A galaxy is a huge collection of gas and dust, countless stars and their planetary systems, all loosely held together by gravity.

Our spectacular galaxy – the Milky Way – began to form just a few hundred million years after the Big Bang. In a neighbourhood of young stars, one star grew incredibly colossal. Burning in such bright and blue, it used all of its fuel within only millions of years. While dying, it collapsed in on itself so hard that a black hole¹ we have given the name Sagittarius A* came into being.

The infant cosmic sinkhole was small in size but heavy in mass, its gravity² allowing it to prey on anything drifting too close. First feeding itself just with stardust, Sagittarius A* began to grow. Its appetite soon reached stars, whether or not smaller black holes too, pulling them inwards into the darkness where nothing could escape.

Becoming larger and larger, Sagittarius A* was able to capture ever more stars and gas into its hold, not all close enough to be consumed but spinning in a slow orbit instead. Over time, an unshaped collection of stars transformed into a massive spiral galaxy containing more than 100 billion stars, if not multiple times more, only a few thousand closest and brightest we can see with our naked eyes from any point on planet Earth.

For us, it may be almost impossible to comprehend the sheer scale of our galaxy – a billion billion kilometres from one side to another, a distance which would take 100,000 years to travel at the speed of light (nearly 300,000 kilometres per second). Yet, Milky Way is just one of hundreds of billions of galaxies out there in the universe.

But the story of the Milky Way will come to an end, too. Over billions of years, smaller galaxies have collided with the Milky Way, experiencing its enormous might and disappearing into its spiral arms. After 4.6 billion years, however, our galaxy will meet its match when it is estimated to clash with Andromeda, the largest galaxy nearby, with as many as a trillion stars. And Milky Way will be no more.

¹ Black holes (dark stars) are born when large enough stars die. They collapse in on themselves at a force that even atoms are crushed in particles and packed together extremely densely. Our yellow star, Sun, is too small to become a black hole. Instead, it will become a white dwarf in which atoms are packed tightly together but not crushed.

² Gravity is an invisible force by which a body draws objects toward itself. Anything with mass has gravity, and objects with more mass have more gravity. Besides, gravity is greater closer to the body. Gravity explains, for example, how stars and planets form, why planets orbit stars, and why you and I can walk on Earth.

Bibliography

Cohen, A. & Cox, B. 2023. The Universe. Dublin, Ireland: HarperCollinsPublishers. 272 p. ISBN 9780008389352. Pages 71-72, 114, 124-126, 160-161, 164-167, 179-181, 187-189, 192.

DK. 2021. Science the Definitive Visual Guide. London, United Kingdom: Dorling Kindersley. 520 p. ISBN 9780241446331. Pages 340-341, 494.

NASA Science (2020). What Is Gravity? Available at: https://spaceplace.nasa.gov/what-is-gravity/en/ (Accessed: 5 August 2023).

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