A couple of weeks ago, the Event Horizon Telescope (EHT) collaboration has revealed, for the first time, the black hole image of the M87 in polarized light. This is the next big step closer to better understanding how accreting materials evolve and how M87 launches the energetic jets, which extend at least 5000 light-years. Light becomes polarized when it propagates through filters like the lenses of polarized sunglasses. Such sunglasses have been used to protect our eyes and enhance our vision by reducing the glare of the sun or the reflected light. Likewise, we can see better the region around the black hole from the polarized light, which is emitted…
Read More >>MasterChef Universe : Spaghetti(fication) with Black Holes (Part III)
This is the final part of the three part series on Spaghettification where finally black holes come into the picture! Black Holes Black holes are regions of space(time) where gravity becomes is so strong that that not even light can escape. The size of this spherical region is specified by a radius called the Schwarzschild radius (in honor of the German physicist and astronomer Karl Schwarzschild). The radius of a black hole is proportional to it’s mass. For example: a black hole having the same mass as our Sun (what astronomers call 1 solar mass) is like a sphere having a Schwarzschild radius of 2.8 km. In comparison the sun’s…
Read More >>Self-similarity: Properties and Applications
In China, there is a popular nursery rhyme: Once upon a time there was a mountain, in which there was a temple, in which there was an old monk telling a story to a little monk. The story he was telling is: Once upon a time there was a mountain, in which there was a temple, in which there was an old monk telling a story to a little monk…… It continues endlessly until the child falls asleep. This rhyme is a typical manifestation of the concept of self-similarity. In mathematics, self-similarity describes the property of an object if a part of it resembles the whole object. In the aforementioned…
Read More >>Persevering with Mars Exploration
February 18th 2021, 12:55 PST. A room in California erupts in cheers and applause as mission control watches its robot land on another planet. After years of preparations and almost seven months of space travel, Perseverance arrived safe and sound on the Red Planet, ready to study its environment for a planned duration of two years. It will join NASA’s Mars Exploration Program lineage of four martian rovers, making it the fifth since 1997 to explore this curious planet. But why do we care about Mars so much? Mars has always been an object of wonder, from the idea that a civilization could inhabit it to Elon Musk’s plans for…
Read More >>To be MAD or not to be MAD: problematic naming conventions in astronomy
Last week’s blog post was entitled To be MAD or not to be MAD. In it, my colleague Doosoo Yoon did a good job of discussing two models used to describe the accretion disks of matter flowing onto a black hole. These models started a discussion in our research group meeting this week for a different reason: the names of the two models MAD and SANE are pretty ableist. As Doosoo pointed out, MAD stands for Magnetically Arrested Disk and SANE stands for Standard And Normal Evolution. Now the MAD model which was created first, about 20 years ago, has a simple acronym and is widely used in the astronomy…
Read More >>To be MAD or not to be MAD
Infalling on to the black hole may drive materials crazy. How on earth can they keep their sanity while all bodies undergo extreme gravity? These days, most researchers who are simulating an accreting flow around a black hole choose the condition of the accretion disc between the “SANE” and “MAD”. Now you may think that the infalling materials would be CRAZIER in the “MAD” disc than the other. In fact, the component for dividing “SANE” and “MAD” is the strength of poloidal magnetic fields. “SANE” stands for Standard and Normal Evolution, and “MAD” stands for Magnetically Arrested Disc. Over the decades, the magnetic field structures around the central black hole…
Read More >>The curious case of FR0s: The relatively new class of radio galaxy
Radio galaxies are a class of active galactic nuclei that shine very brightly at radio frequencies but also radiate across the entire electromagnetic spectrum too. Powered by accretion of matter onto a central fast-spinning supermassive black hole, radio galaxies can display extended radio structures- jets. Jets emit radiation strongly at radio frequencies and can propagate hundreds of kiloparsecs (1 kiloparsec = 3.086 x 1016 km) or more beyond the central black hole that powers them. Jets travel with relativistic velocities, carrying large amounts of energy with them to regions well outside the confines of their host galaxy. Radio galaxies which display these jets can be classified based on their morphology…
Read More >>MasterChef Universe : Spaghetti(fication) with Black Holes (Part II)
This is second part in the series of posts about Spaghettification. In this part we go over the idea of how gravity squeezes objects. We will also briefly discuss how to make tidal forces stronger. Squeezing Now let’s rotate the rod so that it is oriented with both ends equally distant from the Earth, while the rod’s mid point is still located at a distance R from the Earth’s center. Unlike the case when the rod was vertical, here the Earth pulls at both these ends with an equal force directed towards the Earth’s center (white arrows in Figure 2). The force at the left end (point A) can be…
Read More >>MasterChef Universe : Spaghetti(fication) with Black Holes (Part I)
Can black holes make spaghetti? Like Obama, black holes would reply ‘Yes we can’! To top that off they can make spaghetti out of anything – using their ‘gravitational machinery’. In this three part series we will see how black holes employ gravity to do so! Before we go exploring black hole’s ‘spaghetti skills’, in part I, first let us look closer to home, at our very own Earth’s ‘spaghetti skills’ and its connection to the concept of tidal forces. Gravity and Tidal Force Let’s begin with the familiar. Earth produces a gravitational field by the virtue of its mass, and objects immersed in this field feel a gravitational force.…
Read More >>Can you Discriminate between Space and Time? (Part III)
In part II we saw that in a non-rotating black hole, the spatial and temporal coordinates are exchanged. Now we can take a step further, to consider the case of a rotating black hole. The line element in such spacetime has very complicated coefficients, but we don’t need the specific expressions here. So let’s just represent them in terms of the metric components: From the specific forms of those coefficients, we know that the dt2 and dϕ2 terms are always positive while the dtdϕ term is negative. What differs from the non-rotating case is, here the gtt and grr don’t switch signs at the same place, but at rH and…
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