Astrophysics Flashcards
A universe is a large collection of what?
Billions of galaxies
A galaxy is a large collection of…
Billions of stars
Why does gravitational field strength vary?
Any object with mass exerts the force of gravity, and the higher the mass, the higher the force of gravity exerted.
The larger the planet and the higher its mass, the higher the gravitational field strength is
Why does gravitational force cause moons to orbit planets?
Moons and artificial satellites are attracted to their planets, and so are pulled towards them.
This gravitational force keeps them moving in curved paths called orbits
How does gravitational force cause planets to orbit the Sun?
The Sun’s gravity pulls the planets in orbit around it
What are geostationary orbits?
Due station orbit are satellites that always appear in the same position above the arts surface, which is important the satellite communication
Orbit of comets, moon, planets
Comments have elongated, elliptical, orbits,
planets and moons have circular orbits
Orbital speed relationship
(2 x pi x orbital radius)/time period
What is luminosity?
The amount of energy emitted per second by a star
How are stars classified according to the colour?
The colour of a star is linked to its temperature; the hottest stars are blue, and the coolest stars are red
Evolution of a star
A star is first born when a cloud of cold, hydrogen gas and dust collapses due to the pole of gravity. As the cloud collapses, the atoms and molecules move very fast. As molecules collide with each other, the store of kinetic energy is transferred to the internal energy store of the gas, and the temperature rises to several million degrees Celsius. The contracting and heating. All of gas is called a protostar.
The temperature in the gas becomes so high, that hydrogen nuclei began to collide and fusion begins
Then the star becomes a main sequence star, which means that it releases energy from the fusion of hydrogen to form helium. The inward forces of gravity which tend to collapse the star, are balanced by the outward forces created by pressure inside the hot core.
Stars about the size of the sun:
When the supply of hydrogen begins to run out, the start becomes unstable. Without the fusion of hydrogen, the pressure inside the star drops, and the outward forces decrease, and the star begins to collapse. As the star collapses, the temperature of the court increases, even farther and helium begins diffuse to make heavier elements such as carbon and oxygen. The hot core causes the start to swell up into a red giant.
When the start is no longer able to fuse helium, and it’s cool, cool down the star collapses into a white dwarf star and the surface of the white dwarf is hot. Fusion stops, and the stars life is over, at this stage, the white dwarf calls down, and it becomes a dark, called star known as a black dwarf.
Stars much larger than the Sun
When the start reaches the end of its main sequence stage, it begins to collapse, but the star grows into a red super giant. The fusion energy and red supergiants is sufficient for heavier elements to be made in the fusion process. Iron is the heaviest metal made inside stars due to fusion. After millions of years as a red super giant, the star runs out of its nuclear fuel and the cool calls down and inwards and forces of gravity overcome the outward pressure from the centre at the star which means that there is a very rapid collapse of the star. then two things can happen, the star can either turn into a supernova or a neutron star.
The rapid collapse could heat the inside of the star to such a high temperature, that the star explodes, and the remnants of a supernova spread out into space, which eventually form another gas cloud which forms new stars. What could also happen is, the great gravitational forces could cause the centre of the star to collapse into a highly condensed form of matter, which would mean that the court could be led as a neutron star made of only a few neutrons it could also become a black hole
Evolution
Protostar/nebula – star (main sequence) – red giant –white dwarf – black dwarf
Absolute magnitude
How bright a star appears to us, depending on the energy. The start admits per second, and how far the star is away from us. Absolute magnitude measures how bright the star would appear at an agreed set distance away from us. The agreed distance is 10 parsecs
Apparent magnitude
Apparent magnitude is how bright a star appears to the eye
Evolution of the universe
Up to 0.1 second: The early universe is populated by highly energetic particles and photons.
After a few seconds: the universe has cooled sufficiently for, protons, neutrons and electrons to exist
After three minutes- 30 mins : the universe calls, father and nuclear fusion occurs, so that protons fused to form helium 4 nuclei and DEUTERIUM
For the next 700,000 years: the universe continue to expand and cool down.
Over the next billion years: gravity acted on clouds of expanding gases, and the force of gravity pulls the expanding clause of gases into large clumps, which forms stars and galaxies.
