Wednesday, February 28, 2007
Wednesday, February 21, 2007
Further about neutron star and the core of collapsed matter!
Then, it follows that for the typical neutron star discussed earlier, the specific gravity of 5*10**14 yieds a critical radius of 4*10**9 km/sqrt(5*10**14) =180 km approx. Thus the neutron star still falls short of becoming a blackhole (10km radius as against the required 180km). For the collapsed core referred to earlier, the critical radius becomes 180/sqrt(2) km = 127 km, which too should be visible and not a blackhole unless a core of 127 km radius is achieved!
srini
Then, it follows that for the typical neutron star discussed earlier, the specific gravity of 5*10**14 yieds a critical radius of 4*10**9 km/sqrt(5*10**14) =180 km approx. Thus the neutron star still falls short of becoming a blackhole (10km radius as against the required 180km). For the collapsed core referred to earlier, the critical radius becomes 180/sqrt(2) km = 127 km, which too should be visible and not a blackhole unless a core of 127 km radius is achieved!
srini
Monday, February 19, 2007
Getting denser!
For gold, r(critical) becomes 0.7*10**9km (a shining blackhole!); for platinum, it is 0.55*10**9km.
Now going a bit celestial, the density of a neutron star is known to be in the range of 0.5*10**15gm/cc as they are supposed to contain one solar mass per ball of 20km diameter!
Still one takes the core at which gravitation collapses to a steady state, it is about 10**12 kg/cc or 10**15 gm/cc, said to be close to the density of a typical nucleus! i.e double that of a neutron star. Compare it with that of the neutron I had estimated to be! 5*10**136 gm/cc (at least).
srini
For gold, r(critical) becomes 0.7*10**9km (a shining blackhole!); for platinum, it is 0.55*10**9km.
Now going a bit celestial, the density of a neutron star is known to be in the range of 0.5*10**15gm/cc as they are supposed to contain one solar mass per ball of 20km diameter!
Still one takes the core at which gravitation collapses to a steady state, it is about 10**12 kg/cc or 10**15 gm/cc, said to be close to the density of a typical nucleus! i.e double that of a neutron star. Compare it with that of the neutron I had estimated to be! 5*10**136 gm/cc (at least).
srini
Wednesday, February 07, 2007
Critical radius calculation for a material of given density
r(critical) = 2*G*M / c**2 = 2 G * density * (4/3) *pi*r(critical)**3 / c**2;
r(critical) = sqrt(3*c**2/(8*G*pi*density) )= sqrt(2.7*10**16/(8*6.67*10**-11*3.14*density))
With density=1000kg/m**3 for water, r(critical) for water = 4*10**12m approx = 4*10**9km.
Now, it follows that given a value for the material density but assuming homogeneity, the critical value of radius at which the material in spherical form just becomes a blackhole. Further, the critical radius for any other material can be uniquely determined given its specific gravity, i.e. how much heavier than water it is. Taking the average value of specific gravity for our Earth as 5.5, the critical radius would then become 4*10**9 / sqrt(5.5) km = 1.7 * 10**9 km (approx).
In essence, the r(critical) varies with specific gravity in an inverse square root fashion.
With 11.6 for lead, r(critical) becomes about 1.2*10**9 km.
srini
r(critical) = 2*G*M / c**2 = 2 G * density * (4/3) *pi*r(critical)**3 / c**2;
r(critical) = sqrt(3*c**2/(8*G*pi*density) )= sqrt(2.7*10**16/(8*6.67*10**-11*3.14*density))
With density=1000kg/m**3 for water, r(critical) for water = 4*10**12m approx = 4*10**9km.
Now, it follows that given a value for the material density but assuming homogeneity, the critical value of radius at which the material in spherical form just becomes a blackhole. Further, the critical radius for any other material can be uniquely determined given its specific gravity, i.e. how much heavier than water it is. Taking the average value of specific gravity for our Earth as 5.5, the critical radius would then become 4*10**9 / sqrt(5.5) km = 1.7 * 10**9 km (approx).
