Amazing information and facts about Galaxies are discussed in this post. We have described Galaxies in very simple English and the way that a normal person can understand.
GALAXIES
>Introduction;
- The word galaxy is derived from the Greek word γαλαξίας (galaxias), literally "milky", a reference to the Milky Way.
- Galaxies are the basic units of structure in the universe where stars form.
- A galaxy is a large group of stars, gases and dust bound together by gravity.
- Our galaxy is called a Milky Way Galaxy.
- Our galaxy looks like a milky band of light in the sky when you look at it in a really dark area.
- All the stars we see in the night sky are in our own Milky Way Galaxy.
- According to some theories all galaxies are limited by the gravitational pull of the halo of dark matter that surrounds them.
- There is recent evidence that some galaxies may be free of dark matter.
>Physical Characteristics;
- Galaxies range in size from a few hundred million (108) stars to a hundred trillion (1014) stars, each revolving around the center of the mass of its own galaxy.
- Some galaxies are similar to the Milky Way but some are quite different.
- It is thought that almost all major galaxies have supermassive black holes at their centers.
- Galaxies come in many sizes. The Milky Way is big but some galaxies, like our neighbor Andromeda Galaxy are much larger.
>Interesting Facts;
- The average age of the stars in the galaxy is a relatively young 4 to 8 billion years.
- Astronomers recently mapped the rarest type of galaxy called PGC 1000714, it is elliptical galaxy.
- Astronomer Edwin Hubble reveals an estimated 100 billion galaxies in the universe.
- Galaxies are flat due to their rotation that is fast enough that the galaxy can't condense in the radial direction.
>Types of Galaxies;
- In 1936, Astronomer Edwin Hubble introduced a method for identifying kinds of galaxies:
- Astronomer Edwin Hubble divided them into following four main types:
>>1.Spiral Galaxies:
- Spiral galaxies look like spirals/coils with long arms winding toward a bright bulge at the center.
- Most spiral galaxies contain a central bulge surrounded by a flat, rotating disk of stars.
- More than two-thirds of all observed galaxies are spiral galaxies.
- The Milky Way is a large barred spiral galaxy we live in.
- These galaxies have a bulging center which is called the bulge.
- These bulges of a spiral galaxies contain old stars and black holes.
- Our spiral galaxy is 13.51 billion years old.
- Some examples of the spiral galaxies are Milky way, Andromeda galaxy, Whirlpool galaxy and etc.
>>>Types of Spiral Galaxies;
They are divided into following two parallel classes:
a. Normal/Classic spirals:
- The normal spirals have arms that emanate/emerge from the nucleus.
b. Barred spirals:
- The Milky Way is a large barred spiral galaxy.
- Barred spirals have a bright linear feature called a bar.
- This Bar straddles/turns the nucleus, with the arms unwinding from the ends of the bar.
- The Milky Way Galaxy, where the Solar System is located is classified as a barred spiral galaxy.
>>2.Lenticular Galaxies:
- Lenticular Galaxies are basically the intermediate type of galaxies.
- An estimated 20% percent of known galaxies are lenticular.
- These are totally different in their shapes and features from the other three types of galaxies.
- Lenticular Galaxies are basically the combinations of spiral and elliptical galaxies.
- These galaxies have an elliptical shape and ill-defined spiral arms.
- The most common examples of these type of galaxy are Cartwheel galaxy and NGC 4479.
- There are approximately 75 discovered lenticular galaxies in our universe.
>>3.Elliptical galaxies:
- Elliptical galaxies are the most common type of galaxies found in the universe.
- These are spherical or ovoid masses of stars, starved of star-making gases.
- The motion of stars in elliptical galaxies is primarily radial, opposite to the disks of spiral galaxies, which are dominated by rotation.
- The smallest known elliptical galaxy is about one-tenth the size of the Milky Way.
- Elliptical galaxies ca stretch to more than a million light-years across, and contain more than ten trillion stars.
- An elliptical galaxy, has an ellipse-shaped light profile.
- 15% percent of all galaxies are elliptical.
>>4.Irregular galaxies:
- The galaxy that does not have a distinct regular shape is called irregular galaxies.
- Irregular galaxies are often chaotic in appearance.
- Irregular galaxies are approximately 20,000 light years in diameter.
- these have no nuclear bulge nor any trace of spiral arm structure.
- These galaxies do not fall into any of the regular classes of the Edwin Hubble sequence.
- The best known examples of irregular galaxies are the Small and Large Magellanic clouds.
- The Milky Way has two irregular "satellite" galaxies, known as the Large and Small Magellanic Clouds.
- The nearest galaxy to the Milky Way is an irregular galaxy called the Canis Major Dwarf (having one billion stars).
- They are generally bluer in color.
- An estimated 5% percent of known galaxies have an irregular form.
>>>Types of Irregular galaxies;
- Hubble has divided this into two following types:
- These following types are not briefly nor fully explained here in this post.
1.Irr-I:
2.Irr II:
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