Previous stories: S1-2010

Possible New Class of Supernovae Puts Calcium in Your Bones
(21 May 2010)

Hagai Perets and collaborators believe they have discovered a new type of supernova (SN). There are two main types of SN: (i) type Ia, which results from the violent thermonuclear explosion of cold, low mass, white dwarfs in a binary system as they accrete matter from their companion star and usually results in the complete obliteration of the exploding star, and (ii) type II, which occur when young, massive stars run out of nuclear fuel and undergo violent core collapse, producing a neutron star or a black hole.  SN 2005E is unusual in that half of the mass ejected from the SN explosion was calcium, making it one of 8 known “calcium-rich supernovae”.  Perets et al. argue that SN 2005E was not a type II SN, because of the small amount of mass ejected (much smaller than that normally ejected by massive stars) and because SN 2005E is quite removed from any stellar nurseries, where we expect to find type II SN, since these massive stars live fast and die young, and generally don’t have enough time to move far from their birthplace.   They instead argue that SN 2005E came from the explosion of an old, low-mass white dwarf in a binary, which stole helium from its companion. When the temperature and pressure in the surface of the white dwarf reach high enough values, a thermonuclear explosion is ignited, blowing off the outer layers of the star.  Unlike “normal” type Ia SN, SN 2005E  only ejected a small amount of mass (about 0.3 solar masses) and the gas was primarily composed of helium and calcium.  The Perets et al. interpretation is that unstable nuclear burning only caused partial disruption of the white dwarf and the explosive ejected a thin helium layer near stellar surface.  With just  a couple of SN like this ever 100 years, they would produce enough calcium to explain the abundance seen in the Milky Way – and the calcium required for life on Earth and in your bones!  For more information, see

Not all water is the same
(from 14 May 2010)

Continuing on our watery theme from last week, astrobiologists and NASA Mars mission teams have been trying to “follow the water” for some years now in the search for conditions that might be suitable for life.  In this week’s edition of the journal ‘Astrobiology’, PhD students Eriita Jones and her supervisor Charles Lineweaver demonstrate that now all water is good water and conclude that 88% (by volume) of the Earth’s water is not known to host life.  Using temperature, pressure and chemical composition data to constrain the watery environments in which life can survive here on Earth, Jone & Lineweaver say that these constraints can then be applied to extraterrestrial locations.  They find that the temperature limits range from -20C to 122C. In terms of pressure, life is found to exist at depths of 11km under the ocean in the Pacific’s Mariana Trench and in the low pressure environments as high as 10km above sea.  To sustain life on Earth, the water cannot be too salty or too lacking in nutrients either.  They find two potentially uninhabited sources of terrestrial liquid water: (i) hot and deep regions, where high temperature and restrictions on pore space, nutrients, and energy are limiting factors and (ii) cold near-surface regions, where low temperatures and low water activity are limiting factors.  For more information, see

The 4th phase of water
(from 7 May 2010)

The this week’s Herschel First Results Symposium in the Netherlands, Arnold Benz and collaborators presented their discovery of ionised water spectral lines in the Perseus star forming region.  Water is known to form on the surface of grains in regions cooler that -170 C, whereby oxygen and hydrogen form water on grain surfaces via a catalytic reaction.  In star forming regions, water can also be formed when X-ray and UV photons from the young stars dissociate carbon monoxide (CO) in their protostellar envelopes, which then allows the free oxygen atoms to combine with hydrogen to form water.  Benz and his team postulated that in star forming regions, water can also be formed when X-ray and UV photons from the young stars dissociate carbon monoxide (CO) in their protostellar envelopes, which then allows the free oxygen atoms to combine with hydrogen to form water.  It turns out that this water is about 10,000 times more abundant than catalytic ally generated water.  A portion of the oxygen atoms released by the dissociation of CO will be ionised, resulting in ionised water when temperatures reach about -20 C.  Using the superb spectral resolution of the HIFI (Heterodyne Instrument for the Far Infrared) on Herschel, up to 40 different transition lines of water can be detected, each sensitive to a different temperature.    Water plays an crucial role in star formation, as the molecules contributes to the cooling of the gas and dust clouds in which stars form.  And if you want your young stars to host a water planet like the Earth, obviously the system needs some water!  For more information, see

E-ELT site chosen
(from 30 August 2010)

On 26 April 2010, the ESO Council selected Cerro Armazones as the baseline site for the planned 42-metre European Extremely Large Telescope (E-ELT). Cerro Armazones is a mountain at an altitude of 3060 metres in the central part of Chile’s Atacama Desert, some 130km south of the town of Antofagasta and about 20km from Cerro Paranal, home of ESO’s Very Large Telescope.  For more information, see

