Posted on by Vanessa Janek

Cosmology 101: The End

A1689-zD1, one of the brightest and most distant galaxies, is 12.8 billion light years away - an extremely far distance in our expanding universe. Image credit: NASA/ESA/JPL-Caltech/STScI

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Welcome back to the third, and last, installment of Cosmology 101. So far, we’ve covered the history of the universe up to the present moment. But what happens next? How will our universe end? And how can we be so sure that this is how the story unfolded?

Robert Frost once wrote, “Some say the world will end in fire; some say in ice.” Likewise, some scientists have postulated that the universe could die either a dramatic, cataclysmic death – either a “Big Rip” or a “Big Crunch” – or a slower, more gradual “Big Freeze.” The ultimate fate of our cosmos has a lot to do with its shape. If the universe were open, like a saddle, and the energy density of dark energy increased without bound, the expansion rate of the cosmos would eventually become so great that even atoms would be torn apart – a Big Rip. Conversely, if the universe were closed, like a sphere, and gravity’s strength trumped the influence of dark energy, the outward expansion of the cosmos would eventually come to a halt and reverse, collapsing on itself in a Big Crunch.

Despite the poetic beauty of fire, however, current observations favor an icy end to our universe – a Big Freeze. Scientists believe that we live in a spatially flat universe whose expansion is accelerating due to the presence of dark energy; however, the total energy density of the cosmos is most likely less than or equal to the so-called “critical density,” so there will be no Big Rip. Instead, the contents of the universe will eventually drift prohibitively far away from each other and heat and energy exchange will cease. The cosmos will have reached a state of maximum entropy, and no life will be able to survive. Depressing and a bit anti-climactic? Perhaps. But it probably won’t be perceptible until the universe is at least twice its current age.

At this point you might be screaming, “How do we know all this? Isn’t it all just rampant speculation?” Well, first of all, we know without a doubt that the universe is expanding. Astronomical observations consistently demonstrate that light from distant stars is always redshifted relative to us; that is, its wavelength has been stretched due to the expansion of the cosmos. This leads to two possibilities when you wind back the clock: either the expanding universe has always existed and is infinite in age, or it began expanding from a smaller version of itself at a specific time in the past and thus has a fixed age. For a long time, proponents of the Steady State Theory endorsed the former explanation. It wasn’t until Arno Penzias and Robert Wilson discovered the cosmic microwave background in 1965 that the big bang theory became the most accepted explanation for the origin of the universe.

Why? Something as large as our cosmos takes quite a while to cool completely. If the universe did, in fact, began with the kind of blistering energies that the big bang theory predicts, astronomers should still see some leftover heat today. And they do: a uniform 3K glow evenly dispersed at every point in the sky. Not only that – but WMAP and other satellites have observed tiny inhomogeneities in the CMB that precisely match the initial spectrum of quantum fluctuations predicted by the big bang theory.

What else? Take a look at the relative abundances of light elements in the universe. Remember that during the first few minutes of the cosmos’ young life, the ambient temperature was high enough for nuclear fusion to occur. The laws of thermodynamics and the relative density of baryons (i.e. protons and neutrons) together determine exactly how much deuterium (heavy hydrogen), helium and lithium could be formed at this time. As it turns out, there is far more helium (25%!) in our current universe than could be created by nucleosynthesis in the center of stars. Meanwhile, a hot early universe – like the one postulated by the big bang theory – gives rise to the exact proportions of light elements that scientists observe in the universe today.

But wait, there’s more. The distribution of large-scale structure in the universe can be mapped extremely well based solely on observed anisotropies in the CMB. Moreover, today’s large-scale structure looks very different from that at high redshift, implying a dynamic and evolving universe. Additionally, the age of the oldest stars appears to be consistent with the age of the cosmos given by the big bang theory. Like any theory, it has its weaknesses – for instance, the horizon problem or the flatness problem or the problems of dark energy and dark matter; but overall, astronomical observations match the predictions of the big bang theory far more closely than any rival idea. Until that changes, it seems as though the big bang theory is here to stay.

Posted on by Steve Nerlich

Astronomy Without A Telescope – Dark Statistics

The dark flow hypothesis. A region of the observable universe is being influenced by a mysterious something outside the observable universe. Source: universe-review.ca

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The hypothetical dark flow seen in the movement of galaxy clusters requires that we can reliably identify a clear statistical correlation in the motion of distant objects which are, in any case, flowing outwards with the expansion of the universe and may also have their own individual (or peculiar) motion arising from gravitational interactions.

