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{tab= Comet Holmes - Larger than sun}
Comet Holmes - Larger than sun...
At present, Comet Holmes is larger in size than Sun - and hence largest object in our solar system. Expanding cloud of gas and dust around its nucleus measures more than 1.4 million kilometers in diameter. Cloud is expanding at a steady rate of about 0.5 km/sec. Following photograph compares the sizes of the comet and the Sun. Photograph of the comet was taken using 3.6 meter Canada-France-Hawaii Telescope on Mauna Kea (Hawaii). (Sun is photographed by SOHO.) Inset indicates size of Saturn. Tiny cometary nucleus, which has a diameter of 3.6 kilometers, is seen as a white spot in the central region of the Comet Holmes' photograph.
(Click the image to enlarge)
{tab= Making of a Supernova - New Recipe}
Making of a Supernova - New Recipe...
Supernova is an immediate consequence of gravitational collapse of massive dying stars. It is a catastrophic explosion that generates gigantic quantities of energy. Now scientists have discovered that supernovae may result from merging of dead stars themselves. White dwarfs indicate end state of stars with low and medium mass. They are, in fact, compact cores of their progenitors. They are so tightly packed that there cannot be further compaction of matter. But when two such white dwarfs collide, there may be sufficient mass for further gravitational contraction. This will result in further compaction of the matter which constitutes the white dwarfs. This may happen with a simultaneous gigantic explosion, which in nothing but a supernova for distant observers. And such a case has been discovered by Malcolm Hicken and his colleagues from the Harvard-Smithsonian Center for Astrophysics.
Merger of white dwarfs - Artist's Conception
(CfA press release)
This event was observed in a one of the spiral galaxies in the constellation of Hercules. Analysis of the spectroscopic observations of this supernova indicated lack of hydrogen, but presence carbon and silicon layers. The distribution of these elements around the zero point suggested that the explosion involves not a single 'regular star' but a colliding white dwarfs. These white dwarfs are supposed to be spiraling each other before the collision. Total mass of the two must have exceeded Chandrasekhar's limit of 1.4 solar masses. Final product of this process may be a neutron star.
{tab= Competitor to our Solar System}
Competitor to our Solar System?
Stars with planets revolving around them are not uncommon to today's astronomers. More than 250 exoplanets have already been discovered. But no star was known to host more than four planets in its planetary system. Now a star '55 Cancri' from the constellation of Cancer is entitled for this honour. This star has a mass almost similar to that of our Sun and bears a quintuple planetary system. The star is 41 light years away from us. Star was known to have 4 planets revolving around it. Fifth-one was discovered recently by Debra Fischer, San Francisco State University and co-workers using Shane telescope at Lick Observatory (USA). The planet was detected from the wobble it created in parent star. Interestingly, this planet is in 'habitable zone'. If this planet were to have any satellite, it may hold liquid water on it.
Fifth planet - Artist's impression (Credit: NASA)
Newly discovered planet is fourth planet from the parent star and is at a distance slightly shorter than that between Earth and Sun. It is 45 times heavier than our Earth and has an orbital period of 260 days. It is expected to have characteristics similar to those of Saturn. Planet nearest to the parent star in this system is at a distance, one-tenth of that between Sun and Mercury. This planet is of size similar to that of Neptune and completes a revolution around the parent star in less than three days. Fifth and farthest planet is at a distance little greater than that between Jupiter and Sun. This planet is four times heavier than Jupiter (more than 1200 times heavier than Earth) and completes its orbital revolution in about 14 years. Discovery of all the five planets is an outcome of 18 years of continuous observations.
{tab= Race to Moon}
Race to Moon...
Our Moon is getting enriched with artificial satellites. Japanese had their contribution recently and now Chinese are contributing their share. Chinese lunar orbiter Chang’e-1 has entered the lunar orbit. After final maneuver, Chinese lunar orbiter will be slowed down to a speed of 1.59 km/sec. This will place the orbiter in a polar circular lunar orbit at a height of 200 km from surface. In this orbit, it will take 127 minutes to complete a revolution around Moon. This 2,350 kg heavy orbiter was launched on October 24, 2007 from the Xichang Satellite Launch Centre in southwestern Sichuan Province of China. This mission is named after Chinese Goddess of the Moon.
Launching of Chang'e 1
This mission is being executed by Chinese National Space Administration with a support from European Space Agency. The orbiter will carry out three-dimensional imaging of lunar landforms and it will analyse lunar soil to study the distribution of 14 chemical elements across the lunar surface. It will also measure the depth of the soil and will explore space weather between Earth and Moon. These mission objectives will be accomplished within one year of its operation. This mission is considered to be a first step towards China's ambitious programme for landing robotic explorers on the Moon.
{tab= 'Lake District' of Titan}
'Lake District' of Titan...
'Lake District' is a popular tourists' place in England. Now Saturn's largest moon - Titan can also boast to have a 'Lake District'. Tourers would be happy with the news. Cassini has revealed a presence of hundreds of lakes in north polar region of Titan. While orbiting Saturn, Cassini spacecraft is mapping Titan's cloud-covered surface using its radar. In last one and half year, Cassini has mapped more than 60% of this north polar region. Cassini's flybys of over Titan have shown later to have around 400 observable lakes with area greater than 1 sq. km. One of these lakes measures larger than Lake Superior (North America), the biggest fresh water lake of the world. The area of this large Titanian lake is more than 100,000 sq. km. Cassini spacecraft has detected some such lakes even in region around south pole of this Saturnian moon.
Lake on Titan (Credit: NASA)
Now a word of caution for tourists! These lakes are not water lakes but are filled with liquid hydrocarbons like methane and ethane, compounds which make liquified natural gas (LNG). Furthermore, there is a persistent drizzle every morning on Titan. And this drizzle is of methane! Titan is known to have 'methane cycle' instead of 'water cycle'.
{tab= Heavy-weight Riddle}
Heavy-weight Riddle...
Massive stars have black holes as their end states. These black holes of stellar origin are expected to weigh not more than 10 solar masses. But recently, a discovery of a massive black hole of such stellar origin with unthought-of mass, equivalent to 16 solar masses was announced through a press release of Chandra X-ray Observatory. This black hole resides in the galaxy M33, which is about 2.7 million light years away. When discovered, this was the most massive black hole of its kind. But this black hole could not enjoy its supremacy for a long. Within couple of weeks, a discovery of still heavier black hole of stellar origin was announced by Harvard-Smithsonian Centre for Astrophysics and NASA. This black hole is more massive than 23 Suns. It is situated in a dwarf galaxy lying in the constellation of Cassiopeia and is about 1.8 million light years away. Both of these black holes have a stellar companion. These heavy weight black holes have raised doubts about the conventional models of stellar evolution.
Surroundings of black hole - Artist's concept)
(Credit: NASA)
According to conventional models, more than 95% of the stellar mass is shed into space during the evolution of massive stars. This suggests that progenitor of these stars had very high mass and consequently should have had such a large size that they might have formed a common envelope around their companion stars. Jerome Orosz of San Diego State University (USA) argues that such a common envelop around companion stars is not theoretically possible, unless the amount of mass lost from the progenitor during its evolution was ten times less. Jerome Orosz and his colleagues were involved in the discovery of '16 solar mass' black hole. Roy Kilgard of Wesleyan University (USA), who was one of the investigators for the discovery of '23 solar mass' black hole says that these heavy black holes might have been produced in our Galaxy also, but only during its early days. These arguments have turned the discovery of the record-breaking massive black holes into a puzzling vista.
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