Dark energy confirmed
(20 May 2011)
A four-year survey of over 200,000 galaxies lead by Australian astronomers has confirmed that dark energy does indeed exist. Albert Einstein first posited this mysterious force as a consequence of his theory of general relativity, though later called it his “greatest blunder”. Studies of supernovae in the 1990s showed that the universe is expanding at an accelerating rate, and the idea of dark energy was revived. The WiggleZ Dark Energy Survey, using observations from the state-of-the-art spectrograph on the Anglo-Australian Telescope, has provided two independent means for verifying dark energy’s existence. The WiggleZ Dark Energy Survey, using observations from the state-of-the-art spectrograph on the Anglo-Australian Telescope, has provided two independent means for verifying dark energy’s existence. By measuring how quickly galaxies are moving away from Earth the WiggleZ team have shown how dark energy opposes gravity by speeding up the overall rate of expansion of the Universe. Secondly, the WiggleZ team have shown how dark energy opposes gravity by slowing down the growth of clusters and superclusters. “WiggleZ says dark energy is real,” said lead author and SAO’s own Dr Chris Blake. “Einstein remains untoppled.” While the exact physics of dark energy remains a mystery, confirming that it exists is a giant step forward. For more details, see
- Dark energy is real (Swinburne Press Release)
- WiggleZ Dark Energy Survey
- NASA’s Galaxy Evolution Explorer Helps Confirm Nature of Dark Energy (GALEX website)
- The WiggleZ Dark Energy Survey: testing the cosmological model with baryon acoustic oscillations at z=0.6 (Blake et al., 2011, MNRAS, in press)
- The WiggleZ Dark Energy Survey: the growth rate of cosmic structure since redshift z=0.9 (Blake et al., 2011, MNRAS, in press)
Planetary alignment photo opportunity
(13 May 2011)
Planetary alignment photo opportunity. The month of May provides an excellent opportunity for astrophotographers to catch the alignment of four naked-eye planets: Mercury, Venus, Mars and Jupiter. In the southern hemisphere these four planets are visible just before sunrise over the next few weeks.
An article about the alignment on ABC News has prompted SAO’s own Dr Glen Macie to write to the ABC to express his disappointment that astrologers and their pseudo-science continue to receive media coverage. Glen points out that the ABC article failed to state that all science refutes astrology as “superstitious and supernatural nonsense”. There is a large body of scientific researchwhich clearly de-bunks a range of astrological ‘predictions’. If your friends ask for their astrological readings when you tell them you are studying astronomy, you might like to suggest they read Shawn Carlson’s 1985 Nature article “A double-blind test of astrology”. The ABC article cites one astrologer who suggests that “the effect of this planet line-up has been slowly felt by many over the past few months and by the end of May people should be starting to slowly feel better”, to which Glen replies “What rubbish, but I’m sure I will feel better once astrologers stop getting such exposure!” For more information, see
- Planets align for awesome foursome showcase (ABC News, Monique Ross)
- A double-blind test of astrology (Carlson, 1985, Nature, 318, 419) [Swinburne login required]
- What do you mean, “test” astrology? (Skeptico blog) [Contains references to 37 “tests” of astrology]
Frame dragging confirmed by the Gravity Probe B
(6 May 2011)
A NASA press release on 4 May has announced that the Gravity Probe B mission has confirmed two predictions of Einstein’s general theory of relativity: the geodetic effect which hypothesizes that spacetime is distorted by massive objects, and frame dragging which occurs when spinning massive objects pull on spacetime as they rotate. The Gravity Probe B satellite was launched in 2004 and the initial science phase of the operation ran for 1.5 years. Data analysis, however, has taken 5 years to complete. According to the theory of relativity, three-dimensional space and time are connected as a four-dimensional “spacetime”. A massive object, like the Earth, causes a dimple in the fabric of spacetime, and “gravity” is the motion of objects following the curved lines of through the dimple of spacetime.
But when the massive object rotates, like the Earth, the spinning motion twists the dimple and creates a vortex in spacetime through a process called “frame dragging”. Frame dragging was predicted by Austrian physicists Josef Lense and Hans Thirring in 1918 as a consequence of Einstein theory of relativity.
