Showing posts with label BLACK HOLES. Show all posts
Showing posts with label BLACK HOLES. Show all posts
Saturday, May 30, 2015
Friday, October 10, 2014
Thursday, February 20, 2014
SUPERCOMPUTER SIMULATIONS RECREATE X-RAYS FROM AREA OF A BLACK HOLE
FROM: NATIONAL SCIENCE FOUNDATION
Let there be light
Simulations on NSF-supported supercomputer re-create X-rays emerging from the neighborhood of black holes
February 18, 2014
Black holes may be dark, but the areas around them definitely are not. These dense, spinning behemoths twist up gas and matter just outside their event horizon, and generate heat and energy that gets radiated, in part, as light. And when black holes merge, they produce a bright intergalactic burst that may act as a beacon for their collision.
Astrophysicists became deeply interested in black holes in the 1960s, but the idea of their event horizon was first intimated in a paper by Karl Schwarzschild published after Einstein introduced general relativity in 1915.
Knowledge about black holes--these still-unseen objects--has grown tremendously in recent years. Part of this growth comes from researchers' ability to use detailed numerical models and powerful supercomputers to simulate the complex dynamics near a black hole. This is no trivial matter. Warped spacetime, gas pressure, ionizing radiation, magnetized plasma--the list of phenomena that must be included in an accurate simulation goes on and on.
"It's not something that you want to do with a paper and pencil," said Scott Noble, an astrophysicist at the Rochester Institute of Technology (RIT).
Working with Jeremy Schnittman of Goddard Space Flight Center and Julian Krolik of Johns Hopkins University, Noble and his colleagues created a new tool that predicts the light that an accreting black hole would produce. They did so by modeling how photons hit gas particles in the disk around the black hole (also known as an accretion disk), generating light--specifically light in the X-ray spectrum--and producing signals detected with today's most powerful telescopes.
In their June 2013 paper in the Astrophysical Journal, the researchers presented the results of a new global radiation transport code coupled to a relativistic simulation of an accreting, non-rotating black hole. For the first time, they were able to re-create and explain nearly all the components seen in the X-ray spectra of stellar-mass black holes.
The ability to generate realistic light signals from a black hole simulation is a first and brings with it the possibility of explaining a whole host of observations taken with multiple X-ray satellites during the past 40 years.
"We felt excited and also incredibly lucky, like we'd turned up ten heads in a row," Noble said. "The simulations are very challenging and if you don't get it just right, it won't give you an accurate answer. This was the first time that people have put all of the pieces together from first principles in such a thorough way."
The simulations are the combined results of two computational codes. One, Harm3d, re-creates the three-dimensional dynamics of a black hole accreting gas, including its magnetohydrodynamics (MHD), which charts the interplay of electrically conducting fluids like plasmas and a powerful magnetic field.
"The magnetic field is important in the area outside the black hole because it whips the gas around and can dictate its dynamics," Noble said. "Also, the movement of the field can lead to it kinking and trigger a reconnection event that produces an explosive burst of energy, turning magnetic field energy into heat."
Though the MHD forces are critical near the black hole, it is the X-rays these forces generate that can be observed. The second component, a radiative transport code called Pandurata, simulates what real photons do.
"They bounce around inside the gas, they reflect off the disk's surface, and their wavelengths change along the way," he explained. "Eventually, they reach some distant light collector--a numerically approximated observer--which provides the predicted light output of our simulation."
The researchers' simulations were run on the Ranger supercomputer at the Texas Advanced Computing Center, built with support from the National Science Foundation, which also funded the group's research.
The simulations were the highest resolution thin disk simulations ever performed, with the most points and the smallest length-scales for numerical cells, allowing the researchers to resolve very small features. Varying only the rate at which the black holes accrete gas, they were able to reproduce the wide range of X-ray states seen in observations of most galactic black hole sources.
With each passing year, the significance of black holes--and their role in shaping the cosmos--grows.
Nearly every good-sized galaxy has a supermassive black hole at its center, said Julian Krolik, a professor of physics and astronomy at Johns Hopkins University. For periods of a few to tens of million years at a time, black holes accrete incredible amounts of gas ultimately released as huge amounts of energy--as much as a hundred times the power output of all the stars in a black hole host galaxy put together.
"Some of that energy can travel out into their surrounding galaxies as ionizing light or fast-moving jets of ionized gas," Krolik continued. "As a result, so much heat can be deposited in the gas orbiting around in those galaxies that it dramatically alters the way they make new stars. It's widely thought that processes like this are largely responsible for regulating how many stars big galaxies hold."
In this way black holes may act as cosmic regulators--all the more reason to use numerical simulations to uncover further clues about how black holes interact with gas, stars and other supermassive black holes.
Said Noble: "To see that it works and reproduces the observational data when the observational data is so complicated...it's really remarkable."
