What is Radio Astronomy?
Radio telescopes make it possible to observe radio waves from space. It works similarly with optical telescopes, but instead of visible light, radio waves are reflected. Radio waves and microwaves also have longer wavelengths than visible light, which astronomers use to gather data such as frequency, power, and timing of radio emissions from objects. In turn, this enables them to deduce information about space that isn't achievable with optical telescopes.
The largest radio telescope in the world is the Arecibo telescope in Arecibo, Puerto Rico. Though radio telescopes have been used since the 1930s, Arecibo has been instrumental in astronomical discoveries since 1960. Developed and operated by Cornell University, radio telescopes are now very valuable tools in observing objects that we are unable to see with ordinary telescopes.
Since radio telescopes were developed, significant discoveries have been made. Here we list 5 amazing radio telescope discoveries.
Asteroid Imaging with Radio Telescopes
In 1989, the Arecibo telescope picked up an asteroid known as 4769 Castalia. Asteroids had been discovered long before radio telescopes, but this was the first time scientists used technology to create an image of what the asteroid looked like. Thanks to radar imaging, Scott Hudson and Steven Ostro were able to develop a three-dimensional model of the peanut-shaped Castalia.
Modern telescopes can achieve much more detail in their imaging, and two telescopes can be paired for even greater details. Using one telescope to transmit and another to receive can yield considerably more detail than would one telescope, and it is an invaluable technique to obtain radar images of closely approaching, slowly rotating asteroids.
Binary Pulsar and Millisecond Pulsar Discovery
Russell Hulse and Joseph Taylor's discovery of pulsars using radio telescopes in 1974 is the reason why they were awarded the 1993 Nobel Prize in Physics. A binary pulsar is a pulsar that has a white dwarf or neutron star nearby that orbits the pulsar to balance the mass and gravitational direction of the pulsar. Millisecond pulsars are neutron stars with a very fast rotational period.
Astronomers are using pulsars throughout the Milky Way Galaxy as a giant scientific instrument to directly detect gravitational waves which were predicted by Einstein's general theory of relativity.
On January 9, 1992, astronomers Alex Wolszczan and Dale Frail discovered exoplanets that are orbiting a pulsar named PSR 1257+12. Like most of the discoveries on this list, it happened on the Arecibo Observatory in Puerto Rico.
Exoplanets are planets that exist outside our Sun's solar system. The discovered exoplanets are about four times as massive as our planet, and their proportions closely resemble the spacing between Mercury, Venus, and Earth.
These planets are believed to be orbiting the aforementioned pulsar located about 2,300 light-years away in the constellation Virgo. The innermost one circles it every 67 days, while the outer one circles every 98 days. There's also a possible third planet which is farther from the pulsar and orbits it about every 360 days.
Using the Arecibo telescope, Gordon Pettengill developed a theory about the rotation of Mercury. In 1964, Pettengill used the radio telescope to theorize that the true rotation of the planet was actually 59 days. It had been previously thought that Mercury's orbit takes 88 Earth days, but this discovery opened new research on the planet and it was revealed that Mercury rotates three times for every two revolutions around the Sun.
21 CM Hydrogen Line
The 21 CM Hydrogen Line was discovered and observed by Edward Purcell & Harold Ewen in 1951 and since then radio astronomers have been mapping neutral hydrogen in the galaxy. This helps astronomers map the hydrogen in the galaxy, which eventually lead to the publishing of the spiral structure of the Milky Way.
Assuming that the hydrogen atoms are uniformly distributed throughout the galaxy, each line of sight through a galaxy will reveal a hydrogen line. The only difference between each of these lines is the Doppler shift that each of these lines has. Hence, one can calculate the relative speed of each arm of our galaxy. The rotation curve of our galaxy has been calculated using the 21 cm hydrogen line. It is then possible to use the plot of the rotation curve and the velocity to determine the distance to a certain point within the galaxy.