Introduction
From ancient time people are observing galaxies and wanted to know what exactly this structure’s are, They provided many theories like in west they thought that these galaxies are present between earth and moon, but Galileo Galilei was the first to define a galaxy and told that they are are cluster of star like our sun. In this post we will tell you about what galaxies are, how galaxies are formed, type of galaxies and much more about galaxies so let’s dive right in.
What is a galaxy ?
A galaxy is a large cluster of stellar objects, stars, interstellar gases, star systems which are all bound by the gravity of the central supermassive black hole. All the stars we see and our own solar system is also present inside a galaxy.
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| Galaxy, Image source : Wallpaper flare |
All the celestial and stellar objects we see are formed and also end inside the galaxy. Most of the galaxies we see are present inside a cluster of galaxies and there are very few galaxies which show independent existence. Along with this, the galaxy plays an important role in star formation as all the required gas for star formation is provided by the galaxy.
From the very beginning of the universe galaxies have played a central role in bringing chemical reactions and light into the universe. The Galaxy was the climax point of the universe which helped to bring many new elements in the universe by star formation.
How is the galaxy formed ?
In the very beginning of the universe there were no galaxies but large clusters of hydrogen and helium. called the Globular clusters. These Globular clusters collided and started to form larger clusters which eventually formed galaxies.
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| Globular cluster, Image source : Earth sky |
Once the Galaxy formation started in the universe the first Halo stars started to appear, these stars were 100 times more massive than our sun and were purely composed of hydrogen and helium. As they were purely composed of hydrogen and so large in size they started to burn the fuel really quick, which caused them to die faster.
When these stars started the nuclear fusion they formed many new elements and when they died they burst in a supernova and released the element in the universe which we see all around us. The iron in our blood, oxygen required for our living has all come out from a star only, thus we could conclude that we are also made up of stars.
These galaxies started to merge with each other and formed larger galaxies, then later after the hypernova of a large star formed supermassive black holes, these black holes started to influence the galaxy and then the entire galaxy started to revolve around these black holes. This formed the galaxies which we see today.
Classification of the galaxy ?
There are various types of galaxy present in our universe, they are having different shapes and on the basis of shape galaxies are classified into three types -
- Elliptical galaxy
- Spiral galaxy
- Irregular galaxy
Elliptical galaxy
Elliptical galaxies have a rough ellipsoid shape and mostly don’t have much interstellar mass due to which star formation rate is very low in an Elliptical galaxy. These galaxies are mainly composed of old stars which are comparatively small in size and are sparsely distributed in the galaxy.
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| Elliptical galaxy, Image source : Esahubble |
Elliptical galaxies are further classified using no. from E0 to E7. Examples of the Elliptical galaxy are Hercules A, Maffei 1, M49, M59 etc. Elliptical galaxy has two special types cD galaxy and the Shell galaxy.
cD galaxy
cD galaxy also called supergiant ellipticals is a type of Elliptical galaxy which is characterised and specially known for its large halo of star, the Halo of the star is the no. of stars and globular structure around the star. cD Galaxy is the most luminous galaxy still known. Examples of cD galaxy are Holmberg 15A, Messier 87, NeVe 1 etc.
Shell galaxy
Shell galaxies are also a type of Elliptical galaxy, Shell galaxies have an extraordinary feature which no other type of galaxy have is that, the stars present in the galaxy are present in concentric circles which means that they are arranged layer by layer.
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| Shell galaxy |
According to many astrologists these galaxies are formed due to the collision of two galaxies, when the galaxies merge it would have released gravitational waves which caused stars to be arranged in layers.
Spiral galaxy
Spiral galaxy shows a shape of pinwheel, the Spiral galaxy has a flat shape with a centre bulge and spiral arms. The central bulge contains old red stars, and the spiral arms contain young and new stars along with rotating gases and dust. These galaxies have much interstellar mass due to which they have large no. of stars.
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| Spiral galaxy, Image source : Wallpaper cave |
They are the most common type of galaxy in the universe. These Galaxies are further classified using variables like A,B,C. Examples of spiral galaxies are the Milky way, Andromeda galaxy, Cygnus A etc. Spiral galaxy has two types Normal spiral galaxy and Barred spiral galaxy.
Barred galaxy
A Barred galaxy is a type of spiral galaxy. These types of galaxies have a special feature: they have a central bar-like feature which makes them distinctive from other kinds of galaxies. This bar-like structure is mostly perpendicular to spiral arms.
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| Barred galaxy, Image source : Wikipedia |
This bar-like structure is an active site of star formation as most of the interstellar mass is present in the bar. Examples of Barred galaxies are Magellanic clouds, M58, M61 etc.
Irregular galaxy
Irregular galaxies don’t have any proper structure of symmetry, and the interstellar mass is distributed unequally. They are equal in size to the Elliptical and spiral galaxies, but are not common and are rarely found in the universe. They are mostly present in clusters.
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| Irregular galaxy, Image source : Universe today |
Irregular galaxies have a high rate of star formation as the interstellar mass is present more in certain areas. They are usually formed due to interaction of two galaxies which may have caused the irregular shape and structure.
Other classification
Along with this based on various factor such as composition, luminosity, size, structure galaxies are classified into many more types like -
Dwarf galaxy
Dwarf galaxies are called dwarf irregular galaxies. This galaxy is small in size and has comparatively less mass than other galaxies. They are the most common galaxy in the universe.
