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Asteroids are pounding a pulsar

SCIENTISTS USING CSIRO’s Parkes telescope and another telescope in South Africa have found evidence that a tiny star called PSR J0738-4042 is being pounded by asteroids – large lumps of rock in space.

“One of these rocks seems to have had a mass of about a billion tons,” CSIRO astronomer and member of the research team Dr Ryan Shannon said.

PSR J0738-4042 lies 37,000 light-years from Earth in the constellation of Puppis. The environment around the star is especially harsh, full of radiation and violent winds of particles.

“If a large rocky object can form here, planets could form around any star. That’s exciting,” Dr Shannon said.

The star is a special one, a ‘pulsar’ that emits a beam of radio waves. As it spins, its radio beam flashes over Earth again and again with the regularity of a clock.

An artist's impression of an asteroid breaking up

An artist’s impression of an asteroid breaking up. Credit: NASA/JPL-Caltech

Formed from shattered remains

In 2008 Dr Shannon and a colleague predicted how an infalling asteroid would affect a pulsar. It would, they said, alter the slowing of the pulsar’s spin rate and the shape of the radio pulse that we see on Earth.

“That is exactly what we see in this case,” Dr Shannon said. “We think the pulsar’s radio beam zaps the asteroid, vaporising it. But the vaporised particles are electrically charged and they slightly alter the process that creates the pulsar’s beam.”

Asteroids circling a pulsar could have been formed by the remains of the exploding star that produced the pulsar itself, the scientists say. The material blasted out from the explosion could fall back towards the pulsar, developing into a swirling cloud of dusty debris that circles it. Astronomers call it a ‘disc’.

Not the only one

Astronomers have found a dust disc around another pulsar called J0146+61.

Parkes radio telescope

The CSIRO’s Parkes radio telescope. Photo courtesy Shaun Amy.

“This sort of dust disc could provide the ‘seeds’ that grow into larger asteroids,” said Paul Brook, a PhD student co-supervised by the University of Oxford and CSIRO who led the study of PSR J0738-4042.

In 1992 two planet-sized objects were found around a pulsar called PSR 1257+12. But these were probably formed by a different mechanism, the astronomers say.

The new study has been published in The Astrophysical Journal Letters, a leading journal of astronomical research.

Adapted from information issued by CSIRO.

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The ‘missing link’ pulsar

AN INTERNATIONAL TEAM of astronomers using CSIRO radio telescopes in Australia and other ground and space-based instruments, has caught a small star called a pulsar undergoing a radical transformation, described in a paper in the journal Nature.

“For the first time we see both X-rays and extremely fast radio pulses from the one pulsar. This is the first direct evidence of a pulsar changing from one kind of object into another – like a caterpillar turning into a butterfly,” said Dr Simon Johnston, Head of Astrophysics at CSIRO’s Astronomy and Space Science division.

The pulsar and its companion star

The pulsar and its companion star. The ageing pulsar rotates slower and slower, then matter from its companion spins it up again. As the pulsar is spun up, it alternates between emitting X-rays (white) and radio waves (pink). Credit: ESA

The cosmic drama is being played out 18,000 light-years away, in a small cluster of stars (called M28) in the constellation of Sagittarius.

The pulsar (called PSR J1824-2452I) has a tiny companion star, with about a fifth the mass of the Sun. Although small, the companion is fierce, pounding the pulsar with streams of matter.

Normally the pulsar shields itself from this onslaught, its magnetic field deflecting the matter stream into space.

But sometimes the stream swells to a flood, overwhelming the pulsar’s protective ‘force field.’ When the stream hits the pulsar’s surface its energy is released as blasts of X-rays.

Eventually the torrent slackens. Once again the pulsar’s magnetic field re-asserts itself and fends off the companion’s attacks.

“We’ve been fortunate enough to see all stages of this process, with a range of ground and space telescopes. We’ve been looking for such evidence for more than a decade,” said Dr Alessandro Papitto, the paper’s lead author. Dr Papitto is an astronomer of the Institute of Space Studies (ICE, CSIC-IEEC) of Barcelona, Spain.

‘Teenage’ behaviour

The pulsar and its companion form what is called a ‘low-mass X-ray binary’ system. In such a system, the matter transferred from the companion lights up the pulsar in X-rays and makes it spin faster and faster, until it becomes a ‘millisecond pulsar’ that spins at hundreds of times a second and emits radio waves. The process takes about a billion years, astronomers think.

