviolet light, could fill this gap. They compared readings from the telescope with optical and infrared data to look for the telltale signature of rambunctious junior stars.

Follow-up observations of 24 candidates identified in this manner determined that 17 of the stars showed clear signs of youth, validating the team’s approach.

Cool, red, and in the neighbourhood

Astronomers call the low-mass stars in question “M-class” stars. Also known as red dwarfs, these stars glow a relatively cool crimson colour compared to the hotter oranges and yellows of stars like our Sun, and the whites and blues of the most scorching stars.

In many ways, these stars represent a best-case scenario for the direct imaging of exoplanets. They are close and in clear lines-of-sight, which generally makes viewing easier. Their low mass means they are dimmer than heavier stars, so their light is less likely to mask the feeble light of a planet.

AB Pictoris and companion

The star AB Pictoris (with most of its glare blocked out) has a tiny companion that is either a brown dwarf star or a massive planet. This is one of only a handful of planet candidates to have its image taken.

And because they are young stars, their planets are freshly formed, and thus warmer and brighter than older planetary bodies.

The better to see planets with

So far, only a handful of the more than 500 exoplanets on record have actually been “seen” by our ground- and space-based telescopes. The vast majority of foreign worlds have instead turned up via indirect detection methods.

At a very basic level, directly imaging an exoplanet is worthwhile because, after all, “seeing is believing,” Rodriguez said.

As for actually imaging clouds or surface features of exoplanets, however, that will have to wait. Current images of exoplanets, while full of information, resemble fuzzy dots. But as technology advances, ever more information about our close-by planetary brethren will emerge.

The new study was published in the February issue of The Astrophysical Journal and includes co-authors Mike Bessell (Australian National University), Ben Zuckerman (UCLA), and Joel Kastner (Rochester Institute of Technology).

Adapted from information issued by JPL. Images courtesy of NASA / JPL-Caltech / ESO.

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Hungry black holes shred stars

Artist's conception of black holes about to merge

In this artist's conception, two black holes are about to merge. When they combine, gravitational wave radiation will "kick" the new, bigger black hole like a rocket engine, sending it rampaging through nearby stars.

A GALAXY’S CORE IS A BUSY PLACE, crowded with stars swarming around an enormous black hole. When galaxies collide (as they sometimes do), it gets even messier as the galaxies’ black holes spiral toward each other, merging to form an even bigger gravitational monster.

Once it is formed, the monster goes on a rampage, zooming into the surrounding starfields. There it finds a hearty meal, shredding and swallowing stars at a rapid rate.

According to new research by Nick Stone and Avi Loeb (Harvard-Smithsonian Centre for Astrophysics), upcoming sky surveys might offer astronomers a way to catch one of these gorging black holes “in the act.”

Before the merger, as the two black holes whirl around each other, they stir the galactic centre like the blades of a blender. Their strong gravity warps space, sending out ripples known as gravitational waves.

When the black holes merge, they emit gravitational waves more strongly in one direction. That inequality kicks the new black hole into motion in the opposite direction like a rocket engine.

“That kick is very important. It can shove the black hole toward stars that otherwise would have been at a safe distance,” said Stone.

“Essentially, the black hole can go from starving to enjoying an all-you-can-eat buffet,” he added.

Spotting a dying star

When tidal forces rip a star apart, its remains spiral around the black hole, smashing and rubbing together, heating up enough to shine in the ultraviolet or X-rays. This region immediately surrounding the black hole will glow as brightly as an exploding star, or supernova, before gradually fading in a distinctive way.

Artist's conception of the Laser Interferometer Space Antenna

Artist's conception of the Laser Interferometer Space Antenna, a trio of spacecraft that should be able to pick up gravitational waves from merging black holes.

Importantly, a wandering, supermassive black hole is expected to swallow many more stars than a black hole in an undisrupted galactic centre.

