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Exploring the Cosmos 1Y > Mapping the Universe > Flashcards

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
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2
Q

What is observational astronomy?

A
  • astronomy is a largely observational science

- we locate and study astronomical objects based on their emissions

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3
Q

What are the different types of Electromagnetic Radiation?

A 
Radio 
Microwave 
Infrared 
Visible 
Ultraviolet 
X-Ray 
Gamma Rays
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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
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5
Q

What are the characteristics of a light wave?

A
  1. Amplitude
  2. Wavelength
  3. Frequency
  4. Speed
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6
Q

Characteristics of Light Waves - Amplitude

A
  • the maximum value that the wave takes

- the larger the amplitude, the brighter the light

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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
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8
Q

Characteristics of Light Waves - Frequency

A
  • the number of times the wave cycle repeats per second

- measured in cycle/s or Hertz

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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)
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10
Q

How are frequency and wavelength related to the speed of the wave?

A

Speed = frequency x wavelength

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11
Q

Waves and Particles - LIGHT

A
  • although light can be described by a wave, it also exhibits particle-like behaviour
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12
Q

Young and Fresnel

A
  • early 1800’s

- proved the existence of the wave-like property of light through interference

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13
Q

Einstein

A
  • 1905

- showed that light can also possess particle-like properties

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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)
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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
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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
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17
Q

How can light be split into its constituent wavelengths?

A

using either a:

  • Prism
  • Diffraction Grating
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18
Q

How do Prisms work?

A

by Refraction and Dispersion

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19
Q

How do Gratings work?

A

work with Diffraction and Interference

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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)
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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)
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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
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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
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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

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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)

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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
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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
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28
Q

What are the different types of Converging Lenses?

A
  1. Biconvex
  2. Plano-convex
  3. Convex-concave
  • bring light rays to a focus
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29
Q

What are the different types of Diverging Lenses?

A
  1. Meniscus
  2. Plano-concave
  3. Biconcave
  • project light rays outwards
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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
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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
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32
Q

What are the 3 important properties of telescopes?

A
  1. Magnifying Power
  2. Light Gathering Power
  3. Resolving Power
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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
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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

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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)
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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
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37
Q

What are aberrations?

A
  • all the effects that prevent a telescope from working perfectly
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38
Q

What are the two main aberrations that affect telescopes?

A

1) Chromatic Aberration

2) Spherical Aberration

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39
Q

Chromatic Aberration

A
  • different wavelengths are focused to different points
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40
Q

Spherical Aberration

A
  • light rays at different distances from the optical axis are focused to different points
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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
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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
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43
Q

Converging Mirrors - Concave Mirror

A
  • convenient for focussing light rays

- the focal length of the mirror depends on the curvature

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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
  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
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
  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

Exploring the Cosmos 1Y (4 decks)

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