What is spiral galaxy ?
Spiral galaxies are those galaxies that shaped like a spiral.
The arms consist of stars, dust, and gases. At the center, there is a bulge (a flat and rotating disk of a tightly-packed Stars with the Largest formation) and the supermassive black hole at the center of the bulge. The halo of a spiral galaxy is at the end of its arms, where galaxies lose its density (This place is said to be a star cluster). This star cluster is known as globular clusters. Globular clusters have thousands of tight group of old stars. It is believed that spiral galaxies are about 1/4 of all known Galaxies.
Spiral galaxies are one of the brightest galaxies in the Universe. Before 1920 we believe that the milky way is the only galaxies in the Universe. We did see other galaxies like Andromeda as a nebula. But when in 1920 astronomer Edwin Hubble demonstrated that the Andromeda nebula is, in fact, a galaxy, Everything changed.
2/3 of all spiral galaxies have a bar or bright-line type structure composed of stars in the center of the Galaxy and simply said to be barred spiral galaxy. Our Milky Way is a barred spiral galaxy.
Spiral galaxies are classified into two groups, ordinary and barred. The ordinary group is designated by S or SA, and the barred group by SB.
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| Milky-way | An example of Spiral galaxy |
Spiral galaxies are one of the brightest galaxies in the Universe. Before 1920 we believe that the milky way is the only galaxies in the Universe. We did see other galaxies like Andromeda as a nebula. But when in 1920 astronomer Edwin Hubble demonstrated that the Andromeda nebula is, in fact, a galaxy, Everything changed.
2/3 of all spiral galaxies have a bar or bright-line type structure composed of stars in the center of the Galaxy and simply said to be barred spiral galaxy. Our Milky Way is a barred spiral galaxy.
Spiral galaxies are classified into two groups, ordinary and barred. The ordinary group is designated by S or SA, and the barred group by SB.
| Galaxy type | Differences |
|---|---|
| Spiral galaxy, type a (Sa) | Big centeal bulge |
| Spiral galaxy, type b (Sb) | Medium sized central bulge |
| Spiral galaxy, type c (Sc) | Small central bulge |
| Barred spiral galaxy, type a (SBa) | Tight arms(max stars) |
| Barred spiral galaxy, type b (SBb) | Both tight and loose arms |
| Barred spiral galaxy, type c (SBc) | Loose arms(low stars) |
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| NGC 6872 Image credit - ESO/VLT, Judy Schmidt, CC BY 4.0 , via Wikimedia Commons |
NGC 6872 is the Largest known spiral galaxy(barred) with a distance of 212 million light-years.
Segue 2 is the lightest weight known spiral galaxy. It is also known as the faintest satellite of Milky way. It has only about 1000 stars. It is also known as a dwarf spiral galaxy. Very small, low-luminosity spiral galaxies are called dwarf spiral galaxies.
BX442 is the oldest known spiral galaxy with the age of 11 billion years.
Andromeda is the nearest spiral galaxy to milky-way with a distance of 2.5 million light-years. In the next 4.5 billion years., Andromeda will collide with Milky Way.
Segue 2 is the lightest weight known spiral galaxy. It is also known as the faintest satellite of Milky way. It has only about 1000 stars. It is also known as a dwarf spiral galaxy. Very small, low-luminosity spiral galaxies are called dwarf spiral galaxies.
BX442 is the oldest known spiral galaxy with the age of 11 billion years.
Andromeda is the nearest spiral galaxy to milky-way with a distance of 2.5 million light-years. In the next 4.5 billion years., Andromeda will collide with Milky Way.
Is Spiral galaxy-Andromeda is nearest galaxy to Earth ?
Our Milky-way is a part of a local group that has 54 galaxies and dwarf galaxies. And Andromeda is also part of this local group, but it is not the closest one to Earth. Andromeda is the closest spiral galaxy to Earth.
At present, Canis major Dwarf galaxy is the closest galaxy to Earth with a distance of 25,000 light-years from sun and 42,000 light-years from the galactic center of our Milky-way. In earth sky, It is located in the constellation of Canis major.
This dwarf irregular Galaxy is covered with dust in the plane of Milkyway Galaxy and, that's why it was discovered recently in Nov 2003 by an international team led by European and Australian astronomer.
The Galaxy has one billion stars, which are very less comparing to Milkyway. Most of the stars in the Galaxy is a red supergiant.
The Galaxy has one billion stars, which are very less comparing to Milkyway. Most of the stars in the Galaxy is a red supergiant.
The Galaxy is in accretion process with our Galaxy means it will merge with our 400 billion stars galaxy milky way. This process may take more than 1 billion years. And then, after 3.5 billion later, the new Galaxy will collide with the andromeda galaxy.
Before its accretion process, it will also merge globular clusters - NGC 1851, NGC 1904, NGC 2298, and NGC 2808, which orbits the center of our Milkyway.
Before its accretion process, it will also merge globular clusters - NGC 1851, NGC 1904, NGC 2298, and NGC 2808, which orbits the center of our Milkyway.
