BAS Lecture: Friday May 4th 2007
Prof. Mark Birkinshaw
ALMA & SKA
Mark presented an overview of two of the biggest and most ambitious projects in Radio astronomy that are being developed over the next decade. ALMA, the Atacama Large Millimetre/sub-millimetre Array and SKA, the Square Kilometre Array will revolutionise the radio astronomy picture of the Universe
Interferometry
When radio telescopes are compared to optical telescopes the one obvious drawback is in the image resolution: this is due to wavelength of radio waves being much longer than those of visible light by a factor of 105. Therefore to build a radio telescope with similar resolving power as a 5m optical telescope, its receiving dish would need to be around 500km in diameter! To get around this problem radio astronomers use a technique called interferometry. This is where the signals from two or more radio telescopes separated by some distance are combined; if separated by 500km they would act as points on a virtual 500km dish. Another technique used by radio astronomers is aperture synthesis; this is where the radio telescope tracks an object over a time period. As the Earth spins on its axis the telescope gets a slightly different picture of the object. This extra information helps to resolve the image.
ALMA
Telescope
The ALMA telescope will consist of 50 antenna with a 12m diameter dish giving it a high collecting area and will operate between 31 and 950 GHZ that is equivalent to radio wavelengths between 1.0cm and 0.3mm. It will also have smaller antennas to cover larger regions allowing for flexible configuration. The telescope will have ultra high resolution and sensitivity and have high spectral resolution; being able to measure velocities to 10m/s by Doppler effect. It will be sited in North Chile at a place called Chajnantor in the Atacama Desert at an altitude of 5000m.
Science
The ALMA telescope will be able to perform a variety of scientific experiments.
Planetary atmospheres: monitor the weather and atmospheric chemistry on Mars, measure the thermal structure of the Jovian atmosphere, the atmosphere of Titan, volcanoes on Io and the weather on Pluto.
Comets: examine the processes involved in gas venting when comets are heated by the Sun. Extra solar planets: detect Jupiter size planets at three parsecs, study star envelope ejecta, measure velocities in gas clouds to give a better picture of these structures and to examine planetary nebulae.
Magellanic Clouds: study the different types of star birth and death in neighbouring galaxies. Supergiants: study the structure of these massive stars, like Betelgeuse.
Also: Supernovae remnants, star formation in merging galaxies, planet formation and radio galaxies.
SKA
Telescope
The SKA telescope, one of a new concept of radio telescope design that is based on new technology that utilises thousands of radio antenna in a distributed configuration.
There are two main antenna designs: a more conventional steerable 12m dish that will handle the medium to high frequency signals and the less conventional aperture arrays that will handle the low frequency signals. This new technology and configuration means that the telescope can operate on radio frequencies between 100 to 28000Mhz and give it 100 times the sensitivity and 100 times the resolution that of the Very Large Array (VLA). The telescope will be either sited in Australia and New Zealand or South Africa and other African countries.
Science
The telescope will be used to study: structure formation in the early Universe, the effects of dark energy on the position and velocity of billions of galaxies, the timings of pulsars in order to detect gravitational waves using general relativity, synchrotron radiation and polarisation to understand the origins of cosmic magnetism, the formation of proto-planets that could harbour life and survey for intelligent life by detecting their “man-made” radio emissions.