Rahul gives unsolicited advice

Galaxy evolution is a tug of war between the nature of the galaxy (morphology, mass, etc) and nurturing environment of the galaxy (major or minor mergers, ram stripping, etc) and to understand it, we need to understand when nature rules over nurture or otherwise. An interesting way to resolve this question is to study isolated galaxies - isolated in the sense that there are hardly any galaxies in their vicinity. The qualitative 'hardly any' was quantified to create the Catalog of Isolated Galaxies (in 1973) and then revised by the AMIGA people for a more up-to-date study. Understanding the evolution of isolated galaxies inherently tells us more about the role that the nature of the galaxy plays in it's evolution. Today, I was reading up on some interesting papers by the AMIGA people, all three on the HI (neutral Hydrogen) profiles of select isolated galaxies. The three papers can be found here , here and here . I came across this survey recently and only today, as I wa...

For those who don't know, GMRT stands for the Gaint Meter-wave Radio Telescope. Meter because it observed radiation with wavelength of about a meter or about 300 MHz. Ohkay, with that out of the way, let's talk about the actual paper. If you have been following my blog posts, you will understand why studying faint, irregular, dwarf galaxies is important. Faint dwarf galaxies have very low mass and understanding them will help us understand galaxy formation and evolution in the low mass case. Another interesting thing I learnt from the paper, that should've been obvious to me earlier, is that the gravitational force keeping the (gas in the) galaxy together is about the same as that produced by a few supernovae. The reason they are irregular makes sense now because once these galaxies start forming their first stars, which then go on to explode, the galaxy's gas gets pushed out by the explosions. Also interesting is figure 12 from the paper, that tells us that most of ...

If large cameras and telescope capable of probing the low surface brightness objects in the sky is one end of the state-of-the-art in astronomy, the following work would be the state-of-the-art at the other end of the spectrum. While surveys focusing on looking at all of the objects in the sky, choosing speed and number of astronomical objects found over spatial resolution, there are telescopes used specifically to study objects at the highest spatial resolution. The paper ( found here ) talks about a narrow, edge-on disk resolved around the star HD 106906 using the SPHERE instrument on the VLT telescope. Note that I used to word resolved and not detected. For an astronomer, those two words are vastly different. The same way dark matter is discovered but not yet observed, astronomers knew that the aforementioned star had a dusty disk around it. How you ask? Well, for starters, if you have dust in front of a light source, the light source looks dimmer. Secondly, whatever light that t...

I am crazy about the Sloan Digital Sky Survey (SDSS). I worked on data from the SDSS for my first summer project. I learnt about SQLquery to acquire data from the SDSS's servers and I learnt Python to do the relevant data analysis. It's an unbelievable treasure trove of data and is in my opinion, the best place to start off if one is serious in pursuing a career in astronomy. Having said that, a while back I was looking at the various institutional members of the SDSS and I found out that there were NO Indian institution involved with the project. None whatsoever. Now, don't get me wrong, I'm sure that there were Indians involved in the project. I'm saying that there was no institutional support meaning that Indian universities weren't funding the project or actively building instruments for the project or had priority access to the data. And it kind of made me sad. The good news now is the fact that India is a 10% partner in the Thirty Meter Telescope (TMT)...

Well, for starters, the DECam is the Camera on the 4-metre Blanco telescope at the CTIO (Cerro-Tololo Inter-american Observatory). It was originally designed for the DES (Dark Energy Survey) but I guess it's also being used for other astronomical observations. The authors are part of the NGFS (Next Generation Fornax Survey) efforts at the CTIO. Coming to the paper ( found here ), the authors give a preliminary report of the 158 new dwarf galaxies they've discovered in the Fornax cluster central regions. There is a lot more science to come out of the data but a preliminary analysis shows that the dwarf galaxies seem to be clustered within the Fornax cluster core, clustering previous predicted in simulations. The authors also fit the surface brightness distribution for each of the dwarf galaxies found to estimate their effective radii. The dwarfs found seem to be fainter and smaller than similar ones (referred to as Ultra Diffuse Galaxies - UDGs) found in the Virgo cluster and...

