Category Archives: Dark Matter

Earth Might Have Hairy Dark Matter

The solar system might be a lot hairier than we thought.

A new study publishing this week in the Astrophysical Journal by Gary Prézeau of NASA’s Jet Propulsion Laboratory, Pasadena, California, proposes the existence of long filaments of dark matter, or “hairs.”

Dark matter is an invisible, mysterious substance that makes up about 27 percent of all matter and energy in the universe. The regular matter, which makes up everything we can see around us, is only 5 percent of the universe. The rest is dark energy, a strange phenomenon associated with the acceleration of our expanding universe.

Neither dark matter nor dark energy has ever been directly detected, although many experiments are trying to unlock the mysteries of dark matter, whether from deep underground or in space.

Based on many observations of its gravitational pull in action, scientists are certain that dark matter exists, and have measured how much of it there is in the universe to an accuracy of better than one percent. The leading theory is that dark matter is “cold,” meaning it doesn’t move around much, and it is “dark” insofar as it doesn’t produce or interact with light.

Galaxies, which contain stars made of ordinary matter, form because of fluctuations in the density of dark matter. Gravity acts as the glue that holds both the ordinary and dark matter together in galaxies.

According to calculations done in the 1990s and simulations performed in the last decade, dark matter forms “fine-grained streams” of particles that move at the same velocity and orbit galaxies such as ours.

“A stream can be much larger than the solar system itself, and there are many different streams crisscrossing our galactic neighborhood,” Prézeau said.

Prézeau likens the formation of fine-grained streams of dark matter to mixing chocolate and vanilla ice cream. Swirl a scoop of each together a few times and you get a mixed pattern, but you can still see the individual colors.

“When gravity interacts with the cold dark matter gas during galaxy formation, all particles within a stream continue traveling at the same velocity,” Prézeau said.

But what happens when one of these streams approaches a planet such as Earth? Prézeau used computer simulations to find out.

His analysis finds that when a dark matter stream goes through a planet, the stream particles focus into an ultra-dense filament, or “hair,” of dark matter. In fact, there should be many such hairs sprouting from Earth.

A stream of ordinary matter would not go through Earth and out the other side. But from the point of view of dark matter, Earth is no obstacle. According to Prézeau’s simulations, Earth’s gravity would focus and bend the stream of dark matter particles into a narrow, dense hair.

Hairs emerging from planets have both “roots,” the densest concentration of dark matter particles in the hair, and “tips,” where the hair ends. When particles of a dark matter stream pass through Earth’s core, they focus at the “root” of a hair, where the density of the particles is about a billion times more than average. The root of such a hair should be around 600,000 miles (1 million kilometers) away from the surface, or twice as far as the moon. The stream particles that graze Earth’s surface will form the tip of the hair, about twice as far from Earth as the hair’s root.

“If we could pinpoint the location of the root of these hairs, we could potentially send a probe there and get a bonanza of data about dark matter,” Prézeau said.

A stream passing through Jupiter’s core would produce even denser roots: almost 1 trillion times denser than the original stream, according to Prézeau’s simulations.

“Dark matter has eluded all attempts at direct detection for over 30 years. The roots of dark matter hairs would be an attractive place to look, given how dense they are thought to be,” said Charles Lawrence, chief scientist for JPL’s astronomy, physics and technology directorate.

Another fascinating finding from these computer simulations is that the changes in density found inside our planet – from the inner core, to the outer core, to the mantle to the crust – would be reflected in the hairs. The hairs would have “kinks” in them that correspond to the transitions between the different layers of Earth.

Theoretically, if it were possible to obtain this information, scientists could use hairs of cold dark matter to map out the layers of any planetary body, and even infer the depths of oceans on icy moons.

Further study is needed to support these findings and unlock the mysteries of the nature of dark matter.

The mysterious dark energy that speeds the universe’s rate of expansion

The nature of dark energy is one of the most important unsolved problems in all of science. But what, exactly, is dark energy, and why do we even believe that it exists?

