てんもん astronomy

The whole universe started from a single tiny point that expanded rapidly in an explosion approximately 13.7 billion years ago and is still expanding today. All matter that is to ever exist was created in the Bigbang, as is space and time. It is unknown what created the big bang, or what existed before it.

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• Stars are Formed in a nebula, a giant cloud of dust and gas (mainly hydrogen). Over time, the hydrogen gas in the nebula is pulled together by gravity and it begins to spin. As the gas spins faster, it heats up and becomes a protostar. The compression of hydrogen in a protostar continues for hundreds of thousands of years. When the temperature reaches 13 million degrees Celsius, nuclear fusion begins. This converts hydrogen into the next heavier element, helium. Fusion releases massive amounts of energy as heat and light, so the star ignites. The explosive outward force of fusion is balanced by the inward pull of gravity. The two forces can balance each other for billions of years. Stars in this stable state are called main sequence stars. A red super/giant forms after a star has run out of hydrogen fuel for nuclear fusion and has begun the process of dying. As hydrogen has stopped being fused, the gravitational inward force causes the star to collapse. The core gets denser and hotter as it collapses in on itself under its own weight, once the outward force of fusion weakens. The collapsing of the core causes helium to fuse carbon and oxygen. 

Small stars

• After the star runs out of elements to fuse, the stars gradually shed off their outermost layers in a planetary nebula. What's left of the star is an incredibly dense white dwarf.

Large Stars

• After the star runs out of elements to fuse, the pressure of gravity causes it to collapse in on itself. This results in a catastrophic explosion known as a “supernova”. What occurs is that matter in the star's core has fused to form iron. But the iron can't fuse into anything else. So with the explosive force of fusion gone, the star collapses in on itself under gravity. The outer layers are pulled in too, and then they "bounce off" the collapsed core of the star and are blasted out into space.

• Stars 8 to 20 times more massive than the Sun leave behind neutron stars. Neutron stars are extremely dense stars made of the collapsed inner core. Due to the force of gravity, the protons and neutrons in the atoms of the core are fused to create neutrons. They have strong magnetic fields, ejecting particles from their magnetic poles. The results in Neutron stars having two beams of radiation.

• Stars more than 20 times more massive than the Sun leave behind black holes. Stellar black holes form when the centre of a very massive star collapses in upon itself.

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Measuring distances in space - calculations with light years

• A light-year is a unit for measuring distances in space. A light-year is defined as how far light travels in a year. Light is one of the fastest things in the universe. It travels at nearly 300,000 kilometres per second! Or, 9.46 trillion kilometres per year.
• For example, the Sun is 150,000,000,000 m away from Earth, which is the same as 8 light-minutes.

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Stars - absolute vs apparent brightness

• Apparent brightness refers to how bright a star appears to be from earth. This is dictated by its distance from the earth and its luminosity.

• Absolute brightness refers to how bright a star is from the same distance. This takes out the factor of distance from earth and just counts a star’s luminosity

  \n Evidence for the big bang - redshift (and background cosmic microwave radiation)

• The Cosmic Microwave Background (CMB) is the cooled remnant of the first light that could ever travel freely throughout the Universe. This 'fossil' radiation, the furthest that any telescope can see, was released soon after the 'Big Bang'. Scientists consider it as an echo or 'shockwave' of the Big Bang.

• Redshifting refers to dating elements in space. As galaxies get further and further away from each other, the radiation they emit is red-shifted, meaning the waves they emit become less frequent.

• Redshifting increases the wavelength of light.

Steady State Theory 

• The Universe on a large scale doesn't change/evolve with time.
• It has always existed and will continue to exist, looking much as it does now
• The density of the universe remains the same because as the universe expands, matter is continuously being created to fill the gaps.

