Cosmos-Part 2
🍒 Favorite Quotes:
We began as wanderers, and we are wanderers still.
What we do with our world in this time will propagate down through the centuries and powerfully determine the destiny of our descendants and their fate, if any, among the stars.
We make our world significant by the courage of our questions and by the depth of our answers.
If you wish to make an apple pie from scratch, you must first invent the universe.
It is said that men may not be the dreams of God, but rather that the Gods are dreams of men.
🐾 Looking Far in Space = Looking far into the Past:
Light travels at one speed. It cannot travel slower or faster than c = 300,000,000 m/s. This is the speed of causation. We do not observe the world as it is, but as it was some time ago. For example, when you talk to a friend standing 2 meters away, you observe her as she was time t = 2/c seconds ago. Here, c is so much bigger than 2 that this time is instantaneous. This phenomenon is more applicable when we look toward stars and galaxies at a distance of billions of light years. We are observing them as they were billions of years ago. As we look far in space, we also look far into the past.
Last week, one of the space images we saw was of a galaxy cluster that contains 5 galaxies locked in a cosmic gravitational dance. Stephen’s quintet is around 300 million light years away from us, meaning we observe it as it was 300 million years ago.
💥 Stars:
Hydrogen was made during the Big Bang. All the other elements are made in the core of a star. Stars are like factories converting hydrogen to helium, then helium to oxygen and carbon, and so on. Everything from calcium in your bones to iron in your blood comes from a star. Stars die and fling these elements all over the galaxy which accumulate to form planets like ours.
The Sun is in its main sequence. It burns hydrogen into helium. Our star has been doing this for 4-5 billion years and will continue to do so for the next 5 billion years, roughly speaking. When the sun runs out of hydrogen to fuse into helium, it will start using helium as a fuel to make carbon. This is the red giant phase of our Sun’s evolution. It will expand and devour mercury, venus, and even our perfect home. When this happens, we would have left to the outskirts of the solar system. Places like Mars, Europa, and Titan are the worlds we could potentially terraform.
The sun will burn helium for some time, but eventually, it will run out of helium. The red giant will then let go of its outer layers, which will fly outwards. It will look not unlike the Southern Ring nebula that we saw last week courtesy of the James Webb Space Telescope. The only remaining thing of our magnificent sun will be a white dwarf. Not burning anything, but still radiating heat into the universe until it grows cold and disappears.
Although the Sun’s fate is epic, some stars that are bigger than the sun will go out in an even more epic explosion. This explosion by which a star around 8 times larger than our sun ends its life is termed supernova. The resulting core is the neutron star. A lot of the star's material is thrown out, but a neutron star still contains several solar masses in an extremely small object (average diameter of 12 miles).
Neutron Stars are the densest objects in the known universe apart from Black holes. If a Star has several dozens of Sun’s mass, nothing will stop the gravitational collapse after the supernova. The star glitches a hole into our universe that breaks all known physical laws. We have no idea what happens inside a black hole. Maybe at the singularity inside the black hole matter gets concentrated into an infinitely dense point and then expands out in a bang. Black holes might be the edges of universes.
💥 Doppler Effect:
The sound from an extremely fast-moving car is always high pitch when it is moving towards us and low pitch when the car is moving away. Why is that? As the car moves towards the observer the sound waves released get compressed; the frequency of the sound is high. The sound waves are stretched out when it moves away. This phenomenon is called the doppler effect.
Doppler effect is the key to understanding the Big Bang. Like sound, light also acts like a wave. The galaxies moving away from us should have a reddish color that corresponds to a higher wavelength due to the “stretched” effect, and the galaxies that are moving towards us should have a blueish color due to the “compressed” effect.
Edwin Hubble found that wherever he pointed the telescope in the sky, the galaxies were redshifted. The whole universe is moving away from us. The galaxies in our universe are like points on the expanding surface of a balloon.
