A number of key science projects that have been selected for implementation via the SKA are listed below. For almost one hundred years, Einstein 's general theory of relativity has precisely predicted the outcome of every experiment made to test it. Most of these tests, including the most stringent ones, have been carried out using radio astronomical measurements. By using pulsars as cosmic gravitational wave detectors, or timing pulsars found orbiting black holes , astronomers will be able to examine the limits of general relativity such as the behaviour of spacetime in regions of extremely curved space.
The goal is to reveal whether Einstein was correct in his description of space, time and gravity, or whether alternatives to general relativity are needed to account for these phenomena. The sensitivity of the SKA in the 21 cm hydrogen line will map a billion galaxies out to the edge of the observable Universe. The large-scale structure of the cosmos revealed will give constraints to determine the processes resulting in galaxy formation and evolution.
Imaging hydrogen through the Universe will provide a three-dimensional picture of the first ripples of structure that formed individual galaxies and clusters. This may also allow the measurement of effects hypothetically caused by dark energy and causing the increasing rate of expansion of the universe.
The cosmological measurements enabled by SKA galaxy surveys include testing models of dark energy,  gravity,  the primordial universe,  fundamental cosmology tests,  and they are summarized in a series of papers available online. The SKA is intended to provide observational data from the so-called Dark Ages between , years after the Big Bang when the universe became cool enough for hydrogen to become neutral and decouple from radiation and the time of First Light a billion years later when young galaxies are seen to form for the first time and hydrogen becomes again ionized.
By observing the primordial distribution of gas, the SKA should be able to see how the Universe gradually lit up as its stars and galaxies formed and then evolved. This period between the Dark Ages and First Light is considered the first chapter in the cosmic story of creation and the distance to see this event is the reason for the Square Kilometre Array's design. To see back to First Light requires a telescope times more powerful than the biggest radio telescopes currently in the world, taking up 1 million square metres of collecting area, or one square kilometre. It is still not possible to answer basic questions about the origin and evolution of cosmic magnetic fields , but it is clear that they are an important component of interstellar and intergalactic space.
By mapping the effects of magnetism on the radiation from very distant galaxies, the SKA will investigate the form of cosmic magnetism and the role it has played in the evolving Universe. This key science program, called "Cradle of Life", will focus on three objectives: Suitable sites for the SKA telescope must be in unpopulated areas with guaranteed very low levels of man-made radio interference. Many groups are working globally to develop the technology and techniques required for the SKA. Their contributions to the international SKA project are classified as either: Precursors, Pathfinders or Design Studies.
It will employ advanced, innovative technologies such as phased array feeds to give a wide field of view 30 square degrees. All 36 antennas and their technical systems were officially opened in October As of May , all sixty-four The Allen Telescope Array uses innovative 6. The element array now in operation is to be extended to elements.
The dish design has explored methods of low-cost manufacture. The amount of sensory information collected pose a huge storage problem and require real-time signal processing to reduce the information to relevant data. In mid it was estimated the array could generate an exabyte a day of raw data, which could be compressed to around 10 petabytes. It is operated by a consortium of universities led by Cornell University and was completed in The SKA was originally conceived in with an international working group set up in This led to the signing of the first Memorandum of Agreement in Considerable early development work then followed.
Construction of Phase 1 will take place from to providing an operational array capable of carrying out the first science. The funding will come from many international funding agencies. Potential risks for priority astronomical sites in South Africa are protected by the Astronomy Geographic Advantage Act of Put in place to specifically support the South African SKA bid, it outlaws all activities that could endanger scientific operation of core astronomical instruments.
Tools of Radio Astronomy, 5th ed. The Square Kilometre Array: It will conduct astro-biological observations, potentially including the detection of life elsewhere in the Universe via their radio signals. National Key Points in South Africa. Cold gas in galaxies, invisible in the optical range, can be radio-bright when emitting in specific radio spectral lines.
In , concerns were raised over the will to enforce this law when Royal Dutch Shell applied to explore the Karoo for shale gas using hydraulic fracturing , an activity that would have the potential to increase radio interference at the site. An identified remote station location for the southern African array in Mozambique was subject to flooding and excluded from the project,  despite the SKA Site Selection Committee technical analysis reporting that all African remote stations could implement flood mitigation solutions.
