The Square Kilometer Array (SKA)
Planned to be built in remote locations of the Southern Hemisphere, the middle of South Africa, and the West Australian desert is a large intergovernmental radio telescope: the Square Kilometre Array (SKA). Its location, below the equator, will give it the optimal view of the Milky Way and limited exposure to radio interference. It has been developed with a collecting area to be of 1 square kilometer, hence its name, and aim to achieve 50 times more sensitivity of any existing radio instrument to ambitiously survey the sky around 10,000 times faster than we now can.
To achieve this gargantuan square kilometer array of collecting plates, the receiving stations will reach out to distances of 3 thousand kilometers to the least, and therefore. However, constructions that began in 2018 will not be completed until the year 2027. A year after the building began, on the 12th March 2019, the Square Kilometre Array Observatory consortium (SKAO) was signed in Rome by the seven first-member countries to collaborate internationally.
As mentioned, the SKA will be a radio telescope, meaning that it will operate at frequencies ranging from 50 MHz to 20 GHz (equivalent to wavelengths of 3 to 4 centimeters) and will thus be intercepting signals beyond the visible spectrum. But before we delve into the SKA’s technical specifications, let us understand why radio telescopes are used in the first place.
Why do we need radio telescopes?
Although optical telescopes like the Hubble Space Telescope are more present in popular culture than what we call radio telescopes, in the field of radio astronomy, the latter is crucial in allowing man to explore the universe, not through the visible light it emits but rather by detecting the radio waves that these cosmic objects emit. Radio telescopes allow us to see the universe through a different lens, an alternative view that allows us to detect invisible gas and reveal areas of space that may be obscured with cosmic dust.
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Besides, they hold a considerable advantage over optical telescopes, for on the electromagnetic spectrum, radio waves have much lower frequencies than visible light. Thus, by working with longer wavelength signals (smaller frequency), they are unobstructed by cloudy days or poor weather conditions, which will indeed not interfere with the intercepted signals. However, the downsides are that radio telescopes require much larger collecting areas and the price to pay to detect the “invisible sky.”
The interest in detecting this invisible sky, the radio waves emitted from bodies ranging as close as our sun to the abyss of deep space, is that radio signals allow us to intercept the electromagnetic radiation in the transition of states in the hydrogen atom. As we know, hydrogen is widespread in our universe. Thus, intercepting its radiation will allow us to map the intensity of radiation in our universe, imperceptible to the eye.
Fundamentally, the proton and the electron of a hydrogen atom each have a property called “spin,” and the spin in both subatomic particles may either be “aligned” or “non-aligned.” The atom may then transition between both states. When it goes from aligned to anti-aligned, it becomes more stable. It releases energy in the form of a photon whose energy is in the radio part of the electromagnetic spectrum (1420 MHz). Thus, the SKA and other radio telescopes’ job is to intercept the varying levels of intensity of the radio emissions generated by these transitions to produce higher resolution sky surveys.
The SKA will work by simulating one giant radio telescope by combining signals received by thousands of smaller antennas spread over thousands of kilometers in remote areas of the Southern Hemisphere. This technique is known as aperture synthesis, mixing signals from a collection of small telescopes to produce images with the same angular resolution as if all these small telescopes were combined into a single instrument.
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Various parts of the SKA will have extremely wide fields-of-view allowing the multitude of the telescope to survey large areas of the sky simultaneously. As to the frequency coverage of the SKA, it will be developed in three distinct phases. During the first and second ones, the SKA will extend its coverage from 50 MHz to 14 GHz. The third phase will then complete this by complementing it with a range from 14 GHz until 30 GHz.
To cover these frequencies, the SKA will have to use various antenna designs and thus comprise multiple sub-arrays. Firstly, the SKA-low will cover the frequencies from 50 MHz to 350 MHz thanks to radio receiving stations of 90 antenna elements grouped in 100-meter diameters entities. The SKA-mid array, comprising of several thousand dish antennas, will cover the range going from 350 MHz to 14 GHz. Finally, the SKA-survey array will be made up of 12 to 15 meters diameter parabolic dishes and cover frequencies ranging from about 350 MHz to 4 GHz. These arrays will be spawned out on three regions centered around the telescope cores in South Africa and Western Australia.
SKA’s key projects
The aim of the SKA and its feature is to come together to collect and analyze data to address a variety of unanswered questions in the fields of astrophysics and cosmology. In addition, its unforeseen sensitivity and range will allow it to extend the range of the observable universe, delving into horizons that man had never peered into before.
One of the first key projects of the SKA will be to put Einstein’s theory of general relativity to extreme tests. By examining the radiation emitted by pulsars around extremely curved space (such as around black holes), we will be able to tell better whether Einstein’s description of space-time was correct.
The second area that the SKA will be concentrating on is that of dark matter. By imaging the hydrogen emissions throughout the universe, we will be able to map out the galaxies and clusters and their evolution, drawing a link between dark energy and its effect on the expansion and state of the universe. This study of the universe’s evolution will also allow us to understand the period between 300,000 years after the Big Bang and the First Light by observing gas distribution in the Universe. Finally, the SKA will also be used with the prospect of identifying areas prone to extra-terrestrial life.
Big data and data processing
The challenge of the SKAO will then be to process the stream of data and raw information flowing out of the telescope to categorize it and filter it to find meaningful patterns. About a terabyte of data per second will be produced running through a total of 100,000 kilometers of optic fiber dedicated to it – enough to wrap twice around the Earth – allowing the data to be transferred from the antennas to the processors about 100,000 times faster than the estimated broadband speed for 2022.
Making sense of the large data streams is the biggest challenge for the computing power that the two SKA supercomputers will require to process the data would be equivalent to the total power of all the best supercomputers in the world in 2019. The goal will then be to, every year, distribute up to 700 petabytes of analyzed or relevant data, unforeseen numbers in radio astronomy. As such, the SKA is opening up new frontiers in numerous fields of science, a thrilling project for international science collaboration.
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