The giant Orion Molecular Cloud is an extensive area of star formation about 1,500 light years from us, centred on the impressive Orion Nebula. This infrared image of it, from NASA’s Spitzer Space Telescope, shows light from newborn stars within the Orion Nebula. The nebula can be seen from Earth with the naked eye as a hazy ‘star’ in Orion’s sword.
NASA
This computer-generated image shows just how bright scientists believe the heavens will be once Betelguese has gone supernova; it will flood the skies with light – day and night.
When stars are more massive than about eight times the Sun, they end their lives in a spectacular explosion. The outer layers of the star are hurtled out into space at thousands of miles an hour, leaving a debris field of gas and dust. Where the star once was, a small, dense object called a neutron star is often found. While around only 16 kilometres (10 miles) across, the tightly packed neutrons it contains have more mass than the entire Sun. The bright blue dot in the centre of this X-ray image of RCW 103 is believed to show the neutron star that formed when the star exploded in a supernova 2,000 years ago.
NASA
In a single instant, Betelgeuse will release more energy than our sun will produce in its entire lifetime. As the explosion tears the star apart, it will fling out into space all the elements the star has created through its life.
Over millions of years these newly minted elements will spread out to become a nebula, a rich chemical cloud drifting in space. At the heart of it, all that will remain will be the super-dense core of neutrons; the remnants of the star that was once a billion miles across will have been squashed out of all recognition by gravity. This is a neutron star, the ultimate destiny of Betelgeuse; a dense, hot ball of matter which is the same mass as our Sun but only 30 kilometres (19 miles) across.
We may not have seen neutron stars close up, but we have seen them from afar. X-ray images have been taken that give us vital information about these stars, in particular recent pictures of RCW 103, the two-thousand-year-old remnant of a supernova explosion that occurred about 10,000 light years from Earth (see left).
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When Betelgeuse explodes it will be incredibly bright. It will be by far the brightest star in the sky and it may even shine as brightly as a full moon at night and fill the sky as a second sun during the day.
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This may sound like a cosmic graveyard, but it is in the deaths of old stars that new stars are born. This is the Earthly cycle of death and rebirth played out on a cosmic scale. We can see that beautiful cycle happening today in the constellation of Orion. In an area known as the sword handle lies the Orion Nebula. To the naked eye it appears to be a misty patch of light in the night sky, but through a telescope it is a majestic wonder of the Universe. Hidden in its clouds are bright points of light, new stars forming from the clouds of elements blown out by supernova explosions; the new born from the deaths of the old.
It is from such a cycle that we emerged – within a nebula just like this, five billion years ago, our sun was formed. Around that star a network of planets condensed from the ashes, and amongst them was Earth; a planet whose ingredients originated from the nebula, a cloud of elements formed in the deaths of stars, drifting through space.
But that’s not quite the end of the story, because it is now thought that the chemical elements themselves are not the most complex pieces of ‘us’ that were assembled in the depths of space
THE ORIGIN OF LIFE
This seemingly ordinary piece of rock is anything but; this asteroid fragment is older than any rock on Earth and is one of the thousands of meteorites that fall onto our planet every year.
There are thousands of asteroids in our solar system, mostly within an asteroid belt that formed 4,568 million years ago, and on average one meteorite falls to Earth once a month. However, each and every one discovered is hugely important, regardless of its size, as these asteroid pieces give us a real insight into what forms the building blocks of life.
At first sight the graph opposite – depicting the spectrum of the light from the Orion Nebula (taken from the Herschel Space Observatory Telescope) – looks rather uninspiring, but the information that it contains is in fact fascinating. This illustration reveals that the Orion Nebula is not just a cloud of elements; there is complex chemistry happening out there deep in space.
Just like the black lines in the spectrum of the Sun, the peaks on this graph correspond to particular chemical elements, but some of these peaks derive from complex molecules – there is water in the nebula, and sulphur dioxide. Perhaps more surprisingly, there are also complex carbon compounds – methanol, hydrogen cyanide, formaldehyde and dimethyl ether. This is direct evidence for complex carbon chemistry occurring in deep space. This is tremendously exciting because it means that we are seeing the beginnings of the chemistry of life in a vast cloud of interstellar gas.
The connection doesn’t end there; we may be connected to the chemistry out there in space even more directly. The photo opposite is of a meteorite, a piece of rock that fell to Earth from somewhere out in the depths of the Solar System. It is almost certainly older than any rock on Earth because it was formed from the primordial dust cloud, the nebula that collapsed to form the Sun and the planets five billion years ago. When looking inside this ancient rock we discovered something incredibly interesting: it was found to contain amino acids, the building blocks of proteins, which in turn are the building blocks of life. This strongly suggests there was very complex carbon chemistry happening out there in space, forming the building blocks of life, over four and a half billion years ago. It raises the intriguing prospect that the first amino acids on Earth may have formed in the depths of space and been delivered to our planet by meteorites.
