UP part of team that solves mystery of X-shaped radio galaxies with meerKAT telescope

7 May 2020 by Shakira Hoosain

A team of astronomers from South Africa and the USA has used the MeerKAT telescope to solve a longstanding puzzle in ‘X’-shaped radio galaxies by observing a galaxy called PKS 2014-55 that’s situated 800 million light years away from Earth. Previous studies of these unusual galaxies lacked the high-quality imaging provided by the MeerKAT telescope, which was inaugurated in 2018.

This study was carried out by a team from the South African Radio Astronomy Observatory (SARAO), the (US) National Radio Astronomy Observatory (NRAO), the University of Pretoria, and Rhodes University. The results will be published in the journal Monthly Notices of the Royal Astronomical Society.

Dr Kshitij Thorat, a postdoctoral fellow at the University of Pretoria and second author of the paper, explained: "This galaxy is one of many with similar X-shaped morphologies carefully chosen to be studied in a MeerKAT observation campaign which is aimed at solving the mystery of X-shaped radio galaxies. While other telescopes around the world hinted at this object's unusual morphology, it took the crystal-clear image quality of MeerKAT to reveal the underlying physical causes. As a bonus, we have produced one of the most beautiful radio images I have ever seen." 

The image shows two powerful jets of radio waves, indicated in blue colour, each extending 2.5 million light-years (comparable to the distance between the Milky Way and the Andromeda galaxy, our nearest major neighbour). At their centre are the youngest jets of a central black hole, surrounded by an oblong disk of stars. The detail provided in this radio image obtained with the MeerKAT telescope shows that its shape is best described as a “double boomerang”.

Many galaxies far more active than the Milky Way have enormous twin jets of radio waves extending far into intergalactic space. Normally these go in opposite directions, coming from a massive black hole at the centre of the galaxy. However, a few are more complicated and appear to have four jets forming a mysterious ‘X’ on the sky.

Several possible explanations have been proposed to understand this phenomenon. These include changes in the direction of spin of the black hole at the centre of the galaxy and its associated jets; or two separate black holes, each associated with a pair of jets; or a third explanation of material falling back into the galaxy being deflected into different directions forming the other two arms of the ‘X’.

The new MeerKAT observations of PKS 2014-55 strongly favour the third explanation, as they show material “turning the corner” as it flows back towards the host galaxy. The arms or wings of the X are “turned back” by the pressure of low-density intergalactic gas. As they flow back towards the central galaxy, they are deflected by its relatively high gas pressure into the shorter, horizontal, arms of the boomerang.

Professor Roger Deane, who leads the UP astronomy group and is a co-author of the study, said, “Here at the University of Pretoria, we've made a concerted effort over the past two years to build a team that is able to make important scientific discoveries with cutting-edge radio telescopes. 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.” This study is part of an ongoing effort at the University of Pretoria to carry out systematic studies of X-shaped galaxies using next-generation telescopes like MeerKAT and techniques like machine learning, which would find similar but more faraway objects in the universe.

The MeerKAT telescope array consists of 64 radio dishes located in the Karoo semi-desert in the Northern Cape province of South Africa. To make this image, computers combined over a petabyte of data (equivalent to over 100 000 MP3 audio files) from these antennas into a telescope 8 km in diameter.

Lead author William Cotton of the NRAO added, “MeerKAT is one of a new generation of instruments whose power solves old puzzles even as it finds new ones – this galaxy shows features never seen before in this detail which are not fully understood.” Further research into these open questions is already underway.

Bernie Fanaroff, co-author of the study and former director of the SKA South Africa project that built MeerKAT, noted that “MeerKAT was designed to be the best of its kind in the world. It’s wonderful to see how its unique capabilities are contributing to resolving long-standing questions related to the evolution of galaxies.”

The authors of the study are: William Cotton, Kshitij Thorat, Jim Condon, Bradley Frank, Gyula Józsa, Sarah White, Roger Deane, Nadeem Oozeer, Marcellin Atemkeng, Landman Bester, Bernie Fanaroff, Sydil Kupa, Oleg Smirnov, Tom Mauch, Vasaant Krishnan and Fernando Camilo.

Click on the photographs in the sidebar to learn more about PKS 2014-55 and how X-shaped galaxies are formed. 

