Dark Forces

Hubble Space Telescope image of the galaxy cluster Cl 0024+17 superimposed with a blue map showing the cluster's dark matter distribution.Image Credits: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University).




The puzzles of the universe seem to be never ending. The universe is sprinting and the dark energy is forcing the galaxies apart to accelerate the expansion. The dark matter outweighs the ordinary matter. To make matters worse, scientists have no idea about the origins of the dark energy or dark matter.HST, with its determined eyes scanning space had some clues, if not a complete answer. Dark energy was discovered a decade ago by two independent studies on the expansion of the universe. One study was led by Adam Riess of The Space Telescope Institute and John Hopkins University. It is mathematically equivalent to cosmological constant, introduced by Albert Einstein to balance the universe from collapsing under the pull of gravity (However, Einstein removed the constant once the expansion of the universe was discovered by Edwin Hubble). Riess used the HST data to improve the value of the expansion rate of the universe (Hubble constant) to an accuracy of three percent. Ironically, this implies that the dark energy, as Einstein assumed is steadily pushing the fabric of the universe. Riess and other researchers would eventually like to see the Hubble constant refined to a value with an error of no more than one percent, to put even tighter constraints on solutions to dark energy. Science is closing in to comprehend one of the most baffling concepts of modern day Astronomy.








Scientists estimate that 74% of the universe is dark energy, 22% is dark matter leaving the remaining 4% to account for all the galaxies and the intergalactic medium, known as normal matter. In the absence of the dark matter, this ordinary matter would fly apart, because the gravity of the normal matter cannot withstand the never ending assault of the dark energy. The search for the dark matter is a “ghost hunt’ as it is not detectable directly. However, the effect of dark matter is measurable through something called gravitational lensing. This is a technique that utilizes the fact that the light bends in the presence of a strong gravitational field. The HST has observed strong gravitational lensing in different galaxy clusters, which underlines the presence of dark matter as predicted theoretically by the Astrophysicist Fritz Zwicky in 1933. While studying the dwarf galaxies, HST provided strong evidences for the presence of dark matter. Hubble’s sharp view penetrated the cosmos to see that large number of small galaxies remain intact, even as the bigger galaxies around them are being ripped apart by the gravitational force of other galaxies in the cluster. The halo of the dark matter protect them like an invisible shield from the assault of gravitational tug of war going on inside the clusters for several billions of years.
“We were surprised to find so many dwarf galaxies in the core of this cluster that were so smooth and round and had no evidence at all of any kind of disturbance. They must be very, very dark-matter-dominated galaxies.” says Astronomer Christopher Conselice, currently the principal investigator of the HST survey. The halo of the dark matter protects the dwarf galaxies like a shield, from the sword of gravitational forces that emerge from the big galaxies.

Kingdoms of Heaven

The Hubble Ultra Deep Field showing thousands of Galaxies in a small region of our Cosmos.
Credit: S. Beckwith & the HUDF Working Group (STScI), HST, ESA, NASA



While answering a question in the backdrop of his conflict with the Catholic Church, Galileo once declared, “Bible teaches how to go to heaven, not how the heavens go.”

The heavens narrate their stories in a distinct manner and allow humans to discern the mystery of its creation and evolution. Up to now, humans can accomplish this only through the decoding of light. This is because light is a messenger that can convey the untold chronicles of the cosmos, which has been a great source of myths and legends ever since the beginning of humankind. For the ancients, the heavens were the citadel of gods who visited them for various reasons and often punished them with fiery objects. The naked eyes had been the only means to investigate the elements of the Cosmos, and it has changed forever in 1609 AD. Galileo, the father of modern astronomy, developed a new scientific world when he used the power of the telescope to know the heavens. He narrated the accounts of his observation in “the starry messenger” published in 1610 AD.

Telescopes are often referred to as time machines as they escort us back in time. When we peep at a star or any other object a few million light years away, we are in fact seeing that object as it existed a few million years ago. Since Galileo’s first use of the telescope, scientists have been improving the power of telescopes to gaze the unfathomable universe and see how the heavens go. Now, 400 years after the Galilean adventure, the modern astronomers are on the verge of investigating the frontiers of the known universe. A variety of telescopes, operating from ground and space, aid them in this process. If the Galilean ‘spy glasses’ were able to reach just the backyard of our galactic neighborhood, the modern era telescopes take us to closer to the moments of creation known as the Big Bang.

The Hubble Space Telescope (HST) is the most advanced and sensitive telescope ever deployed in space to accelerate the pursuit of the unknown regions of the cosmos. Named after the American Astronomer Edwin Hubble, whose observations in the 1920’s supported the theory of the expanding universe, HST has been in action for the last nineteen years. Since the launch in 1990, most of its original instruments have been upgraded or replaced. The latest and last repair mission was conducted in May, 2009, extending the life span of the telescope for another five years. The instruments on the telescope can observe the edges of the universe in visible light, ultraviolet and infrared ranges of the electromagnetic spectrum. HST, located at about 565km above the earth’s surface with an approximate size of a school bus, completes one full orbit around the earth in 97 minutes. The website devoted to HST (http://hubblesite.org) provides every detail and discoveries of the telescope, and enable the public to track every moment of its voyage.

In addition to the many startling discoveries, HST images became the art work of the cosmos. Furthermore, some existing theories of the universe are overwhelmed by the HST data and they need to be rewritten in the light of the new information. The Hubble Ultra Deep Field or HUDF, completed in 2004, is an image of a small region of space created using HST data accumulated over a period of four months. During this period, Hubble’s 2.4 diameter mirror is turned on to the same spot of the sky to accumulate enough light from the faint galaxies fading away from us. This is the deepest image of the cosmos ever taken by mankind and the most distant objects that could be seen so far. In fact, some of these objects date back to the baby universe, approximately 13 billion years ago, when the galaxies are just forming from the seeds of Big Bang. The image contains an estimated 10,000 galaxies in different shapes and sizes. Each of these galaxies may contain billions of stars and many possible planetary systems. This image will be used to analyze the galaxies that existed between 400 and 800 million years after the creation of the Universe, much before our milky way was even formed. Scientists looking at that image were perplexed at the mere existence of such large number galaxies, and some called it “Kingdoms of Heaven.”

The astounding display of matter and energy is the manifestation of the universe as it evolves. The mysteries of its creation and existence are reaching out to us in the form of light energy. The HST has done more than any other modern telescope to garner that energy, so that scientists could carve the history of the universe for generations to come. Edwin Hubble observed and measured the departure of galaxies using a technique known as the red shift in physics. Now we know that the galaxies not only depart from each other but their exodus is accelerated by the inexplicable dark energy. If our current conception of the universe is correct, in the far future, our own Milky Way galaxy will be left alone in the galactic playground with other galaxies that have receded to the unknown corners of the cosmos. The finite speed of light cannot overcome the infinite space that would be created among the galaxies due to the accelerating nature of their retreat. This scenario would lead future generations to assume that their galaxy and universe are the same. If preserved, the Hubble images might help them during that time of ultimate isolation!