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
Q
What is Interference and what are the two different types?
A
- describes the interaction of two or more waves with each other
1) Constructive
(bright regions)
2) Destructive
(dark regions)
26
Q
Interference of White Light
A
- 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
Q
Why is the mount on which the telescope attached to so important?
A
- it needs to track an object accurately over long durations of time
28
Q
What are the different types of Converging Lenses?
A
- Biconvex
- Plano-convex
- Convex-concave
- bring light rays to a focus
29
Q
What are the different types of Diverging Lenses?
A
- Meniscus
- Plano-concave
- Biconcave
- project light rays outwards
30
Q
Refracting Telescopes
A
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
Q
What were Galileo’s discoveries?
A
- 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
Q
What are the 3 important properties of telescopes?
A
- Magnifying Power
- Light Gathering Power
- Resolving Power
33
Q
Telescopes - Magnification
A
- 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
Q
What is the equation for Magnification?
A
Magnification is given by the ratio of focal length (f) of the objective to the eyepiece
M = f objective / f eyepiece
35
Q
Telescopes - Light Gathering Power (LGP)
A
- 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
Q
Telescopes - Resolving Power
A
- 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
Q
What are aberrations?
A
- all the effects that prevent a telescope from working perfectly
38
Q
What are the two main aberrations that affect telescopes?
A
1) Chromatic Aberration
2) Spherical Aberration
39
Q
Chromatic Aberration
A
- different wavelengths are focused to different points
40
Q
Spherical Aberration
A
- light rays at different distances from the optical axis are focused to different points
41
Q
How does Chromatic Aberration work?
A
- affects refactor telescopes since it is caused by dispersion
- solution is to use lenses made by two compensating materials
42
Q
How does Spherical Aberration work?
A
- 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
Q
Converging Mirrors - Concave Mirror
A
- convenient for focussing light rays
- the focal length of the mirror depends on the curvature
44
Q
Newtonian Reflecting Telescope
A
- 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
Q
Cassegrain Telescope
A
- 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
Q
Prime Focus Telescope - Hale Telescope
A
- 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
Q
Schmidt Telescope
A
- 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
Q
Schmidt-Cassegrain Telescope
A
- 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
Q
Telescope Mounts
A
- the mechanical structure that holds the telescope and can allow precise alignment to track astronomical objects
50
Q
The Altitude-Azimuth Mount
A
- a simple mount used in many large observatories and amateur telescopes
51
Q
The Equatorial Mount
A
- 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
Q
Large Observatories - Keck Telescopes
A
- 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
Q
Large Observatories - Gran Telescopio Canaries
A
- the worlds largest single-aperture optical telescopes, finished in 2009, on La Palma in the Canary Islands
wavelength = optical to mid infra-red
54
Q
Large Observatories - - Very Large Telescope
A
- 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
Q
Active and Adaptive Optics
A
- 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
Q
What else affects telescopes as well as atmospheric refraction?
A
THE ATMOSPHERE
- it blocks some wavelengths of light
- adaptive optics cannot fix this problem
- SO we must go into space!
57
Q
The Hubble Space Telescope
A
- 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
Q
James Webb Space Telescope
A
- 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
Q
Electromagnetic Detectors - Eye
A
- 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
Q
Electromagnetic Detectors - Charged Couple Devices
A
- 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
Q
Electromagnetic Detectors - Mid/Far Infra-red Detectors
A
- 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
Q
Electromagnetic Detectors - UV, X-Ray and Gamma Ray detectors
A
- 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
Q
Electromagnetic Detectors - Gamma Rays
A
- generated by radioactive atoms and in nuclear explosions, in supernova
- used in medicine to kill cancerous cells because they are so harmful
64
Q
Electromagnetic Detectors - X-Rays
A
- 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
Q
Electromagnetic Detectors - Radio Wave
A
- 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
Q
Summary of the Atmosphere
A
- 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
Q
Atmospheric Refraction summary
A
- 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
Q
Atmospheric Scattering
A
- 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
Q
Infra-Red Telescopes
A
- 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
Q
Infra Red Astronomical Satellite (IRAS)
A
- 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
Q
Infra-Red Space Observatory (ISO)
A
- 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
Q
IRAS Discoveries
A
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
Q
ISO Discoveries
A
- 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
Q
Spitzer
A
- 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
Q
UV Telescopes
A
- 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
Q
International Ultraviolet Explorer (IUE)
A
- 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
Q
IUE Observations
A
- 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
Q
Other UV telescopes
A
- Hubble Space Telescope
- The Far Ultraviolet Spectroscopic Explorer (FUSE)
- operated 1999-2007
- sensitivity band 90-120nm
79
Q
X-Ray Telescopes
A
- 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
Q
Chandra Observatory
A
- 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
Q
What four science instruments did Chandra contained?
A
- High Resolution Camera (HRC) - utilise micro channel plates
- Advanced CCD Imaging Spectrometer (ACIS) - makes images and measures the x-ray energy
- High Energy Transmission Grating Spectrometer (HETG) - positioned after mirrors and have fine grating period to diffract high energy x-rays
- Low Energy Transmission Grating (LETG) - positioned after mirrors and have regular spacing
82
Q
X-Ray Multi-Mirror Mission-Newton
A
- 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
Q
Gamma Ray detectors
A
- 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
Q
Scintillators
A
- 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
Q
How is Čerenkov radiation produced?
A
- 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
Q
Čerenkov Detectors
A
- detectors on the ground can see the Čerenkov radiation and infer information about the gamma ray
87
Q
WHIPPLE Air Čerenkov Detectors
A
- the WHIPPLE detectors in Arizona measure Čerenkov radiation from air showers
- radiation is focussed onto photomultipliers at the telescope focus
88
Q
VERITAS
A
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
Q
Common Gamma Ray Observatory
A
- alternatively, can go into space to observe gamma rays
- launched in 1991
- weighed 17,00kg
- de-orbited in 2000
90
Q
What techniques are used to refract or reflect gamma rays?
A
- 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
Q
Origin of Radio Astronomy - Janksy
A
- 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
Q
Origins of Radio Astronomy
A
- 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
Q
Examples of Modern Radio Telescopes
A
Effelsberg 100m diameter radio telescope in Germany
76m diameter radio telescope at Jodrell Bank in Cheshire
94
Q
Aricebo Observatory
A
- 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
Q
Limited Resolution of Optical Resolution
A
- 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
Q
Long Baseline Interferometry
A
- 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
Q
How does Long Baseline Interferometry?
A
- 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
Q
Very Large Array
A
- 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
Q
Very Long Baseline Array (VLBA)
A
- 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
Q
What are the observations from the VLA and VLBA?
A
- 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
Q
What are Neutrinos?
A
- 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
Q
Neutrinos and Supernovae
A
- 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
Q
Super Kamiokande
A
- 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
Q
What signals are given off by neutrinos in photomultipliers?
A
- 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
Q
What are the other neutrino detectors?
A
- 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
Q
What is ICE CUBE?
A
- 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
Q
What were the Early Gravitational Wave Detectors?
A
- the very first design were resonant bar detectors
- they excite the resonances of the test masses which can be monitored
108
Q
Modern Gravitational Wave Detectors
A
- 1978 - a scientist had the idea to detect gravitational waves using a laser interferometer to monitor the distance between suspended masses
109
Q
LIGO
A
- in the US, there are 2 4km sized laser interferometric detectors for gravitational wave detection
- Livingstone, Louisiana
- 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
