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NASA’s Chandra Examines Milky Way at Arms’ Length
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NASA’s Chandra Examines Milky Way at Arms’ LengthTo view this video please enable JavaScript, and consider upgrading to a web browser that
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A new result using NASA’s Chandra X-ray Observatory shows that the outer spiral arms in the Milky Way galaxy may reach wider than previously thought. This finding may lead astronomers to adjust their understanding of our home galaxy’s structure.
A team of astronomers made this discovery by making precise measurements of distances to dust clouds in the Milky Way’s spiral arms using data from both NASA’s Chandra and XMM-Newton, an ESA (European Space Agency) mission with NASA contributions. The results are described in a new paper published Wednesday in the Astronomy & Astrophysics journal.
The researchers determined the distances by studying rings around gamma-ray bursts, some of the brightest bursts of light in the universe, which arise from the collapse of massive stars or the merger of neutron stars. They are located at enormous distances, well beyond the confines of our galaxy.
An artist’s concept showing the Milky Way galaxy as seen from above, with the estimated positions of spiral arms based on previous data, in blue. Overlaid on this is an updated view of the Milky Way showing different positions for the two outermost spiral arms, shown in red and bordered by dashed lines. Both arms may be more distant than previously thought, based on newly processed X-ray data from Chandra and XMM. NASA/CXC/SAO/M.Weiss
This distance measurement technique capitalized on the phenomenon of light echoes, where the light from the gamma-ray burst bounced off dust clouds in the spiral arms. The diameters of the rings in X-rays give the distances to Earth, with larger rings being generated by dust clouds closer to us.
“This is a very direct way – relying only on geometry – to precisely measure distances to the Milky Way’s spiral arms,” said Beatrice Vaia, who led the study while a PhD student in a joint program between Scuola Universitaria Superiore IUSS Pavia and University of Trento in Italy. “Most other methods rely on assumptions about how the Milky Way rotates, which become increasingly uncertain in the outer regions of our galaxy.”
Despite a century of awareness of the Milky Way’s spiral arms, astronomers are still working toward precise characterization of its arms because of Earth’s position within one. Dust and gas also block the view to other arms.
The researchers used three different gamma-ray bursts to determine the distances to three spiral arms in the Milky Way. In order of increasing distances from the Galactic Center, they are the Perseus, the Outer, and the Outer Scutum-Centaurus arms. Along the direction of one of the bursts, they found that both the Outer and Outer Scutum-Centaurus arms are about 10% more distant than astronomers previously thought.
“The differences are small, but any revision of these distances is important because they are so fundamental for understanding our galaxy,” said co-author Ilaria Fornasiero, who was a PhD student in the same program as the leading author. “For example, this could mean that astronomers have to revise estimates of the mass of the galaxy, because that affects how wide the arms stretch.”
The images include X-ray data from Chandra and optical data from Pan-STARRS. The composite image shows X-ray rings generated by a gamma-ray burst (GRB), a bright X-ray source located outside our galaxy. In a phenomenon called light echoes, the X-rays from the GRB bounced off dust clouds in the spiral arms of our galaxy. The diameters of the rings in the Chandra data give the distances of the dust clouds to Earth, with larger rings being generated by dust clouds closer to us. The GRB is located at the center of the circles defining the rings, to the left of the X-ray data outlined by the white square. X-ray: NASA/CXC/INAF/B. Vaia et al.; Optical: Pan-STARRS; Image processing: NASA/CXC/SAO/N.Wolk & P.Edmonds
The team also used their data to estimate that the dust cloud in the most distant arm is about 3,500 light-years wide. These findings show that their measurements apply to the full thickness of the spiral arm, rather than a random, isolated dust cloud that may not fully be representative of the arm’s location.
While this technique provided major improvements in accuracy according to the researchers, it may be difficult to use it for further measurements because bright gamma-ray bursts that are visible through the plane of the galaxy are rare.
