Microwave: The Cosmic Microwave Background (CMB). Shortly after the Big Bang, the Universe cooled enough to allow atoms to form. After this point in time, radiation was able to travel freely through the Universe. Initially, the radiation (known as the CMB) from this epoch had a short wavelength, however as the Universe expanded the wavelength increased. Today, the finger print of the Big Bang is best seen at microwave wavelengths. Below is an image of the CMB made by the Very Small Array. It is effectively a view of the universe at a minute fraction of its current age X-rays: The Crab Pulsar. At the centre of the Crab Nebula is a pulsar – a rapidly rotating neutron star (the compact remains of a dead, massive star) that emits a beam of radio waves. The beam is detected as a pulse of radiation as it sweeps past an observer – similar to a flashing lighthouse. The strong magnetic field around the pulsar propels material in the nebula at speeds close to the speed of light. Heated up, this material emits X-rays. Infrared: The Constellation Orion. Vast regions of dust and gas are warmed by stars and glow brightly in the infrared region of the spectrum. The bright area in the lower right of the image below is Orion’s sword, containing the Great Orion Nebula. Can you spot the star Betelgeuse, which shows up as a blue/white dot in the upper centre? The ring to the right of Betelgeuse is the remnant of a supernova (the dying explosion of a giant star). Image courtesy IRAS Image courtesy VSA Visible: The Eskimo Nebula. The end of the life of a low mass star, like our sun, is marked by the formation of a planetary nebula. When this star ran out of fuel, it threw off its outer layers of gas. This image was taken by the Hubble space telescope, tracing emission from nitrogen (red), hydrogen (green), oxygen (blue) and helium (violet). Image courtesy NASA/HST Image courtesy Chandra Image courtesy NRAO/AUI Radio waves: The Whirlpool Galaxy. A spiral galaxy to be found in the constellation of Canes Venatici. This image was made at radio wavelengths and shows the location of cold gas within the galaxy. The bright red patch on the left of the image is a distant quasar, a type of early galaxy containing a massive black hole. Ultraviolet: The galaxy M94. Here clusters of bright, young stars have formed a ring nearly 7,000 light years across. The stars are very hot and show up in the ultraviolet region of the spectrum. The image was made with a telescope carried aboard a space shuttle. Image courtesy NASA/UIT The Gamma Ray Universe. The highest energy objects in the sky emit gamma rays. Our galaxy, the Milky Way, is the bright band across the image below. The bright spots within it are pulsars (rapidly rotating dead stars; see X-rays above). Other bright points are distant quasars (old galaxies containing massive black holes). Many of the faint sources have an unknown origin. Image courtesy NASA/CGRO Sub-millimetre: Cassiopeia A. At the end of their lives, massive stars explode as supernovae, ejecting large amounts of dust and gas. This image was made with the James Clerk Maxwell Telescope at sub- millimetre wavelengths. It shows the position of cold dust (18K) that was thrown out from a supernova witnessed 300 years ago. Image courtesy JCMT/SCUBA radiomicrowave infrared visible ultraviolet X-raygamma ray Long wavelength Low frequency Short wavelength High frequency sub-mm >10 -1 m m10 -3 m10 -4 m10 -7 m10 -8 m m m< m10 -5 m m m m The Electromagnetic Spectrum: Astronomy