Information taken from Wikipedia and Books by Stephen and Lucy Hawking
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- What is a Galaxy
- What are the types of Galaxies
- What are Elliptical Galaxies
- What are Spiral Galaxies
- What are Lenticular Galaxies
| A Journey Through Space
Information taken from Wikipedia and Books by Stephen and Lucy Hawking. Compiled by Jainil Ajmera, Prakhar Mittal and Sanchit Gupta Contents Unit 1. The Universe The Universe : An Introduction The Big Bang Theory Galaxies What is A Solar System? Types Of Stars Goldilocks Zone Alpha Centauri 55 Cancri Constellations Quasars Redshifts Pulsars Nebula Unit 2. Our Solar System Our Solar System Comets Asteroids Kuiper Belt Meteors, Meteoroids and Meteorites Sun Planets and The Moon Natural Satellites Some facts on Earth Mass Class Unit 3. Space Exploration Rockets Spacesuits Satellites Robotic Space Travel Manned Missions NASA Upcoming Missions Unit 1 : The Universe The Universe : An Introduction The Big Bang Theory You must have imagined how the universe was created? There are many stories of which the one used by scientists is the Big bang theory. Back then, all the matter that you see today was squeezed tightly into an area that was smaller than the atom. After what would be a tiny fraction of a second after the Big bang, everything around looks much the same everywhere. But there is no fireball racing outwards, instead you see a hot sea of material, filling all of the space. What was this material? Scientists aren’t certain but whatever the material may be, it was exotic that we can’t see today even with the best gadgets. This tiny ocean of hot exotic material starts expanding as the space it fills grows bigger and bigger at the speed of light. So, you see a lot of changes happen in the first second after the Big Bang. The expansion of this tiny universe led to the cooling of the hot sea of exotic material. Now when the early universe is still much smaller than an atom, one of the changes in the fluids leads to something known as inflation. The size of this tiny universe doubles, then doubles again and goes on like this. This stretching made the Universe smooth and almost same in all directions. In this process, microscopic ripples are also stretched which will soon be the cause of the birth of stars and galaxies. Inflation ends and releases a large amount of energy and replaces the hot exotic matter with quarks, protons, gluons, neutrons etc. The hot matter either decayed into less exotic materials or it went to far parts of the Universe which we may never see. The material which we see at this point of time is not as hot as the exotic matter, but still hotter than anywhere today. Expansion continues, and eventually the temperature falls enough for the quarks and antiquarks to bind together to form neutrons and protons. There is little to be seen through the plasma fog of the universe which has now become one second old. Now over the few seconds, there are new photons made but still the visibility level in the Universe is very poor. As the Universe gets a few minutes old, the remaining photons and neutrons form the first atomic nuclei, mainly of hydrogen and helium. After the frantic action of the Universe in its first few minutes, it stays the same for the next hundreds of thousands of years. Then, after 380,000 years, the fog finally clears and electrons are captured by the nuclei to form the first whole atoms. Now, only a fading red glow is to be seen which gets dimmer and dimmer. Soon, it isn’t visible at all as we enter the Cosmic Dark Ages. The photons from that glow are still moving which can now be detected through CMBs. The Dark Ages stay for a few hundred millions of years. And a few quiet changes are happening. The microscopic ripples mean that some regions contained more mass than average. This increases the pull of gravity towards those regions, bringing even more mass in. Slowly, over millions of years, dense patches of gas and dark matter gather as a result of the increased gravity. As the gas falls into these patches, atoms speed up and become hotter. Every now and then, the gas becomes hot enough to stop collapsing. If the gas cloud collapses far enough, it breaks into spherical blobs so that the heat can’t get out. Finally, a point is reached when hydrogen nuclei, in the cores of the blobs become so hot and squashed together that they start to merge into nuclei of helium and release nuclear energy. Now, the darkness is over as the first of these blobs burst into bright light. The first stars are born and the Dark Ages are over. The first stars burn their hydrogen quickly, and in their final stages fuse together whatever nuclei they find to make heavier atoms. These atoms are scattered all around and get swept when new stars are born. This process continues- new stars are born and die and create more ash to produce new stars. Soon, the very familiar spiral-shaped galaxy is born- The Milky Way. Nine billion years after the Big bang, the central star of the Solar System, our Sun is born. After four and a half billion years, the only planet that is known to support life, our Earth, is also born to whom still light of some parts of the universe hasn’t reached. Galaxies What is a Galaxy? A galaxy is a group of many stars, along with gas, dust, and dark matter. Gravity holds galaxies together. Everything in a galaxy moves around a centre. The name galaxy is taken from the Greek word Galaxia meaning milky, a reference to our own galaxy, the Milky Way. What are the types of Galaxies? There are various types of galaxies: elliptical, spiral and lenticular galaxies, which can all be with or without bars. All galaxies exist inside the universe. There are probably over 170 billion (1.7x1011) galaxies within distance we can see or the observable universe. What are Elliptical Galaxies? An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They are one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. They range in shape from nearly spherical to highly flat and in size from tens of millions to over one trillion stars. Originally, Edwin Hubble thought that elliptical galaxies may evolve into spiral galaxies, which later turned out to be false. Stars found inside of elliptical galaxies are very much older than stars found in spiral galaxies.  Sombrero Galaxy
What are Spiral Galaxies? Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are surrounded by a much fainter halo of stars, many of which reside in globular clusters. Spiral galaxies are named for the spiral structures that extend from the center into the disk. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disk because of the young, hot OB stars that inhabit them.  The Pinwheel Galaxy
What are Lenticular Galaxies? A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies (like spiral galaxies) which have used up or lost most of their interstellar matter and therefore have very little ongoing star formation.  Spindle Galaxy
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