Ur-galaxies looking good on Paper
South Africa has joined the race to find the very first stars, but radio signals keep getting in the way.
There was a bang, we think. A singularity – a point in space smaller than a pinhead – exploded and released all the energy in our universe. This energy coalesced into subatomic particles, the particles merged into atoms and our cosmic primordial soup of universe congealed into something more tangible, but the universe was opaque. It was so dense that light kept bumping into other particles and could not find a way out: a cosmic Dark Age.
It took 400-million years before the hot, dense soup cooled down enough for light to escape this heaving and expanding mass. And now, about 14-billion years later, astronomers in the Karoo are trying to detect this light, which emerged as the first galaxies and stars were born.
The bakkie bounces on the gravel road away from the seven large dishes baking in the Karoo heat, kicking up a plume of dust into the deep-blue sky. The path to the seven KAT-7 antennas is well worn – KAT-7 is South Africa’s Square Kilometre Array (SKA) prototype, an instrument to show that South Africa has the expertise to host the SKA, which will be the world’s largest radio telescope.
Tony Foley, the head of science operations for SKA South Africa, is driving. “Do you want to see the Paper [Precision Array for Probing the Epoch of Reionisation] experiment? They’re looking for the first galaxies,” he says, turning left on to a much less travelled road.
The antennas look like chicken-wire fish tanks whose sides have begun to collapse, very different from the large dishes a few hundred metres away. They stand about shoulder height and sit passively amid the tufts of yellow grass.
When that swirling mass of energy and particles started to cool billions of years ago, they first merged to form hydrogen, the simplest atom in the universe, and that is what scientists are looking for: the signature of these first hydrogen atoms. Once they began to form, the light could escape. This time is called the Epoch of Reionisation, and was when the first stars and galaxies came to life.
"They're going after one of the key undetected phenomena in the universe," says Justin Jonas, an associate director for science and engineering at SKA South Africa.
"We know it must be there, galaxies and stars did turn on, but [it] hasn’t been detected yet."
This is the sole purpose for Paper. "It's an experiment, as opposed to a facility. It is a different approach to MeerKAT [a 64-dish array South Africa is building that will form part of the SKA], a general-purpose facility. Paper is a focused experiment," says Jonas.
"They've gone about it in a very traditional physics experiment kind of way, starting small and growing it over time to get a good understanding of the experiment and the problem."
"The real challenge is not only peering through the natural sources [of the low frequency signal] between here and that shell [of the reionisation signal], but also the radio frequency interference signals," says Professor Richard Bradley, of the National Radio Astronomy Observatory in the United States and principle investigator on the Paper experiment, which has been funded by the National Science Foundation in that country.
The Earth at this moment is being bombarded by radio signals: high frequency, mid-frequency and low frequency. To detect the signature of the first stars, you need to isolate a frequency band where you expect to find the signature, and isolate the celestial bodies that you know are emitting signals.
Professor Jonathan Sievers, of the University of KwaZulu-Natal, is involved in studying this cosmic epoch. "The difficulty is cleaning the signal we’re looking for from all the other signals in the galaxy. The Milky Way is very bright," he says.
You also need to make sure there is no interference from radios, cellphones, cars, or the many other things that interfere with radio astronomy. Paper is looking at frequencies between 100MHz and 200MHz, and an FM radio goes into the region of about 100MHz.
"It's one of the reasons we chose South Africa," Bradley says.
The SKA site, about 80km away from Carnarvon in the Northern Cape, is protected by the Astronomy Geographic Advantage Act of 2007, which safeguards the area against interference from radio signals.
Although this experiment is investigating one of the great cosmological mysteries, it does not look as impressive as the statuesque dishes in the distance. It looks flimsy, like a super-sized laboratory experiment. Bradley says that, eight years ago, when the Paper experiment was conceived, "we had read about the reionisation theory … [but] we were honest with ourselves, and said, 'We really don’t know how we're going to do this, so let's start small and work our way up and learn as we go.'" The four-antenna project burgeoned into 128 antennas in South Africa, and 23 in West Virginia, where the engineers test the instruments.
Asked why she is interested in studying this period of the universe, Dr Cynthia Chiang, based at the University of KwaZulu-Natal, says: "There is a tremendous amount of information encoded in it; it will give us a 3D map of the universe at a particular epoch. … These are the first pioneering efforts [to detect it]."
But, the $8-million Paper is not the only experiment trying to detect the first stars; the Netherlands has the Lofar [Low Frequency Array] and Australia has the MWA [the Murchison Wide-field Array], which are also searching for this ancient signature. Bradley is not fazed by the competition. "It's always fun to be first, but we also know that, when a discovery is made, it will need to be verified."
Also, the phenomena will need to be studied, and this is where the SKA comes in.
Cosmic background radiation
Jonas likens it to the discovery of cosmic background radiation, the radiation remnants of the Big Bang that permeate the universe.
"It was detected in the 1960s, but it was only in the 1990s that we had instruments that allowed us to study it," he says.
Sievers jokes that he hopes it will not take 30 to 40 years before they are able to study the signature of the first galaxies.
Despite the competition, Bradley says that scientists and engineers from different countries have teamed up to develop a roadmap to study this epoch. "Phase one is what we're doing now: early detection experiments. In phase two, we know what we're looking for and hone in. In phase three, we see our experiment phasing with the SKA."
Asked for an "elevator pitch" of what he does, Bradley says: "I am looking for the evidence of when the first stars were formed. Once we've pinned that down, we can figure out how."