INTRODUCTION
When the feeling of tranquility hits you as the light from the stars pierces through your eyes, everything feels magical and mysterious. What if I say there is more magic to this, more than our eyes can reveal? The light that we see belongs to the visible region, or in other words the visible wavelength is the one that our eyes can sense. There are some invisible waves that can give us more information about the cosmos, of which radio frequencies are of significant prominence. These radio waves that we are going to talk about are the same that your mobile, TV, or radio receives. They have longer wavelengths and lower frequencies compared to that of the visible waves. Any electromagnetic wave with a wavelength greater than 1 mm is a radio wave. Have a look at the Electro-Magnetic Spectrum to know where the radio waves stand.
Electromagnetic spectrum (Image Credits- mini physics)
WHAT IS RADIO ASTRONOMY?
We all know about visible-light astronomy, which can be experienced even at home by observing the night sky through small telescopes. The telescopes use visible light that falls on it and hence when we point it towards an object of our choice, we see it. The clarity of the view depends upon the telescope’s resolution. What will happen when the light is invisible, like radio waves? Our universe sends us light in almost all wavelengths but many don’t reach us because of our atmosphere. We do receive radio waves from distant objects in the sky. The telescope that we use cannot sense it and so we have to build a radio telescope using antennas to receive the radio frequencies.
Australia Telescope Compact Array
Now we might ask, don’t the radio waves from distant objects get interfered with local radio frequencies? The short answer is yes, it does. Since the cosmic radio sources are so weak, they can easily get covered up by man-made interference. Usually transmitting is prohibited in the radio astronomy bands. But still, transmitters using frequencies near those assigned to radio astronomy can cause interference. To minimize this effect, radio astronomers have to skillfully use radio engineering. These days, due to progress in modern technology we can drastically reduce these unwanted signals and get the desired output.
HOW DID WE KNOW ABOUT THE RADIO BEHAVIOUR OF OUR UNIVERSE?
This piece is an interesting story to know. Karl Jansky, who is known as the father of radio astronomy, is the man behind this discovery, which paved the way for an entirely new science. He was working for Bell Laboratories when he encountered a puzzling problem. A static noise was interfering with short-wave radio transatlantic voice communications. He started tracking the source and observed that it pointed towards the sky. It was found out that the radio waves were coming from the center of our milky way. Thus he discovered that the universe also emits radio waves.
MORE ON RADIO TELESCOPES
Giant Metrewave Radio Telescope(GMRT), India (Credits-Wikipedia)
Radio telescopes mostly have large antennas to receive signals with low signal to noise ratio. Also, there are some others that look like small vertical metal frames. The telescope shown in the above image is located in Pune, India. It is a major international facility for work in low-frequency radio astronomy and consists of 30 fully steerable antennas of 45 meters diameter each that provide a total collecting area of 30,000 m2, covering a frequency range of 150 MHz to 1.5 GHz. It is operated by the National Centre for Radio Astrophysics (NCRA), a division of the Tata Institute of Fundamental Research.
Let’s see what a radio telescope is made up of-
i) Antennas- As we know, this collects incoming radio waves. Mostly parabolic dishes are used, which reflects the light to a receiver.
ii) Receiver and Amplifier- The received signals are very weak, hence, electronic amplifiers are used to boost the signal to a measurable level.
iii) Recorder- This is used to record the signals in a computer for further study and analysis.
Often, radio astronomy reveals interesting and important details regarding the cosmos. The below image shows the crab nebula captured in different wavelengths. You can see there are also other wavelengths that the universe emits. Mostly, radio waves are emitted by extreme and energetic events/ physical processes in the universe.
Comparison of images of the Crab Nebula in different wavelengths (Credits- NASA)
SOURCES IN THE SKY AND WHAT HAS RADIO ASTRONOMY TAUGHT US?
Thought to be the afterglow of the Big Bang, the cosmic microwave background signal, was invented through radio astronomy. Though it is weak, it permeates all of space. If you have noticed, even some of the static signal on your TV screen between channels is caused by this radiation. This relatively recent field has helped us with the discovery of several new objects and has given us a deeper understanding of the vast sky. Pulsars, quasars, radio galaxies, rapidly spinning neutron stars, were all detected by observing in the radio wavelengths. There are also other sources that emit radio waves including the Sun, Jupiter, Supernova, etc.
In simple words, doing astronomy in radio has changed our fundamental understanding of the universe and given us much more to learn. There is a lot of exciting new research in the field of radio astronomy and I believe this will lead to a deeper knowledge about the mysterious space that surrounds us.
Stay tuned to Spaconova’s blog section for recent news and ongoing research related to space science.
RESOURCES: NASA, NRAO, TIFR, Space.com
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