Astronomers develop theories of star motions to not only understand how the stars in our galaxy are moving today but also how our galaxy formed and evolves.
The Milky Way is shaped like a spiral, with a region of stars at the center known as the "bar," because of its shape. In the middle of this region, there is a "bulge" that expands out vertically.
In the new work Alice Quillen, professor of astronomy at the University of Rochester, and her collaborators created a mathematical model of what might be happening at the center of the Milky Way.
Unlike the solar system where most of the gravitational pull comes from the Sun and is simple to model, it is much harder to describe the gravitational field near the center of the galaxy, where millions of stars, vast clouds of dust, and even dark matter swirl about.
In this case, Quillen and her colleagues considered the forces acting on the stars in or near the bulge.
As the stars go round in their orbits, they also move above or below the plane of the bar. When stars cross the plane they get a little push, like a child on a swing.
At the resonance point, which is a point a certain distance from the center of the bar, the timing of the pushes on the stars is such that this effect is strong enough to make the stars at this point move up higher above the plane. (It is like when a child on the swing has been pushed a little every time and eventually is swinging higher.) These stars are pushed out from the edge of the bulge.
The resonance at this point means that stars undergo two vertical oscillations for every orbital period. But what is the most likely shape of the orbits in between?
The researchers showed through computer simulations that peanut-shell shaped orbits are consistent with the effect of this resonance and could give rise to the observed shape of the bulge, which is also like a peanut-shell.
The findings are published week in Monthly Notices of the Royal Astronomical Society.
--ANI (Posted on 28-11-2013)