RSSArchive for May, 2011

Star that changed the universe

Andromeda Galaxy with insets of star V1

Observations of a star in the Andromeda Galaxy that changes its brightness in a regular pattern, convinced astronomers that our cosmos was huge. Edwin Hubble's further studies of such stars showed that the universe is expanding.

THOUGH THE UNIVERSE IS FILLED with billions upon billions of stars, observations of a single star in 1923 altered the course of modern astronomy. And, at least one famous astronomer of the time lamented that the discovery had shattered his worldview.

The star goes by the inauspicious name of Hubble variable number one, or V1, and resides two million light-years away in the outer regions of the Andromeda Galaxy. V1 belongs to a special class of pulsating star called Cepheid variables, which can be used to make reliable measurements of large cosmic distances.

The star helped Edwin Hubble show that Andromeda lies beyond our galaxy. Prior to the discovery of V1 many astronomers, including Harlow Shapley, thought ‘spiral nebulae’, such as Andromeda, were part of our Milky Way Galaxy.

Others weren’t so sure. In fact, Shapley and Heber Curtis held a public debate in 1920 over the nature of these nebulae. But it took Edwin Hubble’s discovery just a few years later to settle the debate.

Hubble sent a letter, along with a light curve of V1, to Shapley telling him of his discovery. After reading the note, Shapley reportedly told a colleague, “Here is the letter that destroyed my universe.”

The universe became a much bigger place after Edwin Hubble’s discovery.

Andromeda Galaxy with an overlay of a Cepheid star light curve

Cepheid variable stars like V1 change their brightness with a regular pattern. This characteristic enables astronomers to use them to measure distances in the cosmos, by comparing their apparent brightness with their calculated theoretical brightness. Courtesy NASA, ESA, and Z. Levay (STScI), HHT (STScI/AURA), AAVSO. Acknowledgment: T. Rector (University of Alaska, Anchorage).

Cosmic distance ladder

In commemoration of this landmark observation, astronomers with the Space Telescope Science Institute’s Hubble Heritage Project partnered with the American Association of Variable Star Observers (AAVSO) to study the star.

AAVSO observers followed V1 for six months, producing a plot, or light curve, of the rhythmic rise and fall of the star’s light. Based on this data, the Hubble Heritage team scheduled Hubble Space Telescope time to capture Wide Field Camera 3 images of the star at its dimmest and brightest light levels.

“This observation is a reminder that Cepheid variables are still relevant today,” explains Max Mutchler of the Heritage team. “Astronomers are using them to measure distances to galaxies much farther away than Andromeda. They are the first rung on what astronomers call the cosmic distance ladder.”

Edwin Hubble's original photo of Andromeda

Edwin Hubble's original photo of Andromeda, showing three stars of interest marked 'N'. The one at the top became even more interesting when it was recognised as being variable (hence 'VAR'). This is Hubble's V1 star.

Copies of the photograph Edwin Hubble made in 1923 flew onboard space shuttle Discovery in 1990 on the mission that deployed Hubble. Two of the remaining five copies were part of space shuttle Atlantis’s cargo in 2009 for NASA’s fifth servicing mission to Hubble.

The most important star

Edwin Hubble’s observations of V1 became the critical first step in uncovering a larger, grander universe. He went on to measure the distances to many galaxies beyond the Milky Way by finding Cepheid variables within them. The velocities of those galaxies, in turn, allowed him to determine that the universe is expanding.

“V1 is the most important star in the history of cosmology,” says astronomer Dave Soderblom of the Space Telescope Science Institute, who proposed the V1 observations.

The space telescope that bears his name continues using Cepheids to refine the expansion rate of the universe and probe galaxies that were far beyond Edwin Hubble’s reach.

Adapted from information issued by STScI. Images courtesy NASA, ESA, and the Hubble Heritage Team (STScI/AURA). Acknowledgment: R. Gendler.

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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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Spidernauts make a home in space!

A PAIR OF SPIDERNAUTS are settling in to their new home aboard the International Space Station.