In February , a former Australian SKA Committee chairman raised concerns with South African media about risks at the Australian candidate site, particularly in terms of cost, mining interference and land agreements. SKA Australia stated that all points had been addressed in the site bid. The largest risk to the overall project is probably its budget, which up until now has not been committed.
There has been opposition to the project from farmers and businesses, as well as individuals, since the project's inception. From Wikipedia, the free encyclopedia. Related media on Wikimedia Commons. This section needs additional citations for verification.
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Galaxy formation and evolution and Dark matter. Since the correct answer is not known, physicists and astronomers named the phenomenon dark energy  see also Frieman et al. One important method of distinguishing between these various explanations is to compare the distribution of galaxies at different epochs in the evolution of the Universe to the distribution of matter at the time when the Cosmic Microwave Background CMB, see above was formed, about , years after the Big Bang.
Small distortions "ripples" in the distribution of matter, called baryon acoustic oscillations , should persist from the era of CMB formation until today. Tracking if and how these ripples change in size and spacing over cosmic time can then tell us if one of the existing models for dark energy is correct or if a new idea is needed. The SKA will use the hydrogen emission from galaxies to measure the properties of dark energy. A deep all-sky SKA survey will detect hydrogen emission from galaxies out to redshifts of about 1. The same data set will give us unique new information about the evolution of galaxies.
How the hydrogen gas was concentrated to form galaxies, how fast it was transformed into stars, and how much gas did galaxies acquire during their lifetime from intergalactic space and by merging with other galaxies? Present-day telescopes have difficulty in detecting intergalactic hydrogen clouds with no star formation activity and distant dwarf galaxies, but these sorts of radio sources will be easily detectable by the SKA.
The hydrogen survey will simultaneously give us the synchrotron radiation intensity of all galaxies which is a measure of their star-formation rate and magnetic field strength. The radio-astronomical discovery of pulsars and the indirect detection of gravitational waves from a pulsar-star binary system were rewarded with two Nobel prizes for physics. Pulsars are precise clocks and can be used for further experiments in fundamental physics and astrophysics.
This volume is an up-to-date and comprehensive overview of the engineering of the Square Kilometre Array (SKA), a revolutionary instrument which will be the. The pace of the international Square Kilometre Array (SKA) project is accelerating, with major concept reviews recently completed and a number of technology.
However, no tests in the strong gravitational field around black holes have yet been made. The SKA will search for a radio pulsar orbiting around a black hole Fig. Regular high-precision observations with the SKA of a network of pulsars with periods of milliseconds opens the way to detect gravitational waves with wavelengths of many light years, as expected for example from two massive black holes orbiting each other with a period of a few years resulting from galaxy mergers in the early Universe.
When such a gravitational wave passes by the Earth, the nearby space-time changes slightly at a frequency of a few nHz about 1 oscillation per 30 years. The wave can be detected as apparent systematic delays and advances of the pulsar clocks in particular directions relative to the wave propagation on the sky. We expect that more than 20, new pulsars will be detected with the SKA, compared to about known today.
Almost all pulsars in the Milky Way Fig. Electromagnetism is one of the fundamental forces, but little is known about its role in the Universe. Large-scale electric fields induce electric currents and are unstable , whereas magnetic fields can exist over long times because, mysteriously, single magnetic charges monopoles are missing in the Universe. Data suggest that all interstellar and probably intergalactic space is permeated by magnetic fields, but these are extremely hard to observe.
Radio waves provide two tools: Both methods have been applied to reveal the large-scale magnetic fields in our Milky Way, nearby spiral galaxies Fig. Furthermore, the origin and evolution of magnetic fields is still unknown. The first "seed" fields may originate in the very young Universe or may have been ejected from the first quasars, stars, or supernovae. The SKA will measure the Faraday rotation towards several tens of million polarized background sources mostly quasars , allowing us to derive the magnetic field structures and strengths of the intervening objects, such as, the Milky Way, distant spiral galaxies, clusters of galaxies, and in intergalactic space.