DOWNLOAD a high resolution Image of PKS 2014-55  Image Credit: NRAO/AUI/NSF; SARAO;DES

Researchers

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  Dr Kshitij Thorat

  Dr Kshitij Thorat is an astronomer and a postdoctoral fellow at the University of Pretoria (UP). He is a member of UP’s astronomy group within the Department of Physics at the Faculty of Natural and Agricultural Sciences. He specialises in doing research with the MeerKAT telescope and using artificial intelligence (AI) in astronomy. He’s part of the team that has solved the mystery of X-shaped radio galaxies with the help of striking images from the MeerKAT telescope and second author of the study whose results will be published in the Monthly Notices of the Royal Astronomical Society (with a pre-print available here).
  
  What is your academic background?
  
  I have been doing radio astronomy ever since my days as a PhD candidate, when I helped survey a large area of the sky as seen in “radio” light. Following that, I have been working as a postdoctoral fellow in South Africa for nearly five years. The focus of my research has been objects powered by supermassive black holes jets in the distant universe. One of the main reasons I chose to come over to South Africa for postdoctoral work was the appeal of the MeerKAT telescope, which back then was under construction, and which excels in making detailed images of such objects. My time at Rhodes University as a postdoctoral fellow gave me a chance to participate in some of the very first studies done with MeerKAT. So far, I have co-authored eight publications based on MeerKAT observations and several more are on the way. Many of these have been published in the last year or two, after the inauguration of the telescope. Last year, when a call was made for observation proposals using MeerKAT, we submitted a proposal (one of the only 38 proposals which were accepted) to study a carefully selected sample of X-shaped sources, expecting the telescope to produce images of unprecedented quality. This expectation has been borne out fully. Of course, since MeerKAT (and other telescopes) produce such a large amount of data compared to older telescopes, we need to use a lot of automation and smart algorithms to analyse the data efficiently and effectively. I am an expert in the data-intensive process of converting the petabytes of raw data to beautiful images such as the one seen in this press release. I also focus on machine learning techniques to solve issues arising from the transition of astronomy towards big data regime. One of the issues I am especially interested in is automatically identifying sources with unusual morphologies, for example, X-shaped galaxies. Along with Dr Arun Aniyan, my colleague, I have made a tool to identify radio sources using what are known as convolutional neural networks. We were the first to use this technique in radio astronomy. Since then, the field has advanced quite a bit. We have an active collaboration with UP’s Computational Intelligence Research Group (CIRG), with co-supervised students pursuing AI-enhanced astronomy projects, and this is an ideal place to further this line of research.
  
  How did you become interested in astronomy?
  
  That was a long time ago, when I was still an undergraduate student. Astronomy back home in India was really taking off and one had access to a lot of material on astronomy at a popular level. It was really the amazing pictures of our universe which made me interested in astronomy.
  
  Tell us a bit about how this discovery sheds light on previous ideas and how it changes everything we know about X-shaped galaxies?
  
  Currently there are several ideas on how X-shaped galaxies come by their shape. Two of the most interesting ones are that either something changes in the engine which powers these sources - a supermassive black hole sitting at the centre of the galaxy, or that it has to do with the environment in which these sources sit. You could compare it to the nature-vs-nurture debate in the field of psychology. In this particular case, we found several pieces of definite evidence that the X-shape is caused by the latter explanation. This was suspected through earlier studies of this source, but the far superior observations with MeerKAT were instrumental in confirming the correct formation scenario. The jury is still out on whether most (if not all) X-shaped galaxies are formed in such a way, but we are working on that with further MeerKAT observations of more galaxies.
  
  Radio astronomy has taken off in recent years with South Africa playing a leading role because of MeerKAT and the Square Kilometre Array, how much more is there still to do to make it a mainstream field of study in SA?
  
  We are still a small community in South Africa but with a huge interest from students who want to pursue astronomy at a postgraduate level. The research group at UP has grown quickly, becoming a significant component with the Department of Physics in a short space of time. I would say the next five years will determine to what degree astronomy becomes ‘mainstream’ at UP and in South Africa in general.
  
  

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Related Photos

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  UP researchers solve for cosmic 'X' using South Africa's MeerKAT telescope

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  Annotated image that illustrates how the X-shape is formed