• SAO Astronomy News

Semester 2, 2006

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23rd October, 2006: Collision Course

A Hubble Space Telescope image of the Antennae Galaxies NGC 4038-4039.

Image Credits: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.

While we normally think of serious collisions resulting in death and destruction, the collision of galaxies results in something altogether different - creation! The NASA Hubble Space Telescope (HST) image of the colliding Antennae galaxies is testament to this - throughout the collision of these two spiral galaxies, billions of stars will be formed. The two galaxies are already dotted with brilliant blue star-forming regions and the pink glow of hot hydrogen gas.

The Antennae galaxies take their name from the long antenna-like tidal tails that formed during the initial encounter of the two spiral galaxies approximately 200-300 million years ago. Nearly half of the faint objects in the HST image are young clusters that formed as a result of the collision, each containing tens of thousands of stars. The brightest and most compact of these are known as super star clusters. The detailed HST image has allowed astronomers to better distinguish between stars and super clusters. By dating the clusters, they have found that only about 10% of the super clusters will survive beyond the first 10 million years, with approximately one hundred of the most massive clusters surviving to form regular globular clusters. The remaining clusters will in time disperse, their stars blending into the smooth background of the galaxy.

16th October, 2006: Keeping Track of Local Black Holes

An all-sky map showing all active supermassive black holes out to a distance of 400 million light years from Earth.

Image Credits: NASA/Swift/BAT/Markwardt et al.

The Swift satellite has been used to complete the first census of Active Galactic Nuclei (AGN) in the local universe. The survey, which scanned the entire sky several times over a nine-month period, found more than 200 AGN, each containing a supermassive black hole at its core. The NASA team involved in the survey are confident that they have detected every active supermassive black hole within 400 million light-years of Earth.

The supermassive black holes at the core of each AGN have masses ranging from millions to billions of suns. As gas and even whole stars fall into them they release huge amounts of energy in the form of light that spans the entire electromagnetic spectrum. Much of this light, including visible light, is often blocked by a veil of gas and dust that surround the AGN. Swift, however, is sensitive to high energy x-rays that penetrate the gas and dust. This allows it to detect AGN that are so embedded in dust that they are completely invisible except in the higher-energy x-ray band. Furthermore, Swift can also perform observations at UV and optical wavelengths to provide a quick confirmation of new AGN. This makes Swift is an excellent instrument for performing an unbiased survey of these objects.

The initial census results are just a taste of things to come. With each scan of the sky stacked on top of existing scans, deeper and deeper images can be formed. This is equivalent to taking a long camera exposure with a camera and allows the survey to scan deeper into the universe with each successive observation.

9th October, 2006: Keeping an Eye on Rover

NASA's Mars Reconnaissance Orbiter takes an image of the Opportunity rover.

Image Credits: NASA/JPL/UA

NASA's Mars Reconnaissance Orbiter (MRO) has recently taken a spectacular image of the Opportunity rover perched on the edge of the massive Victoria crater on Mars. The birds-eye view provides mission controllers an excellent way to plan the rover's exploration of the crater.

Meanwhile, back at the crater, Opportunity is beginning to explore the layered rocks in cliffs surrounding the crater. The inner wall of the crater appears to record a longer span of Mars' environmental history than so far studied in the smaller craters that the rover had previously encountered. The images taken so far reveal previously unseen patterns in the layers of rock suggesting that the environmental conditions were not constant. This is all exciting news to the team that has worked for nearly 21 months driving the rover to this destination. The rover will now be taken from crater ridge to ridge to survey the area and to find a safe way to drive down.

2nd October, 2006: Extrasolar Planets Galore!

A Hubble Space Telescope image from the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS), the green circles identify nine stars that are orbited by planets with periods of a few days.

Image Credits: NASA, ESA, and K. Sahu (STScI).

The Hubble Space Telescope has discovered 16 extrasolar planets in a survey that closely observed 180,000 stars at a distance of 26,000 light-years in the densely populated central bulge of our galaxy. The discovery was made as a result of the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS).

The HST observed 180,000 stars continuously over a period of seven days for the tell-tale sign of a transit event, where a hot Jupiter-sized planet passes in front of a star and blocks of order 1-10% of its light. Only hot Jupiter-sized planets with near edge-on orbits can produce a detectable transit event - as a result only about 10% of such planets can be detected by SWEEPS. If consideration is given to orientation of the orbits, the size of the survey area and the number of detections,the findings suggest that the Milky Way is home to about 6 billion Jupiter-sized planets!

25th September, 2006: Up, up and away!