What goes up must come down… right?
Ball image via

Step back a minute and consider a more familiar experience: what happens when you toss a ball straight up into the air? It gradually slows down as gravity tugs on it, finally stopping in mid-air and falling back to the ground. Of course, if you threw the ball hard enough (about 25,000 miles per hour) it would actually escape from the Earth entirely and shoot into space, never to return. But even in that case, gravity would continue to pull feebly on the ball, slowing its speed as it escaped the clutches of the Earth.

But now imagine something completely different. Suppose that you tossed a ball into the air, and instead of being attracted back to the ground, the ball was repelled by the Earth and blasted faster and faster into the sky. This would be an astonishing event, but it’s exactly what astronomers have observed happening to the entire universe!

This illustration shows abstracted ‘slices’ of space at different points in time as the universe expands.
Ævar Arnfjörð Bjarmason, CC BY-SA

Scientists have known for almost a century that the universe is expanding, with all of the galaxies flying apart from each other. And until recently, scientists believed that there were only two possible options for the universe in the future. It could expand forever (like the ball that you tossed upward at 25,000 miles an hour), but with the expansion slowing down as gravity pulled all of the galaxies toward each other. Or gravity might win out in the end and bring the expansion of the universe to a halt, finally collapsing it back down in a “big crunch,” just like your ball plunging back to the ground.

So imagine scientists’ surprise when two different teams of astronomers discovered, back in 1998, that neither of these behaviors was correct. These astronomers were measuring how fast the universe was expanding when it was much younger than today. But how could they do this without building a time machine?

Luckily, a telescope is a time machine. When you look up at the stars at night, you aren’t seeing what they look like today – you’re seeing light that left the stars a long time ago – often many hundreds of years. By looking at distant supernovae, which are tremendously bright exploding stars, astronomers can look back hundreds of millions of years. They can then measure the expansion rate back then by comparing the distance to these far-off supernovae with the speed at which they are flying away from us. And by comparing how fast the universe was expanding hundreds of millions of years ago to its rate of expansion today, these astronomers discovered that the expansion is actually speeding up instead of slowing down as everyone had expected.

What pushes galaxies like these in the Hubble deep field apart?
NASA and A. Riess (STScI), CC BY

Instead of pulling the galaxies in the universe together, gravity seems to be driving them apart. But how can gravity be repulsive, when our everyday experience shows that it’s attractive? Einstein’s theory of gravity in fact predicts that gravity can repel as well as attract, but only under very special circumstances.

Repulsive gravity requires a new form of energy, dubbed “dark energy,” with very weird properties. Unlike ordinary matter, dark energy has negative pressure, and it’s this negative pressure that makes gravity repulsive. (For ordinary matter, gravity is always attractive). Dark energy appears to be smoothly smeared out through the entire universe, and it interacts with ordinary matter only through the action of gravity, making it nearly impossible to test in the laboratory.

Scientists used to think that the expansion of the universe was described by the yellow, green, or blue curves. But surprise, it’s actually the red curve instead.

The simplest form of dark energy goes by two different names: a cosmological constant or vacuum energy. Vacuum energy has another strange property. Imagine a box that expands as the universe expands. The amount of matter in the box stays the same as the box expands, but the volume of the box goes up, so the density of matter in the box goes down. In fact, the density of everything goes down as the universe expands. Except for vacuum energy – its density stays exactly the same. (Yes, that’s as bizarre as it sounds. It’s like stretching a string of taffy and discovering that it never gets any thinner).

Astronomers continue to probe the skies, looking for finer details that can build on what we suspect about dark energy.
Reidar Hahn, CC BY

Since dark energy can’t be isolated or probed in the laboratory, how can we hope to understand exactly what it’s made of? Different theories for dark energy predict small differences in the way that the expansion of the universe changes with time, so our best hope of probing dark energy seems to come from ever more accurate measurements of the acceleration of the universe, building on that first discovery 17 years ago. Different groups of scientists are currently undertaking a wide range of these measurements. For example, the Dark Energy Survey is mapping out the distribution of galaxies in the universe to help resolve this puzzle.

