Information taken from Wikipedia and Books by Stephen and Lucy Hawking


Is Milky Way a Barred Spiral Galaxy?



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Is Milky Way a Barred Spiral Galaxy?

Yes, Milky Way is a Barred Spiral Galaxy.



Which is the nearest galaxy to us?

The closest dwarf galaxy to the Milky Way is Canis Major Dwarf Galaxy while the closest Equivalent galaxy is Andromeda.



#

 

Galaxy

Group
Membership


Notes

  1



Milky Way

Local Group

Home galaxy of Earth

  2




Canis Major Dwarf

Local Group

Satellite of Milky Way (accretion by Milky Way)

  3




Sagittarius Dwarf Sphr SagDEG

Local Group

Satellite of Milky Way (partial accretion by Milky Way)

  4




Ursa Major II Dwarf

Local Group

Satellite of Milky Way (accretion by Milky Way)

  



Large Magellanic Cloud (LMC)

Local Group

Satellite of Milky Way

  5



Boötes Dwarf

Local Group

Satellite of Milky Way

  6



Small Magellanic Cloud (SMC, NGC 292)

Local Group

Satellite of Milky Way

  –




Ursa Minor Dwarf

Local Group

Satellite of Milky Way

  8



Draco Dwarf (DDO 208)

Local Group

Satellite of Milky Way with a large amount of dark matter

*



NGC 2419




Brightest remote MW globular cluster

  9




Sextans Dwarf Sph

Local Group

Satellite of Milky Way

 10




Sculptor Dwarf (E351-G30)

Local Group

Satellite of Milky Way

 11




Ursa Major I Dwarf (UMa I dSph)

Local Group

Satellite of Milky Way

 —



Carina Dwarf (E206-G220)

Local Group

Satellite of Milky Way

 13



Fornax Dwarf (E356-G04)

Local Group

Satellite of Milky Way

 14




Leo II Dwarf (Leo B, DDO 93)

Local Group

Satellite of Milky Way

 15




Leo I Dwarf (DDO 74)

Local Group

Satellite of Milky Way

 16




Leo T Dwarf

Local Group

Satellite of Milky Way

 17



Phoenix Dwarf Galaxy (P 6830)

Local Group

Satellite of Milky Way

 18



Barnard's Galaxy (NGC 6822)

Local Group

Satellite of Milky Way

 *




MGC1

Local Group

Isolated cluster at ~200 kpc from M31

 19



NGC 185

Local Group

Satellite of Andromeda

 20




Andromeda II

Local Group

Satellite of Andromeda

Well I just saw Local Group and Satellite of Milky Way in the above table. What do they mean?

The local group is a group of 100 – 200 galaxies which are very close to each other. And the Satellite of Milky Way means that a galaxy that is merging slowly into our galaxy and after some time it will be a part of the Milky Way.



Is Andromeda bigger than our Milky Way?

The Milky Way is twice the weight of Andromeda but still Andromeda has a larger number of stars than the Milky Way.



Is it true that millions of years later, Andromeda and Milky Way galaxy will merge into each other?

The Andromeda–Milky Way collision is a predicted galaxy collision that will take place in approximately 4 billion years' time between the two largest galaxies in the Local Group—the Andromeda Galaxy and the Milky Way, which contains the Solar System and Earth.

While the Andromeda Galaxy contains about one trillion (1012) stars and the Milky Way contains about three hundred billion (3x1011); the chance of even two stars colliding is negligible because of the huge distances between each pair of stars. For example, the nearest star to the Sun is Proxima Centauri, about 3x107 solar diameters (4x1013 km or 4.27 ly) away. If the Sun were a ping-pong ball in Paris, the equivalent Proxima Centauri would be a pea-sized ball in Berlin (and the Milky Way would be about 1.9x107 km wide, about a third of the distance to Mars).

Stars are much denser near the centres of each galaxy with an average separation of only 1.6x1011 km. But that is still a density which represents one ping-pong ball every 3.2 km. Thus, it is extremely unlikely that any two stars may collide.



What is Canis Mojor Dwarf Galaxy?

The Canis Major Dwarf Galaxy is a supposed small irregular galaxy in the Local Group, located in the same part of the sky as the constellation Canis Major.

The galaxy contains a relatively high percentage of red giant stars, and is thought to contain an estimated one billion stars in all.

