Objects in the Universe
Nebula
Ant NebulaNebulae are large clouds of gas and interstellar dust. They are the birthplace of stars.
Galaxy
NGC 4414 - a spiral galaxyGalaxies are clusters of stars rotating around their centre of gravity
Main-Sequence Star
The Sun - It is ranked as G2VStars vary in size. Fundamentally they are dense gas clouds where the Hydogen nuclei are fused together in a nuclear fusion reaction. This creates large amounts of energy and electromagnetic radiation. They are ranked by size and brightness. Main-sequence stars are in the middle when it comes to luminosity and size.
Planet
Some planetary bodies in our solar systemCold small body orbiting a star.
Red Giant
Red Giants are large stars that have little fusion occurring. They are very bright but do not radiate lots of heat. Less fusion occurs because large stars have exhausted their Hydrogen supply
White Dwarfs
Sirius B in comparison to the EarthWhite Dwarf Stars are small dense stars where fusion doesn't occur anymore. White dwarfs are often the centre of planetary nebulas which was formed when the original star's outer layers drifted from the dwarf centre.
Binary Stars
Alpha Centauri A and B are binary stars.Two stars that orbit around each other. Sometimes a star that is paired with a black hole. The orbits vary from a few thousand miles to several AUs.
Supernova
Crab Nebula - Remnant of supernova from 1054A Supernova is an explosion of a star. This is when the iron core becomes so large that it's gravitational force overcomes the star and forces the protons to bond with electrons creating neutrons. The collapsing matter rebounds off the rigid core creating a huge shockwave. This in turn creates a nebula.
Black Hole
If the star is large enough it will create a black hole instead of a supernova. This is when the core is so large that its gravitational pull is so great that light can't escape its pull.
Neutron Star
A Neutron star is sometimes left behind after a supernova. They have strong magnetic fields and rotate rapidly releasing pulses of electromagnetic waves giving them their other name - pulsar
Quasar
A Quasar is a very luminous compact object. They surround a black hole at a galactic centre.
Comets
Small Ice and Rock fragments with a gas cloud (tail). Some orbit around stars normally in elliptical orbits.
Meteor and Meteorite
A Meteor is a rock fragment. When they enter the earth's orbit they heat up. They normally vaporise. Larger ones do collide with the Earth. When a meteor reaches Earth it becomes a meteorite.
Formation of a Star
- Nebulae - large dust clouds collapse under their own gravity
- The particles lose gravitational potential energy and gain kinetic energy - heating up
- Eventually the cloud becomes so dense Hydrogen nuclei fuse together
- Stable star forms when gravitational pressure equals the radiation pressure
Death of a Star
- Rate of fusion starts to decrease as core becomes mostly fusion products
- Core starts to collapse due to decrease in radiation pressure
- The loss of gravitational potential energy means the star heats up more
- This means the pressure increases and so the star increases in size
- Eventually the Helium nuclei fuse creating huge amounts of pressure and the core collapses in on itself
- The outer layers dissipate leaving an immensely hot white dwarf is left behind in the centre of a planetary nebula
- No more fusion occurs in a white dwarf but it is very hot
- Over time it cools into a black dwarf
In much larger stars than a main-sequence star
- The core collapses in on itself until protons and electrons fuse
- This collapse creates huge amounts of heat followed by an intense release of energy called a supernova
- If the core was dense enough a black hole forms instead as the gravitational strength becomes so strong even light can't escape.
Astronomical Distances
- Astronomical Unit - distance from centre of Earth to the centre of the Sun (1.496 x 10^11m)
- Lightyear - distance light takes to travel in one Earth year (9.461 x 10^15m)
- Parsec - 3.986 x 10^16m
Olbers' Paradox
In the 19th century the Universe was thought to be:
Olbers reasoned that if this was true then the night sky should be as bright as the day sky.
Olbers' Paradox is - The night sky should be bright because the intensity of light is inversely proportional to the radius squared and the number of galaxies is proportional to the radius squared the light reaching earth should be infinite.
He reasoned that the universe is not infinite
- Infinite
- Static
- Mass is uniformly distributed
- Infinitely old
Olbers reasoned that if this was true then the night sky should be as bright as the day sky.
Olbers' Paradox is - The night sky should be bright because the intensity of light is inversely proportional to the radius squared and the number of galaxies is proportional to the radius squared the light reaching earth should be infinite.
