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Deep freeze telescope reveals galactic carbon trail

USING A TELESCOPE INSTALLED at the driest place on earth – Ridge A in Antarctica – a UNSW-led team of researchers has identified a giant gas cloud that appears to be in an early stage of formation. Giant clouds of molecular gas – the most massive bodies in our galaxy – are the birthplaces of stars.

“This newly discovered gas cloud is shaped like a very long filament, about 200 light years in extent and ten light years across, with a mass about 50,000 times that of our Sun,” says team leader, Professor Michael Burton, an astronomer at UNSW Australia. “The evidence suggests it is in the early stages of formation, before any stars have turned on.”

Stunning new way of doing science

The team is using the High Elevation Antarctic Terahertz telescope, or HEAT, at Ridge A, along with the Mopra telescope at Coonabarabran in NSW, to map the location of gas clouds in our galaxy from the carbon they contain.

At 4,000 metres elevation, Ridge A is one of the coldest places on the planet, and the driest. The lack of water vapour in the atmosphere there allows terahertz radiation from space to reach the ground and be detected.

PLATO-R in Antarctica

The PLATO-R observatory at Ridge A. The HEAT telescope is the black object on stilts at left, the instrument module is the yellow box and the solar panel array is on the right. Image Credit: Geoff Sims.

The PLATO-R robotic observatory with the HEAT telescope was installed in 2012 by a team led by UNSW physicist, Professor Michael Ashley, and Dr Craig Kulesa of the University of Arizona.

“We now have an autonomous telescope observing our galaxy from the middle of Antarctica and getting data, which is a stunning new way of doing science. Ridge A is more than 900 kilometres from the nearest people, who are at the South Pole, and is completely unattended for most of the year,” says Professor Burton.

Following the galactic carbon trail

The HEAT telescope detects atomic carbon and the Mopra telescope detects carbon monoxide. “I call it following the galactic carbon trail,” says Professor Burton.

Mopra telescope

The Mopra telescope, near Coonabarabran in NSW.

The discovery of the new galactic cloud, which is about 15,000 light years from earth, will help determine how these mysterious objects develop in the interstellar medium.

One idea is that they are formed from the gravitational collapse of an ensemble of small clouds into a larger one. Another involves the random collision of small clouds that then agglomerate. Or it may be that the molecular gas filament is condensing out of a very large, surrounding cloud of atomic gas.

About one star per year, on average, is formed in the Milky Way. Stars that explode and die then replenish the gas clouds as well as moving the gas about and mixing it up.

The team includes researchers from Australia, Germany and the US. The results have been published in The Astrophysical Journal.

Adapted from information issued by UNSW. Image Credit: Geoff Sims.

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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 student finds ‘living dinosaurs’ in space

Galaxies

Australian astronomers have found "living dinosaur" galaxies in the nearby universe. These types of galaxies had been thought to exist only earlier in the universe.

Using Australian telescopes, Swinburne University astronomy student Andy Green has found ‘living dinosaurs’ in space: galaxies in today’s Universe that were thought to have existed only in the distant past.

The report of his finding—Green’s first scientific paper—appears on the cover of the 7 October issue of the scientific journal, Nature.

“We didn’t think these galaxies existed. We’ve found they do, but they are extremely rare,” said Professor Karl Glazebrook, Green’s thesis supervisor and team leader.

The Swinburne researchers have likened the galaxies to the ‘living dinosaurs’ or Wollemi Pines of space—galaxies you just wouldn’t expect to find in today’s world.

“Their existence has changed our ideas about how star formation is fuelled and understanding star formation is important. Just look at the Big Bang, which is how we all got here,” Glazebrook said.

The galaxies in question look like discs, reminiscent of our own galaxy, but unlike the Milky Way they are physically turbulent and are forming many young stars.

“Such galaxies were thought to exist only in the distant past, ten billion years ago, when the Universe was less than half its present age,” Glazebrook said. “Stars form from gas, and astronomers had proposed that the extremely fast star formation in those ancient galaxies was fuelled by a special mechanism that could exist only in the early Universe—cold streams of gas continually falling in.”

Simulation of a star-forming galaxy

A simulation of a star-forming galaxy. Cold gas (red) flows into a spiral galaxy, feeding the process that forms stars.

But finding the same kind of galaxy in today’s Universe means that that mechanism can’t be the only way such rapid star formation is fuelled.

Instead it seems that when young stars form, they create turbulence in their surrounding gas. The more stars are forming in a galaxy, the more turbulence it has. “Turbulence affects how fast stars form, so we’re seeing stars regulating their own formation,” Green said.

“We still don’t know where the gas to make these stars comes from though,” he said. Understanding star formation is one of the most basic, unsolved problems of astronomy.

Another significant aspect of the paper is that it was authored by a PhD student. As Glazebrook pointed out, being first author of a Nature paper as a student is as rare as the galaxies they’ve discovered. This is an achievement not lost on the young scientist. “Nature is one of the most prestigious journals in science. It was a pleasant surprise for our work to receive this kind of accolade,” Green said.

Anglo-Australian Telescope

The 3.9-metre Anglo-Australian Telescope was one of the telescopes used in the study.

Australian observatories

The study was based on selected galaxies from the Sloan Digital Sky Survey, a kind of census of modern galaxies. “We studied extreme galaxies to compare them with the ancient Universe,” Green said. He observed them using the Anglo-Australian Telescope (AAT) and the Australian National University’s 2.3-metre telescope, both located at Siding Spring Observatory in New South Wales.

Professor Matthew Colless, Director of the Australian Astronomical Observatory, which operates the AAT, said that the study highlighted the value of the instruments found at Australia’s telescopes. “They are ideal for studying in detail the nearby counterparts of galaxies seen in the distant Universe by the eight and 10 metre telescopes,” he said.

