expose-the-light:

10 Things You Didn’t Know About Black Holes

Stars whose size is 10 or 15 times as massive as the Sun, generally have a fate of becoming black holes. Small stars, however, die as white dwarfs or neutron stars. So how do large stars become black holes? As stars begin to grow old, they gradually expand and they slowly run out of their supply of hydrogen and then helium. This causes contraction of their cores and expansion of the outer layers. The stars start becoming cooler and less bright and they come to a stage which is known as the red giant phase. Now, for a star which is even 3 times or more the mass of the Sun, undergoes detonation (a violent release of energy caused by a chemical or nuclear reaction) in cataclysms known as supernovae. Such kind of explosion results in scattering of most of a star into the space. However, it also leaves behind a cold remnant of the star, which is no longer able to execute any nuclear fusion reaction.

As there is no fusion in the dead remnants of a massive supernova star, there is no creation of any energy which can oppose the inward pull of gravity caused by the star’s own mass. Thus, the star enters a phase where it begins to collapse in upon itself. This is the formation of the black hole, wherein, it starts shrinking to zero volume. So, with volume being zero, density becomes infinite, so much that even light becomes unable to escape its massively strong gravitational pull. As a result of this, even the light of the dead remnants of the star gets trapped in its orbit and this dark star evolves to become what is known as a black hole.

• It has been estimated that there might be black holes of enormous size, which may be existing at the center of our galaxy, ‘The Milky Way’. These holes are assumed to be having the mass of 10 - 100 billion suns. Now, that is something which is ‘HUGE’, in block letters!
• Cygnus X-1 is the black hole that is located about 8000 light years away from our planet Earth. This is the closest black hole to Earth, known to man.
• Although, black holes are associated with the reputation of having the strongest suction force, they do not bear the capability to absorb the whole universe. Anything such as planets, light and other matter, can be pulled into the grasp of black holes, only if they happen to cross what is known as the event horizon. The radius of this event horizon is known as the Schwarzschild radius and at this radius, the escape velocity equals the speed of the light. So, once an object has passed through it, it must travel faster than light in order to escape it. That is the reason why, even light cannot escape the event horizon of a black hole.
• As mentioned earlier, in this part of black holes in space, only the largest of stars are capable to end up as black holes. Only these stars are massive enough to get compressed to the Schwarzschild radius. While, smaller stars end up as white dwarfs or neutron stars.
• There are several black holes which exist in binary star systems. Stars which are neighboring such holes, will keep on shrinking as their mass will continually be pulled by these holes. Gradually, the black holes will go on increasing, until the other stars have vanished.
• As light cannot escape from a black hole, it cannot be directly observed. However, scientists use the presence of matters which swirl around the hole. Such matters are usually gas and dust and they heat up and emit radiation which can be detected.
• Talking about our Sun becoming a black hole, the phenomenon won’t occur. This is because the sun is not massive enough to shrink into a black hole. However, it will end up to become a white dwarf, after several billion years.
• The center of a black hole is void of time and space.
• A giant elliptical galaxy in the constellation Virgo, is assumed to home the largest known black hole. This hole is about 3 billion times the mass of the Sun.
• Larger black holes are known to suck up other smaller ones which are close to their vicinity.

No matter, how many facts people come up with, black holes represent an endless journey in the vast darkness of the space. The concept which lay hidden in the lap of black holes, perhaps, is the most appropriate analogy to the saying ‘sky is the limit!’

In the image: Simulation of gas cloud approaching the black hole at the center of the Milky Way

fyeahuniverse:

^{Laser Guide Star to be installed at the VLT}

^{Making high quality observations from Earth’s surface is a challenge. The atmosphere causes turbulence causing the the twinkle that we see in the stars, and also making them blur. Without any correction the resolution of a giant telescope generally isn’t much better than a 0.1m aperture telescope.}

^{In order to compensate for this distortion, astronomers created what is called adaptive optics. Adaptive optics is where they observe a close star and measure the blurring of it. They then use a deformable mirror to cancel out the distortion. However, when there isn’t a close bright star, they need an artificial one. This is where the new laser comes in: it will be much more compact than the previous model and will have a power upgrade from 5W to 18W. This breakthrough in technology will allow much better imaging; a quality higher than Hubble.}

^{(Image credit: TNO/Fred Kamphues/ESO)}

sagansense:

The Antikythera Time Machine

Picture 1: Part of the Antikythera Mechanism, by Marsyas via Wikimedia Commons

Leonardo da Vinci may have left behind sketches of helicopters, tanks and submarines but it is rare that we find actual artifacts that seem so way ahead of their time. Almost like a science fiction tale of archaeologists finding a wristwatch buried deep in an Egyptian pyramid or motorcar under the foundations of Stonehenge, we do have an example of a scientific computer that was built between 150 and 100 BC. It was so advanced, nothing as complex would be developed again until the 14th century.

The Antikythera mechanism was lost to the world for centuries. The device was salvaged in 1900 from a ship that sank en route to Rome, in the 1st century BC, between Crete and the island of Antikythera in the Mediterranean. When one of the fragments was discovered to contain a bronze gear wheel, the idea that this was some kind of astronomical clock was dismissed as too fantastic an anachronism. It was not until 1951 that the investigation was picked up by a British science historian Derek J. de Solla Price. So far 82 fragments have been recovered of what is now considered the oldest known astronomical computer.

The device is made of bronze and contains 30 gears though it may have had as many as 72 originally. Each gear was meticulously hand cut with between 15 and 223 triangular teeth, which were the key to discovering the mechanism’s various functions. It was based on theories of astronomy and mathematics developed by Greek astronomers who may have drawn from earlier Babylonian astronomical theories and its construction could be attributed to the astronomer Hipparchus or, more likely, Archimedes the famous Greek mathematician, physicist, engineer, inventor and astronomer. Why it was built, or for whom is unknown.

Picture 2: Replica Antikythera Based on the research of Professor Derek de Solla Price, in collaboration with the National Scientific Research Center Demokritos and physicist CH Karakalos. image by Marsyas via Wikimedia Commons

The main front dial showed the 365 day Egyptian year and the Greek signs of the Zodiac and could be adjusted to compensate for the extra quarter day in the solar year. The dial probably bore three hands that marked the date and positions of the Sun and Moon, while a separate mechanism showed the Moon’s phases and it likely also displayed the 5 classically known planets, Mercury, Mars, Venus, Jupiter and Saturn.

On the back an upper dial showed 19 year Metonic cycle of Moon phases, the 76 year Callippic cycle (four Metonic cycles) and calculated the 4 year Olympic cycle (four games took place in two and four year cycles) The lower dial showed the 18 year 11 days Saros eclipse cycle and the 54 year 33 day Exeligmos or triple saros cycle. It was driven by a hand crank now sadly lost. It is small, compact and portable with full instructions engraved upon it in Greek, about 95% of which have now been deciphered.

The fragile pieces that remain have been examined and modeled using high-resolution X-ray tomography and gamma rays and various reconstructions and replicas have been built. It has even had a working model constructed out of Lego. I can’t helping thinking that Archimedes would have rather liked Lego, if only we could go back in time and give him a set…

ikenbot:

Annular Eclipse with Fraunhofer Diffraction

by Valerie Hayken

Shot with a Toyo 4x5 Field Camera and Schneider 135mm on film, May 20, 2012.

ikenbot:

Supermassive Black Hole at Work

Image Credit: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz)

Back in 2010, astronomers witnessed an explosion of light from a star that was obliterated by a supermassive black hole. This is an accurate computer simulation of the event that took place.

Space is amazing.