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| Planck has mapped the delicate polarisation of the CMB across the entire sky |
The team has made the most precise map of the “oldest light” in the cosmos.
Earlier observations of this radiation had suggested the
first generation of stars were bursting into life by about 420 million
years after the Big Bang.
Planck’s data indicates this great ignition was well established by some 560 million years after it all began.
“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 the peak of 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 BBC News.
That gap had prompted scientists to invoke complicated
scenarios to initiate re-ionisation, including the possibility that
there might have been an even earlier population of giant stars or
energetic black holes. Such solutions are no longer needed.
No-one knows the exact timing of the very first individual
stars. All Planck does is tell us when large numbers of these stars had
gathered into galaxies of sufficient strength to alter the cosmic
environment.
By definition, this puts the ignition of the “founding stars”
well before 560 million years after the Big Bang. Quite how far back
in time, though, is uncertain. Perhaps, it was as early as 200 million
years. It will be the job of the next generation of observatories like
Hubble’s successor, the James Webb Space Telescope, to try to find the
answer.
Being built now: The James Webb telescope will conduct a survey of the first galaxies and their stars
The history of the Universe
- Planck’s CMB studies indicate the Big Bang was 13.8bn years ago
- The CMB itself can be thought of as the ‘afterglow’ of the Big Bang
- It spreads across the cosmos some 380,000 years after the Big Bang
- This is when the conditions cool to make neutral hydrogen atoms
- The period before the first stars is often called the ‘Dark Ages’
- When the first stars ignite, they ‘fry’ the neutral gas around them
- These giants also forge the first heavy elements in big explosions
- ‘First Light’, or ‘Cosmic Renaissance’, is a key epoch in history
The new Planck result is contained in a raft of new papers just posted on the Esa website.
These papers accompany the latest data release from the
satellite that can now be used by the wider scientific community, not
just collaboration members.
Two years ago, the data dump largely concerned interpretations
of the CMB based on its temperature profile. It is the CMB’s
polarisation features that take centre-stage this time.
It was hoped that Planck might find direct evidence in the
CMB’s polarisation for inflation – the super-rapid expansion of space
thought to have occurred just fractions of a second after the Big Bang.
This has not been possible. But all the Planck data – temperature and
polarisation information – is consistent with that theory, and the
precision measurements mean new, tighter constraints have been put on
the likely scale of the inflation signal, which other experiments
continue to chase.
What is clear from the Planck investigation is that the
simplest models for how the super-rapid expansion might have worked are
probably no longer tenable, suggesting some exotic physics will
eventually be needed to explain it.
“We’re now being pushed into a parameter space we didn’t
expect to be in,” said collaboration scientist Dr Andrew Jaffe from
Imperial College, UK. “That’s OK. We like interesting physics; that’s
why we’re physicists, so there’s no problem with that. It’s just we had
this naïve expectation that the simplest answer would be right, and
sometimes it just isn’t.”
Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/3aKTc2JXhxY/planck-telescope-puts-new-datestamp-on.html
Planck telescope puts new datestamp on first stars
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