c pa k ed G PA ES
of the The secrets of the cosmos revealed
earth’s evil twin
a star is born
weird science
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alien hunting
robot astronauts
Alien life
Spores from the stars In a galaxy of 200 billion planets, we’re probably not alone. But are we natives here on Earth, or merely colonists? And could life on our planet have begun with seeds from space? he recipe for life is simple. First, take hydrogen, oxygen, carbon and nitrogen and combine them to form water, methane and ammonia. Next, assemble these simple molecules into amino acids, followed by proteins, DNA and eventually complete cells. In 1953, Stanley Miller and Harold Urey showed that an electric spark (to simulate lightning) was enough to form all the amino acids found on Earth, given the right starting mixture. The real problem is that the oceans are too big for the primordial soup to have been anything more than a very watery gruel. And without a high enough concentration, the chance encounters between amino acid molecules may have occurred too rarely for life to evolve. One way out of this is to add extra organic molecules directly from outer space. “Amino acids have been detected in meteorites,” says Professor Ralf Kaiser of the University of Hawaii at Manoa. In a study published last year, Professor Kaiser showed that the extreme cold and harsh radiation
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environment of outer space might actually help these molecules form. “In interstellar clouds, there are a lot of ice-coated grains and the galactic cosmic rays and UV radiation can enter these clouds and actually synthesize molecules,” he says. “Amino acids, dipeptides or sugars can be formed in these interstellar ices.” Clouds of these ice grains originally coalesced to form the Kuiper belt when the Solar System formed. This contains millions of asteroid-sized chunks of frozen ammonia, methane and ice, beyond the orbit of Neptune. Some of them were dislodged from their stable orbits to become comets, and so could have bombarded Earth with all the complex molecules needed to kick-start life.
Martian influence So far nothing more complicated than a dipeptide has been detected in space – a dipeptide being two amino acids that have joined together. It’s the simplest sort of protein and is still a long way off a strand of DNA, but if DNA can’t form in deep space,
“Grains 0.0001mm across could cross the Galaxy in around a billion years. Since the Milky Way is around 13 billion years old, there might have been time for life to evolve on a distant planet and then travel through space to a young Earth.” 10
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Alien life
Recent research There are organisms in the stratosphere, but did they come from Earth or space? In July 2013, British researchers sent a weather balloon to a height of 27km (17 miles) and collected samples from the atmosphere there. They retrieved a single fragment from a kind of microscopic algae called a diatom. Bacteria have been found in the stratosphere before and some birds can occasionally fly up to the lower reaches, but diatoms are much heavier than bacteria, so their presence has been the topic of much debate in the scientific community. Professor Milton Wainwright of Sheffield University, who lead the research, has argued that nothing short of a major volcano could lift diatoms to this altitude. Because there were no eruptions within three years of the experiment, the most likely explanation, he says, is that they arrived on comet fragments during the Perseid meteor shower. However, the research has also been the subject of some criticism. So far, no radioactive isotope or amino acid analysis has been performed to prove that this diatom fragment is extraterrestrial. The argument boils down to whether it’s more likely that diatoms could survive in the ice of a comet, or that there is another mechanism that could carry Earth-bound diatoms into the stratosphere.
This scrap of diatom skeleton was found at the very edge of space
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Alien life
Life on a wandering planet They are planets with no stars to orbit or systems to inhabit, but in the last 15 years these orphaned spheres flying through space have become some of the most promising candidates for extraterrestrial life nomad planet harbouring life races through the Universe on a trajectory all of its own. Not orbiting a star in ellipses, as the eight planets in our Solar System do, but hurtling through the void in-between planetary systems as it orbits our Galaxy’s centre of mass directly. We’ve seen these life arks before – in science fiction. From television shows like Star Trek: Deep Space Nine to popular videogames and books (A Game of Thrones author George R R Martin’s first novel, Dying of the Light, was about one such planet), the concept of rogue or interstellar or orphan planets has been with us for decades. But in 1998, Caltech professor of planetary sciences David J Stevenson theorised in his paper Possibility of Life-Sustaining Planets in Interstellar Space that these wandering planets could actually be the ideal locations for life outside of Earth. “Sunlight is nice, but not essential for life so far as we know, ” explains Stevenson when Science Uncovered asks how life could begin and survive on a planet with no home
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star to provide warmth or energy. “Although it may be necessary for the large biomass that we [humans] have.”