Could Einstein’s theory need work?
Sophie Delar

There is one other possibility: maybe scientists have been barking up the wrong tree. Maybe there is no dark energy, and our measurements actually mean that Einstein’s theory of gravity is wrong and needs to be fixed. This would be a daunting undertaking, since Einstein’s theory works exceptionally well when we test it in the solar system. (Let’s face it, Einstein really knew what he was doing). So far, no one has produced a convincing improvement on Einstein’s theory that predicts the correct expansion for the universe and yet agrees with Einstein’s theory inside the solar system. I’ll leave that as a homework problem for the reader.

The Conversation

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New light shed on search for ‘invisible’ dark matter

We can map it, weigh it and simulate it, yet we still have no idea what it is. But dark matter is coming into the spotlight as never before.

Astronomers now know that for every grams worth of atoms in the universe, there are at least five times more of a new, invisible matter neither shining or blocking light.

We can also create model universes inside supercomputers that reproduce in stunning detail what we see around us in the night sky but only by assuming this invisible dark matter passes through us like a ghost.

Finally, in the past decade we have begun to almost routinely map out the invisible, finding it matching the simulation predictions.

Yet of the numerous candidates that particle physicists have thought up for dark matter we are still far from knowing which is right. A quest that is every bit as grand and in some ways even more difficult than the search for the God Particle, the Higgs Boson.

First clues

In 1978, Vera Rubin and Kent Ford discovered that stars in nearby galaxies were not moving as expected. Stars far from the centre of a galaxy – where all the light (and hence mass) was concentrated – were moving far too quickly for the gravity of all the visible matter to hold onto them.

Therefore, some unseen source of matter must be providing the extra gravity to explain the stars in the outer reaches of the galaxy. The idea of dark matter had been brought into view, but next came the question, what actually was it?

Today, more than 40 years later, technological advances in astronomy have enabled astronomers to greatly expand on Vera Rubin’s pioneering work, and have found signs of dark matter in the motion of galaxies and stars everywhere. The motions of visible objects allow us to predict the dark matter distributions and these match the model universes created in supercomputers.

Such observations and simulations have lead to the staggering realisation that the visible matter in our universe is the tip of the iceberg making up just 15.7% of all the mass.

But understanding how dark matter interacts with visible matter is only part of the puzzle. A crucial clue to the identity of the dark matter is whether it interacts with itself, and if so how strongly?

Not so dark?

So how do you study the interactions of a particle you cannot see? The answer lies in gravitational lensing.

Dark Matter Map in colour with red (blue) regions representing high (low) concentrations of dark matter. The dots are clusters of galaxies found by the DES survey (the greater the cluster mass, the larger the dot).
Dark Energy Survey

Massive objects can bend the space around them and when they do this the path of light is also bent, in the same way that a lens does. Just like any prescription glasses, you can have strong and weak gravitational lensing.

If there is a lot of mass tightly packed in a region then it strongly bends the light from background galaxies. This happens at the dense centre of galaxy clusters.

At the edges of the cluster, where the mass is more spread out, the lensing effect is weaker and rather than an obvious warping of the background galaxy image you have a more subtle twist to their shapes.

You can only be sure of this effect by averaging the twisting of dozens of background galaxy images making weak lensing a far more challenging observational tool but the only one that can map the dark matter in the outskirts of a galaxy cluster.

Car crashes in space

It is also possible to look for dark matter self-interactions by studying how galaxies and galaxy clusters collide. When these massive objects pass through each other, there is a chance that the material they are made of will interact too.

This chance is based on the object’s collision cross-section, which can be thought of as the target area it presents for another object to collide with. You also need to take into account the distribution of the objects.

For example, while cars on Earth may collide head-on with a large cross-section, the chances of this actually occurring are far less likely if there’s not much traffic on the road.

So too, stars might seem like big targets but they’re so sparsely distributed within the galaxy that they practically never collide in practice, we’d have to wait a billion times longer than the age of the galaxy for a star to hit our Sun!