He reasoned that the universe is not infinite
We now know that the universe is finite, is expanding, and the age of the universe means that the light from lots of galaxies hasn't reached us yet.
Doppler Effect - Redshift
Hubble noticed that electromagnetic waves we were receiving from galaxies followed the same spectra our sun gives off but had shifted towards the infrared section of the spectrum. Hubble determined that light waves were experiencing the doppler effect as which showed galaxies were recessing (moving away) from the Earth.
The speed of recession can be determined by the equation:
Δλ = v
λ c
Δλ = change in wavelength
λ = Original wavelength of the light
v = speed of recession of the galaxy
c = speed of light
Hubble created a law:
The speed of recession of galaxies from the Earth is proportional to the distance they are away from the Earth.
v = H0D
The constant in this equation is called Hubble's constant (H0)- you need to be able to change the units of Hubble's constant. They are generally found in Km per second per megaparsec. These will cancel to just per second
This helps provide evidence for the big bang as it shows the galaxies are moving from a point of origin as they are all moving away from each other and not being attracted by each others gravitational pull.
Hubble's Constant also helps prove the age of the universe
1/H0 = age of the universe
The speed of recession can be determined by the equation:
Δλ = v
λ c
Δλ = change in wavelength
λ = Original wavelength of the light
v = speed of recession of the galaxy
c = speed of light
Hubble created a law:
The speed of recession of galaxies from the Earth is proportional to the distance they are away from the Earth.
v = H0D
The constant in this equation is called Hubble's constant (H0)- you need to be able to change the units of Hubble's constant. They are generally found in Km per second per megaparsec. These will cancel to just per second
This helps provide evidence for the big bang as it shows the galaxies are moving from a point of origin as they are all moving away from each other and not being attracted by each others gravitational pull.
Hubble's Constant also helps prove the age of the universe
1/H0 = age of the universe
Cosmological Principle
The cosmological principle states that on a macro scale the universe is uniform and isotropic. Meaning the density is constant throughout the universe and is the same in all directions.
Background Radiation
Penzias and Wilson were recording radiowaves with a radiowave telescope from different parts of the sky. They constantly got an unwanted 'noise'.
This noise turned out to be microwaves which were constantly there at the same frequency and intensity no matter what direction the telescope was pointing.
This helped prove the Big Bang Theory - A cosmic microwave background was theorised to exist as aftermath of the big bang
This noise turned out to be microwaves which were constantly there at the same frequency and intensity no matter what direction the telescope was pointing.
This helped prove the Big Bang Theory - A cosmic microwave background was theorised to exist as aftermath of the big bang
Evidence For the Big Bang
Redshift - Shows all galaxies are moving apart so the universe is expanding - must come from a common origin
Background radiation - Microwave remnants from the big bang - throughout universe so must have come from a big bang.
Background radiation - Microwave remnants from the big bang - throughout universe so must have come from a big bang.
History of the Universe
- Universe is infinitely dense, small and hot (Est. 13.7 billion year ago); 0s
- Universe rapidly expands. All forces are one unified force; 10^-43s, 10^27K
- Gravitational Force separates from the other forces - universe contains quarks and photons; 10^-34s, 10^22K
- Strong Force separates from the other forces - imbalance of matter and anti-matter. Leptons form; 10^-16s, 10^16K
- Weak and Electromagnetic forces separate - quarks form hadrons - 4 protons for 1 neutron - annihilation of anti-matter; 10^-3s, 10^10K
- Protons start to fuse producing Helium nuclei; 1000s, 10^7K
- Hydrogen and Helium atoms form;10^5years, 10^4K
- Atoms start to clump together forming stars and galaxies;10^6years, 6000K
- Heavy elements form in the cores of stars; 10^9years, 17K
- (Universe is currently 2.7K)
Critical Density
Critical Density is the density at which the universe expands to a finite size (rate of expansion will tend to zero)
It can be determined using the equation below. Hubble's constant should be in per seconds
It can be determined using the equation below. Hubble's constant should be in per seconds
Fate of the Universe
Critical Density determines the fate of the Universe
If the Universe's current Density:
If the Universe's current Density:
- is smaller than critical density the universe will expand for an infinite amount of time - open universe
- is bigger than critical density the universe will slowly stop expanding and collapse under its own gravity - closed universe
- is equal to critical density the universe will expand towards a finite size (rate of expansion will tend to zero) - flat universe