Astronomy

Physicist John Wheeler is widely credited with coining the term black hole in his 1967 public lecture Our Universe: the Known and Unknown. He used the term to avoid him repeatedly using sentence “gravitationally completely collapsed star” on his lecture. However, Wheeler insisted that someone else at the conference had coined the term and he had merely adopted it as useful shorthand.

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Sometimes objects in the sky that appear strange, or different from normal, have a story to tell and prove scientifically very rewarding. This was the idea behind Halton Arp’s catalogue of Peculiar Galaxies that appeared in the 1960s. One of the oddballs listed there is Arp 261, which has now been imaged in more detail than ever before using the FORS2 instrument on ESO’s Very Large Telescope. The image proves to contain several surprises.

Arp 261 lies about 70 million light-years distant in the constellation of Libra, the Scales. Its chaotic and very unusual structure is created by the interaction of two galaxies that are engaged in a slow motion, but highly disruptive close encounter. Although individual stars are very unlikely to collide in such an event, the huge clouds of gas and dust certainly do crash into each other at high speed, leading to the formation of bright new clusters of very hot stars that are clearly seen in the picture. The paths of the existing stars in the galaxies are also dramatically disrupted, creating the faint swirls extending to the upper left and lower right of the image. Both interacting galaxies were probably dwarfs not unlike the Magellanic Clouds orbiting our own galaxy.

The images used to create this picture were not actually taken to study the interacting galaxies at all, but to investigate the properties of the inconspicuous object just to the right of the brightest part of Arp 261 and close to the centre of the image. This is an unusual exploding star, called SN 1995N, that is thought to be the result of the final collapse of a massive star at the end of its life, a so-called core collapse supernova. SN 1995N is unusual because it has faded very slowly — and still shows clearly on this image more than seven years after the explosion took place! It is also one of the few supernovae to have been observed to emit X-rays. It is thought that these unusual characteristics are a result of the exploding star being in a dense region of space so that the material blasted out from the supernova ploughs into it and creates X-rays.

Apart from the interacting galaxy and its supernova the image also contains several other objects at wildly different distances from us. Starting very close to home, two small asteroids, in our Solar System between the orbits of Mars and Jupiter, happened to cross the images as they were being taken and show up as the red-green-blue trails at the left and top of the picture. The trails arise as the objects are moving during the exposures and also between the exposures through different coloured filters. The asteroid at the top is number 14670 and the one to the left number 9735. They are probably less than 5 km across. The reflected sunlight from these small bodies takes about fifteen minutes to get to the Earth.

The next closest object is probably the apparently bright star at the bottom. It may look bright, but it is still about one hundred times too faint to be seen with the unaided eye. It is most likely a star rather like the Sun and about 500 light-years from us — 20 million times further away than the asteroids. Arp 261 itself, and the supernova, are about 140 000 times further away again than this star, but still in what astronomers would regard as our cosmic neighbourhood. Much more distant still, perhaps some fifty to one hundred times further away than Arp 261, lies the cluster of galaxies visible on the right of the picture. There is no doubt, however, that a much more remote object lies, unrecognised, amongst the faint background objects seen in this marvellous image. (Image credit: ESO)

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On Oct. 5, 2008, just after coming within 25 kilometers (15.6 miles) of the surface of Enceladus, NASA’s Cassini captured this stunning mosaic as the spacecraft sped away from this geologically active moon of Saturn.

Craters and cratered terrains are rare in this view of the southern region of the moon’s Saturn-facing hemisphere. Instead, the surface is replete with fractures, folds, and ridges–all hallmarks of remarkable tectonic activity for a relatively small world. In this enhanced-color view, regions that appear blue-green are thought to be coated with larger grains than those that appear white or gray. Near the top, the conspicuous ridges are Ebony and Cufa Dorsae. Portions of the tiger stripe fractures, or sulci, are visible along the terminator at lower right, surrounded by a circumpolar belt of mountains. The icy moon’s famed jets emanate from at least eight distinct source regions, which lie on or near the tiger stripes. However, in this view, the most prominent feature is Labtayt Sulci, the approximately one-kilometer (0.6 miles) deep northward-trending chasm located just above the center of the mosaic.

This false-color mosaic was created from 28 images obtained at seven footprints, or pointing positions, by Cassini’s narrow-angle camera. At each footprint, four images using filters sensitive to ultraviolet, visible and infrared light (spanning wavelengths from 338 to 930 nanometers) were combined to create the individual frames. The mosaic is an orthographic projection centered at 64.49 degrees south latitude, 283.87 west longitude, and it has an image scale of 196 kilometers (122.5 miles) per pixel. The original images ranged in resolution from 180 meters (594 feet) to 288 meters (950 feet) per pixel and were acquired at distances ranging from 30,000 to 48,000 kilometers (18,750 to 30,000 miles) as the spacecraft receded from Enceladus. The view was acquired at a Sun-Enceladus-spacecraft, or phase, angle of 73 degrees. (credits: NASA/JPL/Space Science Institute)

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Galaxies and the giant black holes at their hubs fit together as if they were made for one another. Did the holes come first and guide the formation of their galaxies, did the galaxies come first and build up holes, or did some common factor sculpt both?

