Science from the ATCA

Below are some of the highlights of the science done with the Australia Telescope Compact Array. The years given are those in which the observations were published.

1991

The ATCA is used to make the first image of a forming radio supernova remnant (SNR 1987A).

Supernova 1987A was a star that exploded in a small neighbouring galaxy, the Large Magellanic Cloud, which can be seen only from the Southern Hemisphere. Light from the explosion reached us in 1987. SN1987A was the brightest and closest supernova since the invention of the telescope four centuries ago, and gave astronomers the best chance they’d ever had to gather data on such explosions. The supernova put out an initial burst of radio emission, then fell radio-quiet – until July 1991, when the University of Sydney’s MOST telescope became the first radio telescope to spot the re-emerging radio supernova remnant. The ATCA, working at higher frequencies, detected this phoenix from the ashes about a month later, and was able to make the first ever picture of such an emerging remnant.

1992
An artist's impression of GRO J1655-40. The system is believed to be a subgiant star orbiting a black hole 6-7 times the mass of the Sun.
Credit: NASA

Astronomers using the ATCA observe the longest radio jets ever found in a radio galaxy (galaxy 0319-453).

1995
3D reconstruction of Jupiter's magnetic field from 20 cm ATCA data.
Image: G.Dulk, Y.Leblanc and R.Sault

The ATCA is used to make the first 3D images of Jupiter’s radiation belts. These observations indicate the properties of the magnetic field closer to the planet than spacecraft have been able to measure.

Jupiter is a strong natural source of radio waves. Much of this radio emission comes from its 'radiation belts' – regions of strong magnetic field that ring the planet. The radio waves come from high-energy electrons trapped in the belts. Because Jupiter rotates once every 10 hours, it’s possible to see the planet from all sides. The 3D images are tomographic reconstructions, built up from views taken at different angles as the planet turns.

1996
Image of the Large Magellanic Cloud made from combined Parkes and ATCA data. Observers: S. Kim et al.

The ATCA is used to make images of two neighbouring galaxies, the Large and Small Magellanic Clouds, which are twenty times more detailed than any previous radio observations.

The Clouds are quite extended objects on the sky – to the eye the Large Magellanic Cloud, for instance, covers about the same area as the Moon. Over several years the telescope has literally pieced together the most detailed pictures ever made of the neutral (atomic) hydrogen gas in the galaxy – the ‘skeleton’ that underlies its visible stars. The picture of the LMC was ‘mosaiced’ together from 1344 separate observations of the ATCA, and shows the galaxy to be shot through with giant holes – ‘superbubbles’ – carved out by exploding stars and stellar winds. It is the most detailed such radio picture ever made of another galaxy.

1998
Supernova 1998bw in the spiral galaxy ESO184-G82.
Credit: European Southern Observatory

ATCA observations are some of the first evidence that the explosions called gamma-ray bursts are linked to exploding stars – supernovae. The ATCA observed the region of the gamma-ray burst GRB 980425, detecting a supernova, SN1998bw, in the galaxy ESO184-G82. The best evidence that the two events were linked came from the estimate of the expansion speed of the radio photosphere.

1999
An optical image of 47 Tucanae (in blue) overlaid with the point radio sources detected (in green).
Observers: D.McConnell, R..Deacon, J.Ables

ATCA imaging of the globular cluster 47 Tucanae–a ball of stars on the outskirts of our Galaxy–reveals 11 point radio sources, 10 of which could be identified as pulsars. The imaging technique provides a new way to detect pulsars that is not subject to the selection effects of the most common method of searching for pulsars: looking for periodic radio signals.

2000

ATCA observations of the giant radio galaxy B0114-476 suggest that the beams from its central engine may have turned off, then restarted, after an initial phase of inactivity. This may explain why giant radio galaxies become so large, with radio emission more than 100 times the length of the optically detectable galaxy.

1999-2001

The ATCA helps to provide candidate fields for the Hubble Deep Field South – an apparently blank piece of sky for the Hubble Space Telescope to observe. Like the previously observed Hubble Deep Field North, this field proved to be rich in ancient galaxies.

Follow-up observations with the ATCA detect an unusual object 5-11 billion light-years distant, optically faint but radio-bright, which could be a new kind of galaxy.

2001
Supernova remnant SNR1987A, imaged by the ATCA at 18.5 GHz (12 mm wavelength) in August 2003.
Observers: R. Manchester et al.

The ATCA makes the first image at short (12-millimetre) radio wavelengths of the supernova remnant 1987A.

2001
The cluster Abell 3667. The coloured image shows the hot gas that lies in space between the galaxies. Yellow contour line show the regions of radio emission, produced by shock waves in the gas as two clusters collided. Radio data: 20 cm ATCA observations; X-ray data: ROSAT (PSPC). Composite image by Melanie Johnston-Hollitt, University of Adelaide and ATNF, using the Synage++ Software of Matteo Murgia, Istituto di Radioastronomia, Bologna, Italy.

ATCA observations of Abell 3667, a cluster of about 500 galaxies, suggest that it was produced by two smaller clusters merging. This is the first observational evidence for this process.

2001

Data from the ATCA and Parkes telescope are combined make the first measurement of the three-dimensional structure of a face-on galaxy (the Large Magellanic Cloud).

2002

The ATCA and NASA’s Chandra X-ray space telescope capture the entire life-cycle of jets from a microquasar, XTE J1550-564, seeing for the first time jets erupt at relativistic speeds, slow down and fade away.

2002

The ATCA helps show the association between the gamma-ray burster GRB 011121 and a supernova, further clinching the connection between the two phenomena

2003

ATCA observations of gamma-ray burster GRB 030329 contribute to measuring the energy involved in the explosion. The total energy release is similar to that of other gamma-ray bursters. The observers conclude that gamma-ray bursters have a common origin–something that was previously in doubt.

2003

The ATCA detects an annual cycle in the scintillating quasar PKS 1257-326. Astronomers use this to develop a technique for high resolution imaging. This quasar, PKS 1257-326, is one of the three most rapidly varying known, with its flux density showing changes of up to 40% in 45 minutes. How fast and how strongly the flux varies depends on the size and shape of the radio source, the size and structure of the gas clouds causing the scintillation, the Earth's speed and direction as it travels around the Sun, and the speed and direction in which the gas clouds are travelling. The researchers have shown that by observing the variability of the radio signal changes over the course of a year, one can create a very high-resolution, two-dimensional picture of the radio-emitting regions of a quasar.

ATCA observations of scintillating quasars started in 1996, and were important in overturning the belief that intra-day variability in quasars is intrinsic.

2004

The ATCA observes a neutron star with a jet travelling at relativistic speed (a significant fraction of the speed of light) – the first time this has been seen. This observation challenges the idea that only black holes can create the conditions needed to accelerate jets to such extreme speeds.