The gas that lies between the stars, however, will absolutely collide (the electromagnetic force ensures that tiny particles will present a much larger cross-section). So if two galaxies collide the gas slams together in a mangled car wreck while the stars sail by just missing each other.

The dark matter may lie somewhere in between these cases, with candidate particles having a tiny cross-section compared to the gas, but more than the stars meaning after a collision a cloud (or halo) of dark matter will trail after the stars but ahead of the gas.

Mixed messages

Recent studies have used gravitational lensing to map out the dark matter in colliding galaxy clusters and a second more detailed look at the Abell galaxy cluster to see if the dark matter lags behind the stars due to some new dark matter self-interaction.

On the larger scale of galaxy cluster interactions, no evidence was found that the dark matter halos of the clusters had interacted (i.e. they still followed the stars).

But on the smaller scale, a displaced lens of mass was detected approximately 4,500 lightyears behind the stars.

The stars had raced ahead of the majority of the mass giving the lensing signal, which is the dark matter. The greater the distance the dark matter lags behind the stars, the greater the dark matter particle’s cross-section which can rule out certain candidates.

Four giant elliptical galaxies lie at the heart of a cluster with dark matter mass indicated by contours. The dark matter appears to lag behind the stars in some cases suggesting they are experiencing a ‘head wind’ as they try to push through the larger halo of dark matter.
ESO/R Massey

Darkness visible?

On small scales there is now tentative evidence that dark matter appears to interact/collide at least a little with clouds of dark matter travelling in the opposite direction. On larger scales we have the tightest constraint yet on how much it can interact with itself.

Between these two lower and upper bounds lie a lot of potential candidates but these two results suggest astronomers may finally be honing in on the elusive dark matter particle – although uniquely confirming the exact candidate will require finding it in a lab on Earth.

This work is therefore particularly timely as funds have been awarded for the world’s first southern hemisphere direct dark matter detector in Stawell, Victoria.

Housed at SUPL (Stawell Underground Physics Laboratory) experiments will try to detect the collision of dark matter particles with atoms and confirm the exact particle responsible and finally bring dark matter into the light and glare of particle physics.

The Conversation

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How can dark matter cause chaos on Earth every 30 million years?

In 1980, Walter Alvarez and his group at the University of California, Berkeley, discovered a thin layer of clay in the geologic record, which contained an unexpected amount of the rare element iridium.

They proposed that the iridium-rich layer was evidence of a massive comet hitting the Earth 66 million years ago, at the time of the extinction of the dinosaurs. The Alvarez group suggested that the global iridium-rich layer formed as fallout from an intense dust cloud caused by the impact. The cloud of dust covered the Earth, producing darkness and cold. In 1990, the large 100-mile diameter crater from the impact was found in Mexico’s Yucatan Peninsula.

A collision would have been disastrous for life on Earth.
Don Davis

The timing of this impact, together with the fossil record, have led most researchers to conclude that this collision caused the mass extinction of the dinosaurs and many other forms of life. Subsequent studies found evidence of other mass extinctions in the geologic past, which seem to have happened at the same time as pulses of impacts, determined from the record of impact craters on the Earth. And these co-incidences occurred every 30 million years.

Why do these extinctions and impacts appear to happen within an underlying cycle? The answer may lie in our position in the Milky Way Galaxy.

Artist’s impression of the Milky Way’s structure.
NASA/JPL-Caltech/ESO/R. Hurt

Our Galaxy is best understood as an enormous disc. Our solar system revolves around the circumference of the disc every 250 million years. But the path is not smooth, it’s wavy. The Earth passes through the mid-plane of the disc once every 30 million years.

An edge-on view of our Milky Way Galaxy shows its disk-like nature.

I believe that the cycle of extinctions and impacts is related to times when the Sun and planets plunge through the crowded disc of our Galaxy. Normally, comets orbit the Sun at the edge of the solar system, very far from the Earth. But when the solar system passes through the crowded disc, the combined gravitational pull of visible stars, interstellar clouds and invisible dark matter disturbs the comets and sends some of them on alternate paths, sometimes crossing the Earth’s orbit, where they can collide with the planet.

