Previous stories: S2-2010

First extragalactic extrasolar planet found??
(19 November 2010)

Astronomers using the MPG/ESO 2.2-metre telescope in Chile report this week that they have discovered an exoplanet orbiting a star that is most likely from another galaxy.  The star, HIP 13044, is thought to have entered our Milky Way from another galaxy.  The star and its planet have been found in a stellar stream of confirmed extragalactic origin.  The Milky Way galaxy is known to have several satellite galaxies (including the Large and Small Magellanic Clouds) and some of the satellite galaxies – like the Sagittarius dwarf spheroidal galaxy – are in the process of merging with the Milky Way.   HIP 13044 and its planet, known as HIP 13044b, are in the Helmi stellar stream in the direction of the constellation Fornax.  Stars in the Helmi stream are thought to have been stripped from a dwarf galaxy that was effectively “eaten” by our own galaxy about six to nine billion years ago.  The host star HIP 13044 is very metal-poor (only 10% that of the Sun), which is common of stars in dwarf galaxies.  The planet, HIP 13044b, has a minimum mass of 1.25 Jupiter masses and orbits its host star in about 16 days. For more details, see

Gigantic gamma-ray bubbles found in the Milky Way
(12 November 2010)

The Fermi Gamma-ray Space Telescope has discovered two gigantic bubbles emanating from the core of the Milky Way.   The gamma-ray-emitting bubbles extend an enormous  10 kpc above and below the galactic plane.  The exact cause of the bubbles is unknown, but Meng Su and collaborators argue that it must have resulted from a huge injection of energy into the Galactic centre over the past 10 million years, either from accretion onto the central supermassive black hole or perhaps a nuclear starburst.  For more details, see

Close encounter with comet Hartley 2
(5 November 2010)

Yesterday the NASA space probe Deep Impact, as part of the EPOXI mission, successfully had a 700-km close encounter  with comet Hartley 2.  This is only the fifth comet with has been visited at close enough range by space probes to obtain images of the nucleus. Hartley 2 is a relatively small comet, with a nucleus only 2km in size (about a third the size of comet Tempel 1 which Deep Impact collided with in July 2005), but it is extremely active and has been releasing about five times the amount of gas and dust as Tempel 1.  The spectacular NASA images clearly show jets of material emanating from the day side of the comet as well as from the terminator (not the “I’ll be back” type, but the day/night interface) – the first time such images of cometary jets have been images.  Comets are often thought of as “dirty snowballs”, containing a relatively well mixed amount of volatile ices, rock, and dust particles.  As their orbits carry them towards the Sun, the ice evaporates and creates a long jet or ‘tail‘ of gas  and dust.  En route to Hartley 2 in September, astronomers were surprised to see a sudden increase in the amount of CN (cyanide) gas released from the comet without a corresponding increase in the amount of dust. It remains a mystery as to why the abundance of CN in the comet’s atmosphere increased by a factor of five over an eight day period in September without a corresponding increase in dust.  As the EPOXI team analyse the close encounter data over the coming months, we will no doubt learn more.  For further details, see

Most massive neutron star discovered
(29 October 2010)

Neutron stars are the end products of the massive stars, generally between 8 and 50 times the mass of the Sun, and are formed from a core-collapse supernova explosion.  Once nuclear fusion in the core of the massive star ceases, there is nothing to hold the core up against the weight of the great mass above it, and so the core collapses.  This squeezes all the electrons and protons together, forming neutrons and neutrinos.  The supernova explosion expels most of the material of the massive star, leaving behind just the tiny central core, which is now composed of neutrons.  Neutrons stars generally have masses between 1.4 and 1.7 solar masses and sizes of about 10 km, making them the densest objects in the Universe.  Determining the mass and radius of neutron stars allows astronomers to better understand their internal structure and the equation of state of their matter.  (The equation of state describes the state of matter for a given set of physical conditions like temperature and pressure. Understanding the state of the very dense matter than makes up neutron stars is an active area of research.)  The neutrons stars generally rotate very rapidly, and if their radiation sweeps past our line of sight they can be observed as a pulsar. In this week’s edition of Nature, Paul Demorest of NRAO and collaborators announce the most massive neutron star yet discovered – 2 solar masses.  The high mass of the  binary millisecond pulsar J1614-2230 rules out some equations of state (like hyperon and boson condensate equations), and the authors suggest that quark matter could be supporting the neutron star.  For more information, see

The universe’s most distant galaxy found
(23 October 2010)