For example, although galaxies have a general tendency to rush away from each other as space-time expands between them, the Milky Way and the Andromeda Galaxy are currently on a gravitationally bound collision course.

So, if you are interested in the motion of the universe at a large scale, it’s best to study bulk flow – where you step back from consideration of individual objects and instead look for general tendencies in the motion of large numbers of objects.

Very large scale observations of the motion of galaxy clusters were proposed by Kashlinsky et al in 2008 to indicate a region of aberrant flow, inconsistent with the general tendency in the motion and velocity expected by the expansion of the universe – and which cannot be accounted for by localized gravitational interactions.

On the basis of such findings, Kashlinsky has proposed that inhomogeneities in the early universe may have existed prior to cosmic inflation – which would represent a violation of the currently favored standard model for the evolution of the universe, known as the Lambda Cold Dark Matter (Lambda CDM) model.

The aberrant bulk flow might result from the existence of a large concentration of mass beyond the edge of the observable universe – or heck, maybe it is another adjacent universe. Since the cause is unknown – and perhaps unknowable, if the cause is beyond our observable horizon – the astronomical interrobang ‘dark’ is invoked – giving us the term ‘dark flow’.

To be fair, a lot of the more ‘out there’ suggestions to account for these data are made by commentators of Kashlinsky, rather than Kashlinsky and fellow researchers themselves – and that includes use of the term dark flow. Nonetheless, if the Kashlinsky data isn’t rock solid, all this wild speculation becomes a little redundant – and Occam’s razor suggests we should continue assuming that the universe is best explained by the current standard Lambda CDM model.

The apparent aberrant 'dark flow' (between the constellations of Centaurus and Vela) is alleged to show up in both close and distant galaxy clusters - where red is most distant, blue is least distant. This would suggest it is something that has been there since the universe was very young. Credit: Kashlinsky, NASA.

The Kashlinsky interpretation does have its critics. For example, Dai et al have provided a recent assessment of bulk flow based on the individual (peculiar) velocities of type 1A supernovae.

The Kashlinsky analysis is based on observations of the Sunyaev–Zel’dovich effect – which involves faint distortions in the cosmic microwave background (CMB) resulting from CMB photons interacting with energetic electrons – and these observations are only considered useful for identifying and observing the behavior of very large scale structures such as galaxy clusters. Dai et al instead use specific data points – being standard candle Type 1a supernovae observations – and look at the statistical fit of these data to the expected bulk flow of the universe.

So, while Kashlinsky et al say we should ignore the motion of individual units and just look at the bulk flow – Dai et al counter with saying we should look at the motion of individual units and determine how well those data fit an assumed bulk flow.

It turns out that Dai et al find the supernovae data can fit the general trend of bulk flow proposed by Kashlinsky – but only in closer (low red shift) regions. More significantly, they are unable to replicate any aberrant velocities. Kashlinsky measured an aberrant bulk flow of more than 600 kilometers a second, while Dai et al found velocities derived from Type 1a supernovae observations to best fit a bulk flow of only 188 kilometers a second. This is a close fit with the bulk flow expected from the Lambda CDM model of the expanding universe, which is around 170 kilometers a second.

Either way, it’s all down to a statistical analysis of general tendencies. More data would help here.

Further reading: Dai et al. Measuring the cosmological bulk flow using the peculiar velocities of supernovae.

Posted on by Anne Minard

Perseus Cluster Thicker Around the Middle Than Thought

Credits: NASA/ISAS/DSS/A. Simionescu et al.; inset: NASA/CXC/A. Fabian et al.

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The Japanese Suzaku X-ray telescope has just taken a close look at the Perseus galaxy cluster, and revealed it’s got a bit of a spare tire.

Suzaku explored faint X-ray emission of hot gas across two swaths of the Perseus Galaxy Cluster. The resulting images, which record X-rays with energies between 700 and 7,000 electron volts in a combined exposure of three days, are shown in the two false-color strips above. Bluer colors indicate less intense X-ray emission. The dashed circle is 11.6 million light-years across and marks the so-called virial radius, where cold gas is now entering the cluster. Red circles indicate X-ray sources not associated with the cluster.

The results appear in today’s issue of Science.

