̽��ֱ�� of Cambridge - Planck satellite

Planck reveals first stars were born late

sc604 — Thu, 05 Feb 2015 16:13:31 +0000

New maps of ‘polarised’ light in the young Universe have revealed that the first stars formed 100 million years later than earlier estimates. ̽��ֱ��new images of cosmic background radiation, based on data released today from the European Space Agency’s Planck satellite, have shown that the process of reionisation, which ended the ‘Dark Ages’ as the earliest stars formed, started 550 million years after the Big Bang.

̽��ֱ��history of our Universe is a 13.8 billion-year tale that scientists endeavour to read by studying the planets, asteroids, comets and other objects in our Solar System, and gathering light emitted by distant stars, galaxies and the matter spread between them.

A major source of information used to piece together this story is the Cosmic Microwave Background, or CMB, the fossil light resulting from a time when the Universe was hot and dense, only 380,000 years after the Big Bang.

Thanks to the expansion of the Universe, we see this light today covering the whole sky at microwave wavelengths.

Between 2009 and 2013, the Planck satellite surveyed the sky to study this ancient light in unprecedented detail. Tiny differences in the background’s temperature trace regions of slightly different density in the early cosmos, representing the seeds of all future structure, the stars and galaxies of today.

Scientists from the Planck collaboration have published the results from the analysis of these data in a large number of scientific papers over the past two years, confirming the standard cosmological picture of our Universe with ever greater accuracy.

̽��ֱ��imaging is based on data from the Planck satellite, and was developed by the Planck collaboration, which includes the Cambridge Planck Analysis Centre at the ̽��ֱ��'s Kavli Institute for Cosmology, Imperial College London and the ̽��ֱ�� of Oxford at the London Planck Analysis Centre.

“ ̽��ֱ��CMB carries additional clues about our cosmic history that are encoded in its ‘polarisation’,” explains Jan Tauber, ESA’s Planck project scientist. “Planck has measured this signal for the first time at high resolution over the entire sky, producing the unique maps released today.”

Light is polarised when it vibrates in a preferred direction, something that may arise as a result of photons – the particles of light – bouncing off other particles. This is exactly what happened when the CMB originated in the early Universe.

Initially, photons were trapped in a hot, dense soup of particles that, by the time the Universe was a few seconds old, consisted mainly of electrons, protons and neutrinos. Owing to the high density, electrons and photons collided with one another so frequently that light could not travel any significant distant before bumping into another electron, making the early Universe extremely ‘foggy’.

Slowly but surely, as the cosmos expanded and cooled, photons and the other particles grew farther apart, and collisions became less frequent. This had two consequences: electrons and protons could finally combine and form neutral atoms without them being torn apart again by an incoming photon, and photons had enough room to travel, being no longer trapped in the cosmic fog.

̽��ֱ��new Planck data fixes the date of the end of these ‘Dark Ages’ to roughly 550 million years after the Big Bang, more than 100 million years later than previously determined by earlier polarisation observations from the NASA WMAP satellite (Planck’s predecessor), and has helped resolve a problem for observers of the early Universe.

̽��ֱ��Dark Ages lasted until the formation of the first stars and galaxies, specifically the formation of very large stars with extremely hot surfaces, which resulted in the energetic UV-radiation that began the process of reionisation of the neutral hydrogen throughout the Universe.

Very deep images of the sky from the NASA/ESA Hubble Space Telescope have provided a census of the earliest known galaxies, which started forming perhaps 300–400 million years after the Big Bang.

̽��ֱ��problem is that with a date for the end of the Dark Ages set at 450 million years after the Big Bang, astronomers can estimate that UV-radiation from such a source would have proved insufficient. “In that case, we would have needed additional, more exotic sources of energy to explain the history of reionisation,” said Professor George Efstathiou, Director of the Kavli Institute of Cosmology.

̽��ֱ��additional margin of 100 million years provided by Planck removes this need as stars and galaxies would have had the time to supply the energetic radiation required to bring the Dark Ages to a close and begin the Epoch of reionisation that would last for a further 400 million years.

Although the joint investigation between Planck and BICEP2, searching for the imprinted signature on the polarisation of the CMB of gravitational waves triggered by inflation, found no direct detection of this signal, it crucially placed strong upper-limits on the amount of primordial gravitational waves.

Searching for this signal remains a major focus of ongoing and planned CMB experiments. “ ̽��ֱ��results of the joint analysis demonstrate the power of combining CMB B-mode polarisation observations with measurements at higher frequency from Planck to clean Galactic dust,” said Dr Anthony Challinor of the Kavli Institute for Cosmology.

Inset image: Polarised emission from Milky Way dust Credit: ESA and the Planck Collaboration

New maps from the Planck satellite uncover the ‘polarised’ light from the early Universe across the entire sky, revealing that the first stars formed much later than previously thought.

We would have needed additional, more exotic sources of energy to explain the history of reionisation

George Efstathiou

ESA and the Planck Collaboration

Polarisation of the Cosmic Microwave Background

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How to explore the whole universe: watch COSMO 2013 live

sj387 — Wed, 04 Sep 2013 10:48:58 +0000

̽��ֱ��past year has been an extraordinary one for particle physicists and cosmologists, with the Planck satellite revealing the Universe’s earliest light, and the tentative discovery of the Higgs-Boson at the Large Hadron Collider (LHC).

Data collected from LHC experiments and the Planck mission - and their implications for the Universe - will be discussed by some of the giants of cosmology and particle physics during this week’s COSMO conference, all of which is being streamed live on YouTube.

Alongside the five-day long scientific conference - with days variously focused on Particle Physics, Cosmic Microwave Background, Large-Scale Structure, Primordial Cosmology and Cosmic Acceleration - there will also be a public symposium tonight, which, with speakers such as Stephen Hawking, Brian Cox and Andrew Liddle, will be a highlight of the COSMO YouTube broadcast.

Andrew Liddle, Professor of Theoretical Astrophysics at the ̽��ֱ�� of Edinburgh, will open the symposium with a talk on cosmology and the Planck satellite, currently being used to map the relic radiation expelled by the Big Bang. COSMOS 2013 is one of the first opportunities for researchers to gather and discuss the recent discoveries, with other lectures on the Planck data from George Efstathiou (Institute of Astronomy) and Ben Wandelt among others.

̽��ֱ��Planck satellite has given us a highly detailed image of the Universe a mere 380,000 years after the Big Bang; and will be used by researchers to learn about the origins of the Universe, its probable fate, and, ultimately, about existence itself.

̽��ֱ��night’s second speaker, Professor Brian Cox, has been credited with helping to demystify physics for the public. ̽��ֱ��former musician is now a particle physicist, Royal Society research fellow and professor at the ̽��ֱ�� of Manchester; he also works on the ATLAS experiment at the CERN super collider. Though a full time lecturer at Manchester, he is a prolific broadcaster and host of many science programmes such as the recent BBC series Wonders of Life.

̽��ֱ��symposium will finish with a talk from Stephen Hawking, the world-famous theoretical physicist, cosmologist and author. Hawking, author of the best-selling A Brief History of Time, gained his Ph.D. at Trinity Hall, Cambridge, was the Lucasian Professor of Mathematics at the ̽��ֱ�� for 30 years and is a Fellow at Gonville and Caius College. He is also the Director of Research at ̽��ֱ��Stephen Hawking Centre for Theoretical Cosmology at the ̽��ֱ��.

Among Hawking’s many achievements is the proposal that black holes are not entirely black, but instead emit a type of thermal radiation now known as “Hawking radiation”. His talk, entitled Fire in the Equations, is likely to prove a spell-binding conclusion to the public evening of COSMO 2013.

COSMO 2013 is sponsored by Intel who are providing the live feed for the public event. Richard Curran, Intel Director Enterprise Server and Software Enabling Group EMEA, said “At Intel we have a long and successful history of working with Professor Hawking. We are proud to be supporting the team in its analysis of the data collected from the Planck satellite and wait with great anticipation to the insights the research can offer us about the universe and its origin. We are excited to open this research up to the public and we hope it encourages more people to take an interest in physics and the amazing work being done”.

Watch speakers such as Stephen Hawking and Brian Cox this evening as the public symposium of the 17th International Conference on Particle Physics and Cosmology, known as COSMO 2013, is broadcast live on YouTube.

Arun Venkataswamy

Orion Nebula / M42

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Planck captures portrait of the young Universe, revealing earliest light

fpjl2 — Thu, 21 Mar 2013 09:44:17 +0000

After years of work, scientists have removed bright foreground emissions from the Planck satellite’s first all-sky image to reveal the Universe’s earliest light – imprinted on the sky when the Universe was just 380,000 years old – and seen today as the Cosmic Microwave Background (CMB), the relic radiation from the Big Bang.

̽��ֱ��results, released today, amount to the most detailed map of the CMB ever created, dating the Universe at 13.82 billion years old. Scientists say that Planck’s findings refine our knowledge of the Universe’s composition and evolution, and provide excellent evidence for the standard model of cosmology.

Findings also show there is nearly a fifth more dark matter in the Universe than previously thought, but less dark energy. A series of scientific papers describing the new results have been published online.

View Planck's history of the Universe here.

̽��ֱ��imaging is based on the initial 15.5 months of data from the European Space Agency’s Planck satellite, and was developed by researchers from the Cambridge Planck Analysis Centre at the ̽��ֱ��’s Kavli Institute for Cosmology, in collaboration with groups from Imperial College London and the ̽��ֱ�� of Oxford at the London Planck Analysis Centre.

̽��ֱ��Planck map of the CMB shows tiny temperature fluctuations that correspond to regions of slightly different densities at very early times, representing the seeds of all future structure - the stars and galaxies of today.

“ ̽��ֱ��CMB temperature fluctuations detected by Planck confirm once more that the relatively simple picture provided by the standard model of cosmology is an amazingly good description of the Universe,” said George Efstathiou, Professor of Astrophysics and Director of the Kavli Institute for Cosmology at the ̽��ֱ�� of Cambridge.

Efstathiou will be giving a public talk on the findings this Saturday as part of the Cambridge Science Festival, where some of the first results from the Planck satellite will be on display.

Planck gives us the most accurate values yet for ingredients that make up the Universe. Normal matter - stars and galaxies - contributes just 4.9% of the mass/energy density of the Universe.

Dark matter, which has thus far only been detected indirectly by its gravitational influence, makes up 26.8%, nearly a fifth more than previously estimated.

Conversely, dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe, accounts for slightly less than previously thought, at around 69%.

Planck data also set a new value for the rate at which the Universe is expanding today. At 67.3 km/s/Mpc, it is significantly different from relatively nearby galaxies, with the slower expansion implying the Universe is a little older than thought – 13.82 billion years.

̽��ֱ��researchers’ analysis also supports theories of ‘inflation’ – a brief but crucial early phase during the first tiny fraction of a second of the Universe’s existence. This initial expansion caused the ripples in the CMB that we see today, and explains many properties of the Universe as a whole.

While predominantly reinforcing our standard model of cosmology, the unprecedented precision of Planck’s map reveals some unexplained features that scientists say might require a new physics to be understood.

Fluctuations in the CMB over large scales do not match the standard model, an anomaly that adds to those from previous experiments such as an asymmetry in the average temperatures on opposite hemispheres of the sky.

One possible explanation might be that the Universe is in fact not the same in all directions on a larger scale than we can observe, so the light rays from the CMB may have taken a more complicated route through the Universe – resulting in some of the unusual patterns observed today.

“Our ultimate goal would be to construct a new model that predicts the anomalies and links them together. But these are early days; so far, we don’t know whether this is possible and what type of new physics might be needed. And that’s exciting,” said Efstathiou.

“By analysing these extraordinary data collected by Planck, we have been able to set the most precise constraints so far on the small number of parameters that we need to characterise the standard model,” he added.

“These range from the density of dark matter and dark energy to the speed at which the Universe is currently expanding and the relative amount of primordial fluctuations – the seeds of cosmic structures to be – on different scales.”

̽��ֱ��Cambridge Planck research team will be exhibiting and talking about their results at the Royal Society Summer Science Exhibition, 2-7 July 2013. Colleagues from the Kavli Institute for Cosmology presented work at last year’s exhibition exploring the large ground-based telescope ALMA, in the Atacama Desert of Chile.

Both the ALMA and Planck displays will be at the Kavli Institute for Cosmology as part of the Cambridge Science Festival this weekend. Dozens of free activities include talks, demonstrations and hands-on experiments for everyone to learn more about Astronomy and research at Cambridge.

Planck research scientist Professor George Efstathiou’s talk, entitled ̽��ֱ��birth of the Universe - the first results from the Planck satellite, will take place at 4pm on Saturday 23 March in the Sackler Lecture Theatre at Cambridge’s Institute of Astronomy.

Photograph of George Efstathiou courtesy of the Development Office, Credit: Nick Turpin

Satellite’s first all-sky image is the most detailed picture to date of the early Universe, giving us a better understanding of its birth.

̽��ֱ��CMB temperature fluctuations detected by Planck confirm once more that the relatively simple picture provided by the standard model of cosmology is an amazingly good description of the Universe

George Efstathiou

ESA/Planck Collaboration

Map of the cosmic microwave background

What is the Cosmic Microwave Background?

̽��ֱ��Cosmic Microwave Background (CMB) is leftover radiation from the Big Bang that fills the entire Universe - the furthest back in time we can explore using light. When the Universe was born, nearly 14 billion years ago, it was filled with hot plasma of particles (mostly protons, neutrons, and electrons) and photons (light). For roughly the first 380,000 years, the photons were constantly interacting with free electrons, meaning that they could not travel long distances - rendering the early Universe opaque, like being in fog.

As the Universe expanded, it cooled, and the fixed amount of energy within it was able to spread out over larger volumes. After about 380,000 years, it had cooled to around 3000 Kelvin (approximately 2700 ºC). At this point, electrons were able to combine with protons to form hydrogen atoms, and the temperature was too low to separate them again. In the absence of free electrons, the photons were able to move unhindered through the Universe: it became transparent.

Over the intervening billions of years, the Universe has expanded and cooled greatly. Due to the expansion of space, the wavelengths of the photons have grown - or ‘redshifted’ - to roughly 1 millimetre and their effective temperature has decreased to just 2.7 Kelvin, or around -270ºC, just above absolute zero. These photons fill the Universe today (there are roughly 400 in every cubic centimetre of space) and create a background glow that can be detected by far-infrared and radio telescopes.

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