STAR SYTEMS AND GALAXIES

Our sun is a single star but most stars are members of groups of two or more, called star systems. Two star systems are called binary. Three star systems are called triple. Proxima Centauri is probably a triple. Alpha Centauri A and Alpha Centauri B are part of a binary sytem. In a binary system usually one star is much brighter than the other. We can detect binary systems easily if one star blocks another, called an eclipsing binary. We have found planets moving around stars in other systems. We can only detect very large planets because the planets must have enough gravity to effect the star.

Kruger 60: the binary pair are orbiting slowly around each other Kruger 60: the binary pair are orbiting slowly around each other. How long does a complete revolution take? Is the movement clockwise or counter clockwise?

GALAXIES Our galaxy is called the Milky Way. Looks hazy to us beause the stars are so bright. There are three main kinds of galaxies, spiral, elliptical, and irregular. Spiral galaxies have a pinwheel shape. They have arms that spiral outward. The Milky Way is a spiral galaxy. We cannot see the center because it is hidden by stars and gases. It is 25,000 light years away. Elliptical galaxies look like flattened balls. They contain little dust and no new stars can form. Old stars only. Irregular galaxies have no shape. The Large Magellanic Cloud is irregular and close to us (160,000 light years away)

(a)An artist’s concept of what the Milky Way would look like from another galaxy. (b)Looking into the center of our galaxy from earth (enhanced infrared) Galactic Planeﾊ(a) Gazing from Earth toward the Galactic center (white arrow) in this artistﾕs conception, we see myriad stars stacked up within the thin band of light known as the Milky Way. Looking in the opposite direction (blue arrow), we still see the Milky Way band, but now it is fainter because our position is far from the Galactic center, with the result that we see more stars when looking toward the center than when looking in the opposite direction. Looking perpendicular to the disk (red arrows), we see far fewer stars

Starburst galaxy. What kind of galaxy is it? slide 10: colliding galaxies #AACGZQCO on astronomy disc

How do the stars in a galaxy move? Stellar Orbits in Our GalaxyﾊStars in the Galactic disk move in orderly, circular orbits about the Galactic center. In contrast, halo stars have orbits with largely random orientations and eccentricities. The orbit of a typical halo star takes it high above the Galactic disk, then down through the disk plane, then out the other side and far below the disk. The orbital properties of bulge stars are intermediate between those of disk stars and those of halo

Sombrero GalaxyﾊThe Sombrero Galaxy, a spiral system seen edge-on Sombrero GalaxyﾊThe Sombrero Galaxy, a spiral system seen edge-on. Spiral arms are not visible in this view.