A montage showing Anousheh's journey to the ISS. Left, preparing to board the Soyuz rocket in Kazakhstan; Centre, The launch; Top Right, Anousheh in the Soyuz TMA-9 spacecraft after launch; Bottom Right, Anousheh with the current and new crew of the ISS.

Image Credits: NASA/Bill Ingalls and NASA TV.

After six months of training, Swinburne Astronomy Online student Anousheh Ansari lifted off on the 18th of September to become the first female space tourist. Anousheh and her travelling companions, NASA's Michael Lopez-Alegria and Russian cosmonaut Mikhail Tyurin, docked with the International Space Station (ISS) on the 20th of September. Anousheh will spend about eight days aboard the ISS before returning to Earth along with two of the station's current occupants.

While onboard the ISS, Anousheh will participate in a number of ESA experiments in the area of human physiology. These tests will investigate the effects of space radiation on the crew, the mechanisms governing the development of muscular atrophy in astronauts and the reaction of the human organism to the space environment. The objective of these experiments is not only to improve the conditions for humans in space but also to shed some light on common diseases affecting people back on Earth.

The staff and students of Swinburne Astronomy Online wish Anousheh a wonderful journey and a safe return to Earth.

18th September, 2006: Einstein at least 99.95% right!

Astronomers observed the orbit of the double pulsar system, PSR J0737-3039A and B, to confirm Einstein's theory of general relativity to within 0.05%.

Image Credit: Michael Kramer, Jodrell Bank Observatory.

An international research team has used three years of observations of a double pulsar to show that Einstein's theory of general relativity is correct to within 0.05%. These results are based on measurements of an effect known as the "Shapiro Delay" - where pulses from one pulsar when passing close to the other are delayed by the curvature of space-time.

The double pulsars, PSR J0737-3039A and B, are the only known example of such a system and together they provide an excellent experimental set-up for measuring effects associated with General Relativity. The pulsars themselves generate radio pulses with extreme regularity that can be used as an exceptionally accurate clock. Each pulsar is a highly compact neutron star weighing roughly a solar mass but with a diameter of only about 20 km. The two pulsars are only separated by a million kilometres and orbit each other every 2.4 hours travelling at speeds of a million kilometres per hour. These conditions allow a number of general relativistic effects to be observed:

  • Gravitational redshift - where the pulse rate from one pulsar is slowed when near to the other as a result of time dilation.
  • Shapiro delay - where the pulses are delayed by the curvature of space-time.
  • Gravitational radiation and orbital decay - where the neutron stars gradually spiral towards each other as a result of energy lost through the emission of gravitational waves.

Astronomers used three of the world's largest radio telescopes at Jodrell Bank, Parkes and Greenbank to precisely measure the variations in pulse arrival times of the system. They found that the movement of the pulsars exactly followed Einsteins predictions. In particular, measurements of the Shapiro delay provided the most precise result - confirming that General Relativity is correct to within 0.05%!

11th September, 2006: Small telescopes scoop a big find

A computer illustration of TrES-2.

Image Credits: Jeffrey Hall, Lowell Observatory.

A network of amateur astronomers has discovered a Jupiter-sized extrasolar planet located 500 light years away. What is impressive is that the planet, TrES-2, was discovered using an off-the-shelf 10 cm camera lens!

TrES-2 was identified by astronomers looking for transiting planets - planets which pass in front of a home star when viewed from Earth. During a transit event a Jupiter-sized planet can block approximately one percent of the stars light - an effect that can be measured by well-equiped amateur telescopes when pointed at the right place and at the right time. To increase the probability of a detection, the Trans-Atlantic Exoplanet Survey (TrES) uses small telescopes to take wide-field images of tens of thousands of stars. This allows many stars to be monitored simultaneously for transit events. When a potential transit event is detected big brother, the 10m W.M. Keck observatory, is called in to make the final verification.

4th September, 2006: SMART-1 makes an impact

SMART-1 impacting the moon as seen through the infrared imagers of the CFHT.

Image Credits: CFHT.

Yesterday, the 366 kg SMART-1 probe was purposefully smashed into the moon and it was all for the good of science - no, really! The event was observed by a number of telescopes around the world in optical, infrared and radio wavelengths. These included the Canada-France-Hawaii Telescope (CFHT), Australia's Mount Pleasant Observatory and the Australia Telescope Compact Array (ATCA). The event was also closely observed by many amateur astronomers from all around the world.

It is hoped that analysis of the impact material and the nature of the impact cloud may give some further insight into the composition of the material just beneath the lunar surface. The highly oblique angle of SMART-1 as it prepared to crash into the moon also provided an opportunity to get some final close-up views of the lunar surface.

28th August, 2006: ... and then there were eight

The Solar System according to resolution 5A which was passed by the IAU on August 24th.