In its current state the pulsar is exhibiting behaviour typical of both kinds of systems: millisecond X-ray pulses when the companion is flooding the pulsar with matter, and radio pulses when it is not.

“It’s like a teenager who switches between acting like a child and acting like an adult,” said Mr. John Sarkissian, who observed the system with CSIRO’s 64-m (210-ft) Parkes radio telescope in eastern Australia.

“Interestingly, the pulsar swings back and forth between its two states in just a matter of weeks.”

This video shows an artist’s impression of the pulsar and its companion star. Credit: ESA

A global effort

The pulsar was initially detected as an X-ray source with the INTEGRAL satellite. X-ray pulsations were seen with another satellite, ESA’s XMM-Newton; further observations were made with NASA’s Swift. NASA’s Chandra X-ray telescope got a precise position for the object.

Then, crucially, the object was checked against the pulsar catalogue generated by CSIRO’s Australia Telescope National Facility, and other pulsar observations. This established that it had already been identified as a radio pulsar.

The source was detected in the radio with CSIRO’s Australia Telescope Compact Array, and then re-observed with CSIRO’s Parkes radio telescope, NRAO’s Robert C. Byrd Green Bank Telescope in the USA, and the Westerbork Synthesis Radio Telescope in The Netherlands. Pulses were detected in a number of these later observations, showing that the pulsar had ‘revived’ as a normal radio pulsar only a couple of weeks after the last detection of the X-rays.

The astronomers involved in these investigations work at institutions in Australia, Canada, Germany Italy, The Netherlands, Spain, Switzerland, and the USA.

Adapted from information issued by CSIRO.

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Astronomers spy on galaxies in the raw

A CSIRO RADIO TELESCOPE has detected the raw material for making the first stars in galaxies that formed when the Universe was just three billion years old – less than a quarter of its current age. This opens the way to studying how these early galaxies make their first stars.

The telescope is CSIRO’s Australia Telescope Compact Array telescope near Narrabri, NSW. “It one of very few telescopes in the world that can do such difficult work, because it is both extremely sensitive and can receive radio waves of the right wavelengths,” says CSIRO astronomer Professor Ron Ekers.

The raw material for making stars is cold molecular hydrogen gas, called H2. It can’t be detected directly but its presence is revealed by a ‘tracer’ gas, carbon monoxide (CO), which emits radio waves.

The Spiderweb

In one project, astronomer Dr Bjorn Emonts (CSIRO Astronomy and Space Science) and his colleagues used the Compact Array to study a massive, distant conglomerate of star-forming ‘clumps’ or ‘proto-galaxies’ that are in the process of coming together as a single massive galaxy. This structure, called the Spiderweb, lies more than ten thousand million light-years away (at a redshift of 2.16).

The Spiderweb, imaged by the Hubble Space Telescope

MAIN IMAGE: The Spiderweb, imaged by the Hubble Space Telescope – a central galaxy (MRC 1138-262) surrounded by hundreds of other star-forming ‘clumps’. (Credit: NASA, ESA, George Miley and Roderik Overzier, Leiden Observatory.) INSET: In blue, the carbon monoxide gas detected in and around the Spiderweb. (Credit: B. Emonts et al, CSIRO/ATCA)

Dr Emonts’ team found that the Spiderweb contains at least sixty thousand million  times the mass of the Sun in molecular hydrogen gas, spread over a distance of almost a quarter of a million light-years. This must be the fuel for the star-formation that has been seen across the Spiderweb. “Indeed, it is enough to keep stars forming for at least another 40 million years,” says Dr Emonts.

Magnifying lens

In a second set of studies, Dr Manuel Aravena (European Southern Observatory) and colleagues measured CO, and therefore H2, in two very distant galaxies (at a redshift of 2.7).

The faint radio waves from these galaxies were amplified by the gravitational fields of other galaxies – ones that lie between us and the distant galaxies. This process, called gravitational lensing, “acts like a magnifying lens and allows us to see even more distant objects than the Spiderweb,” says Dr Aravena.

Dr Aravena’s team was able to measure the amount of H2 in both galaxies they studied. For one of the galaxies (called SPT-S 053816-5030.8), they could also use the radio emission to make an estimate of how rapidly the galaxy is forming stars – an estimate independent of the other ways astronomers measure this rate.

Antennae of CSIRO's Compact Array telescope

Dishes of the CSIRO’s Australia Telescope Compact Array near Narrabri in New South Wales. Photo: David Smyth

Upgraded telescope

The Compact Array’s ability to detect CO is due to an upgrade that has boosted its bandwidth – the amount of radio spectrum it can see at any one time – sixteen-fold (from 256 MHz to 4 GHz), and made it far more sensitive.

