8.1-8.3 - Astrophysics Flashcards
What is the universe
A collection of billions of galaxies
What is a galaxy?
A large collection of billions of stars, stars are astronomical objects such as the sun
What is a solar system?
A collection of stars
What is gravitational field strength?
The strength of gravity on a planet or moon. The larger the mass of a planet the greater its gravitational field strength. The larger the radius of a planet the smaller the gravitational field strength higher the gravitational field strength means larger attractive force towards the centre of that planet or moon.
What is weight?
Weight is the force acting on an object due to gravitational attraction and because of weight objects will stay firmly on the ground and satellites in orbit.
What is gravitational force?
Planets and comets travel around the sun Moons and satellites travel around planets. For this to happen forces must be applied to them between any two objects there is always a force of attraction. This is due to the masses of the objects.
How does mass effect force of attraction?
The gravitational attraction between two objects with small masses us tiny only when one or both objects have very large mass is the force attraction obvious . The Sun is massive containing 99% of mass of the solar system it is the gravitational attraction between this as and each of the planets that holds the solar system together.
How does a body start to orbit?
In order to orbit a body such as a star or planet there has to be a force pulling towards that body, gravity provides this force. The gravitational force exerted by the larger body on the orbiting object is alwasy attractive therefore the gravitational force always acts towards the centre of the larger body the gravitational force will cause the body to move and maintain in a circular path. Planets orbit the sun, moons orbit planets comets orbit the sun.
What is a satellite?
An object that orbits a planet
How do Moons orbit?
Moons orbit planets in a circular path, some planets have more than one moon the closer the moon is to the planet the shorter the time it will take to orbit.
How do comets orbit?
As comets approach the sun, its speed increases as it moves futher away it speeds decreases. Not all comets orbit in the same plane as the planets and some do not even orbit in the same directions
How is orbital speed calculated?
2pie x the orbital radius
Orbital speed equation
speed= distance / time
What does the colour of a star tell us?
The tempreture of the star
What colour does a very hot star emit?
A very hot star emits more blue and therefore looks blue
What colour does a medium star look like?
A star like our sun is yellow
What colour is a cooler star
A cooler colour star is red.
What do objects that are warm emit
Infrared heat.
What do extremly hot objects emit
visible light.
What does the brightness of a star depend on?
The distance the star is from earth and what the star is made from and what kind of nuclear reactions are taking place
Explain the nebula stage of a star (1st stage)
Stars are formed from large clouds of dust and gas particles that are called nebulae. These particles are drawn together over a very long period of time by gravitational forces. These particles are pulled together so tightly that there is a very large increase in tempreture and pressure. As a result of this, nuclear fusion reactions begin. Hydrogen nuclei join together to make a larger nuclei and huge amounts of energy in the form of heat and light are released. The incredible hot ball of gas formed is a prostar.
Explain the Prostar stage of a star (2nd stage)
The forces of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas known as a prostar. All of the particles are pulled together tightly then the density of the prostar will increase. This will result in more frequent collisions between the particles because the partciles are being pulled together so tightly this causes the tempreture to increase
Explain the Main sequence stage of a star (3rd stage)
A main sequence star forms once the prostar becomes hot enough so nuclear fusion will occour within its core. The hydrogen nuclei will fuse to form helium nuclei every fusion releases heat energy which keeps the core hot. Thermal expansion from fusion reactions occours within its core due to the fusion and the force of gravity keeps the star of equilibrium. The inward force due to gravity is equal to the outward pressure force which results from the expanding hot gases inside the star.
Explain the red giant stage of a star (4th stage)
After several billion years when the most of the helium has been fused because the hydrogen has run out because of this fusion reactions in the core will start to die down. This will cause the core to contract and heat up and the star will change colour it will emit more blue and white light the core has shrunk because of the inward force due to gravity will become greater than the outward force due to the pressure dying down a new series of reactions will then occour around the core for example helium nuclei will undergo fusion to form beryllium as the core shrinks more reactions will cause the outer part of the star to expand it will become a red giant and because it is red its surface will start to cool down
Explain the Supernova stage of a star (5th stage)
A supernova forms once the fusion reactions inside the red supergiant’s finally finish the core of the star will collapse suddenly causing a gigantic throwing dust and gas into space to form a new stellar nebula. This exploding star is called a supernova. The matter remaining at the centre of this explosion is a dense body called a neutron star will form
Explain the White dwarf stage of a star (5th stage)
When a star reaches its white dwarf stage the star will start to become unstable and ject the outer layers of dust and gas the core which is left behind will collapse completely due to the pull of gravity and the star will become a white dwarf the amount of energy it emits will decrease because of this.
