25 Years of Hubble Space Telescope

Come April 2015, the Hubble Space Telescope (HST) will mark its 25th anniversary observing the cosmos. Launched in April 1990 aboard the space shuttle Discovery, the HST was built primarily by the US Space Agency, NASA, with contributions from the European Space Agency, ESA. The motivation behind building a space-based telescope as opposed to a ground-based telescope was the absence of atmospheric distortions and light pollution, to which ground-based telescopes are susceptible. Hubble makes observations in the visible electromagnetic spectrum (VIBGYOR) and also in the infrared (IR) and ultraviolet (UV), which flank the visible wavelengths. This entry follows the journey of the Hubble and the plethora of science it has given us (rest assured, pretty pictures included).

Although Hubble has given us an unprecedented view of some of the earliest galaxies in the universe, its early years of operation were rather... shaky. Let us go back to the first few weeks after the launch of Hubble. Being a rather expensive project, there was excitement within the scientific community about the first images that the Hubble would send back to Earth. An example is shown below:

Left: Images from ground based observatories of the time. Right: One of the first images from the HST.

Although the Hubble images were considerably better than the ground-based observatories of the time, they were still nowhere near as sharp as scientists had expected them to be. The telescope wasn't focusing properly. After analysing the images, it was understood that the primary mirror on Hubble was not of the correct shape. Understandably, Hubble became the butt of many jokes. While possible solutions to this problem were being explored, the telescope continued to observe simpler science targets and scientists developed ways to enhance images using image processing techniques.

In December 1993, the first service mission was launched aboard the space shuttle Endeavour. This mission installed the optical corrections necessary in addition to upgrading one of the primary cameras to the improved Wide Field and Planetary Camera 2 (WFPC2). This resulted in a dramatic increase in picture quality and NASA deemed the Hubble Space Telescope a success. Shown below is the improvement in imaging:

Left: Uncorrected image of galaxy Messier 100 (M100). Right: M100 imaged using the new and improved WFPC2 camera.

The pretty pictures were just beginning to flow! Here are a few examples of some of the most iconic Hubble pictures:

1. The Eagle Nebula 

One of the most famous Hubble images, the Eagle Nebula, also known as the 'Pillars of Creation', is a stellar nursery. The gas and dust regions are actively giving birth to new stars.

2. Mars

Hubble image of our neighbouring red planet.

3. ESO 510-G13

A spiral galaxy like our own Milky Way. The visibly warped spiral arms may have resulted due to its interaction with a neighbouring galaxy.

4. Messier 9 Globular Cluster

A globular cluster is a densely packed collection of stars. Messier 9 (M9) is very close to the centre of our galaxy. Its total luminosity is around 120,000 times that of the Sun.

5. Hubble Ultra Deep Field

The iconic Ultra Deep Field image, this contains some of the earliest galaxies, up to 13 billion years old (the age of our universe is 13.8 billion years). Taken in 2004, this image contains approximately 10,000 galaxies.

6. Abell 2218 Galaxy Cluster

A galaxy cluster is a very massive collection of galaxies that are bound together by gravity. The immense gravity of a cluster is strong enough to stretch and shear light, which gives rise to the strikingly beautiful arcs around the centre of the cluster. This phenomenon is known as gravitational lensing.

The Hubble has undoubtedly been one of the most vital tools for advancing astronomy. It has expanded our knowledge of the cosmos beyond imagination. From estimating the age of the universe using very distant supernovae (see earlier posts!) and discovering that almost all massive galaxies have supermassive black holes in their centre, to detecting previously unknown comets and imaging proto-planetary that lead to formation of extra-solar planets, the science that Hubble has provided is staggering!

Hubble received its final service mission in 2009 to prolong the functioning of its instruments, before it will be succeeded by the James Webb Space Telescope (JWST) in 2018/19. The harsh reality is that Hubble's instruments will eventually stop functioning and it will be defunct, but that will not take away one bit the impact it has had on our understanding of the universe at every imaginable scale. All good things must come to an end, but the Hubble is just turning 25 years young!