Birth of a rogue Though there is no consensus on the exact formation process of rogue planets, there are two popular theories, according to Osaka University astrophysicist Takahiro Sumi, whose studies have directly led to the discovery of multiple rogue planet candidates. “We speculate [rogue planets can be] either formed like a planet around a star and then scattered away, or formed like a star by collapsing the gas and dust in the interstellar medium.” It would be easy to imagine star-less rogue planets flying through space completely devoid of warmth. However, a combination of atmospheric pressures and internal heat from radioactive decay at the planet’s core can keep a rogue planet’s surface temperature high enough to maintain liquid oceans, with surface conditions similar to those found at the deepest points of Earth’s seas. Indeed, it’s
A combination of atmospheric pressures and internal heat from radioactive decay at the planet’s core can keep a rogue planet’s surface temperature high enough to maintain liquid oceans. 24
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Alien life
Earth’s nearest nomad How much do we really know about the closest wandering planet to Earth? CFBDSIR 2149-0403 is the closest rogue planet we’ve discovered to date. It may not be sporting the jazziest of names – and may not even technically be a rogue planet at all – but the celestial body known as CFBDSIR 2149-0403, or, more formally, CFBDSIR J214947.2-040308.9, caused quite a stir when it was first spotted by astronomers in 2012. Named after the Canada-France Brown Dwarfs Survey in which it was discovered (the IR part of the name stands for InfraRed, because it was observed using the Wide-field InfraRed Camera, while the numbers designate coordinates), it’s the nearest interstellar planet candidate we know of. It’s also a scant 100 lightyears from our Solar System. Dreams of nearby life might have had to be shelved – despite the presence of methane, at between four and seven times the size of Jupiter it’s much too large to support lifeforms – but while the body doesn’t orbit a star, it’s likely (with an 87% probability, according to the European Southern Observatory paper Astronomy & Astrophysics) to be travelling through space in tandem with an entire group of stars known as the AB Doradus Moving Group. Because we haven’t yet been able to determine its age or the method of its formation, its status as either a planet or a brown dwarf has yet to be determined. Regardless of its eventual classification, its migration across the skies alongside its likely companions is responsible for igniting the world media’s interest in the mystery of rogue planets.
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Solar System
How we came to be We’re sitting on a rock flying at 107,000 kilometres per hour around a hot ball of gas, in the middle of 300 billion other balls of gas. How did that happen? ur Solar System is massive. The Voyager programme’s explorations suggest that the Sun’s influence stretches around 100AU (astronomical units) - 100 times the distance between the Sun and Earth. And everything in it - from gas giants to orbiting moons, to vast collections of ice and rock, to the star itself - had to come from somewhere, or something. The problem is, we don’t know how the Universe, or our corner of it, was formed. We weren’t even close to being there when it happened; the existence of humans is so insignificant it doesn’t even show up on the geological clock. Dozens of theories have been accepted by scientists over the years, but the current favourite - the nebular hypothesis - is a revised version of a theory first proposed in the 18th Century. According to the nebular hypothesis, our Solar System began 4.6 billion years ago. It started as part of a giant molecular cloud, or GMC. This is a large body of hydrogen, with a tiny amount of dust, helium and lithium,
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around 100,000 times the mass of the Sun and around 65 lightyears (or 20 parsecs, for Han Solo fans) across. A GMC floating in space isn’t just a boring cloud: cold, home to magnetic fields and outside of the influence of any other body, the GMC has a tendency to become gravitationally unstable, perhaps as the result of a nearby event like a supernova. In October 2013, scientists studying meteorites reported that much of the complex chemical material from our Solar System may have been donated by a nearby star going boom, so this is certainly a plausible notion.
Gravity of the situation As molecules within the cloud move closer together, their gravitational pull increases, drawing others towards them, which further increases the attraction. Over time - and with a little help from waves of energy - GMCs fragment into smaller nebulae, each pulled by the dominant cluster. One of these, around a parsec across, contained the material used to create our Solar System.