Using four extremely high-precision ping pong ball-sized gyroscopes, the Gravity Probe B experiment measured the tiny shift in the spin axis of the gyroscopes with respect to a fixed distance star. The experiment measured frame dragging effect to 0.039 ± 0.007 arcseconds. For more details, see
- NASA Announces Results of Epic Space-Time Experiment (NASA Science News)
- Spacetime and spin (Gravity Probe B website)
- Einstein Theories Confirmed by NASA Gravity Probe (National Geographic news)
Were the first stars super-fast “spinstars”?
(29 April 2011)
A new study suggests that the first stars in the Universe were not only massive but also fast rotators. Massive stars live fast and die young, surviving for less than 30 million years, making them tricky to study. But when they die in a supernova explosion, they eject their synthesised heavy elements back into the interstellar medium, which is recycled in future generations of stars. Low mass stars, particularly those less massive than the Sun, live a very long time and can contain elements produced by the first generation of stars. Thus old low mass stars can be used to provide insights into the lives of the first stars. Cristina Chiappini of the Institute for Astrophysics in Potsdam and collaborators have used the ESO Very Large Telescope to study the composition of stars in one of the Milky Way’s oldest globular clusters, NGC6522. They found unusually high levels of the heavy elements strontium (Sr) and yttrium (Y) in the surfaces of eight stars in NGC6522, and by studying the ratio of elements in these old stars, they suggest that the first massive stars must have very rapid rotators to produce the internal mixing required to produce these rare heavy elements.
Fast stellar rotation results in mixing between the He-buring core and outer nuclear burning layers of massive stars which don’t normally mix. The nuclear reactions in the overlapping region leads to an enhanced production of radioactive neon, which emit neutrons that are subsequently captured by Fe and other heavy elements to produce Sr and Y. Chiappini et al. suggest that the previous generation of stars could have been rotating as fast as 500 km/s – well above the typical values of ~ 100 km/s for massive stars in the Milky Way, and way above the 2 km/s of our Sun! If their theory is correct and the first stars were rapid rotators, this has a range of consequences for the early Universe. The fate of rapidly rotating stars in more likely to result in gamma-ray bursts, which would impact on the ionising power of the first stars. For more details, see
- Early stars had a fast spin cycle (ABC Science, Stuart Gary)
- A new spin on the first stars (Nature News & Views, Jason Tumlinson)
- Imprints of fast-rotating massive stars in the Galactic Bulge, Chiappini et al. (2011), Nature, 472, 454 [Swinburne login required]
Pluto’s atmosphere thicker than previously thought
(22 April 2011)
Discovered during a stellar occultation in 1988, Pluto’s extremely thin atmosphere is thought to result from evaporating surface ices near perihelion. Pluto’s eccentric orbit (e~0.25) means that while its mean semi-major axis is 39.5 AU, at perihelion its distance from the Sun is just 29.7 AU and at aphelion is is 49.3 AU from the Sun. As Pluto gets closer to the Sun, the surface ices sublimate and produce the atmosphere. As Pluto moves further from the Sun, the atmosphere should freeze out again onto the surface. Spectroscopy shows that the surface ice is dominated by N2, plus some CH4, CO and perhaps ethane. The atmosphere contains mostly N2 with traces of CH4 and possibly of CO, and the surface pressure is only about a microbar (a millionth that of the Earth’s surface pressure). The last perihelion passage occurred in September 1989, so astronomers were surprised to find that their 2002 observations of Pluto’s atmosphere showed that it continued to expand and increase in atmospheric pressure. It was suggested that this was due to the lag time between the gas heating and cooling (just like it is usually warmer at about 2pm rather than local noon when the Sun’s light is the most intense). New observations by Jane Greaves and collaborators using the James Clerk Maxwell Telescope in Hawaii have confirmed the existence of very cold CO in the atmosphere, which acts as a thermostat and helps balance the heating and cooling effects of CH4 and CO. Their results also suggest that the atmosphere is a lot larger than previously thought, taking it from over 100 km thick to well over 3000 km thick, which is about 3 Pluto radii or a quarter the distance from Pluto to Charon. It was thought that by the time NASA’s New Horizons mission arrives a Pluto in 2015, the atmosphere would have re-frozen, but the discovery of CO in such an extended atmosphere suggests that New Horizons will be able to observe the atmosphere. For more details, see
- Pluto bulging with carbon monoxide (ABC Science, Darren Osborne)
- Discovery of carbon monoxide in the upper atmosphere of Pluto (Greaves et al. 2011, MNRAS Letters) [astro-ph link]
- New Horizons
Understanding star formation in filaments
(15 April 2011)
Molecular clouds are the sites of star formation, but the exact conditions required to trigger the onset of star formation is still poorly understood. Observations from infrared satellites have shown that molecular clouds have a filamentary structure and that star preferentially form along the filaments. But the formation of the filaments themselves is not well understood. Gravity, magnetic fields and large-scale turbulence have all been proposed to explain the filamentary structure in molecular clouds. One theory suggests that prestellar cores form via a two step process: large-scale magnetohydrodynamic (MHD) turbulence first generates a network of filaments in the interstellar medium (ISM) and then the densest filaments fragment via gravitational instabilities into prestellar cores.
