A joint collaboration by a team of astronomers from the South African Radio Astronomy Observatory (SARAO), the United States National Radio Astronomy Observatory (NRAO), the University of Pretoria (UP), and Rhodes University have used the MeerKAT telescope to solve the mystery behind the x-shape emanated by certain galaxies. The study observed a galaxy called PKS 2014-55, situated 800 million light years away from Earth, and proposed the reasons for the characteristic x-shape visualised. The results of the study have been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.

MeerKAT is a radio telescope comprising of 64 antennas spanning across the Northern Cape, South Africa, and is a precursor to a much larger telescope initiative. Due to its vast size, MeerKAT is tasked with producing large volumes of data compared to telescopes devised before. This provided the motivation for the use of smart algorithms that could analyse this large volume of data in an efficient way. Dr Kshitij Thorat’s specialisation resides in the use of data-intensive processes that enable the researchers to convert the raw data into pixels that morph into the vivid images of the galaxy released to the public.

mystery behind the x-shape emanated

The galaxy PKS 2014-55 is one of many so-called radio galaxies that possess a mysterious x-shape. Galaxies in the universe possess a black hole at their centre that sometimes generate two jets of radio waves that move in opposite directions. Through the course of astronomical research, several hypotheses have been proposed as possible causes of the unusual ‘x’ morphology. One of these hypotheses is that the presence of two black holes at the centre of the galaxy generate a total of four jets of radio waves that cause the shape to appear. Another hypothesis proposes that the jets surrounding the black hole at the centre of the galaxy creates a haphazard shape. However, the last hypothesis that applies to this particular galaxy mentioned in the study suggests that space material that falls back into the galaxy is deflected to create the characteristic x-shape of the galaxy. The observations outlined in this study support the hypothesis of material deflection. The arms of the x-shape were described as being created by the pressure of the low-density intergalactic gas.

Dr Thorat, a post-doctoral researcher at UP’s astronomy division in the Department of Physics at the Faculty of Natural sciences, is the second author of the research paper who has been actively engaging in the field of radio astronomy, with a focus on supermassive black hole jets, since the start of his PhD research. Dr Thorat has so far co-authored eight publications pertaining to the MeerKAT telescope observations. Dr Thorat explains that the fine details of the structure in this source (due to how large it appears), gives an indication of which type of “tell-tale structural signatures correspond to which particular formation scenario for the x-shaped sources”. Using this, Dr Thorat indicates that the team will be able to conduct statistical studies of these sources. Dr Thorat mentions that this was the first time the MeerKAT telescope was directed to this particular x-shaped galaxy, which allowed them to obtain the vivid images. He explains that the key factor behind making such a good image “being that MeerKAT excels at capturing diffuse structures such as the ones we saw in this source, and the techniques used in analysing the data”.

the team will be able to conduct statistical studies of these sources

Furthermore, Dr Thorat ascertained that artificial intelligence was an important data tool used to sift through the wealth of data that MeerKAT provided. Using artificial intelligence, researchers are able to scan through a myriad of data and find unusual sources such as the x-shaped galaxies in the vast expanses of the sky. Dr Thorat describes the process as “a job akin to finding a needle in a haystack”. Dr Thorat mentions that this study is a pilot that they plan to expand further by surveying more images of vast expanses of the sky to formulate a sizable sample. With this, he explains, the team hopes to “answer the question of how these wonderful sources are formed”. Dr Thorat confirmed that the team’s current projects observe astronomical forms that range in unusual morphologies. Currently, Dr Thorat is working on projects that look at radio sources outside of the Milky Way and study the astrophysics behind them.

Professor Roger Deane, who heads the astronomy research group in the Physics department, was also one of the authors of the research paper and was involved in drafting the proposal concept. Prof. Deane confirmed that his team is heavily involved in large-scale MeerKAT projects that “aim to better understand galaxies, their supermassive black holes, and the co-evolution of these over cosmic time”. Prof. Deane explained that researchers could use studies like that of x-shaped galaxies, to cultivate an understanding that can be used to train machine learning algorithms to search for similar structures in the more distant universe, adding that “certain morphological information is not easy for traditional approaches to capture, which is the motivation for the AI approach”. Through this, Prof. Deane articulates that the team will “be able to better identify and understand the cosmic evolution of these and other intriguing galaxies”.

Prof. Deane noted how consistent efforts have been made to build a dynamic young team of astronomers that are able to tackle important scientific questions using cutting edge radio telescopes such as MeerKAT. Prof. Deane commented on how upon his arrival at UP, he had been the only astronomer in the faculty, and, over the course of two years, was able to build a team of 23 people that range from graduate students to post-doctoral researchers. He asserts that “The rapid growth we’ve seen is both gratifying and encouraging, particularly with the exquisite images the team is making with South Africa’s MeerKAT telescope, a precursor to the Square Kilometre Array”.

Image: NRAO/AUI/NSF; SARAO; DES

SUSANNA ANBU