“We’re relying on the universe to provide us with these events, and so far, over 25 years, we’ve only found a handful that we can use,” said co-author Andrea Tiengo of Scuola Universitaria Superiore IUSS Pavia. “That said, we will continue to be on the lookout for more.”
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory
To learn more about Chandra, visit:
To learn more about NASA’s Chandra mission, visit:
Visual DescriptionThis release features a short video and a series of images, all related to an updated understanding of our home galaxy’s structure. By studying rings of X-ray light echoes, researchers now believe that two of the Milky Way’s spiral arms may be more distant from the center of the galaxy than previously thought.
The updated understanding of the structure of the Milky Way is highlighted in a short video, which compares two artist concept images. In both images, our spiral Milky Way galaxy is shown face-on. It has a bright white core with several arms that spiral out from the center, like long thin clouds corkscrewing counterclockwise. The two longest arms make a full rotation of the spiral galaxy, and curve all the way around to the upper right of the images.
The first image in the video shows the previous understanding of the Milky Way. Here, the two longest arms are curled around the core in a fairly tight spiral. In the second image, which represents the updated understanding, the two longest arms are more loosely spiraled. Visually, this means there is more open space between the curving arms, which are further away from the bright galaxy core. The video fades back and forth between the two artist concept images to illustrate the structural differences between the two understandings.
These findings are further shown by a static image which overlays the new understanding on top of the earlier understanding. In this artist’s concept illustration, dotted lines and different colors are used to differentiate between the two.
A team of astronomers made this discovery by studying gamma-ray bursts that bounce off of dust clouds in the galaxy’s spiral arms. The resulting rings of X-rays, known as light echoes, were detected and mapped by NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. In a supplemental data image, the light echoes resemble concentric arches of neon blue dots trailing across a speckled sky.
Identifying the position of the Milky Way’s spiral arms through X-ray light echoes has allowed astronomers to use geometry, rather than assumptions about galaxy rotation, to better understand the structure of our galaxy.
Share Details Last Updated Jul 02, 2026 Editor Lee Mohon Contact Joel Wallace Megan Watzke Location Marshall Space Flight Center Related Terms Share Details Last Updated Jul 02, 2026 Editor Lee Mohon Contact Joel Wallace Megan Watzke Location Marshall Space Flight Center Related Terms Explore More 7 min read NASA’s Chandra Reveals ‘Red, White, Blue’ Universe for US 250thArticle
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NASA’s Chandra Examines Milky Way at Arms’ Length
5 min read
NASA’s Chandra Examines Milky Way at Arms’ LengthTo view this video please enable JavaScript, and consider upgrading to a web browser that
supports HTML5 video
A new result using NASA’s Chandra X-ray Observatory shows that the outer spiral arms in the Milky Way galaxy may reach wider than previously thought. This finding may lead astronomers to adjust their understanding of our home galaxy’s structure.
A team of astronomers made this discovery by making precise measurements of distances to dust clouds in the Milky Way’s spiral arms using data from both NASA’s Chandra and XMM-Newton, an ESA (European Space Agency) mission with NASA contributions. The results are described in a new paper published Wednesday in the Astronomy & Astrophysics journal.
The researchers determined the distances by studying rings around gamma-ray bursts, some of the brightest bursts of light in the universe, which arise from the collapse of massive stars or the merger of neutron stars. They are located at enormous distances, well beyond the confines of our galaxy.
An artist’s concept showing the Milky Way galaxy as seen from above, with the estimated positions of spiral arms based on previous data, in blue. Overlaid on this is an updated view of the Milky Way showing different positions for the two outermost spiral arms, shown in red and bordered by dashed lines. Both arms may be more distant than previously thought, based on newly processed X-ray data from Chandra and XMM. NASA/CXC/SAO/M.WeissThis distance measurement technique capitalized on the phenomenon of light echoes, where the light from the gamma-ray burst bounced off dust clouds in the spiral arms. The diameters of the rings in X-rays give the distances to Earth, with larger rings being generated by dust clouds closer to us.
