Skip to main content

Gravitational lensing in astronomy and supernovae

Jumping right to the point, astronomers recently discovered a gravitationally lensed supernova.

Simply put, a supernova is a star blowing up. They are some of the brightest objects in the sky. In fact, the most recent supernova in the milky way galaxy was in 1604 and the supernova was so bright that people could see it in the day for over three weeks. It is worth noting that this supernova is at a distance of 20,000 light years.

Gravitational lensing on the other hand is the bending of light due to a massive object near it's path. Einstein's theory of general relativity was in fact experimentally proved when gravitational lensing was first observed as light from stars behind the sun bent around it to reach us. Galaxy and galaxy clusters are the major sources of gravitational lensing from an astronomical perspective. Coincidentally, if another galaxy or part of a galaxy (object galaxy) is behind this massive galaxy cluster closer to us (field galaxy), the object galaxy's features are lensed because of the field galaxy cluster. Such a lensing would create multiple images of the object galaxy as light travelled around the field galaxy along multiple paths.

Incredible lensing features can be observed such as the Einstein's cross. It is interesting to note that because of a difference in path traveled by the light along the different focal paths, if there are temporal variations in the object galaxy, such variations are observed to have a delay between the multiple images of the object galaxy created. Studying such variations can help constrain cosmological parameters such as H_o, the hubble parameter.

Coming back to the point, astronomers recently discovered a quadruply gravitationally lensed supernova. And interesting science can be expected to pour out of the data from these observations. One of the first papers I've noticed as a follow-up of the detection is a new paper constraining the lens model of the field galaxy. It'll be interesting to see what more comes out of such observations.

And last but not the least, these observations were carried out from space by the Hubble Space Telescope (HST). Earth-based observatories have a small chance of observing such faint supernova, especially when they happen at such large distances and this is a testament to the golden goose that is the HST, an investment that keeps on giving back to the scientific community.

[1] Kelly P Et al.
[2] Keren Sharon, Traci L. Johnson
[3] Masamune Oguri

Popular posts from this blog

Animation using GNUPlot

Animation using GNUPlotI've been trying to create an animation depicting a quasar spectrum moving across the 5 SDSS pass bands with respect to redshift. It is important to visualise what emission lines are moving in and out of bands to be able to understand the color-redshift plots and the changes in it.
I've tried doing this using the animate function in matplotlib, python but i wasn't able to make it work - meaning i worked on it for a couple of days and then i gave up, not having found solutions for my problems on the internet.
And then i came across this site, where the gunn-peterson trough and the lyman alpha forest have been depicted - in a beautiful manner. And this got me interested in using js and d3 to do the animations and make it dynamic - using sliders etc.
In the meanwhile, i thought i'd look up and see if there was a way to create animations in gnuplot and whoopdedoo, what do i find but nirvana!

In the image, you see 5 static curves and one dynam…

Pandas download statistics, PyPI and Google BigQuery - Daily downloads and downloads by latest version

Inspired by this blog post :, I wanted to play around with Google BigQuery myself. And the blog post is pretty awesome because it has sample queries. I mix and matched the examples mentioned on the blog post, intent on answering two questions - 
1. How many people download the Pandas library on a daily basis? Actually, if you think about it, it's more of a question of how many times was the pandas library downloaded in a single day, because the same person could've downloaded multiple times. Or a bot could've.
This was just a fun first query/question.
2. What is the adoption rate of different versions of the Pandas library? You might have come across similar graphs which show the adoption rate of various versions of Windows.
Answering this question is actually important because the developers should have an idea of what the most popular versions are, see whether or not users are adopting new features/changes they provide…

Adaptive step size Runge-Kutta method

I am still trying to implement an adaptive step size RK routine. So far, I've been able to implement the step-halving method but not the RK-Fehlberg. I am not able to figure out how to increase the step size after reducing it initially.

To give some background on the topic, Runge-Kutta methods are used to solve ordinary differential equations, of any order. For example, in a first order differential equation, it uses the derivative of the function to predict what the function value at the next step should be. Euler's method is a rudimentary implementation of RK. Adaptive step size RK is changing the step size depending on how fastly or slowly the function is changing. If a function is rapidly rising or falling, it is in a region that we should sample carefully and therefore, we reduce the step size and if the rate of change of the function is small, we can increase the step size. I've been able to implement a way to reduce the step size depending on the rate of change of …