The universe’s most distant galaxy found!  Using the VLT, a group of European astronomers have found the most distant galaxy ever.  The galaxy, romantically named UDFy-38135539, was found in the Hubble Ultra Deep Field and nominated a high redshift (z>8) candidate galaxy.  Matt Lehnert and collaborators conducted follow-up observations with the SINFONI spectrograph on the VLT and have confirmed that the galaxy is at a redshift of z=8.6, when the Universe was less than 600 million years old.  This has fundamental implications for cosmology.  It is known that shortly after the Big Bang, electrons and protons combined to form hydrogen gas. During the so-called “Dark Ages” before stars formed, this cold hydrogen gas was the main competent of the Universe.  Then when the first galaxies formed, their ultraviolet light reionised the hydrogen atoms, splitting them into electrons and protons again.  This was during what is know as the “epoch of reionisation”.  And understanding how and when reionisation happened is one of the major challenges of modern cosmology. The results of Lehnert et al. suggest that UDFy-38135539 is one of the first galaxies that ‘cleared the fog’ of the very early Universe.  The researchers also suggest that the the UV radiation from UDFy-38135539 alone was probably not strong enough to clear the fog, and therefore that other fainter, less massive neighbouring galaxies must have helped.  For more details, see

Evidence for galactic cold gas accretion at high redshift
(15 October 2010)

As discussed in last week’s SAO astronews, cosmological models predict that galaxies were built up in the early universe by cold primordial gas flowing along cosmic filaments into the cores of young galaxies.  This week, a team of European astronomers has used ESO’s Very Large Telescope to test this idea.  Giovanni Cresci and collaborators have found evidence that supports the cold gas accretion model.  In the local universe, we find that disk galaxies have a metallicity gradient which decreases with increasing radius from the centre.  This to assumed to be due to star formation occurring more vigorously towards the centre of the galaxy, leading to local chemical enrichment by supernovae. Cresci and collaborators have found three high redshift (z~3) disk galaxies which have “inverse” metallicity gradients, with low metallicity in the central regions and higher metallicity further out.  They suggest that the gas in the central regions have been diluted by the accretion of low metallicity primordial gas which flows into the deep potential well of the galaxy centres, producing the observed high star formation rates in the ‘pre-enriched’ disks.  They conclude that this evidence supports the predictions of cold flow models.  For more details, see

First discovery of local spiral galaxies with high star formation rates and high turbulence
(8 October 2010)

Stars form in galaxies when clouds of gas locally collapse due to gravity.  Most star formation occurs in disk galaxies, like in the spiral arms of our own Milky Way. In the Milky Way, star forms at a rate of about one per year. But in the distant past (like 10 billion years ago), the star formation rate was much higher than it is today.  Star formation rates in high redshift galaxies were about a hundred times greater than they are today. As well as having much higher star formation rates, high redshift galaxies also have very high gas velocity dispersions due to turbulent motions within the gas.  Our understanding of large scale structure and galaxy formation in the early Universe suggests that cold gas flowed along cosmic filaments into galaxies, fueling the high star formation rates that are observed in high redshift galaxies. In the local Universe, however, there is no longer a reservoir of cold primordial gas available to produce the high star formation rates seen in high redshift galaxies.  This made it all the more surprising when Swinburne’s own PhD student Andy Green and his supervisor Karl Glazebrook found a sample of local disk galaxies with high star formation rates and high velocity dispersions.  What could be producing the high star formation rates?  Green and collaborators suggest that rather than smoothly accreting gas, the local high star forming galaxies might be formed by mergers between similar sized galaxies, or they might result when larger galaxies swallow nearby gas-rich dwarf galaxies.  This would result in a high star formation rate and the violent nature of galaxy mergers could also explain the  increased turbulence.  The results are published in this week’s edition of Nature.  For more details, see

Potentially “habitable” extrasolar planet found
(1 October 2010)

Astronomers using the HIRES spectrometer on the Keck I Telescope, have announced the discovery of an Earth-sized planet orbiting a nearby star. The new planet, Gliese 581g, is at a distance that places it in the middle of the star’s “habitable zone” where liquid water could exist on the planet’s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered. Gliese 581g has a mass 3 to 4 times that of Earth and an orbital period of about 37 days. It is probably a rocky planet with enough gravity to hold on to an atmosphere.  For more details, see

Intergalactic magnetic fields detected
(24 September 2010)

This week Shin’ichiro Ando and Alexander Kusenko of Caltech and UCLA report that they have finally discovered evidence of the universal primordial magnetic field that has permeated space since the Big Bang.   It has been hypothesized for many years that an intergalactic magnetic field should exist, but until now there has been no way to measure the very faint field. Ando and Kusenko used images of active galactic nuclei (AGN), which are galaxies hosting supermassaive black holes, obtained by the Fermi Gamma-ray Space Telescope and found that the images are not as sharp as expected.  Space is filled with radiation from galaxies, as well as the background radiation from the Big Bang. When high-energy photons emitted by a distant source (like an AGN)  interact with the background radiation photons, they can be converted into electron-positron pairs. These electron-positron pairs can also interact and  be converted back into a group of photons at a later time.  If there are intervening magnetic fields along the way, the electrons and positrons can be deflected slightly which results in a slight  blurring of images of the AGNs.  Using stacked images of 170 of the brightest AGNs in the Fermi catalogue, Ando and Kusenko studied the shape of the ANG halos in the gamma-ray images and found that they were broadened (or “blurred”). The halo size and brightness suggests that the average intergalactic magnetic field is of femto-Gauss strength (which is 10-15 smaller than the Earth’s magnetic field). It is possible that the intergalactic magnetic field may have formed in the early universe shortly after the Big Bang and before stars and galaxies formed. For more details, see

