Mapping the Universe Flashcards
1
Q
Why is map making so important for human existence?
A
- it is an integral part of human existence as it helps us to understand our place and navigate throughout the world
2
Q
What is observational astronomy?
A
- astronomy is a largely observational science
- we locate and study astronomical objects based on their emissions
3
Q
What are the different types of Electromagnetic Radiation?
A
Radio Microwave Infrared Visible Ultraviolet X-Ray Gamma Rays
4
Q
What is Light?
A
- an electromagnetic wave
- it is a wave of varying electric and magnetic fields
- it is similar to a wave on string
- light waves can travel in a complete absence of medium, in a vacuum
5
Q
What are the characteristics of a light wave?
A
- Amplitude
- Wavelength
- Frequency
- Speed
6
Q
Characteristics of Light Waves - Amplitude
A
- the maximum value that the wave takes
- the larger the amplitude, the brighter the light
7
Q
Characteristics of Light Waves - Wavelength
A
- the distance between one maximum and another
- or between any two points in consecutive cycles
- the wavelength of light determines the colour
8
Q
Characteristics of Light Waves - Frequency
A
- the number of times the wave cycle repeats per second
- measured in cycle/s or Hertz
9
Q
Characteristics of Light Waves - Speed
A
- all electromagnetic waves in a vacuum travel at the speed of light (ie 300 million metres per second)
10
Q
How are frequency and wavelength related to the speed of the wave?
A
Speed = frequency x wavelength
11
Q
Waves and Particles - LIGHT
A
- although light can be described by a wave, it also exhibits particle-like behaviour
12
Q
Young and Fresnel
A
- early 1800’s
- proved the existence of the wave-like property of light through interference
13
Q
Einstein
A
- 1905
- showed that light can also possess particle-like properties
14
Q
Wave-Particle Duality
A
- the dual nature of light
- light is a wave and at the same time is made of particles called photons
- these also travel at the speed of light
- all waves carry energy, eg the heat from the Sun
- each photon is a packet of energy
- the energy of the light is proportional to the frequency - E = h x f
(h = Planck’s constant)
15
Q
The Spectral Analysis of Light
A
- stars (or dense balls of gas) emit a continuous spectra
- hot diffuse (low density) gas emits photons with a line spectra
- cold gas absorbs photons
- absorption is specific to particular elements
16
Q
Why is the Spectral Analysis of Light very important?
A
It can tell us:
- the chemical composition of an object
- the temperature of an object
17
Q
How can light be split into its constituent wavelengths?
A
using either a:
- Prism
- Diffraction Grating
18
Q
How do Prisms work?
A
by Refraction and Dispersion
19
Q
How do Gratings work?
A
work with Diffraction and Interference
20
Q
What is Refraction?
A
- the physical phenomenon involves when light crosses a boundary between different media
- it is caused because the speed of light is slower in a material than in air or vacuum (eg slower in glass)
21
Q
What is Dispersion?
A
- a phenomenon in which the speed of light in a media changes with the wavelength
- Red light travels about 1% faster than Blue light through glass
- thus the amount that a light beam is refracted varies with wavelength (or colour)
22
Q
What is a Diffraction Grating?
A
- an optical component with a periodic structure which diffracts light in different directions depending on wavelength
- there are transmissive and reflective diffraction gratings
- a typical diffraction grating has a groove spacing of around 500nm
23
Q
How does a Diffraction Grating works?
A
- a mirror reflects all wavelengths of light equally
- a reflective diffraction grating reflects different wavelengths at different angles
- mirror reflection = 0th order
- first spectrum = 1st order
- second spectrum = 2nd order and so on
- to understand how this happens, we need to understand how DIFFRACTION and INTERFERENCE works
24
Q
What is Diffraction?
A
- the spreading of waves when they encounter an objects
- most apparent when the size of the obstruction is similar to the wavelength
25
What is Interference and what are the two different types?
- describes the interaction of two or more waves with each other
1) Constructive
(bright regions)
2) Destructive
(dark regions)
26
Interference of White Light
- with many sources the intensity in the regions of constructive interference is sharply peaked
- the gap between the peaks depends on the separation of the sources compared with the wavelength
- in a diffraction grating, interference occurs between the diffracted light coming from each groove
- since the number of grooves involves is very high (several thousand), the bright regions are sharp
- due to their superior ability to resolve colours, gratings are used more than prisms in astronomical spectrometers
27
Why is the mount on which the telescope attached to so important?