Our Solar System began 4.6 billion years ago. It started as part of a giant molecular cloud, or GMC. This is a large body of hydrogen, with a tiny amount of dust, helium and lithium. 30
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Solar System
Other ideas The nebular hypothesis is not the only explanation for how our Solar System got here
Given that we’re dealing with theories rather than facts, it’s natural that over the years a few other ideas have cropped up and been pushed onto the back burner. The tidal theory suggests that a massive object – perhaps another star – had a near miss with the Sun and in doing so drew out some of its material, which went on to form the planets. Numerous other versions of this theory have been posited since it was first put forward, such as the capture theory, which suggests that filaments of material were ejected from both stars as they passed, and Soviet astronomer Otto Schmidt’s interstellar cloud theory, which proposed that the Sun, already complete, had travelled through an interstellar cloud and emerged covered in a fog of dust and material to be used for planet formation. Perhaps the most interesting alternate theory is that of J Marvin Herndon, who suggests that all planets form as gas giants, and the inner rocky planets are the result of condensation and the raining-out of gaseous planets at the higher temperatures close to the Sun.
Could Earth have started life as a gas giant and then condensed into its rocky form?
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The stars
Lifecycle of a star
Some stars explode, others fade quietly into the darkness, but nothing of any interest would exist in the Universe at all without matter formed in the fiery heart of a star n the inky blackness of interstellar space, a cloud of dust sits motionless. For billions of years it remains that way, occasionally jostled by the weak gravitational ripples of events in its galactic neighbourhood. More time passes and ‘nothing much’ continues to occur. But eventually a larger ripple passes through the cloud – a shockwave caused by a distant supernova, perhaps. Now the dust is forced into a smaller space, and it begins to contract under its own gravity.
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A star is born The dust, which is mostly comprised of hydrogen and helium atoms, begins to clump up, orbiting around itself. It pulls in more and more material from its parent cloud (otherwise known as a nebula). As the clumps grow larger, the pressure of all this material being compressed together causes the temperature to rise. The fragments continue to grow and grow, getting hotter and hotter until they become a giant,
rotating sphere of superhot gas. And so a star is born… almost. What happens next depends on how much material has collected inside this protostar. Those protostars with less than 8% of the mass of the Sun fail to reach temperatures high enough for the nuclear fusion of hydrogen – around 10 million degrees. Some of these failures, the ones about 13 times larger than Jupiter, get hot enough to create deuterium and become known as brown dwarfs. Those even smaller, if they’re orbiting another object, become planets. But the largest fragments – the ones that do manage to achieve hydrogen fusion – begin to stabilise. The energy that their core releases balances out their gravity, preventing further collapse, and the star begins to enter its main sequence. In this phase, the hydrogen collected by the core is slowly turned into helium. How long that takes depends on how hot the star is – large supergiants can burn through their fuel after a few million years, whereas relatively cold, low-mass red dwarfs can remain in the
The dust, which is mostly comprised of hydrogen and helium atoms, begins to clump up, orbiting around itself and pulling in more and more material from its parent cloud. 64
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The stars
Hubble uncovered The Hubble Space Telescope has changed how we see the history of the Universe The first proposals for putting a telescope into space were made in 1923, with the objective of seeing past Earth’s thick, distorting atmosphere to get a clear view of the heavens. NASA conducted a few space telescope experiments in the 1960s, but it wasn’t until 1990 that the Hubble Space Telescope was launched. Within weeks a problem was identified – the mirror inside the telescope was slightly the wrong shape. A solution was devised that effectively put a pair of glasses on the telescope, correcting its optics. This was launched in 1993, and Hubble was then ready for action. The telescope has imaged many different stars in different phases of their lives, including the photogenic nebulae where they’re born. One of its finest hours was in 1995, when astronomers pointed the telescope at an area of complete darkness. The result was the Hubble Deep Field – a stunning view of almost 3,000 galaxies of different shapes, sizes and colours, letting us see what the Universe looked like a billion years ago. Hubble is still sending back data until at least 2014 and is expected to do so until 2020 or so, when it will fall back to Earth. Its successor, the James Webb Space Telescope, will launch in 2018.
The Hubble Space Telescope, producer of so many iconic images, is near the end of its working life
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The stars On a clear night, over 7,000 stars can be seen from Earth with the naked eye. But how can we map them accurately?
In around 134BC, Hipparchus catalogued stars in a system of ‘magnitudes’ from his observatory in Rhodes.
