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March 20, 2019

Big Bang, black holes and the march


March 20, 2019

China recently landed a probe on the far side of the moon. The moon both rotates on its axis and also revolves around Earth. Because it is very close to Earth, it has come into Earth’s gravitational lock and thus it rotates exactly once as it circles around. Hence, there is only one side constantly facing Earth and the other side – the one farther from us – is called the far side of the Moon.

At 385,000 kms, the Moon is the closest heavenly body to our Earth in this vast universe. The closest planet to us is Venus, which is 40 million kms away, while our Sun is 150 million kms away. It takes light from the Sun, travelling at a speed of 300,000 kms per second, eight and a half minutes to get to the Earth.

That the universe is unimaginably vast can be gauged by the fact that of all the stars we see in the sky the one closest to us, Proxima Centauri, is over 4.2 light years away, meaning it takes even light over four years to get to us from Proxima Centauri. There are about 250 billion stars in our galaxy, called the Milky Way, and our star, the Sun, is just one ordinary small yellow star in one of the spiral arms of this galaxy. There is again nothing special about the Milky Way; it is one of approximately 200 billion galaxies that are estimated to exist in the universe.

The nearest large galaxy to us, located at a distance of 2.5 million light years, is named Andromeda, and it contains a trillion stars. Andromeda is observable to the naked eye and was first written about in the tenth century by the Persian scholar Abdul Rahman Al Sufi in his book, ‘Book of Fixed Stars’. Because of the huge distance and the time it takes light to travel from there, when Al Sufi saw Andromeda he saw it as it was 2.5 million years ago.

In 1932, American astronomer Edwin Hubble discovered that all galaxies are receding away from each other and the farther they are the faster they recede. This means that the universe is expanding and creating new space. However, if the universe is expanding now then at some point in the past the galaxies must have been closer to each other and indeed if you go back long enough you would go back to a time when everything was ‘joined’ together. Working backwards from the speed of expansion, scientists figure that the universe may have been created with a massive explosion called the Big Bang about 13.8 billion years ago.

If the universe started with a Big Bang explosion, then there must be after-effects of that huge explosion, just as heat continues to radiate long after an explosion. Interestingly, a few years ago two American scientists accidentally discovered this after-effect, called the cosmic background radiation. Some of the static you see on your television screen when your cable is unplugged is due to this radiation.

Our Sun has a diameter of 1.4 million kms and is so large that we can fit in a million Earths into it. The sun contains 99 percent of all the mass that exists in the solar system – all the planets and asteroids and comets together make up less than one percent of the mass. Given that the Sun is so massive, its weight puts a lot of gravitational pressure on its interior core and heats it up. This results in the joining together (or fusing) of hydrogen atoms and converting them into helium atoms and, because helium atoms are more energy efficient, a little energy is released. This ‘little’ energy from trillions of atoms is the thermonuclear reaction or ‘fusion bombs’ that are constantly going off in the Sun’s interior and which provide energy for all life on Earth. Whether we get energy (or nourishment) from animals or plants, or from fossil fuels or coal, it is all energy stored from the Sun.

Our Sun has been exploding these fusion bombs for five billion years and has enough hydrogen fuel left to go on for another five. This phenomenon is not unique to our Sun; all stars convert hydrogen into helium and in the process emit energy in the form of light. When stars are doing so they are said to be on main sequence; our Sun is one such star.

When stars are done burning their fuel of hydrogen and converting it into helium, they start fusing helium atoms together to produce carbons atoms. When helium is converted into carbon atoms, the core temperature increases even more and now carbon will be converted into other heavier atoms. But eventually when fusion reaches the element of cobalt or iron, the most energy efficient atoms, the process essentially stops.

When hydrogen fusion ends in stars they are said to leave the main sequence; their outer shells expand and cool down and stars turn into what’s called red giants. After about five billion years, our Sun will also turn into a red giant and expand almost to the orbit of our planet Earth. Eventually gravity will win out and under pressure from its own gravity, the Sun will collapse into a white dwarf star.

However, for stars more massive than our Sun, the pressure of gravity will be so large that they will want to shrink to a size even smaller than a white dwarf. These stars may undergo a huge explosion called a supernova, an explosion so huge that it generates more brightness than a billion suns. It is during these explosions that even iron atoms are fused into heavier elements such as uranium. During a supernova explosion a star losses most of its mass and afterwards may again shrink to become a white dwarf.

But even after losing most of their mass, many stars still remain very massive. A Lahore-born physicist Subrahmanyan Chandrasekhar (b1910) worked out that stars which remain 44 percent more massive than our own Sun will continue to contract to such a small size that they might turn into neutron stars. Neutron stars are only about a kilometre across and contain more weight than our Sun. Imagine the density of such a star.

But for more massive stars the collapsing doesn’t stop even at the neutron star level. They continue to collapse and turn into a black hole, a mass so dense that nothing, not even light, can escape its gravity. Because they can’t be seen, they are called black holes.

While the rest of the world is thinking about what happens to distant stars when they run out of fuel, we confuse real learning with the ability to speak English. And in this specious pursuit we deny our children meaningful education. And what happens to those kids who learn some English but nothing else? They are busy nursing on social media their fragile egos that get hurt when women march for freedom and equality.

The writer has served as federalminister for finance, revenue andeconomic affairs.

Twitter: @MiftahIsmail

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