Tag Archives: cosmic microwave background

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos.

Astronomers map over 100 million galaxies to crack dark matter and dark energy puzzle

The Dark Energy Survey (DES) is an ambitious cosmological project that aims to map hundreds of millions of galaxies. In the process, the project will detail hundreds of millions of galaxies, observe thousands of supernovae, map the cosmic web that links galaxies, all with the aim of investigating the mysterious force that is causing the Universe to expand at an accelerating rate.

Using the 570-megapixel Dark Energy Camera on the National Science Foundation’s Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile, the DES has observed a map of galaxy distribution and morphology that stretches 7 billion light-years and captures 1/8 of the sky over Earth.

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos.
Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos. The image is teeming with galaxies — in fact, nearly every single object in this image is a galaxy. Some exceptions include a couple of dozen asteroids as well as a few handfuls of foreground stars in our own Milky Way. (Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA)

Now new results from the DES which collects the work of an international team of over 400 scientists from over 25 institutions from countries including the US, UK, France, Spain, Brazil, and Australia, are in. The findings are detailed in a ground-breaking series of 29 papers and comprises of data collected during the DES’ first three years of operation providing the most detailed description of the Universe’s composition and expansion to date.

The Víctor M. Blanco 4-meter Telescope is seen here at night at Cerro Tololo Inter-American Observatory, with trails of stars high above it. On this telescope is the 570-megapixel Dark Energy Camera — one of the most powerful digital cameras in the world. The Dark Energy Camera was designed specifically for the Dark Energy Survey. It was funded by the Department of Energy (DOE) and was built and tested at DOE’s Fermilab. (DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA)

The survey was conducted between 2013 to 2019 cataloging hundreds of millions of objects, with the three years of data covered in these papers alone containing observations of at least 226 million galaxies observed over 345 nights.

The fact that some of these galaxies are close to the Milky Way and others are much more distant–up to 7 billion light-years away– gives researchers an excellent picture of the evolution of the Universe over around half of its lifetime.

The results seem to confirm the standard model of cosmology, currently the best-evidenced theory of the Universe’s composition and evolution which suggests the Universe was created in a ‘Big Bang’ event and has a composition of 5% ordinary or baryonic matter, 27% dark matter, and 68% dark energy.

The snapshot of the Universe provided by the DES does seem to show that the Universe is less ‘clumpy’ than current cosmological models suggest, however.

Illuminating the Dark Universe

The fact that the ‘Dark Universe’ consists of 95% of the matter and energy in the known cosmos means that there are huge gaps in our understanding of the evolution of the Universe, its past, present, and its future.

These gaps include the nature of dark matter, whose gravitational influence holds galaxies together, and dark energy, the force that is expanding space between the galaxies driving them apart at an accelerating rate.

These effects seem to be in opposition, with one holding matter together and the other working upon space itself to drive matter apart. And it is this cosmic struggle that shapes the Universe which the DES aimed to investigate.

There are two key phenomena which the survey used to do this. Studying ‘the cosmic web’ that links galaxies together in clusters and loose associations gives hints at the distribution and influence of dark matter.

The Dark Energy Survey camera (DECam) at the SiDet clean room. The Dark Energy Camera was designed specifically for the Dark Energy Survey. It was funded by the Department of Energy (DOE) and was built and tested at DOE’s Fermilab. (DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA)

The second phenomenon used by the DES is the bending of light as it travels past curvatures in spacetime created by objects of tremendous mass like galaxies. This effect predicted by Einstein’s theory of gravity–general relativity–is known as ‘gravitational lensing.’

The DES relied on a form of this effect called ‘weak gravitational lensing’ to assess how dark matter is distributed across the Universe, thus inferring its ‘clumpiness.’

Weak graviational lensing was one ofthe phenomenna that teh DES took advantage of to investigation dark matter distributions (ESA)

The data collected by the DES was cross-referenced against measurements carried out by the European Space Agency (ESA) operated mission, the Planck observatory. The orbiting observatory, which operated between 2009 and 2013 and studied the cosmic background radiation (CMB)–an imprint leftover from an event shortly after the Big Bang in which electrons and protons connected thus allowing photons to travel freely for the first time.

Observing the CMB reveals conditions that were ‘frozen in’ to it at the time of this event known as the last scattering and thus gives a detailed picture of the Universe when it was just 400 thousand years old for the DES team to draw from.

