Three stages of the evolution of the galaxy simulation used to model the Milky Way. Face-on and edge-on (bottom) stellar density contours are shown for each
time. Each square panel has a side of about 117,500 light years. The
mass and frequency of satellites galaxies interacting with the disc
decrease with time. (Credit: AIP)
A team of scientists headed by Ivan Minchev from the Leibniz Institute
for Astrophysics Potsdam (AIP) has found a way to reconstruct the
evolutionary history of our galaxy, the Milky Way, to a new level of
detail. The investigation of a data set of stars near the sun was
decisive for the now published results.
he astronomers studied how the vertical
motions of stars - in the direction perpendicular to the galactic disc -
depend on their ages. Because a direct determination of the age of
stars is difficult, the astronomers instead analyzed the chemical
composition of stars: an increase in the ratio of magnesium to iron
([Mg/Fe]) points to a great age. For this study, Ivan Minchev’s team
took advantage of high-quality data regarding stars close to the Sun
from the Radial Velocity Experiment (RAVE).
The scientists found that the rule of thumb “the older a star is, the
faster it moves up and down through the disc” did not apply to the stars
with the highest magnesium-to-iron ratios. Contrary to expectations,
scientists observed an extreme drop in the vertical speed for these
stars.
To understand these surprising
observations, the scientists ran a computer model of the Milky Way,
which allowed them to examine the origin of these slow-moving, old
stars. After studying the computer model, they found that small galactic
collisions might be responsible. It is thought that the Milky Way has
undergone hundreds of such collisions with smaller galaxies in the
course of its history. These collisions are not very effective at
shaking up the massive regions near the galactic center. However they
can trigger the formation of spiral arms and as a consequence move stars
from the center of the Galaxy to the outer parts, where the Sun is.
This “radial migration” process is able to transport outward old stars
(with high values of magnesium-to-iron ratio) and with low up-and-down
velocities. Therefore, the best explanation for why the oldest stars
near our Sun have such small vertical velocities is that they were
forced out of the galactic center by galactic collisions. The difference
in speed between those stars and the ones born close to the Sun thereby
betray how massive and how numerous the merging satellite galaxies
were.
AIP scientist Ivan Minchev: “Our
results will enable us to trace the history of our home Galaxy more
accurately than ever before. By looking at the chemical composition of
stars around us, and how fast they move, we can deduce the properties of
satellite galaxies interacting with the Milky Way throughout its
lifetime. This can lead to an improved understanding of how the Milky
Way may have evolved into the Galaxy we see today.”
The article “A new stellar chemo-kinematic relation reveals the merger history of the Milky Way disc” was published in the Astrophysical Journal Letters on January 20.
Science contact:
Dr. Ivan Minchev,
+49 331-7499 454,
Email: iminchev@aip.de
Media contact:
Kerstin Mork,
+49 331-7499 469,
Email: presse@aip.de
The key topics of the Leibniz Institute
for Astrophysics Potsdam (AIP) are cosmic magnetic fields and
extragalactic astrophysics. A considerable part of the institute's
efforts aim at the development of research technology in the fields of
spectroscopy, robotic telescopes, and e-science. The AIP is the
successor of the Berlin Observatory founded in 1700 and of the
Astrophysical Observatory of Potsdam founded in 1874. The latter was
the world's first observatory to emphasize explicitly the research area
of astrophysics. Since 1992 the AIP is a member of the Leibniz
Association.
