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{tab=Success of PSLV continues}
Success of PSLV continues …
On April 28, ISRO’s Polar Satellite Launching Vehicle PSLV-C9 successfully launched ten satellites in a single mission from Satish Dhawan Space Centre, SHAR. The battery of satellite had 2 Indian and 8 foreign satellites in it. Indian satellites consisted of CARTOSAT-2A and IMS-1, both being remote sensing satellites. While CARTOSAT weighs 690 kg., IMS-1 weighs 83 kg. High-resolution data from CARTOSAT-2A will be used for large scale mapping involving urban and rural development applications. Other eight satellites were nanosatellites developed by Canada, Denmark, Germany, Japan and Netherlands. Total weight of these nanosatellites is 50 kg. It is twelfth consecutively successful PSLV flight. India’s first mission to Moon will use the same vehicle for launching Chandrayaan-1 spacecraft.
Launching of PSLV-C9
[Credit: ISRO]
{tab=Untimely end?}
Untimely end?
Celestial objects, which are potentially dangerous to earth, consist of asteroids and comets. But now, one of the planets also may have to be listed as a dangerous object. And this planet is none but Mercury. Mercury's orbit is going to be changed drastically in future. Of course, time required for Mercury to start behaving in extremely chaotic manner will not be short but may be in terms of billions of years. However, it will be little before our Sun reaches red giant stage and engulfs our Earth. Therefore, it may not be the Sun but Mercury that will bring our world to an end. Reprieve is that the chances of this untimely (!) end are only 1% to 2%.
We think that our solar system is very stable. Simulation studies carried out independently by French and American scientists show that it is not so. This instability will not be manifested for at least 40 million years from now. But after this time period, ill-effects on the path of Mercury will be clearly seen. Jupiter's gravity will start slowly elongating the orbit of Mercury. The eccentricity of Mercury will change from existing 0.2 to more than 0.6 in few billion years. Then Mercury will cross Venus's orbit bringing Venus into trouble. And then it may be our Earth's turn! Mercury may collide with Earth and the later will glow at red-hot temperature for a millennium or so. With this, life on Earth will obviously cease to exist!
{tab=Shaky Sun}
Shaky Sun...
Whenever severe earthquake occurs, our Mother Planet experiences global 'postquake' vibrations. These postquake vibrations continue for several weeks. Sun also experiences similar global postquake ripples. Large solar flares induce intense sunquakes and these intense sunquakes, in turn, induce postquake vibrations. These are the observations made by Solar and Heliospheric Observatory (SOHO) spacecraft which is keeping a continuous watch on Sun.
Uprising Sunquake (1996)
[Credit: SOHO/ESA/NASA]
These peculiar vibrations are not new to astronomers and are known as '5-minute oscillations' (because of their oscillation period of 5 minutes). But the correlation between these vibrations and solar flares was not known so far. The correlation is now clearly established. Whenever the number of flares increases, the strength of the vibrations also increases. Mechanism behind this correlation is not yet understood. But the scientists feel that other sun-like stars also must be exhibiting similar vibrations. In future, it may be possible to use similar phenomenon for detecting the flares on these stars.
{tab=Coldest Star}
Coldest Star...
Can you imagine a star to have surface temperature lower than that on the surface of Venus?.....Or lower than day-time temperature on the surface of Mercury? Yes! Such a star exists. International team of astronomers has discovered a star with a surface temperature as low as 350°C. It is a brown dwarf...and also coldest brown dwarf known so far! This brown dwarf is located 40 light years away from us and it lies in the constellation Cetus. It was discovered under the auspices of 'Canada-France Brown Dwarfs Survey' programme, using the telescopes in Hawaii and Chile.
[Credit: Canada-France Brown Dwarfs Survey programme]
Brown dwarfs are those stars which could not evolve properly. These stars do not have sufficient mass for its core to get adequately compressed. Core temperature in these stars is not high enough for self-sustaining thermonuclear reactions to get triggered. Consequently, surface temperature of the brown dwarf stars is also very low. These stars can be termed as 'cool stars'. This newly discovered cool star is only 15 to 30 times heavier than Jupiter. Stars are spectroscopically tagged as O, B, A, F, G, K, M, L, T in decreasing order of surface temperature. Probably this particular star represents a new class of ultra-cool stars to be recognised as Y-type stars. Spectroscopic studies have revealed presence of ammonia in the atmosphere of the star. It is first time that ammonia is detected in the atmosphere of a brown dwarf. Ammonia is an important ingredient of the atmosphere of Jupiter. Hence, these stars may form a link between brown dwarfs and Jupiter like giant planets.