Setting the Scene for Future Surveys

The DES intensely studied ten regions labeled as ‘deep fields’ which were repeatedly imaged during the course of the survey. These images were stacked which allowed astronomers to observe distant galaxies.

In addition to allowing researchers to see further into the Universe and thus further back in time, information regarding redshift– an increase in wavelength caused by objects receding which can arise as a result of the Universe’s expansion–taken from these deep fields was used to calibrate the rest of the survey. This constituted a major step forward for cosmic surveys providing the researchers with a picture of the Universe painted with stunning precision.

Whilst the DES was concluded in 2019, the sheer wealth of data collected by the survey requires a huge amount of computing power and time to assess. This is why we are only seeing the first three years of observations reported and likely means that the DES still has much more to deliver.

The Vera C Rubin Observatory currently under construction in Chile will pick up where the DES leaves off (LSST Collaboration)

This will ultimately set the scene for the Legacy Survey of Space and Time (LSST) which will be conducted at the Vera C Rubin observatory–currently under construction on the El Penon peak of Cerro Pachon in northern Chile.

Whereas the DES surveyed an inarguably impressive 1/8 of the sky over the earth, the wide-field camera that will conduct the LSST will capture the entire sky over the Southern hemisphere, meaning it will view half of the entire sky over our planet.

A major part of the LSST’s mission will be the investigation of dark matter and dark energy, meaning that when the data from the DES is finally exhausted and its secrets are revealed, a worthy successor will be waiting in the wings to assume its mission of discovery.

First stars formed much later than we thought

The European Space Agency’s Planck satellite has revealed some information which may force us to rethink the evolution of the early Universe.

Visualization of the CMB. Image via NASA.

Our telescopes and other observation tools allow us to see a lot of the Universe today, but we’re so used to it in its current state that it can be hard to imagine how it looked like 13.8 billion years ago. Everything was still in its infancy, without the multitude of stars and galaxies we see today. Back then, everything was a thick, hot haze, a primordial soup of particles – mostly electrons, protons, neutrons and photons.

As the cosmos expanded, it started to cool down a bit and became more rarefied. Astrophysicists believe that the universe became transparent some 380,000 years after its birth, meaning that photons could finally travel through the universe freely. Today, we can still observe some of this ‘fossil light,’ and its distribution yields information about the history, composition, and geometry of the Universe.

This distribution is called the Cosmic Microwave Background, or CMB for short. The release of the CMB indicates the first moment in the Universe when matter was in an electrically neutral state – in other words, when electrons merged with protons to form atoms. After that, matter as we know it started to emerge, but it still took a few hundred million years for the first stars to form. These in turn started to brake down matter into electrons and protons once again, while also sending light (photons) in all directions. It didn’t take long and most — virtually all, except for a few isolated places — matter became ionized.

“The CMB can tell us when the epoch of reionisation started and, in turn, when the first stars formed in the Universe,” explains Jan Tauber, Planck project scientist at ESA.

Astronomers have conducted observations on galaxies with supermassive black holes, finding that the reionization took place when the Universe was 900 million years old. But when this process started (and therefore, when the first stars were formed) is much harder to pinpoint.

The key is still in the CMB.

Cosmic reionisation.
Credit: ESA – C. Carreau

“It is in the tiny fluctuations of the CMB polarisation that we can see the influence of the reionisation process and deduce when it began,” adds Tauber.

The new analysis conducted by Tauber and his team isn’t conceptually different from previous efforts, but it uses a more advanced technology from Planck’s other detector, the High-Frequency Instrument (HFI).

“The highly sensitive measurements from HFI have clearly demonstrated that reionisation was a very quick process, starting fairly late in cosmic history and having half-reionised the Universe by the time it was about 700 million years old,” says Jean-Loup Puget from Institut d’Astrophysique Spatiale in Orsay, France, principal investigator of Planck’s HFI.

This new analysis also showed that these stars were the only sources needed to account for reionizing atoms in the cosmos and that half of this process was completed when the Universe had reached an age of 700 million years.

“These results are now helping us to model the beginning of the reionisation phase,” he concluded.

It’s still a work in progress and the exact ionization age will remain a matter of debate, but the fact that we can infer so much about the early history of the Universe is simply mind blowing.