As reported on March 2009 edition of Scientific American Magazine, Christopher Carilli of the National Radio Astronomy Observatory and his colleagues argued that the holes came first. On the American Astronomical Society meeting in January they presenting their finding that galaxies in the early universe were 30 times more massive than their black holes, whereas present-day galaxies are 1,000 time heavier. “Black holes came first and somehow—we don’t know how—grew the galaxy around them,” Carilli said.

Other astronomers were skeptical, wondering whether the ancient galaxies seem undersized merely because of a statistical selection effect. Even if true, the study does not explain how a black hole can nurture a galaxy; if anything, it should tear it apart.

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Gamma-ray bursts are the universe’s most luminous explosions. Astronomers believe most occur when exotic massive stars run out of nuclear fuel. As a star’s core collapses into a black hole, jets of material — powered by processes not yet fully understood — blast outward at nearly the speed of light. The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star and generate bright afterglows that fade with time.

NASA’s Fermi Gamma-ray Space Telescope recently saw the first gamma-ray burst in high-resolution. The blast had the greatest total energy, the fastest motions, and the highest-energy initial emissions ever seen. This explosion, designated GRB 080916C, occurred at 7:13 p.m. EDT September 15, 2008, in the constellation Carina. Two of Fermi’s instrument, Large Area Telescope and Gamma-ray Burst Monitor, simultaneously recorded the event. Together, the two instruments provide a view of the blast’s initial, or prompt, gamma-ray emission from energies between 3,000 to more than 5 billion times that of visible light.

Nearly 32 hours after the blast, Jochen Greiner of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, led a group that searched for the explosion’s fading afterglow. The team simultaneously captured the field in seven wavelengths using the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND), on the 2.2-meter telescope at the European Southern Observatory in La Silla, Chile. In certain colors, the brightness of a distant object shows a characteristic drop-off caused by intervening gas clouds. The farther away the object is, the redder the wavelength where this fade-out occurs. This gives astronomers a quick estimate of the object’s distance. The team’s follow-up observations established that the explosion took place 12.2 billion light-years away.

With the distance in hand, Fermi team members showed that the blast exceeded the power of approximately 9,000 ordinary supernovae, if the energy was emitted equally in all directions. This is a standard way for astronomers to compare events even though gamma-ray bursts emit most of their energy in tight jets. Coupled with the Fermi measurements, the distance also helps astronomers determine the slowest speeds possible for material emitting the prompt gamma rays. Within the jet of this burst, gas bullets must have moved at 99.9999 percent the speed of light. This burst’s tremendous power and speed make it the most extreme recorded to date.

One curious aspect of the burst is a five-second delay separating the highest-energy emissions from the lowest. Such a time lag has been seen clearly in only one earlier burst. It may mean that the highest-energy emissions are coming from different parts of the jet or created through a different mechanism.

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Stellarium is a free open source planetarium software for your computer. It renders 3D photo-realistic skies in real time with OpenGL and displays stars, constellations, planets, nebulas and others things like ground, landscape, atmosphere, etc., just like what you see with the naked eye, binoculars or a telescope.

A new update for Stellarium, Ver. 0.10.1, has been released on February 5th. This is the first stable version featuring the new Graphical User Interface. It contains all features introduced in 0.10.0 beta (with much less bugs!) as well as: a new script engine (in testing), new translations in Albanian and Bosnian, an improved grid rendering, the possibility to download extra star catalogs in 1 click, and various performance improvements.

Some nice new features include planet lines to trace planet paths across the sky, much more control over how many object labels are displayed per FOV, and a Meridian line (which I thought it should’ve always had from the start), etc.

The program available for All 32-bit MS Windows (95/98/NT/2000/XP), as well as All BSD Platforms (FreeBSD/NetBSD/OpenBSD/Apple Mac OS X), All POSIX (Linux/BSD/UNIX-like OSes), and OS X. Please note that Stellarium has always come with 6 star/object catalogs but there are 5 more star catalogs that you can add manually if you have enough memory for them to load into. Catalog stars_8_2v0_0.cat is the largest add on at 674MB. They are available seperately at sourceforge.net.

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Above is an deep new image from Helix Planetary Nebula (NGC 7293), shows a rich background of distant galaxies, usually not seen in other images of this object.

