“at this stage, we are all trying to fire bullets
at the cosmological constant.” —ADAM RIESS
Einstein passes acceleration test
sented the results and is a coauthor on
a series of papers reporting the findings
online at arXiv.org.
BOSS, a part of the third Sloan
Digital Sky Survey, analyzed about a
quarter million galaxies. The key to the
measurements is the imprint of sound
waves — called baryon acoustic oscillations — frozen into the radiation from
300,000 years after the Big Bang, about
13. 7 billion years ago. These sound waves
caused regularly spaced bumps in the
distribution of galaxies throughout the
cosmos, and so can serve as a sort of
space ruler.
This ruler has allowed the researchers to measure the distance back to an
epoch when the universe was 63 percent
of its current size, at 2,094 million parsecs plus or minus 34 million parsecs, a
precision of 1. 7 percent. (A parsec equals
about 3. 26 light-years.) The findings are
consistent with dark energy as described
by the cosmological constant.
“At this stage, we are all trying to fire
bullets at the cosmological constant,”
said Adam Riess of Johns Hopkins
University, who shared the Nobel Prize
in physics last year for the discovery of
the universe’s accelerated expansion.
“It is a pretty sharp bullet when you are
making measurements that are more
precise than ever before.”
By Elizabeth Quill
Einstein is still the boss, say researchers
with the BOSS project for measuring key
properties of the universe.
BOSS, for Baryon Oscillation Spectroscopic Survey, has measured the distance to faraway galaxies more precisely
than ever before, mapping the universe
as it existed 6 billion years ago. The findings, reported April 1, suggest that the
mysterious “dark energy” causing the
universe to expand at an accelerating
rate was foreseen by Einstein.
To keep the universe static, Einstein
added a term called the “cosmological
constant” to the equations for his theory
of general relativity. In recent years, the
cosmological constant, which describes
a repulsive force occupying all of space,
has been invoked to explain the discovery in 1998 that the universe is expanding faster and faster.
Evidence for accelerated expansion
could be explained either by the negative pressure exerted by the cosmological constant (or some other form of dark
energy) or by some flaw in general relativity. The BOSS results support the dark
energy picture. “We find no deviations
from general relativity on these very
large scales,” said Nikhil Padmanabhan,
a physicist at Yale University who pre-
Newborn pulsars may explain
iron-rich rays
newly born pulsars might explain
a weighty cosmic ray puzzle. Iron
nuclei emitted from these dense
cores left behind by supernova
explosions could account for the
composition of the highest-energy
cosmic rays, Ke fang of the univer-
sity of chicago reported april 2.
Scientists had thought these
cosmic particles were primarily
protons. but observations at the
Pierre auger observatory in argen-
tina have shown a surprising
abundance of heavier iron nuclei
in the rays (SN: 7/18/09, p. 8).
Simulations by fang and her
team suggest that young pulsars
could emit iron nuclei capable of
escaping through the supernova’s
expanding envelope of matter that
would block protons. fewer than
0.01 percent of young pulsars
outside the galaxy could emit
enough iron to explain the auger
observations, fang reported. the
results are also described online
at arXiv.org. — Elizabeth Quill
Space ruler by looking at
clusters of distant galaxies,
astronomers have probed how
the imprint of sound waves
(white circle) serves as a sort
of cosmic ruler through time.
at left are galaxies as they
appeared 3. 8 billion years
ago; at center, 5. 5 billion
years ago; and at right,
13. 7 billion years ago,
soon after the big bang.
Mysterious neutron couplings
a beryllium nucleus packed with
12 neutrons has been spotted
emitting two coupled neutrons, the
first time such a neutron pair has
been seen leaving a nucleus. the
finding, from the Mona collaboration, was presented March 31 by
physicist artemis Spyrou of Michigan State university. the result
offers a new look into the forces
that hold protons and neutrons
together in atomic nuclei and may
help scientists better understand
astrophysical phenomena, such as
the processes occurring in neutron
stars. — Elizabeth Quill
www.sciencenews.org
May 5, 2012 | SCIENCE NEWS | 17
