THE SHAPE OF THE MILKY WAY GALAXY


The universe is ever expanding. Out of the billions of galaxies floating across in the ocean of space in the universe, we live in a galaxy named Milky-Way. When we think about the universe, its size is incomprehensible. When we narrow it down to our galaxy, the size and the elements present in our galaxy also blows away our mind. How did our galaxy get the name Milky Way and what is its shape? Where are we in this huge galaxy? Will our galaxy die? If it does die, when and how does it happen? You and me, let’s dive into the galaxy to find out the answers.

Dive with me.

If you see our galaxy from side, it seems like a straight whitish line with a bulge in the middle. Milky Way got its name from a Greek myth about a goddess Hera who sprayed milk across the sky. Even I don’t know how they came up with that.  I wonder how they saw the stars at night and said “Hey look! That looks like a hippopotamus”.

Yeah, but seriously, when we take snap shots of the night sky filled with stars, we see white spread all across the middle. So yeah, it does seem like milk spread (spilled?).

Before we go ahead, let me remind this to that certain set of people: “The universe may be flat-ish, but THE EARTH IS NOT FLAT!!”

Galaxies comes in different shapes and sizes. Some of the galactic shapes categorized are: spiral, elliptical and irregular. The smallest galaxy , the dwarf galaxy Segue 2 contains just about 1000 stars which has half-light radius about 34 parsecs and with a mass of 550,000 solar masses. The largest galaxy known in the universe is IC1101 containing more than 100 trillion stars and extends up to 2 million light years( light takes 2 million years to travel from one end of the galaxy to another). Yeah, that’s huge. IC1101 is 1.04 billion light years from sun whereas Segue 2 is 110,000 light years from the sun.

Our galaxy, the milky-way galaxy 100-400 billion stars. The solar system is located 27,000 light years from the center of the galaxy. Our galaxy is of spiral shape with huge arms extended outwards. The solar system is located on the inner edge of Orion arm. In our galactic center, there lies an enormous black hole known as Sagittarius A* with ~4.1 million solar masses. From the radius of the sun, the rotational speed is about 240 million years. The whole galaxy moves at a velocity of ~600km/sec through the space. The mass of our galaxy is approximately 890 billion to 1.54 trillion solar masses. The size of the galaxy is ~ 170,000 to 200,000 light years in diameter and nearly 1,000 light years thick.

We have been told that our galaxy’s shape is like a flat disc. Well, discoveries happen in the field of science where one of the latest discoveries changed our view on our galaxy shape. Recent studies suggest that our galaxy is warped and is like in S-shape. Studies suggest that this warping occurred due to the up and down movements of the stars as they travel through the galaxy/ due to galactic collision in during early formation.

Most recent scientific paper “A three-dimensional map of the Milky Way using classical Cepheid variable stars” explains how the warped shape of our galaxy is formed by observing the behaviour of classical Cepheid.

Classical Cepheid’s are a type of Cepheid variable stars i.e. it is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. There is a strong relation in the Cepheid variables between their luminosity and pulsating periods which helps astronomer’s measure intergalactic distances and beyond.

Classical Cepheid’s/ Delta Cepheid’s are giants and super-giant stars that are 4 – 20 times massive than our sun and more than 100,000 times more luminous than our sun. The data was extracted from the project Optical Gravitational Lensing Experiment (OGLE-IV) project where they analyzed the data of 2431 galactic Cepheid’s in the project 4th phase. The positions and distances of these Cepheid’s were converted into Cartesian coordinates where were used to convert the measurements into a 3-D distribution.

“We have produced a three-dimensional map of the Milky Way based on a large number of individual Cepheid’s with measured distances. This represents the young stellar population that extends to about 20 kpc, covering a large portion of our Galaxy, thus illustrating the extent and shape of the young stellar disk. Our work shows that a simple model can reproduce the current distribution of the young stellar disk of the Milky Way with narrow patches of stars of similar age.”- A three-dimensional map of the Milky Way using classical Cepheid variable stars.

The Milky Way’s Cepheid stars are plotted in three dimensions. The stars reveal the galaxy’s warped shape. Cepheids are special stars. They vary in brightness in a particular way that helps scientists make more precise estimates of their distances from Earth. Brighter colors represent Cepheids closer to the warped plane of the galaxy. The warped plane of the galaxy is indicated by the grid. The star icon indicates the sun.

J. SKOWRON/OGLE/ASTRONOMICAL OBSERVATORY/UNIV. OF WARSAW/SCIENCE NEWS/YOUTUBE

Well, to conclude, we the shape of our galaxy recently is known to me in S-shape, somewhat warped. Who knows what the future discoveries hold? Let’s wait and see.

Relax with this music

References:

1) A three-dimensional map of the Milky Way using classical Cepheid variable stars
2) The milky way does the wave: https://phys.org/news/2021-01-milky.html
2) About classical Cepheids: https://en.wikipedia.org/wiki/Cepheid_variable#Classical_Cepheids
4)Neighboring stars to our star: http://www.astro.wisc.edu/~dolan/constellations/extra/nearest.html
5)About Segue2- https://en.wikipedia.org/wiki/Segue_2
6)About IC 1101: https://en.wikipedia.org/wiki/IC_1101
7)About Milky Way galaxy: https://en.wikipedia.org/wiki/Milky_Way
7)https://www.treehugger.com/just-how-big-is-the-smallest-galaxy-in-the-universe-4862842

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