- it needs to track an object accurately over long durations of time
28
What are the different types of Converging Lenses?
1. Biconvex
2. Plano-convex
3. Convex-concave
- bring light rays to a focus
29
What are the different types of Diverging Lenses?
1. Meniscus
2. Plano-concave
3. Biconcave
- project light rays outwards
30
Refracting Telescopes
1608 - Lippershey invented the telescope
1609 - Galilei improved the design of the original with a convex
1611 - Kepler made a further improvement using convex objective and convex eyepiece
- the magnifying power depends on the focal length of the Objective and the Eyepiece
31
What were Galileo's discoveries?
- pointed his telescope up and observed the Moon
- observed that the Moon was not smooth and deduced the existence of mountains and craters
- also pointed his telescope at the Sun and observed Sun spots
- observed objects near Jupiter and over a period of time plotted their positions
- discovered the four moons of Jupiter; Io, Europa, Ganymede and Callisto
- observed the Milky Way and noted that it was billions of stars, vastly increasing the amount of stuff in the heavens
32
What are the 3 important properties of telescopes?
1. Magnifying Power
2. Light Gathering Power
3. Resolving Power
33
Telescopes - Magnification
- this has the effect of making the object appear nearer than it really is
- makes small objects 'big'
- when we say 'big', in astronomical observations the angular dimensions of an object matter more than the physical dimensions
34
What is the equation for Magnification?
Magnification is given by the ratio of focal length (f) of the objective to the eyepiece
M = f objective / f eyepiece
35
Telescopes - Light Gathering Power (LGP)
- the ability to see faint objects, to capture photons
- in order to see dim objects the telescope has to collect as much light as possible
- this means using a large diameter lens or mirror
- it is directly proportional to the area (the square of the diameter)
36
Telescopes - Resolving Power
- the ability to detect fine details or to separate multiple sources in close proximity
- this property is limited by diffraction
- the resolving power depends on the telescope aperture and the wavelength
- shorter wavelength = better resolution
- large apertures provide better resolution
37
What are aberrations?
- all the effects that prevent a telescope from working perfectly
38
What are the two main aberrations that affect telescopes?
1) Chromatic Aberration
| 2) Spherical Aberration
39
Chromatic Aberration
- different wavelengths are focused to different points
40
Spherical Aberration
- light rays at different distances from the optical axis are focused to different points
41
How does Chromatic Aberration work?
- affects refactor telescopes since it is caused by dispersion
- solution is to use lenses made by two compensating materials
42
How does Spherical Aberration work?
- for many lenses, the light rays far from the optical axis are focused at different points compared to the rays close to the axis
- this problem can be solved by shaping lenses and mirrors very carefully
- this aberration affects both refractor telescopes and reflector telescopes
43
Converging Mirrors - Concave Mirror
- convenient for focussing light rays
| - the focal length of the mirror depends on the curvature
44
Newtonian Reflecting Telescope
- designed by Isaac Newton in 1668
- has a primary and secondary mirror
- the small, flat secondary mirror reflects the light out of the side of the telescope tube
- the primary mirror can be easily supported allowing diameters up to 5m
45
Cassegrain Telescope
- light rays are reflected by the primary mirror
- they are then sent back by a diverging secondary mirror and focused behind the telescope
- to do this, a hole has to be made in the primary mirror
- the result is a very compact telescope, a folded design
46
Prime Focus Telescope - Hale Telescope
- at Mount Palomar, California, USA
- diameter primary mirror = 5m
- primary mirror weight = 14,500kg
- focal length primary mirror = 16.8m
- observer / detector sits at the focus
- mirror substrate made in 1934 used pyrex to reduce any deformation as a result of heat
- highly polished aluminium mirror coating
- requires a Serrurier Truss to keep the optics from bending out of place
47
Schmidt Telescope
- invented by the Estonian optician Schmidt in 1930
- uses an aspherical Corrector Lens / Plate to reduce problems associated with a relatively short focal length mirror
- allows a wide field of view and are generally used as survey instruments and for comet and asteroid searches
- UK Schmidt Telescope located at Sidling Spring Observatory, Australia
48
Schmidt-Cassegrain Telescope
- Cassegrain telescopes use a corrector plate