Carried into orbit during the current space shuttle Endeavour mission, the spiders are housed in separate enclosures, with a supply of fruit flies to keep them from getting hungry.

The video above shows a series of single exposures of one of the spider enclosures. The camera got bumped during launch; hopefully the astronauts will be able to refocus it.

The spiders are part of an educational experiment. School kids around the globe are taking part, comparing the antics of the spidernauts with spiders back on Earth.

Here’s a video that shows the spiders’ enclosures:

And let’s just hope they don’t receive a high dose of radiation and mutate into gigantic, horrible Earth-destroying monsters … like this one back in 2007!

Story by Jonathan Nally, SpaceInfo.com.au. Images and videos courtesy NASA / BioServe.

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Australia from Space: Part 2

Kimberley shoreline, Western Australia

The Kimberley is a large region in northern Western Australia. Bordered on the north by the Timor Sea, it is the place where the ancestors of Australia's indigenous inhabitants are thought to have landed after crossing from the Indonesian archipelago. This image shows only a small part of the Kimberley coastline.

THESE BEAUTIFUL IMAGES of the Australian coastline and islands were taken by European astronaut Paolo Nespoli from his vantage point aboard the International Space Station (ISS).

The ISS circles the globe in every 91 minutes, with different parts of our planet’s surface visible underneath each orbit as the Earth rotates.

Elizabeth Reef

Elizabeth Reef in the Tasman Sea, is a coral reef that measures about 8 kilometres long by 5.5 kilometres wide. It is located 45 kilometres from Middleton Reef (see next photo), 160 kilometres from Lord Howe Island, and a little over 500 kilometres from the coast of New South Wales. The reef, normally almost fully submerged except at low tide, has claimed a number of shipwrecks during the years, including a yacht in 2007, whose lone British sailor was winched to safety by a Royal Australian Navy helicopter.

Middleton Reef

Middleton Reef is a twin of Elizabeth Reef, located only 45 kilometres away, and around 200 kilometres from Lord Howe Island. It's almost the same size too, being just 8.9 kilometres long by 6.3 kilometres wide. Like Elizabeth Reef, Middleton is almost entirely submerged except at low tide.

King Sound, Western Australia

King Sound is a gulf in northwestern Western Australia, fed by the Fitzroy River. It has the highest tides in Australia, reaching a height of 11.4 metres at Derby, a town on the shore of the Sound. William Dampier was the first European to explore the Sound, in 1688 aboard the ship Cygnet. This image shows only a small part of the Sound, the full dimensions of which are 120 kilometres in length by 50 kilometres width.

Section of the Great Barrier Reef

The Great Barrier Reef, which stretches 2,600 kilometres along Queensland's coastline, is the world's largest reef system. It has almost 3,000 separate reefs, around 900 islands and covers an area of just under 350,000 square kilometres. This image shows only a tiny part of it.

Adapted from information issued by ESA / NASA.

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It’s official – dark energy is real!

Visualisation of dark energy

Cosmic wrestling match. In this artist's visualisation, dark energy is represented in purple and gravity in green. Dark energy is a uniform force that now dominates over the effects of gravity in the cosmos. Courtesy NASA / JPL-Caltech.

A SURVEY OF MORE THAN 200,000 GALAXIES led by Australian astronomers has shown that ‘dark energy’ is real and not a mistake in Einstein’s theory of gravity.

The finding is conveyed in two papers led by Dr Chris Blake from Swinburne University’s Centre for Astrophysics and Supercomputing, which will be published in the Monthly Notices of the Royal Astronomical Society.

Using the Anglo-Australian Telescope, 26 astronomers contributed to the ‘WiggleZ Dark Energy Survey’ that mapped the distribution of galaxies over an unprecedented volume of the Universe.

Because light takes so long to reach Earth, it was the equivalent of looking seven billion years back in time—more than half way back to the Big Bang.