“The Compact Array complements the new ALMA telescope in Chile, which looks for the higher-frequency transitions of CO,” says Ron Ekers.

Adapted from information issued by CSIRO.

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Telescope takes universe’s temperature

Australia Telescope Compact Array

CSIRO’s Australia Telescope Compact Array, used the make the temperature measurements.

ASTRONOMERS USING a CSIRO radio telescope have taken the universe’s temperature, and have found that it has cooled down just the way the Big Bang theory predicts.

Using the Australia Telescope Compact Array near Narrabri, NSW, an international team from Sweden, France, Germany and Australia has measured how warm the universe was when it was half its current age.

“This is the most precise measurement ever made of how the universe has cooled down during its 13.77 billion year history,” said Dr Robert Braun, Chief Scientist at CSIRO Astronomy and Space Science.

Because light takes time to travel, when we look out into space we see the universe as it was in the past – as it was when light left the galaxies we are looking at. So to look back halfway into the universe’s history, we need to look halfway across the universe.

Cosmic fingerprint

How can we measure a temperature at such a great distance?

Illustration of radio waves coming from a distant quasar through a galaxy in the foreground and then on to Earth.

Radio waves from a distant quasar pass through another galaxy on their way to Earth. Changes in the radio waves indicate the temperature of the gas in that galaxy.

The astronomers studied gas in an unnamed galaxy 7.2 billion light-years away (at a redshift of 0.89).

The only thing keeping this gas warm is the cosmic background radiation – the glow left over from the Big Bang.

By chance, there is another powerful galaxy, a quasar (called PKS 1830-211), lying behind the unnamed galaxy.

Radio waves from this quasar come through the gas of the foreground galaxy. As they do so, the gas molecules absorb some of the energy of the radio waves. This leaves a distinctive ‘fingerprint’ on the radio waves.

From this ‘fingerprint’ the astronomers calculated the gas’s temperature. They found it to be 5.08 Kelvin (-267.92 degrees Celsius): extremely cold, but still warmer than today’s universe, which is at 2.73 Kelvin (-270.27 degrees Celsius).

Exactly as predicted

According to the Big Bang theory, the temperature of the cosmic background radiation drops smoothly as the universe expands.

“That’s just what we see in our measurements,” said research team leader Dr. Sebastien Muller of Onsala Space Observatory at Chalmers University of Technology in Sweden. “The universe of a few billion years ago was a few degrees warmer than it is now, exactly as the Big Bang theory predicts.”

Adapted from information issued by CSIRO. Images David Smyth and Onsala Space Observatory.

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Australian dish charts where stars are born

The Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is the nearest sizeable galaxy to our Milky Way, and is therefore a popular target for astronomers studying the evolution of stars.

ASTRONOMERS HAVE MAPPED in detail the star-forming regions of the nearest star-forming galaxy to our own, a step toward understanding the conditions surrounding star creation.

The researchers, led by University of Illinois astronomy professor Tony Wong—and including Associate Professor Sarah Maddison and PhD student Annie Hughes, both of the Swinburne University of Technology in Melbourne, Australia—have published their findings in the December issue of the Astrophysical Journal Supplement Series.

The Large Magellanic Cloud (LMC) is a popular galaxy among astronomers both for its nearness to our Milky Way and for the spectacular view it provides, a big-picture vista impossible to capture of our own galaxy.

“If you imagine a galaxy being a disc, the LMC is tilted almost face-on so we can look down on it, which gives us a very clear view of what’s going on inside,” Wong said.

Mopra dish

CSIRO's 22-metre-diameter Mopra radio telescope, located near Coonabarabran in NSW.

As the LMC is in the far southern sky, it is an ideal target for Australian telescopes. And indeed, the team used the CSIRO’s 22-metre-diameter radio telescope at Mopra, near Coonabarabran in north-central New South Wales.

Where are stars born?

Although astronomers have a working theory of how individual stars form, they know very little about what triggers the process or the conditions in space that are optimal for star birth.

Wong’s team focused on areas called molecular clouds, which are dense patches of gas—primarily molecular hydrogen—where stars are born. By studying these clouds and their relationship to new stars in the galaxy, the team hoped to learn more about how gas clouds turn into stars.

Using the Mopra dish, the astronomers mapped more than 100 molecular clouds in the LMC and estimated their sizes and masses, identifying regions with ample material for making stars. This seemingly simple task engendered a surprising find.