-- Aaron Dubrow, NSF
Investigators
Scott Noble
Julian Krolik
Jeremy Schnittman
John Boisseau
Karl Schulz
Omar Ghattas
Tommy Minyard
Yosef Zlochower
Manuela Campanelli
Related Institutions/Organizations
Rochester Institute of Tech
Johns Hopkins University
Goddard Space Flight Center
University of Texas at Austin
Let there be light
Simulations on NSF-supported supercomputer re-create X-rays emerging from the neighborhood of black holes
February 18, 2014
Black holes may be dark, but the areas around them definitely are not. These dense, spinning behemoths twist up gas and matter just outside their event horizon, and generate heat and energy that gets radiated, in part, as light. And when black holes merge, they produce a bright intergalactic burst that may act as a beacon for their collision.
Astrophysicists became deeply interested in black holes in the 1960s, but the idea of their event horizon was first intimated in a paper by Karl Schwarzschild published after Einstein introduced general relativity in 1915.
Knowledge about black holes--these still-unseen objects--has grown tremendously in recent years. Part of this growth comes from researchers' ability to use detailed numerical models and powerful supercomputers to simulate the complex dynamics near a black hole. This is no trivial matter. Warped spacetime, gas pressure, ionizing radiation, magnetized plasma--the list of phenomena that must be included in an accurate simulation goes on and on.
"It's not something that you want to do with a paper and pencil," said Scott Noble, an astrophysicist at the Rochester Institute of Technology (RIT).
Working with Jeremy Schnittman of Goddard Space Flight Center and Julian Krolik of Johns Hopkins University, Noble and his colleagues created a new tool that predicts the light that an accreting black hole would produce. They did so by modeling how photons hit gas particles in the disk around the black hole (also known as an accretion disk), generating light--specifically light in the X-ray spectrum--and producing signals detected with today's most powerful telescopes.
In their June 2013 paper in the Astrophysical Journal, the researchers presented the results of a new global radiation transport code coupled to a relativistic simulation of an accreting, non-rotating black hole. For the first time, they were able to re-create and explain nearly all the components seen in the X-ray spectra of stellar-mass black holes.
The ability to generate realistic light signals from a black hole simulation is a first and brings with it the possibility of explaining a whole host of observations taken with multiple X-ray satellites during the past 40 years.
"We felt excited and also incredibly lucky, like we'd turned up ten heads in a row," Noble said. "The simulations are very challenging and if you don't get it just right, it won't give you an accurate answer. This was the first time that people have put all of the pieces together from first principles in such a thorough way."
The simulations are the combined results of two computational codes. One, Harm3d, re-creates the three-dimensional dynamics of a black hole accreting gas, including its magnetohydrodynamics (MHD), which charts the interplay of electrically conducting fluids like plasmas and a powerful magnetic field.
"The magnetic field is important in the area outside the black hole because it whips the gas around and can dictate its dynamics," Noble said. "Also, the movement of the field can lead to it kinking and trigger a reconnection event that produces an explosive burst of energy, turning magnetic field energy into heat."
Though the MHD forces are critical near the black hole, it is the X-rays these forces generate that can be observed. The second component, a radiative transport code called Pandurata, simulates what real photons do.
"They bounce around inside the gas, they reflect off the disk's surface, and their wavelengths change along the way," he explained. "Eventually, they reach some distant light collector--a numerically approximated observer--which provides the predicted light output of our simulation."
The researchers' simulations were run on the Ranger supercomputer at the Texas Advanced Computing Center, built with support from the National Science Foundation, which also funded the group's research.
The simulations were the highest resolution thin disk simulations ever performed, with the most points and the smallest length-scales for numerical cells, allowing the researchers to resolve very small features. Varying only the rate at which the black holes accrete gas, they were able to reproduce the wide range of X-ray states seen in observations of most galactic black hole sources.
With each passing year, the significance of black holes--and their role in shaping the cosmos--grows.
Nearly every good-sized galaxy has a supermassive black hole at its center, said Julian Krolik, a professor of physics and astronomy at Johns Hopkins University. For periods of a few to tens of million years at a time, black holes accrete incredible amounts of gas ultimately released as huge amounts of energy--as much as a hundred times the power output of all the stars in a black hole host galaxy put together.
"Some of that energy can travel out into their surrounding galaxies as ionizing light or fast-moving jets of ionized gas," Krolik continued. "As a result, so much heat can be deposited in the gas orbiting around in those galaxies that it dramatically alters the way they make new stars. It's widely thought that processes like this are largely responsible for regulating how many stars big galaxies hold."
In this way black holes may act as cosmic regulators--all the more reason to use numerical simulations to uncover further clues about how black holes interact with gas, stars and other supermassive black holes.
Said Noble: "To see that it works and reproduces the observational data when the observational data is so complicated...it's really remarkable."
-- Aaron Dubrow, NSF
Investigators
Scott Noble
Julian Krolik
Jeremy Schnittman
John Boisseau
Karl Schulz
Omar Ghattas
Tommy Minyard
Yosef Zlochower
Manuela Campanelli
Related Institutions/Organizations
Rochester Institute of Tech
Johns Hopkins University
Goddard Space Flight Center
University of Texas at Austin
Wednesday, December 11, 2013
UNDERSTANDING A STAR'S SURFACE AND THE EXTREME FORCES OF NATURE
Credit: NASA's Goddard Space Flight Center
Neutron Stars’ X-ray
STORY FROM: LOS ALAMOS NATIONAL LABORATORY
Superbursts Mystify, Inspire Los Alamos Scientists
New neutrino cooling theory changes understanding of stars’ surface
LOS ALAMOS, N.M., Dec. 6, 2013—Massive X-ray superbursts near the surface of neutron stars are providing a unique window into the operation of fundamental forces of nature under extreme conditions.