The survey, which took four years to complete, aimed to measure the properties of ‘dark energy’ a concept first cast by Einstein in his original Theory of General Relativity. The scientist included the idea in his original equations, but later changed his mind, calling the inclusion “his greatest blunder”.

However, in the late 1990s when astronomers began to realise that the Universe was expanding at an accelerating rate, the concept of ‘dark energy’ was revived. This was done by measuring the brightness of distant supernovae—exploding stars.

Diagram illustrating cosmic standard candles and standard rulers

This diagram illustrates two methods that astronomers use to measure how fast the universe is expanding—the "standard candle" method, which involves studying exploded stars in galaxies, and the "standard ruler" method, which involves studying the distances between pairs of galaxies. Courtesy NASA / JPL-Caltech.

“The acceleration was a shocking discovery, because it showed we have a lot more to learn about physics,” Dr Blake said. “Astronomers began to think that Einstein’s blunder wasn’t a blunder at all, and that the Universe really was filled with a new kind of energy that was causing it to expand at an increasing speed.”

Einstein vindicated

The WiggleZ (pronounces ‘wiggles’) project has now used two other kinds of observations to provide an independent check on the supernovae results. One measured the pattern of how galaxies are distributed in space and the other measured how quickly clusters of galaxies formed over time.

Both tests have confirmed the reality of dark energy.

“WiggleZ says dark energy is real,” said Dr Blake. “Einstein remains untoppled.”

According to Professor Warrick Couch, Director of Swinburne’s Centre for Astrophysics and Supercomputing, confirming the existence of the anti-gravity agent is a significant step forward in understanding the Universe.

“Although the exact physics required to explain dark energy still remains a mystery, knowing that dark energy exists has advanced astronomers’ understanding of the origin, evolution and fate of the Universe,” he said.

According to one of the survey’s leaders, Professor Michael Drinkwater from the University of Queensland, the researchers have broken new ground. “This is the first individual galaxy survey to span such a long stretch of cosmic time,” he said.

The WiggleZ observations were possible due to a powerful spectrograph attached to the Anglo-Australian Telescope. The spectrograph was able to make measurements at the super-efficient rate of 392 galaxies an hour, despite the galaxies being located halfway to the edge of the observable Universe.

“WiggleZ has been a success because we have an instrument attached to the telescope, a spectrograph, that is one of the best in the world for large galaxy surveys of this kind,” said Professor Matthew Colless, director of the Australian Astronomical Observatory.

The WiggleZ survey involved 18 Australian astronomers, including 10 from Swinburne University of Technology. It was led by Dr Chris Blake, Professor Warrick Couch and Professor Karl Glazebrook from Swinburne and Professor Michael Drinkwater from the University of Queensland.

Adapted from information issued by AAO / Swinburne University of Technology.

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The Case of the Cosmic Crab

A NEW MOVIE FROM NASA’S Chandra X-ray Observatory shows a sequence of images of the Crab Nebula, taken over an interval of seven months and showing dramatic variations.

The Crab Nebula is one of the most famous objects in the sky. It is the remnant cloud from a supernova (exploding star) that was seen by astronomers in China and other countries in the year 1054.

At the centre of the nebula is a pulsar, a rapidly spinning neutron star. It has a mass greater than our Sun but is only tens of kilometres wide, and is spinning at the rate of 30 times per second.

The pulsar’s spin is gradually slowing down, and as it does so large amounts of energy are injected into its surroundings. In particular, a high-speed wind of matter and anti-matter particles ploughs into the surrounding nebula, creating a shock wave that forms the expanding ‘ring’ seen in the movie.

In addition, ‘jets’ shooting out from the poles of the pulsar spew X-ray emitting matter and antimatter particles in a direction at right angles to the ring.

The goal of the latest Chandra observations was to pinpoint the location of remarkable flares spotted by NASA’s Fermi Gamma Ray Observatory satellite and Italy’s AGILE satellite.