Mapping the stars in the night sky
What tools do Earth-bound scientists have to catalogue and distinguish between the many billions of pinpricks of light in the night sky?
ot all stars are the same. There are big ones, little ones, old ones, young ones, red ones, white ones and everything in-between. But how do we tell the difference when they’re so far away? The earliest efforts to separate stars concentrated on differentiating them by brightness. In around 134BC, Hipparchus catalogued stars in a system of ‘magnitudes’ from his observatory in Rhodes. This graded the brightest stars as magnitude 1, down to magnitude 6 for the dimmest visible stars. Just over 1,000 were recorded in total. The magnitude system lives on today. It was formalised by English astronomer Sir Norman Robert Pogson in 1856 by assigning a magnitude value to every star based on its
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brightness in comparison to Vega, a ‘magnitude 0’ star. There are over 7,000 stars visible to the naked eye, but with the advent of telescopes we are now able to view many more stars of magnitude 7 and dimmer.
Apparent and absolute Two stars with the same apparent magnitudes could actually be rather different – if one is dim but close and the
Once we know a star’s distance from Earth, we can calculate its absolute magnitude.
other is bright but distant, for instance. So how do we know if a star is dim, or simply far away? Stellar astronomers do this by recording the position of stars at different times during the earth’s orbit. By measuring their movement relative to distant background objects, you can calculate the distance of these stars from Earth using simple geometry. This is known as the parallax method. Once we know a star’s distance, and observe its apparent magnitude, we can calculate its absolute magnitude – and therefore work out just how bright it really is. The brightness of a star isn’t the only measurement we can take from Earth, however. The colour of starlight depends on
The stars
The seven most common star types The seven objects that are most frequently found in the Milky Way Over 400 billion stars in our Galaxy have all formed from collapsing clouds of gas and dust, but how they look now depends on their age, size and temperature. A few of the most common stellar objects are described below.
White dwarf
As a red giant expands and sheds its outer layers, only its dense core remains. Although no longer fusing hydrogen, the core consists of carbon and oxygen heated by gravitational collapse to glow white hot – hence the name. It will eventually cool to become a black dwarf.
Red giant
Main sequence star
Because our Solar System lies towards the edge of the Milky Way, we can look out across our own Galaxy
Varying in size from one-fifth to over 10 times the radius of the Sun, these stars are united by the processes inside them. Also sometimes known (rather confusingly) as dwarf stars, they generate energy by the fusion of hydrogen at their core.
Once the majority of hydrogen in a main sequence star is fused, its core contracts and grows hotter and brighter. This causes its outer layers to expand (up to 100 times the radius of the Sun), spreading out their energy and lowering the surface temperature until the star glows red.
An area of nebulosity surrounds and obscures the Milky Way’s central supermassive black hole, Sagittarius A*
Neutron star its temperature, and the temperature of a star helps us work out its age and size. Red stars have a surface temperature of just a few thousand degrees, but those with surface temperatures above 10,000°C or so can glow white, and stars that are even hotter will appear blue in colour. Stars can exist for trillions of years, depending on their size. As they evolve over their lifespan, they will change size, temperature and colour. Our Sun, at just over 4.5 billion years old, glows yellow with a surface temperature of nearly 6,000°C. This makes it brighter than around 85% of the other stars in the Milky Way, most of which are red dwarfs. Aaron Boardley
This remnant of a supernova is an extremely dense core of neutrons. Though only 10km across, it’s heavier than the Sun – this means a thimble-full would weigh a billion tonnes. Neutron stars spin extremely rapidly, too – up to several hundred times per second.
Supernova
When the core of a star that’s far larger than the Sun collapses, the rapid increase in temperature causes the star to explode. It becomes a billion times brighter for several days as it expels its material into space.
Brown dwarf
Black hole
When a star is massive enough that gravity forces it to collapse beyond a neutron star, it becomes a black hole. This creates a gravitational field so immense that nothing can escape it – not even light.
If a star forms with less than onetenth the mass of the Sun, it won’t have the gravitational force to heat its core to fusion-triggering levels. It’s what’s known as a ‘failed star’, and it simply cools off by radiating away what little thermal energy it has.
