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Space, EM waves and Cosmology
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Space, Cosmology and Electro Magnetic waves in Space
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Space
When Looking out into space and in our solar system it's important to know what we're talking about, as well as the size of what we're talking about
The Small to the Big
Do you know the sizes of everything covered in these topics?
Comets and Asteroids
Forming from rock and minerals or ice respectively, one of the smallest things flying around are comets and asteroids.
Though some are formed from the remnants of the formation of our solar system, most are flung from the asteroid belt via gravity
Planets
Planets and dwarf planets are at the forefront of looking out into the night sky. Plants we encounter are categorized into several different types.
Within our solar system we have:
- Terrestrial planets - Made of Rock (Mercury, Venus, Earth, Mars)
- Gas Giants - Composed mainly of hydrogen and helium much like the sun (Jupiter and Saturn)
- Ice Giants - Composed of mainly a frozen surface (Neptune and Uranus)
- Dwarf Planets - Planets that are of a smaller size and are affected by gravitational pull other then a star.
Also known as trans-Neptunian objects, Dwarf planets within our solar system are affected and often have locked orbits in relation to Neptune as well as the sun.
Our Solar System
Consists of the following:
Beyond the Solar System
Just outside the solar system is the Oort Cloud, a roughly spherical grouping of Ice chunks and rocks.
Many large long living comets are believed to have originated from there.
Galaxies
As we 'zoom out' we next encounter Galaxies, formed of vast amount of stars, gas, dust and as far as we know dark matter. There are 4 main types of galaxy:
Elliptical
Spiral
Barred-Spiral
Irregular
Galaxies can come in many different size and can be found alone in space, or within ginormous clusters.
Super Clusters
Clusters of Galaxies can often form Super clusters due to their proximity to other clusters of galaxies.
Our of Galaxy, the Milky way, has over 54 galaxies in it's local cluster, and with even more nearby that makes up the Virgo super cluster. Shown in the middle of the picture to the left.
The Universe
The edge of the Observable universe is 46 billion light years away (14 billion Parsecs), with a diameter estimated to be about 93 billion light years wise (28 billion Parsecs). Everything we know and observe is within this expansive bubble.
For a better visual understanding watch the video here:
Formations of Stars
Formation of Stars
The formation of stars begins when clouds of gas and dust scattered through the universe begin to attract and amass in such concentration that they not only become locked within the body but begin to collapse under it's own gravitational weigh. This is when fusion happens and a star is ignited.
Fusion
Once enough mass has been gained a star begins the process of 'Nucleosynthesis', the process of generating new elements. this process occurs in the core of the star where gravity is at it's highest, or during the collapse of a larger star in an explosive part of it's life cycle.
Basic fusion within stars looks like the diagram to the right and consists of hydrogen colliding together to form helium and large amounts of energy.
Without explosive evolution of a star Fusion can only generate elements up to Iron, and then only if it has the right mass to support the gravitational collapse needed.
Evolution of a Star
Depending on the size of the star there are many different stages it can take across it's lifespan. Most are shown to the right here.
For our sun it's life cycle will follow the above time scale
Around 9 billion years (4.5 billion years from now) a helium core will begin to form expanding the hydrogen shell of the star and causing it's temperature to rise.
Another billion years after that it will begin to rapidly expand now moving up to a carbon core with more elements being created within. This will form a Red giant.
within another billion years the red giant will collapse into a planetary nebula forming a white dwarf at the centre.
Life Cycle of Larger Stars
The more massive a star is the shorter it's lifespan is, with it burning through it's elements at a far greater rate.
With our sun at solar mass of 1 and a life span of around 9 billion year, comparatively a large star of 30 solar masses is only 11 million years, meanwhile on theother side a brown star with solar mass of 0.1 solar masses is around 1000 billion years or more.
As the massive red super giant reaches the end of it's life it begin to create elements upto iron, at which point nuclear fusion can no longer occur. At this point the balance tips of outward energy against gravity and gravity begins to win.
This causes the mass of the star to be pulled in suddenly with great force compressing the core to it's limit before being rebounded off it in a huge shockwave sending lots of it's mass outwards in a supernova.
If the remnants of the star are too massive to form a white dwarf stably it can lead to a neutron star, or in extreme cases a black hole.
White Dwarfs
In comparison to other star white dwarfs are considerable smaller, many being around the size of earth or other terrestrial planets.
For most stars (around 97%) a white dwarf will be the end of their lifespan.