A strong gamma-ray flare was detected from the Crab in September 2010, followed by an even stronger series of “superflares” in April 2011. The gamma-ray satellites were not able to locate the source of the flares within the nebula, but it was hoped that Chandra, with its high-resolution images, would.

Scientists have put together a short sequence of the images taken by Chandra, showing the remarkable changes in the nebula:

Chandra began observing the Crab on monthly intervals beginning six days after the discovery of the gamma-ray flare in September 2010. This established a baseline of seven images before the superflare was seen last month.

What was unexpected, though, was that nothing significant showed up in the Chandra observations as compared with the Fermi observations. Astronomers are now trying to figure out why that is so.

One possible explanation is that the gamma-ray flares picked up by Fermi happened very close to the pulsar, in which case they would have been missed by Chandra, because the Crab pulsar is so bright that the detectors are in essence “overexposed” so variations from that region cannot be observed. (Note that in the movie an artificial source of constant brightness is included to show the position of the pulsar.)

Adapted from information issued by CXC. Crab Nebula image courtesy (X-ray) NASA / CXC / SAO / F. Seward; (optical) NASA / ESA / ASU / J. Hester & A. Loll; (infrared) NASA / JPL-Caltech / Univ. Minn. / R. Gehrz.

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Flying free in space

THE CURRENT FLIGHT of Endeavour will see the final spacewalks done by astronauts using a space shuttle airlock. For the foreseeable future, all further spacewalks will be done by Space Station astronauts using the Station’s airlock. And all these spacewalks will see the astronauts/cosmonauts tethered to the shuttle/Station to keep them from floating away.

But back in 1984, a handful of astronauts did what no one had done before and very few have done since…they flew free, untethered, away from their space vehicle.

Using a Buck Rogers-style backpack called the Manned Manoeuvring Unit (MMU), the astronauts could control their movements using tiny gas jets, flying free from the space shuttle and performing tasks completely on their own.

Bruce McCandless flying free with an MMU

NASA astronaut Bruce McCandless became first 'human satellite' in 1984.

Bruce McCandless—seen in the photo above—was the first to test the MMU. He made his historic flight on February 7, 1984 during mission STS 41-B, becoming the first human satellite.

The MMU wasn’t used after 1984. A smaller version called SAFER—the Simplified Aid for EVA Rescue—was developed and tested in untethered flight on missions STS-64 (1994) and STS-92 (2000). All subsequent spacewalking astronauts have used a backpack with SAFER built in, just in case they became untethered and needed to make a safe return to the shuttle’s/Station’s airlock.

Adapted from information issued by National Air and Space Museum / NASA.

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Endeavour sets sail on final voyage

Endeavour tribute graphic

This NASA graphic is a tribute to the shuttle Endeavour and her past missions. It also features a replica of Captain Cook's vessel, HMB Endeavour, after which the shuttle was named.

NASA’S SPACE SHUTTLE ENDEAVOUR lifted off today on her last mission to the International Space Station. The launch of mission STS-134 took place at 10:56pm Sydney time (12:56pm GMT, and was in every way perfect. There were no problems and no anomalies during the ascent.

Endeavour is now heading towards a docking with the Station at 8:15pm Sydney time (10:15 GMT) on Wednesday, May 18.

The six crewmembers will spend 16 days in space on a mission to deliver a highly sophisticated European instrument designed to identify the cosmic fingerprints left by antimatter and ‘dark matter’ in the Universe.

Endeavour's crew

Endeavour's crew

The search for the mysterious dark matter will be conducted by the 6.9-tonne physics payload, the AMS-02 Alpha Magnetic Spectrometer, which is possibly the most ambitious science payload ever launched to the Station.

“The international science community has great expectations of the data to be collected by AMS-02 to understand key questions such as: what makes up the Universe’s invisible mass?” said Jean-Jacques Dordain, Director General of the European Space Agency (ESA).

Using a giant 1.2-tonne magnet that generates a field 4,000 times stronger than Earth’s own, AMS-02 will analyse high-energy cosmic rays with unprecedented sensitivity and accuracy to look for antimatter and dark matter.

