Astronomers detect the farthest known star of Milky Way
- July 11, 2014
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The distant outskirts of our galaxy harbor valuable clues for understanding its formation and evolution. But the stars out there are few, far between, and far, far away.
Now, astronomers are reporting the discovery of two stars in this distant “halo” that are the furthest ever discovered in our galaxy, the Milky Way, and are being described as possible ghosts of galaxies past.
They're so far away that if you could stand on them and look up to the sky, you'd see the entire Milky Way spiral out there, not just a small part of it, as we see from Earth.
Astronomers led by John Bochanski, a visiting assistant professor at Haverford College in Pennsylvania, were targeting stars in this “halo,” a sparse shroud of stars that surrounds the flatter, spiral disk of our galaxy. The halo stretches to at least half a million light years away. A light-year is the distance light travels in a year.
Previously, only seven stars were known beyond 400,000 light years.
Bochanski and colleagues published a letter July 3 in the journal Astrophysical Journal Letters detailing the discovery of the two stars, classified as “cool red giants” catalogued as ULAS J0744+25 and ULAS J0015+01.
They lie an estimated 775,000 and 900,000 light years away, respectively. To put it in perspective, when light from the further star left the object, “our early human ancestors were just starting to make fires here on Earth,” Bochanski said.
Red giant stars are rare compared to nearby “cool red dwarf” stars, but are nearly 10,000 times brighter, and thus more visible. Using a combination of filters highlighting different components of the light from these giants, the team identified cool red giant candidates from surveys, then confirmed the findings using the 6.5m telescope at the MMT Observatory on Mt. Hopkins in Arizona.
“It is remarkable to find stars this far out in the Milky Way galaxy,” said Daniel Evans, lead for Individual Investigator Programs at the U.S. National Science Foundation's Division of Astronomical Sciences, which funded the research. “These results will undoubtedly shed new light on the formation and evolution of our galactic home.”
The stars' significance goes beyond their record-holding distances because they inhabit the halo, the astronomers said. Some astronomers think that the halo is like a cloud of galactic crumbs, the result of the Milky Way's merger with smaller galaxies over our galaxy's lifetime, said Haverford College astronomer Beth Willman, a co-author of the study.
“Theory predicts the presence of such an extended stellar halo, formed by the destroyed remains of small dwarf galaxies that merged over the cosmic ages to form the Milky Way itself,” Willman said. “The properties of cool red giants in the halo thus preserve the formation history of our Milky Way. These stars are truly ghosts of galaxies past.”
Source : world-science.net