ORION’S MOLECULAR MAKE-UP: This detailed spectrum, obtained by ESA’s Herschel Space Observatory, shows the fascinating chemical fingerprints of potential life-enabling organic molecules in the Orion Nebula.
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The fundamental building blocks of life may have formed in the depths of space and been delivered to our planet by meteorites.
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This is one more beautiful piece of evidence that forces us to think differently about those twinkling lights and smudges of gas and dust in the sky. When we look out into space we are looking at our place of birth. We truly are children of the stars, and written into every atom and molecule of our bodies is the history of the Universe, from the Big Bang to the present day
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Our story is the story of the Universe. Every piece of every one and every thing you love, of every thing you hate, of every thing you hold precious, was assembled in the first few minutes of the life of the Universe, and transformed in the hearts of stars or created in their fiery deaths. When you die those pieces will be returned to the Universe in the endless cycle of death and rebirth. What a wonderful thing to be a part of that universe – and what a story. What a majestic story!
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Supernovae are the long-awaited spectacles of the skies. It is in the death of old stars that new ones are born, and their demise plays a crucial part of the endless cycle of death and rebirth that occurs right across our universe.
NASA
CHAPTER 3
FALLING
FULL FORCE
For all its scale and grandeur, the Universe is shaped by the action of just four forces of nature. Two of these, the weak and strong nuclear forces, remain hidden from everyday experience inside the atomic nucleus. The third force, electromagnetism, is perhaps most familiar to us, as it is the one we marshal to power our lives – electric currents flow because of the action of this force. Finally, there is gravity, the great sculptor – the force that acts between the stars. Gravity shapes the cosmos on the largest distance scales. From the formless clouds of hydrogen and helium that once filled our universe, gravity forged the first stars, sculpted the first planets and arranged them into the exquisite shapes of the galaxies. Having assembled countl
ess billions of solar systems, gravity drives their cycles and rhythms. It is the invisible string behind the revolution of every moon around every planet and every planet around every star. Gravity keeps our feet on the ground and the Universe ticking over.
Gravity is more than a mere gentle presence; it is relentless, and for the largest agglomerations of matter in the Universe – the stars – it is both creator and destroyer. Stars shine in temporary resistance to gravitational collapse, but when they run out of nuclear fuel and the other three forces can no longer rearrange the matter in their cores in order to release energy and resist its inward pull, gravity crushes the most massive of them out of existence. In doing so, it creates the least understood objects in the Universe.
Before embarking on the voyage of their lives, astronauts are prepared for the flight and the sensation of weightlessness in aircrafts such as this C-131 at Wright Air Development Center, which flies at a ‘zero-g’ trajectory. These flight simulators are dubbed ‘vomit comets’ because of the nausea they often induce.
NASA
Soviet cosmonaut Gherman Titov is perhaps not the luckiest of men. In 1960 he was selected alongside Yuri Gagarin for the Soviet manned space programme. Out of the twenty men who started the programme, only these two made it through a fierce selection process that tested their physical and psychological resilience to the limit. Throughout training the two fighter pilots matched each other point for point, but someone had to be first, and Gagarin was given the ticket into the history books. On 12 April 1961, Gagarin became the first human to travel into space, completing a single orbit in 108 minutes before returning to Earth first in Vostok 1 and then by parachute. In one of those interesting bits of space trivia, Gagarin actually arrived back on Earth after his spacecraft, because he ejected at an altitude of 7,000 metres (23,000 feet) due to worries about the safety of the capsule on landing. Vostok 1 arrived safely on the ground 10 minutes before he did.
This bus ride to the Vostok launch on 12 April 1961 was the first part of the journey that was to make Yuri Gagarin a Soviet hero and worldwide celebrity.
NASA
On his return, Gagarin became a Soviet hero and a worldwide celebrity, leaving Titov to become the second man to orbit our planet. Titov’s name will be unfamiliar to most, although to this day he remains the youngest man ever to make the journey into space, at just under 26 years old. He piloted Vostok 2 on 6 August 1961, completing 17 orbits of Earth. Titov also claimed a rather less glamorous place in the history books; on the 25.3-hour mission, he not only became the first man to sleep in space (snoozing for a couple of hours as his spacecraft orbited the planet), but also the first to suffer the symptoms of a condition that has affected almost half of those who have experienced weightlessness for an extended period of time. Titov was the first victim of Space Adaption Syndrome. Known more usually as space sickness, this condition includes a variety of symptoms such as nausea, vomiting, vertigo and headaches as a common reaction to the odd sensations of space travel. Although weightlessness remains one of the great thrills of being an astronaut, it is also one of the most difficult to prepare for. Since Titov introduced medics to Space Adaption Syndrome, space agencies around the world have employed the only method they can of creating weightlessness here on Earth. How is it possible to remove the effects of gravity? The answer is by doing the same thing that Gagarin and Titov did: by falling towards Earth.
