For several years, the Hubble Space Telescope has been watching distant halo stars
' proper motions--their movement across the sky.
are strewn considerably farther in some directions than others.
For the first time, Bergemann's team presented detailed chemical abundance patterns of these halo stars
using the W.
The halo stars
are among the first inhabitants of our galaxy and collectively represent an older population from the stars, like our Sun, that formed later in the disk.
The well- mixed population of halo stars
in these large galaxies represents the aggregate of the dwarf galaxy victims of this cannibalism process, while the dwarf galaxies that are still intact as they orbit their large parent galaxy are the survivors of this process.
The relative youth of many of Andromeda's halo stars
suggests that an intruder crashed into the galaxy some 8 billion years ago, hurling young stars from Andromeda's central disk into the halo.
"Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars
," the paper said.
This movement is different from what astronomers know about the halo stars
near the Sun, which move predominantly in radial orbits.
Already studying a larger catalog of halo stars
, Timothy C.
The team is compiling a much larger sample in a project known as HAL07D, which will contain information on hundreds of halo stars
and help them confirm whether this shell and other structures exist.
To measure the halo's age, Kalirai compared the masses of the halo stars
with those of six newly formed white dwarfs in the ancient globular star cluster M4.
In a new study analyzing highly accurate measurements of the position and velocity of 41 halo stars
near the sun, B.