Astronomy April

Lila Kapur Gandhi
Apr 30
4 min read

Learn about how small we are and how big the universe is, the life cycle of a star, how we are made of stardust and what black holes really are.

Have you ever gazed up at the starry night sky on a clear night and wondered how small we are? Well, I have, and the truth is far more surprising than you could ever have imagined. ‘The Sun’, the closest star to the Earth is the average star size. Many stars are much, much bigger and have much greater density than the sun. Look up at all of those stars and imagine all of them being the same size as the sun. About 80% are in fact, the same size or bigger than our sun. And imagine tonnes of planets with tonnes of moons revolving around each and every one of them. Having a solar system as small as ours is very rare. Now let’s zoom out a bit and look at galaxies, celestial masses of many stars with a centre of gravity, most often a black hole. When mankind sent out the first ever space telescope, the Hubble space telescope, it sent mind-blowing pictures back to Earth, including one of just a small group of star looking objects, which upon further investigation revealed that each and every one of them is a galaxy, most of them larger than ours, the Milky Way. This revealed to astronomers that there are possibly trillions or quadrillions of galaxies in the universe, just showing how small we actually are.

A picture that the Hubble space telescope took of a small group of galaxies, revealing that there are trillions more galaxies than we thought. Image courtesy- Hubble space telescope.

And have you ever wondered whether just like us, stars live and die? Well, believe it or not, stars too have a life cycle! That’s right, just like us, stars live and die. If you don’t already know about it, let me teach you a new word today. ‘Mass’ is just a vague term for anything that has density. If an object is dense, it’s mass is higher than if an object is hollow. Stars that are more dense have higher mass, which means they burn off their energy faster and their life span is shorter than stars which are less dense. First, let me talk about the life cycle of a supergiant star. Supergiant stars are the biggest type of stars. Slowly, their outer layer expands and cools and their core shrinks. This is called the red supergiant stage. If they die, they also create a huge explosion, astronomically referred to as a supernova. Supernovas take place when a star is at the end of it’s life cycle and the energy that is still concealed inside it bursts out in one final explosion. The remainder of the star turns into a black hole, sometimes starting a new galaxy. Average or low mass stars start out as a stellar mass, just like massive stars and then turn into red giants, undergoing the same process as massive stars. After that, they explode just a little bit and turn into planetary nebulas. Finally, the remains turns into one of the densest objects in the universe, a white dwarf star. These tiny stars are thousands of times denser than an osmium atom, the densest element in the periodic table. Once the white dwarf has cooled down, it turns into a black dwarf, a cool, empty mass of stellar remains.

The mass explosion of massive or supergiant stars, a supernova. Image courtesy- spaceplace.nasa.gov

I’m sure that you must be tired reading such a dense edition, (no pun intended!) but guess what, rest your eyes because I have even more for you! When I talked about the life cycle of a star, I mentioned that massive stars turn into black holes. So let’s talk more about these mysterious celestial objects and how we found a way to see them. Black holes are simply a large area with a gravitational pull so strong that no object can escape it. When a massive or supergiant star explodes and becomes a black hole, the extremely dense remains collapse under their own gravity and create a region where even light is cannot escape. As the name suggests, the region is completely black and even if we were to see it, there is no telescope big enough to view it. So astronomers devised a clever method to view the black hole at the centre of the Milky Way. The observed the areas where celestial objects were being sucked in and pieced together many different pictures to catch a glimpse of the black hole.

An image of what a black hole would actually look like up close. Image courtesy- shutter stock

I’m sure you all know we are made out of atoms. But have you ever wondered what those atoms are made up of? The truth is, if you go back 50 billion years ago, when earth didn’t even exist, when stars exploded, they were reborn, but some celestial matter still remained. No one knows how or what caused gases (H- hydrogen, He- helium, N- nitrogen, Co2- carbon dioxide, O- oxygen etc) but the astronomers’ best guess is that they entered our atmosphere through meteoroids, asteroids, meteorites and comets and storms kept making new isotopes as they multiplied in variety. These gases, along with celestial particles formed the fundamentals of life, creating water and early uni-cellular organisms. Theoretically, this means that we are made of stardust!