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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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A new way to weigh planets

Diagram showing the Sun, Earth and Jupiter orbiting a common barycentre

Measurements of signals from pulsars (purple lines) are affected by Earth's movement in its orbit around the Solar System's centre of mass, the barycentre. The barycentre moves too, due to the gravitational influence of the other planets. By working backwards from the pulsar signals, scientists can work out the gravitational pull of the planets, and from that deduce their masses.

  • Radio waves from pulsars affected by Solar System’s gravity
  • Adjusting the pulsar wave measurements gives gravity readings
  • From the gravity readings, the planet’s masses can be found

Astronomers from Australia, Germany, the UK, Canada and the USA have come up with a new way to weigh the planets in our Solar System, using radio signals from pulsars.

“This is first time anyone has weighed entire planetary systems—planets with their moons and rings,” said team leader Dr. David Champion of the Max-Planck-Institut fuer Radioastronomie in Bonn, Germany.

“And we’ve provided an independent check on previous results, which is great for planetary science.”

Measurements of planet masses made this new way could feed into data needed for future space missions.

Until now, astronomers have weighed planets by measuring the orbits of their moons or the trajectories of spacecraft flying past them. That’s because mass produces gravity, and a planet’s gravitational pull determines the orbit of anything that goes around it—both the size of the orbit and how long it takes to complete.

The new method is based on adjustments astronomers have to make to signals from pulsars…small spinning stars that deliver regular ‘blips’ of radio waves.

The Earth is travelling around the Sun, and this movement affects exactly when pulsar signals arrive here. To remove this effect, astronomers calculate when the pulses would have arrived at the Solar System’s exact centre of mass, or barycentre, around which all the planets orbit.

Because the arrangement of the planets around the Sun changes all the time, the barycentre moves around too.

To work out its position, astronomers use both a table (called an ephemeris) of where all the planets are at a given time, and the values for their masses that have already been measured.

If these figures are slightly wrong, and the position of the barycentre is slightly wrong, then a regular, repeating pattern of timing errors appears in the pulsar data.

“For instance, if the mass of Jupiter and its moons is wrong, we see a pattern of timing errors that repeats over 12 years, the time Jupiter takes to orbit the Sun,” said Dr Dick Manchester of CSIRO Astronomy and Space Science.

The CSIRO's Parkes radio telescope

The CSIRO's Parkes radio telescope made most of the pulsar signal measurements.

But if the mass of Jupiter and its moons is corrected, the timing errors disappear. This is the feedback process that the astronomers have used to determine the planets’ masses.

Better measurements of planet masses

Data from a set of four pulsars have been used to weigh Mercury, Venus, Mars, Jupiter and Saturn with their moons and rings.

Most of these data were recorded with CSIRO’s Parkes radio telescope in eastern Australia, with some contributed by the Arecibo telescope in Puerto Rico and the Effelsberg telescope in Germany.

The masses were consistent with those measured by spacecraft. The mass of the Jovian system (Jupiter and its moons)—0.0009547921 times the mass of the Sun—is significantly more accurate than the mass determined from the Pioneer and Voyager spacecraft, and consistent with, but less accurate than, the value from the Galileo spacecraft.

The new measurement technique is sensitive to a mass difference of 200,000 million million tonnes—just 0.003% of the mass of the Earth, and one ten-millionth of Jupiter’s mass.

“In the short term, spacecraft will continue to make the most accurate measurements for individual planets, but the pulsar technique will be the best for planets not being visited by spacecraft, and for measuring the combined masses of planets and their moons,” said CSIRO’s Dr George Hobbs, another member of the research team.

Repeating the measurements would improve the values even more. If astronomers observed a set of 20 pulsars over seven years they’d weigh Jupiter more accurately than spacecraft have. Doing the same for Saturn would take 13 years.

“Astronomers need this accurate timing because they’re using pulsars to hunt for gravitational waves predicted by Einstein’s general theory of relativity”, said Professor Michael Kramer, head of the ‘Fundamental Physics in Radio Astronomy’ research group at the Max-Planck-Institut fuer Radioastronomie.

“Finding these waves depends on spotting minute changes in the timing of pulsar signals, and so all other sources of timing error must be accounted for, including the [influences] of Solar System planets.”

Adapted from information issued by CSIRO / D. Champion, MPIfR.

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Citizen scientists discover rare pulsar

Artist's impression of a pulsar

An artist's impression of a pulsar and the conical beams of radio energy it emits.

  • Rare pulsar found by “citizen scientists”
  • Part of the Einstein@Home physics program
  • Uses the idle time of home PCs to make discoveries

Three citizen scientists, a German man and an American couple, have been credited with the discovery of a rare radio pulsar hidden in data gathered by the Arecibo Observatory in Puerto Rico.

Published today in the journal Science, the deep space discovery is the first of the international programme, Einstein@Home, which utilises the idle time of volunteers’ computers to search the Universe for neutron stars and radio pulsars.

The programme, which uses donated time from the home and office computers of 250,000 volunteers from 192 different countries around the world, is supported by an international consortium of pulsar astronomers.

One of these astronomers is Dr Ramesh Bhat from Melbourne’s Swinburne University of Technology, who considers the public engagement component of the discovery to be a great step forward.

“This discovery, through volunteer computing, demonstrates the importance of engaging the public in such large astronomy projects. It opens up news avenues for making astronomical discoveries,” he said.

A pulsar is the “dead” remnant core of a giant star that exploded at the end of its life. With its matter packed in at an incredible density, just one teaspoonful of pulsar matter has a mass of 5,500 million tonnes.