“Scientists are intrigued by what exactly powers these massive explosions, and understanding this would yield important insights about the fundamental forces in nature, especially on the astronomical/cosmological scale,” said Peter Moller of Los Alamos National Laboratory’s Theoretical Division.
A neutron star is created during the death of a giant star more massive than the sun, compressed to a tiny size but with gravitational fields exceeded only by those of black holes. And in the intense, neutron-rich environment, nuclear reactions cause strong explosions that manifest themselves as X-ray bursts and the X-ray superbursts that are more rare and 1000 times more powerful.
Los Alamos researchers and former postdocs contributed to the paper “Strong neutrino cooling by cycles of electron capture and beta decay in neutron star crusts” that was published in Nature’s online edition of Dec. 1, 2013.
The importance of discovering an unknown energy source of titanic magnitude in the outermost layers of accreting neutron star surfaces is heightened by the unresolved issue of neutrino masses, the recent discovery of the Higgs boson and the fact that highly-neutron-rich nuclei with low-lying states enable “Weak Interactions,” prominent in stellar explosions. (The weak nuclear force is one of four fundamental sources, such as gravity, which interacts with the neutrinos; it is responsible for some types of radioactive decay.)
These hitherto celestially operative nuclei are expected to be within the experimental reach of the Facility for Rare Isotope Beams (FRIB), a proposed user facility at Michigan State University funded by the U.S. Department of Energy Office of Science.
“The terrestrial experimental study of Weak Interactions in highly deformed, neutron-rich nuclei that FRIB can potentially provide is lent support by this ground-breaking Nature letter, since Los Alamos has been one of the few homes to theoretical studies of deformed nuclei and their role in astrophysics, and remains so to this day,” said Moller, who coauthored the paper with a multidisciplinary team including former Los Alamos postdoctoral researchers Sanjib Gupta, now a faculty member at the Indian Institute of Technology (IIT), Ropar and Andrew Steiner, now a research assistant professor at INT, Seattle.
Previously a common assumption was that that the energy released in these radioactive decays would power the X-ray superburst explosions. This was based on simple models of nuclear beta-decay, sometimes postulating the same decay properties for all nuclei. It turns out, however, that it is of crucial importance to develop computer models that realistically describe the shape of each individual nuclide since they are not all spherical.
At Los Alamos scientists have carried out detailed calculations of the specific, individual beta-decay properties of thousands of nuclides, all with different decay properties, and created databases with these calculated properties.
The databases are then used at MSU as input into models that trace the decay pathways with the passage of time in accreting neutron stars and compute the total energy that is released in these reactions.
The new, unexpected result is that so much energy escapes by neutrino emission that the remaining energy released in the beta decays is not sufficient to ignite the X-ray superbursts that are observed. Thus the superbursts’ origin has now become a puzzle.
Solving the puzzle will require that we calculate in detail the consequences of shapes of neutron-rich nuclei, the authors said, and it requires that they simultaneously analyze the role played by neutrinos in neutron star X-ray bursts whose energetic magnitudes are exceeded only by explosions in the nova/supernova class.
The strong nuclear deformations that formed the basis for the neutrino cooling in neutron star crusts also play a role in a number of astrophysical settings, and have been taken into account in studies of supernovae explosions and subsequent collapses, funded by Los Alamos’ Laboratory Directed Research and Development (LDRD) programs.
Nuclear-structure databases valued worldwide
The large databases compiled by use of these and other nuclear-structure models are also used in several other Los Alamos programs. For example in modeling nuclear-reactor behavior, researchers have had to take into account beta-decay both because delayed neutrons are emitted, which governs the criticality of the reactor, and because it generates heat, just as in the neutron star.
Another current application is in nuclear non-proliferation programs. One method for detecting clandestine nuclear material in cargo shipments is to bombard cargoes with a small number of neutrons. If emission of delayed neutrons is detected after neutron bombardment, scientists have a sure signature of fissile nuclear material. The theoretical databases compiled at Los Alamos are not just used internally but are also part of nuclear-structure databases maintained by the International Atomic Energy Agency.
The authors, an international team
The authors on the paper are Hendrik Schatz from MSU; Sanjib Gupta from IIT Ropar; Peter Mller from LANL; Mary Beard and Michael Wiescher from the University of Notre Dame; Edward F. Brown, Alex T. Deibel, Laurens Keek, and Rita Lau from MSU; Leandro R. Gasques from the Universidade de Sao Paulo; William Raphael Hix from Oak Ridge National Laboratory and the University of Tennessee; and Andrew W. Steiner from the University of Washington.
Sunday, September 23, 2012
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