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Huge Newfound Part of Milky Way Rotates Backward


Wed Dec 12



Our Milky Way Galaxy has two distinct parts in its outer reaches that rotate in opposite directions, astronomers announced today.

The galaxy has a bulbous core where stars are tightly packed and orbiting rather furiously around the central black hole. Then there's the big flat disk with its spiral arms, also orbiting the galactic center somewhat in the manner of a hurricane's spiral bands. We live on one of those arms. Around it all is a halo of stars that don't all behave in such an orderly fashion. That much researchers knew.

Now they find the halo has two parts.

"By examining the motions and chemical makeup of the stars, we can see that the inner and outer halos are quite different beasts and they probably formed in different ways at different times," said Daniela Carollo, a researcher at Italy's Torino Observatory and the Australian National University.

The finding, detailed in the Dec. 12 issue of the journal Nature, is based on 20,000 stars observed as part of the Sloan Digital Sky Survey.

The main galactic disk, home to our sun, rotates counterclockwise as seen from above at an average speed of 500,000 mph. Surrounding the disk is what's now called the inner halo. It orbits in the same direction at about 50,000 mph. The outer halo, a sparsely populated region, spins in the opposite direction at roughly 100,000 mph.

There are chemical differences between the two parts, too. Stars in the inner halo have three times as many heavy atoms, including iron and calcium. These heavy elements were produced by massive stars that exploded fantastically and begat subsequent generations of stars.

"The halo is clearly divisible into two, broadly overlapping components," said study team member Timothy C. Beers of Michigan State University. "The discovery gives us a much clearer picture of the formation of the first objects in our galaxy and in the entire universe."

The study adds to other evidence showing the galaxy was not built in a cosmic day. Rather, it assembled over time, gobbling smaller galaxies in one of nature's greatest construction projects.

The inner halo probably formed first, from collisions between smaller galaxies that had been captured by the Milky Way's gravitation. The outer halo formed later, the thinking goes, as small galaxies (orbiting opposite our own) were lured in and torn apart.

"We still have a lot to understand," said Masashi Chiba of Japan's Tohoku University.

To avoid making a new thread about an article on the solar system... here's another one!

Saturn's rings older than first thought?

LOS ANGELES - Saturn's shimmering rings may be as old as the solar system, scientists said Wednesday, debunking earlier theories that the rings were formed during the dinosaur age.

Astronomers had thought Saturn's rings were cosmically young, likely born some 100 million years ago from leftovers of a meteoric collision with a moon, based on data by NASA's Voyager spacecraft in the 1970s.

However, new data from the orbiting international Cassini spacecraft suggest the rings existed as far back as 4.5 billion years ago, roughly the same time the sun and planets formed. The probe also found evidence that ring particles are constantly shattering and regrouping to form new rings.

"Recycling allows the rings to be as old as the solar system although continually changing," said Larry Esposito, a Cassini scientist from the University of Colorado.

The findings were presented at an American Geophysical Union meeting in San Francisco and will be published in the astronomical journal Icarus.

Saturn's trademark arcs have awed astronomers since Galileo's time. Scientists are interested in the rings because they are a model of the disk of gas and dust that initially enveloped the sun and studying them could yield clues about planet formation.

Saturn's ring system consists of seven major rings and thousands of ringlets, mostly made of orbiting ice mixed with dust and rock fragments.

The notion that Saturn's rings may be a permanent feature was based on observations by the ultraviolet spectrograph instrument on Cassini, which viewed the light reflected from the rings and watched stars passing behind them.

The Cassini mission, funded by NASA and the European and Italian space agencies, was launched in 1997 and reached Saturn in 2004. The mission is managed by NASA's Jet Propulsion Laboratory in Pasadena.

Source: Yahoo News.