White Dwarfs
Because of their size, and their resulting composition being that of the creation of heavier elements via fusion within a stars core, they have a very density. with a surface gravity of >100,000G.
For more information watch the video -->
Electron Degeneracy Pressure
Is the principle that allows White Dwarfs to be able to exist in a such a dense state.
With such a high concentration of matter, with no net charge. The atoms would eventually collapse into just the nucleus if not for electron Degeneracy Pressure.
Within white dwarfs the degeneracy pressure must be in a good balance to prevent it from collapsing further inward upon itself to it's own gravity, or explode outward due to the repulsion of electrons within the atoms.
The limit to this is called the Chandrasekhar limit.
This is an important distinction to make compared to main sequence stars that resist collapse due to Thermal Pressure.
Chandrasekhar Limit
Named after Subrahmanyan Chandrasekhar. The Chandrrasker Limit determines whether a white dwarf will be stable for it's life span or not.
The Limit is recognized at 1.44 Solar masses
(roughly equal to 2.765 x 10^30Kg)
Any mass above this will result in an imbalance in electron degeneracy pressure and the stars own gravitational pull resulting in further collapse towards a neutron star of black hole.
Neutron stars
When white dwarfs exceed the Chandrasekhar limit they instead from a neutron star (results from stars with solar mass of 10-29). Such named for the believe that it's inner crust consists of large sheets of compressed neutrons. With the exception of black holes they are the densest thing in the universe.
Neutron Stars and Black Holes
When they form they begin to spin very fast and can form what we call pulsars
Pulsars
Due to the extreme magnetic field created by dense neutron star coupled by the spin which can be up to 40,000 times a minute, a neutron star can appear to 'pulse' as it send outs large amounts of electromagnetic radiation.
Due to the regular pattern created by pulsars on the radio-wave frequency the first encountered one was thought to be a possible alien message of contact.
for a better understanding of pulsars watch this -->
For a better understanding of Neutron stars watch this -->
Black Holes
Only in the last couple of years has the existence of Black Holes gone from theoretical to having proof, a Black Hole is the densest thing in the universe.
It's creation can occur when the collapse of a star exceeds a solar mass of 30, or when two neutron stars collide and merge.
Being only theoretical until recently it still has largely unknown properties, other then the the reason it's 'black' is that one must go faster then the speed of light to escape it's gravitational pull.
The picture, taken over five days of observations in April 2017 using eight telescopes around the world by a collaboration known as the Event Horizon Telescope, depicts luminous gas swirling around a supermassive black hole at the center of M87
For more information watch this video -->
Luminosity vs Temperature
in 1910 Ejnar Hertzprung and Henry Norris Russel plotted 22,000 different stars onto a scatter graph to help better understanding the links between stellar classification, size of stars and their luminosity.
Though many forms of a HR Diagram have been created, it can be used produce predictions of the properties of stars based on known entities with close proximity on the chart.
Several Version of HR Diagrams
Below - Gaia's Colour HR Diagram
Below - HR Diagram showing well known Classifications
Above- HR Diagram showing only white dwarfs with characteristics
To understand how they are made watch this video -->
Electro-Magnetic Waves in Space
Energy Levels of Electrons in Isolated Atoms
While in a gaseous state we refer to atoms as 'isolated'. This is due to the distance between the particles and the low amount of interaction that occurs.
This can arise to many useful properties, including the creation of discrete line spectra formed from hot gases.
Energy Levels in isolated atoms
This is because the electrons can only exist in discrete energy levels
Electons can move up energy levels if they absorb a photon with the exact energy difference between the two levels and this is called excitation.
Energy as Negative Values.
Energy in electrons is said to be a negative value.
This is due to the potential energy of a 'free' electron is presumed to be zero.
Because the work must be done by the atom to bring the electron into an energy level the electron is known as the energy sink and thus has a negative value.
This is because when looking at the potential at an infinite point away as 0 it must be less as it gets closer and thus becomes a negative value
Energy levels in negative values
Using GPE as an example we can see this here -->
Emission Spectrum Lines
The white light spectrum is continuous from red to blue 400-700 nanometers.
However when passing through a gas certain lines of the spectrum go missing.
Emission Spectral Lines
This is because, as said previously, electrons adsorb photons with the energy levels they need to go up an energy level. But most importantly, electrons only absorb photons with the exact energy they need to travel up an energy level.
When looking at the missing lines of colour from the continuous spectrum we can create an emission line spectrum.
