Andrew Yee[_1_]
November 13th 07, 01:31 AM
Pierre Auger Observatory
Contact:
http://www.auger.org/contact/index.html
9-NOV-2007
Auger Observatory closes in on long-standing mystery, links highest-energy
cosmic rays with violent black holes
Scientists of the Pierre Auger Collaboration announced today (8 Nov. 2007)
that Active Galactic Nuclei are the most likely candidate for the source of
the highest-energy cosmic rays that hit Earth. Using the Pierre Auger
Observatory in Argentina, the largest cosmic-ray observatory in the world, a
team of scientists from 17 countries found that the sources of the
highest-energy particles are not distributed uniformly across the sky.
Instead, the Auger results link the origins of these mysterious particles to
the locations of nearby galaxies that have active nuclei in their centers.
The results appear in the Nov. 9 issue of the journal Science.
Active Galactic Nuclei (AGN) are thought to be powered by supermassive black
holes that are devouring large amounts of matter. They have long been
considered sites where high-energy particle production might take place.
They swallow gas, dust and other matter from their host galaxies and spew
out particles and energy. While most galaxies have black holes at their
center, only a fraction of all galaxies have an AGN. The exact mechanism of
how AGNs can accelerate particles to energies 100 million times higher than
the most powerful particle accelerator on Earth is still a mystery.
"We have taken a big step forward in solving the mystery of the nature and
origin of the highest-energy cosmic rays, first revealed by French physicist
Pierre Auger in 1938," said Nobel Prize winner James Cronin, of the
University of Chicago, who conceived the Pierre Auger Observatory together
with Alan Watson of the University of Leeds. "We find the southern
hemisphere sky as observed in ultra-high-energy cosmic rays is non-uniform.
This is a fundamental discovery. The age of cosmic-ray astronomy has
arrived. In the next few years our data will permit us to identify the exact
sources of these cosmic rays and how they accelerate these particles."
Cosmic rays are protons and atomic nuclei that travel across the universe at
close to the speed of light. When these particles smash into the upper
atmosphere of our planet, they create a cascade of secondary particles
called an air shower that can spread across 40 or more square kilometers (15
square miles) as they reach the Earth's surface.
"This result heralds a new window to the nearby universe and the beginning
of cosmic-ray astronomy," said Watson, a spokesperson of the Pierre Auger
Collaboration. "As we collect more and more data, we may look at individual
galaxies in a detailed and completely new way. As we had anticipated, our
observatory is producing a new image of the universe based on cosmic rays
instead of light."
The Pierre Auger Observatory records cosmic ray showers through an array of
1,600 particle detectors placed 1.5 kilometers (about one mile) apart in a
grid spread across 3,000 square kilometers (1,200 square miles). Twenty-four
specially designed telescopes record the emission of fluorescence light from
the air shower. The combination of particle detectors and fluorescence
telescopes provides an exceptionally powerful instrument for this research.
While the observatory has recorded almost a million cosmic-ray showers, only
the rare, highest-energy cosmic rays can be linked to their sources with
sufficient precision. Auger scientists so far have recorded 81 cosmic rays
with energy above 4 x 10**19 electron volts, or 40 EeV. This is the largest
number of cosmic rays with energy above 40 EeV recorded by any observatory.
At these ultra-high energies, the uncertainty in the direction from which
the cosmic ray arrived is only a few degrees, allowing scientists to
determine the location of the particle's cosmic source.
The Auger collaboration discovered that the 27 highest-energy events, with
energy above 57 EeV, do not come equally from all directions. Comparing the
clustering of these events with the known locations of 318 Active Galactic
Nuclei, the collaboration found that most of these events correlated well
with the locations of AGNs in some nearby galaxies, such as Centaurus A.
"Low-energy cosmic rays are abundant and come from all directions, mostly
from within our own Milky Way galaxy. Until now the only source of cosmic
ray particles known with certainty has been the Sun. Cosmic rays from other
likely sources such as exploding stars take meandering paths through space
so that when they reach Earth it is impossible to determine their origins.
But when you look at the highest-energy cosmic rays from the most violent
sources, they point back to their sources. The challenge now is to record
enough of these cosmic bullets to understand the processes that hurl them
into space," said Paul Mantsch, project manager of the Pierre Auger
Observatory.
Cosmic rays with energy higher than about 60 EeV lose energy in collisions
with the cosmic microwave background, radiation left over from the Big Bang
that fills all of space. But cosmic rays from nearby sources are less likely
to lose energy in collisions on their relatively short trip to Earth. Auger
scientists found that most of the 27 events with energy above 57 EeV came
from locations in the sky that include the nearest AGNs, within a few
hundred million light years of Earth.
Scientists think that most galaxies have black holes at their centers, with
masses ranging from a million to a few billion times the mass of our sun.
The black hole at the center of our Milky Way galaxy weighs about 3 million
solar masses, but it is not an AGN. Galaxies that have an AGN seem to be
those that suffered a collision with another galaxy or some other massive
disruption in the last few hundred million years. The AGN swallows the mass
coming its way while releasing prodigious amounts of radiation. The Auger
result indicates that AGNs may also produce the universe's highest-energy
particles.