For the next stage of his research, Green plans to use one of these 10 metre telescopes—in fact the largest optical telescope in the world at the Keck Observatory—to take an even closer look at the rare galaxies he has discovered. Green admitted: “Really, we need a bigger telescope, the Giant Magellan Telescope, to understand star formation. But, until it’s constructed, Keck is the best tool available.”

Green’s access to the Keck will be possible thanks to Swinburne’s agreement with Caltech, which gives the Swinburne astronomers access to the Keck Observatory in Hawaii for up to 20 nights per year.

Adapted from information issued by Swinburne University / Rob Crain / James Geach / Virgo Consortium / Andy Green / Swinburne Astronomy Productions. AAT photo by Barnaby Norris.

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Big stars aren’t special

Artist's impression of the dusty cloud surrounding the star IRAS 13481-6124

Artist's impression of the dusty cloud surrounding the star IRAS 13481-6124, and the jets of particles spat out by the star. Observations suggest big stars such as this one—20 times the mass of the Sun—are born in the same way as smaller stars.

  • Dusty cloud discovered encircling a young star
  • Star is 20 times as massive as the Sun
  • Big stars form the same way as small ones

Astronomers have obtained the first image of a dusty disc-shaped cloud closely encircling a massive baby star, providing direct evidence that massive stars form in the same way as their smaller brethren.

The discovery, made thanks to a combination of the European Southern Observatory’s (ESO) telescopes, is described in an article in this week’s issue of Nature.

“Our observations show a disc surrounding an embryonic young, massive star, which is now fully formed,” says Stefan Kraus, who led the study. “One can say that the baby is about to hatch!

The team of astronomers looked at an object known by the cryptic name of IRAS 13481-6124. About twenty times the mass of our Sun and five times its radius, the young central star, which is still surrounded by its pre-natal cocoon, is located about 10,000 light-years away.

From archival images obtained by the NASA Spitzer Space Telescope as well as from observations done with the APEX 12-metre submillimetre telescope, astronomers discovered the presence of a jet, or focused stream of particles.

“Such jets are commonly observed around young low-mass stars and generally indicate the presence of a disc,” says Kraus.

Circumstellar discs are an essential ingredient in the formation process of low-mass stars such as our Sun. However, it is not known whether such discs are also present during the formation of stars of more than about 10 times the mass of the Sun, where the strong light emitted might prevent mass falling inwards towards the star.

For instance, it has been proposed that massive stars might form when smaller stars merge.

A view of the dust cloud surrounding IRAS 13481-6124

A real view of the dust cloud surrounding the star. Combining the light from multiple telescopes enabled a more detailed view to be made of it.

Telescope team effort

In order to discover and understand the properties of this disc, astronomers employed ESO’s Very Large Telescope Interferometer (VLTI). By combining light from three of the VLTI’s 1.8-metre Auxiliary Telescopes with the AMBER instrument, the facility enables astronomers to see details equivalent to those a telescope with a mirror of 85 metres in diameter would see.

The resulting resolution is about 2.4 milliarcseconds, which is equivalent to spotting the head of a screw on the International Space Station from the ground, or more than 10 times the resolution possible with current visible-light telescopes in space.

With this unique capability, complemented by observations done with another of ESO’s telescopes, the 3.58-metre New Technology Telescope at La Silla, Kraus and colleagues were able to detect a disc around IRAS 13481-6124.

“This is the first time we could image the inner regions of the disc around a massive young star”, says Kraus. “Our observations show that formation works the same for all stars, regardless of mass.”

The astronomers conclude that the system is about 60,000 years old, and that the star has reached its final mass. Because of the intense light of the star—30,000 times more luminous than our Sun—the disc will soon start to evaporate.

The flared disc extends to about 130 times the Earth–Sun distance—or 130 astronomical units (AU)—and has a total mass similar to that of the star, roughly 20 times the Sun.

Adapted from information issued by ESO / Spitzer / NASA / JPL / S. Kraus.

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Space observatory’s first results

The first scientific results from the European Space Agency’s (ESA) Herschel infrared space observatory are revealing previously hidden details of star formation.

New images show thousands of distant galaxies furiously building stars and beautiful star-forming clouds draped across the Milky Way. One picture even catches an ‘impossible’ star in the act of formation.

Herschel is the largest astronomical telescope ever to be placed into space. The diameter of its main mirror is four times larger than any previous infrared space telescope and one and a half times larger than Hubble.

As stars begin to form, the surrounding dust and gas is warmed up to a few tens of degrees above absolute zero and starts to emit at far-infrared wavelengths. The Earth’s atmosphere completely blocks the majority of these wavelengths and thus observations from space are necessary.

Using its unprecedented resolution and sensitivity, Herschel is conducting a census of star-forming regions in our Galaxy.

“Before Herschel, it was not clear how the material in the Milky Way came together in high enough densities and at sufficiently low temperatures to form stars,” says Sergio Molinari, Istituto di Fisica dello Spazio Interplanetario, Roma.

Herschel is also a prime instrument for detecting one of the smallest forms of matter: molecules. It has made the first discovery in space of a new ‘phase’ of water. It is electrically charged and unlike the more familiar phases, namely solid ice, liquid water and gaseous steam, it does not occur naturally on Earth.

In the birth clouds surrounding young stars, however, where ultraviolet light is pumping through the gas, this irradiation can knock an electron out of the water molecule, leaving it with an electrical change.

“These are still early days for Herschel and this is just the beginning of all the science that we will get from this mission in the years to come,” says Goran Pilbratt, ESA Herschel Project Scientist.