All images courtesy Hubble picture gallery. More pictures can be found here! http://hubblesite.org/gallery/

SuperMoon

In light of the Supermoon event on 10 August 2014, here is an astronomically delayed blog post about, you guessed it right, the supermoon phenomenon! (It's hard to squeeze in multiple puns in a single sentence)

The supermoon is a fascinating event, and the phenomenon behind it is quite simple too. It occurs when the full moon coincides with the moon being closest to Earth on its elliptical orbit. This leads to the moon appearing brighter and larger. In orbital mechanics, the elliptical orbit of the moon around the Earth gives rise to points of greatest and least distance, called perigee and apogee, respectively. This is shown in the figure below:

In this illustration, point 1 marks the perigee, point 2 marks the apogee
and point 3 marks the position of Earth.
Source: http://en.wikipedia.org/wiki/Perigee#mediaviewer/File:Apogee_(PSF).png

Over the years, there have been several claims about the supermoon being responsible for natural disasters such as earthquakes, tsunamis and floods. However, no conclusive research has supported these claims. The oceanic tides result from the combined effect of the sun and moon's gravitational pull, and the tides are indeed highest during a full moon. However, this effect is not particularly strong, and does not lead to significant rising of the high tide compared to the normal amount.

I was lucky enough to witness the supermoon on 10 August, 2014 thanks to a surprisingly clear night, especially after torrential rains early in the day. Sitting on a hill top, which was illuminated only by the intense light of the supermoon, I couldn't help but get slightly philosophical. I have often turned to the cosmos in search of inspiration and motivation, and this was one such occurrence.

With news of humanitarian crises pouring out from almost every corner of our planet, I wonder in which direction our `intelligent' civilisation is headed. Have we become a threat to our very own existence? It seems that today's society is fueled by hatred and self-centrism. The term `humane' is slowly losing its value. I don't think scientific and technological advancement alone is enough to entitle us to call ourselves an `advanced' civilisation. There is no progress without empathy, compassion, equality, trust and love, the truly human values. Every pinch of grey matter is valuable. Every drop of blood is precious.

I urge you to spare a few moments and watch Carl Sagan's Pale Blue Dot (linked here):
https://www.youtube.com/watch?v=p86BPM1GV8M

And finally, sitting on top of the moonlit hill, I realised this. Very few human creations have an implicitly comforting nature. But the sound of a train in the dark of the night and the guiding signal from a light house in a vast sea of loneliness are, in my opinion, two of the most soothing sensory stimuli. Can we turn to the cosmos to teach us to love one another and live in peace and harmony? Can we use science and technology for the betterment of not just humans, but nature itself? Can we be selfless and make a positive change through our lives? I think we can. All we need to do is, every once in a while, look up and wonder.

The Big Bang, Inflation and BICEP2

17^th March 2014 marked a historic day in cosmology. The team working on the BICEP2 experiment at the South Pole announced their results, which confirmed detection of the first direct evidence of the theory of the origin of our universe, the so-called ‘cosmological inflation’. This was immediately followed by shock and awe in the scientific community worldwide, with the media covering this discovery extensively. So what exactly is the inflationary model of the universe and why is this discovery so ground breaking? Let’s try and find out!

To understand any model that describes our universe, it is essential to treat space and time as a unified set of coordinates, known as ‘spacetime’. Here, time is treated simply as a coordinate, in addition to (x, y, z) that we already use to describe the three dimensional space. Thus, spacetime has 4 coordinates, (t, x, y, z). Another key ingredient that aids in forming models of the universe is the cosmological principle. This states that the universe appears to be roughly ‘homogenous and isotropic’, i.e. it appears roughly uniform in any and every direction in space that we look. Now that the basics are in place, we can proceed to track the models that describe the evolution of our universe.

In 1929, Edwin Hubble made a landmark discovery. Using his fairly sophisticated telescope, he observed that all the galaxies seemed to be moving away from us, and further the galaxy was situated, faster it was receding away from us. Tracking back this behaviour, one can easily conclude that all the galaxies must have been very close to each other in the past, quite possibly even condensed into a single blob of matter, and were suddenly flung outwards. This would result in every galaxy moving away from each other today. This can be understood by considering the following example: Imagine you have a deflated balloon, and you mark small dots on its surface with a marker. When you start inflating the balloon, you would notice that all the dots are receding away from each other. This is what the ‘big bang theory’ postulated. That all the visible matter was once condensed into a single entity, and a ‘bang’ resulted in everything that we see today moving away from each other.

This model, however, had its own problems. The most pressing one was that the universe looks roughly the same in every direction that we look. Comparing the distances between the farthest galaxies in the east direction with the farthest ones in west, we conclude that the distance between them is too large for light to have travelled from one galaxy to another (the speed of light being a universal constant) in the known lifetime of our universe (roughly 14 billion years). Thus, the 2 galaxies could never have been in causal contact! Despite this, why do they still appear homogenous? This is almost like a situation in which you encounter an alien flying in from a galaxy far, far away, and that they look exactly the same as us humans, sharing the same DNA! You would immediately be tempted to think that our species must have been in contact at some time in the past to account for the striking similarities. The big bang failed to explain how these two patches of the sky were causally connected at one point in time. This is where the inflationary model came to the rescue.

