The Milky Way – the home to our home – is one of the most common forms of galaxies out there in the universe.
Though pretty common, the Milky Way galaxy is one hell of an interesting galaxy with mind-boggling facts that will make you say – “Really? Is that even possible?”
Let us find out 40 wonderful Milky Way facts and in the process, find out exactly where we lie on this vast ocean of celestial objects.
Milky Way Galaxy Facts 1-10
1. In India, the Milky Way has been referred to as Aakash Ganga, which literally translates into: “Ganga of the heavens.”
2. The Chinese call it the Silver River. In Chinese mythology, there was a weaver woman who used to weave clothes for gods, and there was a herdsman who was in love with this weaver. The gods wanted to separate the two and put this Silver River between them.
3. The ancient Greeks called this galaxy the Milky Circle. As per Greek Mythology, suckling Heracles was being fed by Hera. Accidentally, some milk spilled over, giving birth to the Milky Circle.
4. The ancient Greeks had another explanation too! They looked upon the galaxy as a road that led to Mount Olympus.
5. Okay, there is yet another explanation found in Greek mythology. This one says that the Milky Way is the path of ruins left behind by the chariot of Sun God Helios.
6. The Milky Way reminded the Romans about milk, and hence, they called it the Milky Road.
7. Democritus was the first man in the world to claim that the Milky Way was made up of stars. He was a Greek philosopher who lived circa 460 BCE to 370 BCE.
8. It was not until the 17th Century CE that Democritus’ claim was proven by Galileo Galilei who eventually used his telescope (the first one ever made in 1610 CE) to validate that the light band that has been called as Milky Circle by the Greeks or Milky Road by the Romans or the Aakash Ganga by the Indians or the Silver River by the Chinese was actually the light emitted by numerous individual stars.
9. Scientists estimate that this galaxy has somewhere between 100 and 400 billion stars. However, at night when we look up at the sky and manage to get a glimpse of the galaxy, we are able to see 0.0000025% of all stars present in the galaxy.
10. Scientists believe that at the very center of Milky Way galaxy sits a supermassive or gargantuan Black Hole that is known as Sagittarius A*.
Milky Way Galaxy Facts 11-20
11. Can you guess the number of planets that sit in this galaxy? Well, the scientists estimate that there are at least (if not more) 100 billion planets hanging out there in our galaxy… And we still think we are all alone in this universe?
12. Okay, here is another problem – the Milky Way is not the only galaxy out there. We read about Andromeda Galaxy which is on a collision course with the Milky Way. That’s just another one out there.
In fact, the Universe is dotted with galaxies. There are billions of galaxies in the universe. Scientists say that there are at least 100 billion galaxies in the known universe. You still believe we are alone?
13. Scientists have found some really weird planets like the one where molten glass rains down or the one which is known as a burning ice planet and even a diamond planet. There is absolutely no scarcity of such oddities in our galaxy but there are, according to scientists, about 11 to 40 billion planets that are similar to Earth, and can possibly host life.
14. The Milky Way galaxy took birth some 12.5 billion years ago – give or take 3 billion years. The galaxy has been growing ever since. In fact, it is a cannibal galaxy that feeds on other surrounding small galaxies. And… it will continue to do so.
15. Scientists estimate that about 7 stars are born in the Milky Way every single year (we are talking about new stars being born and not counting the ones that are consumed from other galaxies).
Also, a supernova explosion takes place in our galaxy once in about every 200 years. This has been calculated using the method of mapping aluminum-26 isotope which is usually found in the region where a star dies or takes birth.
16. At the very center of our galaxy is a bulge which extends out on either side of the two-dimensional plane of the spiral galaxy. Interestingly, this bulge is caused by hydrogen and it is really weird, because the molecules of hydrogen are not only being pulled away from the galactic center, but are also known to have separate vibrating frequencies.
Scientists blame this on black matter saying that when the black matter moves through galactic clouds, ripples are created, affecting Milky Way’s gravitation, enticing hydrogen molecules away from the center.
17. This central bulge of the galaxy is extremely thick. We mean, the distance between the topmost point of the bulge to its bottom-most point is 10,000 light years.
18. Our entire Solar System sits at a distance of nearly 27,000 light years from Milky Way’s galactic center.
19. The Milky Way is just a part of a cluster of galaxies known as the Local Group. This Local Group contains about 40 galaxies. This Local Group again is a member of a Local Supercluster, which is made up of multiple clusters of galaxies like the Local Group.
So, just how big is the Local Supercluster? One edge of the Local Supercluster is separated from the other edge by a distance of 10 million light years.
20. Our Solar System is circumnavigating around the Milky Way’s galactic center at a speed of about 220 kilometers a second. If a human can travel at that speed, it will take just 175 seconds to circumnavigate around Earth’s equator! You think that is fast? Think again!
At that speed, it takes our Solar System to complete one rotation around the galactic center in 250 million years. So, since the birth of our Solar System some 4.6 billion years ago, it has managed to rotate around the galactic core at the most 20 times.
Since the humans came to existence, the Solar System has managed to complete only 1/1250th of one complete rotation.
Milky Way Facts 21-30
21. Since it takes 250 million years for the Solar System to travel around the galactic core of the Milky Way, 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 the galactic core is known as Galactic Year.
So, 1 Earth Year = 365 days and 1 Galactic Year = 250 million years.
22. While we have the habit of saying that the Milky Way is a spiral galaxy, it is not absolutely true. In fact, the Milky Way is a Barred Spiral Galaxy. This type of galaxy has a central bar-like structure which is made of stars.
23. Apart from the central bulge, the rest of the galaxy is pretty much flat like a disk.
24. All images of the 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 the 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.
25. 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.
26. Our galaxy, though not the most massive one out there in space, is incredibly big. Scientists estimate that the 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.
27. Even if we assume 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?
28. Scientists believe that our Milky Way galaxy is one of the oldest galaxies in the 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.
29. 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.
30. This Virgo Supercluster 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.
Milky Way Facts 31-40
31. 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
32. 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)
33. Interestingly, our Solar System sits in the Orion Cygnus Arm, and not in any of the four major arms.
34. The arms of the galaxy have higher dust density and interstellar gas density compared to the average of the whole Milky Way taken together.
35. The arms 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 a gas cloud of low density in which gas is partially ionized. Presence of this region indicates that a star has been recently formed.
36. Barring the central bulge, the average thickness of the rest of the Milky Way is about 1000 light years.
37. A number of estimates have been provided regarding the mass of the 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.
That’s nearly 50% of the total mass of our neighboring Andromeda Galaxy. Recent mathematical studies show that the minimum mass of the Milky Way is 0.8 x 1012 solar mass and the maximum is 4.5 x 1012 solar mass.
38. Scientists say that the Milky Way’s majority of mass comes from dark matter (which is an invisible matter but interacts with other matter using gravitation).
39. 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 the 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 the form of atoms and remaining 1/3rd is in the form of molecules. Additionally, 1% of the total mass of the Milky Way comes in the form of interstellar dust.
40. Surrounding the disk of the Milky Way is a halo of spherical shape composed of globular clusters and very old stars. These stars are the 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 the galaxy and some are as far out as 200,000 light years from the 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 the 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.
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