This color-composite image of the Helix Nebula was created from images obtained using the the Wide Field Imager (WFI), an astronomical camera attached to the 2.2-meter Max-Planck Society/ESO telescope at the La Silla observatory in Chile. The blue-green glow in the center of the Helix comes from oxygen atoms shining under effects of the intense ultraviolet radiation of the 120,000 degree Celsius central star and the hot gas. Further out from the star and beyond the ring of knots, the red color from hydrogen and nitrogen is more prominent. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. The image was created from images through blue, green and red filters and the total exposure times were 12 minutes, 9 minutes, and 7 minutes, respectively.

The Helix Nebula lies about 700 light-years away in the constellation Aquarius the Water Bearer. It is one of the closest and most spectacular examples of a planetary nebula. These exotic objects have nothing to do with planets, but are the final blooming of Sun-like stars before their retirement as white dwarfs. Shells of gas are blown off from a star’s surface, often in intricate and beautiful patterns, and shine under the harsh ultraviolet radiation from the faint, but very hot, central star. The main ring of the Helix Nebula is about 2 light-years across, or half the distance between the Sun and its closest stellar neighbor. (Image credits: ESO)

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Many ancient astronomical texts describe the color of Sirius, the brightest star in the sky, as red. These include works by Ptolemy and Lucius Seneca amongst others. The fact has been puzzled Astronomers for many years since Sirius is appears blue with the naked eye.

In 1985, German astronomers Wolfhard Schlosser and Werner Bergmann published an account of an 8th century Lombardic manuscript, which contains “De cursu stellarum ratio” by St. Gregory of Tours. The Latin text taught readers how to determine the times of nighttime prayers from positions of the stars, and Sirius is described within as rubeola ‘reddish’. The authors proposed this was further evidence that one of the stars on Sirius’ binary system (known as Sirius A and Sirius B), had been a red giant at the time. However, other scholars replied that it was likely St. Gregory had been referring to Arcturus instead.

The possibility that stellar evolution of either Sirius A or Sirius B could be responsible for this discrepancy has been rejected by astronomers on the grounds that the timescale of thousands of years is too short and that there is no sign of the nebulosity in the system that would be expected had such a change taken place. An interaction with a third star, to date undiscovered, has also been proposed as a possibility for a red appearance. Alternative explanations are either that the description as red is a poetic metaphor for ill fortune, or that the dramatic scintillations of the star when it was observed rising left the viewer with the impression that it were red. To the naked eye, it often appears to be flashing with red, white and blue hues when near the horizon. The real answer remains a mystery.

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A first-time visitor to the inner solar system which had already spotted with the naked eye from some locales, could make a spectacle of itself when it comes closest to Earth on February 24, 2009 at the distance of 0.41 AU. Current estimates peg the maximum brightness at 4th or 5th magnitude, which means dark country skies would be required to see it. No one can say for sure, however, because this appears to be Lulin’s first visit to the inner solar system and its first exposure to intense sunlight. Surprises are possible.

First spotted by a young Chinese astronomy student Quanzhi Ye in 2007 and Named for the observatory in Taiwan where it was discovered, Lulin has a greenish cast because sunlight illuminates two gases — cyanogen and diatomic carbon — in its Jupiter-sized atmosphere.

Researchers believe that this is Lulin’s first foray to the inner solar system, and that it probably originated in the deep freeze of the Oort Cloud, a comet reservoir thousands of times farther from the sun than the Earth lies. If so, energetic charged particles called cosmic rays, common in space, may have bombarded Lulin’s surface for eons, creating a thick crust of organic compounds. The crust could make it difficult for the comet’s supply of frozen water and other volatile ices, which readily turn to gas in the warmth of the inner solar system, to break through the surface. It’s the venting of these gases that drags out dust particles and forms a comet’s showy tail. A thick crust could dim the show.

This image was captured on February 6 from New Mexico. Lulin is the top green object, which has a dust tail (red) to the left and an ion tail (blue ) to the right. The greenish object below Lulin is a double star. (IMAGE CREDIT: Rolando Ligustri/C.AS.T, www.castfvg.it)

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Asteroid Icarus (1566 Icarus) have unusual characteristic is that at perihelion it is closer to the Sun than Mercury. Named after Icarus of Greek mythology, who flew too close to the Sun, the asteroid was discovered in 1949 by Walter Baade.

Icarus makes a close approach to Earth at gaps of 9, 19, or 38 years. Rarely, it comes as close as 6.4 Gm (16 lunar distances and 4 million miles), as it did on June 14, 1968. The last close approach was in 1996, at 15.1 Gm, almost 40 times as far as the Moon. The next close approach will be June 16, 2015 at 8.1 Gm (5 million miles).

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