New results from the ESA Herschel space observatory now confirm that these filaments are the main birth sites of prestellar cores, and supports the notion that the filaments result from large-scale turbulence. Using the five Herschel wavebands from the PACS and SPIRE instruments from 70-500 μm, Doris Arzoumanian and collaborators made both temperature and density maps of the star forming cloud IC 5146 in the constellation of Cygnus. They identified 27 filaments and determined the radial density profile of each filament, finding that most of the filaments have a similar characteristic width, with a median value of 0.10 ± 0.03 pc or about 20,000 AU, independent of the filament density or length. Arzoumanian et al. argue that the near constant filament width supports the large-scale turbulence model of filament formation. The filaments are hypothesized to form in the post-shock region of mildly supersonic converging gas flows. Since molecular clouds are so cold (about 10 K), the sound speed is quite low (~0.2 km/s) so relatively low speed flows will be supersonic. This characteristic width of ~0.1 pc corresponds well with the sonic scale, which is the boundary between supersonic and subsonic flows. Herschel project scientist Göran Pilbratt says “The connection between these filaments and star formation used to be unclear, but now thanks to Herschel, we can actually see stars forming like beads on strings in some of these filaments.” For more details, see
- Herschel links star formation to sonic booms (ESA website)
- Characterizing interstellar filaments with Herschel in IC 5146 (Arzoumanian et al., 2011, A&A, 529, L6)
Unusual gamma-ray burst caught in the act
(8 April 2011)
NASA’s Swift, Chandra and Hubble space telescopes have joined forces to image a very unusual gamma-ray burst. Gamma-Ray Bursts (GRBs) are the most violent, high-energy explosions in the Universe and can release more energy in 10 seconds than our Sun will emit over its entire 10 billion year lifetime. GRBs are usually very rapid events, generally lasting for a few seconds and never more than a few hours. Long period GRBs (which last more than 2 seconds) are thought to result from core collapse supernova of massive stars, while the origin of short period GRBs is less well understood and may result from merging neutron stars. The Swift satellite’s Burst Alert Telescope detected the first in a series of blasts from GRB 110328A on Monday 28 March and a week later high-energy radiation is still being detected. Swift determined a rough position of the GRB in the constellation of Draco, and on Monday 4 April, HST and Chandra both imaged the source in the optical and X-ray and confirmed that the emission is coming from the centre of a small galaxy. What makes this GRB so unique is its intense brightness, longevity and variability. Typically, GRBs flare for no more than several hours before waning. GRB 110328A continues to brighten and fade more than a week after its initial detection. Since April 3, it has brightened more than five times. Using the information from these three space telescopes as well as a range of ground-based telescopes, it seems likely that, given the GRB’s location in the centre of a galaxy, it is the result of a star being torn apart by the galaxy’s central black hole. Assuming this is the case, as the star is being torn apart by tidal forces near the black hole, a jet of x-ray and gamma-ray radiation formed along the black hole’s rotation axis. Andrew Levan from the Univeristy of Warwick, who led the Chandra observations, adds that a process called relativistic beaming can explain the peculiar brightness of the GRB. If this jet were pointed in the Earth’s direction, our view of the radiation down the jet would result in a brightness burst like the one observed. For more details, see
- NASA Telescopes Join Forces to Observe Unprecedented Explosion (HubbleSite)
- Chandra Observes Extraordinary Event (Chandra website)
Using starquakes to peer inside red giants
(1 April 2011)