A timeline showing the evolution of our universe. Inflation exponentially expands the space in a very short period of time.

Image: http://planck.cf.ac.uk/science/timeline/universe

The inflationary model was initially proposed by Alan Guth in 1980, and further refined by Andrei Linde, Andreas Albrecht and Paul Steinhardt. Cosmological inflation is the sudden exponential expansion of space with the expansion rate being greater than the speed of light, when the universe was just 10^-36 seconds old. This inflation continued till about 10^-32 seconds, but in this short period of time the universe had grown drastically in size. The energy scales at which the inflation model operates determine these time scales. Higher the energy, smaller the time scale at which it acts. Following the end of inflation, the universe continued to expand, but at a much smaller rate. A direct consequence of this model was that parts of the universe could have been connected in the past, and as a result of exponential expansion of space, they appear to never have been in contact when observed today. This beautifully explained why the universe looks homogenous and isotropic!

Einstein’s General Relativity predicted that this sudden expansion of the universe must give rise to something known as ‘gravitational waves’. I urge you to look it up, as they are extremely fascinating. These waves should be neatly imprinted in the remnant of the big bang that is observable today, the cosmic microwave background (CMB) radiation.

The BICEP2 experiment remarkably observed these gravitational waves in the CMB, thus providing the first direct evidence of cosmological inflation. This is the reason why there has been pandemonium in the scientific community over the past week, as this strongly supports our models of the beginning of the universe. This is a huge leap in our understanding of its origin and evolution! Even though their findings look quite comprehensive at first glance, several experiments all around the world are rushing to confirm their results. When confirmed by several other experiments, a Nobel Prize is guaranteed! The only question is, will the theorists who proposed the model or the team that discovered the signatures receive it. In either case, this is an amazing leap for human understanding of our universe and demonstrates the amazing capabilities of current science and technology.

The sun sets behind BICEP2 (in the foreground) and the South Pole Telescope (in the background). (Steffen Richter, Harvard University)

Image: http://bicepkeck.org/visuals.html

LOFAR: The Netherlands and Radio Astronomy

Apologies for the slightly delayed blog post (to all four of you who are still reading this). In my defence, I spent the entire last week in the Netherlands, giving presentations and attending PhD interviews. The experience was absolutely brilliant, speaking with some of the most accomplished scientists and meeting with current PhD students and applicants from all around the world. It is in situations like these when you truly realise how similar people from all over the world are, and how you can strike conversations about absolutely anything and everything with complete strangers!

Astronomy is one of the top subjects of research in the Netherlands. This little country is moving mountains to establish itself as one of the top players in the already vast field of astronomy and astrophysics. One of the key projects that has truly cemented the Dutch presence on the world map is the ground-breaking radio telescope called Low-Frequency Array or LOFAR. LOFAR is said to be the largest connected-telescope ever built, with data being collected and processed from 48 large stations. 40 of these stations are situated in the Netherlands, 5 are in Germany and one each is in the UK, Sweden and France. LOFAR enables, for the first time, sensitive observations from the lowest possible frequencies accessible from the ground, at around 10 MHz up to frequencies of 1400 MHz.

Aerial photograph of the Superterp, the heart of the LOFAR core, from August 2011. The large circular island encompasses the six core stations that make up the Superterp. Three additional LOFAR core stations are visible in the upper right and lower left of the image.

Image and further reading: http://inspirehep.net/record/1233495/plots

The science case for LOFAR is the most interesting bit. Essentially, one of the main aims is to probe large-scale structure formation in the early universe. We observe a lot of large clusters of galaxies, but know very little about how and when they were actually formed. Galaxy clusters are the largest observed cosmological structures in the universe, consisting of 100 to a 1000 galaxies held together by gravity. One of the key features is that these galaxies are ‘embedded’ in a very hot and energetic intra-cluster medium (ICM). A lot of interesting physical phenomena are observed in such a setting, which makes their study really exciting.