The Perseus cluster (03hh 18m +41° 30‘) is the brightest extragalactic source of extended X-rays.

Lead author Aurora Simionescu, an astrophysicist at Stanford, and her colleagues note that until now, most observations of galaxy clusters have focused on their bright interiors. The Suzaku telescope was able to peer more closely at the outskirts of the Perseus cluster. The resulting census of baryonic matter (protons and neutrons of gas and metals) compared to dark matter offers some surprising observations.

It turns out the fraction of baryonic matter to dark matter at Perseus’s center was consistent with measurements for the universe as a whole, but the baryonic fraction unexpectedly exceeds the universal average on the cluster’s outskirts.

“The apparent baryon fraction exceeds the cosmic mean at larger radii, suggesting a clumpy distribution of the gas, which is important for understanding the ongoing growth of clusters from the surrounding cosmic web,” the authors write in the new paper.

Source: Science. See also JAXA’s Suzaku site

Posted on by VirtualAstro

Coming to a Sky Near You: The Realm of Galaxies

The original Hubble Ultra-Deep Field (Credit NASA, ESA, and S. Beckwith (STScI) and the HUDF Team).

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We live on a planet which orbits a star, and along with a hundred billion other stars, our Sun orbits the centre of our Milky Way galaxy. It doesn’t just stop there; our galaxy is one of hundreds of billions of galaxies in our Universe that gravitationally clump together in groups or clusters.

Throughout Spring in the northern hemisphere, astronomers and people interested in the night sky are going to be in for a galactic treat, as this is the time of year we can see the Coma/Virgo Super cluster or “Realm of Galaxies”.

Galaxies are massive islands of stars, gas and dust in the Universe; they are where stars and planets are born and eventually die. Galaxies are cosmic factories of creation — where it all happens on a very grand scale. To give you an idea of size, it would take you roughly 100,000 years to travel across the disc of the Milky Way at the speed of light!

Andromeda Galaxy.

The Milky Way is the second largest member of our local group of galaxies with Andromeda being the largest. Other members of our local group include the Triangulum galaxy and large and small Magellanic Clouds.

Virgo Galaxy Cluster - NOAO/AURA/NSF

The Coma/ Virgo Super cluster dominates our intergalactic neighbourhood; it represents the physical centre of our Local Super cluster and influences all the galaxies and galaxy groups by the gravitational attraction of its enormous mass.

Unfortunately galaxies are almost impossible to see with the naked eye, so you will need powerful binoculars or a large telescope, such as a Dobsonian to see most of the brighter galaxies in this region.

The cluster contains approximately 2,000 elliptical and spiral galaxies of which approximately 20 or more are observable using amateur equipment. This includes 16 Messier objects such as the Black eye spiral Galaxy M64, and elliptical galaxies, M86 with its plume, massive M87 at its centre and beautiful spiral M88, to name just a few.

From Left to Right M64, M86 and M88 (Credit NASA)

To find the approximate location of the Realm of Galaxies, first find the constellation of Leo – the lion — easily found in the South East this time of year with the backwards question mark overhis head. Go past Leo’s rear end and you will be in the bowl asterism of Virgo, to the bottom left of Leo and the faint constellation of Coma Berenices (Berenices hair) top left of Leo. This is the Realm of Galaxies!

Star Chart to help you find the Realm of Galaxies (Credit Adrian West)

Download a map of this region or use a star atlas to find your way around this area and try and spot as many galactic delights (faint fuzzies) as you can. As a bonus, the ringed Planet Saturn is just below this area too at the moment!

Give yourself plenty of time, wrap up warm and just think, you are looking for the largest structures in the Universe, hundreds of millions of light years away from Earth.

Posted on by Vanessa Janek

Cosmology 101: The Present

A map of the CMB as captured by the Wilkinson Microwave Anisotropy Probe. Credit: WMAP team
A map of the Cosmic Microwave Background (CMB) as captured by the Wilkinson Microwave Anisotropy Probe. Credit: WMAP team

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Welcome back! Last time, we discussed the first few controversial and eventful moments following the birth of our cosmos. Looking around us today, we know that in the span of just a few billion years, the universe was transformed from that blistering amalgam of tiny elementary particles into a vast and organized expanse just teeming with large-scale structure. How does something like that happen?

