A brief description of galactic clusters and their detection

 

The oldest galaxies are observed today as elliptical, and to be found in clusters. These clusters are the remnants of older protoclusters that dominated the landscape of outer space in the universe's early years, years that witnessed the formation of the first stars and, subsequently, the first galaxies. In  regions of space where the population density of stars is low and the closest cluster farther away from the closest star, more recently formed galaxies may be found. These relatively emptier regions are called 'general fields'.

A galaxy takes hundreds of millions of years to form fully, and involves processes quite complex; imagine, the simplest among them are nuclear transmutations! At the same time, the phenomenology of the entire sequence - the first steps taken, the interaction of matter and radiation at large scales, the influence of the rest of the universe on the galaxy's formation itself - can be understood by peering into history through some of Earth's most powerful telescopes. The farther through their lenses we look, the deeper into the universe's history we are gazing. And so, looking hard enough, we may observe a protocluster in its formative years, and glean from the spectacle the various forces at play!

That is what two astronomers and their team from the National Astronomical Observatory of Japan (NAOJ) have done. Using the Multi-object Infrared Camera and Spectrograph (MOIRCS - mounted on the Subaru Telescope), Drs. Masao Hayashi and Tadayuki Kodama identified a highly dense and active protocluster 11 billion light-years from Earth (announced September 20, 2012). In other words, the cluster they are looking at exists 11 billion years in our past, at a time when the universe was only 2.75 billion years old! Needless to say, it makes for an excellent laboratory, one that need only be carefully observed  to answer our burning questions.

[caption id="attachment_24068" align="aligncenter" width="440"] USS1558-003 (The horizontal and vertical axes show relative distances in right ascensions and declinations in arcminute units with respect to the radio galaxy. North is up, and east is to the left. The black dots are all galaxies selected in this field. Magenta dots show old, passively evolving galaxies. Blue squares represent star-forming galaxies with H-alpha emission lines, while red ones show red-burning galaxies. Large gray circles show the three clumps of galaxies.)[/caption]

The first among them is why galaxies "choose" to cluster themselves. The protocluster, as usual named inelegantly as USS1558-003, actually consists of three large closely-spaced clusters of galaxies, with an astral density as much as 15 times that of the general fields in the same cosmic period and a star-formation rate equivalent to a whopping 10,000 Suns/year. These numbers effectively leave such clusters peerless in their formative libido, as well as naked in the eyes of infrared telescopes such as the MOIRCS, without with such bristling cosmic laboratories could not have been found.

Because of the higher star-formation rate, a lot of energy is traded between different bits of matter. However, there is an evident problem of plenty: what do the telescopes look for? Surely, they must somehow be able to measure the amount of energy riding on each exchange. However, the frequency of the associated radiation is not confined to any one bracket of the electromagnetic spectrum - even if only thermal or visible radiation is being tracked. What exactly do the telescopes look for, then?

Leave alone the quintillions of kilometers; the answer to this question lies in the angstroms, within the confines of hydrogen atoms. Have a look at the image below.

The galaxies marked by green circles are emitting radiation with a wavelength of 656 nm, also called H-alpha radiation. It falls within what is called the Balmer series of hydrogen's emission spectrum, named for Johann Balmer, who discovered the formula for the eponymous series of emission-frequencies in 1885. The presence of an H-alpha line in the emitted radiation is an unmistakable sign of the presence of hydrogen: Radiation is emitted at precisely 656 nm (in the form of a photon of that wavelength) when excited electrons in the hydrogen atom drop from the third to the second energy levels.

The Balmer series, and the H-α line, are important tools used in astronomical spectroscopy: It is not just that they indicate the presence of hydrogen, but where and in what quantities, too. Those values throw light on which stages of formation the stars of that galaxy are in, the influence of the reactive region's neighborhood, and where and how star-formation is initiated. In fact, by detecting and measuring the said properties of hydrogen, Kodama et al have already found that, in a cluster, star-formation begins at the core - just where the density of extant stars is already high - and gradually spreads outward to its periphery. In the present-day, this finding contrasts with the shape and structure of elliptical galaxies, which have a different mass distribution from what an in-to-out star-formation pattern suggests.

These are only the early stages of Kodama's and his team's research. As they sum it up,

We are now at the stage when we are using various new instruments to show in detail the internal structures of galaxies in formation so that we can identify the physical mechanisms that control and determine the properties of galaxies.

Not that it needs utterance, but: This is important research. Astronomy and astrophysics are costly affairs when the genre is experimental and the scale quite big, rendering finds such as that of USS1558-003 very providential as well as insightful. We may have just spotted the Higgs boson, we may just have begun on a long journey to find the smallest thing in the universe. However, as it stands, of the largest things in the universe we have very little to say, too.

 

A short essay on a passion

This is a little something I wrote as part of an entrance test for my application to The New Indian Express. The section asked for a 500-word essay on something I'm passionate about, and I wrote about my fascination with astroparticle physics.