A stationary black hole disrupts one star every 100,000 years. But in the best-case scenario, a wandering black hole could disrupt a star every decade.

Astronomers would have a much better change of spotting the latter events, particularly with new survey facilities like Pan-STARRS and the Large Synoptic Survey Telescope.

The siren call of gravity

Catching the dying scream from a disrupted star is a good start. However, astronomers really want to combine that information with gravitational wave data from the black hole merger.

The Laser Interferometer Space Antenna (LISA), a future mission designed to detect and study gravitational waves, could provide that data.

Gravitational wave measurements can potentially yield very accurate distance measurements (to better than one part in a hundred, or 1 percent) to the scene of the black hole crime. However, they won’t be able to provide precise sky direction co-ordinates.

Spotting a star’s tidal disruption will let astronomers pinpoint the galaxy containing the recently merged black-hole binary, thus providing the direction.

By correlating the host galaxy’s redshift (a change in its light caused by the expanding universe) with an accurate distance, astronomers can infer the ‘equation of state’ of dark energy.

In other words, they can learn more about the force that’s accelerating cosmic expansion, and which dominates the cosmic mass/energy budget today.

“Instead of ‘standard candles’ like supernovae, the black hole binary would be a ‘standard siren.’ Using it, we could create the most accurate cosmic ‘ruler’ possible,” stated Loeb.

Adapted from information issued by CfA. Black hole artwork by David A. Aguilar (CfA).

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Updated census of Sun-like stars

Artist's impression of a star like our Sun

Artist's impression of a star like our Sun with an orbiting planet in the foreground. The Kepler mission is studying such stars by tracking changes in their brightness.

  • Kepler is a space observatory that measures star brightnesses
  • Brightness oscillations reveal secrets of stars’ sizes, ages and composition

USING NASA’S KEPLER SPACE TELESCOPE, scientists have detected changes in brightness in 500 Sun-like stars, giving a much better idea about the nature and evolution of the stars.

Prior to Kepler’s launch in March 2009, astronomers had identified changes in brightness, or oscillations, of only about 25 stars similar to our Sun in size, age, composition and location within the Milky Way galaxy.

Although Kepler’s primary job is to find Earth-like planets that might be able to support life, it also provides a big boost to ‘asteroseismology’…the study of stars by measuring their natural oscillations.

Those oscillations provide clues about star basics such as mass, radius and age, as well as clues about their internal structure.

“This helps us understand more about the formation of stars and how they evolve,” said Steve Kawaler, an Iowa State University professor of physics and astronomy, a co-author of the research paper and a leader of the Kepler Asteroseismic Investigation.

“These new observations allow us to measure the detailed properties of stars at an accuracy that wasn’t possible before.”

Kepler is orbiting the Sun carrying a photometer, or light meter, to measure changes in star brightnesses. The photometer includes a telescope 94cm in diameter connected to a 95-megapixel CCD camera.

Artist's impression of the Kepler spacecraft

Artist's impression of the Kepler spacecraft

The instrument is pointed at the Cygnus-Lyra region of the Milky Way. It is expected to continuously observe about 170,000 stars for at least three and a half years.

Golden age for star studies

The Kepler Asteroseismic Investigation is using Kepler data to study different kinds of stars.

Kepler has provided astronomers with so much new information, the scientists say they’re “entering a golden era for stellar physics.”

Data from the 500 Sun-like stars gives astronomers a much better understanding of the stars, their properties and their evolution. It also gives astronomers data to test their theories, models and predictions about the stars and the galaxy. And it gives astronomers enough data to make meaningful statistical studies of the stars.

“But this is just the start of things,” Kawaler said. “This is a first broad-brush analysis of the data we’ve seen. This is a preview of this new tool and the kind of detailed census that we’ll be able to do.”

Among the projects to come are studies to determine the ages of all these Sun-like stars, and studies of the host stars of the Earth-like planets.

