Home Universe 20 Interesting Milky Way Facts – Part II

20 Interesting Milky Way Facts – Part II

by Sankalan Baidya
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Milky Way Look Alike NGC 6744

In our previous article on Milky Way we learned some really fascinating facts about the galaxy but we are not done yet. There are many more interesting facts that will force your jaws to drop. We will speak about those facts in our second and last part of 20 interesting Milky Way facts article. You ready? We will be picking up where we left last time.

Interesting Milky Way Facts: 1-10

1. Last thing we spoke in the previous article was how long it takes for the Solar System to travel around the galactic core of Milky Way. It is 250 million years! Essentially, the Sun travels once around the galactic core in 250 million years and hence, the Earth also takes the same time. This one complete rotation made by Earth around galactic core is known as Galactic Year.

So, 1 Earth Year = 365 days and 1 Galactic Year = 250 million years.

2. While we have the habit of saying that Milky Way is a spiral galaxy, it is not absolutely true. In fact, Milky Way is a Barred Spiral Galaxy. This type of galaxy has a central bar-like structure which is made of stars.

3. Apart from the central bulge that we spoke of in the last article’s point #16, the rest of the galaxy is pretty much flat like a disk.

4. All images of Milky Way that we have seen till date are either images of other galaxies or are beautifully created artistic impressions. This is because, our solar system is 27,000 light years from the center of galactic core and we do not have sufficient technology to get high enough in space to capture the whole galaxy in one single frame. We don’t have a real image of our own galaxy.

5. Having said that, we need to say that all galaxies that we have photographed till date are hundreds of thousands and millions of light years away from us. This makes them far enough to be captured in a single frame.

6. Our galaxy, though not the most massive one out there in space, is incredibly big. Scientists estimate that Milky Way is at least 100,000 to 120,000 light years in diameter. Some think that it is 150,000 to 180,000 light years in diameters.

7. Even if we take that the Milky Way is 100,000 light years in diameter, do you have any idea of how many kilometers it makes? Let us try:

1 light year = 300,000 x 60 x 60 x 24 x 365 = 300000 x 3153600 = 9,460,800,000,000 kilometers.

So, 100,000 light years = 946,080,000,000,000,000 kilometers = 946,080 trillion kilometers.

Got it?

8. Scientists believe that our Milky Way galaxy is one of the oldest galaxies in known universe and was created some 13.6 billion years ago. Our universe was formed, according to scientists, some 13.798 billion years ago – give or take 0.037 billion years.

9. Okay, in our last article we said that our Milky Way galaxy is a part of Local Supercluster which stretches out over a distance of 10 million light years. Funny thing, this Local Supercluster is just a small part of an even bigger group known as Virgo Supercluster.

10. This Virgo Supercluster which fans out to a distance of 100 million light years and is composed of at least 100 galaxy groups like the Local Supercluster. Funny again, the Virgo Supercluster is just a small part of Laniakea Supercluster, which spreads out with a diameter as big as 520 million light years and has at least 100,000 galaxies.

Interesting Milky Way Facts: 11-20

11. Scientists say that our Milky Way has 4 arms and at least 2 spurs or smaller arms. Here is a quick list of the four primary arms of the galaxy:

  • 3-kpc Arm and Perseus Arm
  • Norma and Outer Arm
  • Scutum-Centaurus Arm
  • Carina-Sagittarius Arm

12. Apart from the aforementioned 4 major arms of Milky Way, there are two smaller arms which are:

  • Orion-Cygnus Arm
  • A new outer arm (name not available)

13. Interestingly, our Solar System sits in the Orion Cygnus Arm and not in any of the four major arms.

14. The arms of the galaxy have higher dust density and interstellar gas density compared to the average of the whole Milky Way taken together.

15. The arms also give birth to more stars than the center of the galaxy. This has been confirmed using molecular clouds and H II regions. H II region in astronomy refers to gas cloud of low density in which gas in partially ionized. Presence of this region indicates that a star has been recently formed.

16. Barring the central bulge, average thickness of the rest of the Milky Way is about 1000 light years.

17. A number of estimates have been provided regarding the mass of Milky Way. In 2014, a study was published where it was estimated that the total mass of our galaxy is 8.5 x 1011 solar masses. This is nearly 50% of the total mass of our neighboring Andromeda Galaxy. Recent mathematical studies however show that the minimum mass of Milky Way is 0.8 x 1012 solar mass and the maximum is 4.5 x 1012 solar mass.

18. Scientists say that Milky Way’s majority of mass comes from dark matter (which is an invisible matter but interacts with other matter using gravitation).

19. If dark matter is ignored and only stars are counted, the total mass of the galaxy is somewhere between 4.5 x 1010 solar mass and 6.43 x 1010 solar mass. Apart from the stars, about another 10 to 15% of Milky Way’s total mass comes from gases, of which hydrogen covers 90% and helium covers 10% of total gaseous mass. Again 2/3rd of the hydrogen is present in form of atoms and remaining 1/3rd is in form of molecules. Additionally, 1% of the total mass of Milky Way comes in form of interstellar dust.

20. Surrounding the disk of Milky Way is a halo of spherical shape and composed of globular clusters and very old stars. These stars are oldest known objects of the universe and perhaps as old as the universe itself. 90% of the halo objects are within the distance of 100,000 light years from the center of galaxy and some are as far out as 200,000 light years from center of galaxy.

The Milky Way is sitting inside a big gaseous halo

Recent discoveries show that the whole of the galaxy including the spherical halo of stars is embedded deep in a massive gaseous halo which extends to hundreds and thousands of light years beyond the outer limits of the spherical stellar halo. This gas has a temperature of 1 to 2.5 million kelvins and has a total mass of the mass of all stars in Milky Way!

Okay, did we say that the Milky Way is not stagnant in one place? It is moving at a speed of nearly 630 kilometers every one second, which turns out to be just over 2.2 million kilometers an hour. Okay! That’s kind of too much for us on this small planet that we live on.

Sources: 1, 2, 3, 4

Image Source (Wikimedia Commons)

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