In essence, the r(critical) varies with specific gravity in an inverse square root fashion.
With 11.6 for lead, r(critical) becomes about 1.2*10**9 km.
srini
Tuesday, February 06, 2007
SEARCH FOR EXTRA-TERRESTRIAL LIFE THROUGH RADIO, TV SIGNALS!
Astronomers plan to search 1000 nearby stars for television broadcasts and other signals that could indicate extra-terrestrial life, the Harvard-Smithsonian center said. The project planned for early 2008, would use a new radio telescope to search for radio traffic similar to that found on the Earth. Current efforts to find extra-terrestrial life look towards messages deliberately beamed across space – an approach that would miss any civilisation that does not advertise its existence as the Earth does. The new effort would search a portion of the electromagnetic spectrum used on the Earth for more mundane purposes – radar, television and FM radio broadcasts. It was hoped that spurious signals from people but not meant for us would be picked up according to the director of communications at the centre.
srini
Astronomers plan to search 1000 nearby stars for television broadcasts and other signals that could indicate extra-terrestrial life, the Harvard-Smithsonian center said. The project planned for early 2008, would use a new radio telescope to search for radio traffic similar to that found on the Earth. Current efforts to find extra-terrestrial life look towards messages deliberately beamed across space – an approach that would miss any civilisation that does not advertise its existence as the Earth does. The new effort would search a portion of the electromagnetic spectrum used on the Earth for more mundane purposes – radar, television and FM radio broadcasts. It was hoped that spurious signals from people but not meant for us would be picked up according to the director of communications at the centre.
srini
Monday, February 05, 2007
COSMIC REVELATION
Astronomers unveil detailed 3-D map of universe
A team of astronomers has unveiled a three-dimensional map that sheds light on the mysterious dark matter that makes up a quarter of the universe. The map shows that the dark matter forms a filamentous skeleton upon which visible matter congregates, eventually producing stars, Nature magazine has reported. The composition of the dark matter is unclear but it is believed that without it the universe could not exist. The dark matter is thought to act as glue, holding galaxies together. ‘This is the first time that such a large scale three-dimensional picture of dark matter has been produced, and it will allow cosmologists to probe deeper into the nature of this elusive matter”, the report said.
The map also has a few puzzles within it. Some areas show clumps of dark matter that aren’t accompanied by the bright features associated with conventional visible material (made of Baryonic matter) and vice versa.
“On the large scale, the general picture is as expected, but there are some small-scale discrepancies”, it was reported, based on the map synthesized from hundreds of slightly overlapping images from the Hubble space telescope’s cosmic evolution survey.
Astronomers unveil detailed 3-D map of universe
A team of astronomers has unveiled a three-dimensional map that sheds light on the mysterious dark matter that makes up a quarter of the universe. The map shows that the dark matter forms a filamentous skeleton upon which visible matter congregates, eventually producing stars, Nature magazine has reported. The composition of the dark matter is unclear but it is believed that without it the universe could not exist. The dark matter is thought to act as glue, holding galaxies together. ‘This is the first time that such a large scale three-dimensional picture of dark matter has been produced, and it will allow cosmologists to probe deeper into the nature of this elusive matter”, the report said.
The map also has a few puzzles within it. Some areas show clumps of dark matter that aren’t accompanied by the bright features associated with conventional visible material (made of Baryonic matter) and vice versa.
“On the large scale, the general picture is as expected, but there are some small-scale discrepancies”, it was reported, based on the map synthesized from hundreds of slightly overlapping images from the Hubble space telescope’s cosmic evolution survey.
“The existence of large clumps of isolated dark matter and visible matter flies in the face of everything we know”, according to a cosmologist from the University of Durham, U.K.
srini
Thursday, February 01, 2007
Supernova remnant RCW86 – Dating modified to AD 185
According to a recent study, the supernova remnant RCW 86 is much younger than previously thought, pointing towards a modified date of about AD 185. The formation of the remnant appears to coincide with a supernova observed by Chinese astronomers in AD 185. The study used data from NASA’s Chandra X-ray observatory and the European space agency’s XMM-Newton observatory. Previous suggestions to this effect have been confirmed by the new X-ray data, the lead author reported.
