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Aussie shares Nobel Prize for physics

Artist's impression of a black hole

In 1998, two research teams announced the discovery that the expansion of the universe was accelerating.

THE ROYAL SWEDISH ACADEMY OF SCIENCES has awarded the Nobel Prize in Physics for 2011 to the leaders of the teams that discovered the accelerating expansion of the universe.

One half of the prize has been awarded to Saul Perlmutter (The Supernova Cosmology Project, Lawrence Berkeley National Laboratory and University of California) and the other half jointly to Brian P. Schmidt (The High-z Supernova Search Team, Australian National University, Australia) and Adam G. Riess (The High-z Supernova Search Team, Johns Hopkins University and Space Telescope Science Institute, Baltimore, USA).

In 1998, cosmology was shaken at its foundations as the two teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role.

The research teams raced to map the Universe by locating the most distant supernovae (exploding stars). More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors, opened the possibility in the 1990s to add more pieces to the cosmological puzzle.

The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact starthat is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy.

Brian Schmidt, Saul Perlmutter, Adam Riess

Recipients of the 2011 Nobel Prize for Physics— Brian Schmidt, Saul Perlmutter and Adam Riess.

Greatest enigma in physics

All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected—this was a sign that the expansion of the Universe was accelerating.

The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.

For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.

The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma—perhaps the greatest in physics today.

What is known is that dark energy constitutes about three quarters of the Universe.

Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.

More information: Check out this great video on dark energy and the expansion of the universe. It features one of the Nobel Prize winners, Saul Perlmutter.

Adapted from information issued by the Royal Swedish Academy of Sciences.

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Cosmic expansion rate confirmed

Galaxy cluster

As the universe expands, galaxies move further apart from one another. The rate at which the expansion is proceeding is determined by the Hubble constant, which has been newly measured with high precision.

  • Hubble constant used to gauge size and age of the universe
  • Previous measurements had a level of uncertainty
  • New measurement method confirms earlier results

A STUDENT WITH THE with the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia, has calculated how fast the Universe is growing by measuring the Hubble constant.

“The Hubble constant is a key number in astronomy because it’s used to calculate the size and age of the Universe,” said PhD candidate Mr Florian Beutler.

As the Universe expands, it carries other galaxies away from ours. The Hubble constant links how fast the galaxies are moving with how far they are away from us.

By analysing light coming from a distant galaxy, the speed and direction of that galaxy can be easily measured. But determining the galaxy’s distance from Earth is much more difficult.

Until now, this has been done by measuring the brightness of individual objects (such as certain kinds of stars) within a galaxy and using what we know about those objects to calculate how far away the galaxy must be.

This approach is based on some well-established assumptions but is prone to systematic errors, leading Mr Beutler to tackle the problem using a completely different method.

Plot of 6df Galaxy Survey data

In this plot of 125,000 galaxies from 6df Galaxy Survey data, each dot is a galaxy and Earth is at the centre. (The dark slices are regions blocked from view.) The amount of galaxy clustering has been used (along with other data) to measure the expansion rate of the universe.

New method uses super survey

Published in the Monthly Notices of the Royal Astronomical Society, Mr Beutler’s work draws on data from a survey of more than 125,000 galaxies carried out with the UK Schmidt Telescope in eastern Australia.

Called the 6dF Galaxy Survey, this is the biggest survey of relatively nearby galaxies, covering almost half the sky.

Galaxies are not spread evenly through space, but are clustered. Using a measurement of the clustering of the galaxies surveyed, plus other information derived from observations of the early Universe, Mr Beutler has measured the Hubble constant with an uncertainty of less than 5%.

The new measurement is 67.0 (±3.2) kilometres per second per megaparsec. A megaparsec is 1 million parsecs, or 3.26 million light-years.

Good agreement

“This way of determining the Hubble constant is as direct and precise as other methods, and provides an independent verification of them,” says Professor Matthew Colless, Director of the Australian Astronomical Observatory and one of Mr Beutler’s co-authors.

“The new measurement agrees well with previous ones, and provides a strong check on previous work.”

The measurement can be refined even further by using data from larger galaxy surveys.