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Mysterious Universe
How the Universe started
Around 13.8 billion years ago, in a moment too brief to imagine and at temperatures too high to comprehend, space and time came into existence in a burst of creation stronomers have come up with a mind-boggling picture of how the Universe began. Their answer, which fits observations of its current behaviour, is that it simply erupted 13.8 billion years ago, in an event dubbed the Big Bang. But while it’s a powerful image, the term is actually a misnomer. This was no explosion within a previously unoccupied space, but rather a bursting into existence of everything – space, time, matter and energy – all at the same moment. It is impossible to ask what happened before the Big Bang because time simply didn’t exist, and it happened everywhere because everywhere was within this unimaginably tiny region. This bizarre scenario reveals that the original Universe was an incredibly dense fireball, containing nothing that we might recognise today – a state that our laws of physics find it impossible to explain. This briefest of moments is known as the Planck Era, named after the German theoretical physicist Max Planck. During that brief moment, the Universe grew a trillion times in size in a trillionth of a second. In less than a millionth of a second, cosmologists believe
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that the temperature plummeted (from 10 billion trillion trillion degrees Celsius to a relatively cool ten trillion degrees Celsius) and the Universe expanded from its infinitely dense start to a diameter of around one billion kilometres. The fundamental forces of nature – strong nuclear, weak nuclear, electromagnetic and gravitational – had separated out, too.
Plasma soup From the original bundle of energy emerged a hot soup of plasma containing fundamental particles and antiparticles. Reactions between these produced the first protons, neutrons and other heavier particles – and within 100 seconds, when the Universe had grown to many hundreds of lightyears wide, the nuclei of virtually all its helium atoms had formed. Following this incredibly active start, there followed a period lasting many thousands of years when the Universe continued its relentless expansion – it continued to cool, but everything was still too energetic for particles to stay together long enough for any atoms to be produced.
From the original bundle of energy emerged a hot soup of plasma containing fundamental particles and antiparticles. Reactions between these produced the first protons, neutrons and other particles. 88
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Mysterious Universe
The state of the Universe Our Universe may be one of many, or could shrink again in a Big Crunch
Images © Festival della Scienza fron Genova
In the first half of the 20th Century, a now discredited ‘steady state’ rival theory for the Universe held that it had always existed and that new matter was being continuously created as it expanded. However, following the detection of cosmic microwave background – the faint echo of the Big Bang – this idea was effectively killed off completely. Since then, new alternatives have emerged proposing that the Universe is continually expanding then contracting in a series of Big Bangs and Big Crunches. Extensions to this idea suggest that we could be part of a multiverse, where separate universes appear and expand alongside each other like bubbles. One supporter of such a concept, Sir Roger Penrose, believes that some circular features observed in the cosmic microwave background are likely to be ‘bruises’ left by collisions with other universes. Four such bruises have been tentatively identified, although their existence is extremely controversial – the general view being that the patterns that have been found in the CMB data don’t actually exist.
Sir Roger Penrose suggests patterns found in CMB data point to collisions with other universes
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Mysterious Universe
Dark energy
Seemingly conjured up by the void of space, this interstellar force has thrown off gravity and is set to one day plunge our Universe into darkness he 2011 Nobel Prize in Physics was awarded to three men who had, in the late ’90s, proven that our expanding Universe would neither slow down nor fall back into itself under its own mass. According to their discoveries, not only would the Universe continue to expand, it would do so more and more quickly. This means that in trillions of years, galaxies will be so far apart from each other that light from the most distant will never reach any others. Only those clusters of galaxies that are close enough to be bound by gravity will remain together. The question is, what is causing the Universe to expand faster and faster in spite of the attraction of its own gravity? This force has been given the name ‘dark energy’.
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The rise of dark energy According to current theories, dark energy has existed since the Big Bang, but the gravity of visible and dark matter made it insignificant in the early Universe. About 5 billion years ago, the increasing distances between galaxies reduced the effects of gravity, and dark energy became more powerful. The Universe began to accelerate and has been doing so ever since. The 21st Century now has a new picture of the Universe. Visible matter – from galaxies to you and me – makes up only 4.9% of the Universe; dark matter a further 26.8%. The remaining 68.3% is dark energy. James Russell
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Mysterious Universe
The Victor M Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile will look further into the past than ever before
Dark Energy Survey
High on a Chilean mountain, the hunt for the nature of dark energy intensifies Over 200 scientists from 23 institutions have embarked on a large-scale research project that aims to shed light on the properties of dark energy. “On 31 August 2013 we began the full-scale science survey, which will extend into 2019,” says Dr Brian Nord, a researcher with the Dark Energy Survey project. “We will take data for 100 nights per year for five years. DES will observe a larger patch of sky, farther out into the Universe than any other optical telescope has before – almost 8 billion years into the past.” The project lies at the forefront of cosmological research. “Dark energy is one of the most fundamental problems in physics today,” continues Nord, “and we must use the Universe as our laboratory. The biggest question that we are looking at now is whether dark energy will change with time. Is it static throughout the history of the Universe, or has it changed over the last 13.7 billion years?”