Geological events such as pulses of volcanic eruptions occur on that same 30-million-year schedule.
D W Peterson, National Park Service, CC BY

Recognition of this 30-million-year galactic cycle is the key to understanding why extinctions happen on a regular schedule. But it may also explain other geologic phenomena as well. In further studies, we found that a number of geological events, including pulses of volcanic eruptions, mountain building, magnetic field reversals, climate and major changes in sea level show a similar 30 million year cycle. Could this also be related to the way our solar system travels through the Galaxy?

Dark matter is invisible but its gravity bends and magnifies the light of galaxies located far behind it.
NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA

A possible cause of the geological activity may be interactions of the Earth with dark matter in the Galaxy. Dark matter, which has never been seen, is most likely composed of tiny subatomic particles that reveal their presence solely by their gravitational pull.

As the Earth passes through the Galaxy’s disc, it will encounter dense clumps of dark matter. The dark matter particles can be captured by the Earth and can build up in the Earth’s core. If the dark matter density is great enough, the dark matter particles eventually annihilate one another, which adds a large amount of internal heat to the Earth that can drive global pulses of geologic activity.

Dark matter is concentrated in the narrow disc of the Galaxy, so geologic activity should show the same 30-million-year cycle. Thus, the evidence from the Earth’s geological history supports a picture in which astrophysical phenomena govern the Earth’s geological and biological evolution.

And if you’re wondering about your own prospects for encountering this dark matter-driven phenomenon? We’re just passing through the Galaxy’s dense disk within the last couple of million years, so a comet shower may be in the offing.

The Conversation

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NASA’s Hubble, Chandra Find Clues that May Help Identify Dark Matter

WASHINGTON, March 26, 2015 /PRNewswire-USNewswire/ — Using observations from NASA’s Hubble Space Telescope and Chandra X-ray Observatory, astronomers have found that dark matter does not slow down when colliding with itself, meaning it interacts with itself less than previously thought. Researchers say this finding narrows down the options for what this mysterious substance might be. Dark… Continue reading

Astronomers Propose Dark Matter Theory

Astronomers are still further than they’d like to be to solving the mystery that is dark matter, concentrations of mysterious, invisible energy throughout the universe that may have impacted our own planet more than we think. While they were once thought to be part of a “dark sector,” a hidden quantum field out of the standard model of the universe that just reflects the matter around it. Instead, it may be something more interesting: its particles interact the way that galaxy clusters collide.

When this type of event takes place, hot gases filling the gaps between stars within these galaxies begin colliding and splattering in every direction, a movement similar to water hitting and splashing off a flat surface. About 90 percent of the matter in these clusters is actually dark matter – so does dark matter also splatter like water?

New research, however, has eliminated this colorful possibility – therefore limiting what types of particles constitute dark matter, and reducing the possibility that they hide away mirrors of our visible universe.

How does this work? Our own galaxy has billions of stars – just a miniscule fraction of the hundreds of billions scattered throughout the visible universe – a countless array of stars, planets, galaxies, and then even the debris – the dust and gas that’s responsible for producing all of it – but even this is totals up to just 15 percent of the universe at best. The rest is dark matter – which is detected by its extreme gravitational pull that it exerts on the matter it surrounds. It is impervious to light, neither radiating nor reflecting it. However, they are able to spot the patches of dark matter due to light bending around it.

David Harvey, who is a postdoctoral researcher at the Swiss Federal Institute of Technology Lausanne, is among the ranks of scientists actively trying to solve the mystery of dark matter, which led him to study galactic collisions – events where 90 percent of what collides is actually dark matter.

“[Galaxy cluster mergers] are incredibly messy,” said Harvey. “You’ve got [the stars], the highest densities of dark matter and hot gas all swirling together.”

While this has been the epicenter of dark matter studies for decades, interest has renewed due to changes in technology. “We wanted to have a big statistical sample that tries to average over all these different merging scenarios, and try to get a statistical idea of what dark matter is doing during these cosmological crashes.”

