The
Milky Way galaxy, perturbed by the tidal interaction with a dwarf
galaxy, as predicted by N-body simulations. The locations of the
observed stars above and below the disk, which are used to test the
perturbation scenario, are indicated. Credit: T. Mueller/C. Laporte/NASA/JPL-Caltech
An international team of astronomers led by the Max Planck Institute
for Astronomy (MPIA) has made a surprising discovery about the
birthplace of groups of stars located in the halo of the Milky Way
galaxy.
These halo stars are grouped together in giant structures
that orbit the center of the galaxy, above and below the flat disk of
the Milky Way. Researchers thought the stars might have formed from
debris left behind by smaller galaxies that invaded the Milky Way in the
past.
But in a study published February 26 in the journal Nature, astronomers
now reveal compelling evidence showing that some of these halo
structures actually originate from the Milky Way's disk itself. The
observations were made using the W. M. Keck Observatory on Maunakea,
Hawaii.
"This phenomenon is called galactic eviction," says co-author Judy Cohen,
the Kate Van Nuys Page Professor of Astronomy at Caltech. "These
structures are pushed off the plane of the Milky Way when a massive
dwarf galaxy passes through the galactic disk. This passage causes
oscillations, or waves, that eject stars from the disk, either above or
below it depending on the direction that the perturbing mass is moving."
"The
oscillations can be compared to sound waves in a musical instrument,"
says lead author Maria Bergemann of MPIA, who works in the field of
galactoseismology, which models the history of interactions between our
galaxy and its satellite galaxies. "We now have the clearest evidence
for these oscillations in our galaxy's disk obtained so far!"
As a
next step, the astronomers plan to analyze additional stars, including
those in other stellar structures farther away from the disk. They also
plan to determine the masses and ages of these stars in order to pin
down the time limits of when this galactic eviction took place.
Read the full story from the W. M. Keck Observatory here.
Contact:
Whitney Clavin
(626) 395-1856
wclavin@caltech.edu
Source: Caltech/News