Make-up of the universe 4.9%
is stars, galaxies, gas and everything we know
What is causing the Universe to expand faster and faster in spite of the attraction of its own gravity?
68.3% is dark energy
26.8% is dark matter
According to the latest cosmological principles, everything we can see makes up less than 5% of the entire Universe
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Sci-fi and technology
Back to the future The laws of physics don’t forbid time travel, but they don’t make it easy either. Here’s how it could happen ime travel is entirely possible – so feasible, in fact, that you’ve probably experienced it already. You just wouldn’t have noticed it happening. One of the consequences of Einstein’s special theory of relativity (the one that deals with objects moving close to the speed of light) means that time stretches when you move relative to another object. In effect, time moves more slowly for you than it would for a ‘stationary’ observer. Okay, we’re dealing with tiny fractions of seconds, but someone who’s been to Australia and back would be a tiny bit younger than an identical twin who stayed at home – they’re effectively travelling into the future. These relativistic effects, while
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small, are so significant that the atomic clocks on GPS satellites are adjusted by around 40 microseconds (40 millionths of a second) a day to keep everything accurate.
One-way ticket Once you start to approach the speed of light (a whopping 300,000km per second), the effects become more pronounced - a few days for you could be equivalent to thousands of years back home. Before you get too excited though, this is pretty limited as the basis of a time machine because potential destinations would be restricted to the future, and you’d never be able to return to the present you’d left – as Charlton Heston discovered in the original
Alternative theories of time travel Five ways time travel could be made to work – if you had unlimited resources at your disposal, that is
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Travelling nearly as fast as light
Thanks to Einstein’s special theory of relativity, travelling close to the speed of light would make time move more slowly for you than it does for people back home – enough to allow you to see a future way beyond your natural lifespan.
Travelling faster than light
With those infamous neutrino sightings from 2011 now put down to experimental error, it looks like nothing can travel faster than the speed of light. If, however, there were some way of outrunning a photon, it could alter the way an object moves through spacetime.
Sci-fi and technology Planet of the Apes movie. Even if you could find astronauts willing to set out on a one-way mission to the future, keeping them alive would be another issue, because accelerating to close to the speed of light and then decelerating back down again is going to either take a prohibitively long time, or require forces large enough to turn a human body into jelly. Travelling backwards in time opens up a whole new set of challenges - assuming it’s even possible at all. Again, potential answers lie in Einstein’s theories of relativity, this time the general theory (the one that explains gravity by linking space and time as one entity called spacetime). Crucially, the equations that underpin the theory do not forbid going back in time, though they would rely on phenomena and conditions that have never been observed in the physical universe around us. But if it were somehow possible to generate ‘negative energy’ (and we don’t know if this ‘exotic matter’ is feasible in the real world), it would theoretically be possible to force spacetime to bend in the opposite direction from usual. Then, using wormholes – essentially bridges between two points in spacetime - it might then be possible to move between two points in time. All rather more complicated than firing up Doc Brown’s DeLorean… Richard Edwards
GPS satellites have to make tiny daily clock adjustments to account for relativity
Doughnut-shaped time loops
Around black holes, gravity can bend spacetime. So if you could create a time loop around an intense source of gravity, you could theoretically move back and forth through the ‘closed time-like curve’. But you could only go back as far as when the time machine was first built.
Tipler cylinder
Instead of relying on black holes for your gravity, the theory here is that by taking some material 10 times the mass of the Sun, rolling it into a dense cylinder of infinite length and spinning it at a few billion revolutions per minute, you could warp spacetime enough to allow time travel. Simple!
The equations that underpin Einstein’s theories do not forbid going back in time.
Cosmic superstrings
String theory could provide a more esoteric solution. Some scientists believe that cosmic superstrings – narrow tubes of energy that stretch right across the Universe – may contain enough mass to warp spacetime if two parallel strings came close enough together.
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