The Canis Major Dwarf Galaxy is classified as an irregular galaxy and is now thought to be the closest neighbouring galaxy to our location in the Milky Way, being located about 25,000 light-years away from our Solar System and 42,000 light-years from the Galactic Center. It has a roughly elliptical shape and is thought to contain as many stars as the Sagittarius Dwarf Elliptical Galaxy, the previous contender for closest galaxy to our location in the Milky Way.

Astronomers believe that the Canis Major Dwarf Galaxy is in the process of being pulled apart by the gravitational field of the more massive Milky Way galaxy. The main body of the galaxy is extremely degraded.

Which is the largest known galaxy?

IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster. It is 1.07 billion light years away in the constellation of Serpens. It was discovered in June 19, 1790 by William Herschel.



The galaxy has a diameter of approximately 6 million light years i.e. 5,676,317,041,000,000,000,000 kilometers, which makes it currently (as of 2012) the largest known galaxy in terms of breadth. It is the central galaxy of a massive cluster containing a mass (mostly dark matter) of roughly 100 trillion stars. Being more than 50 times the size of the Milky Way and 2000 times as massive, if it were in place of our galaxy, it would swallow up the Large Magellanic Cloud, Small Magellanic Cloud, Andromeda Galaxy, and Triangulum Galaxy. IC 1101 owes its size to many collisions of much smaller galaxies about the size of the Milky Way and Andromeda galaxies.

IC 1101
What is a Solar System?


Types Of Stars

A star is a star, right? Well, not exactly. There are many different types of stars, from the tiny brown dwarfs to the red and blue supergiants. There are even more bizarre kinds of stars, like neutron stars and Wolf-Rayet stars. Let’s take a look at all the different types of stars there are.



1. Main Sequence Stars

A star is said to be born once nuclear fusion commences in its core. At this point it is, regardless of mass, considered a main sequence star. This is where the majority of a star's life is lived. Our Sun has been on the main sequence for about 5 billion years, and will persist for another 5 billion years or so before it transitions to become a Red Giant Star.


2. Red Giant Stars

Once a star has used up all of its hydrogen fuel in its core it transitions off the main sequence and becomes a red giant. Depending on the mass of the star it can oscillate between various states before ultimately becoming either a white dwarf, neutron star or black hole. One of our nearest neighbors (galactically speaking), Betlegeuse is currently in its red giant phase and is expected to go supernova at any time.



3. White Dwarfs

When low-mass stars, like our Sun, reach the end of their lives they enter the red giant phase. But the outward radiation pressure overwhelms the gravitational pressure and the star expands farther and farther out into space. Eventually, the outer envelope of the star begins to merge with interstellar space and all that is left behind is the remnant of the star's core. This core is a smoldering ball of carbon and other various elements that glows as it cools. While often referred to as a star, a white dwarf is not technically a star as it does not undergo nuclear fusion. Rather it is a stellar remnant, like a black hole or neutron star. Eventually it is this type of object that will be the sole remains of our Sun billions of years from now.



4. Neutron Stars

A neutron star, like a white dwarf or black hole, is actually not a star but a stellar remnant. When a massive star reaches the end of its life it undergoes a supernova explosion, leaving behind its incredibly dense core. A soup-can full of neutron star material would have about the same mass as our Moon. There only objects known to exist in the Universe that have greater density are black holes.


6. Brown Dwarfs

Brown Dwarfs are not actually stars, but rather "failed" stars. They form in the same manner as normal stars, however they never quite accumulate enough mass to ignite nuclear fusion in their cores. Therefore they are noticeably smaller than main sequence stars. In fact those that have been detected are more similar to the planet Jupiter in size, though much more massive (and hence much denser).


7. Variable Stars

Most stars we see in the night sky maintain a constant brightness (the twinkling we sometimes see is actually an atmospheric effect and not a variation of the star), but some stars actually do vary. While some stars owe their variation to their rotation (like rotating neutron stars, called pulsars) most variable stars change brightness because of their continual expansion and contraction. The period of pulsation observed is directly proportional to its intrinsic brightness. For this reason, variable stars are used to measure distances since their period and apparent brightness (how bright they appear to us on Earth) can be sued to calculate how far away they are from us.


Well there are three more types of stars but we will not discuss them in detail -



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