Another key project of LOFAR is to study very energetic ‘active’ galaxies. It is now well established that in the centre of every galaxy lies a supermassive black hole (SMBH). An active galaxy is one in which the central SMBH is constantly gobbling up mass and wreaking havoc. Such galaxies exhibit high levels of brightness in almost every order of the electromagnetic spectrum, be it radio emission, visible light or x-ray emission. We currently understand very little as to how such active galaxies appeared in the early universe, how they evolve and what are the processes involved in such violent environments.

For my master’s project, incidentally, I am studying these active galaxies as the sources of the very exciting ultra high-energy cosmic rays (UHECRs). UHECRs have puzzled scientists for decades, and we currently do not fully understand how such high energies are achieved in the particles that are constantly bombarding us from outer space. I aim to write a blog post about it in the near future!

The Netherlands is a beautiful country, with friendly and welcoming people. The institutes I visited as part of the PhD selection programme, Leiden Observatory and University of Amsterdam are absolutely fantastic and are deeply involved with top class research. With LOFAR, this country is certainly making its presence felt and is pioneering ground-breaking research, in a hunt to answer the pressing, currently unresolved problems in astrophysics.

Supernovae as Probes of Dark Energy

In the wake of the excitement surrounding the discovery of a Type Ia supernova by a group of University College London (UCL) students and staff (yay!) from the University of London Observatory, I asked my good friend Suhail Dhawan to write a piece about the importance of type Ia supernovae in an attempt to justify this hysteria. Suhail is currently pursuing his PhD from the European Southern Observatory (ESO), Munich and is working on supernovae. Apart from being really smart, he is hilariously funny too (am I the best wingman or what?!).

Check out his fun-filled blog here: http://seventhgradedropout.blogspot.co.uk

Suhail and I have always been very passionate about astrophysics. This post is the kind of stuff that we talk about and believe it or not, plan to do for the rest of our lives, despite the fact that this will most probably lead us to live a life of poverty… Enjoy!

In 1929, Edwin Hubble, at Mt. Wilson observatory, discovered that the universe was expanding and that faraway galaxies were receding from us at a velocity proportionate to their distance. This was truly one of the most remarkable observations. Even Einstein was of the opinion that our universe is static. Hubble’s discovery however, led him to comment that failing to realise this was, in his own words, his “greatest blunder”.

One of the questions that emerged now was to measure how the rate of expansion would change over time. It was initially posited that the expansion should decelerate, since the galaxies attract each other gravitationally. Several cosmologists aimed to pin down the amount of deceleration.

In order to measure the deceleration, one would have to determine the distance to a faraway object. Cosmological distances are measured by a distant object’s apparent luminosity or brightness to its absolute or intrinsic brightness. For this purpose, a 'standard candle' was required. This term refers to a class of astrophysical objects, which has a uniform intrinsic brightness, and therefore, the apparent brightness gives a robust measure of the distance to the object. The term ‘standard candle’ is fairly accurate. Imagine you have a candle and you know its brightness and how far it is from you. Now, if there were to be another candle placed some distance away, you could easily measure its ‘apparent’ brightness. Comparing that with the brightness of the candle you have, you can make a fairly accurate estimate of how far the observed candle is from you.

Supernovae of spectral type Ia were seen to meet the ‘standard candle’ criterion. This spectral type refers to those supernovae, which are created from a binary system in which one of the components is a compact object that accretes matter from a donor star and explodes upon reaching a critical mass limit. As there is a definite mass limit after which the accreting star explodes, Ia supernovae have the same intrinsic luminosities (or brightness).

Accretion of matter by a compact star from a massive donor star.

Image credits: http://www.einstein-online.info/spotlights/galactic-binaries

In the late 90s, two research groups, using these Type Ia supernovae, found that the value of the deceleration was negative. This pointed to a mysterious force that was pushing objects away at an accelerated rate. By fitting the observations to models of the universe from theory, they found that the mysterious fluid, which was termed as 'Dark Energy' makes up nearly three-quarters of the universe!

However, the story with supernovae isn’t complete yet. An improvement in technology and the advent of charge-coupled devices (CCDs) meant that we were able to discover many more of these objects. Upon analysing the data in the early 90s, it was seen that Type Ia supernovae weren't as homogenous a class as originally thought. To overcome the problem, there were several ingenious corrections proposed. It was argued successfully that explosions that were intrinsically brighter also faded away more slowly, an effect attributed to the amount of nickel produced in the explosion. Similar relations between the intrinsic luminosity and colour, and the mass of the host galaxy were found, which were used to calibrate the objects. 

