Archive for December 19, 2012

Venus Transit And Lunar Mirror Could Help Astronomers Find Worlds Around Other Stars

December 19, 2012 Leave a comment

When Venus passes in front of the Sun it hides a part of our star’s rotating surface. Because of rotation, the spectrum of the Sun (created splitting the different colours of light using a spectrograph) is slightly different on each side. On one side, the solar surface is rotating towards the observer and so its light will be ‘blueshifted’, meaning the lines seen in a spectrum move towards shorter wavelengths. On the other, the surface is rotating away from the observer, so its light is ‘redshifted’, meaning that the lines move towards longer wavelengths.

By looking at the reflected light from the lunar surface, this is averaged out as a broadening of the various lines. When Venus moves in front of the Sun from east to west, it first blocks out the surface moving towards us and then the surface moving away from us. This causes a distortion in the spectral lines known as the “Rossiter-McLaughlin effect”.

The astronomers realised that the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph installed on a 3.6m telescope at La Silla in Chile, part of the European Southern Observatory (ESO), would be sensitive enough to detect the effect and that the Moon would be in the right place too. The Moon was slightly ahead of the Earth in its orbit, so ‘saw’ the transit a couple of hours later than terrestrial observers. This also meant that the Moon was in the night time sky in Chile, making it possible for the La Silla telescope to operate safely and observe the change in the solar spectrum.

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Alcohol Constrains Physical Constant In The Early Universe

December 19, 2012 Leave a comment

Radio-astronomical observations of a distant galaxy indicate that the ratio of the proton’s mass to that of the electron has hardly changed over cosmic history. This fundamental constant of nature has changed by 10-7 or less, equivalent to a maximum of one hundred thousandth of a percent, in the past 7 billion years. Scientists from VU University Amsterdam and the Max-Planck-Institut für Radioastronomie (MPIfR) used the Effelsberg 100-m radio telescope to obtain accurate measurements of methanol absorption at several characteristic frequencies. Methanol, the simplest form of the family of alcohol molecules, was observed in a distant galaxy at redshift z=0.89 toward the quasar system PKS1830-211. The resulting stringent limit on the proton-to-electron mass ratio shows that molecules and molecular matter are, with high accuracy, the same now as 7 billion years ago. The work is published online in Science Express on 13 December 2012.

A fundamental constant such as the proton-to-electron mass ratio cannot be calculated from any currently known theory, it can only be measured. The Earth-bound experiments agree upon its value but the explanation for it is still missing. Therefore, a possibility remains that the proton-to electron mass ratio was different in different places in the universe or at different epochs in cosmic history. The methanol molecule is a very sensitive probe for detecting a drift of the proton-electron mass ratio. Some lines in the microwave spectrum of this molecule would undergo a rather large shift upon a variation of the proton-to-electron mass ratio µ, while other lines are not affected (so-called “anchor lines”). Recently the Amsterdam group found that the hindered internal rotational motion in molecules such as methanol (in fact also a quantum tunneling process) can give rise to very high sensitivity coefficients. The sensitivity of each spectral line can be expressed in a value K, which may be calculated.

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