The investigation is led by a four-member steering committee: Kawaler, Chair Ron Gilliland of the Space Telescope Science Institute based in Baltimore, Jorgen Christensen-Dalsgaard and Hans Kjeldsen, both of Aarhus University in Denmark.

Adapted from information issued by Iowa State University. Illustration by Gabriel Perez Diaz, Instituto de Aastrofisica de Canarias (MultiMedia Service). Kepler illustration courtesy NASA.

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Diamond stars in a sea of colour

R136

R136 is a group of young, hot, massive stars in the 30 Doradus Nebula in the Large Magellanic Cloud, a galaxy close to our Milky Way.

THIS MASSIVE, YOUNG STELLAR grouping, called R136, is only a few million years old and resides in the 30 Doradus Nebula, a turbulent star-birth region in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way.

Many of the diamond-like icy blue stars are among the most massive stars known. Several of them are over 100 times more massive than our Sun. These hefty stars are destined to pop off, like a string of firecrackers, as supernovae in a few million years.

The image, made from exposures in ultraviolet, visible, and red light by Hubble’s Wide Field Camera 3, spans about 100 light-years.

Despite being in another galaxy, the nebula is close enough to Earth that Hubble can resolve individual stars, giving astronomers important information about the stars’ birth and evolution. There is no known star-forming region in our galaxy as large or as prolific as 30 Doradus.

The brilliant stars are carving deep cavities in the surrounding material by unleashing a torrent of ultraviolet light, and hurricane-force stellar winds (streams of charged particles), which are etching away the enveloping hydrogen gas cloud in which the stars were born.

The image reveals a fantasy landscape of pillars, ridges, and valleys, as well as a dark region in the centre. The brilliant stars can also help create a successive generation of offspring—when the winds hit dense walls of gas, they create shockwaves, which compress the gas and potentially triggers a new wave of star birth.

The cluster is a rare example of the many super star clusters that formed in the distant, early universe, when star birth and galaxy interactions were more frequent. Previous Hubble observations have shown astronomers that super star clusters in faraway galaxies are common.

The LMC is located 170,000 light-years away and is a member of the Local Group of Galaxies, which also includes the Milky Way.

The Hubble observations were taken October 20-27, 2009. The blue colour is light from the hottest, most massive stars; the green from the glow of oxygen; and the red from fluorescing hydrogen.

Full-size image suitable for screen wallpaper (1280 x 1280 pixels)

Adapted from information issued by NASA, ESA, and F. Paresce (INAF-IASF, Bologna, Italy), R. O’Connell (University of Virginia, Charlottesville), and the Wide Field Camera 3 Science Oversight Committee.

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Aquarius younger by billions of years

Stars in the Milky way

Astronomers have identified a massive swarm of stars within the Milky Way, now known as the Aquarius Stream, that seem to be the remains of a smaller, external galaxy that was destroyed by the Milky Way's gravitational pull.

AN INTERNATIONAL TEAM of astronomers has discovered a new stream of stars in our Milky Way, thanks to data collected at the ANU Siding Spring Observatory.

The research, led by Dr Mary Williams from the Astrophysical Institute Potsdam (AIP), is part of the Radial Velocity Experiment (RAVE) and used data from Siding Spring to measure the velocities of 250,000 stars.

The new ‘Aquarius Stream’ is named after the constellation of Aquarius in which it resides. The stream of stars is a remnant of a smaller galaxy in our cosmic neighbourhood, which was pulled apart by the gravitational pull of the Milky Way about 700 million years ago.

Dr Mary Williams, a former graduate student of the Research School of Astronomy and Astrophysics at ANU, said the Aquarius Stream was particularly hard to find, located deep within the Milky Way where it was indistinguishable from the huge quantity of stars blocking our view of it.

Aquarius Stream map

Astronomers have identified a massive swarm of stars within the Milky Way, now known as the Aquarius Stream, that seem to be the remains of a smaller, external galaxy that was destroyed by the Milky Way's gravitational pull.