“This is a very direct way – relying only on geometry – to precisely measure distances to the Milky Way’s spiral arms,” said Beatrice Vaia, who led the study while a PhD student in a joint program between Scuola Universitaria Superiore IUSS Pavia and University of Trento in Italy. “Most other methods rely on assumptions about how the Milky Way rotates, which become increasingly uncertain in the outer regions of our galaxy.”
Despite a century of awareness of the Milky Way’s spiral arms, astronomers are still working toward precise characterization of its arms because of Earth’s position within one. Dust and gas also block the view to other arms.
The researchers used three different gamma-ray bursts to determine the distances to three spiral arms in the Milky Way. In order of increasing distances from the Galactic Center, they are the Perseus, the Outer, and the Outer Scutum-Centaurus arms. Along the direction of one of the bursts, they found that both the Outer and Outer Scutum-Centaurus arms are about 10% more distant than astronomers previously thought.
“The differences are small, but any revision of these distances is important because they are so fundamental for understanding our galaxy,” said co-author Ilaria Fornasiero, who was a PhD student in the same program as the leading author. “For example, this could mean that astronomers have to revise estimates of the mass of the galaxy, because that affects how wide the arms stretch.”
The images include X-ray data from Chandra and optical data from Pan-STARRS. The composite image shows X-ray rings generated by a gamma-ray burst (GRB), a bright X-ray source located outside our galaxy. In a phenomenon called light echoes, the X-rays from the GRB bounced off dust clouds in the spiral arms of our galaxy. The diameters of the rings in the Chandra data give the distances of the dust clouds to Earth, with larger rings being generated by dust clouds closer to us. The GRB is located at the center of the circles defining the rings, to the left of the X-ray data outlined by the white square. X-ray: NASA/CXC/INAF/B. Vaia et al.; Optical: Pan-STARRS; Image processing: NASA/CXC/SAO/N.Wolk & P.EdmondsThe team also used their data to estimate that the dust cloud in the most distant arm is about 3,500 light-years wide. These findings show that their measurements apply to the full thickness of the spiral arm, rather than a random, isolated dust cloud that may not fully be representative of the arm’s location.
While this technique provided major improvements in accuracy according to the researchers, it may be difficult to use it for further measurements because bright gamma-ray bursts that are visible through the plane of the galaxy are rare.
“We’re relying on the universe to provide us with these events, and so far, over 25 years, we’ve only found a handful that we can use,” said co-author Andrea Tiengo of Scuola Universitaria Superiore IUSS Pavia. “That said, we will continue to be on the lookout for more.”
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory
To learn more about Chandra, visit:
To learn more about NASA’s Chandra mission, visit:
Visual DescriptionThis release features a short video and a series of images, all related to an updated understanding of our home galaxy’s structure. By studying rings of X-ray light echoes, researchers now believe that two of the Milky Way’s spiral arms may be more distant from the center of the galaxy than previously thought.
The updated understanding of the structure of the Milky Way is highlighted in a short video, which compares two artist concept images. In both images, our spiral Milky Way galaxy is shown face-on. It has a bright white core with several arms that spiral out from the center, like long thin clouds corkscrewing counterclockwise. The two longest arms make a full rotation of the spiral galaxy, and curve all the way around to the upper right of the images.
The first image in the video shows the previous understanding of the Milky Way. Here, the two longest arms are curled around the core in a fairly tight spiral. In the second image, which represents the updated understanding, the two longest arms are more loosely spiraled. Visually, this means there is more open space between the curving arms, which are further away from the bright galaxy core. The video fades back and forth between the two artist concept images to illustrate the structural differences between the two understandings.
These findings are further shown by a static image which overlays the new understanding on top of the earlier understanding. In this artist’s concept illustration, dotted lines and different colors are used to differentiate between the two.
