"Long before it's in the papers"
February 11, 2015

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Study finds first stars were born “late”

Feb. 11, 2015
Courtesy of ESA
and World Science staff

New maps from the Eu­ro­pe­an Space Agen­cy’s Planck sat­el­lite show the first stars formed much lat­er than pre­vi­ously thought, sci­en­tists say.

The sat­el­lite maps so-called po­lar­ized light across the sky—light be­lieved to have been trav­el­ing to­ward us since the almost dawn of time, and pro­vid­ing a cer­tain view of the early uni­verse. 

The find­ings were de­scribed in 15 pa­pers sub­mit­ted to the re­search jour­nal As­tron­o­my & As­t­ro­phys­ics last week.

The his­to­ry of our Uni­verse is a 13.8 billion-year tale that sci­en­tists try to read by stu­dy­ing the plan­ets, as­ter­oids, comets and oth­er ob­jects in our So­lar Sys­tem, and by look­ing at dis­tant stars, ga­lax­ies and the ma­te­ri­al be­tween them.

Im­por­tant in­forma­t­ion comes from the Cos­mic Mi­cro­wave Back­ground, “fos­sil light” be­lieved to come from when the Uni­verse was hot, thick, fog­gy soup, some 380,000 years af­ter its birth in a “Big Bang.” Be­cause the uni­verse is still ex­pand­ing from that in­i­tial ex­plo­sion, sci­en­tists be­lieve, the light waves in it ex­pand al­so. As a re­sult this light reaches us in a lower-energy form knows as mi­cro­wave light.

Be­tween 2009 and 2013, Planck sur­veyed the sky to study this light in un­prec­e­dent­ed de­tail, proj­ect phys­i­cists ex­plain. Ti­ny dif­fer­ences in its tem­per­a­ture trace re­gions of slightly dif­fer­ent dens­ity, or com­pact­ness, in the early cos­mos—thought to rep­re­sent the seeds of fu­ture stars and ga­lax­ies.

The light al­so car­ries further clues “en­coded in its ‘po­lar­iz­a­tion’,” or the ori­enta­t­ion of its waves, said Jan Tauber, the agen­cy’s Planck proj­ect sci­ent­ist. A de­tailed, full-sky meas­ure­ment of this po­lar­iz­a­tion led to “the un­ique maps” now re­leased, he added.

Light is po­lar­ized when its many waves tend to all vi­brate in the same di­rec­tion. This may arise as a re­sult of pho­tons – the par­t­i­cles of light – bounc­ing off oth­er par­t­i­cles, which is thought to be what hap­pened in this case.

The scientific account goes like this. The pho­tons were orig­i­nally trapped in a hot, thick, fog­gy soup of par­t­i­cles which, by the time the Uni­verse was a few sec­onds old, con­sisted mainly of bits of atoms called elec­trons, pro­tons and neu­tri­nos. Slowly but sure­ly, the uni­verse ex­pand­ed, cool­ing down in the pro­cess, and the “fog” lifted. This had two re­sults: the par­t­i­cles called elec­trons and pro­tons could com­bine and form atoms with­out be­ing de­stroyed by light par­t­i­cles bump­ing in­to them. And pho­tons, the light par­t­i­cles them­selves, had room to trav­el with­out bump­ing in­to the atoms. And the light could get to us.

But the light is al­so thought to re­tain a mem­o­ry of its last en­coun­ter with the elec­trons—a mem­ory en­coded in its po­lar­iz­a­tion.

As the back­ground light trav­eled through space and time the first stars al­so left a mark on it, phys­i­cists say. That al­so af­fects the po­lar­iz­a­tion, they add, and this da­ta now in­di­cates that these stars started to shine about 550 mil­lion years af­ter the Big Bang—end­ing the fog­gy “Dark Ages.” 

That is more than 100 mil­lion years lat­er than pre­vi­ously thought, but ac­tu­ally helps to solve a prob­lem, the phys­i­cists said. That’s be­cause the pre­vi­ous time es­ti­mates con­flicted with deep im­ages of the sky, in­di­cat­ing that the ear­li­est known ga­lax­ies could not have been pow­er­ful enough to end the dark ages much ear­li­er.

One dis­ap­point­ment that has emerged: dust from our own gal­axy is ob­scur­ing a lot more of the early-u­niverse pic­ture than was hoped, said Torsten Enßlin, lead­er of the Planck tech­ni­cal team at the Max Planck In­sti­tute for As­t­ro­phys­ics.

“Po­lar­ized emis­sion from dust in our Milky Way is sig­nif­i­cant over the en­tire sky, dash­ing ear­li­er hopes that some ar­eas might be clean enough to of­fer an un­con­tam­i­nated view of the early uni­verse,” he said. On the bright side, he not­ed, that same dust of­fers in­ter­est­ing in­forma­t­ion about ga­lac­tic weath­er.


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New maps from the European Space Agency’s Planck satellite show the first stars formed much later than previously thought, scientists say. The satellite maps so-called polarized light across the sky, believed to have been traveling toward us since the dawn of time and representing conditions in the early universe. The findings were described in 15 papers submitted to the research journal Astronomy & Astrophysics last week. The history of our Universe is a 13.8 billion-year tale that scientists try to read by studying the planets, asteroids, comets and other objects in our Solar System, and by looking at distant stars, galaxies and the material between them. Important information comes from the Cosmic Microwave Background, “fossil light” believed to come from when the Universe was hot, thick, foggy soup, some 380,000 years after its birth in a “Big Bang.” Because the universe is still expanding from that initial explosion, scientists believe, the light waves in it expands also. As a result this light reaches us in a form knows as microwave light. Between 2009 and 2013, Planck surveyed the sky to study this light in unprecedented detail, project physicists explain. Tiny differences in its temperature also trace regions of slightly different density, or compactness, in the early cosmos—thought to represent the seeds of all future structures, such as stars and galaxies. The light also carries additional clues “encoded in its ‘polarization’,” or the orientation of its waves, said Jan Tauber, the agency’s Planck project scientist. A detailed, full-sky measurement of this polarization led to “the unique maps” now released, he added. Light is polarized when its many waves tend to all vibrate in the same direction. This may arise as a result of photons – the particles of light – bouncing off other particles, which is thought to be what happened in this case. The photons were originally trapped in a hot, thick, foggy soup of particles that, by the time the Universe was a few seconds old, consisted mainly of bits of atoms called electrons, protons and neutrinos. Slowly but surely, the universe expanded, cooling down in the process, and the “fog” lifted. This had two results: the particles called electrons and protons could combine and form atoms without being destroyed by light particles bumping into them. And photons, the light particles themselves, had room to travel without bumping into the atoms. And it could get to us. But the light is also thought to retain a memory of its last encounter with the electrons—reflected in its polarization. As the background light traveled through space and time the first stars also left a mark on it, physicists say. That also affects the polarization, they add, and this data now indicates that these stars started to shine about 550 million years after the Big Bang—ending the foggy “Dark Ages.” That is more than 100 million years later than previously thought, but actually helps to solve a problem, the physicists said. That’s because the previous time estimates conflicted with deep images of the sky, indicating that the earliest known galaxies could not have been powerful enough to end the dark ages much earlier. One disappointment that has emerged: dust from our own galaxy is obscuring a lot more of the early-universe picture than was hoped, said Torsten Enßlin, leader of the Planck technical team at the Max Planck Institute for Astrophysics. “Polarized emission from dust in our Milky Way is significant over the entire sky, dashing earlier hopes that some areas might be clean enough to offer an uncontaminated view of the early universe,” he said. On the bright side, he noted, that same dust offers interesting information about galactic weather.