What will eventually become one of the world’s most sensitive radio telescopes has taken its first true peak at the cosmos that it was built to observe. Still in its infancy, SKA-LOW will comprise the low-frequency aperture array of the Square Kilometre Array (SKA) radio interferometer, which will ultimately span across two continents and several countries.
Astronomers have successfully used two SKA-LOW stations, comprising of 256 antennas each, to observe the Centaurus A galaxy, obtaining fringes ‒ successful correlation of signals received by antennas pertaining to the two telescope stations ‒ for the very first time. The University of Malta is one of nine institutions across six countries forming part of a consortium working on SKA-LOW.
Radio interferometry involves the employment of multiple small antennas, as opposed to more traditional single, large radio telescope dishes. These smaller antennas are much more cost effective and provide less of an engineering challenge.
The whole premise of radio interferometry is that multiple small antennas, spread over large distances, can achieve the same resolution as a single dish telescope with a diameter equivalent to the largest distance between the two farthest antennas in the array. Increasing the number of antennas in between this farthest distance ‒ called the longest baseline ‒ increases the overall sensitivity of the instrument.
SKA-LOW will ‒ upon completion ‒ employ a total of 512 stations, each composed of 256 log-periodic antennas.
But why are such large instruments ‒ translating to long baselines between antennas in radio interferometry ‒ needed for radio astronomy anyway?
Increasing the number of antennas in between this farthest distance ‒ called the longest baseline ‒ increases the overall sensitivity of the instrument
Radio astronomers have been dealt the short end of the stick in this matter. With radio waves having the longest wavelengths in the electromagnetic spectrum, they also require the largest telescope aperture diameters to achieve required resolutions. What can be resolved by a visible light telescope with mere centimetres of aperture needs, in some cases, kilometres of aperture to be resolved to the same level in the radio light regime.
So why bother with radio astronomy at all?
To put it simply, radio astronomy offers us a unique window onto the universe, one that is not possible in any other kind of light. In radio astronomy, we can look through clouds of dust, which other kinds of light cannot penetrate, allowing us to look into the midst of such denser regions ‒ such as the very cores of galaxies.
Radio galaxies ‒ galaxies with an active supermassive black hole in their centre ‒ can be observed and studied in stunning detail, with huge lobes of material above and below the galactic plane being best visible in radiowaves.
Additionally, we can look further away and thus further back in time with radiowaves than with any other kind of light, allowing us to observe the first billion years of our universe’s history. This, in turn, gives us the opportunity to study primitive galaxies and the formation of the first stars in our universe, among other phenomena.
Josef Borg completed a PhD in Astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a post-doctoral researcher in space bioscience at the Faculty of Health Sciences at the University of Malta.
Sound Bites
ORCs in space? Another Odd Radio Circle (ORC) observed by astronomers: Over 371,000 light years across, the newly discovered ORC was discovered in the MIGHTEE survey carried out by the MEERKAT telescope. ORCs are typically associated with specific galaxies, with large circles of radio emission found around entire galaxies. What sets the latest found ORC apart from other ORCs is that it seems to be fainter and leans to one side of the galaxy.
For more soundbites, listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2.
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DID YOU KNOW?
• Pulsars are actually a type of stellar remnant, called a neutron star: After a giant star goes supernova, its remnant core can form two distinct objects, depending on its mass – either a neutron star or a black hole. Collapsed cores of stars which stop at the neutron star stage still have immense densities, and typically spin at extremely high speeds – some even several times every second. Twin beams of energy are released from the neutron star magnetic poles due to a misalignment with its rotation axis, and as the neutron star rotates, these can be seen as pulses of energy from Earth, as a beam of energy rotates in and out of view.
• Quasars are active galaxies with strong emission in the radio regime: An active galaxy refers to a galaxy that has an active supermassive black hole at its centre, that is, a supermassive black hole that is actively ‘feeding’ on material falling towards it. As the material falls into the black hole, it accelerates and releases energy across the electromagnetic spectrum, including in radio waves. Since such galaxies are extremely far away; most quasars indeed look like points of light, not too different at first glance from the appearance of singular stars – hence the term quasar, shorted from ‘quasi-stellar radio source’.
For more trivia, see: www.um.edu.mt/think.