Planck reveals first stars were born late

February 12, 2015

New maps from ESA's 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. They also include information about our own Milky Way, showing that the contribution from dust in our galaxy is much more widespread than previously thought and revealing complex structures in the Galactic magnetic field. Researchers at the Max Planck Institute for Astrophysics developed important software components for Planck and take part in the scientific interpretation of the mission data; in particular, they contributed to the analysis of the signals from galaxy clusters, from gravitational lensing of the CMB, from Galactic dust and magnetic fields, as well as from primordial magnetic fields.

Fig. 1: A visualisation of the polarisation of the Cosmic Microwave Background, or CMB, as detected by ESA's Planck satellite over the entire sky. A small fraction of the CMB is polarised - it vibrates in a preferred direction. In this image, the colour scale represents temperature differences in the CMB, while the texture indicates the direction of the polarised light. The patterns seen in the texture are characteristic of "E-mode" polarisation, which is the dominant type for the CMB. Credits: ESA and the Planck Collaboration — **Fig. 1:** A visualisation of the polarisation of the Cosmic Microwave Background, or CMB, as detected by ESA's Planck satellite over the entire sky. A small fraction of the CMB is polarised - it vibrates in a preferred direction. In this image, the colour scale represents temperature differences in the CMB, while the texture indicates the direction of the polarised light. The patterns seen in the texture are characteristic of "E-mode" polarisation, which is the dominant type for the CMB. *Credits: ESA and the Planck Collaboration*

**Fig. 1:** A visualisation of the polarisation of the Cosmic Microwave Background, or CMB, as detected by ESA's Planck satellite over the entire sky. A small fraction of the CMB is polarised - it vibrates in a preferred direction. In this image, the colour scale represents temperature differences in the CMB, while the texture indicates the direction of the polarised light. The patterns seen in the texture are characteristic of "E-mode" polarisation, which is the dominant type for the CMB.
*Credits: ESA and the Planck Collaboration*

The history of our Universe began 13.8 billion years ago and for researchers trying to understand its evolution, one major source of information is the Cosmic Microwave Background, or CMB. This fossil light is 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, Planck 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 numerous scientific papers over the past two years, confirming the standard cosmological picture of our Universe with ever greater accuracy (see e.g. here).

Fig. 2: Detailed view of the polarisation map from Fig. 1, across a small patch of the sky measuring 5º across. Credits: ESA and the Planck Collaboration — **Fig. 2:** Detailed view of the polarisation map from Fig. 1, across a small patch of the sky measuring 5º across. *Credits: ESA and the Planck Collaboration*

**Fig. 2:** Detailed view of the polarisation map from Fig. 1, across a small patch of the sky measuring 5º across.
*Credits: ESA and the Planck Collaboration*

"The detailed map of CMB temperature structures is one of the key scientific results of the 21st century," explains Simon White, director at the Max Planck Institute for Astrophysics and Co-Investigator of Planck. "It is a high-fidelity image of the boundary of our visible Universe, showing us its detailed structure when it was 40,000 times younger than today and giving us our best indication of what happened at even earlier times."

"But there is more: the 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, such as electrons. This is exactly what happened when the CMB originated in the early Universe. Planck's polarisation data provide an independent way to measure cosmological parameters and thus confirm the details of the standard cosmological picture determined from CMB temperature fluctuations.

However, as the CMB light travelled through space and time it was also influenced by the first stars and the polarisation data now indicates that these started to shine about 550 million years after the Big Bang, ending the "Dark Ages". This is more than 100 million years later than previously thought but actually helps to resolve a problem: Previous studies of the CMB polarisation seemed to point towards an earlier dawn of the first stars, while very deep images of the sky indicated that the earliest known galaxies in the Universe (forming perhaps 300-400 million years after the Big Bang) would not have been powerful enough to succeed at ending the Dark Ages within 450 million years. The new evidence from Planck significantly reduces the problem, indicating that the earliest stars and galaxies alone might have been enough.

Fig. 3: The interaction between interstellar dust in the Milky Way and the structure of our Galaxy's magnetic field, as detected by ESA’s Planck satellite over the entire sky. 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. Interstellar clouds of gas and dust are 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 at MPA and 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. Credits: ESA and the Planck Collaboration — **Fig. 3:** The interaction between interstellar dust in the Milky Way and the structure of our Galaxy's magnetic field, as detected by ESA’s Planck satellite over the entire sky. 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. Interstellar clouds of gas and dust are 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 at MPA and 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. *Credits: ESA and the Planck Collaboration*

**Fig. 3:** The interaction between interstellar dust in the Milky Way and the structure of our Galaxy's magnetic field, as detected by ESA’s Planck satellite over the entire sky.
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.
Interstellar clouds of gas and dust are 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 at MPA and 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.
*Credits: ESA and the Planck Collaboration*

"Mit seinen neun Frequenzkanälen ist Planck bestens dafür geeignet, um das kosmologische Signal und die Vordergrundstrahlung zu entwirren. Allerdings müssen wir bei der Analyse der Daten sehr vorsichtig sein", erklärt Torsten Enßlin, Leiter des Planck Software-Teams am Max-Planck-Institut für Astrophysik. "Unsere Ergebnisse zeigen, dass der Beitrag von Staub in unserer Milchstraße über den gesamten Himmel hinweg signifikant ist - damit werden alle früheren Hoffnungen zunichtegemacht, dass einige Bereiche sauber genug sein könnten, um einen direkten Blick auf das frühe Universum zu erhaschen. Das polarisierte Licht des Staubes zeichnet die galaktischen Magnetfeldlinien mit einer fantastischen Detailtreue nach und ermöglicht bisher ungeahnte Einblicke in Wetterphänomene in unserer Milchstrasse."

