BOSS

[HVAC]

Some six billion light years ago, almost halfway from now back to the
big bang, the universe was undergoing an elemental change. Held back
until then by the mutual gravitational attraction of all the matter it
contained, the universe had been expanding ever more slowly. Then, as
matter spread out and its density decreased, dark energy took over and
expansion began to accelerate.

Today BOSS, the Baryon Oscillation Spectroscopic Survey, the largest
component of the third Sloan Digital Sky Survey (SDSS-III), announced
the most accurate measurement yet of the distance scale of the universe
during the era when dark energy turned on.

"We've made precision measurements of the large-scale structure of the
universe five to seven billion years ago -- the best measure yet of the
size of anything outside the Milky Way," says David Schlegel of the
Physics Division at the U.S. Department of Energy's Lawrence Berkeley
National Laboratory (Berkeley Lab), BOSS's principal investigator.
"We're pushing out to the distances when dark energy turned on, where we
can start to do experiments to find out what's causing accelerating
expansion."

How to measure expansion in an accelerating universe

Accelerating expansion was announced less than 14 years ago by both the
Supernova Cosmology Project (SCP) based at Berkeley Lab and the
competing High-z Supernova Search Team, a discovery that resulted in
2011 Nobel Prizes for the SCP's Saul Perlmutter and High-z Team members
Brian Schmidt and Adam Riess. Acceleration may result from an unknown
something dubbed "dark energy" -- or, dark energy may be just a way of
saying we don't understand how gravity really works.

The first step in finding out is to establish a detailed history of
expansion. Unlike supernova searches, which depend on the brightness of
exploding stars, BOSS uses a technique called baryon acoustic
oscillation (BAO) to determine the distances to faraway galaxies.

Baryon acoustic oscillation measures the angle across the sky of
structures of known size, the peaks where galaxies cluster most densely
in the network of filaments and voids that fill the universe. Since
these density peaks recur regularly, the angle between appropriate pairs
of galaxies as precisely measured from Earth reveals their distance --
the narrower the apparent angle, the farther away they are.

Knowing the distance to an object tells its age as well, since its light
travels from there to here at known speed. And the redshift of the light
reveals how the universe has expanded since that time, as expansion
stretches space itself; the wavelength of light traveling through space
toward Earth stretches proportionally, becoming redder and revealing the
expansion of the universe since the light left its source.

"BOSS's first major cosmological results establish the accurate
three-dimensional positions of 327,349 massive galaxies across 3,275
square degrees of the sky, reaching as far back as redshift 0.7 -- the
largest sample of the universe ever surveyed at this high density," says
Martin White of Berkeley Lab's Physics Division, a professor of physics
and astronomy at the University of California at Berkeley and chair of
the BOSS science survey teams. "BOSS's average redshift is 0.57,
equivalent to some six billion light-years away. BOSS gives that
distance to within 1.7 percent -- 2,094 megaparsecs plus or minus 34
megaparsecs -- the most precise distance constraint ever obtained from a
galaxy survey."

The origin of BAO, the regular clustering of ordinary matter (called
"baryons" by astronomical convention), was the pressure of sound waves
(thus "acoustic") moving through the universe when it was still so hot
that light and matter were mixed together in a kind of soup, in which
the sound waves created areas of regularly varying density
("oscillation"). By 380,000 years after the big bang, expansion had
cooled the soup enough for ordinary matter to condense into hydrogen
atoms (invisible dark matter was also part of the soup) and for light to
go its separate way.

At that moment variations in density were preserved as variations in the
temperature of the cosmic microwave background (CMB), a phenomenon first
measured by Berkeley Lab astrophysicist George Smoot, for which he
shared the 2006 Nobel Prize. The warmer regions of the CMB signal areas
where the density of matter was greater; these regions seeded the
galaxies and clusters of galaxies that form the large-scale structure of
the universe today. Thus the cosmic microwave background establishes the
basic scale of baryon acoustic oscillation used to measure the expansion
history of the universe.

BOSS's data on galaxy clustering and redshifts can be applied not only
to BAO but also to a separate technique called "redshift space
distortions" -- a direct test of gravity that measures how fast
neighboring galaxies are moving together to form galaxy clusters.

