Australian Sky & Telescope — July 2017

http://www.skyandtelescope.com.au 17

SKA ORGANISATION

Prospects and challenges

With its huge frequency range (50 to 350 megahertz for

SKA-low, and 350 megahertz to 14 gigahertz for SKA-mid),

the first phase of the Square Kilometre Array is already going

to be an incredibly versatile instrument. According to British

radio astronomer Phil Diamond, Director General of the

SKA Organisation, the project is similar in scale to other big

observatories such as ALMA, the James Webb Space Telescope

and the European Extremely Large Telescope, and will

contribute to a vast number of science topics. “It will cover

almost everything, from fundamental physics to extraterrestrial

life,” he says, adding, “Yes, SETI is in the science case.”

The SKA will reveal the cosmic distribution of hydrogen

gas throughout space and time, able to reach back to the

universe’s first 100 million years. This distribution will shed

light on the evolution of galaxies and the history of star

formation, since both of these processes use hydrogen as a

building block — and, when enough radiation is involved,

can ionise its atoms on large scales, transforming the

hydrogen landscape. Studying cosmic evolution and the

growth of the universe’s large-scale structure should also

provide more information on the role and nature of dark

matter and dark energy.

On a less cosmic scale, the SKA is sensitive enough to detect

the faint radio waves that are emitted by rotating carbon-

bearing molecules, both in large molecular clouds and in

protoplanetary disks, giving insight into prebiotic chemistry.

Its data will enable astronomers to map intergalactic magnetic

fields by measuring the fields’ effects on the polarisation of

radio waves, or by observing synchrotron radiation from

electrons spiraling around magnetic field lines.

As for fundamental physics, SKA1 will be a superb pulsar

observatory. By meticulously measuring the pulse arrival

times of dozens of millisecond pulsars all over the sky for

many years on end, astronomers hope to finally detect

extremely low-frequency gravitational waves from binary

supermassive black holes in remote galaxies. Just like the

recent detections of higher-frequency spacetime ripples

from merging black holes, such observations would provide

stringent tests of Einstein’s theory of general relativity and

might lead the way to a successful description of quantum

gravity. The gravitational waves will (hopefully) appear in

SKA1-mid’s data, while SKA1-low’s observations will provide a

baseline to clean out noise.

Building the SKA is not going to be easy, though. The

Great Karoo is a desert-like, almost uninhabited area. Tens

of kilometres of gravel roads and tracks had to be sealed

to allow easier access to the observatory from Carnarvon.

Nearby farmers need to be convinced that MeerKAT

(and SKA after it) is not producing harmful radiation,

and conversely that they need to keep sources of radio

interference to an absolute minimum. The local population

turns out to be very suspicious of the ever-growing facility,

with some worried it will devolve into a land grab and

SKA1-MID

Artist’s concept

Location:

South Africa

Frequency range:

~

dishes (including 64

MeerK AT dishes)

Total

collecting

area:

33,000 m^2

Maximum

distance

between dishes:

150 km

Total raw data output:

2 terabytes

per second

62 exabytes

SKA1-MID per year

Enough to fill up

340,000 laptops

with content every day

Compared to the Jansky Very Large Array, the current

best similar instrument in the world:

better

resolution

more

sensitive

the survey

speed

MHz to GHz

(^350 )
60x5x4x
or 126
tennis
courts
average
x340,