Universe The

Document Sample
Universe The Powered By Docstoc
					 The Universe at different wavelengths


  One way of extending our perceptions of the Universe is to
  look at many different wavelengths, seeking to capture the
 emissions of photons of differing frequencies. By associating
these photons with different processes at work, a wider picture
                  of the Universe emerges.
Three radio telescopes tuned to 408 MHz (close to a broadcast
television channel). Near this frequency, cosmic radio waves are
generated by high energy electrons spiralling along magnetic
fields. In the resulting false colour image, the galactic plane runs
horizontally through the centre, but no stars are visible. Instead,
many of the bright sources near the plane are distant pulsars, star-
forming regions and supernova remnants, while the grand looping
structures are pieces of bubbles blown by local stellar activity
The image shows the temperature distribution of the
cosmic microwave background radiation over the celestial
sphere, as observed by the COBE satellite at a wavelength
of 5.7 mm, once the effect of the Earth’s motion through
the background radiation has been removed.
Three major sources contribute to the far-infrared sky: our Solar System,
our Galaxy and our Universe. This image, in false colour, is the highest
resolution projection yet created of the entire far-infrared sky (60 –
240 mm). Our Solar System shows itself most prominently by the S-
shaped blue sash called zodiacal light, created by small pieces of rock
and dust orbiting between the Sun and Jupiter. The thin band of light-
emitting dust that crosses the middle of the image indicates the disc of
our Galaxy.
This is composite image taken from Earth orbit, well inside our
Milky Way Galaxy. In light just a little too red for human eyes to
see – 'near infrared' electromagnetic radiation – the disc and centre
of our Galaxy stand out, giving an appearance probably similar to
seeing our Galaxy from the outside in visible light.
This panorama view of the sky is really a drawing. It was made in the
1940s under the supervision of astronomer Knut Lundmark at the
Lund Observatory in Sweden. To create the picture, draftsmen used a
mathematical distortion to map the entire sky onto an oval shaped
image with the plane of our Milky Way Galaxy along the centre and
the north galactic pole at the top. 7000 individual stars are shown as
white dots, size indicating brightness.
 UV whole sky map. The plot is in galactic coordinates (the plane
of our Galaxy runs horizontally through the middle) and reveals the
positions of distant quasars, galaxies, stars, star clusters, nebulae,
novae and supernovae – testifying to IUE's broad range of
capabilities. The ecliptic plane is also visible running diagonally
through the centre, traced out by many observations of solar system
objects.
X-rays are about 1000 times more energetic than visible light photons
and are produced in violent and high temperature astrophysical
environments. Instead of the familiar steady stars, the sky would
seem to be filled with exotic binary star systems composed of white
dwarfs, neutron stars and black holes, along with flare stars, x-ray
bursters, pulsars, supernova remnants and active galaxies.
This processed image represents a map of the entire sky at photon
energies above 100 MeV. These gamma-ray photons are more than 40
million times more energetic than visible light photons and are
blocked from the Earth's surface by the atmosphere. In the early 1990s
NASA's Compton Gamma Ray Observatory, in orbit around the Earth,
scanned the entire sky to produce this picture. A diffuse gamma-ray
glow from the plane of our Milky Way Galaxy is clearly seen across
the middle. The nature and even distance to some of the fainter
sources remain unknown
Diffuse gas clouds laced with radioactive aluminium atoms (Al 26) line
the plane of our Milky Way Galaxy! Relying on the Compton Effect,
the COMPTEL instrument onboard NASA's immense orbiting
Compton Gamma Ray Observatory can 'see' the 1.8 MeV gamma rays
emitted by the radioactive decay. The radioactive Al 26 clouds are seen
to lie in clumps near the plane, with some slightly above and below it.
The brightest feature looks like a mysterious inverted 'V', just to the
left of centre.
Interstellar space is filled with extremely tenuous clouds of gas which are
mostly hydrogen. The proton and electron in hydrogen spin like tops but
can have only two orientations; spin axes parallel or antiparallel. It is a
rare event for hydrogen atoms in the interstellar medium to switch from
the parallel to the antiparallel configuration, but when they do they emit
radio waves with a wavelength of 210 mm and a corresponding
frequency of exactly 1420 MHz. Radio telescopes tuned to this
frequency have mapped the neutral hydrogen in the sky.
Our Earth is not at rest. The Earth moves around the Sun. The Sun
orbits the centre of the Milky Way Galaxy. The Milky Way Galaxy
orbits in the Local Group. The Local Group falls toward the Virgo
Cluster of galaxies. But these speeds are less than the speed that all of
these objects together move relative to the microwave background. In
this all-sky map, microwave radiation in the Earth's direction of
motion appears blueshifted and hence hotter, while radiation on the
opposite side of the sky is redshifted and colder