Explain the neutron star stage of star (6th stage)
At the centre of a supernova explosion a dense boy called a neutron star will form which is densely packed with neutrons if the neutron star has a mass that is approximately 5 times greater than that of our sun or more at the centre it will continue to collapse under the fore of gravity until it forms a black hole. A black hole is extremly dense point in space no even light can escape
Explain the red super giant stage of a star (stage 4)
A star that is larger than the sun follows a slightly different path at the end of its life. After the stable period the main sequence the star runs out of hydrogen gas in its core. once this happens the fusion reactions in the core will start to die down this causes the core to shrink and heat up the core will shrink because of the inward force duw to gravity is greater than the outward force due to the pressure of the expanding gases. A new series of fusion reactions will then occour the helium nuclei will undergo fusion to form beryllium fusion reactions cuse the outer part of the star to expand and become a red supergiant
What is Absolute magnitute
The apparent magnitude of a star if it were placed 32.6 light years away from earth
What is Apparent magnitude
the brightness that we perceive a star from earth
Where does the luminosity go on Hertzsprung russel diagram
Y axis dim at the bottom bright at the tiop
Where does the tempreture go on a Hertzsprung diagram
X axis cool on the left warm on the right
What are the main features of the Hertzsprung russel diagram
Most stars lie on the main sequence this is the band os stars going from top left to bottom right
Where do the white dwarfs lie on the diagram
slightly to the left and below the main sequence are the white dwarfs
Where do the supergiant’s and the red supergiant’s lie on the diagram
Slightly above the main sequence to the right.
Explain the big bang theory
-Around 14 billion years ago the universe began from a very small region that was really hot and dense there was a giant explosion which was known as the big bang. This caused the universe to expand from a singe point cooling as it does so to form the universe. Each point expands away from the others this is seen from galaxies moving away from each other. As a result of the initial explosion the universe continues to expand.
What are the two pieces of evidence for the big bang theory
-Galactic red shift
-Cosmic microwave background radiation (CMBR)
How is galactic red shift related to evidence for the big bang theory?
-By observing light spectrums from supernovae in other galaxies there is clear evidence to suggest that distant galaxies are moving further apart even faster than nearby galaxies. The light spectrum show that light from distant galaxies is redshifted which is evidence that the universe is expanding. There have been conclusions that All galaxies are moving away from earth and that galaxies are moving away from each other
-This is what is expected after an explosion. Matter is first densely packed and as it explodes it moves out in all directions getting further and further from the source of explosion. Some matter will be lighter and travel at greater speed further from the source of explosion. Some matter heavier and closer to the source of explosion.
-If was to look back in time and compare the distances of the galaxies it would be seen that galaxies would become closer and closer together until the entire universe was a single point.
-Almost all stars show red-shift the futher away the star the greater the red shift showing it has a higher velocity this suggest that the universe is still expanding
How is CMBR evidence for the big bang theory
-Cosmic microwave background radiation is a type of electromagnetic radiation which is a remnant from the early stages of the universe. It has a wavelength of around 1mm making it a microwave. According to the Big Bang theory the early universe was extremely hot and dense environment because of this it emitted thermal radiation energy which was left over from the big bang this energy or CMBR can be detected from all parts of the universe supporting the fact that the big bang explosion we can tell that CMBR is spread out all of the universe
Explain what galactic red shift is
-red shift is the apparent change in wavelength and frequency of light recived from stars. When stars move away from earth the light received appears to have a longer wavelength and a lower frequency the light shifts towards the red end of the spectrum
-If an object moves away from an observer the wavelength of light increases. This is known as redshift as the light moves towards the red end of the spectrum. If an object moves towards an observer the wavelength of light decreases this is known as blueshift as the light moves towards the blue end of the spectrum
-An increase in wavelength is a decrease in frequency
-Galactic redshift proves evidence for the big bang theory and the expansion of the universe redshift provides evidence that the universe is expanding because: Red-shift is observed when the spectral lines from the distant galaxy move closer to the red end of the spectrum this is because light waves are stretched by the expansion of the universe so the wavelegnth increases the indicates that the galaxies are moving away from us. Light spectrum produced from distant galaxies are red shifted more than near galaxies which are blue this shows the greater the distance to the galaxy the greater the redshift this means that the futher away a galaxy is the faster it is moving away from earth. This observations imply that the universe is expanding and therefore support the big bang
