Day One
I am Vai Krishnan, and I look forward to documenting my experience of my work experience here at ICRAR for the next for days!
Our day started at 9, and we started off with a tour of the building at Curtin by our supervisor, Ronniy Joseph. Ronniy was extremely friendly and gave us a tour of the building, a quick PowerPoint of a summary of what astronomers do, and what goes on here in ICRAR. We had a short break where we got to talk to the other students, and then we went to PhD students, to talk to them about their experiences – and what they were aiming for. I talked to Mark – a student who was doing research on the Epoch of Reionisation (EoR). He gave us a rundown of cosmic microwave background radiation, redshift and blueshift, and the light emitted from hydrogen, which has a wavelength of 21cm.
We were then led to a meeting – where members talked about recent space and astronomical news. First, we talked about a new technology for cameras – inspired by the human eye, where instead of a shutter there are receptors which can react to constant illumination – meaning that we can take better photo’s during the daytime. The second topic we talked about was the all famous discovery of the black hole: M87. We were told about how it was found, using the telescopes all around the world, what the picture shows, the way the black hole was spinning, a simulation of how the image would have occurred, and some calculations as to the actual size of the singularity being 10x smaller than the shadow shown on the image of M87.
After that, we had a lengthy lunch break, and then we delved into the engineering side of things. We started by looking at the Murchison Widefield Array (MWA), and how it was structured, with every weird design having some purpose. It started with one spider like antenna, which is designed to absorb the radio waves efficiently, anywhere from 7- 300MHz. There are then 16 of these antennas on a tile, and there are 256 of these tiles spread out across Murchison, meaning there are 4096 antennas, although only half are in use at a time (due to computing power). We went through the steps of how the MWA collects, analyses and uses the data it receives from space, and then we went to the labs to look at some models of the antennas, that were real life replicas.
We finished the day talking to some more PhD students, talking firstly to two PhD students about pulsars, which are densely packed stars with a diameter of roughly 10km, however they are extremely dense and magnetised, leading to the creation of a pulsar. We have found 2700 pulsars, and most of them have been found in the Milky Way. We did some calculations to find out the radius of the pulsar which within all the exciting physics that the PhD students were studying.
I can’t wait for my next day! I look forward to the rest of the week and more amazing astronomy.
Day Two
Hi everyone! On our 2nd day at work experience, we went to the ICRAR site at UWA. We were met by Greg Rowbotham, who was very friendly and nice. We started off the day with a tour of the campus, with Greg showing us the usual safety plans, and then we went to watch a video – it was a summary of cosmology by Alan Duffy. The video was quite intricate, and it taught us about the composition of the universe (baryons, dark matter, dark energy), that the universe is flat, the Hubble constant (the expansion rate of the universe), and cosmic microwave background. This was quite useful as it gave us some background knowledge for when we talked to the PhD students later in the day.
After a short break, we went to a meeting room with Greg, and he took us through the process of weighing a galaxy. This was all calculated through light – the emission of light from the electrons of a hydrogen atom within the galaxy – we saw a double horn structure on a graph which shows us the velocity the galaxy. Greg taught us a formula using velocity, the radius of the galaxy and the gravitational constant to find the mass of the galaxy, and we also found the distance of the galaxy from us.
After that, we had lunch and then started talking to some PhD students. The first student we talked to was one who told us all about simulations. Firstly, she told us of the two types of simulations: Hydrodynamical and Semi – Analytical models. We went through what it meant to simulate using the two methods, the restraints of current technology, and what simulations can actually tell us. We learned that in hydrodynamical simulations thousands if not hundreds of thousands of particles are put in a box and are left to be simulated on their own – so the computer does all the work, which can be very computationally intensive, whereas in semi analytical simulations the particles are simulated using gravity alone first, and then the messy physics are added later.
The next PhD student we talked to talked to us about Galactic Dynamics. This was about how objects moves, and this can be predicted based on the mass of those objects. She particularly looked at merging spiral galaxies, and how they would look once they were simulated.
The final PhD student we talked to was on an exchange from England, here for 6 months. In his work, he did many things. He did multiwavelength cataloguing (where he supported other astronomers), he studied very high redshift galaxies, dealt with deep field images, AGN feedback in massive galaxies, Photometric Redshift Algorithms, and more. He talked to us about how he catalogued millions of galaxies using his algorithm, which is used because the traditional way of comparing emissions to the redshifted ones was far too impractical for millions of galaxies. He also talked to us about Active Galactic Nucleus (AGN) feedback – this is the expulsion of hydrogen and other gases from a galaxy through jets at either end of a supermassive black hole at the centre of a galaxy. He also told us about a theoretical way that these jets are formed, one that has not yet been simulated. It starts with the magnetic field of the black hole, which is very strong, and the gases in the galaxy becoming ionised. The ionised gasses then are accelerated around the magnetic fields, close to the speed of light, at which they are expelled into space, and can travel many millions of light years away.
My 2nd day at ICRAR was just as amazing as the first and has proven to be an amazing experience!
Day Three
For the 3rd day, we were back at Curtin and for the first half of the day we got straight into speaking to the PhD students. We started with a talk to Chris – a scientist working on a project after he had finished his PhD. He talked to us about what his project was about, which was the distortion of results of lower frequency radio wavelengths by a layer of the atmosphere (the outermost layer) called the ionosphere. He showed us how you can simulate what you expect to see in the sky, and then observe actual results, and subtracting one image from another gives you some position vectors showing how the data has been distorted. After doing this many of hundreds of times, we are able to create a movie of the interaction of the ionosphere, through the position and movement of the vectors. This is important as we can see how the ionosphere moves, and hopefully in the future we can predict when it will be bad for viewing objects and when it will be good, to minimise the amount of errors in our viewing.
