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.

Posted on by Anne Minard

Message in a Wobble: Black Holes Send Memos in Light

Where is the Nearest Black Hole
Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)

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Imagine a spinning black hole so colossal and so powerful that it kicks photons, the basic units of light, and sends them careening thousands of light years through space. Some of the photons make it to Earth. Scientists are announcing in the journal Nature Physics today that those well-traveled photons still carry the signature of that colossal jolt, as a distortion in the way they move. The disruption is like a long-distance missive from the black hole itself, containing information about its size and the speed of its spin.

The researchers say the jostled photons are key to unraveling the theory that predicts black holes in the first place.

“It is rare in general-relativity research that a new phenomenon is discovered that allows us to test the theory further,” says Martin Bojowald, a Penn State physics professor and author of a News & Views article that accompanies the study.

Black holes are so gravitationally powerful that they distort nearby matter and even space and time. Called framedragging, the phenomenon can be detected by sensitive gyroscopes on satellites, Bojowald notes.

Lead study author Fabrizio Tamburini, an astronomer at the University of Padova (Padua) in Italy, and his colleagues have calculated that rotating spacetime can impart to light an intrinsic form of orbital angular momentum distinct from its spin. The authors suggest visualizing this as non-planar wavefronts of this twisted light like a cylindrical spiral staircase, centered around the light beam.

“The intensity pattern of twisted light transverse to the beam shows a dark spot in the middle — where no one would walk on the staircase — surrounded by concentric circles,” they write. “The twisting of a pure [orbital angular momentum] mode can be seen in interference patterns.” They say researchers need between 10,000 and 100,000 photons to piece a black hole’s story together.

And telescopes need some kind of 3D (or holographic) vision in order to see the corkscrews in the light waves they receive, Bojowald said: “If a telescope can zoom in sufficiently closely, one can be sure that all 10,000-100,000 photons come from the accretion disk rather than from other stars farther away. So the magnification of the telescope will be a crucial factor.”

He believes, based on a rough calculation, that “a star like the sun as far away as the center of the Milky Way would have to be observed for less than a year. So it is not going to be a direct image, but one would not have to wait very long.”

Study co-author Bo Thidé, a professor and program director at the Swedish Institute of Space Physics, said a year may be conservative, even in the case of a small rotation and a need for up to 100,000 photons.

“But who knows,” he said. “We will know more after we have made further detailed modelling – and observations, of course.  At this time we emphasize the discovery of a
new general relativity phenomenon that allows us to make observations, leaving precise quantitative predictions aside.”

Links: Nature Physics

Posted on by Vanessa Janek

Universe Could be 250 Times Bigger Than What is Observable

Cosmic Noise
This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689, containing about 1,000 galaxies and trillions of stars. Credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology, and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford (Johns Hopkins University)

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Our Universe is an enormous place; that’s no secret. What is up for discussion, however, is just how enormous it is. And new research suggests it’s a whopper – over 250 times the size of our observable universe.

Currently, cosmologists believe the Universe takes one of three possible shapes:

1) It is flat, like a Euclidean plane, and spatially infinite.
2) It is open, or curved like a saddle, and spatially infinite.
3) It is closed, or curved like a sphere, and spatially finite.

While most current data favors a flat universe, cosmologists have yet to come to a consensus. In a paper recently submitted to Arxiv, UK scientists Mihran Vardanyan, Roberto Trotta and Joseph Silk present their fix: a mathematical version of Occam’s Razor called Bayesian model averaging. The principle of Occam’s Razor states that the simplest explanation is usually the correct one. In this case, a flat universe represents a simpler geometry than a curved universe. Bayesian averaging takes this consideration into account and averages the data accordingly. Unsurprisingly, the team’s results show that the data best fits a flat, infinite universe.

But what if the Universe turns out to be closed, and thus has a finite size after all? Cosmologists often refer to the Hubble volume – a volume of space that is similar to our visible Universe. Light from any object outside of the Hubble volume will never reach us because the space between us and it is expanding too quickly. According to the team’s analysis, a closed universe would encompass at least 251 Hubble volumes.