*Lambda's symbol =
Energy in Wavelengths
Photon Energy and Energy in Wavelengths
Wavelength is related to energy and frequency by E = hf = hc/Lambda
Where E = energy,
h = Planck's constant (6.63 x 10^-34 Js)
f = frequency
c = the speed of light (3x10^8 m/s)
Lambda = wavelength.
The energy of each photon is inversely proportional to the wavelength of the associated EM wave.
Specific Spectral Emission
Because of the unique energy levels that each element has, and the fact we know electrons will only absorb photons of the exact energy difference, we can conclude that different elements will create different spectral emissions.
Atoms and their Spectral lines
But it's in the reverse that we find use in this being able to identify distant gas clouds in space and their compositions due to the emission spectral lines created by them.
Absorption
When looking at clouds of cool gas we only see the absorption line spectrum as the electrons have only absorbed the specific energy levels required. the black lines found in the continuous spectrum indicate which levels the atoms required.
Absorption
Diffraction Grating
White light is really a mixture of the whole continuous spectrum, and to be able to view required things such as spacial gratings we need to split it up into it's continuous form.
Doing this allows us to identify atoms due to their atomic spacing along the spectrum by matching their spectral lines.
Diffraction grating
White light Source
Diffraction Grating
Spectrum
Wien's displacement Law
Black body = A body the absorbs all wavelengths of electromagnetic radiation
States that the black-body radiation curve for different temperatures will peak at different wavelengths. These wavelengths are inversely proportional to the temperature.
Wien's displacement Law
Lambda m = is the intensity of the wavelength at it's largest
T = temperature
We can use this to calculate the surface temperature of a star, as long as a star can be considered to be a black body (and this is almost true in most cases), we can use Wien's Law to work out its surface temperature by taking its spectrum and identifying the wavelength of maximum emission.
From this we get the following:
Luminosity of a Star
The Luminosity of a star can be determined through the following equation:
This is measured in Watts/m^2
Luminosity
Luminosity is used to give a precise measurement to the apparent brightness given by any star within a parallax distance.
For a better understanding watch this video -->
Radius of a star
the radious of a star can be a tricky thing to determine with the inaccuracy of our telescopes and trying to determine the exact edge where light is emitted from the star. Thus we can use what we've learnt so far to determine it's radius if we already know the other factors.
We can once again use the formula
By knowing it's luminosity and temperature by studying the transmitted light we can determine it's Radius and thus the size of any star.
Radius of a star
For an example of this watch this video -->
Cosmology
Astronomical Units
In space different entities are really really far away. thus instead of relying on a standard measurement we would use in everyday things we scale up and use large measurement standards for a better, and easier, understanding.
Astronomical Units
One such measurement is the Astronomical unit or Au.
1 AU = the distance between the earth and the sun.
1 AU = roughly 150 million kilometers.
and is used to measure things mainly within our own solar system.
Astronomical Units cont.
When looking further than our solar system we begin to use light years as a measurement.
1 Light Year = the distance it takes light to travel in a single year
1 Light Year = 9.4607 x 10^12 KM
When measuring distances outside our solar system we tend to use Parsecs.
1 Parsec = the distance from the Sun to an astronomical object with a parallax angle of 1 arc second.
1 Parsec = 3.3 Light Years
For a quick recap watch this -->
Parallax
Is the idea that when observing objects while moving, objects that are closer appear to be moving faster than object that are further away.
Parallax
We can use this idea to measure an angle while we are at different sides of the sun to create a triangle and calculate the angle between them. This is called the parallax angle.
From there we can use trigonometry to discover the distance to that star.
For another explanation watch this video -->
More Parallax
There is a simple relationship between a star's distance and its parallax angle: d = 1/p
The distance d is measured in parsecs and the parallax angle p is measured in arcseconds.
This simple relationship is why many astronomers prefer to measure distances in parsecs.
More Parallax
This method is however limited by the telescopic power we have on earth can only be used to accurately measure distance of up to 100 parsecs
The Cosmological Principle.
Is the notion that the universe is 'Homogeneous' - which means that it has the same properties throughout all of it. And that it is 'Isotropic' - meaning that it has uniformity throughout it's dimensions
Cosmological Principle
William Keel describes this phenomena as "Viewed on a sufficiently large scale, the properties of the universe are the same for all observers"
By why is this important ?
Because of uniformity across the universe we can make several observations and learn key facts about the universe.
For example: galaxies that are further away have a high frequency to be of a fragmented structure, which would suggest that galaxies have an evolution or life cycle style existence.
Another example: Galaxies that most distant away tend to be closer together, and have a much smaller content of heavy elements. This leads us to an understanding that for the galaxy to be the same across the heavier elements must have come from something other then the universe itself. thus leading to the implication that heavier elements where not formed during the big bang but purely through nucleosynthesis.
Doppler Effect and Shift
At one point in your life you've probably experienced the Doppler effect, in which as a noise rushes past it appears to sound different
This is due to the compression of waves on a moving source. as it moves towards you it will be a higher frequency, and while moving away a lower frequency.
Doppler effect and shift
Though our personal experience is of it in sound it can occur in all wave form including light, which we can use when looking out into the galaxy
By measuring the shift in light as it's transmitted from an interstellar object we can determine whether it is moving away or towards us
Doppler Equation
Because at a constant frequency and wavelength match (thanks to our homogeneous universe) wavelength and frequency can be interchanged in this equation.
Doppler Equation
Using this equation we can use a perceived wavelength or frequency to determined whether it has blue or red shifted. because of the constant velocity of the light at the speed of light.
Hubble's Law
Hubble law was the discovery and proof that the universe is expanding due to the large existence of redshift within our universe.
It is cited as the first observation of our galaxy expanding and is one of the route proofs for the big bang theory.
Hubble's Law
For more information watch this video
It is often expressed by the equation:
v = H0D
with H0 the constant of proportionality (Hubble constant) between the "proper distance" D to a galaxy, which can change over time, and its speed of separation v
Red Shift in an Expanding Universe
Following what we know of hubble's Law and Red-shift, coupled with hubble's discovery that almost everything in the galaxy is moving away from us we are led to support the conclusion that the universe is current expanding, not only that but it's expanding at an increasing rate
Red Shift
By looking in all direction and viewing everything red shifting we infer that everything is moving away from us. But more to this if we where to turn back time we could infer that everything was moving towards a single point in which the creation of the known universe started.
Hubble Constant
Earlier we mentioned Hubble's Constant but what is it?
It's a unit of measurement that is given to the rate of the expanding universe. And it can be worked out by plotting the distance and velocity of interstellar objects in relation to a particular point in space.
Hubble Constant
With the implication that the universe is accelerating in it's expansion the Hubble Constant is at the forefront to our understanding of it's evolution.
However it's true value is still debated today.
The Big Bang Theory
The Big bang theory is that the universe was nothing until a large expansion of space time and matter occurred.
Big Bang Theory
Starting from the smallest sub-atomic particles the rapid expansion occurred for space time the laws of physics and the universe we know to be come formed over the course of the last 13.77 years
For an explained timeline watch this video -->
Evidence for the Big Bang
Starting with Hubble's discovery that the universe was moving away from us it led to believe that there must have been an origin point that everything is moving away from.
Evidence for Big Bang
However this in contrary to our understanding of gravity, that everything should be pulling themselves towards each other. Therefore it is reasoned that there must be something that initially 'pushed' everything away from each other to begin with.
Supporting this is the existence of cosmic background radiation, microwave radiation that permeates the entire universe. This discovery led to the understanding that at some point a radiation field of extremely high pressure and temperature would have dominated the entire universe.
Cosmic Background Radiation (CBR)
When measuring Cosmic Background Radiation we get the above readings on temperature (with red being hotter and blue being colder)
Spacetime
Is the built theory of three dimensional space with the forth dimensional addition of time.
We originally had a very fixed version of what space was but through Einstein's work we understand that space can become covered and isn't always flat.
Space Time
When looking out into space at interstellar objects we can understand that light is sometimes bent and curved not always traveling in a straight line.
Black holes for example get their name from the idea that light curves in so heavily that it never curves back out. Watch the video for a more in-depth explanation.
The Age of the Universe
As mentioned previously with Hubble's discovery of redshift meaning interstellar objects are moving away from us it's possible to think backwards to a central point that they may have all come from and the time it would take for this to happen would be the age of the Universe.
Age of the Universe
Thus we can use the equation: Time = Hubble Constant^-1
For a better understanding watch the video -->
Dark Matter/Energy
Dark matter and dark energy are modern theories derived from the idea that when we look out into the observable universe there appears to be something missing.
Though we can observe the effects that these things have on the universe, they don't react with light and thus cannot be seen, thus 'dark'. What we can observe is the effect that they have on the things around them.
Dark Matter / Energy
Because of these effects we are almost 100% sure that they exist, however that is as far as we can get, and the rest has ended up in major speculation and is at the front of scientific discovery in modern times.
For more watch the video -->