Conventional wisdom states that most of the molecular gas in a galaxy is apportioned to a few large clouds. However, Wong’s team found many more low-mass clouds than they expected—so many, in fact, that a majority of the dense gas may be sprinkled across the galaxy in these small molecular clouds, rather than clumped together in a few large blobs.

MAGMA image of the LMC

False-colour image of the Large Magellanic Cloud galaxy combining maps of neutral atomic hydrogen gas (red), hydrogen energised by nearby young stars (blue), and new data from Wong’s team which roughly show the locations of dense clouds of molecular hydrogen (green). It's thought that stars form within molecular hydrogen clouds.

Star formation widespread in the LMC galaxy

The large numbers of these relatively low-mass clouds means that star-forming conditions in the LMC may be relatively widespread and easy to achieve.

To better understand the connection between molecular clouds and star formation, the team compared their molecular cloud maps to maps of infrared radiation, which reveal where young stars are heating cosmic dust.

“It turns out that there’s actually very nice correspondence between these young massive stars and molecular clouds,” Wong said.

“We can say with great confidence that these clouds are where the stars form, but we are still trying to figure out why they have the properties they do,” he added.

Adapted from information issued by University of Illinois at Urbana-Champaign. Mopra photo courtesy CSIRO. MAGMA image of LMC courtesy Tony Wong, University of Illinois.

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Aussie astronomer wins top prize

Artist's impression of a pulsar

2011 Young Tall Poppy of the Year for NSW award recipient, Dr George Hobbs of the CSIRO, uses observations of pulsars (artist's impression) in the hunt for gravitational waves.

CSIRO ASTRONOMER Dr George Hobbs has become the 2011 Young Tall Poppy of the Year for NSW.

The award was presented at the Powerhouse Museum in Sydney on Thursday 3 November. Dr Hobbs was chosen from a field of eleven Young Tall Poppies to receive the top honour.

The Young Tall Poppy Science Awards, given each year by the Australian Institute of Policy and Science, recognise excellent early career research and passion in communication and community engagement.

Dr Hobbs, based in Sydney at CSIRO Astronomy and Space Science, works on pulsars—small stars with regular clock-like radio signals.

Dr George Hobbs

Dr George Hobbs

He leads a program on CSIRO’s Parkes radio telescope to search for gravitational waves, using pulsars as markers.

“Gravitational waves are ripples in spacetime,” Dr Hobbs said. “Einstein predicted them but they’ve never been observed directly.”

“Of course, we hope to be the first to do this.”

Engaging the next generation

Dr Hobbs is also a key scientist in an outreach program called PULSE@Parkes, which allows students to control the Parkes telescope over the internet and use it to observe pulsars.

CSIRO will use the experience of PULSE@Parkes to develop remote-observing education programs for the Australian SKA Pathfinder radio telescope it is now building in WA.

The Parkes radio telescope

The Parkes radio telescope

At a recent PULSE@Parkes session, students had the thrill of seeing a pulsar turn its signal on and off while they watched: a very rare phenomenon, occurring in just a handful of the 2000-odd known pulsars.

“Then I and the other scientist stood in front of the students and offered quite different ideas about why this might be happening,” Dr Hobbs said.

“They were seeing real science in action.”

In addition to these activities, Dr Hobbs also finds time to do other ground-breaking science, including a fundamental discovery about how pulsars work.

This year he was also named by the Chinese Academy of Sciences as an International Young Scientist of China, for his collaborative work with institutions in Xi’an, Urumqi and Beijing.

And what car does 34-year-old Dr Hobbs drive? A Nissan Pulsar, of course.

Adapted from information issued by CSIRO. Images courtesy David McClenaghan (CSIRO) and NASA.

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Milky Way galaxy is a ‘snake pit’

CSIRO's Australia Telescope Compact Array

CSIRO's Australia Telescope Compact Array was used to make a map of galactic gas polarisation.

A PIT OF WRITHING SNAKES. That’s what the first picture of turbulent gas inside our Milky Way galaxy looks like.

Professor Bryan Gaensler of the University of Sydney, Australia, and his team used a CSIRO radio telescope in eastern Australia to make the ground-breaking image, published in the journal Nature today.

The space between the stars in our Galaxy is not empty, but is filled with thin gas that continually swirls and churns.

“This is the first time anyone has been able to make a picture of this interstellar turbulence,” said Professor Gaensler. “People have been trying to do this for 30 years.”

