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 “In the quest for Earth-like planets, we have now identified numerous systems which are excellent candidates to harbor them. Where they persist as white dwarfs, any terrestrial planets will
likely not be habitable, but may have been sites where life developed during a previous epoch."

Jay Farihi, of the University of Leicester

One of the great feats of the NASA's Spitzer Space Telescope was to capture, for the first time, enough light from planets outside our solar system, known as exoplanets, to identify molecules in their atmospheres

Now, using NASA’s Spitzer Space Telescope, an international team of astronomers have found that at least 1 in 100 white dwarf stars show evidence of orbiting asteroids and rocky planets, suggesting these objects once hosted solar systems similar to our own.

White dwarf stars are the compact, hot remnants left behind when stars like our Sun reach the end of their life cycle. Their atmospheres should consist entirely of hydrogen and helium but are sometimes found to be contaminated with heavier elements like calcium and magnesium. The new observations suggest that these Earth-sized stars are often polluted by a gradual rain of closely orbiting dust that emits infrared radiation picked up by Spitzer.

The data suggest that at least 1% to 3% of white dwarf stars are contaminated in this way and that the dust originates from rocky bodies like asteroids. In our Solar System, minor planets are the left over building blocks of the rocky terrestrial planets like the Earth. The Spitzer results imply that asteroids are found in orbit around a large number of white dwarfs, perhaps as many as 5 million in our own Milky Way Galaxy.

The new findings indicate the dust is completely contained within the Roche limit of the star -- close enough that any object larger than a few kilometers would be ripped apart by gravitational tides (the same phenomenon which led to the creation of Saturn's rings). 

This backs up the team’s hypothesis that the dust disks around white dwarfs are produced by tidally disrupted minor planets.  In order to pass this close to the white dwarf, an asteroid must be perturbed from its regular orbit further out – and this can occur during a close encounter with as yet unseen planets.

Because white dwarfs descend from main sequence stars like the Sun, the team’s work implies that at least 1% to 3% of main sequence stars have terrestrial planets around them.

Perhaps the most exciting and important aspect of this research is that the composition of these crushed asteroids can be measured using the heavy elements seen in the white dwarf.

Dr Farihi sees this as a crucial step forward. “With high quality optical and ultraviolet observations (e.g. the Hubble Space Telescope), we should be able to measure up to two dozen different elements in debris-polluted white dwarfs.  We can then address the question, 'Are the rocky extrasolar planets we find similar to the terrestrial planets of our Solar System?'”

Posted by Casey Kazan.

Adapted from materials provided by Royal Astronomical Society.

Links:

http://www.spitzer.caltech.edu/Media/happenings/20090420/

http://www.sciencedaily.com­ /releases/2009/04/090419211631.htm
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The Antennae Galaxies are among the closest known merging galaxies. The two galaxies, also known as NGC 4038 and NGC 4039, began interacting a few hundred million years ago, creating one of the most impressive sights in the night sky. They are considered by scientists as the archetypal merging galaxy system and are used as the standard to validate theories about galaxy evolution.

The Antennae Galaxies, located in the constellation of Corvus, the Crow, are named for the two long tails of stars, gas and dust that resemble the antennae of an insect.

These "antennae" are a physical result of the collision between the two galaxies, which provides us with a preview of what may happen when our Milky Way galaxy collides with the neighboring Andromeda galaxy in several billion years. Although galaxy mergers today are not common, it is believed that in the past they were an important channel of galaxy evolution.

Andromeda and the Milky Way are approaching one another at a speed of 100 to 140 kilometers per second (62–87 miles/sec). However, this does not mean it will definitely collide with the Milky Way, since the galaxy's tangential velocity is unknown. If they do collide, the two galaxies will likely merge to form a monster elliptical galaxy.

New research on the Antennae Galaxies using the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope shows that this benchmark pair of interacting galaxies is in fact much closer than previously thought - 45 million light-years instead of 65 to 100 million light-years.

An international group of scientists led by Ivo Saviane from the European Southern Observatory has used Hubble's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to observe individual stars spawned by the colossal cosmic collision in the Antennae Galaxies. They reached an interesting and surprising conclusion. By measuring the colors and brightnesses of red giant stars in the system, the scientists found that the Antennae Galaxies are much closer than previously thought: 45 million light-years instead of the previous best estimate of 65 million light-years.

The team targeted a region in the relatively quiescent outer regions in the southern tidal tail, away from the active central regions. This tail consists of material thrown from the main galaxies as they collided. The scientists needed to observe regions with older red giant stars to derive an accurate distance. Red giants are known to reach a standard brightness, which can then be used to infer their distance. The method is known as the tip of the red giant branch (TRGB).

Posted by Casey Kazan. Adapted from a Hubble Space Telescope release.

Source link:

http://www.spaceref.com/news/viewpr.html?pid=25413