What they have learned about these collisions, which feel more like mergers, is that they aren’t as violent as one might think. The stars are often so far apart when they take place that they tend to neatly fold together in place.

Between the galaxies, however, lies a heavy blanket of gas crackling with charged particles. Once the galaxy clusters come together, this gas spews in every direction.

“If we measure the dark matter [after the collision], and should it lie where the galaxies are, we know the dark matter is completely collisionless, and doesn’t interact with itself at all,” Harvey said. “And if it should lie where the gas is, we’d say that the dark matter is actually interacting with itself a lot, like a liquid.”

So far, the researchers compared data from 30 different galaxy-cluster collisions with the help of NASA’s Hubble Space Telescope and the Chandra X-ray Observatory. What they found was equally striking: dark matter appears to behave similar to stars, remaining largely unaffected in the collision. Perhaps these observations suggest that dark matter is made of similar components to stars?

So what about the splattering gas? This is due to the gas behaving like a solid, in the same way that liquids bubble and cling together in a microgravity environment. Atomic protons interact in such a way as well.

By comparison, dark matter doesn’t behave like a gas, interacting less with its own particles than the protons of atoms interact with each other. This has led many to suspect that dark matter is made up of dark protons or electrons, sort of a mirror version of the atom.

“Chances are that dark matter is not made up of dark protons interacting with dark protons, and chances are, there is not a mirror universe out there with these dark particles,” said Harvey. “The caveat is that theorists could change some of their parameters, so the field is still open to what [dark matter] could be, but we’re narrowing it down.”

James Sullivan
James Sullivan is the assistant editor of Brain World Magazine and a contributor to Truth Is Cool and OMNI Reboot. He can usually be found on TVTropes or RationalWiki when not exploiting life and science stories for another blog article.

How the Large Hadron Collider Might Disprove the Big Bang

First proposed in 1927 by Belgian physicist Georges Lemaitre as the “Hypothesis of the Primeval Atom,” the Big Bang Theory (mostly associated with the sitcom but popularized in movies since Disney’s Fantasia), remains the predominant explanation for the origin of how our universe got to be the way it is today – starting from a particle smaller than an atom that inflated some 13.8 billion years ago.

It wasn’t always, though. For another forty years, despite the increasing evidence of an ever-expanding universe – galaxies drifting apart from each other, of varying ages and shapes; an abundance of light chemicals like hydrogen (about 75% of the universe) and helium; and the presence of cosmic microwaves, radiation that transitioned from visible light (some of the leftover radiation can be seen in the static given off by analog TV signals) – many astronomers clung to a steady-state model of the universe that gradually acquires matter. Astronomer Fred Hoyle even derisively referred to it once as the “Big Bang” and the name stuck.

So was there anything before it? We don’t know. Then again, there also was no time or space before the Big Bang event either. Some evidence has been proposed that the universe has always existed, eons before the Big Bang set everything in its current state. The overwhelming majority of the universe is invisible, and sometimes the question is raised of whether the universe really is singular – or is it one of many? Nothing is sacred as the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN) is unleashed in Geneva this week.

If the Large Hadron Collider finds miniature black holes, it may provide the evidence we need that parallel universes in fact do exist, and potentially that the Big Bang did not occur as cosmologists once envisioned. Already, the particle accelerator, currently the largest in the world, discovered the Higgs boson, known as the God Particle, which physicists suspect is what provides other particles with mass.

If these holes give off a specific wavelength of energy, they could be further testimony for a rather controversial theory known as ‘rainbow gravity,’ proposing that our universe may reach an indefinite distance back in time, without a singular point of origin, and no cosmic inflation event necessary to start the beginning of matter as we know it.

The theory is reconciled from Einstein’s theory of general relativity and suggests that varying wavelengths of light affect gravity in different ways. Were you to look backwards in time, the universe is more dense than in the present. Although it comes close to an extreme and infinite density, it never quite gets there. Consequently, its concept of the early universe is a bit different than the picture we have now.