Turbulence makes the Universe magnetic, helps stars form, and spreads the heat from supernova explosions through the Galaxy

“We now plan to study turbulence throughout the Milky Way. Ultimately this will help us understand why some parts of the Galaxy are hotter than others, and why stars form at particular times in particular places,” Professor Gaensler said.

Spectacular image

Gaensler and his team studied a region of our Galaxy about 10,000 light-years away in the constellation Norma.

They used CSIRO’s Australia Telescope Compact Array near Narrabri, NSW, because “it is one of the world’s best telescopes for this kind of work,” as Dr Robert Braun, Chief Scientist at CSIRO Astronomy and Space Science explained.

The radio telescope was tuned to receive radio waves that come from the Milky Way. As these waves travel through the swirling interstellar gas, one of their properties—polarisation—is very slightly altered, and the radio telescope can detect this.

(Polarisationis the direction the waves “vibrate”. Light can be polarised—for instance, some sunglasses filter out light polarised in one direction while letting through other light.)

Gas turbulence map of part of the Milky Way

A map has been made of the gas in our Milky Way galaxy. The 'snakes' are regions of gas where the density and magnetic field are changing rapidly as a result of turbulence.

The researchers measured the polarisation changes over an area of sky and used them to make a spectacular image of overlapping entangled tendrils, resembling writhing snakes.

The “snakes” are regions of gas where the density and magnetic field are changing rapidly as a result of turbulence.

Best match

The “snakes” also show how fast the gas is churning — an important number for describing the turbulence.

Team member Blakesley Burkhart, a PhD student from the University of Wisconsin, made several computer simulations of turbulent gas moving at different speeds.

These simulations resembled the “snakes” picture, with some matching the real picture better than others.

By picking the best match, the team concluded that the speed of the swirling in the turbulent interstellar gas is around 70,000 kph—relatively slow by cosmic standards.

Adapted from information issued by CSIRO. Images courtesy B. Gaensler et al. (data: CSIRO/ATCA) and David Smyth, CSIRO.

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‘The Dish’ finds a ‘diamond planet’

Artist's visualisation of the pulsar and its orbiting planet

An artist's visualisation of the pulsar and its orbiting planet, which astronomers think could be made partly of diamond or a diamond-like substance. The blue squiggly line represents the beams of radio waves emanating from the pulsar. The orange bubble represents the size of the Sun, showing that the the planet's orbit has about the same radius as the Sun (about 600,000 km), yet it whizzes around in just two hours!

  • Planet detected orbiting a pulsar 4,000 light-years away
  • It’s actually the remnant core of what was once a star
  • Probably made of compressed carbon—diamond!

ASTRONOMERS USING ‘THE DISH’—CSIRO’s radio telescope near Parkes, NSW—believe they’ve found a small planet made of diamond, orbiting an unusual star.

The discovery was made by an international research team, led by Professor Matthew Bailes of Swinburne University of Technology in Melbourne, Australia, and is reported today in the journal Science.

“Although bizarre, this planet is evidence that we’ve got the right understanding of how these binary systems evolve,” said Dr Michael Keith of CSIRO Astronomy and Space Science, one of the research team members.

Not fitting the pattern

The researchers, from Australia, Germany, Italy, the UK and the USA, first found an unusual star called a pulsar, now named PSR J1719-1438, using the 64-m Parkes radio telescope in eastern Australia.

Pulsars are small spinning stars about 20 km in diameter—the size of a small city—that emit a beam of radio waves. As the star spins and the radio beam sweeps repeatedly over Earth, radio telescopes detect a regular pattern of radio pulses.

The researchers followed up their discovery with the Lovell radio telescope in the UK and one of the Keck telescopes in Hawaii, and noticed that the arrival times of the pulsar’s pulses were systematically altered—in a way that must be caused by the gravitational pull of a small planet orbiting the pulsar.

The CSIRO's Parkes radio telescope

The CSIRO's Parkes radio telescope

Small, heavy and fast

The modulations of the radio pulses reveal several things about the planet.

First, it orbits the pulsar in just two hours and ten minutes, and the distance between the two objects is 600,000 km—a little less than the radius of our Sun.

Second, the companion must be small, less than 60,000 km (that’s about five times the Earth’s diameter). The planet is so close to the pulsar that, if it were any bigger, it would be ripped apart by the pulsar’s gravity.

But despite its small size, the planet has slightly more mass than Jupiter.

