Now, a speedometer for determining the velocities of stars

Berlin, September 10 : An international team of scientists have developed a new instrument that can be called as a speedometer for determining the velocities of stars and other celestial bodies, which is a thousand times more accurate than previous methods.

Events on a cosmic scale are often barely discernable on Earth. This explains why astronomers are currently not able to prove directly that the universe is expanding at an ever-increasing rate, nor can they search for planets that are roughly the same size as Earth and revolve around a sun-like star.

An international team of researchers working with staff at the Max Planck Institute of Quantum Optics has now tested a measurement method that will allow such measurements to be carried out.

The scientists use a frequency comb to determine the colour of the light emitted by a celestial body with great accuracy. In a frequency comb, spectral lines, whose colour can be very accurately determined, are lined up in sequence.

The physicists then compare these spectral lines with the spectrum of astronomical sources.

Their aim for the future is to use this method to determine velocity changes of astronomical bodies with an accuracy of one centimeter per second.

This would make their method a thousand times more precise than the methods currently available, and would enable them to search for Earth-like planets or to test whether the expansion of the universe really is accelerating.

Planets outside of our solar system give themselves away only indirectly: As they revolve around their own particular star, the star experiences repulsion, and moves closer to or away from Earth in a periodic motion.

Astronomers can measure this using the Doppler Effect.

The light of a moving star shifts. If it is approaching, its light seems to shift towards blue; if it is moving away, it seems to be redder.

Using the frequency comb, the scientists were able to determine the colour of the starlight much more accurately.

"We are hoping that we will then even be able to measure shifts of one centimetre per second," said Thomas Udem, who heads the project at the Max Planck Institute of Quantum Optics in Garching, Germany.

At present, astronomers can only observe the Doppler effect for stars moving towards or away from Earth at a speed of ten meters per second.

The improved measurement accuracy could also help to determine whether the expansion of the universe is speeding up within a period of ten years or so. This is a conclusion drawn from the measurement of the cosmic microwave background.

ANI