When a massive star runs out of fuel, it collapses on itself, creating a supernova that can outshine an entire galaxy. The intense explosion hurls the outer layers of the star into space and produces powerful shock waves. The remains of the star and the material it encounters are heated to millions of degrees and can emit intense X-ray radiation for thousands of years.
In the stellar work, the debris in RCW 86 was studied to estimate when its progenitor star originally exploded. It was also calculated how quickly the shocked or energized shell is moving in RCW 86, by studying one part of the remnant. Combining this expansion velocity with the size of the remnant and a basic understanding of how supernovas expand, led to the estimation of the age of RCW 86 afresh – as about 2000 years old.
The younger age for RCW 86 may explain an astronomical event observed almost 2000 years ago. In AD 185, Chinese astronomers (and possibly the Romans) recorded the appearance of a new bright star. The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with the modern observations of supernovas. However, uncertainties about the age provided significant doubt about the association.
The smaller age estimate for the remnant follows directly from a higher expansion velocity. By examining the energy distribution of the X-rays, a technique known as spectroscopy, the team found that most of the X-ray emission was caused by high energy electrons moving through a magnetic field. This is well known process that gives rise to low energy radio emission. However, only very high shock velocities can accelerate the electrons to such high energies that X-ray radiation is emitted. The difference in age estimates for RCW 86 is due to differences in expansion velocities measured for the supernova remnant. The authors speculate that these variations arise because RCW 86 is expanding into an irregular bubble blown by a wind from the progenitor star before it exploded. In some directions, the shock wave has encountered a dense region outside the bubble and slowed down, whereas in other regions the shock remains inside the bubble and is still moving rapidly. These regions give the most accurate estimate of the age.
srini
According to a recent study, the supernova remnant RCW 86 is much younger than previously thought, pointing towards a modified date of about AD 185. The formation of the remnant appears to coincide with a supernova observed by Chinese astronomers in AD 185. The study used data from NASA’s Chandra X-ray observatory and the European space agency’s XMM-Newton observatory. Previous suggestions to this effect have been confirmed by the new X-ray data, the lead author reported.
When a massive star runs out of fuel, it collapses on itself, creating a supernova that can outshine an entire galaxy. The intense explosion hurls the outer layers of the star into space and produces powerful shock waves. The remains of the star and the material it encounters are heated to millions of degrees and can emit intense X-ray radiation for thousands of years.
In the stellar work, the debris in RCW 86 was studied to estimate when its progenitor star originally exploded. It was also calculated how quickly the shocked or energized shell is moving in RCW 86, by studying one part of the remnant. Combining this expansion velocity with the size of the remnant and a basic understanding of how supernovas expand, led to the estimation of the age of RCW 86 afresh – as about 2000 years old.
The younger age for RCW 86 may explain an astronomical event observed almost 2000 years ago. In AD 185, Chinese astronomers (and possibly the Romans) recorded the appearance of a new bright star. The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with the modern observations of supernovas. However, uncertainties about the age provided significant doubt about the association.
The smaller age estimate for the remnant follows directly from a higher expansion velocity. By examining the energy distribution of the X-rays, a technique known as spectroscopy, the team found that most of the X-ray emission was caused by high energy electrons moving through a magnetic field. This is well known process that gives rise to low energy radio emission. However, only very high shock velocities can accelerate the electrons to such high energies that X-ray radiation is emitted. The difference in age estimates for RCW 86 is due to differences in expansion velocities measured for the supernova remnant. The authors speculate that these variations arise because RCW 86 is expanding into an irregular bubble blown by a wind from the progenitor star before it exploded. In some directions, the shock wave has encountered a dense region outside the bubble and slowed down, whereas in other regions the shock remains inside the bubble and is still moving rapidly. These regions give the most accurate estimate of the age.
srini
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