The American response to the Vostok programme was Project Mercury, a series of six manned launches which included the historic flights of Alan Shephard, the first American in space, on 5 May 1961, and John Glenn, the first American to orbit Earth. The astronauts selected for the programme, known as the ‘Mercury Seven’, became celebrities in the United States, and all of them eventually flew into space. The final flight of the Mercury Seven was John Glenn’s Space Shuttle mission in 1998, which he completed at the age of 77. The Tracy brothers in the TV series Thunderbirds were named after five of the Mercury Seven: Scott (Carpenter), Virgil (‘Gus’ Grissom), Alan (Shephard), Gordon (Cooper) and John (Glenn). Wally Schirra and Deke Slayton missed out. (I think Wally and Deke would have been great names for Thunderbirds pilots. The days when astronauts were bigger than rock stars are sadly missed.)
Astronauts prepare for Extravehicular Activity by practising techniques on a Hubble Space Telescope mock-up in the Neutral Buoyancy Laboratory. Underwater conditions simulate the weightlessness experienced in space.
NASA
During training for Project Mercury, perhaps after hearing about the experiences of Titov, NASA developed a way of flying a regular military aircraft to take would-be astronauts on an unusual ride. Using a C-131 aircraft, weightlessness was achieved by flying an unconventional flight path. This parabolic path creates a brief period of around 25 seconds during which all the occupants of the plane experience the sensation of weightlessness. This is because they are actually weightless; it may be brief, but when repeated twenty or thirty times in succession, the physiological effects are just as intense as those felt in space. This led to the C-131 being named the ‘Vomit Comet’, a name that has stuck with every plane used for this task ever since.
I’ve known about the Vomit Comet since I was a child, because I was, and still am, passionate about the space programme. Imagine my delight when I heard we were going to ride in it for our film on gravity. Who cares if it makes you feel rough, if the Mercury Seven could face it, so could I.
The Vomit Comet is the perfect place to experience the two related aspects of the force of gravity that hold the key to understanding what gravity actually is. Firstly, it is possible to completely cancel out the effects of gravity by simply falling towards the ground. This sets gravity apart from all the other forces of nature; it is not possible to negate the effect of electric charge, other than by adding more electric charge of the opposite sign. The Comet achieves the removal of gravity simply by flying along the trajectory that a cannon ball would take when fired out of a gun. The plane doesn’t just drop to the ground like a lift with a severed cable, of course (because then it would be impossible to control), but the acceleration of the plane towards the ground is exactly the same as the acceleration you would experience in a falling lift or a parachute jump (if you neglect air resistance). In numbers, the plane must accelerate towards the ground at 9.81 metres per second squared to cancel out the force of gravity. In order to keep the plane under control, it also flies forward at its usual flight speed. This results in the plane flying along a parabolic path. The fact that the effects of gravity are completely removed in freefall is very interesting, and the converse is also true: it is also possible to add to Earth’s gravitational pull by accelerating.
The race for space was on in the 1960s, as the US and Soviet nations battled to be the first to launch a human being into space.
NASA
Everyone knows that astronauts in space are weightless and float around inside their spacecraft, but not everybody knows why. It is not because they are a long way from Earth that gravity is absent (they are in fact only a few hundred miles above Earth’s surface, and the strength of Earth’s gravitational field in near-Earth orbit is not too different to the strength on the surface), it is that the effects of gravity are removed by falling, which is important point number one.
We flew in a modified Boeing 727-200, which is still used today for training shuttle astronauts. During the flight I was also able to demonstrate another strange but equally important and related aspect of gravity. Isaac Newton knew it when he wrote down his theory of gravity in 1687, as did Galileo many decades before him. The strange thing is this: all objects fall at the same rate under the force of gravity, even though gravity acts on objects in proportion to their mass. Newton and Galileo knew this to be the case because they did experiments and noticed that it was true, but they had absolutely no idea why. If you think about it for a moment, it is very odd indeed. Newton found that the gravitational force between two objects, such as Earth and you, is proportional to
the product of their masses. So the force you feel due to the pull of Earth’s gravity is proportional to the mass of Earth multiplied by the mass of you. If you were to double your mass, the force between you and Earth would double. But, the rate at which you accelerate towards Earth because of its gravitational pull is also proportional to your mass, and when you work everything out it turns out that your mass completely cancels out, so therefore all things fall at the same rate under gravity. This looks very strange and was famously demonstrated by Apollo 15 Commander Dave Scott on the surface of the Moon in 1971. Scott dropped a feather and a hammer to the ground and, of course, both hit the ground at the same time. The reason you can’t do this on Earth is because air resistance slows the feather down, but in the high vacuum of the Lunar surface the only force acting on the falling objects is gravity. No matter how much physics you know, this is entertaining to watch because it isn’t in accord with common sense! Surely a cannon ball should fall to the ground faster than a single atom? The answer is, no, it doesn’t, and here is something to think about for later on: even a beam of light falls to the ground at the same rate as a cannon ball. Understanding this concept is key to understanding gravity.
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Wonders of the Universe Page 13