The sheer size of radio dishes, moving slowly as they track particular cosmic targets, has become synonymous with radio astronomy over the decades that this relatively novel branch of astronomy has been pursued. Due to the nature of the long wavelength of radiowaves, obtaining high resolution images necessitates very large aperture telescopes. For comparison, an optical (visible light) telescope observing at 500nm (green light) can achieve a resolution of 0.5 arcseconds with 0.25m of aperture – a radio telescope observing at a frequency of 1GHz (30cm wavelength) needs to be 150km across to achieve the same resolution! For this reason, radio interferometry has replaced large single radio dishes as the instrument of choice in radio astronomy.
Radio interferometers make use of several smaller radio receivers which work in unison to observe a single target. The resolution of the entire array of radio antennas is defined by the maximum distance between antennas in the entire array – one can achieve the resolution of very large dishes by placing antennas the distance of the dishes’ diameter apart. The disadvantage this incurs in total aperture can be mitigated by using several of the cheaper, significantly easier to construct smaller antennas, thus constructing the radio interferometer – an array of receiving antennas.
Malta is one of several countries working on the construction of the Square Kilometre Array (SKA), which shall be the largest radio interferometer in the world upon its completion. Researchers within the Institute of Space Sciences and Astronomy (ISSA) at the University of Malta are working on the Low Frequency Aperture Array (LFAA), a component of SKA-Low – the low frequency component of the entire SKA. My doctoral dissertation, under the supervision of Kristian Zarb Adami and Alessio Magro at ISSA, indeed focused in part on the calibration of prototype verification stations for the LFAA. Calibration is a necessary step in the entire data processing pipeline for radio interferometry, since incoming radio waves are perturbed by a number of different effects before they are recorded by the individual antennas.
Therefore, calibration involves measuring the true telescope response and comparing it against a model telescope response, taking into account the sky being observed (and therefore, a sky model) as well as the actual telescope being used (a telescope model). My study focused on developing such a novel calibration routine for AAVS-1, in particular using per-element patterns to model the instrumental response and thus obtain far more accurate response models for the telescope. Apart from developing such calibration routines for the SKA, I also developed calibration pipelines for the BEST-2 array in Medicina, Bologna, which is primarily used for the observation of space debris, as well as for the MEXART array in Mexico, involved in interplanetary scintillation observations.
The work carried out in this doctoral dissertation was partially funded by the Endeavour Scholarship Scheme, which scholarships are part-financed by the European Union – European Social Fund (ESF) – Operational Programme II – Cohesion Policy 2014-2020.
Josef Borg completed a PhD in Astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a researcher at the Faculty of Health Sciences at the University of Malta.
Sound bites
SpaceX aiming for July for Starship orbital launch despite regulatory reviews.
• Gwynne Shotwell, president for Space X, says Space X is “shooting for July” for the first orbital launch of the company’s vehicle “Starship”, this notwithstanding the fact that Space X is still lacking the regulatory approvals needed for the launch. Speaking at the National Space Society’s International Space Development Conference (ISDC) on June 25, Shotwell said the company was pressing ahead with plans for an orbital flight involving the Super Heavy booster and Starship upper stage from the company’s Boca Chica, Texas, test site.
https://spacenews.com/spacex-aiming-for-july-for-starship-orbital-launch-despite-regulatory-reviews/
China’s super heavy rocket to construct space-based solar power station.
• China aims to use a new super heavy-lift rocket, currently under development, to build a large space-based solar power station in geostationary orbit. Several launches of the upcoming Long March 9 rocket would be used to construct space-based solar power facilities 35,786 kilometres above the earth, according to Long Lehao, chief designer of China’s Long March rocket series.
https://spacenews.com/chinas-super-heavy-rocket-to-construct-space-based-solar-power-station/
For more sound bites listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2 https://www.fb.com/RadioMochaMalta/
Did you know?
• Karl Jansky stumbled upon radio emissions originating from the Milky Way in the 1930s. In what was probably the single, most important event that gave birth to the branch of radio astronomy, Karl Jansky noticed observations of static noise recurring once every 24 hours while testing out radio antennas for trans-Atlantic communications. These were indeed coming from the Milky Way’s galactic core, where a strong radio source – Sagittarius A* - is present.
• Radio interferometers were responsible for the observation of the M87 black hole, published in 2019. High resolution radio astronomy is required for observations of small targets, covering extremely small areas in the sky. As such, the high resolving power of radio interferometers is needed in such cases. The famed observation of the supermassive black hole in Virgo A is one such example, making use of the Event Horizon Telescope (EHT), a planet-wide interferometer.
• Most bright radio sources are obscure at optical wavelengths. With some notable exceptions, most of the brightest targets in the radio sky are dim in the visible light regime, and vice versa. The main reason for this is that targets which peak in visible light are normally hotter objects – most notably, individual stars – which are not particularly bright at radio wavelengths. Conversely, regions around black holes, which are bright in the radio sky due to emissions such as synchrotron radiation, are otherwise relatively dim in visible light.