The
Planck astronomy satellite's new submillimeter wavelength image of
ripples in the cosmic background, as refined with data taken with the
South Pole BICEP2/Keck Array facilities. Scientists from the two teams
combined their data to conclude that previously reported measurements
attributed to the effects of cosmic inflation are instead almost
certainly due to the effects of galactic dust. Credit: ESA, NASA, Planck/BICEP.
The
universe was created 13.7 billion years ago in a blaze of light: the
big bang. Roughly 380,000 years later, after matter (mostly hydrogen)
had cooled enough for neutral atoms to form, light was able to traverse
space freely. That light, the cosmic microwave background radiation
(CMBR), comes to us from every direction in the sky uniformly ... or so
it first seemed. In the last decades, astronomers discovered that the
radiation actually has very faint ripples and bumps in it at a level of
brightness of only a part in one hundred thousand – the seeds for future
structures, like galaxies.
Astronomers have conjectured that these ripples also contain traces
of an initial burst of expansion -- the so-called inflation – which
swelled the new universe by thirty-three orders of magnitude in a mere
ten-to-the-power-minus-33 seconds. Clues about the inflation should be
faintly present in the way the cosmic ripples are curled, an effect
that is expected to be perhaps one hundred times fainter than the
ripples themselves. One year ago, CfA astronomers working at the South
Pole amazed the world by reporting evidence for such curling, the
"B-mode polarization," and cautiously calculated that the measured
strength supported the simplest models of inflation.
Other exotic processes are at work in the universe to make this
daunting measurement even more challenging. The principal one is the
scattering of light by dust particles in the galaxy that have been
aligned by magnetic fields; the light is polarized and twisted in a way
that emulates the curling effects of inflation. In 2009, the European
Space Agency, with NASA as a partner, launched the Planck satellite to
study the CMBR. The first papers from Planck substantially refined the
values of key cosmological parameters. In the course of studying the
cosmic light, it unavoidably encountered emission from dust grains.
Writing in the latest issue of Physical Review Letters, CfA
astronomers K.D. Alexander, C.A. Bischoff, I. Buder, J. Connors, C.
Dvorkin, K.S. Karkare, J. Kovac, S. Richter, and C.L. Wong joined over
one hundred colleagues in reporting their analysis of the galactic dust
contribution to the curled CMBR signature using data from both South
Pole and Planck experiments.
The scientists conclude that the previously reported curl signal is
genuine, but almost certainly due to galactic dust, whose effect turned
out to be considerably stronger than had been previously expected,
swamping the cosmological signal. The new paper provides much more
sensitive limits to cosmological effects, however, and notes that
several next-generation experiments at the South Pole and elsewhere are
continuing to probe even more deeply. In the next few years, they
predict, substantial progress towards finding the faint traces of
inflation will be made, and the improved results used to refine the
details of cosmic inflation.
Reference(s):
"Joint Analysis of BICEP2/Keck Array and Planck Data," P.A.R. Ade et al. (BICEP2/Keck and Planck Collaborations, Physical Review Letters 114, 101301, 2015
