Saturday, April 24, 2010

What physical processes do we observe with LOFAR?

LOFAR stands for LOw-Frequency ARray, and it is a radio telescope. This means it is sensitive to electromagnetic waves whose wavelengths are very long, typically longer than one metre, corresponding to frequencies of 250 MegaHertz (MHz) or less. Other examples of electromagnetic radiation are optical and infrared light, X-rays and gamma-ray radiation. All of these
have much shorter wavelengths (higher frequencies) than radio emission.

The waves detected by LOFAR are of the same type as those used by FM radio. When you tune to 92-95 FM for Radio 4, that's actually tuning the receiver in your radio to 92-95 MHz. In fact LOFAR has a gap between 80-120 MHz. It does not observe at these frequencies since the signal from the FM radio stations overwhelms all other signals, making it virtually impossible to detect any emission from space.

Electromagnetic waves are radiated when a charged particle is accelerated. An example is an electron that is suddenly accelerated by a change in an electric field or a magnetic field. It will radiate some energy away in the form of electromagnetic waves.

In a series of 3 blog posts over the next couple of weeks I will summarise three important physical processes that can be observed with LOFAR to study astrophysical objects outside of our Solar System: free-free emission, synchrotron radiation and the hydrogen 21cm transition.

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