What defines a galaxy?
• 6 min read. Galaxies are sprawling systems of dust, gas, dark matter, and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain supermassive black holes at their centers.
How many galaxies are they?
While estimates among different experts vary, an acceptable range is between 100 billion and 200 billion galaxies, said Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland.
What is galaxy and its types?
Types of Galaxies Astronomers classify galaxies into three major categories: elliptical, spiral and irregular. These galaxies span a wide range of sizes, from dwarf galaxies containing as few as 100 million stars to giant galaxies with more than a trillion stars.
What is the name of our galaxy?
The Milky Way Galaxy
Astronomy > The Milky Way Galaxy. Did you know that our star, the Sun, is just one of hundreds of billions of stars swirling within an enormous cosmic place called the Milky Way Galaxy? The Milky Way is a huge collection of stars, dust and gas.
What is galaxy made of?
The Milky Way galaxy is made of billions of stars, and gas and dust, all bound together by mutual gravitational attraction, as well as a lot of dark matter. The diameter of our galaxy is about 100,000 light years [e1] across (the visible material at least – the dark matter halo goes beyond that).
Is the Earth in a galaxy?
We live on a planet called Earth that is part of our solar system. But where is our solar system? It’s a small part of the Milky Way Galaxy. A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems.
What is the biggest known galaxy?
IC 1101
The biggest known galaxy, first described in a 1990 study from the journal Science (opens in new tab), is IC 1101, which stretches as wide as 4 million light-years across, according to NASA (opens in new tab). Galaxies are often bound to each other gravitationally in groups that are called galaxy clusters.
How are galaxies born?
Galaxies are thought to begin as small clouds of stars and dust swirling through space. As other clouds get close, gravity sends these objects careening into one another and knits them into larger spinning packs.
Is galaxy bigger than Earth?
Answer: Assuming a diameter for the Milky Way galaxy of about 15 kpc, which is about 4.6×10^(17) km, and a diameter for the Earth of about 12756 km, the ratio of the diameter of the Milky Way galaxy to that of the Earth is about 3.6×10^(13).