Big Bang Theory

• The whole universe started from a single tiny point that expanded rapidly in an explosion approximately 13.7 billion years ago and is still expanding today.
• All galaxies are constantly moving apart from each other, as there is no surface
• Matter was thrown out in all directions, forming starts then galaxies
• Both space and time were created

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Planet Formation

Planets are born from clouds (nebula) of gas and dust that orbit new stars. The material in the nebula not absorbed into the Sun swirled around it into a flat disk of dust and gas, held in orbit by the Sun’s gravity. This disk is called an accretion disk. The material in the disk accumulated by further accretion — from sticking together. Each planet began as microscopic grains of dust in the accretion disk. The atoms and molecules began to stick together, or accrete, into larger particles. By gentle collisions, some grains built up into balls and then into objects a mile in diameter, called planetesimals. These objects were big enough to attract others by gravity rather than by chance.

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BIG HISTORY 8 THRESHOLDS

1. The big bang
2. Stars light up
3. New chemical elements
4. Earth and the solar system
5. Life on earth
6. Collective learning
7. Agriculture
8. The modern revolution

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Big Bang (threshold one)

The whole universe started from a single tiny point that expanded rapidly in an explosion approximately 13.7 billion years ago and is still expanding today. All matter that is to ever exist was created in the Bigbang, as is space and time. It is unknown what created the big bang, or what existed before it.

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Stars Light Up (threshold two)

After the Big Bang, the Universe expanded and cooled. It took some time (about 380,000 years), but eventually, it was cool enough for the simplest atoms, hydrogen and helium, to form. The early Universe consisted almost entirely of hydrogen and helium for a very long time. Over time, the hydrogen gas in the nebula is pulled together by gravity and it begins to spin. As the gas spins faster, it heats up and becomes a protostar. The compression of hydrogen in a protostar continues for hundreds of thousands of years. When the temperature reaches 13 million degrees Celsius, nuclear fusion begins. This converts hydrogen into the next heavier element, helium. Fusion releases massive amounts of energy as heat and light, so the star ignites. The explosive outward force of fusion is balanced by the inward pull of gravity. The two forces can balance each other for billions of years. Stars in this stable state are called main sequence stars.

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New Chemical Elements (threshold three)

• After the star runs out of elements to fuse, the pressure of gravity causes it to collapse in on itself. What occurs is that matter in the star's core has fused to form iron. But the iron can't fuse into anything else. So with the explosive force of fusion gone, the star collapses in on itself under gravity. This results in a catastrophic explosive explosion known as a “supernova”. In a supernova, enough energy is released to create every element of the periodic table.

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Earth and the solar system (threshold four)

• Our Sun is a star that was formed from the collapse of a huge cloud of gas and dust particles. More than 99 per cent of this material went to make up the Sun, but wisps of matter orbited around it at various distances. Over time, the matter in each orbit was drawn together by gravity. The gravitational pull created violent collisions into lumps of matter that eventually formed the planets. This process, which we call accretion, is how our Earth has formed approximately 4.5 billion years ago.
• New stars have clouds of chemical matter that spin around the planet. Gravitational pull brings clumps of such matter together. This is called accretion. Over time, such lumps of matter turn into planets.
• Radiation from the sun spits away lighter elements, creating solid planets

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98% of matter in the universe is hydrogen and helium. However, the other 2% is atoms coming together in various arrays.

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what is a galaxy?

A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity.

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What is plasma and how does it form?

Plasma is a state of matter in which atoms have broken down by heat. This produces freely moving protons and electrons – a "soup" of charged particles.

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Nuclear Fusion in the Sun

In the Sun, freely moving protons collide and "fuse" together. This causes hydrogen atoms (with 1 proton) to become helium (2 protons). This is known as nuclear fusion in the sun. This results in large amounts of energy being released. This energy is released as heat and light.

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Balancing the fusion? How does the not explode?

The inward gravitational force balances with the outward force of nuclear fusion.

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What is a nebula?

A nebula is a giant cloud of dust and gas in space. It is the nebula where stars are formed.

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A star expands to become a red giant when?

When the hydrogen supply in the core runs out. This causes fusion to stop. The force of gravity causes the star to collapse in on itself. This causes the core to heat up significantly, enough so to fuse helium into carbon and iron, releasing great amounts of energy.