Mystery of massive stars formation solved?
(from 23 April 2010)

It has long been know that massive stars, those between 10 and 100 time the mass of our Sun, begin hydrogen fusion while they are still collapsing, so why doesn’t the stellar radiation from nuclear fusion heat the infalling cloud and stop the collapse? New computer simulations show that the gravity acts on the massive collapsing gas cloud to form dense filaments which help feed material onto the growing young star as well as absorb the stellar radiation, protecting the collapsing cloud from being blown away. Thomas Peters of the Center of Astronomy at the University of Heidelberg and collaborators ran 3D gas dynamical simulations of the gravitational collapse of a massive, rotating molecular cloud that is heated by both non-ionizing and ionizing radiation. They find that local gravitational instabilities in the accretion flow (the gas falling onto the star) results in the formation of lower mass companions, and rather than ionising radiation stopping the growth of the massive star, the low mass companions compete for the accreting gas and eventually limits the growth of the massive star. For more information, see

Water in space
(from 16 April 2010)

It is believed that the water on Earth was delivered by comets early in the Solar System’s history, and that the comets were formed from the interstellar material that formed the cloud out of which our Solar System was created. So how is water formed in space? We know that the universe is abundant in hydrogen and we know that it can combine with molecular oxygen (O2) and ozone (O3) in the low temperature and pressure conditions of the interstellar medium (ISM), where T~10-100K and P~10^-14 mbars. The problem is that recent observations of the ISM find very little gaseous O2, and indeed O3 has never be
en detected in these regions. While atomic oxygen (O) is plentiful, gas phase reactions between H and O at these low pressures and temperatures cannot account for the amount of water observed in the ISM. Dust grains are known to be important in the formation of molecules in the ISM, providing a surface on which chemical reactions can take place. Victoria Frankland and collaborators at Heriot-Watt University have been conducting laboratory experiments to study surface chemistry to understand how oxygen atoms and molecules behave on the surface of dust and ice grains. Their preliminary results suggest that oxygen atoms may become trapped inside the icy mantles of the grains, which might explain the missing atomic oxygen as well as the formation of water in the ISM. The results were presented at the Royal Astronomical Society’s National Astronomy Meeting in Glasgow this week. For more details, see

Astronomers detect methane and carbon dioxide in Triton’s summer southern hemisphere
(from 9 April 2010)

Triton, Neptune’s large retrograde satellite, has a surface temperature of a very chilly -235C, but as the surface “warms up” during the summer years (a season lasts about 40 years on Triton), frozen nitrogen, methane, and carbon monoxide on the surface sublimate and add gas to the very thin atmosphere.  Using the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES) on the 8.2m VLT in Chile, Emmanuel Lellouch and collaborators have made the first infrared spectroscopic observations of Triton and confirmed the existence of methane gas (which was detected in the UV by the Voyager2 spacecraft in 1989), as well as detected carbon monoxide for the first time.   The atmospheric pressure is about four time higher than found by Voyager, suggesting that Triton’s atmospheric context is seasonably variable.  The amount of CO in the atmosphere affects the satellite’s temperature and planetary scientists will now need to revisit their climate models of Triton. (CRIRE now allows astronomers to study distant planetary bodies in great detail.  For more details, see

Cosmic background magnetic field strength measured for the first time
(from 2 April 2010)

It is well know that galaxies have magnetic fields but their origin remains uncertain.  It is generally thought that galactic magnetic fields arose from an amplification of some weaker “seed” field, for which there are two models.  Astrophysical or “bottom-up” models assume that the seed magnetic fields formed by the motions of plasma in proto-galaxies in the primordial universe which then propagated out into space, while cosmological or “top-down” models assume that the seed fields were produced in the early universe soon after the Big Bang, growing in strength as stars and galaxies formed.  New research by Andrii Neronov and Ievgen Vovk of the Geneva Observatory published in this week’s edition of ‘Science’ magazine suggests that the cosmological top-down model is correct.  By studying blazars, Neronov & Vovk have for the first time be able to provide  a lower limit on the intensity of the weak unamplified intergalactic magnetic fields.  Blazars are the bright cores of active galaxies that are orientated in such a way that they spew jets of energetic particles directly toward the Earth.  Like all photons, gamma-rays from blazars will travel through space unperturbed by magnetic fields.  But if a gamma-ray photon collides with another photon of much lower energy, it can split into an electron and a positron. Being electrically charged, the electron and positron will be deflected by magnetic fields. The particles recombine to form a gamma-ray but of lower intensity than the initial gamma-ray.  Neronov & Vovk searched through blazar data from Fermi and the High Energy Stereoscopic System (HESS) gamma-ray telescopes for gamma-rays of an intensity assuming that it had not split into particles and been deflected by an intergalactic magnetic field – but failed to find any. The lack of detection suggests that electrons and positrons were deflected by a magnetic field on their journey to the Earth.  They suggest that magnetic fields in intergalactic space must exist with a strength of at least 3e−16 Gauss (or one ten-million-billionths of the Earth’s field strength).  Being able to put a lower bound of the magnetic field strength of intergalactic space – not associated with galaxies or clusters – suggests that there was some process that acted on very wide scales throughout the universe, and hence supports the cosmological model.  For more information, see