Antimatter is believed to have been created on a par with normal matter during the Big Bang, but it seems to have disappeared from the Universe we know today. Dark matter is estimated to account for around 90% of our Universe’s mass, but it has not been detected directly so far.

Endeavour is scheduled to return to Earth on June 1.

Adapted from information issued by ESA / NASA.

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Endeavour’s final voyage

SPACE SHUTTLE ENDEAVOUR, the youngest of NASA’s shuttle fleet, is due to launch on its final voyage at 10:56pm, Sydney time, on Monday, May 16. (That’s 8:56am, US EDT, Monday.)

With a crew of six, and carrying one of the largest and heaviest pieces of gear yet taken to the International Space Station—the antimatter-hunting Alpha Magnetic Spectrometer 2 (AMS2)—Endeavour’s 16-day mission will the second-last of the shuttle programme.

As well as AMS2, Endeavour is also carrying a pallet of critical spare parts, and astronauts will conduct four spacewalks to connect up the new gear, and make some repairs.

These will be the final spacewalks of the space shuttle programme. There will not be any spacewalks during the Atlantis’ final shuttle flight, at this stage still set for late June.

The video above gives an outline of Endeavour’s mission and its crew.

Story by Jonathan Nally, SpaceInfo.com.au. Video and images courtesy NASA.

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Our damaged, wrinkly Moon

Surface of the Moon

The ups and downs of the Moon's battered surface hint at the processes that have shaped it for eons.

WRITTEN ON THE MOON’S WEARY FACE are signs of the damage it has endured for the past 4.5 billion years. From impact craters to the dark plains or ‘maria’ left behind by volcanic eruptions, the scars are all that remain to tell the tale of the past.

But these features only hint at the processes that once acted—and act today—to shape the surface.

To get more insight, Meg Rosenburg and her colleagues at the California Institute of Technology have put together the first comprehensive set of maps revealing the slopes and roughness of the Moon’s surface, based on detailed data collected by the Lunar Orbiter Laser Altimeter (LOLA) on NASA’s Lunar Reconnaissance Orbiter.

Like wrinkles on skin, the roughness of craters and other features on the Moon’s surface can reveal their age.

“The key is to look at the roughness at both long and short scales,” says Rosenburg, who is the first author on the paper describing the results, published in the Journal of Geophysical Research earlier this year.

The roughness depends on the subtle ups and downs of the landscape, a quality that the researchers get at by measuring the slope at locations all over the surface.

A lunar maria

The lunar maria are smooth regions of solidified lava.

To put together a complete picture, the researchers looked at roughness at a range of different scales—the distances between two points—from 17 metres to as much as 2.7 kilometres.

“Old and young craters have different roughness properties—they are rougher on some scales and smoother on others,” says Rosenburg. That’s because the older craters have been pummelled for eons by meteorites that pit and mar the site of the original crater, changing its shape.

“Because this softening of the terrain hasn’t happened at the new impact sites, the youngest craters immediately stand out,” says Gregory Neumann, a co-investigator on LOLA at NASA’s Goddard Space Flight Centre.

By looking at where and how the roughness changes, the researchers can get important clues about the processes that shaped the Moon.

A roughness map of the material surrounding Orientale basin, for example, reveals subtle differences in the ejecta, or debris, that was thrown out when the crater was formed by a giant object slamming into the Moon.

That information can be combined with a contour map that shows where the high and low points are.

“By looking at both together, we can say that one part of Orientale is not just higher or lower, it’s also differently rough,” Rosenburg says. “That gives us some clues about the impact process that launched the ejecta and also about the surface processes that later acted to modify it.”

The smooth plains of the maria, which were created by volcanic activity, have a different roughness “signature” from the Moon’s highlands, reflecting the different origins of the two terrains. Maria is Latin for “seas,” and they got that name from early astronomers who mistook them for actual seas.

Adapted from information issued by Elizabeth Zubritsky, NASA’s Goddard Space Flight Centre.

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