The Telegraph
Saturday , June 10 , 2017

Indian role in measuring star mass

Illustration shows how the Hubble telescope was used to weigh the white dwarf

New Delhi, June 9: Scientists led by an Indian-origin astronomer in the US have directly measured the mass of a star for the first time using principles of Albert Einstein's century-old theory that says gravity bends light.

Kailash Chandra Sahu at the Space Telescope Science Institute and his collaborators have used the Hubble Space Telescope and calculated that the mass of a nearby white dwarf star is about 68 per cent of the Sun's.

While astronomers have measured the masses of myriad stars in the past, the novelty lay in the technique that the scientists employed. They observed the white dwarf as it passed in front of a distant star and, during the close alignment, they measured the deflection of the star's light by the white dwarf's gravity that would make its position in the sky appear offset by about two milliarcseconds from its actual position.

"This deviation is so tiny that it's like trying to observe a firefly move near a light bulb in Delhi from Chennai," Sahu told The Telegraph. Using the deflection measurements, the researchers calculated the dwarf's mass.

Scientists first observed the deflection of light during an eclipse in 1919. Since then, astronomers have widely used this gravitational microlensing effect to study images of distant galaxies.

Sahu and his colleagues searched more than 5,000 stars for the right alignment that would help them weigh a star -- and picked on the white dwarf located 17 light years away, and the star about 5,000 light years away.

"This is a huge technological achievement - it's very challenging to measure such a small deflection," Dipankar Bhattacharya, a senior astronomer at the Inter-University Centre for Astronomy and Astrophysics, Pune, who was not associated with the feat. "It is also heartening the mass of the white dwarf detected through such a direct method is nearly the same as had been predicted by stellar evolution theories. This validates our models of stellar evolution," he added.

Howard Bond, an astronomer at Pennsylvania State University, has called the new measurement a fresh "triumph" for the Hubble Space Telescope, a space-observatory launched by the US National Aeronautics and Space Administration 27 years ago.

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