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May 14, 2006, 11:16 AM CT

Fast Winds from Dying Stars

Fast Winds from Dying Stars
Credit: Credit: X-ray: NASA/CXC/RIT/J.Kastner et al.; Optical/IR: BD +30 & Hen 3: NASA/STScI/Univ. MD/J.P.Harrington; NGC 7027: NASA/STScI/Caltech/J.Westphal & W.Latter; Mz 3: NASA/STScI/Univ. Washington/B.Balick
This panel of composite images shows part of the unfolding drama of the last stages of the evolution of sun-like stars. Dynamic elongated clouds envelop bubbles of multimillion degree gas produced by high-velocity winds from dying stars. In these images, Chandra's X-ray data are shown in blue, while green and red are optical and infrared data from Hubble.

Planetary nebulas - so called because some of them resemble a planet when viewed through a small telescope - are produced in the late stages of a sun-like star's life. After several billion years of stable existence (the sun is 4.5 billion years old and will not enter this phase for about 5 billion more years) a normal star will expand enormously to become a bloated red giant. Over a period of a few hundred thousand years, much of the star's mass is expelled at a relatively slow speed of about 50,000 miles per hour.

This mass loss creates a more or less spherical cloud around the star and eventually uncovers the star's blazing hot core. Intense ultraviolet radiation from the core heats the circumstellar gas to ten thousand degrees, and the velocity of the gas flowing away from the star jumps to about a million miles per hour.

This high speed wind appears to be concentrated into opposing supersonic funnels, and produces the elongated shapes in the early development of planetary nebulas (BD+30-3639 appears spherical, but other observations indicate that it is viewed along the pole.) Shock waves generated by the collision of the high-speed gas with the surrounding cloud create the hot bubbles observed by Chandra. The origin of the funnel-shaped winds is not understood. It may be correlation to strong, twisted magnetic fields near the hot stellar core.........

Posted by: Edwin      Permalink         Source


May 10, 2006, 10:53 PM CT

New Milky Way Companions Found

New Milky Way Companions Found

The Sloan Digital Sky Survey (SDSS-II) announced recently (May 8) the discoveries of two new, very faint companion galaxies to the Milky Way.

The first was found in the direction of the constellation Canes Venatici (the Hunting Dog) by SDSS-II researcher Daniel Zucker at Cambridge University (UK). His colleague Vasily Belokurov discovered the second in the constellation Bootes (the Herdsman).

"I was poring over the survey's map of distant stars in the Northern Galactic sky - what we call a Field of Streams -- and noticed an overdensity in Canes Venatici," Zucker explained. "Looking further, it proved to be a previously unknown dwarf galaxy. It's about 640,000 light years (200 kiloparsecs) from the Sun. This makes it one of the most remote of the Milky Way's companion galaxies".

Zucker emailed Belokurov with the news, and, just as discoveries often build upon one another, Belokurov excitedly emailed back a few hours later with the discovery of a new, even fainter dwarf galaxy. The new galaxy in Bootes, which Belokurov called 'Boo,' shows a distorted structure that suggests it is being disrupted by the Milky Way's gravitational tides. "Something really bashed Boo about," said Belokurov.

Eventhough the dwarf galaxies are in our own cosmic backyard, they are hard to discover because they are so dim. In fact, the new galaxy in Bootes is the faintest galaxy so far discovered, with a total luminosity of only about 100,000 Suns. But because of its distance (640,000 light years) it appears almost invisible to most telescopes. The prior dimness record holder was discovered last year in Ursa Major using SDSS-II data.........

Posted by: Edwin      Permalink         Source


May 9, 2006, 11:47 PM CT

Venus Express Has Reached Final Orbit

Venus Express Has Reached Final Orbit

Less than one month after insertion into orbit, and after sixteen loops around the planet Venus, ESA's Venus Express spacecraft has reached its final operational orbit on 7 May 2006.

Already at 21:49 CEST on 6th May, when the spacecraft communicated to Earth through ESA's ground station at New Norcia (Australia), the Venus Express ground control team at ESA's European Spacecraft Operations Centre (ESOC) in Darmstadt (Germany) received advanced confirmation that final orbit was to be successfully achieved about 18 hours later.