A team of astronomers made this discovery by studying gamma-ray bursts that bounce off of dust clouds in the galaxy’s spiral arms. The resulting rings of X-rays, known as light echoes, were detected and mapped by NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. In a supplemental data image, the light echoes resemble concentric arches of neon blue dots trailing across a speckled sky.
Identifying the position of the Milky Way’s spiral arms through X-ray light echoes has allowed astronomers to use geometry, rather than assumptions about galaxy rotation, to better understand the structure of our galaxy.
Share Details Last Updated Jul 02, 2026 Editor Lee Mohon Contact Joel Wallace Megan Watzke Location Marshall Space Flight Center Related Terms Share Details Last Updated Jul 02, 2026 Editor Lee Mohon Contact Joel Wallace Megan Watzke Location Marshall Space Flight Center Related Terms Explore More 7 min read NASA’s Chandra Reveals ‘Red, White, Blue’ Universe for US 250thArticle
2 days ago
5 min read NASA’s Chandra Discovers Possible Supernova Remnant in Galactic Center
Article
3 weeks ago
5 min read NASA Finds Young Stars Dim in X-rays Surprisingly Quickly
Article
3 months ago
Keep Exploring Discover More Topics From NASA
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Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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NASA is recruiting research participants for the agency’s next simulated deep space mission. Beginning no earlier than August 2027, research volunteers will spend one year living and working in interplanetary environments at the agency’s Johnson Space Center in Houston, operating under isolated conditions expected during crewed missions to the Moon or Red Planet.
Insights from this new, yearlong experience, called the Moon and Mars Exploration Analog, can be used to help keep astronauts safe and mission-ready during future planetary surface operations. The results also could inform plans for a sustained lunar presence through the agency’s Moon Base and future Artemis missions.
NASA is looking for applicants for the approximately year-long mission simulation, which will take place in two confined habitats. In addition to specific physical and education requirements, volunteers must be willing to take part in a multi-day selection process and pass NASA’s physical and psychological assessments, found on the Moon and Mars Exploration Analog web page. Candidates also should have a strong desire for unique, rewarding experiences, and interest in contributing to NASA’s work to prepare for extended stays on the lunar surface and the first crewed mission to Mars.
The Moon and Mars Exploration Analog evolves elements of the agency’s HERA (Human Exploration Research Analog) and CHAPEA (Crew Health And Performance Exploration Analog) missions into a single, integrated mission to streamline how researchers evaluate astronaut adaptation across the full range of potential mission scenarios. Using the HERA habitat as a spacecraft and the CHAPEA habitat as a base, the volunteers will live and work in confined, isolated environments that simulate months-long flights to and from other planetary surfaces. They also will mimic surface operations, including mock Mars walks and using a rover to travel to exploration sites located beyond the main habitat.
Throughout the Moon and Mars Exploration Analog mission, researchers will study crew health and performance under resource limitations and mission demands. These missions also help NASA assess and validate hardware, technologies, protocols, requirements, and other systems designed to support crew health and performance on long-duration deep space missions, all without leaving Earth. The effort will provide valuable data for NASA’s Human Research Program, which innovates ways to keep astronauts healthy and mission-ready.
To apply, visit:
As part of the Golden Age of innovation and exploration, NASA will send astronauts on increasingly difficult missions to explore more of the Moon for scientific discovery, economic benefits, establish an enduring human presence on the lunar surface, and to build on the foundation for the first crewed missions to Mars.
For more about NASA’s Human Research Program, visit:
NASA Seeks Volunteers for New Yearlong Simulated Moon, Mars Mission
NASA is recruiting research participants for the agency’s next simulated deep space mission. Beginning no earlier than August 2027, research volunteers will spend one year living and working in interplanetary environments at the agency’s Johnson Space Center in Houston, operating under isolated conditions expected during crewed missions to the Moon or Red Planet.
Insights from this new, yearlong experience, called the Moon and Mars Exploration Analog, can be used to help keep astronauts safe and mission-ready during future planetary surface operations. The results also could inform plans for a sustained lunar presence through the agency’s Moon Base and future Artemis missions.