While this all sounds very surreal – Earth would scarcely feel the impact of rainbow gravity. Black holes, however, would pick up on it considerably – increments that could be sizable and measurable, and easily within the range of the LHC.

“We have calculated the energy at which we expect to detect these mini black holes in gravity’s rainbow [a new theory]. If we do detect mini black holes at this energy, then we will know that both gravity’s rainbow and extra dimensions are correct,” said CERN researcher Dr. Mir Faizal to

This week will be the LHC’s second run, after being shut down for new installations at the beginning of 2013. It will be fully operational by Wednesday with its beams opening full circle.

When the 27 km accelerator is active it will begin hammering together protons at a rate nearly twice the energy needed to discover Higgs boson.

Rolf Heuer, Director General of CERN, hailed the switch-on as unprecedented, ‘a new era for physics’ that could shed some light on those not so visible forces in the universe: dark matter, dark energy and super-symmetry.

“I want to see the first light in the dark universe. If that happens, then nature is kind to me,” said Heuer.

Then there is that sci-fi fantasy that almost seems within reach of the LHC – a bridge between two worlds, or rather, two universes – a probability that another parallel dimension could bleed into our own.

Do the physicists have an explanation for this yet?

“Just as many parallel sheets of paper, which are two dimensional objects [breadth and length] can exist in a third dimension [height], parallel universes can also exist in higher dimensions,” added Dr Faizal.

“We predict that gravity can leak into extra dimensions, and if it does, then miniature black holes can be produced at the LHC.

“Normally, when people think of the multiverse, they think of the many-worlds interpretation of quantum mechanics, where every possibility is actualised. This cannot be tested and so it is philosophy and not science.

“This is not what we mean by parallel universes. What we mean is real universes in extra dimensions.

“As gravity can flow out of our universe into the extra dimensions, such a model can be tested by the detection of mini black holes at the LHC.”

Since its two-year hibernation, the new and improved LHC has quite a few things to brag about before being fired up for its next run: newer, more powerful magnets, superior cryogenics (you read that right – the LHC is in fact the coldest place on Earth, with an epic cooling system that can keep noble gases like krypton in liquid form), higher voltage and even higher energy beams that mean an acceleration nearly twice what it made on its first run.

Frances Saunders, president of the IOP, said, “This has been a massive effort by all the scientists and engineers at CERN to upgrade the LHC and its detectors and get it ready to operate at almost double the collision energies of the first run.

“As well as allowing greater study of the Higgs boson there is much anticipation amongst the physics community as to what else may be found at these higher energies, testing our theories and understanding of concepts such as supersymmetry and potentially giving greater insight into the 95 per cent of the universe that is composed of dark matter and dark energy.”

James Sullivan
James Sullivan is the assistant editor of Brain World Magazine and a contributor to Truth Is Cool and OMNI Reboot. He can usually be found on TVTropes or RationalWiki when not exploiting life and science stories for another blog article.

Hidden in plain sight: the Milky Way’s new companions

When we think of cosmology, we often imagine the largest telescopes peering into the deepest space, collecting the feeble light from exploding stars or the first galaxies.

But for some cosmologists – like the Galactic Archaeologists – the focus is the local universe, asking if we can learn about the evolution of our own Milky Way from what we see around us.

While this local universe is, well, local, how little we know about it can come as quite a surprise; we simply haven’t scanned the immensity of the entire sky in enough detail to reveal its secrets. But new surveys with new telescopes are opening up the sky, and what they are revealing is quite surprising.

Our new cosmic friends

So, what have they discovered?

Two new papers appeared just this month – one from a team based in the US and another by an independent group in the UK – announcing the discovery of new “dwarfs” of the southern sky, small galaxies with only a few hundreds of millions of stars. (Our Milky Way is thought to have several hundred billion stars.)

In fact, both papers presented the discovery of the same eight dwarf galaxies, with the British team identifying potentially one more.

