The Milky Way Galaxy

The Milky Way Galaxy




 Its name is a translation of the Latin Via Lactea, in turn translated from the Greek , referring to the pale band of light formed by stars in the galactic plane as seen from Earth


 The Milky Way is the galaxy which is the home of our Solar System together with at least 200 -400 billion other stars and their planets, and thousands of clusters and nebulae, including at least almost all objects which are not galaxies on their own.


 The objects in the Milky Way Galaxy orbit their common center of mass, called the Galactic Center.



 The Milky Way is actually a giant, as its mass is probably between 750 billion and one trillion solar masses, and its diameter is about 100,000 light years.



 The Milky Way Galaxy is the spiral-shaped galaxy which its core is called Central Bulge.



 There are four major spiral arms which is


 Norma Arm


 Scutum-Centaurus Arm or Scutum-Crux


 Sagittarius Arm


 Perseus Arm



 There are 2 small partial arms called Orion Arm and Cygnus Arm.



 There is a belief that there might be a large black hole in the core region.


 This map shows the full extent of the Milky Way galaxy - a spiral galaxy of at least two hundred billion stars. Our Sun is buried deep within the Orion Arm about 26000 light years from the centre.


 In the year of 2005, Spitzer’s Infrared was sent into the space to find out about the bar of the Milky Way Galaxy.


 In general, 80% of spiral galaxies have no bar. Theoretically, the bar was formed from stability of the spiral that developed from instability spiral which means that the bar was formed to compensate the stability.




Guidelines from the new survey


 Spitzer’s infrared had made evidence from 800,000 photograph including 110 million stars in the Milky Way Galaxy.

 Two major spiral arms that are related with the bar of the galaxy


 Scutum-Centauraus Arm and Perseus Arm which are very big and dense. Inside the arm there are young bright stars and red-giant that is nearly extinct.
 Not only that, there is a discovery of 2 new arms called Far-3 kiloparsec Arm and Near-3 kiloparsec Arm.

 As for Norma Arm and Sagittarius Arm, they are types of dangerous gas filled with Ultra-hot gas with hotter than 1 million degree.


 Ultra-hot gas is a collision of the atom of gas from the collection of young bright stars related by halo of hot gas. It happens very fast.

The Largest Star

Largest Star by Massive : pistol star

-200 times of solar mass

-25000 light years far away

Largest Star by Luminosity : LBV 1806-20

-38 million solar luminosity

-30000-40000 light years far away




Largest Star by Radius : VY Canis Majoris

-1800 radii




-5000 light years far away



How could they know?

Massive-Star birth




Giant molecular cloud, GMC collapse because of the instability gravitational of the molecules.

And it became a protostar. Which some of them have larger mass than the sun but some don’t.



Luminousity




apparent magnitude


Δm = mf − mb


2.512Δm = ΔL


mf-magnitude number of a brighter star


mb- magnitude number of a fainter star


ΔL- variation in brightness


Radius


Angular size

It means if it far the angular size is small so we have to use the things to help.


Angular size(arc second) = size(km) / distances(parsec)




Things help to find angular size.

1.Inferometer
2. Telescope