Galaxy: Definition, Formation & 5 Interesting Facts

Galaxy: Definition, Formation & 5 Interesting Facts

What is a Galaxy?

Galaxy refers to a massive collection of dust, gas, and billions of stars. Every star has their own planetary systems. A galaxy holds all these stars together with the help of a powerful gravitational field. 

For 12 days, the Hubble Space Telescope observed a minimal area in space and discovered about 10,000 galaxies of different sizes, shapes, compositions, and colours. According to researchers and astronomers, there is a possibility that there are more than one hundred billion galaxies (i.e., 100,000,000,000!!!!) in the universe.

Formation of Galaxies

The early universe’s idea is based on the modern cosmological models governed by the Big Bang theory that took place about 13-14 billion years ago.

The explanation about the formation of galaxies lies primarily on the combination of two different theories.

According to the first theory, galaxies formed when massive dust and gas clouds collapsed influenced by their own gravitational pull, leading to the formation of stars.

The second theory, which has witnessed more support in recent years, states that the young universe comprises numerous small “lumps” of matter, which clomps together, leading to galaxies. Hubble Space Telescope has observed and photographed many such lumps, which may be the predecessors to modern galaxies.

The theory also says that most of the modern elliptical galaxies were initially spiral. 

The galaxy-formation process is still ongoing, and the universe is continually evolving. Smaller galaxies are often gulped up by larger ones with their gravitational pull. Our Milky Way galaxy might also enclose the ruins of several smaller galaxies that it has absorbed during its long lifetime. 

The bright galaxies that we see today might have formed my merging smaller galaxies. 

Oldest Galaxy

GN-z11 galaxy
GN-z11 galaxy
image source: Wikipedia

The earliest ideas regarding galaxies suggest that they were formed when clusters of invisible dark matter pulled in surrounding dust and gas producing stars. According to scientists and astronomers, the early formation of galaxies was a violent process that involved heating of the gas. 

GN-z11 found in the Ursa Major constellation is the most distant and oldest known galaxy in the observable universe. The name GN-z11 comes from its location in the GOODS-North field of galaxies and its spectroscopic redshift number [z = 11.09]. Its redshift number tells that it is located at a distance of approximately 32 billion light-years. GN-z11 existed 13.4 billion years ago (that is why it is sometimes incorrectly stated to be at a distance of 13.4 light-years from the Earth.) about 400 million years after the Big Bang. 

Astronomers and researchers worked with Hubble’s Wide Field Camera 3 for measuring the distance to GN-z11. They split the light into its component colors to estimate the redshift produced by the expansion of the universe.

Nearest Galaxy

The Canis Major Dwarf Galaxy or the Canis Major Overdensity is the nearest from our Milky Way galaxy at a distance of about 2500 Light-years. Canis Major is a dwarf, irregular galaxy located in the Canis Major constellation.

 According to astronomers and researchers, Canis Major is likely to be pulled apart by the Milky Way galaxy’s enormous gravitational field. The primary body of the galaxy happens to be nearly degraded. Hence, there is confusion regarding the true nature of the overdensity. The study of Canis Major and its constituent stars has provided proof that more massive galaxies can expand by engulfing the smaller ones.

canis major
Canis Major
Image source: Till CrednerCanisMajorCCCC BY-SA 3.0

The Andromeda Galaxy is regarded as the nearest Major Galaxy located at a distance of 2.5 million light-years from the Milky Way. The Andromeda galaxy is said to holds about twice the number of stars as the Milky WayThe formation of the galaxy took place about 10 billion years ago. Andromeda merged and gulped several smaller galaxies to reach the size it is today.

Like the Milky Way, Andromeda also happens to be a barred spiral galaxy. However, it does not have a very distinct spiral shape due to its interactions with galaxy satellites M110 and M32. Andromeda is best seen with the naked eye during the autumn nights in the Northern Hemisphere.

Andromeda Galaxy
Image source: Adam EvansAndromeda Galaxy (with h-alpha)CC BY 2.0

Largest Galaxy

The Largest galaxy known to humans as of now is IC 1101. The galaxy is around 50 times bigger than Milky Way’s size and about 2,000 times more massive. IC 1101 is a supergiant lenticular galaxy that is located approximately 5.5 million light-years across. The galaxy has the largest black hole in the universe and houses some of the oldest stars.

IC 1101 Galaxy
image source: NASA/ESA/Hubble Space Telescope, IC 1101 in Abell 2029 (hst 06228 03 wfpc2 f702w pc), marked as public domain, more details on Wikimedia Commons

Galaxy Vs. Universe

People often confuse these two terms. At times they even term them to be synonyms. But these two terms are vastly different.

Galaxy refers to the collection of stars, dust, asteroids, planets, moons etc. held together by a strong gravitational field.

The universe essentially translates as everything that exists, i.e., the galaxies (100 billion), the matter between the galaxies (dark matter) etc. The universe is the largest possible existing entity. Nothing lies beyond it.  

Color of Galaxies

color of galaxies
color of galaxies
Image source: Joshua Schroeder, Galaxy color-magnitude diagramCC BY-SA 3.0

The color of galaxies mostly arises from its stellar composition and gas clouds.

The galaxies with more population of older stars tend to have a reddish appearance. When stars grow old and are on the verge of getting collapsed, they exhaust most of their resources. The lack of fuel and energy enables them to produce less heat, and therefore, they produce a red shine. Generally, old elliptical galaxies appear to be red in color.

The galaxies with more population of young and bright stars tend to have a blueish appearance. This happens because young stars are filled with energy resources and release enormous amounts of heat-producing a bluish-white shine. Generally, spiral galaxies appear bluish in color. 

5 Interesting Facts

  1. The galactic centers blow out enormous bubbles of hot gas and energy particles.
  2. Some of the oldest stars of the Milky Way are considered to be as old as the Universe.
  3. 90% of the mass of the Milky Way galaxy is formed of dark matter. This is why a mysterious dark halo covers the galaxy.
  1. The galactic centers blow out enormous bubbles of hot gas and energy particles.
  2. Some of the oldest stars of the Milky Way are considered to be as old as the Universe.
  3. 90% of the mass of the Milky Way galaxy is formed of dark matter. This is why a mysterious dark halo covers the galaxy.

To know more about the types of galaxies visit

To know more about the Milky Way galaxy visit

To know more about telescopes visit

About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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