As I follow the endless path, looking for references in papers, I came across this - the HI rogues gallery . It is a " Collection of maps of HI in Weird Galaxies and Weird HI in otherwise Normal Galaxies " and wow is it a beautiful collection. The whole reason astronomers are interested in HI (neutral Hydrogen) in the universe is because it is the fundamental fuel that makes stars. Also, there's loads and loads of it in galaxies and in the Inter-galactic medium (theoretically).  And in galaxies, this HI extends wayy beyond the boundary defined by the stellar population of the galaxy. This fact can be used to understand the (baryonic) gravitational potential of the galaxy it is embedded in, and the dark matter halo it is embedded in. If you dig through the gallery, you will come across interesting examples showing  intergalactic debris with no optical counterparts ! This is interesting as it helps us understand the history of the galaxies, their environments and the dis...

I've been coming across a lot of work, in the optical and the radio domain to identify and understand dwarf/satellite galaxies, stellar tidal streams and neutral HI (HI is neutral Hydrogen and HII is singly ionized hydrogen i.e a proton) in the universe. This is one of many such efforts (a few of which I will write about later on) where the authors used the SKA pathfinder telescope BETA/ASKAP to observe the galaxy group IC 1459. The full paper can be found here . Let me first tell you why it's a challenge to observe neutral HI in the local universe and why these results are so interesting, IMO. All galaxies form from HI (again, neutral Hydrogen) but once the galaxy/stars start(s) forming, neutral HI close to the sources of radiation get ionized into HII. Only HI in the outer reaches of the galaxy is left unionized. And given that it's at the edge of the galaxy, it's not nearly dense enough to emit strongly. Don't get me wrong, there is still a good amount of HI i...

Well, I got to know a couple of days back that there was a Lunar-based Ultraviolet telescope. I finally got to read the paper today ( that can be found here ) and it's quite interesting. For those of you who remember, the Chinese landed a Lander on the moon and tried sending a rover on the lunar surface (which quickly failed). Apparently, that Lander had a UV telescope on it. As soon as I read the abstract, the first questions that came to my mind was when exactly they observe. If you think about it, we see the moon at night because it reflects the sun's light meaning that if it's night time for us, it is day time on the moon. The same way, if I were on the moon, I'd be able to see the earth because it will reflect the sun's light. Astronomers on earth prefer moonless nights because the night skies are darker. In the same way, the lunar based telescope had to take into account the fact that earth shines bright at night time when designing their telescope and plan...

I was discussing with a friend of mine about why early pictures of moon, say from the apollo missions, were so blurry. Well, astronomers don't enjoy the kind of speeds you and I do every day on our mobile phones, laptops and desktops. Most of us get impatient about low internet speeds, curse our service if the internet connection changes from 3G/H/H+to 2G. On the other hand, the data transmission rate from space craft back to earth is in the range of 100s of kbps. Deep space network , the title of this post, is a collection of radio antenna distributed all over the earth which are used to communicate with space craft and  DSN NOW  is a site which shows which antenna is communicating with which satellite, what the transmission rate is, what frequency they are transmitting at and so on. There are a lot more satellites than there are antenna so i guess data is pulled from the satellites based on demand or maybe periodically. As of now, MAVEN, the NASA mars mission is operating a...

A telescope. What do you think it is?! The common perception is that a telescope is a device which is used to look at the stars! Telescopes have mirrors oriented in a a particular fashion which helps us look at stars! Well, this is just part of the story and the tip of an ice berg. A telescope can be described as any device which has the following parts A reflecting surface, to reflect the incoming electromagnetic radiation A receiver which can decipher this electromagnetic signal into a digital signal which we can understand and analyze! So, in the common perception, the reflecting surface is a mirror, one which has been ground to a micrometer finish and one which has been coated to be a (perfect) reflecting surface. And this setup is for observations in the visible part of the electromagnetic (EM) spectrum.  Note :   In the context of this blog post, light will refer to EM radiation of any frequency and not just the visible frequencies ...