When I was eight years old, I peered through a telescope for the first time in my life. It was a small device, no more than two metres long, and yet it let me glimpse a brilliant view of Jupiter: it was the size of a marble, magnificently striated in hues of brown, red and orange. Then, when I was 13, I went to the Birla Planetarium in Hyderabad, where I revisited my five-year old fascination with Jupiter as I sat spellbound in the arena as a cosmic dance played out in the canvas stretched above my head: stars flew around, tumbling in and out of the horizon, the rings of Saturn floating serenely in space, moons rising and setting through a mélange of blues, yellows and greens.

It was a performance I haven’t forgotten to this day, remembering it as an eternally unfolding story, a few hundred pages in the epic saga of the universe. It could have been the charismatic voice of the narrator, it could have been the undisturbed loneliness on the night of my stargazing, it could even have been my mindless interest thereafter to find out more and more about the travellers in the heavens, but today, those memories are the seeds of my passion for astroparticle physics.

Many people – even science graduates – hear the name and think it’s a “big deal”. It is not. Astroparticle physics is the study of the stuff that stars are made of, and by extension, as Carl Sagan said, the stuff that we are made of. It is the search for and the understanding of the smallest particles that make up this universe one elegant phenomenon at a time. And just as my curiosity toward it was aroused one cloudless night in a small town in South India, so has it sustained: not within classrooms, not under the guidance of pedantic lecturers, but in my room, in the books I bought to teach myself more about it, in problems I solved, the simulations I ran and the experiments I conducted, in my mind where I could never rest without knowing how the universe worked.

In the last 15 years, I have learned where the stars come from that fascinate little children as little, bright spots in the sky, I have learned what the comets that streak Hollywood’s most romantic scenes really are, and I have learn all about our sun and the significance of human life. Most importantly, I have painted a glittering picture of the world for myself having met a wide range of people – young and old – simply by learning what I don’t know about and teaching what I do to anyone who is willing to listen. It is not a passion that I ever see fading because it has been an integral part of my growing years, a symbol of my parents’ support and my friends’ patience, and my own strengths, weaknesses and perseverance.

Interactions between a planetary system and an FFP: A fuzzy approach

For many years, astronomers and cosmologists thought planets were always bound to stars, doomed to journey in one parabolic orbit until the star that held it in its place died. However, recent far-ranging forays into regions of space lying much beyond the solar system and observations of vast sweeps of space by farsighted telescopes have revealed a clutch of exoplanets that don't orbit any star. Instead, they wander the universe as nomadic bodies, owing no other body any allegiance.

Because of their non-aligned nature, interesting things happen when they get too close to a proper planetary system with a star at the centre. The free-floating planet (FFP) exerts its gravitational force on the system and distorts its gravitational force distribution. For the sake of simplicity, let's assume that the system consists of one sun-like star and one Jupiter-like planet going round it. As the FFP gets close enough, the force that holds the planet (BP, for binary planet) around the star will experience a pull because the newcomer will have a gravitational field that pulls the BP away from the star.

There are four possible outcomes when this encounter happens, and the probability of one outcome happening over another is determining by a set of two parameters. The first is d, the impact parameter, and the second is φ, which essentially is the position of the BP in its journey around the star. For reasons better left untold, the value of d is less than zero if the FFP is on one side of an appropriately chosen reference line, usually one that runs through the centre of the star and bifurcates the planetary system into two symmetrical mechanical systems. When the FFP is on the other side, d is positive.



The four possible outcomes are:

1. Fly-by - The newcomer just flies by, leaving the planetary system untouched and unperturbed


2. Exchange - The newcomer swaps its position with the BP, becoming the new journeyman and liberating the BP into nomadhood


3. Resonance - The newcomer joins the planetary system and becomes the second journeyman


4. Disruption - The newcomer distorts the incumbent gravitational field enough to break up the system and leave all three wandering

(The likelihood of each of these outcomes is more precisely determined by the energy of the system at its centre-of-gravity. However, the ergonomics of the system is dependent absolutely o the masses of the star, the BP and the FFP, the approach-velocity of the FFP, r₀, the distance between the BP and its star - all of which are fixed constants - and φ and d - both of which are the only controllable variables.)

After this point, it becomes incredibly difficult to assess the probability of each outcome because of the immense variability in the BP's position relative to the newcomer. So, three smart physicists at the University of Thessaloniki, with access to what I can only imagine to be a bare-minimum of computing resources, decided to tackle the problem statistically.

In statistical mechanics, there is a lack of predictability: there are no formulae that correlate the behaviour of millions of small events to the entire system. Instead, there may be a few well-established formulae that provide correlations between other aspects of the system and its state. And when comes to statistical mechanical modelling, these few formulae are used to simulate the system in different states and look for patterns. Then, with the help of such patterns, a conclusion can be gradually drawn about the influence of small-scale patterns on large-scale ones.

In this case, the physicists of Thessaloniki programmed the initial conditions of the system into a computer: velocity of the incoming FFP, φ, d, masses of the FFP, BP and the star, and r₀. Then, they brought the newcomer close enough to the planetary system to affect its mass distribution 350,000 different times, each cycle corresponding to a uniquely chosen value of φ and d. In doing this, they gained a statistical understanding of the system that solidified an "estimated" understanding of it into a perfectly understood one.