Let’s recap. When we left off, the universe was a chaotic soup of simple matter and radiation. A photon couldn’t travel very far without bumping into and being absorbed by a charged particle, exciting it and later being emitted, just to go through the cycle again. After about three minutes, the ambient temperature had cooled to such an extent that these charged particles (protons and electrons) could begin to come together and form stable nuclei.

But, despite the falling temperature, it was still hot enough for these nuclei to start to combine into heavier elements. For the next few minutes, the universe cooked up various isotopes of hydrogen, helium and lithium nuclei in a process commonly known as big bang nucleosynthesis. As time went on and the universe expanded even further, these nuclei slowly captured surrounding electrons until neutral atoms dominated the landscape. Finally, after about 300,000 years, photons could travel freely across the universe without charged particles getting in their way. The cosmic microwave background radiation that astronomers observe today is actually the relic light from that very moment, stretched over time due to the expansion of the universe.

If you look at a picture of the CMB (above), you will see a pattern of differently colored patches that represent anisotropies in the background temperature of the cosmos. These temperature differences originally stemmed from tiny quantum fluctuations that were dramatically blown up in the very early universe. Over the next few hundred million years, the slightly overdense regions in the spacetime fabric attracted more and more matter (both baryonic – the kind that you and I are made of – and dark) under the influence of gravity. Some small regions eventually became so hot and dense that they were able to begin nuclear fusion in their cores; thus, in a delicate dance between external gravity and internal pressure, the first stars were born. Gravity then continued its pull, dragging clumps of stars into galaxies and later, clumps of galaxies into galaxy clusters. Some massive stars collapsed into black holes. Others grew so heavy and bloated that they exploded, spewing chunks of metal-rich debris in every direction. About 4.7 billion years ago, some of this material found its way into orbit around one unassuming main sequence star, creating planets of all sizes, shapes, and compositions – our Solar System!

Billions of years of geology and evolution later, here we are. And there the rest of the universe is. It’s a pretty striking story. But what’s next? And how do we know that all of this theory is even close to correct? Make sure to come back next time to find out!

Posted on by Nancy Atkinson

PAMELA Uncovers Cosmic Ray Surprise

PAMELA data show clear deviations from a single power law model between protons and helium nuclei. Credit: Adriani, et. al, Science.

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High energy particles called cosmic rays are constantly bombarding Earth from all directions, and have been thought to come from the blast waves of supernova remnants. But new observations from the PAMELA cosmic ray detector show an unexpected difference in the speeds of protons and helium nuclei, the most abundant components of cosmic rays. The difference is extremely small, but if they were accelerated from the same event, the speeds should be the same.

The PAMELA instrument. Image courtesy of Piergiorgio Picozza

PAMELA, the Payload for Anti-Matter Exploration and light-Nuclei Astrophysics, is on board the Earth-orbiting Russian Resurs-DK1 satellite. It uses a permanent magnet spectrometer along with a variety of specialized detectors to measure the abundance and energy spectra of cosmic rays electrons, positrons, antiprotons and light nuclei over a very large range of energy from 50 MeV to hundreds of GeV.

Just as astronomers use light to view the Universe, scientists use galactic cosmic rays to learn more about the composition and structure of our galaxy, as well as to find out how things like how nuclei can accelerate to nearly the speed of light.

Oscar Adriani and his colleagues using the PAMELA instrument say their new findings are a challenge to our current understanding of how cosmic rays are accelerated and propagated. “We find that the spectral shapes of these two species are different and cannot be well described by a single power law,” the team writes in their paper. “These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy.”

Instead, the team concludes, the acceleration and propagation of cosmic rays may be controlled by now unknown and more complex processes.

Supernova remnants are expanding clouds of gas and magnetic fields and can last for thousands of years. Within this cloud, particles are accelerated by bouncing back and forth in the magnetic field of the remnant, and some of the particles gain energy, and eventually they build up enough speed that the remnant can no longer contain them, and they escape into the Galaxy as cosmic rays.

One key question that scientists hope to answer with PAMELA data is whether the cosmic rays are continuously accelerated over their entire lifetime, whether the acceleration occurs just once, or if there is any deceleration.

Scientists say that determining the fluxes in the proton and helium nuclei will give information about the early Universe as well as the origin and evolution of material in our galaxy.

Adriani and his team hope to uncover more information with PAMELA to help better understand the origins of cosmic rays. They say possible contributions could be from additional galactic sources, such as pulsars or dark matter.

