Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NASA-funded X-ray Instrument Settles Interstellar Debate

30.07.2014

New findings from a NASA-funded instrument have resolved a decades-old puzzle about a fog of low-energy X-rays observed over the entire sky.

Thanks to refurbished detectors first flown on a NASA sounding rocket in the 1970s, astronomers have now confirmed the long-held suspicion that much of this glow stems from a region of million-degree interstellar plasma known as the local hot bubble, or LHB. 


This animation illustrates solar wind charge exchange in action. An atom of interstellar helium (blue) collides with a solar wind ion (red), losing one of its electrons (yellow) to the other particle. As it settles into a lower-energy state, the electron emits a soft X-ray.

Image Credit: NASA's Goddard Space Flight Center

At the same time, the study also establishes upper limits on the amount of low-energy, or soft, X-rays produced within our planetary system by the solar wind, a gusty outflow of charged particles emanating from the sun.

"Interactions between the solar wind and neutral atoms in comets, the outer atmospheres of planets, and even interstellar gas produce soft X-rays," explained team member Steve Snowden, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We need to account for these processes because the X-rays they produce complicate our observations of the wider universe."

Decades of mapping the sky in X-rays with energies around 250 electron volts -- about 100 times the energy of visible light -- revealed strong emission precisely where it shouldn't be. This glow, known as the soft X-ray diffuse background, is surprisingly bright in the gas-rich central plane of our galaxy, where it should be strongly absorbed. This suggested the background was a local phenomenon, arising from a bubble of hot gas extending out a few hundred light-years from the solar system in all directions.

Improved measurements also made it increasingly clear that the sun resides in a region where interstellar gas is unusually sparse. Taken together, the evidence suggests our solar system is moving through a region that may have been blasted clear by one or more supernova explosions during the past 20 million years.

In the 1990s, a six-month all-sky survey by the German X-ray observatory ROSAT provided improved maps of the diffuse background, but it also revealed that comets were an unexpected source of soft X-rays. As scientists began to understand this process, called solar wind charge exchange, they realized it could occur anywhere neutral atoms interacted with solar wind ions.

Within the last decade, some scientists have been challenging the LHB interpretation, suggesting that much of the soft X-ray diffuse background is a result of charge exchange," said F. Scott Porter, a Goddard astrophysicist also participating in the study. "The only way to check is to design an instrument and make measurements." 

Led by Massimiliano Galeazzi, a professor of physics at the University of Miami in Coral Gables, Florida, an international collaboration developed a mission to do just that. The team includes scientists from NASA, the University of Wisconsin -- Madison, the University of Michigan at Ann Arbor, the University of Kansas at Lawrence, Johns Hopkins University in Baltimore, Maryland, the French National Center for Scientific Research (CNRS), headquartered in Paris, and other institutions.

Galeazzi and his colleagues rebuilt, tested, calibrated, and adapted X-ray detectors originally designed by the University of Wisconsin and flown on sounding rockets in the 1970s. Components from another instrument flown on space shuttle Endeavour in 1993 also were given new life. The mission was named DXL, for Diffuse X-ray emission from the Local Galaxy. 

On Dec. 12, 2012, DXL launched from White Sands Missile Range in New Mexico atop a NASA Black Brant IX sounding rocket, reaching a peak altitude of 160 miles (258 km) and spending five minutes above Earth's atmosphere. The mission design allowed the instrument to observe a worst-case scenario involving charge exchange with interstellar gas.

The solar system is currently passing through a small cloud of cold interstellar gas as it moves through the galaxy. The cloud’s neutral hydrogen and helium atoms stream through the planetary system at about 56,000 mph (90,000 km/h). While hydrogen atoms quickly ionize and respond to numerous forces, the helium atoms travel paths largely governed by the sun's gravity. This creates a "helium focusing cone" downstream from the sun that crosses Earth's orbit and is located high in the sky near midnight in early December.

"This helium focusing creates a region with a much greater density of neutral atoms and a correspondingly enhanced charge exchange rate," Snowden said.

The solar wind is accelerated in the sun's corona, the hottest part of its atmosphere, so its atoms have been ionized -- stripped of many of their electrons. When a neutral atom collides with a solar wind ion, one of its electrons often jumps to the charged particle. Once captured by the ion, the electron briefly remains in an excited state, then emits a soft X-ray and settles down at a lower energy. This is solar wind charge exchange in action.

To establish a baseline for the soft X-ray background, the researchers used data captured by the ROSAT mission in September 1990 in a direction looking along, rather than into, the helium focusing cone. The results, published online in the journal Nature on July 27, indicate that only about 40 percent of the soft X-ray background originates within the solar system.

"We now know that the emission comes from both sources but is dominated by the local hot bubble,” said Galeazzi. "This is a significant discovery. Specifically, the existence or nonexistence of the local bubble affects our understanding of the area of the galaxy close to the sun, and can, therefore, be used as a foundation for future models of the galaxy structure."

Galeazzi and his collaborators are already planning the next flight of DXL, which will include additional instruments to better characterize the emission. The launch is currently planned for December 2015.

"The DXL team is an extraordinary example of cross-disciplinary science, bringing together astrophysicists, planetary scientists, and heliophysicists," added Porter. "It’s unusual but very rewarding when scientists with such diverse interests come together to produce such groundbreaking results."

Related Links:

Download HD video and additional images from NASA Goddard's Scientific Visualization Studio

Paper: "The Origin of the Local 1/4-keV X-ray Flux in Both Charge Exchange and a Hot Bubble"

Paper: "Pressure Equilibrium between the Local Interstellar Clouds and the Local Hot Bubble"

DXL Launches Successfully (12.13.2012)

Imagine the Universe! The Soft X-ray Diffuse Background 

Francis Reddy

NASA's Goddard Space Flight Center, Greenbelt, Maryland

Francis Reddy | Eurek Alert!

Further reports about: NASA ROSAT X-ray atmosphere energy interstellar measurements planetary system supernova explosions

More articles from Physics and Astronomy:

nachricht Nanotechnology for energy materials: Electrodes like leaf veins
27.09.2016 | Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

nachricht First quantum photonic circuit with electrically driven light source
27.09.2016 | Westfälische Wilhelms-Universität Münster

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First quantum photonic circuit with electrically driven light source

Optical quantum computers can revolutionize computer technology. A team of researchers led by scientists from Münster University and KIT now succeeded in putting a quantum optical experimental set-up onto a chip. In doing so, they have met one of the requirements for making it possible to use photonic circuits for optical quantum computers.

Optical quantum computers are what people are pinning their hopes on for tomorrow’s computer technology – whether for tap-proof data encryption, ultrafast...

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

Im Focus: Complex hardmetal tools out of the 3D printer

For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.

Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...

Im Focus: Launch of New Industry Working Group for Process Control in Laser Material Processing

At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.

In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Laser use for neurosurgery and biofabrication - LaserForum 2016 focuses on medical technology

27.09.2016 | Event News

Experts from industry and academia discuss the future mobile telecommunications standard 5G

23.09.2016 | Event News

ICPE in Graz for the seventh time

20.09.2016 | Event News

 
Latest News

New switch decides between genome repair and death of cells

27.09.2016 | Life Sciences

Nanotechnology for energy materials: Electrodes like leaf veins

27.09.2016 | Physics and Astronomy

‘Missing link’ found in the development of bioelectronic medicines

27.09.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>