Radio Astronomy below the Clouds

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Radio Astronomy below the Clouds!
Peter Barthel Kapteyn Astronomical Institute,
Groningen NOVA Education Committee
by day AND by night!!
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Radiation
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What is radiation?
- handy in the dark .. - other name for
electromagnetic wave - the only way for
astronomers to investigate the universe
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Properties of radiation

• Wave character (like sound)
• Particle character photons
• Propagates even through vacuum
• Vacuum velocity c 299.792.458 m/s (about
  108 million km/h) in other media lower

Radiation transports energy every photon
contains energy, and the shortest wavelengths
photons are richest in energy.
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Light as wave phenomenon
Light propagates even through vacuum
Waves can interfere so can light!
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Radiation as a wave
E h n
Energy constant times frequency
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Radiation as particles
Ccd
A CCD (Charge Coupled Device) counts photons
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Rainbow
White light contains a rainbow of colors, in
which every color has its own specific wavelength
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The spectrum
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The electromagnetic spectrum
Visible light is just a very small part of the
e.m. spectrum
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Ultraviolet
(10 390 nanometer)
More energetic than visible light Ozone layer
protects, but we do get tan!
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X-rays
(0.03 3 nanometer)
Penetrates deep medical use, plus luggage .
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Gamma rays
( shorter than 0.03 nanometer)
Very energetic! Released in radio-active decay
dangerous.
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Infrared
(720 nanometer 300 micrometer)
Less energetic than light heat
radiation Remote control security devices
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Microwaves
(300 micrometer 3 centimeter)
Radar you know ..
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Radio waves
(3 centimeter - kilometers)
E.m. radiation with longest wavelengths Use
radio, communication (gsm), ..
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Radio radiation comes in different types

• Synchrotron continuum
• Thermal continuum (ff, or bremsstrahlung)
• Line radiation, from atoms or molecules
• Black body radiation (Planck law)
• Spectrum discriminates!

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Black body radiation
Hot, warm, cool, cold bodies radiate X-rays
through radio waves
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White hot
Red hot
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3K background radiation peaks at
microwaves other objects peak in mm, submm, or
far-IR
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Doppler effect
Lower pitch
Higher pitch
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Doppler effect
Doppler shift (hence velocity) can be measured
using line radiation
Object in rest
Object receding redshift!
(object approaching blueshift)
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Our atmosphere
Protects against dangerous radiation from space
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Atmospheric windows

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Larger implies sharper
A large telescope provides a large magnification,
or resolution
wavelength
l
Diffractionlimit ?
D
diameter
Angles are being measured in degrees, arcminutes
(degree/60) and arcseconds (arcmin/60)
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However optical seeing is limiting factor .
Diffraction limit cannot be reached, due to
atmospheric troubling. Solutions - go into
space - use adaptive optics
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Hubble Space Telescoop
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The other window RADIO
Detect the electric field variations, using
sensitive reflecting antenna plus receiver
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Parkes
Radio waves do not suffer from seeing
effects. In principle one could increase the
telescope diameter ad libitum in order to gain
resolution
However, at long radio wavelengths big dishes
such as Parkes 64m still have resolution of tens
of arcminutes
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The MPI 100m telescope in Effelsberg, near Bonn,
the largest steerable dish in the world
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Still larger Arecibo 300m
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Synthesis telescope
technique that won Nobel prize!
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Very Large Array
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Westerbork Synthesis Radio Telescope
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Many interferometry pairs!!
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MERLIN provides baselines up to several hundreds
of kms
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Next step decouple telescopes and perform
correlation of the signals (the actual
interferometry) at a later stage, in central
processor
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VLBI Very Long Baseline Interferometry (since
1970s)
NRAO VLBA
Angular resolutions down to milliarcseconds can
be achieved!
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The interferometry is performed at a central
processor, using magnetic tapes written at each
participating radio telescope. Dwingeloo (JIVE)
is European facility, VLBA uses Socorro (New
Mexico)
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The 25m Dwingeloo telescope was in 1957 for a
short period of time the largest in the world.
Major task was mapping of the Milky Way, our
Galaxy.
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Electronflip
The structure of our Milky Way galaxy
we learned from the radio astronomers
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Kepler rotatie
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Not uniformly distributed but in HI arms!!
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Schematic view of Milky Way

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Messier 101

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Andromeda radio
M31, in Andromeda
Radio, 21 cm
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The other Local Group spiral, M33
Note the power of the Doppler shift!
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Galaxies stars, gas and dust
Messier 83

( and dark matter)
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Radio astronomers uncovered Active Galaxies

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Gigantic radio-emitting clouds around distant
galaxies

1954 CYGNUS A
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CENTAURUS A

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VIRGO A

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Radio Luminosities, in lobes and jets amount up
to 1040 W

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Misleading serene beauty ..

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slumbering power house in the Sombrero galaxy

Radio- and X-ray nucleus!
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The ultimate source is hidden deep in the nucleus

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on the light-day scale

?AGN
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NATURE OF THE ACTIVITY

• Hot accretion disk
• Massive black hole
• Hot gas
• Radio jets

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The central mass in M87 weighs over 109 Msun

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In M106 nearly 108 Msun

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Future developments
Atacama Large Millimeter Array
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SKA
LOFAR
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In near future optical interferometry
while VLBI in space is also being explored
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INTERMEZZO WAARNEMEN
Astronomy Astrophysics

• Observing e.m. radiation and interpretation of
  this radiation

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The power of telescopes

• compare human eye
• (8000mm/8mm)2 106
• long integration time another factor 104
  to 105
• 1011 more sensitive!

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Radiowaarnemingen zijn vrij van atmosferische
twinkeling m.b.v. interferometrie kan de
hoekresolutie worden opgevoerd tot boogseconden
(WSRT) of milliboogseconden (VLBI)