Journal References:

  1. Matthieu Tristram and Collaboration. Planck intermediate results. XLVII. Planck constraints on reionization history. Astronomy & Astrophysics, 2016; DOI: 10.1051/0004-6361/201628897
  2. Planck Collaboration. Planck intermediate results. XLVI. Reduction of large-scale systematic effects in HFI polarization maps and estimation of the reionization optical depth. Astronomy & Astrophysics, 2016; DOI: 10.1051/0004-6361/201628890

Universe may be curved, not flat

It is currently believed that we live in a lopsided Universe: cosmologists reached this conclusion by examining the detailed structure of the left over radiation from the Big Bang. Now, two cosmologists presented data which seems to suggest that our Universe is actually curved slightly, in a saddle-like fashion; if correct, their model would invalidate the long standing idea that the cosmos is flat.

universe curved

Cosmic microwave background (CMB) is the thermal radiation left over from the “Big Bang” of cosmology. It is fundamentally important for measurements, because it is the oldest light in the universe, dating to what is called the epoch of recombination (the period during which charged electrons and protons first became bound to form electrically neutral hydrogen atoms – so REALLY early). NASA’s Wilkinson Microwave Anisotropy Probe provided the first hints of an Universal asymmetry in 2004, but some believed that was a technological error, and hoped that NASA probe’s successor, the European Space Agency’s Planck spacecraft would fix that error. But as it turns out, the Planck spacecraft confirmed the anomaly.

To explain those results, Andrew Liddle and Marina Cortês, both at the University of Edinburgh, UK, have taken on the gargantuan task of proposing a new model of cosmic inflation – a theoretized period in which the Universe expanded dramatically, growing by a few orders of magnitude in a fraction of a second.

In their paper, published this week in Physical Review Letters, Liddle and Cortês toy with the idea that aside from the initial quantum field (the inflation), there was also a secondary quantum field which caused the curvation of the Universe. The authors’ work is the first to explain the lopsidedness from first principles.

However, the problem is that numerous different measurements suggest that the Universe is flat, some of which can’t be fully explained with this new, curved model. Future improved measurements will likely show which hypothesis is right.

Scientific source: Nature doi:10.1038/nature.2013.13776

Via Nature.

Scientists reproduce conditions from early universe

Physicists have successfully reproduced a pattern resembling the cosmic microwave background radiation in an experiment which used ultracold cesium atoms in a vacuum chamber. This is the first experiment which recreates at least some of the conditions from the Big Bang.

“This is the first time an experiment like this has simulated the evolution of structure in the early universe,” said Cheng Chin, professor in physics. Chin and his associates reported their feat in the Aug. 1 edition of Science Express, and it will appear soon in the print edition of Science.

universe big bang

The cosmic microwave background radiation (CMB or CMBR) is basically the thermal radiation left over from the Big Bang. It is very interesting for astrophyicists because it apparently exhibits a large degree of uniformity throughout the entire universe (it has more or less the same values everywhere you look for it). If you analyze the “void” between stars and even galaxies with a sufficiently sensitive radio telescope, you’ll see a faint background glow, almost exactly the same in all directions, that is not associated with … anything. The glow has the most energy in the microwave spectrum. Its rather serendipitous discovery took place in 1964, and it earned its finders a Nobel prize in 1978.

You can think of this radiation as the echo of the Big Bang – by studying it, we get a somewhat clear idea how the Universe looked some 380,000 years following its ‘birth’ – incredibly early; it doesn’t go much before or after, it’s basically a snapshot of the past. But as it turns out, under certain conditions, a cloud of atoms chilled to a billionth of a degree above absolute zero in a vacuum chamber displays phenomena similar to those which followed the big bang.

“At this ultracold temperature, atoms get excited collectively. They act as if they are sound waves in air,” he said.

This neatly correlates with what cosmologists speculated:

“Inflation set out the initial conditions for the early universe to create similar sound waves in the cosmic fluid formed by matter and radiation,” Hung said.

big bang

The tiny universe which was simulated in Chin’s laboratory measured no more than 70 microns across (about as big as a human hair) – but the physics is the same regardless of the size of your universe.

“It turns out the same kind of physics can happen on vastly different length scales,” Chin explained. “That’s the power of physics.”

