Highly accurate measurements about a star's features can be made by using its gravity
so far only optical and radio telescopes have been the tools for astronomers. Even with these powerful tools, the stars being far away are usually visible only as point sources of light. But recently, in a highly unusual set of observations, gravity of one star has been used to magnify the light from a distant star, allowing astronomers to observe features of the star which are not ordinarily visible with telescopes, not even the Hubble Space Telescope (hst) (Science, Vol 275, No 5305).
Gravitational lensing is a very definite prediction of the Einstein's theory of gravitation. The essential idea is that light from a background object is bent by the gravitational attraction of a foreground object, much like the bending of light by ordinary lenses.Depending upon the alignment, the sizes of the source object and the lensing object and a host of other factors, different kind of phenomenon like the famous Einstein rings are observed. Lensing has been observed for very distant objects like quasars and there have even been reports of microlensing, that is, lensing of background objects by very small (about Jupiter sized) brown dwarfs in our own galactic halo. Recently, a multinational collaboration called massive compact halo object (macho), has reported an amazing gravitational lensing event which has allowed them to study a star, Red Giant, located about 30,000 light years from us with a resolution which is several thousand times better than the hst .
In this particular event, the macho collaboration noticed an unusually good alignment of the earth and the two stars, the source and the lens. Immediately, a worldwide alert was issued and telescopes around the world started collecting data on the spectrum and other parameters of the event. The interesting thing about the event was that it allowed astronomers for the first time to observe the details of the surface of the Red Giant with an unprecedented accuracy. This will be useful in testing out many theories about the structure and dynamics of such stars. Though the original aim of the macho collaboration was to search for dark matter in the galactic halo, the group may along the way help us understand many of the paradoxes about the universe and its constituents.
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