Astronomers Find Nearby Galactic Highway

Jun 09, 2006

Astronomers have discovered a long, slender stream of ancient stars racing across the northern sky. The stream is about 30,000 light-years from Earth and flowing high over the Milky Way at some 230 kilometers per second, or more than half a million miles per hour.

The discovery was made by Canadian astronomer Carl Grillmair and his colleague Odysseas Dionatos from the Astronomical Observatory of Rome. Grillmair presented the findings this week at the 208th American Astronomical Society meeting in his hometown of Calgary.

"What we can see of the stream is over 30,000 light years long," Grillmair said, "although it may actually be much longer than that since we are currently limited by the extent of the survey data. I would actually be somewhat surprised if the stream doesn't extend completely around the Galaxy."

The astronomers think the stars on this cosmic highway date back nearly to the beginning of the universe and are the fossil remains of a star cluster that, in its prime, contained between 10,000 and 100,000 stars.

The ancient cluster was torn apart over billions of years by the tidal forces of the Milky Way galaxy.

"The discovery gives new weight to a theory that, while the Milky Way now contains only about 150 such giant star clusters, it may once have been swarming with thousands of them," Grillmair said. "If this idea is correct, there may be hundreds or even thousands of such stellar streams ringing our galaxy.

On the sky, the stream is narrower than the pinky finger held at arm's length. Although it spans more than 130 times the diameter of the full Moon, or roughly one-third of the northern sky, the individual stars in the stream are too faint to be seen with the unaided eye.

The narrowness of the stream indicates the original cluster was not torn apart violently, but rather pulled out gently, perhaps a thousand or so each time the cluster passed near the Milky Way's center. The orphaned stars continue to follow one another along their original orbit, long after their parent cluster has dissolved completely away.

The stream was discovered using the Sloan Digital Sky Survey, through a technique called matched filtering. Using the colors and brightness of stars like DNA markers, the scientists assigned to each star a probability that it could have a particular age and distance.

By examining how these probabilities are distributed across the sky, Grillmair and Dionatos were able to push through the vast sea of foreground stars in the Milky Way and see the stream floating out among the dark and lonely reaches of the galactic halo.

"The stream's path on the sky is very smooth," Grillmair said. "The lack of any substantial wobbling tells us that, at least within a distance of 30,000 light years, there are no large concentrations of invisible dark matter. The stream is a remarkable find and provides a new avenue of research into the makeup of our galaxy and how gravity behaves on large scales."

Six such streams have been found in recent years, three of them by Grillmair and his team, and all but one of them in the Sloan Digital Sky Survey.

Studies of the streams discovered so far point to a massive halo of invisible dark matter surrounding the galaxy that is very close to spherical in shape. How far this halo extends, how it was formed, how lumpy it is, and what the dark matter is made of, are among the big questions astronomers are currently trying to answer.

Copyright 2006 by Space Daily, Distributed United Press International

Explore further: Black hole hunters tackle a cosmic conundrum

Related Stories

United States, China team explore energy harvesting

7 hours ago

Six authors have described their work in harvesting energy in a paper titled "Ultrathin, Rollable, Paper-Based Triboelectric Nanogenerator for Acoustic Energy Harvesting and Self-Powered Sound Recording." ...

China's struggle for water security

9 hours ago

Way back in 1999, before he became China's prime minister, Wen Jiabao warned that water scarcity posed one of the greatest threats to the "survival of the nation".

Canada revises upward CO2 emission data since 1990

9 hours ago

Canada revised its greenhouse gas emission data from 1990 to 2013 in a report Friday, showing it had higher carbon dioxide discharges each year, and a doubling of emissions from its oil sands.

Fish found in suspected tsunami debris boat quarantined

19 hours ago

The wreckage of a fishing boat that appears to be debris from the 2011 Japanese tsunami was carrying some unexpected passengers—fish from Japanese waters—when it was spotted off the Oregon coast.

Recommended for you

Radio astronomy backed by big data projects

1 hour ago

As the leading edge of the Square Kilometre Array (SKA) project, the Murchison Widefield Array (MWA) radio telescope is at the forefront of the big data challenges facing radio astronomy, presenting and solving ...

Black hole hunters tackle a cosmic conundrum

19 hours ago

Dartmouth astrophysicists and their colleagues have not only proven that a supermassive black hole exists in a place where it isn't supposed to be, but in doing so have opened a new door to what things were ...

Image: Thor's Helmet nebula in the X-ray spectrum

Apr 20, 2015

This brightly coloured scene shows a giant cloud of glowing gas and dust known as NGC 2359. This is also dubbed the Thor's Helmet nebula, due to the arching arms of gas stemming from the central bulge and ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.