Next, we talked about binary systems (orbit of two stars), and how they can emit x rays and radio ways. We learned that in order for this to happen, we need to have a black hole as one of the two stars in orbit, and the black hole will pull some of the contents of the star into the black hole, and this accretion disk of hot plasma will emit x rays. There will be points at which a lot of mass is dumped from the star onto the black hole, and in order to get rid of this excess, the black hole will create jets at either pole, which propel radio waves out.
We then talked to another PhD student about cosmic rays, which are high energy particles that are made up of protons, neutrons and electrons. We currently are not sure where the come from, however we do know that they are quite common, and when they reach the atmosphere, they split up into many subatomic particles, mainly muons. The muons are charged with a charge of -1, however they have much more mass than the electron, so they are able to penetrate kilometres deep into the earth, and these subatomic particles are what we detect.
After lunch, we talked about gamma ray bursts (GRB), and we learned that there were two types of GRB’s: Short GRB’s and Long GRB’s. Did you know that gamma ray bursts were originally found by a US satellite during the cold war, when they were looking if the Russians were developing any nuclear warheads, however they detected radiation coming from outside of our solar system? Short GRB’s are thought to be created due to the merger of two compact objects (black hole or neutron stars). They have a duration of less than two seconds and have an average life span of 0.3 seconds. Long GRB’s are thought to be created as the result of a hypernova, have a duration greater than 2 seconds, and an average life span of around 30 seconds.
Later we spoke about the MWA arrangements, to an engineer. We saw how the higher frequency waves tend to split the observation way – meaning if you point the MWA in one direction it will also detect radiation from another direction, depending on the angle and the frequency of the wave. We also saw that the way to counteract this is to place more elements per stile instead of the standard 16 and in a non-grid fashion, with a random sort of way.
We then got to analyse some black hole data, where we learned some basic Linux terminals commands, and the program DS9. We were able to compare three images of the same body, and because of this we were able to determine how much (if at all) the object we were studying (a black hole in our case) was moving.
Day three was an amazing day, the last at Curtin, which was sad but in the two days we were there I learned so much!
Day Four
With the start of day four we got straight into speaking to PhD students, and we started with a third year PhD student. He studied the hydrogen in galaxies, and how the hydrogen is affected by groups of galaxies. He does this using the double-horned graph, and he looks for asymmetries. If the two horns are equal, this means that the galaxy is travelling away from us as fast as the galaxy is travelling towards us. However, if there are any asymmetries then we can tell that there is some interference in the travel of the galaxy.
After we talked, we went back to the lounge area and had a morning tea, to celebrate Easter. There was plenty of food and it was quite lively. After filling ourselves with chocolate, we went to talk to another third year PhD student called Ahmed. He showed us his field of work, which I happened to find incredibly interesting. His line of work was how galaxies interact, through the hydrogen gas distribution in galaxies. He mainly focused on the collision of galaxies, particularly where a smaller galaxy plunges through the centre of a larger galaxy. This creates a ring of hydrogen gas in a ripple, which travels outwards from the centre of the galaxy. If this happens early on in a galaxy, then the hydrogen ripples towards the outside and it forms bright pink spots in the galaxy. These pink spots have so much rapid formation of stars, and the stars that are formed are OB stars, which are stars that emit an ultraviolet radiation. A galaxy that has the hydrogen pushed to the edges is called a ring galaxy, and there are roughly 150 ring galaxies in the local group. I learned that the medium between galaxies is known as the inter galactic medium, and it is made up of hydrogen gas and other elements from stars that have broken down long ago. We learned that as galaxies move through space, the gas at the leading edge of a galaxy is compressed and the gas at the ending edge expands. When the galaxy moves, if the conditions are met, then the hydrogen is stripped away from the galaxy, in a process called RAM pressure stripping. The denser the intergalactic medium the faster the stripping occurs, and the faster the galaxy is going the faster the stripping occurs. We determined the equation (b=ρv^2)
After this, we went with Pete to the top of the UWA building, where there were two optical telescopes located, inside their respective domes. I was awestruck at how cool these telescopes looked, the fact that we can operate them from home and that they can take such high-resolution images despite being relatively close to the city centre!
Next, we talked to a PhD student, also about galaxies. However, this time we talked about a hidden, often disregarded component of the galaxies: dust. We learned that dust is a solid material that absorbs UV or optical photons. They then re emit those photons in the IR or radio spectrum. This dust is made up of either silicate – which are oxygen rich, or organic compounds – which are carbon rich. The reason why we can see galaxies in infrared and radio waves is because they do not get absorbed by the dust, and the little radio waves and infrared waves that are emitted by the dust itself have low enough flux (brightness) that we can disregard them. Dust influences the process of star formation as well. It starts with one atomic hydrogen getting stuck in the dust, and another atomic hydrogen interacts with the first and they chemically bind to make nuclear hydrogen (H2). In the process of making this bond, heat is also released into the environment, freeing the hydrogen from the dust. This process is far more efficient than the random bonding of atomic hydrogen. We also learned that the dust can grow over time, if the galaxy has enough metallic species available.
Over the course of these four days, I have learned so much and this experience has opened my eyes as to just how varied the field of astronomy is. I feel that this has inspired me to follow astronomy in my career path, and I am extremely grateful for this opportunity.
Thank you,
Vai Krishnan