Abstract: PAMELA Measurements of Cosmic-Ray Proton and Helium Spectra

Source: Science

Posted on by Steve Nerlich

Astronomy Without A Telescope – Knots In Space

A double Einstein ring. Either two distant galaxies are coincidentally lined up directly behind a closer massive galactic cluster - or it's a donut-shaped portal to an alternate universe. Tough choice, huh?

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So finally you possess that most valuable of commodities, a traversable wormhole – and somehow or other you grab one end of it and accelerate it to a very rapid velocity.

This might only take you a couple of weeks since you accelerate to the same velocity as your end of the wormhole. But for a friend who has sat waiting at the first entrance to the wormhole, time dilation means that ten years might have passed while you have mucked about at close-to-light-speed-velocities with the other end of the wormhole.

So when you decide to travel back through the wormhole to see your friend, you naturally maintain your own frame of reference and hence your own proper time, as is indicated by observing the watch on your wrist. So when you emerge at the other end of the wormhole, you can surprise your ageing partner with a newspaper you grabbed from 2011 – since he now lives in 2021.

You encourage your friend to come back with you through the wormhole – and traveling ten years back in time to 2011, he spends an enjoyable few days following his ten year younger self around, sending cryptic text messages that encourages his younger self to invent transparent aluminum. However, your friend is disappointed to find that when you both travel back through the wormhole to 2021, his bank account remains depressing low, because the wormhole is connected to what has become an alternate universe – where the time travel event that you just experienced, never happened.

You also realize that your wormhole time machine has other limits. You can further accelerate your end of the wormhole to 100 or even 1000 years of time dilation, but it still remains the case that you can only travel back in time as far as 2011, when you first decided to accelerate your end of the wormhole.

But anyway, wouldn’t it be great if any of this was actually possible? If you looked out into the universe to try and observe a traversable wormhole – you might start by looking for an Einstein ring. A light source from another universe (or a light source from a different time in an analogue of this universe) should be ‘lensed’ by the warped space-time of the wormhole – if the wormhole and the light source are in your direct line of sight. If all of that is plausible, then the light source should appear as a bright ring of light.

The theoretical light signatures of a donut-shaped 'ringhole' type wormhole and a Klein bottle 'time machine'. The ringhole signature is a double Einstein ring - and the Klein bottle signature is two concentric truncated spirals. A Klein bottle time machine is a wormhole of warped space-time where the exit has the identical spatial position as the entrance - so going through it means you should only travel in time. Credit: González-Díaz and Alonso-Serrano.

In fact there’s lots of these Einstein rings out there , but a more mundane cause for their existence is generally attributed to gravitational lensing by a massive object (like a galactic cluster) situated between you and a bright light source – all of which are still in our universe.

A recent theoretical letter has proposed that a ringhole rather than a wormhole structure might arise from an unlikely set of circumstances (i.e. this is pure theory – best just to go with it). So rather than a straight tube you could have a toroidal ‘donut’ connection with an alternate universe – which should then create a double Einstein ring – being two concentric circles of light.

This is a much rarer phenomenon and the authors suggest that the one well known instance (SDSSJ0946+1006) needs to be explained by the fortuitous alignment of three massive galactic clusters – which is starting to stretch belief a little… maybe?

Whether or not you find that a convincing argument, the authors then propose that if a Klein bottle wormhole existed – it would create such an unlikely visual phenomenon (two concentric truncated spirals of light) that surely then we might concede that such exotic structures exist?

And OK, if we ever do observe two concentric truncated spirals in the sky that could be pause for thought. Watch this space.

Further reading: González-Díaz and Alonso-Serrano Observing other universes through ringholes and Klein-bottle holes.

Posted on by Steve Nerlich

Astronomy Without A Telescope – Black Holes: The Early Years

High Mass Xray binaries were probably commonly in the early universe and the black hole partner may have shaped the destiny of the later universe. Credit: ESO.

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There’s a growing view that black holes in the early universe may have been the seeds around which most of today’s big galaxies (now with supermassive black holes within) first grew. And taking a step further back, it might also be the case that black holes were key to reionizing the early interstellar medium – which then influenced the large scale structure of today’s universe.

To recap those early years… First was the Big Bang – and for about three minutes everything was very compact and hence very hot – but after three minutes the first protons and electrons formed and for the next 17 minutes a proportion of those protons interacted to form helium nuclei – until at 20 minutes after the Big Bang, the expanding universe became too cool to maintain nucleosynthesis. From there, the protons and the helium nuclei and the electrons just bounced around for the next 380,000 years as a very hot plasma.