- very popular design for consumer manufacturers since it is compact and lightweight with a relatively long focal length compared to a refracting telescope employing lenses
49
Telescope Mounts
- the mechanical structure that holds the telescope and can allow precise alignment to track astronomical objects
50
The Altitude-Azimuth Mount
- a simple mount used in many large observatories and amateur telescopes
51
The Equatorial Mount
- a mount whereby one rotational axis is aligned with the Earths rotational axis and so tracks star movements across the sky
- the Right Ascension drive rotates 360 degrees in 23 hours and 56 minutes, the time it takes the Earth to rotate
- declination is the angle from the Celestial equator
52
Large Observatories - Keck Telescopes
- the summit of Manua Kea in Hawaii
- contains several instruments, both cameras and spectrometers mainly near the infra-red
- the 2 telescopes can operate independently or together as an interferometer having an effective mirror size of 85cm
- equipped with adaptive optics
53
Large Observatories - Gran Telescopio Canaries
- the worlds largest single-aperture optical telescopes, finished in 2009, on La Palma in the Canary Islands
wavelength = optical to mid infra-red
54
Large Observatories - - Very Large Telescope
- four optical telescopes in an array on Cerro Paranal in the Atacama Desert, Chile
- each unit be used separately or all four used together via interferometry
- the mirror surface can be slightly deformed using an array of 150 actuators to fix for atmospheric disturbances and gravitational deformations
55
Active and Adaptive Optics
- the twinkling of stars at night or a desert mirage are both the result of atmospheric refraction
- this can limit the resolving power of a telescope
- solution is to use adaptive optics to continually adjust the mirror shape and thus correct the error
- active optics adjust the geometry of the primary mirror
56
What else affects telescopes as well as atmospheric refraction?
THE ATMOSPHERE
- it blocks some wavelengths of light
- adaptive optics cannot fix this problem
- SO we must go into space!
57
The Hubble Space Telescope
- launched by NASA in 1990
- named after Edwin Hubble
- orbits the Earth 15x a day
- Cassegrain focus (UV to IR)
- initially had severe spherical aberration problems until it was fixed in 1993 with a correcting lens
58
James Webb Space Telescope
- successor to the Hubble Space telescope
- designed to look for the first galaxies that formed after the Big Bang
- planned launch in 2018
- an infrared space telescope, with a mirror diameter of 6.5m
59
Electromagnetic Detectors - Eye
- the retina is a transparent layer of nervous tissue made up of millions of light receptors
- the retina also contains cells called rods (low light monochromatic vision) and cones (colour)
- the retina is connected to the brain by the optic nerve
60
Electromagnetic Detectors - Charged Couple Devices
- light can behave as a particle as well as a wave
- when a photon (light) hits an atom, it can knock an electron out of its orbit
- electrons held in 'wells' made from electric fields
- each silicon site is called a pixel
- the amount of charge at each site (electrons) is proportional to the incident light
- CCD's can work at near infra-red, visible and UV wavelengths
61
Electromagnetic Detectors - Mid/Far Infra-red Detectors
- this range of the EM spectrum corresponds to around 0.2mm, which we detect as heat
- photons at these wavelengths are absorbed by the material and its energy increases the temperature
- the temperature can be measured by the change to electrical conductivity
62
Electromagnetic Detectors - UV, X-Ray and Gamma Ray detectors
- all of these are more energetic than other EM radiation of higher wavelength
- have enough energy to remove one or more electrons from targets they hit
- can cause an electron to move up an energy level
- in some detectors, each photon causes a shower or avalanche of electrons
- the electrons produced are collected and the total amount of charge is proportional to the intensity of light
63
Electromagnetic Detectors - Gamma Rays
- generated by radioactive atoms and in nuclear explosions, in supernova
- used in medicine to kill cancerous cells because they are so harmful
64
Electromagnetic Detectors - X-Rays
- some x-ray detectors, called scintillation detectors absorb the energy and re-emit it as a small flash of visible light, measured on CCDs
65
Electromagnetic Detectors - Radio Wave
- the principle behind radio wave detection is to use a conductor, an antenna, which contains electrons and will oscillate with the same frequency of the incoming wave
- these oscillations produce a detectable current
66
Summary of the Atmosphere
- responsible for the 3 phenomena when making astronomical observations:
1) REFRACTION
- stars are artificially misplaced
- twinkling
2) SCATTERING
- short wavelengths scattered more than long wavelengths
- blue sky
3) ABSORPTION
- dimming
- extinction
67
Atmospheric Refraction summary
- light from stars passes through layers of different density
- higher density = slower light speed = more refraction
- it affects the apparent position of stars
- it also produces the twinkling effect of stars - atmospheric turbulence - therefore telescopes are generally located above the clouds up mountains
68
Atmospheric Scattering
- light can scatter off gas molecules in the atmosphere
- the amplitude of the transmitted wave is reduced
- the scattering depends on wavelength, with short wavelengths (blue) being scattered more
- the Sun looks red / yellow
- the atmosphere scatters blue light (400nm) 9 times more than red light (700nm)
- sunsets are red only because only red light can travel through the "thicker" atmosphere
69
Infra-Red Telescopes
- near IR telescopes can operate on Earth
- mid-IR and far-IR telescopes must be placed on satellite
PROBLEM - the telescope itself can emit more IR radiation than the astronomical sources it is trying to detect
SOLUTION - cool down the telescope instruments, using liquid helium in order to remove the IR background of telescope
70
Infra Red Astronomical Satellite (IRAS)
- first IR satellite launched in 1983
- Netherlands / UK / USA project
- no pointing - just surveying
- polar orbit - always 90 degrees from the Sun
- worked for 10 months until the liquid He ran out
- only 62 detectors
- very low resolution
- despite this, IRAS increased the number of catalogued objects by 70%, detecting around 350,000 infrared sources
71
Infra-Red Space Observatory (ISO)
- launched in 1995
- operated for 28 months
- similar in design to IRAS
- two modules (Payload and Service Module)
- observed at wavelengths from 2.5 micrometers to 240 micrometers
- used a diffraction spectrometer to detect different molecules
- mirror made of Beryllium which is a lightweight, stiff metal with low heat capacity so it cools quickly and efficiently
- orbital period = 24 hours
72
IRAS Discoveries
Some discoveries:
- disk of dust grains with a temp of 80K
- six new comets
- strong IR emission from interacting galaxies
- also made the first direct observation of the centre of the galaxy
73
ISO Discoveries
- Supernova remnant Cassiopeia A, an exploded star in our galaxy in 1680
- water in the Orion Nebula
- still in production at a rate 60 Earth oceans every day
- detected a large amount of cosmic dust, thought to be empty, between galaxies
- planet formation around dying stars
74
Spitzer
- named after Lyman Spitzer
- launched in 2003 and operated until 2009
- observed at wavelengths from 3 to 180 micrometers
- cassegrain design
Orbit:
- heliocentric - follows the Earth in its orbit around the Sun
- placed in 'deep space', where ambient temperatures are around 30-40K
- used nature to keep cool it so carried less liquid helium
- less coolant = less mass = cheaper!
- designed to have an Earth trailing orbit, where there is much less sources of IR noise and thus less coolant required
75
UV Telescopes
- UV light includes wavelengths between 10 - 350nm
- UV band is very important because H can be excited by these wavelengths
- Lyman Spitzer was a strong promoter os UV astronomy
- UV radiation is almost completely absorbed by the Earth's atmosphere so we need to place UV telescopes in space
- UV spectrum band is divided into 3 sub-bands: near Uv, far UV and extreme UV
- near UV = nearest to visible
- extreme UV = closest to the X-ray band
UV light is emitted by stellar objects at about 10,000 K
76
International Ultraviolet Explorer (IUE)
- NASA, SERC and ESA joint project
- 1978-1996 originally planned to operate for 3 years but used for 18 years
- 115 - 350nm wavelength band
- Cassegrain 45cm diameter primary mirror
- spectroscopy rather than imaging
- equipped with modified TV cameras
77
IUE Observations
- observed the planets in our solar system except for Mercury (too close to the Sun)
- Hailey's Comet was observed extensively
- astronomers could determine that it lost close to a billion tons of water as it passed through inner solar system
- observed Supernovae 1987a
78
Other UV telescopes
- Hubble Space Telescope
- The Far Ultraviolet Spectroscopic Explorer (FUSE)
- operated 1999-2007
- sensitivity band 90-120nm
79
X-Ray Telescopes
- x-rays are emitted by very hot matter with temperature exceeding 1 million K
- typical wavelength of x-rays is 0.1nm which is comparable to the distance between the atoms in a solid
- allows x-rays to penetrate inside solids and wide application in medicine and security
PROBLEM - the wavelengths of x-rays are so small, mirrors are transparent to them so how can they still be used for focussing?
SOLUTION - we need to trick x-rays photons to think that matter is more dense than it really is
- use grazing incidences
80
Chandra Observatory
- launched in 1999
- one of the most sophisticated X-ray telescopes built to date
- mirror roughness was 0.7nm
- smoothest surfaces ever produced
- optical telescopes typically have around 20nm roughness
81
What four science instruments did Chandra contained?
1. High Resolution Camera (HRC) - utilise micro channel plates
2. Advanced CCD Imaging Spectrometer (ACIS) - makes images and measures the x-ray energy
3. High Energy Transmission Grating Spectrometer (HETG) - positioned after mirrors and have fine grating period to diffract high energy x-rays
4. Low Energy Transmission Grating (LETG) - positioned after mirrors and have regular spacing
82
X-Ray Multi-Mirror Mission-Newton
- the European Space Agency XMM-Newton mission is very similar to Chandra
- sensitive to X-rays and also part of the UV spectrum
- launched in 1999
- weighs 3800kg, 10m long and contains 3 x-ray telescopes
- orbits the Earth once every 48 hours in a elliptical orbit
83
Gamma Ray detectors
- lowest energy gamma rays are about 100,000 times more energetic than visible light photons
- produced from radioactive decay or nuclear reactions
- wavelength range is t work with gamma rays
- most gamma rays will pass through the detector
- even 6cm of concrete may only reduce the intensity by about 50%
- just have to hope that sufficient gamma rays interact with the material in the detector
84
Scintillators
- when a gamma ray hits certain materials, like plastics or even liquids, the material can emit light
- this is called Scintillation and occurs because the gamma ray can easily ionise the atoms in the detector
- the photomultiplier s detect the light given off when the excited electron recombines with the ionised atom
eg PVT and Lead Tungstate
85
How is Čerenkov radiation produced?
- gamma rays interact with atoms in the upper atmosphere to create showers of charged particles
- these energetic particles travel close to the speed of light in a vacuum (c = 300 million m/s)
- in the atmosphere, where the speed of light is slower than the vacuum, the particles create a shock wave of light
- this is analogous to a sonic boom for fast moving aircraft which move faster than the speed of sound
- the blue light given off in the reactor pools at nuclear power stations
86
Čerenkov Detectors
- detectors on the ground can see the Čerenkov radiation and infer information about the gamma ray
87
WHIPPLE Air Čerenkov Detectors
- the WHIPPLE detectors in Arizona measure Čerenkov radiation from air showers
- radiation is focussed onto photomultipliers at the telescope focus
88
VERITAS
Very Energetic Radiation Imaging Telescope Array System
- successor to WHIPPLE
- located at Fred Lawrence Whipple Observatory in Arizona
- an array of four 12m detectors, based on the same design as WHIPPLE
89
Common Gamma Ray Observatory
- alternatively, can go into space to observe gamma rays
- launched in 1991
- weighed 17,00kg
- de-orbited in 2000
90
What techniques are used to refract or reflect gamma rays?
- can't use grazing incidences!
1. Partial or total absorption of the gamma ray energy within a high-density medium such as a large crystal of sodium iodide
2. Collimation using heavy absorbing material, to block out most of the sky and realise a small field of view
3. At sufficiently high enough energies, utilisation of the conversion process from gamma rays to electron-positron pairs in a spark chamber which leaves a tell-tale directional signature of the incoming photon
91
Origin of Radio Astronomy - Janksy
- started in 1931 when Janksy built up a directional antenna to study the origin of noise in radio broadcasting
- the study was commissioned by Bell laboratories
92
Origins of Radio Astronomy
- directional antenna = an antenna whose sensitivity is maximum in one direction
- this means you can determine the origin of the radio emission
- one of the noises that Janksy detected occurred during the day BUT each day the noise started 4 minutes earlier than the day before
- this implied that the source was one of cosmic origin
- radio waves are long wavelengths so rough surfaces are allowed
- however long wavelength requires a large detector otherwise suffer from low resolution
93
Examples of Modern Radio Telescopes
Effelsberg 100m diameter radio telescope in Germany
76m diameter radio telescope at Jodrell Bank in Cheshire
94
Aricebo Observatory
- the world's largest single aperture telescope
- 305m in diameter
- 1974 - attempt to communicate with potential extraterrestrial life in globular cluster M13
- message of 23x73 pixels
- not possible to move the dish
- instead, the detector is moved around to observe different objects in the sky
95
Limited Resolution of Optical Resolution
- optical telescopes can have a telescope diameter millions, even billions, of times larger than the wavelength of light they observe - high resolution
- radio wavelengths range from 1mm to 100's km
- depending on the wavelength, even very large detectors may only resolve objects the size of the full moon
96
Long Baseline Interferometry
- in order to increase the resolution of telescopes astronomers build arrays of radio telescopes
- it is possible to interfere the signals between them to provide better resolution of a source
- the VLBA consists of 10 telescopes placed all over the Earth can have an interferometer size of 8600km
- this means it can resolve objects that are less that 1/1000th of an arc second
- even better than optical telescopes!!!