But there is an important difference – and one that works greatly to our advantage:

“It took the whole universe about 380,000 years to evolve into the CMB spectrum we’re looking at now,” Chin said. But the physicists were able to reproduce much the same pattern in approximately 10 milliseconds in their experiment. “That suggests why the simulation based on cold atoms can be a powerful tool,” Chin said.

If you want, you can think of the Big Bang in oversimplified terms as an explosion which made a big BOOM! These sound waves began interfering with each other creating complicated patterns – the so-called Sakharov acoustic oscillations.

“That’s the origin of complexity we see in the universe,” he said.

This is indeed a powerful tool to find out more about our infant universe, but this is just the first step. Chin and his team plan to move on to use these Sakharov oscillations to study the property of this two-dimensional superfluid at different initial conditions, then cross check their results with what is observed by cosmologists. They will use the same type of experiment but branch out to other fields of cosmology, including the formation of galaxies and even black hole dynamics.

“We can potentially use atoms to simulate and better understand many interesting phenomena in nature,” Chin said. “Atoms to us can be anything you want them to be.”

Interestingly enough, nobody on this team was a cosmologist.

Journal Reference: C.-L. Hung, V. Gurarie, C. Chin. From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in a Quenched Atomic Superfluid. DOI: 10.1126/science.1237557

Cosmic microwave background seen by Planck

Map of the earliest recorded light paints broad picture of the ancient Universe

Cosmic microwave background seen by Planck

Cosmic microwave background seen by Planck. (c) ESA

Using the incredible  Planck cosmology probe astronomers at the European Space Agency have assembled a map of the “oldest light” in the sky – the cosmic microwave background (CMB) that was thrown into space in all directions just a few hundred thousand years after the Big Bang and which is still picked up here on Earth today.

What’s exciting about the map is that it confirms the current fundamental “cosmological inception” theory – the Big Bang theory. However there are some features and ideas that need to be refined and rethought as a result of the findings. For instance, according tot the new Planck all-sky map, the Universe is  13.82 billion years or 50 million years older than previous estimates. Also, there seems to be more matter (31.7%) and slightly less “dark energy” (68.3%) – the mysterious force that drives the Universe apart and causes an accelerated expansion.

The trace the map, cosmologists studied the CMB – light that was allowed to escape after the early Universe cooled down to allow the formation of hydrogen atoms some 380,000 years ago. By studying temperature fluctuations of the CMB –  seen as mottling in the map – scientists can better assess their current theoretical models with actual data on anomalies, since these fluctuations are thought to actually  reflect the differences in the density of matter when the light first escaped. These ripples are thought to have given rise to today’s vast cosmic web of galaxy clusters and dark matter.

anomaliesWhile some statistical analysis isn’t on par with data provided by the Planck map, cosmologists should rejoice as the news that their fundamental theories reflect reality. Especially those relating to the birth of the Universe, which is thought to have started as hot, dense state in an incredibly small space, and then expanded and cooled.

A cosmic baby picture

Other projects like the Cosmic Background Explorer and the Wilkinson Microwave Anisotropy Probe have provided earlier drafts of the “baby Universe”, however the map obtained from data gathered by the $900 million (€700 million) Planck probe launched in 2009 is the most detailed yet.

“The extraordinary quality of Planck’s portrait of the infant Universe allows us to peel back its layers to the very foundations, revealing that our blueprint of the cosmos is far from complete. Such discoveries were made possible by the unique technologies developed for that purpose by European industry,” says Jean-Jacques Dordain, ESA’s Director General.

“Since the release of Planck’s first all-sky image in 2010, we have been carefully extracting and analysing all of the foreground emissions that lie between us and the Universe’s first light, revealing the cosmic microwave background in the greatest detail yet,” adds George Efstathiou of the University of Cambridge, UK.

What also came as a surprise was a rather discrepant anomaly. Apparently, there’s an asymmetry in average temperature distribution across the Universe, as the southern sky hemisphere is slightly warmer than the north. Another significant anomaly is a cold spot in the map, centred on the constellation Eridanus, which is much bigger than would be predicted.

Nevertheless, cosmologists which have been dreaming about such a map for decades will now have their work cut out for them. Armed with this map, they now have the necessary resources or at least another tool at hand to prove or disprove some of the most controversial theories in cosmology today, like those discussing the rapid and far-reaching inflation of the Universe in its first moments from inception or the claim that there are six or seven spatial dimensions in addition to the three we perceive.

source: ESA