Cosmic-ray astronomy is challenging, because low-energy cosmic rays provide
no reliable information on the location of their sources: as they travel
across the cosmos, they are deflected by galactic and intergalactic magnetic
fields that lead to blurry images. In contrast, the most energetic particles
come almost straight from their sources, as they are barely affected by the
magnetic fields. Unfortunately, they hit Earth at a rate of only about one
event per square kilometer per century, which demands a very large
observatory.
Because of its size, the Auger Observatory can record about 30
ultra-high-energy events per year. The Auger collaboration is developing
plans for a second, larger installation in Colorado to extend coverage to
the entire sky while substantially increasing the number of high-energy
events recorded.
"Our current results show the promising future of cosmic-ray astronomy,"
said Auger cospokesperson Giorgio Matthiae, of the University of Rome. "So
far we have installed 1400 of the 1600 particle detectors of the Auger
Observatory in Argentina. A northern site would let us look at more galaxies
and black holes, increasing the sensitivity of our observatory. There are
even more nearby AGNs in the northern sky than in the southern sky."
The Pierre Auger Observatory is being built by a team of more than 370
scientists and engineers from 17 countries.
"The collaboration is a true international partnership in which no country
contributed more than 25 percent of the US$54-million construction cost,"
said Danilo Zavrtanik, of the University of Nova Gorica and chair of the
Auger Collaboration Board. The names of the funding agencies contributing to
the Pierre Auger Observatory are found at
http://www.auger.org/contact/agencies.html
and the names of the participating institutions are listed at
http://www.auger.org/collaboration/auger_institutions.html
Groundbreaking for the southern hemisphere site of the Pierre Auger
Observatory took place on March 17, 1999, in Argentina's Mendoza Province.
Following a period of detector deployment and testing, scientific data
collection began in January, 2004.
"Argentina is pleased to host and participate in this unique scientific
endeavor," said Alberto Etchegoyen, of Comision Nacional de Energ Atomica,
and Southern Observatory spokesperson, "and now, looking back into these
years of efforts and excitement, a feeling of gratitude and respect arises
for all collaboration members who took care of every single minor detail
leading to today's announcement."
The observatory is named for French scientist Pierre Victor Auger
(1899-1993), who in 1938 was the first to observe the extensive air showers
generated by the interaction of high-energy cosmic rays with the Earth's
atmosphere.
[NOTE: Images supporting this release are available at
http://www.auger.org/media/image_highlights.html ]
Contact:
http://www.auger.org/contact/index.html
9-NOV-2007
Auger Observatory closes in on long-standing mystery, links highest-energy
cosmic rays with violent black holes
Scientists of the Pierre Auger Collaboration announced today (8 Nov. 2007)
that Active Galactic Nuclei are the most likely candidate for the source of
the highest-energy cosmic rays that hit Earth. Using the Pierre Auger
Observatory in Argentina, the largest cosmic-ray observatory in the world, a
team of scientists from 17 countries found that the sources of the
highest-energy particles are not distributed uniformly across the sky.
Instead, the Auger results link the origins of these mysterious particles to
the locations of nearby galaxies that have active nuclei in their centers.
The results appear in the Nov. 9 issue of the journal Science.
Active Galactic Nuclei (AGN) are thought to be powered by supermassive black
holes that are devouring large amounts of matter. They have long been
considered sites where high-energy particle production might take place.
They swallow gas, dust and other matter from their host galaxies and spew
out particles and energy. While most galaxies have black holes at their
center, only a fraction of all galaxies have an AGN. The exact mechanism of
how AGNs can accelerate particles to energies 100 million times higher than
the most powerful particle accelerator on Earth is still a mystery.
"We have taken a big step forward in solving the mystery of the nature and
origin of the highest-energy cosmic rays, first revealed by French physicist
Pierre Auger in 1938," said Nobel Prize winner James Cronin, of the
University of Chicago, who conceived the Pierre Auger Observatory together
with Alan Watson of the University of Leeds. "We find the southern
hemisphere sky as observed in ultra-high-energy cosmic rays is non-uniform.
This is a fundamental discovery. The age of cosmic-ray astronomy has
arrived. In the next few years our data will permit us to identify the exact
sources of these cosmic rays and how they accelerate these particles."
Cosmic rays are protons and atomic nuclei that travel across the universe at
close to the speed of light. When these particles smash into the upper
atmosphere of our planet, they create a cascade of secondary particles
called an air shower that can spread across 40 or more square kilometers (15
square miles) as they reach the Earth's surface.
"This result heralds a new window to the nearby universe and the beginning
of cosmic-ray astronomy," said Watson, a spokesperson of the Pierre Auger
Collaboration. "As we collect more and more data, we may look at individual
galaxies in a detailed and completely new way. As we had anticipated, our
observatory is producing a new image of the universe based on cosmic rays
instead of light."
