Cosmic re-ionisation to be explored in the Karoo

September 14th, 2016, Published in Articles: EE Publishers, Articles: EngineerIT


A great mystery confronting astronomers is expected to be resolved with the installation of a new telescope array in the Karoo, the hydrogen epoch of re-ionisation array (HERA).

HERA construction materials are sourced and fabricated from within South Africa – predominantly from the Carnarvon area (Picture by Danny Jacobs)

HERA construction materials are sourced and fabricated from within South Africa – predominantly from the Carnarvon area (Picture by Danny Jacobs)

Cosmic re-ionisation corresponds to the epoch when the neutral intergalactic medium (IGM) is re-ionised by the first luminous objects (stars, black holes). Probing this last unexplored phase of cosmic evolution was emphasised by the astronomy community in the 2010 Decadal Survey, the primary area with extraordinary “discovery potential” in the study of cosmic structure formation.

Questions to be resolved include: when and how did the first galaxies form out of cold clumps of hydrogen gas and start to shine — when was our “cosmic dawn”? Observations and calculations suggest that this phenomenon occurred when the universe was roughly half a billion years old, when light from the first stars was able to ionise the hydrogen gas in the universe from atoms into electrons and protons — known as the epoch of re-ionisation.

The HERA brings more international funding to South Africa with a $9,5-million investment to expand its capabilities, announced by the US National Science Foundation. HERA is located only a few kilometres from the MeerKAT radio telescope, which began initial science operations in July 2016.

The array currently has  19 14 m radio dishes at the Square Kilometre Array (SKA) Losberg site near Carnarvon. The array will soon be increased to 37 dishes. This innovative telescope aims to detect the distinctive signature that would allow astronomers to understand the formation and evolution of the very first luminous sources: the first stars and galaxies in the universe. The HERA radio telescope follows in the footsteps of a precursor instrument the precision array for probing the epoch of reionisation (PAPER) also located in the Karoo. The much more sensitive HERA, operating in the Karoo with minimal man-made radio interference, will explore the billion-year period after hydrogen gas collapsed into the first galaxies, a few hundred million years after the Big Bang, through the ignition of stars throughout the universe – the first structures of the universe we observe today.

“The universe was formed in a hot Big Bang of particles and radiation 14-billion years ago, but soon cooled down and was dark for hundreds of millions of years, before any stars formed. Nobody yet knows when these stars formed. The HERA array increases the chances that signs of the first stars and galaxies ever to be created will soon be detected – in South Africa’s Northern Cape,” explains SKA South Africa chief scientist, Dr. Fernando Camilo.

Four hundred thousand years after the Big Bang, the universe was largely made up of neutral hydrogen, the simplest and most common element. Eventually, while the universe at large expanded, ever-larger clouds of hydrogen gathered due to their mutual gravitational attraction. In time, some of these clouds became dense and hot enough that hydrogen atoms fused and the first stars formed. These first brilliant objects flooded the universe with ultraviolet light that split or ionised all the hydrogen atoms between galaxies into protons and electrons – the beginning of cosmic reionisation.

SKA South Africa senior astronomer Dr. Gianni Bernardi said that HERA – which operates at low radio frequency – has enough sensitivity to detect cosmic reionisation and we hope to map it very precisely by statistically measuring how the fraction of neutral hydrogen changed with cosmic time. HERA has the potential to transform our knowledge in one of the main SKA science areas.”The work is impressive because the telescope’s minimalist design makes it a relatively inexpensive structure. Because each antenna will point in a fixed direction, they do not have to move around. project engineer Kathryn Rosie is responsible for HERA’s construction in the Karoo. “HERA is a truly Karoo-based instrument. Construction materials are sourced and fabricated from within South Africa – predominantly from the Carnarvon area. Because the bulk materials of construction are light industry materials such as wood and PVC pipe, there is opportunity for local businesses, which don’t necessarily have a ‘high technology’ customer base, to be a part of this awesome science instrument. We have local contractors installing our main support poles, cutting our structural elements to size, and making up our reflector surface panels from bulk supplied material,” said Rosie.  The University of California, Berkeley, leads the experiment in collaboration with partner teams from the USA, UK, Italy and South Africa. Participating South African institutions include Rhodes University, the University of KwaZulu-Natal, the University of the Western Cape, the University of Witwatersrand and SKA South Africa. Connecting HERA to MeerKAT, Dr. Rob Adam, SKA South Africa MD said that among other investigations, MeerKAT will study evolved galaxies in the later universe, while HERA will peer back nearer to the dawn of time, when the first stars and galaxies were being formed, and that in this way they address complementary scientific questions.

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