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Articles: Devotion | Quest for Infinity - 08
- Prof. venkata ramanamurty mallajosyula
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OK, Vera Rubin’s studies have shown that there probably is some dark matter out there. Can we have more concrete evidence for it? That question has been addressed, via the search for what are called MACHOS. MACHO [MAssive Compact Halo Object] is the name given to one type of dark matter called brown dwarfs. A brown dwarf is a celestial object anywhere between 10 to 80 times heavier than our Jupiter [which is a pretty heavy planet by the way]. Brown dwarfs do not emit much light since there is no thermo-nuclear process taking place within. Thus, a brown dwarf that is far away would not be seen even the best telescope man can build. Any other way to detect the existence of the brown dwarf? Sure, and that is by noting that the brown dwarf has gravitational pull even though it might not be visible.
Vera Rubin
Astronomers said, “Hey, wait a minute. Sure we cannot see the brown dwarf but how about detecting its presence by gravitational microlensing?” The idea behind this technique is illustrated in Figure 4. In a manner of speaking, it is all like the famous experiment done earlier to detect the bending of light by gravity; this time, the bending is used to detect the presence of MACHO. Keeping this in mind, it should be easy to follow Figure 4.
This figure illustrates the principle of microlensing, using which MACHOs are detected. In (a) we have a star whose light reaches the Earth without any obstruction. In (b), a MACHO intervenes, eclipsing the star. As a result, light beams that would have gone away from the Earth are now pulled in. This causes a net enhancement of the light intensity if starlight. In (c) is illustrated how the intensity of starlight peaks, while the MACHO is transiting across the line connecting the Earth to the star.
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