Launched on 9 November 2005, Venus Express arrived to destination on 11 April 2006, after a five-month interplanetary journey to the inner solar system. The initial orbit - or 'capture orbit' - was an ellipse ranging from 330 000 kilometres at its furthest point from Venus surface (apocentre) to less than 400 kilometres at its closest (pericentre).

As of the 9-day capture orbit, Venus Express had to perform a series of further manoeuvres to gradually reduce the apocentre and the pericentre altitudes over the planet. This was achieved by means of the spacecraft main engine - which had to be fired twice during this period (on 20 and 23 April 2006) - and through the banks of Venus Express' thrusters - ignited five times (on 15, 26 and 30 April, 3 and 6 May 2006).........

Posted by: Edwin      Permalink         Source


May 7, 2006, 10:07 PM CT

Rainbow of a Galaxy

Rainbow of a Galaxy

NASA's Spitzer, Hubble, and Chandra space observatories teamed up to create this multi-wavelength, false-colored view of the M82 galaxy.

The lively portrait celebrates Hubble's "sweet sixteen" birthday.........

Posted by: Edwin      Permalink         Source


May 7, 2006, 10:04 PM CT

The Infrared Universe

The Infrared Universe

NASA's Spitzer Space Telescope is using its infrared eyes to turn the dark and dusty cosmos into a beautiful garden of colorful objects.

Wow!........

Posted by: Edwin      Permalink         Source


May 3, 2006, 10:53 PM CT

XMM-Newton Provides Impressive Sky Survey

XMM-Newton Provides Impressive Sky Survey
For the past four years, while ESA's XMM-Newton X-ray observatory has been slewing between different targets ready for the next observation, it has kept its cameras open and used this spare time to quietly look at the heavens. The result is a 'free-of-charge' mission spin-off - a survey that has now covered an impressive 25 percent of the sky.

The rapid slewing of the satellite across the sky means that a star or a galaxy passes in the field of view of the telescope for ten seconds only. However, the great collecting area of the XMM-Newton mirrors, coupled with the efficiency of its image sensors, is allowing thousands of sources to be detected.

Furthermore, XMM-Newton can pinpoint the position of X-rays coming from the sky with a resolution far superior to that available for most prior all-sky surveys. This is sufficient to allow the source of these X-rays to be found in a number of cases.

By comparing XMM-Newton survey's data with those obtained over a decade ago by the international ROSAT mission, which also performed an all-sky survey, researchers can now check the long-term stability, or the evolution, of about two thousand objects in the sky.

An initial look shows that some sources have changed their brightness level by an incredible amount. The most extreme of these are variable stars and more surprisingly galaxies, whose unusual volatility may be due to large quantities of matter being consumed by an otherwise dormant central black hole.........

Posted by: Edwin      Permalink         Source


May 1, 2006, 0:00 AM CT

Secrets Of Fossil Galaxy Clusters

Secrets Of Fossil Galaxy Clusters

Taking advantage of the high sensitivity of ESA's XMM-Newton and the sharp vision of NASA's Chandra X-Ray space observatories, astronomers have studied the behaviour of massive fossil galaxy clusters, trying to find out how they find the time to form.

Many galaxies reside in galaxy groups, where they experience close encounters with their neighbours and interact gravitationally with the dark matter - mass which permeates the whole intergalactic space but is not directly visible because it doesn't emit radiation.

These interactions cause large galaxies to spiral slowly towards the centre of the group, where they can merge to form a single giant central galaxy, which progressively swallows all its neighbours.

If this process runs to completion, and no new galaxies fall into the group, then the result is an object dubbed a 'fossil group', in which almost all the stars are collected into a single giant galaxy, which sits at the centre of a group-sized dark matter halo. The presence of this halo can be inferred from the presence of extensive hot gas, which fills the gravitational potential wells of many groups and emits X-rays.

A group of international astronomers studied in detail the physical features of the most massive and hot known fossil group, with the main aim to solve a puzzle and understand the formation of massive fossils. In fact, according to simple theoretical models, they simply could not have formed in the time available to them!........

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April 27, 2006, 11:57 PM CT

Spectacular View Of Ongoing Comet Breakup

Spectacular View Of Ongoing Comet Breakup
Hubble Space Telescope is providing astronomers with extraordinary views of comet 73P/Schwassmann-Wachmann 3 as it disintegrates before our eyes. Recent Hubble images have uncovered many more fragments than have been reported by ground-based observers. These observations provide an unprecedented opportunity to study the demise of a comet nucleus.