97
How does Long Baseline Interferometry?
- signals from each telescope are digitally stored for analysis
- each telescope also has an accurate atomic clock to time stamp the incoming signals
- the telescopes are in different positions so there can be a delay depending on their relative orientation to the source
- the data can be analysed later to pinpoint the location of the source
98
Very Large Array
- 27 telescopes in New Mexico, USA
- each unit telescope is 25m in diameter
- the telescopes positions can be adjusted to achieve a variety of resolutions
99
Very Long Baseline Array (VLBA)
- 10 radio telescopes spread over North America
- can also be combined with four more telescopes across the world, including Aricebo and Effelsberg to give the High-Sensitivity Array
100
What are the observations from the VLA and VLBA?
- two very large (bigger than galaxy) jets of relativistic particles ejected from host galaxy
- strong radio emission from lobes
- Quasi-Stellar Radio Sources (Quasars) can be so bright they drown out light from galaxy surrounding them
- jets of particles ejected from accretion disk surrounding black hole at centre
101
What are Neutrinos?
- subatomic particles that are electrically neutral
- not affected by electromagnetic forces
- they are the products of the nuclear reactions within stars
- there are also lots of them, around 50 billion passing through a 1cm(2) area every second
- so weakly interacting that they can travel faster through the Sun from the core where they were created
- pass straight through the Sun in just 2 seconds
- very difficult to detect as they can travel through the whole Earth with almost no chance of colliding with an atom
102
Neutrinos and Supernovae
- supernovae are an intense source of neutrinos
- a flash of neutrinos are produced when the star explodes
- the most numerous particles in the universe, but the majority where produced during the Big Bang
- need to detect them when studying solar physics, supernovae and the origin of the universe
- HOWEVER, since they so weakly interact only a few events detected each day, even though the numbers of neutrinos is so high!
103
Super Kamiokande
- located in a mine under Mount Kamioka in Japan
- the mountain helps to reduce the background from gamma ray showers
- 50,000 tonnes of water
- 11,000 photomultiplier tubes detect the Čerenkov light from neutrino interactions with the water
- a boat is needed to service the photomultiplier tubes
104
What signals are given off by neutrinos in photomultipliers?
- give a very distinctive signal in these tubes
- Čerenkov cone
- Super Kamiokande detected neutrinos from SN 1987a, a supernova observed in the Large Magellanic Cloud on February 1987
105
What are the other neutrino detectors?
- the Sea and Antarctic can host kilometre size detectors
PROBLEM:
- natural radiation limits the energy
- construction can be difficult
- light can be emitted by marine organisms / animals
106
What is ICE CUBE?
- a neutrino observatory at the South Pole
- has been taking data since 2006
- a 1km(3) array of around 5000 photomultiplier tubes buried 1.5km below the surface
- detect neutrinos via their Čerenkov radaiton to learn about:
> gamma ray burst sources
> neutrino oscillations and high energy particle physics
> dark matter
107
What were the Early Gravitational Wave Detectors?
- the very first design were resonant bar detectors
| - they excite the resonances of the test masses which can be monitored
108
Modern Gravitational Wave Detectors
- 1978 - a scientist had the idea to detect gravitational waves using a laser interferometer to monitor the distance between suspended masses
109
LIGO
- in the US, there are 2 4km sized laser interferometric detectors for gravitational wave detection
1. Livingstone, Louisiana
2. Hanford, Washington
- has recently been upgraded to advanced LIGO, with mirrors suspended by four silica fibres to get rid of unwanted thermal noise
- one of the largest high vacuum systems in the world
- removes acoustic noise