The Pierre Auger Observatory records cosmic ray showers through an array of
1,600 particle detectors placed 1.5 kilometers (about one mile) apart in a
grid spread across 3,000 square kilometers (1,200 square miles). Twenty-four
specially designed telescopes record the emission of fluorescence light from
the air shower. The combination of particle detectors and fluorescence
telescopes provides an exceptionally powerful instrument for this research.
While the observatory has recorded almost a million cosmic-ray showers, only
the rare, highest-energy cosmic rays can be linked to their sources with
sufficient precision. Auger scientists so far have recorded 81 cosmic rays
with energy above 4 x 10**19 electron volts, or 40 EeV. This is the largest
number of cosmic rays with energy above 40 EeV recorded by any observatory.
At these ultra-high energies, the uncertainty in the direction from which
the cosmic ray arrived is only a few degrees, allowing scientists to
determine the location of the particle's cosmic source.
The Auger collaboration discovered that the 27 highest-energy events, with
energy above 57 EeV, do not come equally from all directions. Comparing the
clustering of these events with the known locations of 318 Active Galactic
Nuclei, the collaboration found that most of these events correlated well
with the locations of AGNs in some nearby galaxies, such as Centaurus A.
"Low-energy cosmic rays are abundant and come from all directions, mostly
from within our own Milky Way galaxy. Until now the only source of cosmic
ray particles known with certainty has been the Sun. Cosmic rays from other
likely sources such as exploding stars take meandering paths through space
so that when they reach Earth it is impossible to determine their origins.
But when you look at the highest-energy cosmic rays from the most violent
sources, they point back to their sources. The challenge now is to record
enough of these cosmic bullets to understand the processes that hurl them
into space," said Paul Mantsch, project manager of the Pierre Auger
Observatory.
Cosmic rays with energy higher than about 60 EeV lose energy in collisions
with the cosmic microwave background, radiation left over from the Big Bang
that fills all of space. But cosmic rays from nearby sources are less likely
to lose energy in collisions on their relatively short trip to Earth. Auger
scientists found that most of the 27 events with energy above 57 EeV came
from locations in the sky that include the nearest AGNs, within a few
hundred million light years of Earth.
Scientists think that most galaxies have black holes at their centers, with
masses ranging from a million to a few billion times the mass of our sun.
The black hole at the center of our Milky Way galaxy weighs about 3 million
solar masses, but it is not an AGN. Galaxies that have an AGN seem to be
those that suffered a collision with another galaxy or some other massive
disruption in the last few hundred million years. The AGN swallows the mass
coming its way while releasing prodigious amounts of radiation. The Auger
result indicates that AGNs may also produce the universe's highest-energy
particles.
Cosmic-ray astronomy is challenging, because low-energy cosmic rays provide
no reliable information on the location of their sources: as they travel
across the cosmos, they are deflected by galactic and intergalactic magnetic
fields that lead to blurry images. In contrast, the most energetic particles
come almost straight from their sources, as they are barely affected by the
magnetic fields. Unfortunately, they hit Earth at a rate of only about one
event per square kilometer per century, which demands a very large
observatory.
Because of its size, the Auger Observatory can record about 30
ultra-high-energy events per year. The Auger collaboration is developing
plans for a second, larger installation in Colorado to extend coverage to
the entire sky while substantially increasing the number of high-energy
events recorded.
"Our current results show the promising future of cosmic-ray astronomy,"
said Auger cospokesperson Giorgio Matthiae, of the University of Rome. "So
far we have installed 1400 of the 1600 particle detectors of the Auger
Observatory in Argentina. A northern site would let us look at more galaxies
and black holes, increasing the sensitivity of our observatory. There are
even more nearby AGNs in the northern sky than in the southern sky."
The Pierre Auger Observatory is being built by a team of more than 370
scientists and engineers from 17 countries.
"The collaboration is a true international partnership in which no country
contributed more than 25 percent of the US$54-million construction cost,"
said Danilo Zavrtanik, of the University of Nova Gorica and chair of the
Auger Collaboration Board. The names of the funding agencies contributing to
the Pierre Auger Observatory are found at
http://www.auger.org/contact/agencies.html
and the names of the participating institutions are listed at
http://www.auger.org/collaboration/auger_institutions.html
Groundbreaking for the southern hemisphere site of the Pierre Auger
Observatory took place on March 17, 1999, in Argentina's Mendoza Province.
Following a period of detector deployment and testing, scientific data
collection began in January, 2004.
"Argentina is pleased to host and participate in this unique scientific
endeavor," said Alberto Etchegoyen, of Comision Nacional de Energ Atomica,
and Southern Observatory spokesperson, "and now, looking back into these
years of efforts and excitement, a feeling of gratitude and respect arises
for all collaboration members who took care of every single minor detail
leading to today's announcement."
The observatory is named for French scientist Pierre Victor Auger
(1899-1993), who in 1938 was the first to observe the extensive air showers
generated by the interaction of high-energy cosmic rays with the Earth's
atmosphere.
[NOTE: Images supporting this release are available at
http://www.auger.org/media/image_highlights.html ]