Our Sun, and all other main sequence stars, are powered by the nuclear fusion of hydrogen into helium. Once the supply of hydrogen in the stellar core is exhausted, the star becomes a red giant. During the red giant phase, hydrogen burning takes place in a shell around the inert helium core. Eventually the core temperature and pressure rises to the point where helium is ignited. The size and brightness of the star remains constant during the red giant phase, making it extremely difficult to determine what is happening deep inside the star. Astroseismologist Tim Bedding from Sydney University and his collaborators have been using the Kepler space telescope to monitor the light from hundreds of red giants over the course of a year. The turbulent motions in the star cause small changes in the surface brightness, and can also produce “star quakes” that cause sound waves to travel through the star. By studying the travel times of these waves, astroseismologists can probe the stellar interior and determine the density of different layers (just as geologists use earthquakes to study the Earth’s interior structure). For red giants with the same mass, size and luminosity, Bedding and collaborators have found two clear groups, allowing them to distinguish between hydrogen-shell-burning red giants and those that are also burning helium in their cores. They can also distinguish between low-mass red giants which ignite helium explosively in what is called the “helium core flash”, and more massive red giants which ignite helium more gently. For more details, see
- Giant stars reveal inner secrets for the first time (Sydney University)
- The inner lives of red giants (Nature article by Travis Metcalfe) [Swinburne login required]
- Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars (Bedding et al. 2011, Nature, 471, p580) [Swinburne login required]
Planetary nebula of a binary
(25 March 2011)
It is a pleasure to announce some SAO alumni news this week! SAO’s own Graduate Certificate graduant Jeff Stanger (who completed his degree in 2005) has just published a paper in the Publications of the Astronomical Society of Australia (PASA) on the planetary nebula K 1-6. Planetary nebulae are a brief phase in the evolution of low to intermediate mass stars (< 8 Msun) following the asymptotic giant branch (AGB) phase. Shell burning during the AGB phase result in pulsations that drive enormous mass loss, and the star effectively ejects its outer envelope. As the mass-loss rate drops, the outer envelope detaches from the star and the stellar core becomes visible. As the exposed core increases in temperature, its UV radiation ionises the surrounding ejected material, which lights up and becomes visible in the optical as a planetary nebula. The morphology of planetary nebulae are extremely diverse and are likely driven by the stellar properties, whether the central star is in fact a binary, and the episodic nature of the AGB mass-loss and hence the clumpiness of the ejected envelope material.
K 1-6 was initially noted as a faint nebulosity visible in Palomar Observatory Sky Survey and classified as a “probable planetary nebula”. With a group of ten year 11 students from Sydney Girls High School, Jeff Stanger (former science teacher at Sydney Girls High) and collaborators used the 2-metre Faulkes Telescope North in Hawaii to observe the nebula with the aim of confirming its status. Narrow-band Halpha and [O III] images taken with Faulkes, along with ultraviolet images from GALEX and archival X-ray data from ROSAT, led the authors to conclude that K 1-6 is most likely an old bona fide planetary nebula of a binary or even ternary stellar system. This project was part of the Space To Grow program, an Australian Research Council Linkage Grant funded science education project between professional astronomers, teachers and high school students. For more details, see
- K 1-6: An Asymmetric Planetary Nebula with a Binary Central Star (Frew et al. 2011, PASA, 28, 83)
- Planetary nebulae (Cosmos article)
- Faulkes Telescope Project (and their article on the paper)
MESSENGER commences Mercury orbit
(18 March 2011)
The NASA spacecraft MESSENGER successfully completed a 15-minute engine burn today to place it orbit about Mercury, making it the first spacecraft to orbit our inner-most planet. The Mariner 10 space craft completed three fly-bys of Mercury in 1974 and 1975, mapping just under half the planetary surface. MESSENGER completed two fly-bys in 2008 and 2009, providing stunning new images of this least explored planet.
|Mariner 10 map of Mercury||MESSENGER map of Mercury (true + false colour)|
MESSENGER was launched in August 2004, completing two fly-bys of Venus in 2006 and 2007, reaching Mercury for its first fly-by in January 2008. So why has it taken another three years to get into orbit?? Being the closest planet to the Sun, Mercury’s orbit is very fast and the spacecraft needed to “catch up” with the planet. This required gravity assists from both Venus and Mercury. Each flyby increased the average speed relative to the sun, and decreased MESSENGER’s speed relative to Mercury. For an animation of the orbit insertion maneuver, click here.
