December 13, 2012
New Results Pave Way For Future Of X-ray Astrophysics Research
Lee Rannals for redOrbit.com — Your Universe Online
Scientists are paving the way for future X-ray astrophysics research by explaining why observations from orbiting X-ray telescopes do not match theoretical predictions.
The team used powerful X-rays from the Linac Coherent Light Source (LCLS) at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory to study and measure a key process at work in extreme plasmas like those found in stars, black holes and other cosmic objects.
The 28-person team dissected a process in multi-million-degree space plasmas that produces some of the brightest cosmic X-ray signals.
"Measurements conducted at the LCLS will be important for interpreting X-ray emissions from a plethora of sources, including black holes, X-ray binaries, stellar coronae and supernova remnants, to name a few," Gregory V. Brown, a physicist at Lawrence Livermore National Laboratory (LLNL) who participated in the research, said in a statement.
In order to model and analyze the extreme forces and conditions that generate X-ray emissions from these extreme objects, scientists use a combination of computer simulations and observations from space telescopes.
However, when studying an "Fe16-plus" iron ion, these methods produced conflicting results. This iron nucleus with only 10 probing electrons is of particular interest because it produces some of the brightest cosmic X-ray signals. However, satellite measurements show these signals are more than 30 percent dimmer than leading theories predict.
Researchers thought this was because computer models failed to show collisions between the iron ions and electrons. The scientists turned to direct measurements in the laboratory to get to the bottom of it.
They created and trapped Fe16-plus ions using a device known as an electron beam ion trap, or EBIT. They then used the X-ray laser to probe and measure the properties of the ions.
The scientists discovered that collisions with electrons were not a factor at all.
"Our results show that the problem, or at least a large part of the problem, lies in our ability to model the structure of the ions," which is crucial for understanding the larger physical processes taking place in celestial sources, Brown said.
Some of the scientists have already started new calculations to improve the atomic-scale astrophysical models, while others analyze data from follow-up experiments conducted at LCLS in April.
"Almost everything we know in astrophysics comes from spectroscopy," team member Maurice Leutenegger of NASA's Goddard Space Flight Center who participated in the study, said in the statement.
He said that spectroscopy is used to measure and study X-ray and other signatures, and the LCLS results are valuable in a variety of astrophysical context.
Max Plank Institute for Nuclear Physics developed the EBIT instrument used in the experiments.
"We all had very little sleep for weeks in a row, but the scientific payoff was well worth it." Sven Bernitt, a graduate student from Heidelberg, who was in charge of the campaign, said in a statement.
The researchers reported their findings in the journal Nature.