There were photons too, but there was little chance for these photons to do anything much except be formed and then immediately reabsorbed by an adjacent particle in that broiling hot plasma. But at 380,000 years, the expanding universe cooled enough for the protons and the helium nuclei to combine with electrons to form the first atoms – and suddenly the photons were left with empty space in which to shoot off as the first light rays – which today we can still detect as the cosmic microwave background.

What followed was the so-called dark ages until around half a billion years after the Big Bang, the first stars began to form. It’s likely that these stars were big, like really big, since the cool, stable hydrogen (and helium) atoms available readily aggregated and accreted. Some of these early stars may have been so big that they quickly blew themselves to pieces as pair-instability supernovae. Others were just very big and collapsed into black holes – many of them having too much self-gravity to permit a supernova explosion to blow any material out from the star.

And it’s about here that the reionization story starts. The cool, stable hydrogen atoms of the early interstellar medium didn’t stay cool and stable for very long. In a smaller universe full of densely-packed massive stars, these atoms were quickly reheated, causing their electrons to dissociate and their nuclei to become free ions again. This created a low density plasma – still very hot, but too diffuse to be opaque to light any more.

Well, really from ions to atoms to ions again - hence the term reionization. The only difference is that at half a billion years since the Big Bang, the reionized plasma of the interstellar medium was so diffuse that it remained - and still remains - transparent to radiation. Credit: New Scientist.

It’s likely that this reionization step then limited the size to which new stars could grow – as well as limiting opportunities for new galaxies to grow – since hot, excited ions are less likely to aggregate and accrete than cool, stable atoms. Reionization may have contributed to the current ‘clumpy’ distribution of matter – which is organized into generally large, discrete galaxies rather than an even spread of stars everywhere.

And it’s been suggested that early black holes – actually black holes in high mass X-ray binaries – may have made a significant contribution to the reionization of the early universe. Computer modelling suggests that the early universe, with a tendency towards very massive stars, would be much more likely to have black holes as stellar remnants, rather than neutron stars or white dwarfs. Also, those black holes would more often be in binaries than in isolation (since massive stars more often form multiple systems than do small stars).

So with a massive binary where one component is a black hole – the black hole will quickly begin to accumulate a large accretion disk composed of matter drawn from the other star. Then that accretion disk will begin to radiate high energy photons, particularly at X-ray energy levels.

While the number of ionizing photons emitted by an accreting black hole is probably similar to that of its bright, luminous progenitor star, it would be expected to emit a much higher proportion of high energy X-ray photons – with each of those photons potentially heating and ionizing multiple atoms in its path, while a luminous star’s photon’s might only reionize one or two atoms.

So there you go. Black holes… is there anything they can’t do?

Further reading: Mirabel et al Stellar black holes at the dawn of the universe.

Posted on by Vanessa Janek

Cosmology 101: The Beginning

Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.
Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.

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Editor’s note: The article “The Universe Could be 250 Times Bigger Than What is Observable” sparked a sizable discussion among our readers, with several suggesting UT should have a series of articles about cosmology — a Cosmology 101, if you will. Our newest writer, Vanessa D’Amico, who wrote the aforementioned article, begins the Cosmology 101 series today, starting at the very beginning.

How did the universe get its start? It’s one of the most pressing questions in cosmology, and likely one that will be around for a while. Here, I’ll begin by explaining what scientists think they know about the first formative seconds of the universe’s life. More than likely, the story isn’t quite what you might think.

In the beginning, there was… well, we don’t really know. One of the most prevalent misconceptions in cosmology is that the universe began as an immensely small, inconceivably dense collection of material that suddenly exploded, giving rise to space as we know it. There are a number of problems with this idea, not least of all the assumption implicit in an event termed the big “bang.” In truth, nothing “banged.” The notion of an explosion brings to mind an expanding tide of material, gradually filling the space around it; however, when our universe was born, there was no space. There was no time either. There was no vacuum. There was literally nothing.

Then the universe was born. Extremely high energies during the first 10-43 seconds of its life make it very difficult for scientists to determine anything conclusive about the origin of the cosmos. Of course, if cosmologists are correct about what they believe may have happened next, it doesn’t much matter. According to the theory of inflation, at about 10-36 seconds, the universe underwent a period of exponential expansion. In a matter of a few thousandths of a second, space inflated by a factor of about 1078, quickly separating what were once adjoining regions by unfathomable distances and blowing up tiny quantum fluctuations in the fabric of spacetime.