MESSENGER will orbit Mercury for 12 months, covering just two Mercury solar days (which are 176 Earth days long), studying the surface features and the planet’s gravity, magnetic field and tenuous atmosphere. The mission aims to answer six questions: Why is Mercury so dense? What is Mercury’s geologic history? What is the nature of Mercury’s magnetic field? What is the structure of the core? What is the polar material made of? What is the composition of the tenuous atmosphere? For more details, see
It’s life Jim…. or is it?
(11 March 2011)
NASA astrobiologist Richard Hoover has reported the discovery of fossilised alien microbes on three meteorites which he claims are extra-terrestrial. The discovery of extra-terrestrial life, if confirmed, has enormous implications for astrobiology and life in the universe. Hoover reports on microfossils that appear similar to cyanobacteria – also known as blue-green algae – found on the inner surface of freshly fractured meteorites. Cyanobacteria are photosynthetic aquatic bacteria, which means they live in water and produce their own energy via photosynthesis, and they are the oldest fossils on Earth (about 3,5 billion years old). Hoover discusses the carbon content and morphology of the microfossils and argues that the “size, structure, detailed morphological characteristics and chemical compositions of the meteorite filaments are not consistent with known species of minerals”. However, his findings are controversial. Carl Pilcher, director of NASA’s Astrobiology Institute, points out that the meteorites in the Hoover sample fell to Earth over 100 years ago and have been “heavily handled by humans – so you would expect to find microbes in these meteorites.” David Morrison, also of the NASA Astrobiology Institute points out “thousands of meteorites have been examined over the past 50 years without finding any evidence of fossil life”. He goes on the argue that we know a lot about the parent bodies of the meteorites, which are small bodies, and that “cyanobacteria on a small airless world sounds like a joke”. Evidence of life in the famous Martian meteorite AHL84001, which in 1996 was claimed to contain evidence of 4 billion year old fossilised microbial life from Mars, also remains inconclusive. F0r more details, see
- Signs of ‘alien life’ found in meteorites (Deborah Zabarenko, ABC Science)
- NASA shoots down alien fossil claims (ABC News)
- Fossils of Cyanobacteria in CI1 Carbonaceous Meteorites (Hoover, 2011)
P.S. For an interesting follow-up on the Hoover paper by the Journal of Cosmology, follow this link! [24 March 2011]
Large Hadron Collider can’t find any superparticles
(4 March 2011)
The Large Hadron Collider, or the LHC, is a 27 km circular particle accelerator buried about 100 m underground near the French-Swiss border. It is the world’s largest and highest energy proton-proton collider designed to study the interactions between sub-atomic particles. One of the main experiments of the LHC is to test the standard model of particle physics. The standard model attempts to describe fundamental particles and their interactions via the electromagnetic, weak and strong nuclear forces. In the 1860s, Maxwell unified electricity and magnetism, demonstrating that light is a particle (or photon) as well as an electromagnetic wave. In the 1960s, Maxwell’s electromagnetic force was unified with the strong and weak nuclear forces, when it was discovered that under high enough energies the electromagnetic and weak forces combine to result in an electroweak force. Particles physicists have managed to find all the particles predicted by the standard model except one: the elusive Higgs boson. The standard model does have a few problems, however, like no being able to explain dark matter, which makes up most of the matter in the Universe, or dark energy, the force that accelerates the expansion of the Universe. Supersymmetry is supposed to solve the problems of the standard model. In supersymmetry theory, every normal particle has a heavier “supersymmetrical” partner. Many of these super particles are unstable and rarely interact with matter, which could be used to explain dark matter. The LHC has been trying to find these super particles for the past year, but so far has failed. Just as the Michelson-Morey experiment in 1887 was designed to detect the ether through with electromagnetic waves were thought to travel, failure by the LHC to support supersymmetry in the next year or two will likely result in many theorists abandoning the standard model, just as physicists of the late 1800s abandoned the idea of the ether and agreed that light could travel through a vacuum. For more details, see