What is meant by spiral galaxy?
Spiral galaxies are twisted collections of stars and gas that often have beautiful shapes and are made up of hot young stars. Most of the galaxies that scientists have discovered so far are spiral galaxies, as opposed to the other two main categories of galaxy shapes — elliptical and irregular.
What is a spiral galaxy Wikipedia?
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge.
How many spiral galaxies are there?
There are currently 3 classifications of classical spiral galaxies and another 3 for barred spiral galaxies: 1. Spiral galaxy type A – abbreviation Sa – they have a big central bulge and smooth, broad spiral arms.
How spiral galaxies are formed?
Astronomers believe that a galaxy’s spiral structure originates as a density wave emanating from the galactic center. The idea is that the entire disk of a galaxy is filled with material. The spiral arms of a galaxy mark where in the galaxy the density wave recently passed, causing new stars to form and burn brightly.
What are two types of spiral galaxies?
Spiral galaxies appear as flat, blue-white disks of stars, gas and dust with yellowish bulges in their centers. These galaxies are divided into two groups: normal spirals and barred spirals.
Why is the galaxy spiral?
Astronomers believe that galaxies have spiral arms because galaxies rotate – or spin around a central axis – and because of something called “density waves.” Galactic density waves are like water waves. A spiral galaxy’s rotation, or spin, bends the waves into spirals.
What is the average size of a spiral galaxy?
Spiral galaxies come in a wide range of sizes, from 5 to 100 kiloparsecs across, have masses between 109 and 1012 solar masses, and luminosities ranging from 108 to 1011 time that of the Sun. The majority of spiral galaxies rotate in the sense that the arms trail the direction of the spin.
Why do we think we live in a spiral galaxy?
Our Solar System is about 25,000 light years away from the center of our galaxy – we live in the suburbs of our galaxy. Just as the Earth goes around the Sun, the Sun goes around the center of the Milky Way. The concentration of stars in a band adds to the evidence that the Milky Way is a spiral galaxy.
Why does the Milky Way have spiral arms?
Astronomers believe that galaxies have spiral arms because galaxies rotate – or spin around a central axis – and because of something called “density waves.” A spiral galaxy’s rotation, or spin, bends the waves into spirals. Stars pass through the wave as they orbit the galaxy center.
How many stars are in a typical spiral galaxy like our own?
It is very difficult to count the number of stars in the Milky Way from our position inside the galaxy. Our best estimates tell us that the Milky Way is made up of approximately 100 billion stars. These stars form a large disk whose diameter is about 100,000 light years.