NASA is looking for applicants for the approximately year-long mission simulation, which will take place in two confined habitats. In addition to specific physical and education requirements, volunteers must be willing to take part in a multi-day selection process and pass NASA’s physical and psychological assessments, found on the Moon and Mars Exploration Analog web page. Candidates also should have a strong desire for unique, rewarding experiences, and interest in contributing to NASA’s work to prepare for extended stays on the lunar surface and the first crewed mission to Mars.
The Moon and Mars Exploration Analog evolves elements of the agency’s HERA (Human Exploration Research Analog) and CHAPEA (Crew Health And Performance Exploration Analog) missions into a single, integrated mission to streamline how researchers evaluate astronaut adaptation across the full range of potential mission scenarios. Using the HERA habitat as a spacecraft and the CHAPEA habitat as a base, the volunteers will live and work in confined, isolated environments that simulate months-long flights to and from other planetary surfaces. They also will mimic surface operations, including mock Mars walks and using a rover to travel to exploration sites located beyond the main habitat.
Throughout the Moon and Mars Exploration Analog mission, researchers will study crew health and performance under resource limitations and mission demands. These missions also help NASA assess and validate hardware, technologies, protocols, requirements, and other systems designed to support crew health and performance on long-duration deep space missions, all without leaving Earth. The effort will provide valuable data for NASA’s Human Research Program, which innovates ways to keep astronauts healthy and mission-ready.
To apply, visit:
As part of the Golden Age of innovation and exploration, NASA will send astronauts on increasingly difficult missions to explore more of the Moon for scientific discovery, economic benefits, establish an enduring human presence on the lunar surface, and to build on the foundation for the first crewed missions to Mars.
For more about NASA’s Human Research Program, visit:
LINK Spacecraft Set for Mission to Boost NASA's Swift Observatory
LINK Spacecraft Set for Mission to Boost NASA’s Swift Observatory
A first-of-its-kind mission to raise the orbit of NASA’s Neil Gehrels Swift Observatory is poised for launch no earlier than Thursday, July 2, 5:09 a.m. EDT (9:09 p.m. UTC+12), from Kwajalein Atoll, part of the Republic of the Marshall Islands in the South Pacific Ocean. A robotic servicing spacecraft called LINK, built by Katalyst Space, will blast into orbit on a Northrop Grumman Pegasus XL rocket attached to the belly of the company’s Stargazer aircraft, shown here in this photograph from the evening of Tuesday, June 16, 2026.
After launch, LINK will attempt to rendezvous with, grapple, and slowly raise Swift’s altitude over several months, preventing it from re-entering Earth’s atmosphere later this year. If this daring mission is successful, it will be the first time a commercial robotic mission has captured a NASA spacecraft that is both uncrewed and not originally designed to be serviced in space.
Follow the Swift blog to learn more about the mission.
Image credit: NASA/Ron Beard
LINK Spacecraft Set for Mission to Boost NASA’s Swift Observatory
A first-of-its-kind mission to raise the orbit of NASA’s Neil Gehrels Swift Observatory is poised for launch no earlier than Thursday, July 2, 5:09 a.m. EDT (9:09 p.m. UTC+12), from Kwajalein Atoll, part of the Republic of the Marshall Islands in the South Pacific Ocean. A robotic servicing spacecraft called LINK, built by Katalyst Space, will blast into orbit on a Northrop Grumman Pegasus XL rocket attached to the belly of the company’s Stargazer aircraft, shown here in this photograph from the evening of Tuesday, June 16, 2026.
After launch, LINK will attempt to rendezvous with, grapple, and slowly raise Swift’s altitude over several months, preventing it from re-entering Earth’s atmosphere later this year. If this daring mission is successful, it will be the first time a commercial robotic mission has captured a NASA spacecraft that is both uncrewed and not originally designed to be serviced in space.
Follow the Swift blog to learn more about the mission.
Image credit: NASA/Ron Beard