Although these corrections were crucial for the discovery of dark energy, we need more precise constraints to understand its nature. Recent studies have shown that these objects are truly standard when observed in the near infrared wavebands. This is extremely exciting from viewpoint of cosmology. With planned surveys to observe a larger dataset in these bands, out to greater distances, there is optimism about finding new and exotic physics that describes the universe.

The Black Hole Information Paradox

After showing the world that the Universe began as a point of singularity, and the event responsible for the creation of the Universe was the ‘Big Bang’, Stephen Hawking turned his attention towards the mysterious cosmological objects called Black Holes. A black hole is formed when a very massive star runs out of fuel and explodes as a Supernova. The explosion throws away the outer gaseous layers and leaves behind a very massive core packed into a region of very little radius. The black hole has a gravitational pull so strong, even light cannot escape from its surface. The region that demarcates the ‘point of no return’ for light, or as a matter of fact, any other object is known as the event horizon of the black hole.

So the first thought that naturally creeps into our minds is that since the gravitational pull of a black hole is so strong, there should not be any particles or radiation emitted from it. This is precisely what the theory of General Relativity predicts. However, Stephen Hawking showed the world that black holes do in fact emit, if one were to take into account quantum perturbations in and around the event horizon of a black hole. This, quite fittingly, is called ‘Hawking Radiation’.

It is important here to remember one very extravagant statement made by the great physicist John Wheeler, “black holes have no hair!” This most certainly does not imply that black holes are bald. What it truly means is that the properties of a black hole which can be observed from outside its event horizon are dependent on only three classical parameters, its mass, electric charge and angular momentum. All other information (or hair) about particles falling into a black hole is inaccessible to observers outside the event horizon.

A very simple idea about the origin of Hawking radiation can be formulated if we were to consider quantum vacuum fluctuations in the gravitational field of a black hole. A quantum fluctuation is a temporary appearance of energetic particles, as allowed by Heisenberg's uncertainty principle in quantum mechanics. These fluctuations lead to particle-antiparticle production out of pure energy, albeit for a very short period of time. If either of the two particles fell into the black hole and the other escaped the black hole's gravitational pull by a phenomenon known as ‘quantum tunnelling’, the particle which escaped will give rise to Hawking radiation. In order to conserve the total energy in this sequence of events, the particle that fell into the black hole must contain negative energy. This means that the black hole is slowly losing energy and hence, mass. It would eventually evaporate!

Therefore, the information about every particle that ever fell into the black hole, and that of the black hole itself will one day completely disappear. This proposition hits right at the heart of quantum mechanics, which postulates that the behaviour of a particle at any point in the future can be predicted if one were to possess ample information about its current state, which is nicely packed into its 'wave function'. The wave function informs us about a particle's position, velocity, momentum, energy, etc. at any given time. This abrupt loss of information was called the black hole information paradox.

Since millions of black holes have been discovered in the universe, the occurrence of this paradox cannot be quarantined to just one particular situation. If the information paradox exists in the case of a black hole, then it must exist everywhere else in the universe too.

Stephen Hawking remained convinced that information was indeed getting destroyed in a black hole, and that quantum mechanics will have to be suitably modified to take into account these occurrences. This annoyed quite a number of physicists around the world. One of the most offended was John Preskill, who bet Stephen Hawking and was sure that information was not destroyed in a black hole. The winner of this bet would receive an encyclopedia of the winner’s choice, in which information never gets destroyed for sure.

Another notable physicist who was troubled by Hawking’s claim was Leonard Susskind, who wanted to ‘save’ quantum mechanics and publicly declared war against Hawking! He, however, maintained that the two are good friends and their war is only that of ideas. The debate was eventually settled when Susskind showed that information of particles entering a black hole was not lost, but it was smeared or ‘painted’ on its event horizon and got completely scrambled. This is knows as the 'Holographic Principle'. Susskind gave a precise string-theory interpretation, which involved a much higher number of dimensions than the three dimensions of space and one of time. It also took into account the non-zero entropy of slightly longer strings that make up the event horizon of a black hole.

Now that the argument was settled, Stephen Hawking had to gift a copy of ‘Total Baseball: The Ultimate Baseball Encyclopedia’ to John Preskill. Comparing the scrambled and useless information that was emitted by a black hole to ‘burning an encyclopedia’, Hawking remarked that he might as well have gifted Preskill the ‘ashes’.

Kip Thorne, John Preskill and Stephen Hawking. Preskill bet that the information can be recovered, with Hawking and Thorne betting that it is destroyed

Image source: theory.caltech.edu