Mirror image molecules in Orion


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Mirror-image molecules sorted in the Orion Nebula

But Pasteur’s hope for a cosmic driver comes true only locally

A predominance of either left-handed or right-handed versions of molecules is likely within huge dust clouds imaged by Japanese astronomers. The electric field of light rays coming from the clouds corkscrews to the left or corkscrews to the right, with “circular polarization”. The different kinds of clouds are clearly distinguishable in a massive star-forming region within the Orion Nebula, called BN/KL. Yellow denotes left-handed light, and red, right-handed. The largest yellow and red features are about 100 times wider than the Solar System, and the astronomers suggest that the polarized light will favour the formation of left-handed or right-handed molecules. The conspicuous dots left of centre near the bottom are bright young stars of the Trapezium group — strong winds  from which have helped the astronomers by blowing away dust that otherwise would obscure the BN/KL region of interest. Credit: Near-infrared (2.14 μm) image with the SIRPOL polarization instrument, NAOJ.

On seeing this report by Tsubasa Fukue and Motohide Tamura of the National Astronomical Observatory of Japan (with colleagues in Japan, UK, Australia and USA) my mind went straight back to Louis Pasteur.

Alanine, an amino acid, has mirror-image forms. L (laevo) rotates the electric field of light to the left and and D (dextro) to the right. Image NAOJ.

Although immortalized for the germ theory of disease, Pasteur’s initial claim to fame came from a discovery he made as a young student – namely that molecules from living sources have effects on the polarization of light, but the same molecules made synthetically do not. This is the phenomenon of chirality, or handedness. Chemists had to learn to think three-dimensionally about versions of molecules that are mirror images of each other. In the example shown here, every amino acid molecule in living things on Earth is of the left-handed (L) kind.

Molecular handedness is a fundamental feature of life and Pasteur suspected that some fundamental feature of the Universe was responsible for it. The phenomenon has been both a puzzle and a spur for investigators of the origin of life. The fact that carbon compounds in meteorites show the same bias in handedness as that seen on Earth suggests that some physical process was at work throughout the Solar System, at least.

The astronomers now offer an answer. Circularly polarized light pervading the dust cloud in which the Sun and its planets were born would have prompted our molecular bias. The scenario is made convincing by the sheer size of the clouds in Orion possessing one polarity or the other. But it ‘s not the Universe-wide mechanism that Pasteur expected. It seems that if the Solar System had originated in a cloud with the opposite kind of circularly polarized light, all our amino acids would be dextro.

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Tarantula’s Superstar


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The Tarantula’s Superstar

The star at the very centre of this picture, called R136a, turns out to be nearly ten million times brighter than the Sun. It’s now revealed to be by far the most massive star ever discovered. Its current mass is 265 times that of the Sun and it probably had 320 solar masses at birth. The superstar lies 165,000 light-years away in a neighbouring galaxy, the Large Magellanic Cloud, at the very heart of a huge nebula aptly called the Tarantula. The European Southern Observatory (ESO) obtained this infra-red image with the MAD adaptive optics instrument on the Very Large Telescope in Chile. Credit: ESO/P. Crowther/C.J. Evans

The report by Paul Crowther of Sheffield and his colleagues, released today, is in press in the Monthly Notices of the Royal Astronomical Society, under the title “The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Mstellar mass limit.”.

The Tarantula Nebula in a mosaic of images from ESO's 2.2-metre telescope. Credit: M. Schirmer, T. Erben, M. Lombardi, IAEF Bonn, ESO

What fascinates me is to picture the young superstar R136a, and her obese sisters b and c, hurling off gas equivalent to dozens of suns. Combined with the pressure of their intense radiation, the resulting winds have shaped the Tarantula Nebula with its spidery arms that stretch 500 light-years from the stormy centre.

The theorists will now have a merry time explaining how such a massive star could form from a gas cloud without breaking up into a swarm of normal objects. The discovery also lends credence to an idea that very massive stars can explode as supernovae, scattering chemical elements into space, without leaving any relic like a neutron star or black hole.

Fierce stellar black hole


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A fierce stellar black hole

To get this X-ray image, to be published in Nature tomorrow, NASA’s Chandra satellite stared at a galaxy 13 million light-years away in the Sculptor Constellation for a total of 14 hours. The tartan pattern of pixels is a symptom of the great distance. A stellar black hole, or microquasar, seen location-wise in blue (X-rays of 2-8 keV), is throwing out two huge jets of hot gas reaching to the yellow-red hot-spots (X-rays of lesser energy). The contour lines are for emissions from hydrogen atoms measured by the Cerro Tololo Inter-American Observatory. Other observations by the European Southern Observatory help to confirm that we’re seeing an exceptionally massive and greedy microquasar shedding much of its energy in the form of long jets of hot gas. From one jet end to the other is about 300 parsecs or 1000 light-years – roughly the distance from the Solar System to the bright stars of Orion.

Nigel Calder comments: Apologies for two brief “Pick of the pics” in a row. I’ve been busy with writing unrelated to this blog.


Manfred W. Pakull, Roberto Soria and Christian Motch, “A 300 parsec long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793”, Nature, 466, pp. 209–212, 8 July 2010. The text of the paper is available here: http://www.eso.org/public/archives/releases/sciencepapers/eso1028/eso1028.pdf