They have two kinds of structures: some are irregular in structure and some are spherical in structure. This dwarf galaxy are mostly present as satellite galaxy to large galaxy and orbit them.
Starburst galaxy
Starburst galaxies are having intense star formation. They have a huge load of interstellar mass due to which star formation takes place on a large scale there. They are compactly arranged which increases the luminosity and concentration of the galaxy.
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| Starburst galaxy, Image source : Space |
They also have an active galactic nucleus with a large concentration of stars there. They have a short lifespan as due to intense star formation interstellar mass gets exhausted quickly.
Radio burst galaxy
A radio burst galaxy releases a huge burst of radio waves, these radio bursts have short duration but have so much power that they can be detected from million light year distances.
The origin of this burst is still not clear, it is thought that it occurs due to the collision of neutron stars or due to some black hole activities. This type of galaxy is rare and is not found easily.
Active galaxy
Active galaxies have a bright and high luminosity nuclei (centre) this nuclei releases huge loads of electromagnetic radiation. Such a luminosity and brightness is thought to occur due to the presence of extremely strong supermassive black holes. They also release jets of particles and radiation at a very high speed.
Interaction of galaxy
Interaction of galaxies plays a central role in stellar evolution. Mostly when two galaxies are having enough momentum they pass through each other without merging.
This kind of interaction helps in exchange of interstellar mass such as gases and dust, and it also triggers star formation as gases and dust is compressed due to interaction of gravity between two galaxies.
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| Two galaxy merging, Image source : Universe today |
But in some cases the momentum is not enough to stop the merger; this causes the merger of two galaxies to form a larger galaxy. This merger causes release of extremely powerful gravitational waves and tidal waves.
Such a merger changes the structure of the galaxy and can also form features like tidal tails. Such a merger triggers star formation on a large scale and causes the birth of extremely bright nuclei.
Most of the merger of galaxies takes place between a dwarf galaxy and the main galaxy. But sometimes there is merger of large galaxy also this is a very violent phenomenon and causes merger of extremely powerful supermassive black holes, such an event would releases extremely powerful gamma rays and gravitational waves,
Which galaxy do we live in ?
The galaxy in which we reside is the Milky way galaxy, our galaxy has a diameter of 1,00,000 light years and a mass of 1.5 trillion solar masses. Our galaxy is a barred spiral galaxy with a central bar and spiral arms.
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| Milky way galaxy, Image source : Britannica |
Our solar system is located on the outer part of the spiral arm called the Orion arm. Our solar system is 26,000 light years away from the centre of the galaxy.
The Milky Way is currently young and in the era of star formation, this era of star formation will last till 100 billion years. Our galaxy Milky way is currently cannibalising the dwarf galaxy called Sagittarius dwarf elliptical galaxy and Canis major dwarf galaxy.
Our Milky way is going to collide with another galaxy called Andromeda in five to six billion years. The Andromeda galaxy is the closest galaxy to the Milky way, Both the Milky way galaxy and the Andromeda galaxy are part Virgo supercluster.
Which is the biggest galaxy in the universe ?
It is difficult to determine the exact size of a galaxy as they are constantly changing, but according to latest observations the biggest galaxy is the IC 1101. This galaxy has a diameter of 5.5 million light years and has a mass of 100 trillion solar masses.
This galaxy is a supergiant elliptical galaxy and is located 1.07 billion light years away from earth, in the constellation serpens. There could be even larger galaxies but due to limitations of the telescope we are not able to observe them.
How do galaxies die ?
Galaxies don’t die like the other celestial bodies like a star dies. Galaxies have a slow and gradual death, A galaxy starts to die when most of the interstellar mass like gases and dust is used by the star.
This stops the birth of new stars and the luminosity of the galaxy start to fall, as the luminosity of the galaxy falls all other activities also stop upon galaxy thus causing death of the Galaxy.
A galaxy could also die due to loss of star. Over time stars could be stripped away from a galaxy due to gravitational pull of another galaxy. As the no. of star reduces the activity inside the galaxy also reduces thus causing death of the galaxy.
Conclusion
So this was all for today, hope that you would have learned something new about Galaxies. Important points of today’s post were -
- A galaxy is a large cluster of stellar objects, stars, interstellar gases, star systems which are all bound by the gravity of the central supermassive black hole.
- Globular clusters collided and started to form larger clusters which eventually formed galaxies.
- The first Halo stars were 100 times more massive than our sun and were purely composed of hydrogen and helium.
- Elliptical galaxies have a rough ellipsoid shape and mostly don’t have much interstellar mass.
- Spiral galaxy shows a shape of pinwheel, the Spiral galaxy has a flat shape with a centre bulge and spiral arms.
- Irregular galaxies don’t have any proper structure of symmetry, and the interstellar mass is distributed unequally.
- Dwarf galaxy is small in size and has comparatively less mass than other galaxies.
- The Andromeda galaxy is the closest galaxy to the Milky way, Both the Milky Way galaxy and the Andromeda galaxy are part Virgo supercluster.
- According to the latest observations, the biggest galaxy is the IC 1101.
- Galaxies have a slow and gradual death
Thank you for Reading