IAU/Martin Kornmesser.

The state of astronomy sure changes fast! Two weeks back our Solar-System had 9 planets, last week a definition of "planet" being proposed at the IAU would have boosted that number up to at least 12 ... and now it seems that we have only 8!

The International Astronomical Union voted to pass a number of resolutions in a meeting in Prague on August 24th. One of these defined the term "planet" along with two new classes of object. To quote the resolution:

(1) A "planet" is a celestial body that (a) is in orbit around
    the Sun, (b) has sufficient mass for its self-gravity to overcome
    rigid body forces so that it assumes a hydrostatic equilibrium
    (nearly round) shape, and (c) has cleared the neighbourhood
    around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around
    the Sun, (b) has sufficient mass for its self-gravity to overcome
    rigid body forces so that it assumes a hydrostatic equilibrium
    (nearly round) shape , (c) has not cleared the neighbourhood
    around its orbit, and (d) is not a satellite.

(3) All other objects except satellites orbiting the Sun shall be
    referred to collectively as "Small Solar-System Bodies". 

As a result, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune maintain their planetary status, whilst Pluto, Ceres, 2003 UB313 and other round'ish objects have now been relegated to a class known as "dwarf" planets. All remaining irregular bits of rubble now simply become small Solar-System bodies.

21st August, 2006: To be, or not to be - What was the question?

Well, the question is: What is a planet? This has turned out to be a surprisingly difficult question to answer because of scientific, cultural and historic issues. Nonetheless, after two years of deliberations, a panel of seven astronomers, writers and historians believe that they have come up with an answer. They believe that:

   "A planet is a celestial body that (a) has sufficient mass for its
   self-gravity to overcome rigid body forces so that it assumes a
   hydrostatic equilibrium (nearly round) shape, and (b) is in orbit
   around a star, and is neither a star nor a satellite of a planet."

How does this affect the way we see our own Solar System? For starters, there are 12 Solar System objects that already fit this new definition: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. Ceres, discovered by Giuseppe Piazzi on New Years day in 1801, was originally classified as a planet but then re-classified as the first of a new class of object known as an asteroid - it has remained under this classification for over 150 years. However, Ceres is sufficiently massive and spherical to be re-instated as a planet under the new definition.

The 12 planets of our Solar System according to the new definition of a planet being proposed at an IAU meeting on August 24th.

Image Credit: IAU/Martin Kornmesser.

Pluto, a world that has had its planethood questioned over the past few years, will formally maintain its planetary status under the new IAU definition. Even more surprisingly, it will become the first "double planet". Its moon Charon is so large in comparison to Pluto that the centre of mass of the system lies between the two worlds. As a result Charon is now also considered to be a planet.

The object that reinvigorated the whole planet debate, 2003 UB313, will also be given planetary status under the new definition. 2003 UB313, more affectionately known as "Xena", was discovered in 2005 and orbits the Sun at over twice the distance of Pluto. The reason Xena threw a spanner in the works was because of its size - it was estimated to be larger than that of Pluto. Using logical reasoning that suggested that if Pluto was a planet then Xena too should be defined as a planet.

Other would-be planets that may meet the criteria of the new definition of a planet.

Image Credit: IAU/Martin Kornmesser.

... but wait there's more! Not only do you get ex-asteroid, an ex-planet, an ex-satellite and a brand new would-be world but we'll throw in an entire set of collectors-edition, colour-coordinated rocky and icy worlds. As you may have guessed, the new IAU definition will open the flood gates for a host of new "planets". Currently there are at least a dozen further candidate objects that may be re-classified as planets. These include other asteroids such as Vesta, Pallas and Hygiea which may follow the path of Ceres into planethood based on their round'ish shapes. Others include the more recently discovered outer Solar System objects such as Sedna, Quaoar, Orcus, Ixion and Varuna.

The IAU draft resolution will also be defining a new official term - a "Pluton". Plutons reside in orbits around the Sun that take over 200 years to complete ie. they have orbits beyond that of Neptune. Some of the objects that fall under the Pluton definition include Pluto, Charon, 2003 UB313, Sedna, Quaoar, Orcus, Ixion and Varuna.

The IAU will vote on a draft definition of what constitutes a planet at an IAU meeting in Prague on the 24th of August.

14th August, 2006: Hourglass-Shaped Magnetic Field Proves Theory Right

The star forming region IRAS 4A.

Image Credits: NASA/JPL/CfA.

The Smithsonian's Submillimeter Array (SMA) has found evidence of an hourglass-shaped magnetic field in a star formation region. While this has been long predicted by theory this is the first conclusive evidence of the effect.

In order for a star to form the collapsing molecular cloud core would need to overcome the support provided by its magnetic field. Theory predicted that the competition between gravity pulling inward and magnetic pressure pushing outward would produce a warped, hourglass pattern in the magnetic field within the collapsed core. This is what the SMA detected in observations of NGC 1333 IRAS 4A, a protostellar system located approximately 980 light-years from Earth.

7th August, 2006: Hubble constant still holds true

Six of 38 galaxy clusters observed with the Chandra X-ray Telescope.

Image Credits: NASA/CXC/MSFC/M.Bonamente et al.

Scientists have observed a total of 38 galaxy clusters with the Chandra X-ray Observatory to determine the Hubble constant using an independent technique to those used previously. To their relief they found that their results were consistent with previous determinations of the constant.

Using a combination of X-ray and radio observations, astronomers were able to determine the Hubble constant with the help of the Sunyaev-Zeldovich effect. In this effect, cosmic microwave background photons gain energy in an interaction with electrons that pervade the enormous galaxy clusters. The overall effect is that the microwave background signal is distorted in the direction of the clusters. The radio observations were used to measure the distortions and the Chandra X-ray observatory was used to measure the physical size of the galaxy clusters. The observations allowed the distance to each of the clusters to be determined.

Using this method astronomers found the Hubble constant to be 76.9 kilometres per second per mega-parsec. Taking into consideration the uncertainties this result is consistent with values determined by other techniques and suggests that the Universe is 12-14 billion years old.

31st July, 2006: Welcome to SAO Semester 2, 2006

XMM-Newton's view of supernova remnant RCW 103.

Image Credits: ESA.

There's was no let up on the news front over the break so I'll dive straight in with some of the highlights. The International Astronomical Union (IAU) has approved new names for Pluto's moons S/2005 P1 and P2 - they are now officially called Nix (the goddess of darkness and night) and Hydra (a monster with the body of a serpent and nine heads). Meanwhile, in light of the discovery of an object larger than Pluto in the outer Solar System, 2003 UB313 (A.K.A. Xena), the IAU will be meeting in August to decide whether our Solar System has 8 or 10 planets. The result of this meeting is sure to stir up some debate and a flurry of updates to astronomy textbooks around the world.

ESA's SMART-1 is just about to run out of fuel and if its orbit were to decay naturally it would crash into the far side of the Moon's surface. In order to maximise the science output of the mission, ESA spacecraft controllers have begun a series of thruster firings to ensure that SMART-1 impacts on the near side of the moon. This will not only favour scientific observations from Earth but will also allow for further close-up views of the lunar surface. SMART-1 is expected to impact the moon on the 3rd of September, 2006.

The space shuttle Discovery has made a triumphant return into space dropping off a 3,175 kg load of clothing, food and supplies to the International Space Station (ISS) and picking up 1,800 kg of unneeded hardware and rubbish. The crew also completed a total of three space-walks for routine maintenance, repairs and training. The return of the shuttle means that construction of the ISS can now once again continue. There is also hope once more for a mission to fix the ailing Hubble Space Telescope which has suffered problems with its gyroscopes and more recently with its Advanced Camera for Surveys (ACS).

The Cassini spacecraft is half-way through its mission but is busy as ever taking images of Saturn's rings, Titan, Enceladus and other moons. Meanwhile the veteran travellers Spirit and Opportunity are well into their extended missions and have been looking at meteorites on the Martian surface whilst ESA's Mars Express continues gazes from up above to take detailed stereo images of the Martian surface.

In the inner Solar System, ESA's Venus Express has reached its final 24 hour orbit around Venus. ESA have released the first science update from the mission revealing that the night side cloud deck extends much higher than previously thought and that the south pole has a surprisingly complex vortex. So far Venus Express has a clean bill of health, except for a malfunction in its Planetary Fourier Spectrometer.

On the science front, ESA's XMM-Newton observatory has taken X-ray images of the 2000 year old supernova remnant RCW103. The observations have revealed that the central neutron star is not acting its age - it is spinning much too slowly at 6.7 hours per revolution. This is tens of thousands of times slower than that expected for a young neutron star and is more typical for a source that is many millions of years old. The strange behaviour of this object is believed to be a result of an accretion disk or a powerful magnetic field.

In more X-ray news, NASA's Chandra X-ray observatory has taken a one million second image of the centre of the Milky Way. Apart from the supermassive black hole, the recent observation reveals three massive star clusters that are living a rather hectic existence in an extreme environment.

Finally, in Aussie news, the Mileura Widefield Array - Low Frequency Demonstrator has been awarded funding by the National Science Foundation. The array is being constructed in the Australian outback and when completed will look back to the early Universe to find evidence of the first stars and galaxies.