“It was right on our doorstep, but we just couldn’t see it,” said Dr Williams.

Dr Williams used the RAVE data to draw conclusions about the formation of the Milky Way.  She said that by astronomical standards, the 700-million-year-old Aquarius stream is exceptionally young. Other known streams of stars located on the outskirts of our galaxy are billions of years old.

Professor Matthias Steinmetz, project leader of the multinational RAVE collaboration at AIP said he is optimistic the method used by Dr Williams and her team will lead to many more discoveries of this kind.

“We want to understand the formation history of our Milky Way,” he said. “We want to find out how frequently constellations have merged with neighbouring galaxies in the past, and how many we are to expect in the future.”

While much about the galaxy surrounding our planet Earth remains unknown, astronomers are certain about one thing—the Milky Way’s next huge collision will be with the Andromeda galaxy. This cosmic collision is predicted to take place in about three billion years—unless one of the dwarf galaxies discovered over the past few years beats Andromeda to it.

This video shows a highly speeded up computer simulation of the collision between the Milky Way and Andromeda. See what happens to the shape of the Milky Way following the collision:

RAVE is a multinational project, involving scientists from Australia, Germany, France, UK, Italy, Canada, the Netherlands, Switzerland, Slovenia and the USA.

Adapted from information issued by ANU. Images courtesy ANU and Hubble Heritage Team (AURA / STScI / NASA / ESA).

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Hubble looks 10,000 years into the future

  • Hubble studies stars in the Omega Centauri cluster
  • Measures stellar motions over a period of four years
  • Data used to predict future motion of the stars

Astronomers are used to looking millions of years into the past. Now scientists have used the NASA/ESA Hubble Space Telescope to look thousands of years into the future.

Looking at the heart of Omega Centauri, a globular cluster in the Milky Way, they have calculated how the stars there will move over the next 10,000 years.

The globular star cluster Omega Centauri has caught the attention of sky watchers ever since the early astronomer Ptolemy first catalogued it 2,000 years ago. Ptolemy thought Omega Centauri was a single star and probably wouldn’t have imagined that his “star” was actually a beehive swarm of nearly 10 million stars, all orbiting a common centre of gravity.

The stars are so tightly crammed together in the cluster that astronomers had to wait for the Hubble Space Telescope before they could look deep into the core of the “beehive” and resolve the individual stars.

Hubble’s vision is so sharp that it can even measure the motion of many of these stars, and over a relatively short span of time.

A precise measurement of star motions in giant clusters can yield insights into how such stellar groupings formed in the early Universe, and whether an intermediate-mass black hole, one roughly 10,000 times as massive as our Sun, might be lurking among the stars.

Diagram showing projected movement of stars in Omega Centauri

Hubble's multi-colour snapshot (top) of the central region of the giant globular cluster Omega Centauri. The lower illustration charts the future positions of the stars highlighted by the white box in the top image. Each streak represents the motion of the stars over the next 600 years.

Razor-sharp vision the key

Analysing archived images taken over a four-year period by Hubble’s Advanced Camera for Surveys, astronomers have made the most accurate measurements yet of the motions of more than 100,000 cluster inhabitants, the largest survey to date to study the movement of stars in any cluster.

“It takes sophisticated computer programs to measure the tiny shifts in the positions of the stars that occur over a period of just four years,” says astronomer Jay Anderson of the Space Telescope Science Institute in Baltimore, USA, who conducted the study with fellow Institute astronomer Roeland van der Marel.

“Ultimately, though, it is Hubble’s razor-sharp vision that is the key to our ability to measure stellar motions in this cluster.”

Van der Marel adds: “With Hubble, you can wait three or four years and detect the motions of the stars more accurately than if you were using a ground-based telescope and were waiting 50 years.”