Each time they brought the planet closer to the system, the value of φ they picked had to lie between 0 and 360 (for obvious reasons). The value of d, on the other hand, had to lie between 7r₀ and -7r₀ because of the assumption that the BP would be Jupiter-like, and in being Jovian like that, that's the value of d at which disturbances would begin to be felt. Such conditions are called initial conditions and play a very important role in fuzzy logic, which is the encompassing branch of logic at work in this example.

[caption id="attachment_21228" align="aligncenter" width="450" caption="The gap between crisp logic and fuzzy logic is the same as between precision and significance: sometimes, all you need to know is what's going to make all the difference, and fuzzy logic is a good way to get that information."][/caption]

Fuzzy logic is the set of mathematical tools that work with the fact that given a set of ground rules and an initial state, the final state can be deciphered to a heartening degree of accuracy, a degree dependent only on the accuracy of the ground rules. This gives us a basis for exploring the nature of satellite concepts to those currently understood: by using what we already know as initial conditions and an initial state, we get a fuzzy idea of the nature of the new concept. Fuzzy logic is particularly powerful when studying very large systems wherein the interference of chance is great.

The abstract of the original paper can be found here.

Employment opportunities for the neutrino!

With the discovery of (a possible case of) superluminary travel, physics is surely set to change. At the same time, the volume of physical information we are capable of perceiving and interacting with can't change. Our communication systems will continue to be modeled with photonic properties in mind. Time machines will continue to languish in the cells of science fiction because of the elusive nature of the neutrino. What I'm really excited about are:

1. The "tweaks" that will be made to the Standard Model to accommodate this para-relativity phenomenon,


2. Possible new explanations for the information paradox associated with black holes,


3. The resurgence of and boost for neutrino telescopy


4. Detectors based on superluminary sensors, and


5. The rise of the string theorist!

Employment opportunities for the neutrino!

With the discovery of (a possible case of) superluminary travel, physics is surely set to change. At the same time, the volume of physical information we are capable of perceiving and interacting with can't change. Our communication systems will continue to be modeled with photonic properties in mind. Time machines will continue to languish in the cells of science fiction because of the elusive nature of the neutrino. What I'm really excited about are:

1. The "tweaks" that will be made to the Standard Model to accommodate this para-relativity phenomenon,


2. Possible new explanations for the information paradox associated with black holes,


3. The resurgence of and boost for neutrino telescopy


4. Detectors based on superluminary sensors, and


5. The rise of the string theorist!

Aurora

Beyond the mountains, the crowning guardians,
There was an horizon that spanned the sky
From the seven stars in the cold East
To the sun hidden forever on the brink of the West.
At the foot of a glacier, where the moon turned blue,
I was come finally to the end of my way
Where there was an aurora every day.

In the cold warmth of the infinite loneliness,
Within a loud silence, slept a new world.
In the dark virgin waters, an unborn child swam,
And I knew somehow it was the coming of man.
The sun was never to rise in my eyes again;
I was finally come to the end of my way
Where there was an aurora every day.

A fierce wind lay to rest the reeds around me.
The flock of birds in the distance only reminding me
Of the many, many miles lying open behind my back,
My footprints in the mud showing my children the track-
I knew I was somewhere in a place they called home.
I was finally come to the end of my way
Where there was an aurora every day.

Blackbird's Egg

Ephemeral and lasting these sons of constant attention remain, swimming seas of white and seeking like brave fools the short-lived happiness that words bring. A bloodied chest of rubies with a curse screaming above their head, and I am pushed away, slowly, steadily, and I deliberately forget to fight as noiseless wonders fracture to an unforgiving life. My hollowness has been stolen and in its place is a black bird.

[caption id="attachment_819" align="alignright" width="420" caption="Broken sky, wholesome rain"][/caption]

A dreaded wall climbs high and lifts magnanimously on its bank a small green frog. The calendar is moving away, tearing slowly across the lines, the numbers are released up and down both at once. Ripples settle down in silence and the moon comes to watch a storm gently falling asleep in the morning. Jan-jan-jan, one by one, push the sun out. Was-now flaps its wings in a blur but white lingers, a black sun rises in the north, and the morning blooms now-was.

Dissension and debate rage on the outside while a sharp illness pricks within. Give me your promise, broken at birth, and exploit my choices as a preference. Blood on the world's hands and scratches on the queen's back, the marauder runs into eternity behind the pillars of creation. Reason gives fast pursuit but the catch is never done. Why must it be when the end is the end is the end? Raindrops slither down the damp wood and our fires won't burn for any bribe. The crime is only slavery... not you, my darling.

I'm a radioactive toy filled with evaporating purposes. Keep my right to freedom and keep my right to the skies. Give me the freedom to give up when I longer can, give me the freedom to throw my arms up, give me the freedom to shed a tear. To cry shamelessly. Dark patches of dried blood flake away into the wind while the sun sets slowly beyond the mountain, and sunflowers meet the Earth whence they came. The leaf, is airborne, skyward, as a souvenir of the true day.