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IN QUEST OF MATTERS UNKNOWN
Would you believe it if you were told that right at the center of the Milky Way is located a dangerous fountain of antimatter spewing out energy at an astonishing rate? It sounds almost fictional. After all, antimatter is perhaps the most-celebrated stuff of science fiction, be it Star Trek’s starships using the energy from matter-antimatter annihilation for their light-speed propulsions or Professor Robert Langdon (quite famous among Dan Brown’s fans) trying to save Vatican City from an antimatter bomb in Angels and Demons. But beyond fiction, antimatter and its occurrence in the Universe have continued to fascinate physicists like anything.
Now, think about what all things money can buy, a mansion in South Mumbai(looking at you Antilia), Mike Tyson’s golden bathtub, William Shatner's kidney stone (Star Trek freaks, if you know you know) this probably doesn’t even cut it, keep going higher and higher. A single gram of antimatter of Hydrogen sits at around $62.5 trillion dollars per gram. Yeah, you heard that right alright! To get a feel of just how big of a deal this is, it takes 326 Jeff Bezos’s(that is if Blue Origin doesn’t burn out his billions) or 530 Mark Zuckerberg’s (you know, the evil twin of Andy Samberg) to buy one gram of antimatter. And unlike all the ridiculously expensive things, the description for this is so simple. It is the counterpart to Matter which we (including the cyborgs) are made of. Yeah, that’s right, it is just Matter made out of Anti-particles rather than particles.
About a year before the world was moving towards “The Great Depression of 1929”, our good old “Mathematical-beauty” obsessed friend Paul Dirac was struck with the idea of Antimatter. If you want to know what kind of a genius Dirac was, imagine Einstein-meets- Feynman-meets-Edward Witten….and this isn’t even an exaggeration! He was as imaginative as Einstein, as much a great problem solver as Feynman, and highly mathematical as Ed Witten was. It was the first quarter of the 20th century that led humanity to new ways of thinking about nature. Theories like relativity and quantum mechanics were flourishing, an amazing time to be a physicist.
Paul Dirac was trying to reconcile relativity theory with quantum mechanics, which in those times seemed like one had nothing to do with another. Paul Dirac finally came up with the theory that combined quantum mechanics, used to describe the subatomic particles, with Einstein’s special theory of relativity. He achieved this through complex mathematical calculations while preserving the mathematical beauty(Classic Dirac, really!). When Dirac was once asked about his thoughts on the Dirac Equation, which came out of that unification he said, “ I found it beautiful”.
His equation not only works for an electron with a negative charge. It also works for a particle that behaves like an electron with a positive charge. At first, Dirac did not appreciate the significance of this finding, and even ignored it out of what he would call “pure cowardice”.
Eventually, he came to realize that the theory bring out something entirely new to science- “The Anti-particles”
Every particle of normal matter we now know of has an antimatter analog that is identical to itself except for the electric charge possessed. For example, electrons have a negative charge whereas its antimatter analog, positron, has a positive charge. When matter and antimatter particles come in contact, it immediately results in their mutual annihilation giving out pure energy. Most of this energy produced is in the form of ionizing radiations, like the gamma rays, which may convert to heat or light forms on contact with normal matter nearby. It is observed that the amount of energy released is proportional to the total mass of the colliding matter and antimatter particles, in accordance with the well renowned mass-energy equivalence equation,
E = mc^2.
Antimatter is likely to be created when high-energy particle collisions occur. Naturally, this is produced in cyclic processes at high energies such as in pulsars or X-ray binaries or near supermassive black holes. Artificially, antimatter has been created in particle accelerators in trace amounts. The center of the Milky Way, also known as the galactic center, a chaotic dense region with stars and clouds of gas, is packed with mysteries - the supermassive black hole Sagittarius A, the wispy magnetic filaments, dense stellar superclusters, the massive fountain spewing antimatter - to name a few. In places like CERN, physicists have managed to create antiparticles and have opened the doorway to the anti-world and what lies ahead. We have only predicted that the properties of antimatter could resemble normal matter, but what if they didn’t? What if their behaviors differ in strange ways from what is expected? Imagine an antimatter apple that would fly up into the air, unlike the one which is expected to fall down.
Another thing that triggered curiosity is the asymmetry in the distribution of matter and antimatter. There should have been equal amounts of both in the early universe after the Big Bang. But as of now, we can see that most of the antimatter has somehow disappeared and almost all stellar objects are made entirely of matter. Spontaneous transformations have been recorded between Matter and antimatter before they decay to give out energy. There must have been an event or entity that must have favored the decay to the normal matter side resulting in decreased concentration of antimatter in the universe now.
In the 1970s, when NASA launched Compton Gamma Ray Observatory in search of gamma rays in the galaxy, Astrophysicist William Purcell speculated that he would find antimatter at the center of our Milky Way. When one of the satellite’s instruments couldn’t detect half of the positrons counted by the other instruments, the astrophysicists had to, in fact, set out for a search. This search, led by Dr. Purcell of Northwestern University, ended in unexpected findings. About 50% of the missing positrons showed up in a cloud, 3500 light-years from the galactic center, initially thought to be a region devoid of any matter. Million billions of matter-antimatter annihilation took place within the clouds releasing violent gamma-ray emissions. Resembling a fountain with antimatter gushing out of it to reach trillions of miles in space, scientists called it “The antimatter fountain”.
This discovery brings us with a series of questions about its nature and its origin. Primarily, questions regarding how antimatter appeared there confused the scientists. They came up with several explanations, but none satisfactory. Of the lot, many favored the idea about the presence of a massive black hole at the center of the galaxy. The intense heat produced, due to the matter being pulled in by the black hole, might have created the Positron. This is seen as the diffuse glow of gamma radiation at the galaxy’s center. It might also be the result of multiple starbursts happening in the central region of the galaxy. An extent of its origin was explained satisfactorily by the INTEGRAL satellite whose data suggest that the antimatter must have come from what is known as X-ray binaries. These are systems of two stars - one normal and the other either remnants of an exploded star. The remnants, known as a neutron star or a black hole, emitted X - rays when the gases from the companion star fell on it. Similar is the case when a binary system of white dwarfs interact. When the stars orbit around each other, the system loses gravitational energy causing them to orbit closer. This eventually leads to a thermonuclear supernova that acts as a source of antimatter.
But these discoveries didn't put an end to the questions from coming.
How long has the fountain been there? Are there similar activities in other regions of the galaxy? And, if the antimatter was created by a binary system, how is it producing such an enormous amount to sustain the cloud? The answers to these never-ending questions are still being figured out by scientists. That leaves a lot of room for the new researchers to explore what is seemingly relatively virgin territory.
Written by Megha Suresh, Sandesh Katakam, Krishna Vijayan
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