The first scientific paper based on observations performed with South Africa's new KAT-7 radio telescope, has been accepted for publication by the prestigious journal Monthly Notices of the Royal Astronomy Society.
"This is a significant milestone for South Africa's SKA project, proving that our engineers are able to deliver a cutting-edge scientific instrument, and that our scientists are able to use it for frontier science," says Derek Hanekom, South Africa's Minister of Science and Technology. "It bodes well for the delivery of our 64-dish MeerKAT telescope, currently under construction in the Karoo, and for our ability to play a key role in building and commissioning thousands of SKA antennas over the next ten years."
Using the new KAT-7 telescope in the Karoo and the existing 26 m radio telescope at the Hartebeesthoek Radio Astronomy Observatory (HartRAO), South African and international astronomers have observed a neutron star system known as Circinus X-1 as it fires energetic matter from its core in extensive, compact jets that flare brightly. The details of the flares are visible only in radio waves.
Circinus X-1 is an X-ray binary (or two-star system) where one of the companion stars is a high-density, compact neutron star (a neutron star is an extremely dense and compact remnant of an exploded star, only about 20 km in diameter.) The two stars orbit each other every 16.5 days in an elliptical orbit. When the two stars are at their closest, the gravity of the dense neutron star pulls material from the companion star. A powerful jet of material then blasts out from the system.
During the time that KAT-7 observed Circinus X-1 (13 December 2011 to 16 January 2012), the system flared twice at levels among the highest observed in recent years. KAT-7 was able to catch both these flares and follow them as they progressed. This is the first time that the system has been observed in such detail during multiple flare cycles.
"One way of explaining what is happening is that the compact neutron star gobbles up part of its companion star and then fires much of this matter back out again," explains Dr Richard Armstrong, an SKA Fellow at the University of Cape Town and lead author of the paper reporting these results. "The dramatic radio flares happen when the matter Circinus X-1 has violently ejected slows down as it smashes into the surrounding gas."
At the same time Circinus X-1 was being observed at HartRAO at two higher frequencies as part of a long-term study of this object. "The flares are much stronger at the higher frequencies and by combining the three sets of measurements, we could study how each flare evolved as time progressed and investigate details of the turbulent interactions of the jet," adds HartRAO Emeritus Astronomer Dr George Nicolson, a pioneer of radio astronomy in South Africa.
"These types of observations help us to understand how matter is accreted onto extremely dense systems, such as neutron stars and black holes," Armstrong says. "They also shed light on how neutron stars are able to generate these powerful outflows and associated radio bursts."
"KAT-7 was really intended as an engineering test bed to refine the design and systems for the MeerKAT telescope that we are working on now, but we are absolutely delighted that it has turned out to be a top quality science instrument, capable of producing significant science," says Professor Justin Jonas of Rhodes University, who is also the associate director for science and engineering at the SKA South Africa Project Office. "We plan to continue using KAT-7 to do science until at least 2015 when part of the 64-dish MeerKAT telescope will become available to researchers."
Scientists from the SKA Project in South Africa and local and international universities worked together on both the observations and the analysis. This work is part of the development for the ThunderKAT project on MeerKAT, which will find many more of these types of systems in the galaxy, and search for new types of radio systems that change rapidly with time.
The two leaders of the ThunderKAT project, Professor Rob Fender of the University of Southampton and Professor Patrick Woudt of the University of Cape Town, explain that the ThunderKAT project searches for all types of radio bursts and flashes in KAT-7 and MeerKAT data on timescales from seconds to years. Finding and studying the systems that produce these outbursts will allow us to test the extremes of physics, and are beyond anything achievable in any laboratory on Earth. "These systems provide a unique glimpse of the laws of physics operating in extraordinary regimes", Woudt says, "and nearly all such events are associated with transient radio emission."
The ThunderKAT project is already well under way, and besides these observations, has made targeted observations of other exciting systems including the flaring black hole candidate Swift J1745.1-2624, the diffuse radio structure around the black-hole binary GRS 1915+105, as well as a system that is very close to our Sun, the brown dwarf binary WISE 1049-5319.

If you've never looked through a telescope, if you've always wanted to see the rings of Saturn or the craters of the Moon with your own eyes, then get down to Brightwater Commons in Randburg tonight.  The Johannesburg centre of the Astronomical Society of South Africa are trying out a bit of Sidewalk Astronomy on the lawn facing the skateboard ramps, meaning that they're bringing their telescopes and making them available for casual passer's by to have a quick look and see what it is they do.  They will be setting up from about 17h30, so there should be something to see as soon as it gets dark.  They are a very friendly and approachable bunch, and always keen to share the universe with anybody who shows an interest, so don't be shy!

The most famous sidewalk astronomy group was founded in San Francisco in the 1980's by the iconic John Dobson, who pioneered the use of cheap materials and simple designs to let anybody build their own telescope.  It makes for great outreach, simply because it brings astronomy to the people, rather than waiting for them to visit an observatory or a planetarium.

This is the first time the JHB centre is trying out sidewalk astronomy, and they are keen to see how many people are interested.  Please show your support and make the trip!