Amateur and professional astronomers around the world have been tracking the spectacular disintegration of 73P/Schwassmann-Wachmann 3 for years. As it plummets towards a close encounter with the Sun, swinging round the Sun on 7 June and heading away to begin another loop round the Solar System, the comet will pass the Earth on 12 May, at a distance of 11.7 million kilometres, or 30 times the distance between Earth and the Moon.

The comet currently comprises a chain of over 33 separate fragments, named alphabetically, and stretching across several degrees on the sky (the Sun and Moon each have an apparent diameter of about 1/2 a degree). Ground-based observers have noted dramatic brightening events associated with some of the fragments indicating that they are continuing to break up and that some may disappear altogether.

Hubble caught two of the fragments, B and G, shortly after major outbursts in activity. The resulting images reveal that an amazing process of hierarchical destruction is taking place, in which the larger fragments are continuing to break up into smaller chunks. Several dozen "mini-fragments" are to be found trailing behind each main fragment, probably associated with the ejection of house-sized chunks of surface material that can only be detected in these very high-resolution Hubble images.........

Posted by: Edwin      Permalink         Source


April 26, 2006, 8:09 PM CT

The Art of Asteroid Avoidance

The Art of Asteroid Avoidance Just what can a little spacecraft do to deflect an asteroid - a lot say some scientists. Credit: SpaceDaily
Col. Gen. Vladimir Popovkin, commander of the Russian Military Space Forces, told a news conference Friday that the national satellite network lacked a spacecraft capable of preventing an asteroid strike.

He also said chances of such a collision were infinitely small, and it was inexpedient to spend huge sums on neutralizing this unlikely threat. Still, the general might be underestimating the scale of the asteroid threat.

Over the last few decades there has been a great deal of debate about the level of danger posed by impacts from asteroids and comets. It appears the world needs to take the threat of asteroid strikes a lot more seriously.

Astronomers have already spotted about 800 asteroids, solid rocky celestial bodies, with a diameter of over 1,000 meters (3,250 feet) moving along circumsolar elliptical orbits. However, there may be as a number of as 2,000 large asteroids, and some 135,000 rocks with a diameter of 100 meters (325 feet) and more.

It should be noted that asteroid orbits are unstable and tend to change under the influence of gravitational fields of the terrestrial planets - Mercury, Venus, Earth and Mars.

An asteroid, which flashed past our planet at a distance of 5 million kilometers (3.1 million miles) in November 1996, returned in September 2004 and flew by just 1.5 million kilometers (930,000 miles) from Earth's surface. In March 1989, a 300 meter (975 foot) asteroid crossed the terrestrial orbit and missed the Earth by just six hours. Astronomers spotted the rock only when it was receding into space.........

Posted by: Edwin      Permalink         Source


April 25, 2006, 8:11 PM CT

Nanedi Valles Valley System On Mars

Nanedi Valles Valley System On Mars

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, show the Nanedi Valles valley system, a steep-sided feature that may have been formed in part by free-flowing water.

The HRSC obtained these images on 3 October 2004 during orbit 905 at a ground resolution of approximately 18 metres per pixel. The images have been rotated 90 degrees clockwise, so that north is to the right.

They show the region of Nanedi Valles, a roughly 800-kilometre valley extending southwest-northeast and lying at approximately 6.0 degree North and 312 degree East in the region of Xanthe Terra, southwest of Chryse Planitia.

In the colour image, Nanedi Valles ranges from approximately 0.8- to 5.0-kilometre wide and extends to a maximum of about 500 metres below the surrounding plains. This valley is relatively flat-floored and steep-sloped, and exhibits meanders and a merging of two branches in the north.

The origin of these striking features remains heavily debated.

Some scientists point to sapping (erosion caused by ground-water outflow), while others suggest that flow of liquid beneath an ice cover or collapse of the surface in association with liquid flow is responsible for the valley's formation.

While the debate continues, it seems likely that some sort of continuous flow rather than a single flooding event created these features.........

Posted by: Edwin      Permalink         Source


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