Galaxies

Galaxies

Oursun belonngs to a giant whirlpool of stars called the millky way. Huge collections of stars are called galaxies, and like all galaxies the milky is unimaginably vast. Galaxies come in  many owny galaxy, but others are fuzzy balls or shapeless clouds.The smallest have just a few million stars. The largest contain trillions. 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 each star, the nearest star to the Sun would be 6 km (4 miles) away. The furthest would be 130,000 km (80,000 miles) away. The stars in a galaxy are held together by gravity   and travel slowly around the galactic heart. In  many galaxies, including ours,a supermassive blck hole lies  hidden in the centre. Stars and other material  are sucked into this comic  plughole by  gravity and disapper 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 buleg. Curving around this are two vast spiral arms and several smaller arms.The Milky Way is thought to be a barred sprial (see panel),but we can’t see its shape clearly from Earth as we view it from the inside. In the night sky, the Milky Way appers only as a milky band of  light.

Galactic centre

This photo from an infrared (heat-sensitive) telescope shows stars and gas clouds packin the centre of the  Milky Way. A supermassive black hole lies hidden somewhere in this ares.

Solar System

Our Solar System is in a minor spiral arm called the Orion Arm. We orbit the centre of the galaxy once every 200 million years, travelling at about 200km (120 miles) a second.

Crab Nebula

Clouds of gas and dust occur throughout the Milky Way, especially in the sprial arms.The Crab Nebula is a cloud of werckege left behind by a dying star that exploded.

Globular cluster

Not all the Milky Wayn’s stars are in the main disc of the galaxy. Many are  in globular clusters –tightly  packed ball  of ancient stars floating above and  below the galaxy in a spherical region called the halo

Galaxy shapes

Astronomers classife  galaxies into just a few  main types, depending on the shpe we observe from Earth. Spiral: A central hub of stars is surrounded by spiral arms curving out. Elliptical : More than half of all gelaxies are simple ball shapes. Barred spiral : A straight bar runs across the centre, connecting sprial arms . Irregular :Galaies with no clear shape are classified as irregular.