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{tab= Weighing a black hole}
Weighing a black hole...
Is it too difficult to weigh a supermassive black hole - the one that sits at the centre of the galaxies? Henceforth, it may not be that difficult! Astronomers have invented a novel method for determining the mass of supermassive black holes which reside in the core of the galaxies. Method involves simply measuring the maximum temperature of the hot gases in the core of the galaxy. Temperature of the gases can be determined from the spectrum of the light emitted by them. Temperature can then be correlated to the mass of the black hole. More massive is the black hole, higher will be the temperature of the gases rushing towards it. Since the temperature near the vicinity of the black hole is of the order of millions of degrees, the light emitted by these gases is in X-ray region. This light can be picked up by X-ray space observatories like Chandra.
Composite picture of NGC 4649: (i) Chandra X-ray Observatory (purple) and (ii) Hubble Space Telescope (blue)
[Credit: NASA / CXC / University of California / STScI]
This technique was successfully applied to a giant elliptical galaxy, NGC 4649 (popularly known as M60). This galaxy lies in the constellation Virgo. It hosts one of the heaviest known supermassive black holes at its core. Conventional methods show that it is 3.4 billions times as heavy as our Sun. The conventional methods compute the mass of centrally located galactic black hole from the velocities of the stars in the galaxy or from the velocities of the gases around its core. These velocities are influenced by the gravitational attraction of the black hole, gravitational attraction itself being dependant on the mass of the black hole. The mass estimated by the newly developed method conforms to the traditionally determined mass. The new technique is based on ten year old prediction of Fabrizio Brighenti (Italy) and William Mathews (US), who foresaw the correlation between mass of the black hole and temperature of the surrounding gases.
{tab= Second-in-command}
Second-in-command ...
Eta Carinae is the brightest known star in our Galaxy. So far no other star seemed to compete with it. But now a star coming somewhat closer to it in brightness is known to the astronomers. This star lies at a distance of 26,000 light years, in Peony nebula near the Galactic centre. While Eta Carinae shines with a cumulative luminosity of about 4.7 million Suns, Peony nebula star has a brightness equal to that of 3.2 million Suns. Eta Carinae and Peony nebula star, both, were originally blue giants and are now evolved into what are known as Wolf-Rayet stars. They have masses in the range of 100 to 200 Suns and are at the end of their life cycle. They are losing their mass rapidly through the escaping stellar wind. They may explode as supernovae at any time. The brightness of the Peony nebula star was estimated by unveiling the dust curtain around it. This was achieved through the infra-red observations carried out by NASA's Spitzer Space Telescope.
Peony nebula star (inside the circle)
[Credit: NASA / JPL / Caltech / Potsdam University]
Albeit all this, it is obvious that these two stars may lose their supremacy in near future. Leader of the research team involved in these studies, Lidia Oskinova of Potsdam University (Germany), also admits - "There are probably other stars just as bright ......... that remain hidden from view!". What it requires to view these stars, is nothing but to effectively pierce through the Galactic dust that is environing them.
{tab= Surprising messages}
Surprising messages…
NASA's Messenger had a flyby over Mercury in last January. It will have two more flybys in the coming fifteen months. It will finally settle in an orbit around this least explored planet in year 2011. In the very first flyby itself, Messenger has issued the glimpses of lot of surprises that are in store. Messenger has revealed that the Mercurial magnetic field has distinct north and south poles. It has also shown that crust of the Mercury is iron-deficient. These observations indicate that the Mercury’s magnetism is generated inside its body and not locally in the crust. Dense core of this planet is exhibiting a dynamo effect - an effect similar to that in our Earth’s core. This dynamo effect is responsible for the magnetic field of Mercury. But there is a hitch here! For dynamo effect to take place, planet requires molten core. On the contrary, core of Mercury is expected to be solidified long back.
 
False colour image showing volcanic vents (Orange patches) and Wrinkles on the surface
[Credit: NASA]
Mercury is a heavily cratered planet. However, the craters on Mercury are much shallower than lunar craters. Plain fields are also seen on the surface of Mercury. It is now clear that volcanoes have played a salient role in designing this unusual surface. Messenger has identified volcanic vents on the surface of Mercury. Lava that has erupted from these volcanoes is responsible for the formation of smooth plains. This inference has got rid of the earlier impression that flatness of the basins is due to ejecta from the large meteorite impacts. Equally interesting are the wrinkles seen on the surface. They are formed due to shrinkage of surface that occurred three to four billion years ago, during the cooling of the core. All this information shows that that geological history of Mercury is very complex and also much different from that of our Moon. Astronomers are eagerly waiting for Messenger’s next Mercury flyby of October ’08 to explore these facts further.
{tab= SOHO – Not out 1500}
SOHO – Not out 1500 !
SOHO (Solar and Heliospheric Observatory) has proved to be the greatest comet hunter in the history of astronomy. Tally of the comets discovered by SOHO crossed the celebrated figure of 1,500 on June 25, 2008. This number exceeds total number of all other comets discovered so far. The newly discovered comet is very faint and small. It was first spotted by amateur astronomer Rob Matson (USA) in the images taken by SOHO. It required only 13 years for SOHO to reach this historic mark of 1,500. SOHO had its 500th comet discovered on August 12, 2002 and 1,000th comet discovered on August 6, 2005.
1,500th comet [Credit: NASA/ESA]
SOHO was launched in the year 1995. Its main task is to keep a continuous watch on Sun from the space. While carrying out this duty, it relishes watching the sun-grazing comets. About eighty-five percent of the fifteen hundred comets discovered by SOHO are themselves fragments of a huge comet that plunged around the Sun many centuries ago. (Probably, this was the same comet which was observed by Aristotle and Ephorus in 371 B.C.) The fragments are known as Kreutz group comets. Group bears the name of nineteenth century German astronomer, Heinrich Kreutz, who established the relationship of the sun-grazing comets to each other. These cometary fragments come from deep space and pass within 0.01 A.U. (1,500,000 km) of Sun. During this perihelion passage, most of these comets are evaporated due to solar heat.
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