X-ray binaries with a Galactic black hole (BHXRBs) have recently been detected in GeV and TeV γ-rays. The radiative mechanism responsible for this emission is not yet fully understood and both leptonic and hadronic processes seem viable. In the former scenario, electrons are accelerated to high energies and dominate the non-thermal spectrum with synchrotron and inverse Compton scattering. In the latter case, protons are also accelerated as well and contribute (or even dominate) in the most energetic regime of the spectrum via neutral pion decay. In the past few years, I have been working on understanding these physical processes, focusing mostly on the hadronic ones. But allow me first to…
Read More >>Warps and twists around black holes
Twisted jets? Warped disks? It’s all possible in black holes! Hi all! Today I will talk a bit about our recent paper on the different types of disks you can have around black holes. As perhaps you would know, in 2019, the Event Horizon Telescope collaboration (EHTC) released the first-ever photos of the inner regions of the galaxy M87 (see link here). The EHTC studied an extensive suite of theoretical models of accreting black holes and tried to see which models looked similar to the observed images. These models simulate how the gas accretes onto a spinning or non-spinning black hole and then calculates how photons of light produced by…
Read More >>What cooling can do for Sagittarius A*
Making an assumption is inevitable and reasonable in many research projects since it is practically impossible to handle all physics we know in a single study; even if it is feasible, it would rather squander resources, which are given to us. However, it is always required to evaluate carefully whether the assumptions are applicable for the particular project. Otherwise, the results may not be able to convince the community, even when the causal connection is well proven to be true. In this post, I will introduce my recent work talking about one assumption people used to make for the study of Sagittarius A*: radiative cooling can be ignored. The supermassive…
Read More >>War of the Clouds: Relativistic jet-cloud interactions
The powerful jets launched by a supermassive black hole feeding on material at the centre of a galaxy, comprise some of the most powerful and highly energetic sources of sustained energy in the known Universe. Launched with velocities close to the speed of light, jets transport large amounts of energy from the central regions of their host galaxies and deposit it into their surroundings. Jets emit radiation across the entire electromagnetic spectrum, but emit radiation particularly strongly at radio frequencies. As the jets travel outwards from the central region of their host galaxy they can come into contact with a variety of obstacles, alongside complex and even hostile environments, which…
Read More >>Things need to change
This is going to be a hard post for me to write, and for everyone to read. It will not discuss science, because today I want to talk about something that I think is far more important.TW: sexual assault discussion below. My main hobby is PC gaming, and many of my favorite games (Starcraft 1 and 2, Dota 2, World of Warcraft) in the past few years have turned into full blown electronic sports (or e-sports) – they are now played competitively by full time e-athletes, and the competition is as fierce, enthralling and exciting as any sport. In the past week or so, more and more people (mostly involving…
Read More >>The Cubic Kilometer Neutrino Telescope or KM3NeT
Can you smell this? It’s the fragrance of gunpowder! Let us then investigate the “smoking gun”! Oh, I love this expression! But why do we relate the expression, “smoking gun”, to astrophysical neutrinos? The answer is simple. We cannot observe particles being accelerated to high energies in situ. To be more precise, we cannot observe protons/nuclei gaining energy of the order of 1015 eV (or even 1020 eV sometimes) in the distant Universe. Then, how can we study these kinds of particles? Indirectly of course! Just let these protons/nuclei gain enough energy so as to be able to interact with their ambient medium and voila! The interactions of accelerated protons/nuclei…
Read More >>An extraordinary burst overshone the radio sky
Fast radio bursts are enigmatic transient sources that attracted many studies in the past 13 years. They are radio bursts that release a huge amount of energy within milliseconds time. For many years, they were only observed from very distant galaxies. Given the large distances, those extragalactic fast radio bursts remain mysterious events (find here a review by Emily Petroff). On Apr 28, 2019, an extremely bright millisecond-duration radio burst was caught from a magnetar in our Miky Way! The radio bursts were detected by two radio telescopes — Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Survey for Transient Astronomical Radio Emission 2 (STARE2). They are powerful radio arrays…
Read More >>The runner’s trails: the characteristic features of fast-moving X-ray Binaries or Bow-shock Pulsars
In today’s post, I will talk about a subset of compact objects (neutron stars or stellar mass black holes), which run with very high spatial velocity through the interstellar medium. Those runners, in general, imprint characteristic signatures on their way: trails and bubbles. For the case of static objects (i.e., no proper motion), which the relativistic jets (or winds) from the compact objects interact with the ambient medium, the theoretical model of the evolution has been studied well over the decades: (1) the early momentum-driven phase, where the ram pressure of the jet is significant for the dynamical evolution, (2) the energy-driven phase, where the slowed-down outflow inflates supersonically expanding…
Read More >>A sensitive new radio catalogue for M83
Something slightly different today. Recently I posted about some work I was involved with where we discovered a candidate X-ray binary in the galaxy M83. However, that work came out of a much larger project completely unrelated to X-ray binaries. For the past few years, I have been working with a number of collaborators all over the world (Rick White, Knox Long, Bill Blair, Roberto Soria, and Frank Winkler) to observe, map, and create a deep new radio catalogue of the face-on spiral galaxy M83. This work has just been accepted for publication in MNRAS, so expect to see it in full very soon. Using radio observations with the Australia…
Read More >>When black hole jets disappear
Today I will be previewing a neat result me and Tom have been working on for the past few months. It’s going to be a bit more technical than my usual post, so please bear with me. In September 2017, a new black hole X-ray binary called Maxi J1535-571 was discovered, and Tom started observing it with ATCA, an Australian radio telescope. At the same time, many of our collaborators also looked at the source with infrared, optical and X-ray observatories, producing lots of really interesting data to analyze. This is really useful because while X-ray and optical data gives us some information about the material falling towards the black…
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