Radio Astronomy: Seeing the Unseen
By Siri Paramesh
Cosmofluencer (Season 2)
Radio astronomy is a branch of astronomy that involves the observation of celestial objects at radio frequencies. This blog gives a glimpse into the intriguing world of radio astronomy.
What is Radio Astronomy?
Our eyes are built to see the cosmos in visible light. However, objects in the universe radiate many other types of light, across what’s called the “electromagnetic spectrum”. Light travels through space in waves, like ripples in a pond. Each ripple has a peak and a trough, which is called a cycle. An object emitting radio waves gives off many cycles in a very short period. During each cycle, the wave moves a short distance, which is called its wavelength. The below image depicts the EM spectrum.
There’s a hidden universe out there, radiating at wavelengths and frequencies we can’t see with our eyes. Each object in the cosmos gives off unique patterns of radio emissions that allow astronomers to get the whole picture of a distant object. Radio astronomers study emissions from gas giant planets, blasts from the hearts of galaxies, or even precisely ticking signals from a dying star.
Today, radio astronomy is a major branch of astronomy and reveals otherwise hidden characteristics of celestial bodies and cosmic phenomena
Studying Radio Astronomy
The radio portion of the electromagnetic spectrum can come from energetic objects and processes in the universe as well as cold, dark objects that emit no visible light. Because different objects give off different wavelengths, radio astronomers use various methods and instruments to detect them. One type of instrument is a large antenna that looks like a satellite TV dish. It’s called a radio telescope. While single-dish radio telescopes are essential, NRAO’s (National Radio Astronomy Observation) telescopes consist of many dishes linked together in giant arrays to gather detailed radio images of distant objects.
Seeing or imaging is an important part of all astronomy, regardless of the type of light being studied. While radio telescopes don’t take pictures in the same way that visible-light telescopes do, the radio signals they detect are converted into data that can be used to make images. Radio astronomy data streams are brought together and processed in a computer. The output can be turned into images that are coloured in different ways to show characteristics of the object such as its temperature or the strength of radio emissions from different regions. The resulting images let scientists and the public see the otherwise invisible radio objects.
Click here to learn more about the NRAO’s telescopes.
Radio Telescopes
Optical telescopes – telescopes that collect visible light – show us shining stars, glowing gas, and dark dust but that’s not enough to fathom what is happening in space. To overcome this, telescopes are tuned to different parts of the electromagnetic spectrum to create a better picture that reveals more about hidden cosmic objects.
Radio waves from space were first detected in the 1930s but little was done to follow them up until after the Second World War. In the post-war period, scientists and engineers were among the pioneers of radio astronomy.
Now, just as optical telescopes collect visible light, bring it to a focus, amplify it, and make it available for analysis by various instruments, so do radio telescopes collect weak radio light waves, bring it to a focus, amplify it, and make it available for analysis. We use radio telescopes to study naturally occurring radio light from stars, galaxies, black holes, and other astronomical objects. These specially designed telescopes observe the longest wavelengths of light, ranging from 1 millimeter to over 10 meters long.
Naturally occurring radio waves are extremely weak by the time they reach us from space. A cell phone signal is a billion times more powerful than the cosmic waves our telescopes detect.
In its simplest form, a radio telescope has three basic components:
- One or more antennas pointed to the sky, to collect the radio waves
- A receiver and amplifier to boost the very weak radio signal to a measurable level, and
A recorder to keep a record of the signal.
Radio Interferometry
The difficulty in achieving high resolutions with single radio telescopes led to radio interferometry, developed by British radio astronomer Martin Ryle and Australian engineer, radio physicist, and radio astronomer Joseph Lade Pawsey and Ruby Payne-Scott in 1946. Modern radio interferometers consist of widely separated radio telescopes observing the same object that are connected using coaxial cable, waveguide, optical fiber, or other types of transmission line. This not only increases the total signal collected but it can also be used in a process called aperture synthesis to vastly increase resolution. This technique works by superposing the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. Many different separations between different telescopes are required to produce a high-quality image.
Example: The Circinus Galaxy
The Circinus galaxy is a galaxy in the constellation Circinus. It’s one of the closest major galaxies to the Milky Way.
- The CSIRO (Commonwealth Scientific and Industrial Research Organisation), Australia’s national science research agency, used their radio telescopes to map the cold hydrogen gas in the Circinus galaxy. This Cold hydrogen gas (coloured blue) is the fuel for star formation and a tracer for dark matter in galaxies.
- The warm dust of space (coloured red) and stars (shown in green) were mapped using data from mid-infrared instruments. When combined, these three images reveal gas and stars in the inner disk and spiral arms of the galaxy.
Detecting the Cosmic Microwave Background
The cosmic microwave background (CMB or CMBR) is microwave radiation that fills all space in the observable universe. It is a remnant that provides an important source of data on the primordial universe. CMB is landmark evidence of the Big Bang theory for the origin of the universe
With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson.
Present and Future Trends in Radio Astronomy
CSIRO and the SKA project
The SKA project is an international effort to build the world’s largest and most capable radio astronomy observatory, designed to enable transformational science that will change our understanding of the Universe
To know more about the project, Click here.
Australia Telescope National Facility
Australia Telescope National Facility (ATNF) is one of the world’s most advanced radio astronomy facilities and the only one of its kind in the southern hemisphere.
Click here to learn more about ATNF.
The science and engineering behind radio astronomy can also benefit our everyday lives, for instance:
- The fast wireless LAN technology, which was developed from the expertise in radio astronomy, led to fast Wi-Fi. It is now the way most of us access the internet without wires.
- Pulsars offer potential as extremely accurate clocks and are possible alternatives to satellite-based global positioning systems.
For the newest radio telescope, the innovative ‘phased array feed’ receivers with a wide field of view are being developed. This technology offers enormous potential for other applications such as satellite communications.
Conclusion
Radio astronomy has led to a substantial increase in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars, and radio galaxies. This is because radio astronomy allows us to see things that are not detectable in optical astronomy. Such objects represent some of the most extreme and energetic physical processes in the universe.
The cosmic microwave background radiation was also first detected using radio telescopes. In addition, radio telescopes have also been used to investigate objects much closer to home, including observations of the Sun and solar activity, and radar mapping of the planets. The Study of gas and dust clouds is another major application. Radio astronomy helps intricately study gas and dust clouds.
Thus we see that Radio astronomy helps detect and analyze hidden celestial objects that are not visible otherwise. It also helps understand the key elemental constituents of stars and complete galaxies. Radio astronomy has led to substantial increases in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars, and radio galaxies which play a major role in understanding the universe.