Science - Physics - Space Physics - P8 Flashcards
what’s a nebula ?
a cloud of dust and gas that stars initially form
what does gravity turn a nebula into ?
protostar
what is a protostar ?
a cloud of dust and gas which clumps together due to gravity
what does the gravitational attraction do to the protostar ?
causes its density to increase so the particles within the protostar increases and particles within the protostar collides more frequently, causing the temperature to rise
what happens when the temperature in the protostar gets too high ?
hydrogen nuclei undergos nuclear fusion to form helium nuclei which gives out lots of energy and keeps the core of the star hot
how is a star born ?
-hydrogen nuclei undergos nuclear fusion when temperature rises too much to form helium nuclei
-this gives out massive amounts of energy which keeps the core of the star hot
- star is born
how are planets made ?
smaller masses of gas and dust around the star may be pulled together to make planets which orbit the star
what happens after a star has been formed ?
it enters a long, stable period
how is a star stable once it has been formed ?
- energy released by the nuclear fusion provides an outward pressure that tries to expand the star which balances the force of gravity pulling everything inwards
what is another word for a star being stable ?
a star being in equilibrium
what is a main sequence star ?
the star when it is in a stable period
how long does a main sequence star roughly last for ?
7 billion years
give an example of a main sequence star ?
sun
what happens at the end of a main sequence stars life ?
- hydrogen runs out
- fusion of helium occurs and the star is no longer a main sequence star
what do stars produce ?
all naturally occurring elements in the universe
how do stars about the size of the sun die ?
- small star about the size of the sun expands into a red giant when it starts to run out of oxygen
- it then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula
- this leaves behind a hot, dense, solid core - a white dwarf
- as a white dwarf cools down it emits less energy
- when it no longer emits a significant amount it becomes a black dwarf
what is a red giant ?
what the star expands into when it runs out of hydrogen
why is a red giant red ?
because the surface of the star cools
what is a white dwarf ?
a hot dense solid core which is left behind from a planetary nebula
what is a planetary nebula ?
formed when a red giant becomes unstable and ejects a layer of dust and gas
what is a black dwarf ?
formed when a white dwarf cools down - something which eventually disappears in sight
what happens when stars much larger than the sun die ?
- expands into red super giants when they start to run out of hydrogen
- they expand and contract multiple times forming elements less heavy than iron
- when red super giants runs out of elements to use they become unstable
- they explode into a supernova forming elements heavier than iron, ejecting them into the universe forming planets and stars
- the exploding supernova throws the outer layers of dust and gas into space leaving a very dense core called a neutron star
- if the star is big enough it becomes a black hole instead
what are red super giants ?
formed from stars larger than the sun, they expand and contract multiple times when stars start to run out of oxygen, forming elements as heavy as iron in nuclear reactions
how is a supernova formed ?
when red super giants run out of elements to fuse and become unstable and explode into a supernova
what do supernovas do ?
form elements heavier than iron and ejects them into the universe to form new planets and stars, throwing outer layers of dust and gas into space
how are neutron stars formed ?
when supernovas throw out lots of layers of dust and gas into space, they leave behind a neutron star with a dense core
what is a black hole ?
a dense point in space so not even light can escape from it
how is a black hole formed ?
when a neutron star is big enough it becomes a black hole
what star does the solar system contain ?
the sun
what is the solar system made up of other than the sun ?
it is made up of everything that orbits the sun
what is an orbit ?
the path on which one object moves around another
what is the sun orbitted by ?
- planets
- dwarf planets
- satellites
what is a planet ?
large objects which orbit a star
how many planets orbit the sun ?
8
what makes something a planet ?
- they have to be large enough to have gravity strong enough to have pulled in any nearby objects apart from their natural satellites
what is a dwarf planet ?
planet-like objects which orbit stars but are too small
give an example of a dwarf planet ?
pluto
what is a satellite ?
objects that orbit a second more massive object
what are the 2 types of satellite ?
- natural satellites
- artificial satellites
what is a natural satellite example ?
the moon
what is an artificial satellite ?
satellites humans have built
what is galaxy is our solar system a part of ?
milky way
what is a galaxy ?
a massive collection of billions of stars that are all held together by gravity
what keeps an object within its object ?
gravity
what does it mean if an object is moving in a circle ?
it is constantly changing direction which means it is constantly accerlerating
what needs to happen for an object to accelerate ?
there must be a force acting on it
for circular motion what direction is the force at ?
towards the centre of the circle
what is the force acting towards the centre of the circle in objects in our solar system ?
gravitational force - between a planet and the sun
what is an orbit a balance between ?
the force providing the acceleration and the forward motion of the object
what keeps an object travelling in a circle when it is orbiting ?
instantaneous velocity
what is instantaneous velocity ?
velocity which is at right angles to the acceleration and force of gravity
what does the size of orbit depend on ?
an objects speed
the closer you get to a star or planet, what happens to the gravitational force ?
it gets stronger
the stronger the gravitational force, what does the object need to travel in to stay in orbit ?
the faster the object needs to travel
for an object in a stable orbit if the speed of the object changes, what happens ?
the size (radius) of it orbit must also change
if the object moves faster, what happens to the size of its object ?
it is smaller
what is red shift ?
the shift in observed wavelength of light from a source moving away from a stationary observer. The wavelength is shifted towards the red end of the electromagnetic spectrum
when does red shift occur ?
when the source of light is moving away from the observer - the light wave is ‘stretching out’ as the source moves away
as the light from most distant galaxies has been red shifted, what does this suggest about the galaxies ?
they are moving away from us
what do measurements of the red shift indicates ?
most distant galaxies are moving away from us very quickly
which kind of galaxy has a greater red shift ?
distant galaxies
what does distant galaxies red shifting further away from us than closer ones suggest about us ?
galaxies are moving away from each other = the universe is expanding
what is the big bang theory ?
- initially all matter in the universe was occupied in a very small space - this tiny space was very dense and very hot
- then it exploded and space started expanding - the expansion is still going on
what is the big bang theory supported by ?
red-shift measurements so is the generally accepted theory
how do scientists come up with theories like the big bang ?
observations
what happens when scientists find new evidence which isn’t explained by their current theory ?
they have to make a new theory or change a current one to explain what they have observed
give an example of an unexplained observations that scientists have found about space ?
- galaxies are moving away from us faster and faster
- scientists think the universe is mostly made up of dark matter and energy, and are seen as the reasons for the accelerated expansion of the universe - but no one knows what they are
what is dark matter ?
the name given to a known substance which holds galaxies together but does not emit any electromagnetic radiation