What if dark energy isn't an unknown force or substance, but instead a
shortcoming of Albert Einstein's General Theory of Relativity, our
best-yet theory of gravity? General Relativity predicts how fast
galaxies should be moving toward one another in galaxy clusters, and, in
the aggregate, how fast the structure of the universe should be growing.
Any departure from its predictions would mean the theory is flawed.

"We depend on redshift to know expansion rates and how structure was
growing at different times in the past," says Beth Reid, a Hubble Fellow
at Lawrence Berkeley National Laboratory who directed the BOSS study of
redshift space distortions. "But redshifts aren't uniform. Galaxies are
carried along in the Hubble flow as the universe expands, but they also
have their own velocities. They tend to fall toward denser regions, for
example. Because the ones on the far side of a dense region are coming
toward us, their redshift makes them look closer than they really are;
the opposite is true for the galaxies on the near side, which are
falling away from us -- they look farther away."

Statistical analysis of the redshifts of the hundreds of thousands of
galaxies in the BOSS dataset can take into account the peculiarities of
local variation and still produce a dependable measure of distance, the
Hubble expansion rate, and the growth rate of structure in the universe.
With these techniques, Reid and her colleagues have measured gravity on
a scale of 100 million light years, far larger than the most accurate
gravity measure yet, which is based on the distance from Earth to the
moon. Their conclusion: Einstein was right.

The right tools to do the job

BOSS obtained these best-yet measures with the wide-field Sloan
Telescope at the Apache Point Observatory in New Mexico, designed
especially for galaxy surveys but mounting a spectrograph far more
sophisticated than was available to earlier SDSS surveys.

"The 2.5-meter Sloan Telescope remains the world's premier facility for
wide-field spectroscopy because it uses fiber-fed spectrographs, which
offer a huge numerical advantage," says Natalie Roe, director of
Berkeley Lab's Physics Division and instrument scientist for BOSS, who
directed construction of the new spectrographs.

For each 15-minute exposure, covering three degrees of the sky, a
thousand optical fibers are inserted by hand into aluminum "plug plates"
and positioned at the telescope's focal plane; each fiber is targeted on
a specific distant bright galaxy, selected from earlier SDSS imaging.
The BOSS instrument uses 50 percent more fibers than earlier SDSS runs,
each with finer diameter; for more coverage and finer resolution the new
spectrograph incorporates two red cameras using the thick, red-sensitive
astronomical CCDs invented and fabricated at Berkeley Lab, as well as
two new blue cameras.

"All the data collected by BOSS flows through a data-processing pipeline
at Berkeley Lab," says Stephen Bailey of the Physics Division, who
describes himself as the "baby sitter of the pipeline." Working with
Schlegel at Berkeley Lab and Adam Bolton at the University of Utah,
Bailey "turns the data into something we can use -- catalogues of
hundreds of thousands of galaxies, eventually well over a million, each
identified by their two-dimensional positions in the sky and their
redshifts." The data are processed and stored on the Riemann computer
cluster, operated by Berkeley Lab's High-Performance Computing Services
group.

The current crop of BOSS papers is based on less than a quarter of the
data BOSS will continue to collect until the survey ends in 2014. So
far, all lines of inquiry point toward the so-called "concordance model"
of the universe: a "flat" (Euclidean) universe that bloomed from the big
bang 13.7 billion years ago, a quarter of which is cold dark matter --
plus a few percent visible, ordinary, baryonic matter (the stuff we're
made of). All the rest is thought to be dark energy in the form of
Einstein's cosmological constant: a small but irreducible energy of
puzzling origin that's continually stretching space itself.

But it's way too soon to think that's the end of the story, says
Schlegel. "Based on the limited observations of dark energy we've made
so far, the cosmological constant may be the simplest explanation, but
in truth, the cosmological constant has not been tested at all. It's
consistent with the data, but we really have only a little bit of data.
We're just beginning to explore the times when dark energy turned on. If
there are surprises lurking there, we expect to find them."







--
"OK you cunts, let's see what you can do now" -Hit Girl
http://www.youtube.com/watch?v=CjO7kBqTFqo

[Painius]

On Fri, 30 Mar 2012 15:36:10 -0400, HVAC <mr....@gmail.com> wrote:

>moon. Their conclusion: Einstein was right.

Well click my heels and call me Sparky!

Anybody else profoundly surprised by this?

Happy days *and*...
Starry starry nights !

--
Indelibly yours,
Paine @ http://astronomy.painellsworth.net/
Only you can make the most of yourself.