The Earth is currently passing through a belt of debris left behind by Halley's comet, and as small stones and bits of grit plough into our atmosphere at speeds of 66 kilometers per second, they will briefly flare and burn up as a meteor.  At this point in our orbit, we're pointed towards the faint star Eta Aquarii, so each meteor in the shower will appear to shoot away from that star.  This is why the meteor shower is called the Eta Aquarids, and it happens every year around this time.  

This is a particularly good year, as the Moon will only rise early in the morning, making the sky dark and meteors easy to spot.  South African observers can expect to see about 55 meteors per hour when the shower peaks on 5 - 6 May.

 Late last year, a pair of spacecraft completed their mission to probe the hidden inner structure of the Moon by precisely mapping out its gravitational field.  The Gravity Recovery and Interior Laboratory (GRAIL) mission revealed details and features that had never been seen before like tectonic structures, volcanic landforms, basin rings, crater central peaks and many simple bowl-shaped structures.  

The GRAIL mission worked by sending two small spacecraft (GRAIL-A and GRAIL-B) into the same orbit around the Moon, each about the size of a washing machine.  The craft were equipped  with a device called the Lunar Gravity Ranging System, to measure the distance between them (which varied from 65 to 225 kilometers as the mission progressed through different stages) to an accuracy of microns.  If the leading spacecraft were to pass through a region of slightly higher gravity, it would speed up by a very small amount, causing the gap between the two craft to open up slightly.  By measuring these subtle changes, scientists can accurately map the Moon's gravity field, and from this calculate its mass distribution, which in turn reveals the structure beneath the surface.

Recent observations by NASA's Chandra have found much of the Milky Way's missing mass in the form of a vast halo surrounding the galaxy.  

It has been known for many decades that the amount of material which we can see in a galaxy is not enough to account for the speeds at which various stars and clouds orbit the centre. Objects towards the edge should move slowly and objects near the core should move rapidly, which is what we observe in our Solar System.  In reality, though, we see that the outer edges move significantly faster than simple orbital mechanics would suggest, and the most likely explanation is that there is a lot of mass unaccounted for, spread throughout the galaxy and upsetting the calculations.  Current leading cosmological theories predict something called Dark Matter, which is a form of matter that does not interact with the rest of the universe in any way except through gravity, making it invisible and intangible.  But even when dark matter is taken into account, the Milky Way galaxy still spins too fast.

The Chandra Observatory, a space telescope designed to observe the universe in X-rays, has now solved the mystery by spotting a vast cloud of normal matter spread in a halo around the entire Milky Way galaxy.  This matter is in a gas form, and so thinly spread out that it is invisible to direct observations.  However, when Chandra observed a number of known X-ray sources in the sky, an analysis of the colour spectrum of their light revealed absorption lines caused by oxygen ions in the light path.  Astronomers estimate the temperature of this hot gas at between 1 and 2.5 million Kelvins, or several hundred times hotter than the surface of the Sun.  It is also huge, containing a mass of gas of at least 10 billion Suns, and possibly as much as 60 billion Suns.

This gas halo is distinct from a smaller halo of less hot gas which astronomers have known about for some time - this warm halo is well studied, and others like it have been seen around other galaxies.

The largest structures in the universe are galactic clusters, spanning millions of light years in diameter.  Typically, the galaxies at the centre of these clusters are very old, with little new star formation taking place.  But new observations by NASA's Chandra X-ray Observatory, the National Science Foundation's South Pole Telescope, and eight other world-class observatories have shown that this is not always the case.  Galaxies at the centre of the Phoenix cluster, located about 5.7 billion light years away and with a diameter of 7.3 million light years, are spawning new stars at a record-breaking pace.  The region is also pumping out X-rays more powerfully than any other cluster.

It has been known for some time that galactic clusters contain vast reservoirs of gas, holding more material than all the actual galaxies combined.  This gas is so hot that it emits X-rays which can be seen by the Chandra orbital X-ray telescope, which is the only way it can be seen from such a great distance.  Scientists had long expected that this gas should gradually sink to the centre of the cluster under gravity, and provide material to fuel star formation, but observations had always shown the central regions to instead be dormant, populated entirely with old stars.  The hypothesis was that jets of expelled material from the supermassive black hole (SBH) at the core of the central galaxy add enough energy to the system to keep the cloud from collapsing.  This has been observed happening in other galactic clusters, like the Perseus cluster.

But the Phoenix cluster shows that this mechanism does not necessarily work in all cases.  Phoenix's central galaxy has a relatively quiet SBH which is not jetting enegetically enough to stop the gas cloud from collapsing.  As a result, the galaxy is producing new stars at a rate of about 740 per year -- more than two brand new stars every single day!

This cannot continue for long though, as much of the in-falling gas will end up near the SBH.  Some of this material will fall into the black hole, but the rest will be whipped around by tidal forces and ejected at extremely high speeds, causing the jets to flare up and restore the balance to the cluster.  The question now is whether this is a normal cycle for galactic clusters, or if Phoenix is just having a temporary blip in the natural order.

The Phoenix cluster originally was detected by the National Science Foundation's South Pole Telescope, and later was observed in optical light by the Gemini Observatory, the Blanco 4-meter telescope and Magellan telescope, all in Chile. The hot gas and its rate of cooling were estimated from Chandra data. To measure the star formation rate in the Phoenix cluster, several space-based telescopes were used, including NASA's Wide-field Infrared Survey Explorer and Galaxy Evolution Explorer and ESA's Herschel.