A stripped-down dwarf

“This high density of the planet provides a clue to its origin,” Professor Bailes said.

The team thinks that the ‘diamond planet’ is all that remains of a once-massive star, most of whose matter was siphoned off towards the pulsar.

But pulsar J1719-1438 and its companion are so close together that the companion can only be a very stripped-down ‘white dwarf’ star, one that has lost its outer layers and over 99.9 per cent of its original mass.

“This remnant is likely to be largely carbon and oxygen, because a star made of lighter elements like hydrogen and helium would be too big to fit the measured orbit,” said CSIRO’s Dr Keith.

The density means that this material is certain to be crystalline—that is, a large part of the star may be similar to a diamond.

The pulsar and its planet lie 4,000 light-years away in the constellation of Serpens (the Snake). The system is about an eighth of the way towards the Galactic Centre from the Earth.

Diamond planet Easy Q&A

What have they found?

  • They’ve spotted a system that comprises a weird kind of star, called a pulsar, and a medium-sized planet that is probably made of almost pure carbon…which is most likely in the form of diamond or a diamond-like substance.
  • The system is 4,000 light-years from Earth—that’s 40 thousand trillion kilometres away!
  • The pulsar emits radio waves in a regular pattern as it spins, like a lighthouse, which is what the CSIRO’s Parkes radio telescope picked up.
  • The planet itself cannot be seen as it is too small and too far away.

If they can’t see the planet, how do they know it’s really there?

  • Its presence is inferred by the distorting effect it has on the pulsar’s powerful radio emissions.
  • It whizzes around its star in just two hours (compared to one year for Earth around the Sun).
  • The data was analysed using an incredible supercomputer at Swinburne University in Melbourne.
  • The planet is about 5 times as wide as the Earth, but much, much heavier.

So why do they think it is made of diamond?

  • Now here’s the interesting bit, because the planet actually seems to be the dense, remnant core of a star, rather than a traditional planet.
  • Many stars, as they burn up their hydrogen fuel, end up having cores made of carbon.
  • The star changed into a planet, with only it’s core remaining.

How did it change from a star into a planet?

  • Because the pulsar has a huge gravitational pull and is a cosmic cannibal!
  • The pulsar and the other star would have been orbiting very close to each other.
  • The pulsar would have pulled all the outer gas layers off the other star—99.9 percent of its mass—eventually leaving it with just its carbon core.
  • If we could have seen it happening, it would have looked like a huge whirlpool of gas coming off the doomed star and spiralling onto the neighbouring pulsar.

What do astronomers hope to learn from these types of star systems?

  • For one thing, pulsars are the “end points”—the dying stages—in the lives of many kinds of big stars, so learning more about them tells us about the evolution and life cycle of those stars and the wider universe.
  • But pulsars also are important for understanding and testing laws of physics.
  • Astronomers can use them as “natural laboratories” for testing theories, such as Einstein’s theory of gravity.
  • That’s because you can only go so far testing some theories in the laboratory—to really put them to the test, you need to study massive objects travelling at high speed, and that’s what pulsar systems are.

Main text adapted from information issued by CSIRO. Q&A by Jonathan Nally, SpaceInfo.com.au Images courtesy Swinburne Astronomy Productions and David McClenaghan, CSIRO.

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Galaxies are running out of gas

A star-forming region

Compared to earlier cosmic epochs, galaxies these days are running of out of the gas raw material with which to make new stars. (Hubble Space Telescope image.)

THE UNIVERSE FORMS FEWER STARS than it used to, and a CSIRO study has now shown why—compared to the past, galaxies today have less gas from which to make stars.

Dr Robert Braun (CSIRO Astronomy and Space Science) and his colleagues used CSIRO’s Mopra radio telescope near Coonabarabran, NSW, to study far-off galaxies and compare them with nearby ones.

Light (and radio waves) from the distant galaxies takes time to travel to us, so we see the galaxies as they were between three and five billion years ago.

Galaxies at that stage of the Universe’s life appear to contain considerably more molecular hydrogen gas than comparable galaxies in today’s Universe, the research team found.

Stars form from clouds of molecular hydrogen. The less molecular hydrogen there is, the fewer stars will form.

The research team’s paper is in press in Monthly Notices of the Royal Astronomical Society.

Raw material for stars

Astronomers have known for at least 15 years that the rate of star formation peaked when the Universe was only a few billion years old and has declined steeply ever since.

“Our result helps us understand why the lights are going out,” Dr Braun said. “Star formation has used up most of the available molecular hydrogen gas.”

Mopra radio telescope

CSIRO's Mopra radio telescope near Coonabarabran in New South Wales.

After stars form, they shed gas during various stages of their lives, or in dramatic events such as explosions (supernovae). This returns some gas to space to contribute to further star formation.

“But most of the original gas—about 70%—remains locked up, having been turned into things such as white dwarfs, neutron stars and planets,” Dr Braun said.

“So the molecular gas is used up over time. We find that the decline in the molecular gas is similar to the pattern of decline in star formation, although during the time interval that we have studied, it is declining even more rapidly.”

Dark energy the demon

Ultimately, the real problem is the rate at which galaxies are “refuelled” from outside.

Gas falls into galaxies from the space between galaxies, the intergalactic medium. Two-thirds of the gas in the universe is still found in the intergalactic medium—the space between the galaxies—and only one third has already been consumed by previous star formation in galaxies, astronomers think.

“The drop-off in both gas availability and star formation seems to have started around the time that Dark Energy took control of the Universe,” Dr Braun said.

Up until that time, gravity dominated the Universe, so the gas was naturally pulled in to galaxies, but then the effect of Dark Energy took over and the Universe started expanding faster and faster.

This accelerating expansion has probably made it increasingly difficult for galaxies to capture the additional gas they need to fuel future generations of star formation, Dr Braun speculates.

Adapted from information issued by CSIRO; NASA, ESA, STScI/AURA.

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Dishes take shape in the desert

ASKAP dishes

The Australian Square Kilometre Array Pathfinder, or ASKAP, is under construction in the remote Western Australian desert.

THE CSIRO’S LATEST RADIO TELESCOPE—the Australian Square Kilometre Array Pathfinder, or ASKAP—is now taking shape in the remote Western Australian desert.

When completed in 2012 it will comprise 36 dishes all acting in concert to produce the same result as one big dish. Cutting-edge receiver technology invented by CSIRO scientists will give it an extremely wide field of view. This, coupled with high-speed electronics and an ultra-fast optical fibre link to a dedicated computing centre in Perth, will make ASKAP arguably the best radio telescope system in the world.

ASKAP’s first five years of observations are already booked out by teams from around the world, and the science studies it will tackle are some of the biggest around—how did the earliest stars and galaxies form; how have galaxies evolved through time; what role has magnetism played in the cosmos; and can Einstein’s theories stand ever-more stringent tests?

Antony Schinckel

ASKAP Project Director, Antony Schinckel

ASKAP is also the Australian and New Zealand “pathfinder” for the ultimate prize—the Square Kilometre Array, or SKA. The SKA will be a vast collection of thousands of dishes and antennae spread across an area the size of a continent. A decision will be made next year by an international committee, as to whether the SKA will be hosted in Australia-New Zealand or southern Africa. The linked telescopes will make images ten times more detailed than those of the Hubble Space Telescope.

SpaceInfo.com.au wanted to get an update on progress with ASKAP, so we spoke to the man in charge—ASKAP Project Director Antony Schinckel, of CSIRO’s Astronomy and Space Science division—to find out how things are going in the WA desert:

Can you give us a rundown on the state of construction of ASKAP?

We’re very happy with how things are going—we’re at the point where there is substantial activity on site. Major infrastructure construction commenced in May. The first phase of that was that the company doing the work needed to put in their temporary accommodation camp, as there are no motels for hundreds of kilometres!

Between now and early December we’ll complete all of the 30 remaining antenna foundations, the access tracks to each antennae, fibre and power distribution around the site and to each antenna, and then the central building as well—all of the primary infrastructure that doesn’t include the science instruments and power systems.

It must be a difficult task, building hi-tech facilities that are essentially in the middle of nowhere?

With these remote sites there are a lot of logistics that need to be understood and got moving properly, but the contractors have a fair bit of experience with that. Most of it is normal civil engineering, although there are a few subtleties—for instance, the concrete foundations for the antennae need to be a certain minimum stiffness.

The unusual bits in a sense are the optical data fibre links between the antennae and the central site. Our raw data rate will be phenomenally high, about 74 terabits per second for the total 36 antennae. That data then goes into some special equipment (the beam former and the correlator) which ramps down the rate fairly significantly before it is sent via cable down to Perth.

ASKAP antenna

ASKAP will comprise 36 hi-tech antennae

How are you going to handle the enormous amounts of data produced by the 36 ASKAP antennae?