{tab=Omega Centauri ... a galaxy?}
Omega Centauri - Not a cluster but galaxy?
Omega Centauri is a famous deep sky object. No skygazer having an access to southern skies can miss this object. As it holds millions of old stars in a small diameter of about 200 light years, it is considered to be a globular cluster belonging to our Milky Way Galaxy. But tomorrow, one should not be surprised to hear that it itself is a galaxy – a dwarf galaxy! If the designation of this object be changed, credit should go to the probable black hole sitting at the centre of this cluster.
Eva Noyola of Max-Planck Institute (Germany) and her colleagues estimated the velocities of stars inside this globular cluster using the data obtained from Hubble Space telescope and Gemini South telescope (Chile). The velocities were observed to be very high. These observations led to consider an existence of intermediate size black hole at the centre of the globular cluster. Mass of this black hole is expected to be equivalent to 40,000 Suns. Eva Noyola further thinks that Omega Centauri may be a dwarf galaxy divested of its outer stars. As the cluster is located close to the plane of our Milky Way Galaxy, these stars might had been lost through an interaction with the Galaxy. This dwarf galaxy could have had initially a mass of about 10 million solar masses, which is now reduced to 5 million solar masses. Some scientists think that such intermediate-size black holes may be a key to the formation of supermassive black holes found at the heart of bigger galaxies.
{tab=Smallest black hole}
Smallest black hole...
Astronomers are interested in knowing smallest possible mass for a black hole having a stellar origin. The predicted lower limit is between 1.7 and 2.7 solar masses. A dead star with a mass less than this will be either a neutron star or a white dwarf. (Lowest limit for mass of neutron star is 1.4 solar masses.) NASA's scientists have now discovered a small black hole with a mass equal to 3.8 solar masses. Though the mass is still far from the predicted limit, this discovery is considered to be a big step towards the reality. Because smallest black hole known so far has a mass of about 6.3 solar masses.
Black hole is drawing material from its companion (Artist's concept)
[Credit: NASA]
If a black hole has a companion star orbiting around it, black hole draws material from the later gravitationally. This extracted material, while spiralling towards the black hole, gains sufficient energy to emit X-rays. Intensity of these X-rays varies in a near-periodic manner. Period of variation depends on mass of the black hole. Incidentally, the black hole under scrutiny has a companion star, from which the black hole is imbibing material. X-rays emitted during this process were temporally characterised by NASA's Rossi X-ray Timing Explorer satellite. Mass of the black hole was calculated from the results. And it turned out to be the smallest stellar black hole discovered so far!
{tab=Titan is in hurry}
Titan is in hurry...
Rotation of our Moon around its own axis is synchronised with its revolution around Earth. Similarly, Titan was also supposed to be having a rotation synchronous with its revolution around its parent planet, Saturn. Titan should then complete one rotation in 15.9454 days. But radar observations carried out by Cassini show that Titan is speeding up. This is evidenced by the shift of the surface features of Titan from the expected position. The features are shifted by 31 kilometres in a period of about 20 months. This corresponds to an annual change of 0.36° in its rotational speed. Though the change is only 0.004%, it is suggestive of a geologically important fact.
Surface of Titan
[Credit: NASA/JPL]
Titan has an atmosphere which is one and half times denser than that of Earth. This heavy atmosphere can have significant effect on the rotation of frozen crust of Titan. It may result in the crust showing different rotation than that of rest of the body. But for this to happen, crust has to be detached from the core. And it is probably the ocean of water and ammonia that is detaching the crust of Titan from its core! Such ocean should exist below the crust of Titan at a depth of about 100 km. If this hypothesis is correct, then maximum change in the rotation of Titan should occur between the years 2008 and 2010 as predicted from the expected seasonal changes. The prediction will be tested by Cassini spacecraft in coming years. This link between the rotation of Titan and its anatomy is really interesting. Cassini radar scientist, Ralph Lorenz, rightly says - "It has given us a window into Titan's interior beneath the surface."
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