Methane-eating microbes produce oxygen!
(from 26 March 2010)

Microbiology news of particular to our HET618 students was announced in this week’s edition of ‘Nature’. Until now there have only been three known pathways by which organisms can produce oxygen: photosynthesis, chlorate respiration and detoxification (or the enzymatic conversion) of reactive oxygen species.  Katarina Ettwig and collaborators have just discovered a fourth biological pathway, whereby microbes extract energy from via chemical ‘denitrification’, which releases nitrogen and oxygen from nitrogen oxides. Methylomirabilis oxyfera can survive in layers of methane-rich but oxygen-poor mud at the bottom of lakes and rivers, living on a diet of methane and nitrogen oxides. With the help of an enzyme M. oxyfera combines nitric oxide molecules to form nitrogen and oxygen, and then uses the oxygen to metabolize methane to produce water and carbon dioxide. It has been suggested that such organisms could have thrived on methane sources on early Earth and on other planets and moons, such as Mars which has localised regions of enhanced methane, and Saturn’s satellite Titan which has shallow pockets of liquid methane.  For more information, see

First Planck images of the Milky Way’s cold dust
(from 19 March 2010)

The Planck satellite is mapping the large scale Universe in the microwave part of the spectrum (which one of its primary science goals being the measure and Cosmic Microwave Background).  Using the High Frequency Instrument, Planck has mapped the solar neighbourhood out to about 500 light years from  the Sun at 350 and 540 microns. These frequencies map the cold dust content of the Milky Way galaxy and have revealed a detailed filamentary structure.  The map clearly shows warmed dust near the midplane of the Galaxy and molecular clouds and diffuse cirrus.  The filamentary structure seen in the cold dust from molecular clouds and cirrus are effected by a range of forces, including galactic rotation, gravity, stellar radiation and magnetic fields.  For more information, see

Astronomers use Keck to find the smallest known binary system to date
(from 12 March 2010)

HM Cancri consists of two white dwarf stars that orbit each other in just 5.4 minutes, which is the shortest known orbital period of any pair of stars.  Discovered in 1999 by the ROSAT satellite, HM Cancri was first detected as a weak X-ray source. In 2001 the X-ray and optical data suggested HM Cancri consisted of two white dwarfs orbiting each other in 5.4 minutes.  This would suggest that the combined binary system is only about 8 times the diameter of the Earth!  Using the spectrometer on the 10m Keck I telescope, Gijs Roelofs and collaborators have detected a 5.4-minute period shift in the helium emission lines, confirm the binary’s 5.4-minute period.  Thus HM Cancri represents a new “cosmic laboratory” with which astronomers can study both the evolution of stars and general relativity.  The binary system must be emitting gravitational radiation and will be an important target for the future LISA satellite.  For more information, see

The asteroid that killed the dinosaurs
(from 5 March 2010)

A new study has confirmed that an asteroid impact ended the reign of the dinosaurs ~65.5 million years ago. The Cretaceous-Paleogene boundary (formerly known as the KT boundary) marked one of the largest mass extinctions of the past 500 million years, including the end of the dinosaurs. There are many locations around the world which show a thin layer of sediment in the rock record at the KT boundary that is particularly rich in iridium. Iridium is an element that this rare in the Earth’s surface rocks but quite common in meteorites. This lead to the hypothesis that a giant asteroid impact wiped out the dinosaurs. The asteroid theory was supported by the discovery of the 200 km wide Chicxulub Crater on the coast of the Yucatan peninsula, Mexico. However, the end of the Cretaceous period also saw extreme volcanic activity in the Deccan Traps area in western Indian. While the Earth’s crust is low in iridium, the core contains higher iridium abundances which may be brought to the surface by volcanism. An alternative to the impact theory is that a long period of volcanic eruptions deposited the global iridium layer, and the release of sulfur and carbon dioxide during these eruptions triggered global climate change that resulted in a mass extinction. Peter Schulte and collaborators present a detailed study of the evidence in the impact versus volcanism theories in this week’s edition of “Science” magazine and conclude that the evidence weighs more strongly toward the giant impact theory. For more details, see

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