That’s quite a bit larger than you might think. Primordial light from just after the birth of the Universe started traveling across the cosmos about 13.75 billion years ago. Since special relativity states that nothing can move faster than a photon, many people misinterpret this to mean that the observable Universe must be 13.75 billion light years across. In fact, it is much larger. Not only has space been expanding since the big bang, but the rate of expansion has been steadily increasing due to the influence of dark energy. Since special relativity doesn’t factor in the expansion of space itself, cosmologists estimate that the oldest photons have travelled a distance of 45 billion light years since the big bang. That means that our observable Universe is on the order of 90 billion light years wide.

To top it all off, it turns out that the team’s size limit of 251 Hubble volumes is a conservative estimate, based on a geometric model that includes inflation. If astronomers were to instead base the size of the Universe solely on the age and distribution of the objects they observe today, they would find that a closed universe encompasses at least 398 Hubble volumes. That’s nearly 400 times the size of everything we can ever hope to see in the Universe!

Given the reality of our current capabilities for observation, to us even a finite universe appears to go on forever.

Posted on by Mark Thompson

Planck Unveils the Wonders of the Universe

Six areas of the sky in which distant galaxies can be seen by Planck, overlaid on the Planck’s first all-sky image. The emission from our own Galaxy, seen in blue and white, has to be removed before the distant population of galaxies can be seen. Each square inset image is around the same size as the Full Moon. Image credit: ESA / Planck Collaboration.

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The mission began on 13th August 2009 with a goal to image the echo’s of the birth of the Universe, the cosmic background radiation. But scientists working on the European Space Agency’s (ESA) Planck mission got more than they bargained for making ground breaking discoveries and shedding light on old mysteries. By studying light from the far reaches of the Universe, Planck has to look through the rest of the Universe first and it was during this, that the incredible discoveries were made.

The crazy thing about looking at the far reaches of the Universe is that we actually look back in time as it takes billions of years for the light to reach us here on Earth. This enables astronomers to look back in time and study the evolution of the Universe almost back to the Big Bang itself. Amongst the discoveries was evidence for an otherwise invisible population of galaxies that seem to be shrouded in dust billions of years in the past. Star formation rates in these galaxies seem to be happening at an incredible pace, some 10-1000 times higher than we see in our own Milky Way galaxy today. Joanna Dunkley, of Oxford University, said “Planck’s measurements of these distant galaxies are shedding new light on when and where ancient stars formed in the early universe”.

One of the challenges of getting a clear view of these galaxies though has been removing the so called ‘anomalous microwave emission’ (AME) foreground haze. This annoying and poorly understood interference, which is thought to originate in our own Galaxy, has only just been pierced through with Planck’s instruments. But in doing so, clues to its nature have been unveiled. It seems that the AME is coming from dust grains in our Galaxy spinning several tens of billions of times per second, perhaps from collisions with incoming faster-moving atoms or from ultra-violet radiation. Planck was able to ‘remove’ the foreground microwave haze, leaving the distant galaxies in perfect view and the cosmic background radiation untouched.

Its also the ideal instrument to detect very cold matter in the form of dust in our Galaxy and beyond, thanks to its broad wavelength coverage. During its study, it detected over 900 clumps of cold dark dust clouds which are thought to represent the first stages of star birth. By studying a number of nearby galaxies within a few billion light years, the study shows that some of them contain much more cold dust than previously thought. Dr David Clements from Imperial College London says “Planck will help us to build a ladder connecting our Milky Way to the faint, distant galaxies and uncovering the evolution of dusty, star forming galaxies throughout cosmic history.”

These results make Planck a roaring success but it doesn’t stop there. Other results just published include data on galaxy clusters revealing them silhouetted against the cosmic microwave background. These clusters contain thousands of individual galaxies gravitational bound together into gigantic strings and loops.

The Planck mission, which was in development for 15 years is already providing some ground breaking science in its first few years of operation and its exciting to wonder what we will see from it in the years that lie ahead.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro