ESA Planck Telescope: Sky Survey changes date on early stars

Planck has mapped the delicate polarisation of the CMB across the entire sky

Scientists working on ESA's Planck satellite say the first stars in the Universe lit up later than was previously thought.

The team has made the most precise map of the "oldest light" in the cosmos.

Earlier observations of this radiation had suggested that the first generation of stars burst into life about 420 million years after the Big Bang.

The new Planck data now indicates they fired up around 560 million years after the Universe got going.

"This difference of 140 million years might not seem that significant in the context of the 13.8-billion-year history of the cosmos, but proportionately it's actually a very big change in our understanding of how certain key events progressed at the earliest epochs," said Prof George Efstathiou, one of the leaders of the Planck Science Collaboration.

Subtle signal
The assessment is based on studies of the "afterglow" of the Big Bang, the ancient light called the Cosmic Microwave Background (CMB), which still washes over the Earth today.

The European Space Agency's (ESA) Planck satellite mapped this "fossil" between 2009 and 2013.

It contains a wealth of information about early conditions in the Universe, and can even be used to work out its age, shape and do an inventory of its contents.

Scientists can also probe it for very subtle "distortions" that tell them about any interactions the CMB has had on its way to us.

Forging elements
One of these would have been imprinted when the infant cosmos underwent a major environmental change known as re-ionisation.

It is when the cooling neutral hydrogen gas that dominated the Universe in the aftermath of the Big Bang was then re-energised by the ignition of the first stars.

These hot giants would have burnt brilliant but brief lives, producing the very first heavy elements. But they would also have "fried" the neutral gas around them - ripping electrons off the hydrogen protons.

And it is the passage of the CMB through this maze of electrons and protons that would have resulted in it picking up a subtle polarisation.

Impression: The first stars would have been unwieldy behemoths that burnt brief but brilliant lives

The Planck team has now analysed this polarisation in fine detail and determined it to have been generated at 560 million years after the Big Bang.

The American satellite WMAP, which operated in the 2000s, made the previous best estimate for re-ionisation at 420 million years.

The problem with that number was that it sat at odds with Hubble Space Telescope observations of the early Universe.

Hubble could not find stars and galaxies in sufficient numbers to deliver the scale of environmental change at the time when WMAP suggested it was occurring.

Planck's new timing "effectively solves the conflict," commented Prof Richard McMahon from Cambridge University, UK.

"We had two groups of astronomers who were basically working on different sides of the problem. The Planck people came at it from the Big Bang side, while those of us who work on galaxies came at it from the 'now side'.

"It's like a bridge being built over a river. The two sides do now join where previously we had a gap," he told reporters.

That gap had prompted scientists to invoke complicated scenarios for how re-ionisation could have occurred, including the ideas that there were an even earlier population of giant stars or energetic black holes. Such solutions are no longer needed.

The finding is also good news for the next generation of observatories like the James Webb Space Telescope, which will have the power to see right through the epoch of re-ionisation.

ESA's Planck Satellite: The magnetic field along the galactic plane

Credit: ESA/Planck Collaboration. 

Acknowledgment: M.-A. Miville-Deschênes, CNRS – Institut d’Astrophysique Spatiale, Université Paris-XI, Orsay, France

While the pastel tones and fine texture of this image may bring to mind brush strokes on an artist's canvas, they are in fact a visualisation of data from ESA's Planck satellite.

The image portrays the interaction between interstellar dust in the Milky Way and the structure of our Galaxy's magnetic field.

Between 2009 and 2013, Planck scanned the sky to detect the most ancient light in the history of the Universe, the cosmic microwave background.

It also detected significant foreground emission from diffuse material in our Galaxy which, although a nuisance for cosmological studies, is extremely important for studying the birth of stars and other phenomena in the Milky Way.

Among the foreground sources at the wavelengths probed by Planck is cosmic dust, a minor but crucial component of the interstellar medium that pervades the Galaxy. Mainly gas, it is the raw material for stars to form.

Interstellar clouds of gas and dust are also threaded by the Galaxy's magnetic field, and dust grains tend to align their longest axis at right angles to the direction of the field.

As a result, the light emitted by dust grains is partly 'polarised', it vibrates in a preferred direction, and, as such, could be caught by the polarisation-sensitive detectors on Planck.

Scientists in the Planck collaboration are using the polarised emission of interstellar dust to reconstruct the Galaxy's magnetic field and study its role in the build-up of structure in the Milky Way, leading to star formation.

In this image, the colour scale represents the total intensity of dust emission, revealing the structure of interstellar clouds in the Milky Way.

The texture is based on measurements of the direction of the polarised light emitted by the dust, which in turn indicates the orientation of the magnetic field.

This image shows the intricate link between the magnetic field and the structure of the interstellar medium along the plane of the Milky Way.

In particular, the arrangement of the magnetic field is more ordered along the Galactic plane, where it follows the spiral structure of the Milky Way. Small clouds are seen just above and below the plane, where the magnetic field structure becomes less regular.

From these and other similar observations, Planck scientists found that filamentary interstellar clouds are preferentially aligned with the direction of the ambient magnetic field, highlighting the strong role played by magnetism in galaxy evolution.

The emission from dust is computed from a combination of Planck observations at 353, 545 and 857 GHz, whereas the direction of the magnetic field is based on Planck polarisation data at 353 GHz.

ESA’s Planck satellite capture the Milky Way's magnetic fingerprint

The magnetic field of our Milky Way Galaxy as seen by ESA’s Planck satellite. 

This image was compiled from the first all-sky observations of polarised light emitted by interstellar dust in the Milky Way. 

The magnetic field is displayed using a visualisation technique called line integral convolution (LIC). 

Credit: ESA Planck Collaboration

Our Galaxy's magnetic field is revealed in a new image from ESA’s Planck satellite. This image was compiled from the first all-sky observations of 'polarised' light emitted by interstellar dust in the Milky Way.

Light is a very familiar form of energy and yet some of its properties are all but hidden to everyday human experience.

One of these, polarisation, carries a wealth of information about what happened along a light ray's path, and can be exploited by astronomers.

Light can be described as a series of waves of electric and magnetic fields that vibrate in directions that are at right angles to each other and to their direction of travel.

Usually, these fields can vibrate at all orientations. However, if they happen to vibrate preferentially in certain directions, we say the light is 'polarised'.

This can happen, for example, when light bounces off a reflective surface like a mirror or the sea.

Special filters can be used to absorb this polarised light, which is how polarised sunglasses eliminate glare.

In space, the light emitted by stars, gas and dust can also be polarised in various ways.

By measuring the amount of polarisation in this light, astronomers can study the physical processes that caused the polarisation.

In particular, polarisation may reveal the existence and properties of magnetic fields in the medium light has travelled through.

The map presented here was obtained using detectors on Planck that acted as the astronomical equivalent of polarised sunglasses.

Swirls, loops and arches in this new image trace the structure of the magnetic field in our home galaxy, the Milky Way.

In addition to its hundreds of billions of stars, our Galaxy is filled with a mixture of gas and dust, the raw material from which stars are born.

Even though the tiny dust grains are very cold, they do emit light but at very long wavelengths – from the infrared to the microwave domain.

If the grains are not symmetrical, more of that light comes out vibrating parallel to the longest axis of the grain, making the light polarised.

If the orientations of a whole cloud of dust grains were random, no net polarisation would be seen.

However, cosmic dust grains are almost always spinning rapidly, tens of millions of times per second, due to collisions with photons and rapidly moving atoms.

BOSS quasars track the expanding universe with precision

An artist's conception of how BOSS uses quasars to measure the distant universe. 

Light from distant quasars is partly absorbed by intervening gas, which is imprinted with a subtle ring-like pattern of known physical scale. 

Astronomers have now measured this scale with an accuracy of two percent, precisely measuring how fast the universe was expanding when it was just 3 billion years old. 

Credit: Zosia Rostomian, Lawrence Berkeley National Laboratory, and Andreu Font-Ribera, BOSS Lyman-alpha team, Berkeley Lab.

The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the use of quasars to map density variations in intergalactic gas at high redshifts, tracing the structure of the young universe.

BOSS charts the history of the universe's expansion in order to illuminate the nature of dark energy, and new measures of large-scale structure have yielded the most precise measurement of expansion since galaxies first formed.

The latest quasar results combine two separate analytical techniques. A new kind of analysis, led by physicist Andreu Font-Ribera of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and his team, was published late last year.

Analysis using a tested approach, but with far more data than before, has just been published by Timothée Delubac, of EPFL Switzerland and France's Centre de Saclay, and his team.

The two analyses together establish the expansion rate at 68 kilometers per second per million light years at redshift 2.34, with an unprecedented accuracy of 2.2 percent.

"This means if we look back to the universe when it was less than a quarter of its present age, we'd see that a pair of galaxies separated by a million light years would be drifting apart at a velocity of 68 kilometers a second as the universe expands," says Font-Ribera, a postdoctoral fellow in Berkeley Lab's Physics Division.

"The uncertainty is plus or minus only a kilometer and a half per second." Font-Ribera presented the findings at the April 2014 meeting of the American Physical Society in Savannah, GA.

BOSS employs both galaxies and distant quasars to measure baryon acoustic oscillations (BAO), a signature imprint in the way matter is distributed, resulting from conditions in the early universe.

While also present in the distribution of invisible dark matter, the imprint is evident in the distribution of ordinary matter, including galaxies, quasars, and intergalactic hydrogen.

"Three years ago BOSS used 14,000 quasars to demonstrate we could make the biggest 3-D maps of the universe," says Berkeley Lab's David Schlegel, principal investigator of BOSS.

"Two years ago, with 48,000 quasars, we first detected baryon acoustic oscillations in these maps. Now, with more than 150,000 quasars, we've made extremely precise measures of BAO."

The BAO imprint corresponds to an excess of about five percent in the clustering of matter at a separation known as the BAO scale.

Recent experiments including BOSS and ESA's Planck satellite study of the cosmic microwave background put the BAO scale, as measured in today's universe, at very close to 450 million light years, a "standard ruler" for measuring expansion.

BAO directly descends from pressure waves (sound waves) moving through the early universe, when particles of light and matter were inextricably entangled; 380,000 years after the big bang, the universe had cooled enough for light to go free.

The cosmic microwave background radiation preserves a record of the early acoustic density peaks; these were the seeds of the subsequent BAO imprint on the distribution of matter.

More information: "Quasar-Lyman α Forest Cross-Correlation from BOSS DR11: Baryon Acoustic Oscillations," by Andreu Font-Ribera, et al., has been submitted to the Journal of Cosmology and Astropartical Physics and is now available online at arxiv.org/abs/1311.1767.

ESA Planck satellite: Maps detail Universe's ancient light

The map shows tiny deviations from the average background temperature, where blue is slightly cooler and red is slightly warmer. 

The cold spots are where matter was more concentrated and later collapsed under gravity to form stars and galaxies. 

Image: ESA/Planck Collaboration

A spectacular new map of the "oldest light" in the sky has just been released by the European Space Agency.

Scientists say its mottled pattern is an exquisite confirmation of our Big-Bang model for the origin and evolution of the Universe.
But there are features in the picture, they add, that are unexpected and will require ideas to be refined.

The map was assembled from 15 months' worth of data acquired by the 600m-euro (£515m) Planck space telescope.

It details what is known as the cosmic microwave background, or CMB - a faint glow of microwave radiation that pervades all of space.

Its precise configuration, visible in the new Planck data, is suggestive of a cosmos that is slightly older than previously thought - one that came into existence 13.82 billion years ago.

This is an increase of about 50 million years on earlier calculations.

The map's pattern also indicates a subtle adjustment is needed to the Universe's inventory of contents.

It seems there is slightly more matter out there (31.7%) and slightly less "dark energy" (68.3%), the mysterious component thought to be driving the cosmos apart at an accelerating rate.

Planck is the third western satellite to study the CMB. The two previous efforts - COBE and WMAP - were led by the US space agency (Nasa). The Soviets also had an experiment in space in the 1980s that they called Relikt-1.

• The CMB's temperature fluctuations are put through a number of statistical analyses
• Deviations can be studied as a function of their size on the sky - their angular scale
• When compared to best-fit Big Bang models, some anomalies are evident
• One shows the fluctuations on the biggest scales to be weaker than expected
• Theorists will need to adjust their ideas to account for these features

The CMB is the light that was finally allowed to spread out across space once the Universe had cooled sufficiently to permit the formation of hydrogen atoms - about 380,000 years into the life of the cosmos.

It still bathes the Earth in a near-uniform glow at microwave frequencies, and has a temperature profile that is just 2.7 degrees above absolute zero.

But it is possible to detect minute deviations in this signal, and these fluctuations - seen as mottling in the map - are understood to reflect the differences in the density of matter when the light parted company and set out on its journey all those years ago

The fluctuations can be thought of as the seeds for all the structure that later developed in the cosmos - all the stars and galaxies

Scientists subject the temperature deviations to a range of statistical analyses, which can then be matched against theoretical expectations.

This allows them to rule in some models to explain the origin and evolution of the cosmos, while ruling out a host of others.

The team that has done this for Planck's data says the map is an elegant fit for the standard model of cosmology - the idea that the Universe started in a hot, dense state in an incredibly small space, and then expanded and cooled.

At a fundamental level, it also supports an "add-on" to this Big Bang theory known as inflation, which postulates that in the very first moments of its existence the Universe opened up in an exponential manner - faster than light itself.

But because Planck's map is so much more detailed than anything previously obtained, it is also possible to see some anomalies in it.