In today’s post I will talk about Compton scattering – a physical process by which light and matter interact. Interestingly, this process is responsible for colouring our sky and also for generating electromagnetic radiation from the most energetic phenomena in the universe. A Brief History This phenomenon was first discovered by Arthur H. Compton in 1923, for which he won the Nobel Prize in 1927. This process was also an important evidence of the particle nature of light, i.e, it proved that light (or electromagnetic radiation) exhibits particle like behaviour. In other words, if light only behaved like waves then the energy lost by light during Compton scattering could not…

With the Event Horizon Telescope results just a few days away, I thought it would be great to discuss how exactly a jet is launched from a black hole. The thought is counter-intuitive. Black holes are depicted as these giant “vacuum cleaners” in the centre of galaxies, eating up anything that has the misfortune of venturing close to it. Black holes are nicer than that, sometimes even throwing stuff out. This “stuff” is in the form of highly magnetised plasma and travels at near light speed (hence, a “jet”), shining over many orders of magnitude in distance. Above: VLBA 2 cm image of the parsec scale jet in the galaxy…

In this post I thought I’d write a bit about my Master’s thesis, which eventually (thanks to a good bit of luck, as you will see) led to my very first paper. During my master’s thesis I worked (together with Fabrizio Tavecchio and Gabriele Ghisellini at the Merate Observatory, near Milan) on understanding the properties of AGN jets on large scales – and by large, I mean hundreds of kiloparsecs or more, way beyond the edge of the galaxy hosting the central black hole. Historically, these sources have been observed in the radio frequency, and to this day they are generally referred to as “radio-loud AGN” – even though scientifically,…

Hi all, Over January and February, we had an exchange student, Wanga Mulaudzi from the University of Cape Town, come to Amsterdam to work with us on a new project. This project uses multiwavelength data from an outbursting black hole X-ray binary to model how the jet physics evolved during the outburst. With Wanga, we collated radio, mm, infrared and optical observations to trace the jet evolution, as well as X-ray observations to determine how the accretion flow was changing and driving the jet evolution. Due to the multiwavelength and multi-disciplinary nature of this project, this project included many of us in Sera’s group: myself, Matteo, Sera, Fe, Tobi, and…

With my post, I would like to summarize work that my colleagues and I published recently (Beuchert et al. 2019, A&A, 610, 32). Let me start with a general introduction to provide the necessary context needed to understand what “jets” are. One of the major open questions in astrophysics deals with the most powerful objects in the Universe. We find them in the very centers of so-called Active Galaxies, where we expect at least one very heavy black hole (a Million to a Billion solar masses) to reside. In the consequence of its attractive force combined with friction occurring within the dense matter in orbit around it, matter will slowly spiral…

Hi all, Firstly, I hope you all had a great holiday period! Over the Christmas break, I had a paper published in ApJ letters (links at the bottom of the page) that I thought I might summarise here. This paper was focused on the radio emission from a newly discovered X-ray transient called IGR J17591-2342. In this post, I want go through events in chronological order, which should show our thinking and highlight the reason for our paper. However, before I get too carried away, I first need to introduce something called the radio/X-ray correlation for accreting stellar-mass compact objects. There is a well-studied non-linear relationship between the radio and…

This morning I came into work to read some super exciting news in my email! A gamma-ray burst (GRB) has been detected by ground based TeV facility MAGIC for the very first time, with extremely high significance! There has been an impressive multi-wavelength campaign to try to constrain more details of the source, and it seems to be extremely bright, almost 100 times as bright as the “typical” GRB. This is not surprising because the source, while somewhat nearby by GRB scales, is still many billions of light years away, so it had to be very bright or we would not have detected it. If you want to read more…

Fantastic Beasts (and where to find them) Most galaxies on our universe seem to harbor, at their center, the amazing beast known as a supermassive black hole (to know more about black holes see my previous post here). What do we mean by word supermassive? Astronomers compare the mass of most objects in the universe with the mass of the most massive object in our vicinity, i.e., our sun. Supermassive black holes are millions to billions of times more massive than our sun. To put it simply, millions of our suns together would weigh as much as these beasts! For a nice visualization see this link. Light from the vicinity of…

As one of fundamental forces, gravity works its magic on the physics of the largest scales, helping us understand how celestial objects form and move. Sir Isaac Newton in the 17th century formulated a mathematical equation depicting the effect two objects have on each other by virtue of their mass. Newton’s theory successfully predicted the presence of Neptune and continues to guide us in solving high school mechanics problems, apart from describing gravitational forces relating to small masses with velocities much lower than the speed of light. With Albert Einstein’s revolutionary theory of general relativity (or just GR) in 1915, an entirely new view of the heavens was brought to…

Hi, readers. I am Doosoo Yoon, who recently has joined Sera’s group. Since I started my academic career in astronomy, I have strongly interested in performing numerical simulations to figure out how astrophysical phenomena can be interpreted. In my first post, I would like to briefly talk about some basic processes of computational astrophysics and mindset for building a Matrix-world, from several articles I’ve read. Conducting research with numerical simulation requires three main components: understanding of dominant physical processes for the problem of interest, programming them with numerical algorithms and utilizing maximum capabilities of the computers for the simulations (Elmegreen 2011). In fact, all theoretical equations need to be approximated,…