New lunar crater catalogue reveals impact history
(17 September 2010)

Understanding the cratering history of the moon can tell us a lot about the population of small bodies in the early solar system.  The spatial density of craters on the lunar surface and the number of craters of specific sizes can be used to infer information about the age of the surface and the sequence of geological events. Imaging of the lunar surface can help with crater counts, but past studied have been hampered by uneven coverage of the lunar surface, different resolution of different imaging cameras, and a range of solar illumination that makes it difficult to compare data from different spacecraft missions. Using  the NASA Lunar Reconnaissance Orbiter (LRO), James Head of Brown University and collaborators have produced a catalogue of over all lunar craters over 20 km is size.  Rather than using images of the lunar surface, the team used the LRO’s laser altimeter to produce a detailed catalogue of 5185 craters.  The catalogue shows that some regions of the lunar surface are so heavily bombarded with impact craters that they have reached a state of “saturation equilibrium”. This means that the total number of craters remains constant, because new craters destroy old craters underneath them.  This means that these regions cannot be dated with crater counting techniques. There are also regions on the lunar surface that have undergone very little modification since their formation, which Head’s team suggest would be the most interesting regions for future mission as they likely contains the most ancient lunar samples.  The catalogue also supports the idea of two major impactor populations in early solar system history, known as the periods of “initial heavy bombardment” and “late heavy bombardment”.  The data show a clear difference in the size-frequency distribution of craters (and hence impactors) in the older highland regions of the Moon and younger mare craters.   There appears to be a clear separation between the initial heavy bombardment period that occurred at the time of Moon formed, and the late heavy bombardment between 4 and 3.8 billion years ago. The team’s findings are reported in this week’s edition of Science. For more details, see

More supernova evidence found in meteorites
(10 September 2010)

It has been suggested for several decades that the formation of our Sun and solar system may have been kick started by a nearby supernova explosion, causing our local molecular cloud to collapse and triggering star formation.  This idea comes from the tiny amounts of aluminum-26 and iron-60, which are both short–lived radioisotopes, found in tiny “pre-solar grains” in meteorites.  Cosmochemist Nicolas Dauphas from the University of Chicago and collaborators have extracted tiny nanoparticles from the primitive meteorite Orgueil which are highly enriched in chromium-54.  These presolar grains are only 100 nanometers in size, which is about 1000 times thinner than a human hair.  These neutron-rich isotopes are produced in type Ia and II supernovae and the Cr-54 enrichment seen in the grains found by Dauphas and collaborators can only come from supernovae.  But the strange thing about these isotopes is that they are not distributed uniformly throughout bodies in our Solar System.  Different planets and meteorites have different amounts of Al-26, Fe-60 and Cr-54 in them.  Indeed, Al-26 and Fe-60 are not found on Earth.  It is now thought that the a supernova sprayed a bunch of finely grained particles into the nebula which gave rise to our Solar System, but that during the formation process, these presolar grains were dynamically sorted by size. These grain size–sorting resulted in some grains being disproportionally incorporated into the meteorites and planets around the newly forming sun.  Dauphas and collaborators also hope that their research will be able to finally differentiate between the type of supernova that seeded our solar system with the isotopes – be it a type II supernova that results from the core–collapse of a massive star, or a type Ia supernova which results from the thermonuclear explosion on the surface of a small, extremely dense white–dwarf star in a binary system.  For more details, see

UV radiation helps create water around old carbon star
(3 September 2010)

When water was first found around the aging carbon-rich red giant star (or asymptotic giant branch [AGB]  star) called IRC+10216 in 2001, astronomers were puzzled because it was thought that water would be almost absent in carbon-rich stars.  Oxygen atoms should only be found in carbon monoxide and silicon monoxide molecules in these stars.  It was suggested that perhaps the water came from evaporating icy bodies likes comets. But with only a single water line found around a single carbon-rich AGB star, it was very difficult for astronomers to learn more about the formation of water.  A team led by Leen Decin from University of Leuven in Belgium used the Herschel satellite to observe IRC+10216, and they found dozens of new water lines in the far-infrared and sub-millimetre spectrum of the star.   Some of the water lines result from highly excited states that require temperatures greater than 1000°C.  This rules out the theory of evaporating icy comets, which would only deposit water in the cool outer regions of the star. Instead, the water must be present in the warm inner envelope of the star.  In this week’s edition of Nature, Decin et al. suggest that the water may be produced photochemically.  The outer layers of AGB stars are generally clumpy, and this lumpy structure allows UV protons from  nearby stars to penetrate the circumstellar envelope around the evolved star.  IRC+10216 is so cool that it emits most of its energy in the infrared, so it seems more likely that the UV photons come from an exterior source.  The high energy UV photons can then knock off oxygen atoms from carbon monoxide (CO) and silicon monoxide (SiO), releasing oxygen atoms which can then combine with molecular hydrogen (H2) to form water (H2O). This UV photochemistry also explains the high abundance of other molecules like ammonia (NH3). For more details, see

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