The astronomers used the Hubble images, which were taken in 2002 and 2006, to make a movie simulation of the frenzied motion of the cluster’s stars. The movie shows the stars’ projected migration over the next 10,000 years.

Identified as a globular star cluster in 1867, Omega Centauri is one of roughly 150 such clusters in the Milky Way. The behemoth stellar grouping is the biggest and brightest globular cluster in the Milky Way, and one of the few that can be seen by the unaided eye.

Located in the constellation of Centaurus, Omega Centauri can be seen in the southern skies.

Adapted from information issued by NASA / ESA / J. Anderson & R. van der Marel (STScI).

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“Super stars” uncovered

Artist's impression of the relative sizes of young stars

This artist's impression shows the relative sizes of young stars, from the smallest ones called "red dwarfs", with about 0.1 solar masses, through low mass "yellow dwarfs" such as the Sun and massive "blue dwarf' stars with more than 8 times the mass of the Sun, to the newly-discovered 300 solar mass star R136a1.

  • Stars found with 100+ times more mass than the Sun
  • Stellar record now stands at 320 solar masses
  • Did they form large, or did smaller stars merge?

“Super stars” born with hundreds of times the mass of our Sun, have been spotted in star clusters within our galaxy and in a neighbouring galaxy.

One of the stars, at birth, would have had over 300 times the mass of the Sun.

The UK-led team of astronomers studied two young star clusters—NGC 3603, located 22,000 light-years from Earth within our Milky Way galaxy; and R136a, located 165,000 light-years away in the Large Magellanic Cloud, a satellite galaxy of the Milky Way.

Both clusters are “star factories” where stars have formed from clouds of gas and dust.

The discovery of the giant stars might help solve a long-standing puzzle in astronomy—just how massive can stars become, and how do they get to be so massive?

Note that by “massive” the astronomers are not referring to the stars’ physical size—although the new “super stars” certainly are very large. Rather, they’re referring to how much mass they contain.

The team used archived data from the Hubble Space Telescope, plus new observations obtained with the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile.

The Tarantula Nebula (left) and star cluster R136a (right)

A region of the Large Magellanic Cloud galaxy seen with the Very Large Telescope (left), as well as a new image of the R136 cluster obtained with the MAD adaptive optics instrument on the Very Large Telescope (right). R136a contains the most massive star found so far.

Several of the stars studied have surface temperatures in excess of 40,000 degrees Celsius, which is almost 8 times hotter than the Sun. The stars are also tens of times bigger and millions of times brighter.

Computer models suggest that stars like these must have started off with masses greater than 150 times the mass of the Sun.

Stellar heavyweight champion

The heavyweight champion, in the RMC 136a cluster, is a star called R136a1. It is the most massive star known, with a current mass around 265 times that of the Sun. At birth, it must have been over 320 solar masses.

Young star cluster R136a

R136 is a cluster of young, massive and hot stars located inside one of the Milky Way's neighbouring galaxies, the Large Magellanic Cloud, 165,000 light-years away.

These kinds of hot, huge stars lose a lot of their mass by blowing off “winds” into space.

“Unlike humans, these stars are born heavy and lose weight as they age,” says astronomer Paul Crowther. “Being a little over a million years old, the most extreme star R136a1 is already ‘middle-aged’ and has undergone an intense weight loss programme, shedding a fifth of its initial mass over that time, or more than fifty solar masses.”

Two of the heavyweight stars in the NGC 3603 cluster are in orbit around each, a double star system. Using simple physics laws, the astronomers could calculate their masses at 120 and 92 times that of the Sun. At birth, they would have been 148 and 106 solar masses respectively.

Woking out how such huge stars formed in the first place is a major challenge for astronomers.

“Either they were born so big or smaller stars merged together to produce them,” says Crowther.

Story by Jonathan Nally, Editor, SpaceInfo.com.au

Images courtesy ESO / P. Crowther / C.J. Evans / M. Kornmesser.

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