Die Daten lieferten auch wichtige neue Einblicke in den frühen Kosmos und seine Bestandteile, einschließlich der faszinierenden dunklen Materie und der schwer fassbaren Neutrinos; auch diese Ergebnisse werden in den heute veröffentlichten Arbeiten beschrieben. Selbst die noch frühere Geschichte des Kosmos kann mit den Planckdaten eruiert werden, bis zurück zur Phase der Inflation - einer kurzen Zeit der beschleunigten Expansion, als das Universum gerade erst einen winzigen Bruchteil einer Sekunde alt war. Als ultimative Signatur dieser Epoche suchen die Astronomen nach Hinweisen auf Gravitationswellen, die durch die Inflation ausgelöst wurden und später die Polarisation des CMB prägten.

Frühere Berichte über einen direkten Nachweis dieses Signals mussten angesichts der Planckkarten des polarisierten Lichtes revidiert werden, wie letzte Woche berichtet. Kombiniert man allerdings die neuesten Planck-Daten mit neuen Ergebnissen von anderen Experimenten, so können die Grenzwerte für diese primordialen Gravitationswellen noch genauer bestimmt werden. Die neuen Obergrenzen sind bereits in der Lage einige Inflationsmodelle auszuschließen.

Hinweise:

Eine Reihe von wissenschaftlichen Arbeiten, die die neuen Ergebnisse beschreiben, wurde am 5. Februar veröffentlicht. Sie können hier heruntergeladen werden.

Die neuen Ergebnisse von Planck basieren auf kompletten Himmelskarten erstellt von 2009 bis 2013. Neue Daten, einschließlich der CMB-Temperaturkarten in allen neun Frequenzbändern von Planck und die beobachteten Polarisationskarten in vier Frequenzen (30, 44, 70 und 353 GHz), werden ebenfalls heute veröffentlicht.

Mehr über Planck

Planck wurde 2009 gestartet, um den gesamten Himmel mit zwei hochmodernen Geräten in neun Frequenzen zu vermessen: das LFI (Low Frequency Instrument) enthält drei Frequenzbänder im Bereich von 30 bis 70 GHz, und das HFI (High Frequency Instrument) umfasst sechs Frequenzbänder im Bereich von 100 bis 857 GHz.

HFI beendete seine Aufnahmen im Januar 2012, während LFI weiterhin bis zum 3. Oktober 2013 wissenschaftliche Beobachtungen machte, bevor es am 19. Oktober 2013 ausgeschaltet wurde. Sieben der neun Frequenzkanäle von Planck wurden mit polarisationsempfindlichen Detektoren ausgestattet.

Die Planck Science Collaboration besteht aus allen Wissenschaftlern, die zur Entwicklung der Mission beigetragen haben, und die jetzt an der wissenschaftlichen Auswertung der Daten (während der proprietären Zeit) beteiligt sind. Diese Wissenschaftler sind Mitglieder einer oder mehr der vier Konsortien: das LFI-Konsortium, das HFI-Konsortium, das DK-Planck-Konsortium und das Planck-Wissenschaftsbüro der ESA. Die beiden Datenverarbeitungszentren für Planck unter europäischer Führung befinden sich in Paris und Triest.

Die LFI-Konsortium wird geleitet von N. Mandolesi, Università degli Studi di Ferrara, Italien, (stellvertretender PI: M. Bersanelli, Università degli Studi di Milano, Italien) und war verantwortlich für die Entwicklung und den Betrieb von LFI. Das HFI-Konsortium wird geleitet von J.L. Puget, Institut d'Astrophysique Spatiale in Orsay, Frankreich (stellvertretender PI: F. Bouchet, Institut d'Astrophysique de Paris, Frankreich) und war verantwortlich für die Entwicklung und den Betrieb von HFI.

Kontakt:

Prof. Simon White
Direktor
Max-Planck-Institut für Astrophysik
Tel: +49 89 30000-2211
E-mail: swhite(a)mpa-garching.mpg.de

Dr. Torsten Enßlin
Max-Planck-Institut für Astrophysik
Tel.: +49 89 30000-2243
email: tensslin(a)mpa-garching.mpg.de

Dr. Hannelore Hämmerle
Pressesprecherin
Max-Planck-Institut für Astrophysik
Tel. +49 89 30000-3980
E-mail: pr(a)mpa-garching.mpg.de

Links:

Vollständige ESA Pressemitteilung: Planck reveals first stars were born late
Wissenschaftliche Arbeiten, die die neuen Ergebnisse beschreiben.