Well, it’s going to be a really interesting challenge how we treat this. We can’t afford to archive the absolute raw data—the volume is just too high. So working out which are the critical data products to archive right up front is going to prove a real challenge. We’ve clearly got some plans on which ones are the most important, but it’ll be fascinating to see over the next few years if we end up archiving those or finding we have to modify it a little bit.

The Pawsey Centre in Perth is a key part of this in terms of the data reduction.

The actual fibre in the ground that CSIRO has put in, is through a contract with AARNet with major sub-contracts to CCTS and North Coast Holdings, out of Geraldton. The fibre has now been fully laid and tested. The fibre is all buried, which is easier long term than having it up on aerial poles. The fibre is better protected when buried. There are three booster huts along the length of the fibre.

There are two remote booster huts that are solar powered with the possibility of back-up diesel if required. And there’s one in the town of Mullewa, which is just on grid power with back-up.

As far as terrain goes, there’s a gentle slope 350km up from Geraldton to the site—we end up at an elevation of about 370 metres.

How will you supply electrical power to such a remote site?

With power, our intention long-term is to have as a renewable a power source as we possibly can. For all sorts of obvious reasons, we want to go with generating most of our power through whatever renewable resources we have. Out in that region of Western Australia in particular, solar power is extremely attractive. It’s one of the places with the highest solar insolation in the world. So solar will be a substantial part of it.

To begin with we’ll have a base power capability from diesel generators, but over a number of years we’ll be expecting to be adding or start off with some solar on top of the diesel, and then in a couple of more years we have some additional funds that will enable us to expand that significantly around 2013-14.

ASKAP dish being installed

The CSIRO has been particularly pleased with the quality of the antennae, built by the 54th Research Institute of China Electronics Technology Group Corporation (known as CETC54).

Power storage is something of an issue. That’s partly why we’ve put the funding back a couple of years, to see what eventuates with power storage options by the time ASKAP is really up and operational. The focus now is on what we need to get it going.

You have six dishes installed and two more being installed right now. What’s the schedule for the rest of them?

It’s a fairly continuous process of installing the remaining antennae right through this year and into early 2012, at about 3 to 4 per month. A team from the Chinese manufacturer, CETC54, comes out to supervise their construction.

With the dishes, there’s one point there that we’ve been particularly thrilled with. We specified a surface accuracy of 1mm but the delivered capability substantially exceeds that—most of the antennae are coming in with an accuracy of about 0.5mm. This means in the long-term they could be used to do observations at much higher frequencies than originally planned, giving us very good long-term flexibility.

Another thing that CETC54 has achieved is that we don’t have to adjust the surfaces. They’ve come up with a manufacturing technique in China and then at installation here that means it’s literally a case of just bolting the dish panels together … there’s no fine adjustment necessary here in Australia.

Given that it is such remote site, will there be people stationed there on a regular basis?

No, not for operations. Like most telescopes these days, it can be operated by remote control from anywhere. However, with an array as big and as complex as this—36 antennae, vast data rates, these huge specialised digital systems—it really is a dramatic step forward. The telescope is about a factor of 10 more powerful than any other radio telescope in the world. So regular maintenance will be required to keep the system up and running, and there will be people going out to the site to do that.

The road to ASKAP

ASKAP is being built in one of the remotest parts of the world, 350 kilometres inland from Geraldton in Western Australia.

Finally, from a personal standpoint, what’s it like to be out there in the WA desert? The conditions must be pretty challenging.

Many telescopes are built in remote sites, but mostly they’re built where there’s already some level of infrastructure. For us working out at Boolardy Station, you have to bring in absolutely everything. You know intellectually that that’s true, but nonetheless on the day when you realise you really do need that special screwdriver, you find it is 350km away! It’s one of those classics where you know philosophically how to do something, and you think you’ve got it covered…but boy, there really is no give and take on that.

Summers out there are pretty warm. We’ve managed to move schedules around to deal with that, and it’s quite manageable; it’s just a case of thinking things out sensibly. We’ve worked a lot with regional contractors in WA who are experienced at this and we’ve shifted our mindset to suit the climate.

The wildlife situation reminds us that we’re living in Australia. The numbers of kangaroos, emus, goannas and snakes, has been quite impressive. Snakes in particular are the most dangerous local wildlife, but we’ve got good procedures in place to deal with them.

Story by Jonathan Nally, SpaceInfo.com.au. Images courtesy CASS / Terrace Photographers / Paul Bourke and Jonathan Knispel (Supported by WASP (UWA), iVEC, ICRAR, and CSIRO).

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