The Magellanic Clouds and the Auxiliary Telescopes at the Paranal Observatory in the Atacama Desert in Chile. Only six of the nine newly discovered satellites are present in this image.
V. Belokurov, S. Koposov (IoA, Cambridge). Photo: Y. Beletsky (Carnegie Observatories)

How did two disparate teams identify the same galaxies at the same time? And just what do these observations tells us about the universe? It’s an interesting tale!

Thinking theoretically

Let’s start with the formation and evolution of galaxies.

Over the past 30 years, with the explosive growth of computing power, our cosmological understanding has been revolutionised with synthetic universes revealing how galaxies are born from the featureless cosmic soup of the Big Bang.

Unlike the real universe, through our universe-within-a-computer we can accurately track the motions of mass, watching both dark matter and gas flow together, building galaxies over cosmic time. In these synthetic universes, we would expect the Milky Way to be surrounded by many thousands of smaller dwarfs.

If the Milky Way is really accompanied by such a wealth of smaller galaxies, it would be strong evidence that our ideas of galaxy evolution are pointing in the right direction. So, are they there?

The sky’s the limit

The problem with finding dwarfs is that there is a lot of sky to look at. Dedicated survey telescopes with specialised optics are required.

Over the last few decades, the Sloan Digital Sky Survey (SDSS) has patiently imaged a huge swath of the northern sky, finding many millions of distant galaxies.

But Sloan also yielded many more dwarf galaxies in our own backyard, some reasonably large, with billions of stars, as well as some so puny, with a thousand stars or so, that it is difficult to know whether it is really a galaxy or just an errant bunch of stars.

And are the huge numbers of dwarf galaxies predicted by our model universe within a computer actually there? The simple answer is: no!

Instead of many thousands, SDSS saw only a handful. This missing satellites problem has significant implications for our understanding of galaxy evolution. But to know just how the problem bad is, we need to know just how missing the dwarfs really are!

While a spectacular success, SDSS, based in the US, has only stared at the northern sky. Before we can fully answer the question, we need a complete census. We need to survey the southern sky!

There is a steadily growing army of survey telescopes in the south, including VISTA in Chile and SkyMapper here in Australia. But, at the moment, out in the lead is a survey that is not focused on local universe at all.

The Dark Energy Survey

The discovery of dark energy has revolutionised our view of cosmology, revealing that the expansion of the universe is accelerating. But the fact that we don’t really know what dark energy is means it remains one of the biggest astrophysical mysteries.

Astronomers have planned new observational approaches to uncover the secrets of dark energy. Currently, a new camera, DECam, on the Blanco 4m Telescope in Chile is on the case.

Its goal is the Dark Energy Survey (DES), a search for the subtle influence of dark energy on our observations of the distant universe. To do this, DECam will survey a huge swath of the southern sky.

Collateral science

As DECam stares into the distant universe, it also captures all the things in between, so its data will be a goldmine for a broad range of science. Within the DES collaboration are astronomers primed to reap the scientific rewards on offer.

So why two papers on the same objects at the same time? As DECam collects data, chunks are periodically given away to the entire astronomical community, allowing as much science as possible to be squeezed from the observations.

Astronomers outside the DES collaboration are equally hungry to search for DECam dwarf galaxies. The act of sharing data does maximise the science, but even the astronomers taking the data cannot hang around as there is a good chance they will be scooped.

Distribution of the galactic satellites on the sky. The underlying background image is the Infrared Map produced by the 2MASS survey.
S. Koposov, V. Belokurov (IoA, Cambridge). Background: 2MASS

What did we learn?

The discovery of these new dwarfs does not solve the missing satellite problem, but is providing clues to bridge our gap between the observed and theoretical universe.

The clustering of these dwarfs around the Magellanic Clouds may point towards all of these galaxies having fallen together into the Milky Way as a small group. If this really is the accretion of a group, it opens an exciting window onto galaxy evolution.

But it’s important to remember that these new galaxies were found in the first year’s worth of data from DECam, with more data becoming available on a yearly basis.

With more and more sensitive eyes pointing at the sky, we can expect many more dwarfs of the southern sky to be revealed.

The Conversation

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