Today’s story starts in 1967, at the height of the Cold War. The US Air Force has been using its Vela satellites to monitor any traces of gamma-ray radiation, a dead giveaway of nuclear tests being conducted on Earth. The goal is to make sure that the USSR is complying with the 1963 Nuclear Test Ban Treaty. On July 2nd, 1967, the Vela 3 and 4 satellites detect a gamma-ray flash that doesn’t look like anything observed before. Over time, they start seeing more and more of these events; according to myth, this was a terrifying find which was immediately classified. Nobody knew that such signals can originate from space,…
Read More >>Finding a candidate X-ray binary in another galaxy
Recently, I have been involved in a study looking for potential X-ray binaries in the relatively nearby spiral galaxy M83. And we think we found one! Here we refer to a microquasar as either a black hloe or neutron star X-ray binary. This work was led by Prof. Roberto Soria at the University of the Chinese Academy of Sciences, and was accepted for publication last week. Here is a link to the arXiv pre-print version. Finding a microquasar Jets from microqusars can produce shock-ionised bubbles as they shoot material out into their surroundings. These bubbles can look like peculiar shaped supernova remnants (SNRs, see Ping’s post for more details on…
Read More >>The changing sky monitored by ancient astronomers
Our ancestors have been monitoring the night sky since 5000 years ago, making astronomy the oldest natural science. Most stars seen on the night sky have been there for millions to billions of years, except that they rise and descend along with the Earth’s rotation. But if one is very patient and lucky, one could see that the sky is changing. For astrological purposes and other reasons, the variation of the sky had been recorded by ancient astronomers. In addition to the comets and meteors, many transient events occur outside of our Solar systems. The astronomical term “transient” expresses the phenomena that some celestial objects switch on and off their…
Read More >>Cherenkov Telescope Array (CTA)
SPOILER ALERT! We are in the year 2030 AD! So, if you do not wish to learn your future, you should stop reading now! Alright, for those of you who are still curious. Hundreds of new Supernovae have been detected. Structures in Supernova Remnants have shed light on particle acceleration, particle interactions and have also helped improve our understanding of diffusion. Powerful pulsars, both with and without surrounding wind nebulae (PWNe), have been detected on the Galactic plane shining light on the mystery of both magnetic fields and the evolution of such systems. Observations and theoretical work focusing on the closest supermassive black hole to Earth, Sgr A*, have yielded…
Read More >>Decelerating jets
I recently published my first paper in my Ph.D., focussing mainly on how jets accelerate from black hole accretion disks using first-principles general relativistic magneto-hydrodynamic simulations. It is an important question, how jets become relativistic, achieving high enough kinetic energy to affect the intergalactic medium upon collision. It turns out that the shape of jet matters a lot and that means, the ambient medium (i.e., the environment surrounding the black hole and the accretion disk) really needs to be evolved properly. Interestingly, when you evolve your simulation enough to give instabilities some time to work their magic, the jet begins to slow down. This slowdown happens because instabilities pick up…
Read More >>The journey of lights to a black hole
In today’s post, I would like to briefly talk about the features shown in the recent black hole image, and the efforts many people have paid for interpreting them. Someone would say that a black hole must be in the form of singularity, which makes it extremely difficult to prove its existence. However, over the decades, many theoretical works have been devoted to understanding the nature of the black hole and the effects of the general relativity; and providing the observational signatures that are expected. By the huge efforts of the international collaboration, the event horizon telescope (EHT) team has revealed the unprecedented image of the nucleus of the nearby…
Read More >>Jet launching in the black hole system MAXI J1535-571
Today I thought I would discuss results from my recent paper in ApJ (ArXiv link here). This paper presented results from a very long and comprehensive radio monitoring campaign of the black hole X-ray binary MAXI J1535-571 and included many people within the group. Using observations that I personally took with the Australia Telescope Compact Array (ATCA) (Figure 1), we were able to track the radio jet throughout the entirety of its 2017/2018 outburst. We found some very interesting and important results from this campaign. For the next part, you need to know that two types of jets are observed from black hole X-ray binaries. During lower accretion rates we…
Read More >>Sometimes, a star gets very unlucky…
Today I’ll be writing about the very first topic I ever did research in, during my Bachelor’s thesis: Tidal Disruption Events (or TDEs), or the most dramatic way in which a star’s life can end. Before getting into cool astrophysics stuff, let me remind you of how tides (roughly) work. Because of gravitation, the Moon attracts the Earth; however, because gravitation depends on the distance between two objects, points on the Earth that are closer to the Moon are attracted more, and vice versa. If the thing that’s being attracted isn’t solid – say, an Ocean – the result is that the Ocean gets deformed by gravity: In practice it’s…
Read More >>Helen Sawyer Hogg Prize Public Lecture in Montreal
I had the great honour last night of participating in an annual public lecture series put on by the Canadian Astronomical Society/Société Canadienne d’Astronomie (CASCA) and the Royal Astronomical Society of Canada. It was a pretty amazing thing to see my name on the same page as the prior speakers, many of whom have served as inspirations for me, like Vera Rubin, Dame Jocelyn Bell Burnell, and Fiona Harrison. This evening lecture for the public (though many scientists from the CASCA meeting also attended) was the first time I’d given a full hour public lecture, since normally most public talks are around 20 minutes, and it was a real pleasure…
Read More >>Unraveling a mystery in the Spanish Sierra Nevada
Very soon, in August, I will have the honor to visit and use a radio dish of 30 meter diameter on Pico Vileta in the Spanish Sierra Nevada, the IRAM 30-m telescope. I will be able to use it for unraveling a long-standing mystery related to an extremely energetic object within our own Galaxy. While I have been using radio-telescope data before, this is certainly something new and exciting for me. As observational astronomers, we are taking a lot of time submitting proposals to telescopes in order to eventually get to observe our desired object. In my case, these objects were mostly very massive black holes that are extracting gravitational…
Read More >>
