How galaxies are formed?

Astronomers aren't certain of exactly how galaxies formed. After the Big Bang, space was made up almost entirely of hydrogen and helium. Some astronomers think that gravity pulled dust and gas together to form individual stars, and those stars drew closer together into collections that ultimately became galaxies.


Galaxies are collections of stars, gas, dust and dark matter held together by gravity. Their appearance and composition are shaped over billions of years by interactions with groups of stars and other galaxies.





Using several different telescopes, astronomers have discovered a distant galaxy whose stars appear to have formed 200 million years after the Big Bang, the explosive event that brought the universe into being. That's about 300 million years earlier than the oldest previously known galaxies.


For many years scientists have studied our own solar system. But until the last few years, we knew of no other solar systems. This may seem surprising, as the Sun is one of about 200 billion stars (or perhaps more) just in the Milky Way galaxy alone.

Does every galaxy have a sun?
For many years scientists have studied our own solar system. But until the last few years, we knew of no other solar systems. This may seem surprising, as the Sun is one of about 200 billion stars (or perhaps more) just in the Milky Way galaxy alone.


How are galaxies discovered?

Observational firsts. Lord William Parsons, Earl of Rosse discovered the first spiral nebula from observing M51 (recognition of the spiral shape without the recognition of the object as outside the Milky Way). Recognition of the Milky Way and the Andromeda nebula as two separate galaxies by Edwin Hubble.

William Parsons, 3rd Earl of Rosse photo.jpg
William Parsons

 
Earl of Rosse
Source: Wikipedia

What processes formed the galaxies?
Instead of large gas clouds collapsing to form a galaxy in which the gas breaks up into smaller clouds, it is proposed that matter started out in these “smaller” clumps (mass on the order of globular clusters), and then many of these clumps merged to form galaxies, which they were drawn by gravitation to form galaxy

What are the 4 types of galaxies?
This classification system is known as the Hubble Sequence. It divides galaxies into three main classes with a few variations. Today, galaxies are divided into four main groups: spiral, barred spiral, elliptical, and irregular.

How is the spiral galaxy formed?
The bulge and halo of the Milky Way (and other Sa and Sb galaxies) are composed mostly of old stars. This indicates that the bulges and halos of spiral galaxies probably formed through the primordial collapse of individual gas clouds early in the history of the Universe.


How old are spiral galaxies?
The oldest spiral galaxy on file is BX442. At eleven billion years old, it is more than two billion years older than any previous discovery. Researchers think the galaxy's shape is caused by the gravitational influence of a companion dwarf galaxy.

What type of galaxy is the Milky Way?
The mass distribution within the Milky Way closely resembles the type Sbc in the Hubble classification, which represents spiral galaxies with relatively loosely wound arms. Astronomers first began to suspect that the Milky Way is a barred spiral galaxy, rather than an ordinary spiral galaxy, in the 1960s.


What is at the center of the Milky Way galaxy?
The complex astronomical radio source Sagittarius A appears to be located almost exactly at the Galactic Center (approx. 18 hrs, −29 deg), and contains an intense compact radio source, Sagittarius A*, which coincides with a supermassive black hole at the center of the Milky Way.


Why are there galaxies?
Galaxies have magnetic fields of their own. They are strong enough to be dynamically important: they drive mass inflow into the centers of galaxies, they modify the formation of spiral arms and they can affect the rotation of gas in the outer regions of galaxies.


Why does every galaxy have a black hole?
This is a class of astronomical objects that have undergone gravitational collapse, leaving behind a rounded region of space from which nothing can escape, not even light. Observational evidence indicates that all or nearly all massive galaxies contain a supermassive black hole, located at the galaxy's center.


Are there planets in other galaxies?
An extragalactic planet, also known as an extragalactic exoplanet, is a star-bound planet, or rogue planet, located outside of the Milky Way galaxy. Due to the huge distances to such worlds, they would be very hard to detect directly. However, indirect evidence suggests that such planets may exist.


Who found Andromeda galaxy?
Edwin Hubble
His result placed the Andromeda Nebula far outside our galaxy at a distance of about 450,000 parsecs (1,500,000 light-years). Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of Andromeda.
  

Is a galaxy a celestial body?
In astronomy, the terms object and body are often used interchangeably. ... Examples of astronomical objects include planetary systems, star clusters, nebulae, and galaxies, while asteroids, moons, planets, and stars are astronomical bodies.


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