They also have incredibly powerful magnetic fields, and emit focused beams of radio energy that can be picked up on Earth by radio telescopes. As the pulsar spins, its radio beams repeatedly sweep across our field of view like a lighthouse, hence the term “pulsar”.

Discovered with home computers

Revealed with the help of computers owned by Chris and Helen Colvin from the US and Daniel Gebhardt from Germany, the new pulsar—called PSR J2007+2722—is a neutron star that rotates 41 times per second.

Arecibo Observatory

The giant dish of the Arecibo Observatory is used to pick up the radio patterns from pulsars.

It is in the Milky Way, approximately 17,000 light years from Earth in the constellation Vulpecula. Unlike most pulsars that spin as quickly and steadily, PSR J2007+2722 sits alone in space, and has no orbiting companion star.

“Such objects are very rare and it is fair to admit that we do not have a good understanding of how such objects form in the first place,” Bhat said.

Astronomers consider the finding especially interesting since it is likely to be a recycled pulsar that lost its companion. Alternatively it could be a young pulsar born with a lower-than-usual magnetic field.

“No matter what else we find out about it, this pulsar is bound to be extremely interesting for understanding the basic physics of neutron stars and how they form,” said Jim Cordes, the chair of the Einstein@Home consortium.

A combined effort

The discovery is a boost to the major ongoing international survey of pulsars that generated the data containing PSR J2007+2722.

Due to the huge amounts of data involved the survey relies on the enormous processing power of supercomputers around the world, including the Swinburne University supercomputer, as well as the home computers of thousands of participating volunteers.

Einstein@Home is based at the Centre for Gravitation and Cosmology at the University of Wisconsin–Milwaukee, and at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, Hannover).

“This is a thrilling moment for Einstein@Home and our volunteers. It proves that public participation can discover new things in our universe. I hope it inspires more people to join us to help find other secrets hidden in the data,” said Bruce Allen, leader of the project and Director at the Max Planck Institute.

Adapted from information issued by Swinburne University / NAIC – Arecibo Observatory, a facility of the NSF.

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Pulsars aren’t perfect

Artist's impression of a pulsar

An artist's impression of a pulsar. Blue lines represent its surrounding magnetic fields, while the purple beams represent the radio waves it emits.

  • Pulsars are small, spinning, magnetised stars
  • Emit regular pulses of radio waves
  • Act like celestial clocks

CSIRO astronomer George Hobbs and colleagues in the UK, Germany and Canada report in the journal Science that they’ve taken a big step towards solving a 30-year-old puzzle—why the “cosmic clocks” called pulsars aren’t perfect.

Pulsars are small, spinning stars that emit a beam of radio waves. When the beam sweeps over the Earth we detect a highly-regular “pulse” of radio waves. The rate at which the pulses repeat, fast or slow, depends on how fast the pulsar spins and therefore how often its radio beam flashes across the Earth.

The work is based on observations of 366 pulsars collected over several decades with the 76m radio telescope at the Jodrell Bank Observatory, run by the University of Manchester, and grew out of work George Hobbs did for his PhD thesis.

Each pulsar generates a cocoon of magnetic fields around itself—its magnetosphere.

The astronomers found that a pulsar’s magnetosphere switches back and forth between two different states.

“We don’t know exactly what happens,” Dr Hobbs said.

“But one idea is that from time to time there is a surge of charged particles—electrons, for instance—whirling through the magnetosphere. Such a surge could apply the brakes a bit to the pulsar spin, and also affect the pulsar’s radio beam.”

The change in a pulsar’s magnetosphere shows up both in the shape of the radio pulses recorded on Earth and the regular pattern of the pulses’ arrival times.

“Pulsars are very stable timekeepers, but not perfect,” said Dr Andrew Lyne of the University of Manchester, lead author of the Science paper and George Hobbs’ PhD supervisor.

“They have what we call ‘pulsar timing noise’, where the spin rate appears to wander around all over the place. This had baffled people for decades.”

Jodrell Bank 76m radio telescope

The Jodrell Bank 76m radio telescope

One of the aims of Dr Hobbs’ PhD thesis was to find an effective way to filter out this ‘timing noise’.

“We worked out how to do this, and along the way we were prompted to think hard about the nature of the timing noise,” Dr Hobbs said.

Haven’t solved all the mysteries yet

The key advance was noticing that when the pulsar timing changed, so did the shape of the radio pulse. “This ran against accepted thinking,” Dr Hobbs said. “Everyone had said they were unrelated. But we’ve shown they are.”

Now astronomers can compensate for ‘timing noise’ by using the pulse shape change to spot when the pulsar magnetosphere has changed its state—this will show when the pulsar spin rate has also changed.

“We now have a more fundamental understanding of how pulsars work,” Dr Hobbs said.

“We’ve shown that many pulsar characteristics are linked, because they have one underlying cause.”

Armed with this understanding, astronomers will find it easier to compensate for errors in their pulsar “clocks” when they use them as tools—for instance, in trying to detect gravitational waves, which is something Dr Hobbs is doing with CSIRO’s Parkes radio telescope.

But Dr Hobbs adds that there is no explanation yet as to why a pulsar’s magnetosphere flips from one state to another.

“The switching seems random in some pulsars and regular in others,” he said.

“We haven’t solved all the mysteries yet.”

Adapted from information issued by CSIRO / Russell Kightley / Jodrell Bank Centre for Astrophysics.