The presence of life on other planets is a fundamental issue for astronomy and biology.
The SKA will contribute to this question in several ways. Firstly, it will be able to detect the thermal radio emission from centimeter-sized "pebbles" in protoplanetary systems Fig. The SKA will allow us to detect a protoplanet separated from the central star by spacings of order the Sun-Earth separation out to distances of about light years. Prebiotic chemistry - the formation of the molecular building blocks necessary for the creation of life - occurs in interstellar clouds long before that cloud collapses to form a new solar system with planets. Ionospheric radar experiments similar to those on Earth will be detectable out to several thousand light years, and Arecibo-type radar beams, like those that we use to map our neighbor planets in the solar system, out to as far as a few ten thousand light years.
SETI will also search for such artificial signals superimposed onto natural signals from other objects. From the five Key Science Projects see above two major science goals have been identified that drive the technical specifications for the first phase SKA While the experiments described above are exciting science, the history of science tells us that many of the greatest discoveries happen unexpectedly and reveal objects which are completely different from those which had been envisaged during the planning phase of a new-generation telescope.
The unique sensitivity of the SKA will certainly reveal new classes of cosmic objects which are totally beyond our present imagination. We are looking forward to such surprises. The resolving power is proportional to the frequency and to the largest baseline between the outermost antennas and hence is much higher than for single dish telescopes.
The signals are combined in a central computer correlator. While the radio images from present-day interferometric telescopes are generally produced offline at the observer's institute, the enormous data rates of the SKA will demand online image production with automatic software pipelines. With a collecting area of about one square kilometer, the SKA will be about ten times more sensitive than the largest single dish telescope m diameter at Arecibo Puerto Rico  , and fifty times more sensitive than the currently most powerful interferometer, the Karl G.
The SKA will continuously cover most of the frequency range accessible from ground, from 50 MHz to 3 GHz corresponding to wavelengths of 10 cm to 6 m in the first phase, later to be extended to at least 14 GHz 2 cm. The third major improvement is the enormously wide field of view, ranging from about 40 square degrees at 50 MHz to about 18 square degree at 1. The speed to survey a large part of the sky, particularly at the lower frequencies, will hence be ten thousand to a million times faster than what is possible today.
To meet these ambitious specifications and keep the cost to a level the international community can support, planning and construction of the SKA requires many technological innovations such as light and low-cost antennas, detector arrays with a wide field of view, low-noise amplifiers, high-capacity data transfer, high-speed parallel-processing computers and high-capacity data storage units. The realization needs multifold innovative solutions which will soon find their way into general communication technology. The frequency range spanning more than two decades cannot be realized with one single antenna design, so this will be achieved with a combination of two types of antennas for the low and mid-frequency ranges:.
An aperture array of simple dipole antennas with wide spacings a "sparse aperture array" for the low-frequency range about 50 - MHz Fig. This is a software telescope with no moving parts, steered solely by electronic phase delays. It has a large field of view and can observe towards several directions simultaneously. An array of several thousand parabolic dishes of 15 meters diameter each for the medium frequency range about MHz - 14 GHz , each equipped with wide-bandwidth single-pixel "feeds" Fig. The surface accuracy of these dishes will allow a later receiver upgrade to higher frequencies.
The overall extent of the array determines the angular resolution, which will be about 0.
Dense aperture arrays comprise up to millions of receiving elements in planar arrays on the ground which can be phased together to point in any direction on the sky. Due to the large reception pattern of the basic elements, the field of view can be up to square degrees.
The first full-size station made up of antenna prototypes has seen its initial deployment at the Murchison Radio Observatory MRO in . The technology of dense phased-array feeds PAF can also be adapted to the focal plane of parabolic dishes. Such a "radio camera" is composed of many elements pixels which are controlled and combined electronically. This allows the dishes to observe over a far wider field of view than when using a classical single-pixel feed. The major components of the first two prototype dishes are presently manufactured in China, Germany, and Italy.
As an "Advanced Instrumentation Programme" for the full SKA SKA2 , two additional technologies for substantially enhancing the field of view in the medium frequency range about 1 - 2 GHz are under rapid development: