What is in our Galaxies
Our sun belongs to a giant whirlpool of stars called the Milky way. Huge collections of stars are called galaxies. and like all galaxies the milky way is an unimaginably vast
Galaxies come in many shapes and sizes, some are spiral like our own galaxy, but others are fizzy balls for shapeless clouds. The smallest have just a few million stars. The largest container trillion.
Although they look packed with stars, galaxies are mostly empty space.If you made a scale model of the Milky way with a grain of sand for its stars, the nearest stars to the sun would be 6 km away . The furthest old be 130, 000 km away.the stars in galaxy are held together by gravity and travel slowly around the galactic heart. In many galaxies including ours, supermassive black holes are hidden in the center. Stars and other material are sucked into this cosmic plughole by gravity and disappear forever.
The Milky way
If you could look down on the Milky way galaxy from above, the view would be like flying over a glittering city at night. Most of the galaxy's 200 billion stars are in the central bulge. Curving around this are you washed spiral arms and several smaller arms. The milky way is thought to be a barred spiral, but we can't see its shape clearly from Earth as we view it from the inside. In the night sky the Milky way appears only as a milky band of light.
Galaxy shapes
astronomers classify galaxies into just a few main types, depending on the shape
we observe from Earth.
1. Spiral
Central hub of stars is surrounded by spiral arms carving out
2. Barred spiral
A straight bar runs across the centre connecting spiral arms.
3. Elliptical
More than half of all galaxies are simple ball shapes
4. Irregular
Galaxies with no clear shapes are classified as irregular shapes.
How spiral arms form?
The stars in galaxies orbit the center , taking millions of years to make one circuit. Spiral arms appear, where stars pass in and out of crowded areas. Like cars passing temporally through a traffic jump full stop one theory is that this traffic jams happen because the orbits of different stars don't line up neatly.
1. If stars all head neat parallel orbits. The galaxy would have no spiral arms
2 stars orbit don't line up neatly e, crowded zones form giving the galaxy spiral arms.
Colliding galaxies
Sometimes galaxies crash and clear each other apart. Individual stars don't collide , but gas clouds do, and gravity pulls the colliding galaxies into few shapes.
End of Milky way
In a billion years our galaxy will collide with the Andromeda galaxy. This artist impression shows what the sky might look like as they merge
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