“Big surveys, like the one used for this work, generate numerous scientific outcomes for astronomers internationally,” says Professor Lister Staveley-Smith, ICRAR’s Deputy Director of Science.

Adapted from information issued by ICRAR / Images courtesy ICRAR / Chris Fluke, Centre for Astrophysics & Supercomputing, Swinburne University of Technology / NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA.

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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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Dark energy dilemma

PHYSICISTS CAN’T SEE IT and don’t know much about what it is, but they think dark energy makes up 70 percent of the universe. In this video, Professor Saul Perlmutter, one of the world’s leading scientists trying to understand dark energy, explains the role it plays in causing our universe to expand.

Adapted from information issued by Lawrence Berkeley National Laboratory / KQEDondemand.

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Astronomy 1 trillion years from now

Artist’s conception of the cosmic view a trillion years from now.

A trillion years from now, the sky will look very different. Will astronomers still be able to work out that the Big Bang happened?

ONE TRILLION YEARS FROM NOW, alien astronomers in our galaxy will have a difficult time figuring out how the universe began. They won’t have the evidence that we enjoy today.

Edwin Hubble made the first observations in support of the Big Bang model. He showed that galaxies are rushing away from each other due to the universe’s expansion.

More recently, astronomers discovered a pervasive afterglow from the Big Bang, known as the cosmic microwave background, left over from the universe’s white-hot beginning.

In a trillion years, when the universe is 100 times older than it is now, alien astronomers will have a very different view. The Milky Way will have merged with the Andromeda Galaxy to form the ‘Milkomeda Galaxy’. Many of its stars, including our Sun, will have burned out.

And the universe’s ever-accelerating expansion will send all other galaxies rushing beyond our “cosmic horizon,” sending them forever out of view.

The same expansion will cause the cosmic microwave background (CMB) to fade out, stretching the wavelength of CMB photons to become longer than the visible universe.

The universe will become dark and dull.

Artist's impression of a hypervelocity star.

Future astronomers will study hypervelocity stars to deduce the laws of the cosmos.

Shooting stars

Without the clues of the CMB and distant, receding galaxies, how will these far-future astronomers know the Big Bang happened?

According to Harvard theorist Avi Loeb, clever astronomers in the year 1 trillion CE could still infer the Big Bang and today’s leading cosmological theory, known as ‘lambda-cold dark matter’ or LCDM. They will have to use the most distant light source available to them—’hypervelocity’ stars flung from the centre of Milkomeda.

“We used to think that observational cosmology wouldn’t be feasible a trillion years from now,” said Loeb, who directs the Institute for Theory and Computation at the Harvard-Smithsonian Centre for Astrophysics.

“Now we know this won’t be the case. Hypervelocity stars will allow Milkomeda residents to learn about the cosmic expansion and reconstruct the past.”

About once every 100,000 years, a binary-star system wanders too close to the black hole at our galaxy’s centre and gets ripped apart. One star falls into the black hole while the other is flung outward at a speed greater than 1.5 million kilometres per hour—fast enough to be ejected from the galaxy entirely.

No need for faith

Finding these hypervelocity stars is more challenging than spotting a needle in a haystack, but future astronomers would have a good reason to hunt diligently. Once they get far enough from Milkomeda’s gravitational pull, these stars will get accelerated by the universe’s expansion.

Andromeda galaxy

Andromeda, the nearest big galaxy, will one day merge with our Milky Way.

Astronomers could measure that acceleration with technologies more advanced than we have today. This would provide a different line of evidence for an expanding universe, similar to Hubble’s discovery but more difficult due to the very small effect being measured.

By studying stars within Milkomeda, they could infer when the galaxy formed. Combining that information with the hypervelocity star measurements, they could calculate the age of the universe and key cosmological parameters like the value of the cosmological constant (the lambda in LCDM).

“Astronomers of the future won’t have to take the Big Bang on faith. With careful measurements and clever analysis, they can find the subtle evidence outlining the history of the universe,” said Loeb.

This research appears in a paper accepted for publication in the Journal of Cosmology and Astroparticle Physics.

Adapted from information issued by CfA. Artwork courtesy David A. Aguilar (CfA). Hypervelocity star artwork courtesy NASA, ESA, and A. Feild (STScI). Andromeda image courtesy Caltech.

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