Inflation is an appealing theory for a number of reasons. First of all, it explains why we observe the universe to be homogeneous and isotropic on large scales – that is, it looks the same in all directions and to all observers. It also explains why the universe visually appears to be flat, rather than curved. Without inflation, a flat universe requires an extremely fine-tuned set of initial conditions; however, inflation turns this fine-tuning into a trick of scale. A familiar analogy: the ground under our feet appears to be flat (even though we know we live on a spherical planet) because we humans are so much smaller than the Earth. Likewise, the inflated universe is so enormous compared to our local field of view that it appears to be spatially flat.

As the theory goes, the end of inflation gave way to a universe that looked slightly more like the one we observe today. The vacuum energy that drove inflation suddenly transformed into a different kind of energy – the kind that could create elementary particles. At this point (only 10-32 seconds after the birth of the universe), the ambient temperature was still far too hot to build atoms or molecules from these particles; but as the seconds wore on, space expanded and cooled to the point where quarks could come together and form protons and neutrons. High-energy photons continued to dart around, continually striking and exciting charged protons and electrons.

So what happened next? How did this chaotic soup of matter and radiation become the vast expanse of organized structure that we see today? What’s going to happen to the universe in the future? And how do we know that this is the way the story unfolded? Make sure to check out the next few installments of Cosmology 101 for the answers to these questions and more!

Posted on by Anne Minard

Galaxy Size Matters … And This is Not a Rorschach Test

False color image of the Lockman-hole area of the sky at infrared wavelengths as imaged by the Herschel Space Observatory. Credit: ESA/SPIRE Consortium/HerMES Consortium

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When it comes to forming stars, the size of a galaxy does matter, according to research out today in the online version of Nature.

But it doesn’t have to be as massive as we once thought.

Alexandre Amblard, an astrophysicist at the University of California, Irvine, and his colleagues used new data from the Herschel Space Observatory to peer into Lockman Hole area of the sky, where extragalactic light comes from star-forming galaxies out of reach for even the world’s most powerful telescopes.

The Lockman Hole is a patch of the sky, 15 square degrees, lying roughly between the pointer stars of the Big Dipper.

Called submillimetre galaxies, the study subjects emit light at wavelengths between the radio and infrared parts of the spectrum, so studying them requires novel approaches borrowing from both radio and optical astronomy. The galaxies by themselves are too blurry to be resolved with individual far-infrared telescopes – but their average properties can be observed and analyzed, which is exactly what Amblard and his colleagues did.

The authors measured variations in the intensity of extragalactic light at far-infrared wavelengths, and derived statistics for the level of clustering of light halos. They assume that the clustering reflects the underlying distribution of dark matter, and fit the data to a halo model of galaxy formation, which connects the spatial distribution of galaxies in the Universe to that of dark matter.

Distribution of dark matter when the Universe was about 3 billion years old, obtained from a numerical simulation of galaxy formation. The left panel displays the continuous distribution of dark matter particles, showing the typical wispy structure of the cosmic web, with a network of sheets and filaments, while the right panel highlights the dark matter halos representing the most efficient cosmic sites for the formation of star-bursting galaxies with a minimum dark matter halo mass of 300 billion times that of the Sun. Credit: VIRGO Consortium/Alexandre Amblard/ESA

Amblard and his colleagues discovered an enormous fact: the ‘haloes’ of dark matter that surround the Universe’s most active star-forming galaxies are each more massive than about 300 billion solar masses.

What’s even more interesting is that the new threshold for star formation is actually smaller than some previous estimates.

“I think there was one prediction that put the number around 5000 billion times that of the sun, but that was just a prediction from a theory of galaxy formation.“ said Asantha Cooray, also an astrophysicist at UC Irvine and second author on the new paper. “The general consensus was that it may be between 100 to 1000 billion times the sun. We now have a more precise answer from this work.”

Cooray said he’s most excited “that we can look at a detailed image of the sky showing distant, star-forming galaxies and infer not only details about the stars and gas in those galaxies but also about the amount of dark matter needed to form such galaxies. Beyond inferring the presence, we still don’t know exactly what dark matter is.”

The results appear online ahead of print today on Nature’s website.