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Hubble Space Telescope Home NASA’s Hubble Sees… Hubble Space Telescope Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts News Hubble News Hubble News Archive Social Media Media Resources Multimedia Multimedia Images Videos Sonifications Podcasts E-books Lithographs Fact Sheets Glossary Posters Hubble on the NASA App More Online Activities 5 Min Read NASA’s Hubble Sees Aftermath of Galaxy’s Scrape with Milky Way
This artist’s concept shows a closeup of the Large Magellanic Cloud, a dwarf galaxy that is one of the Milky Way galaxy’s nearest neighbors. Credits:
NASA, ESA, Ralf Crawford (STScI) A story of survival is unfolding at the outer reaches of our galaxy, and NASA’s Hubble Space Telescope is witnessing the saga.
The Large Magellanic Cloud, also called the LMC, is one of the Milky Way galaxy’s nearest neighbors. This dwarf galaxy looms large on the southern nighttime sky at 20 times the apparent diameter of the full Moon.
Many researchers theorize that the LMC is not in orbit around our galaxy, but is just passing by. These scientists think that the LMC has just completed its closest approach to the much more massive Milky Way. This passage has blown away most of the spherical halo of gas that surrounds the LMC.
Now, for the first time, astronomers been able to measure the size of the LMC’s halo – something they could do only with Hubble. In a new study to be published in The Astrophysical Journal Letters, researchers were surprised to find that it is so extremely small, about 50,000 light-years across. That’s around 10 times smaller than halos of other galaxies that are the LMC’s mass. Its compactness tells the story of its encounter with the Milky Way.
“The LMC is a survivor,” said Andrew Fox of AURA/STScI for the European Space Agency in Baltimore, who was principal investigator on the observations. “Even though it’s lost a lot of its gas, it’s got enough left to keep forming new stars. So new star-forming regions can still be created. A smaller galaxy wouldn’t have lasted – there would be no gas left, just a collection of aging red stars.”
This artist’s concept shows the Large Magellanic Cloud, or LMC, in the foreground as it passes through the gaseous halo of the much more massive Milky Way galaxy. The encounter has blown away most of the spherical halo of gas that surrounds the LMC, as illustrated by the trailing gas stream reminiscent of a comet’s tail. Still, a compact halo remains, and scientists do not expect this residual halo to be lost. The team surveyed the halo by using the background light of 28 quasars, an exceptionally bright type of active galactic nucleus that shines across the universe like a lighthouse beacon. Their light allows scientists to “see” the intervening halo gas indirectly through the absorption of the background light. The lines represent the Hubble Space Telescope’s view from its orbit around Earth to the distant quasars through the LMC’s gas. NASA, ESA, Ralf Crawford (STScI)
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Though quite a bit worse for wear, the LMC still retains a compact, stubby halo of gas – something that it wouldn’t have been able to hold onto gravitationally had it been less massive. The LMC is 10 percent the mass of the Milky Way, making it heftier than most dwarf galaxies.
“Because of the Milky Way’s own giant halo, the LMC’s gas is getting truncated, or quenched,” explained STScI’s Sapna Mishra, the lead author on the paper chronicling this discovery. “But even with this catastrophic interaction with the Milky Way, the LMC is able to retain 10 percent of its halo because of its high mass.”
A Gigantic Hair Dryer
Most of the LMC’s halo was blown away due to a phenomenon called ram-pressure stripping. The dense environment of the Milky Way pushes back against the incoming LMC and creates a wake of gas trailing the dwarf galaxy – like the tail of a comet.
“I like to think of the Milky Way as this giant hairdryer, and it’s blowing gas off the LMC as it comes into us,” said Fox. “The Milky Way is pushing back so forcefully that the ram pressure has stripped off most of the original mass of the LMC’s halo. There’s only a little bit left, and it’s this small, compact leftover that we’re seeing now.”
As the ram pressure pushes away much of the LMC’s halo, the gas slows down and eventually will rain into the Milky Way. But because the LMC has just gotten past its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the whole halo will be lost.
Only with Hubble
To conduct this study, the research team analyzed ultraviolet observations from the Mikulski Archive for Space Telescopes at STScI. Most ultraviolet light is blocked by the Earth’s atmosphere, so it cannot be observed with ground-based telescopes. Hubble is the only current space telescope tuned to detect these wavelengths of light, so this study was only possible with Hubble.
The team surveyed the halo by using the background light of 28 bright quasars. The brightest type of active galactic nucleus, quasars are believed to be powered by supermassive black holes. Shining like lighthouse beacons, they allow scientists to “see” the intervening halo gas indirectly through the absorption of the background light. Quasars reside throughout the universe at extreme distances from our galaxy.
This artist’s concept illustrates the Large Magellanic Cloud’s (LMC’s) encounter with the Milky Way galaxy’s gaseous halo. In the top panel, at the middle of the right side, the LMC begins crashing through our galaxy’s much more massive halo. The bright purple bow shock represents the leading edge of the LMC’s halo, which is being compressed as the Milky Way’s halo pushes back against the incoming LMC. In the middle panel, part of the halo is being stripped and blown back into a streaming tail of gas that eventually will rain into the Milky Way. The bottom panel shows the progression of this interaction, as the LMC’s comet-like tail becomes more defined. A compact LMC halo remains. Because the LMC is just past its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the residual halo will be lost. NASA, ESA, Ralf Crawford (STScI)
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The scientists used data from Hubble’s Cosmic Origins Spectrograph (COS) to detect the presence of the halo’s gas by the way it absorbs certain colors of light from background quasars. A spectrograph breaks light into its component wavelengths to reveal clues to the object’s state, temperature, speed, quantity, distance, and composition. With COS, they measured the velocity of the gas around the LMC, which allowed them to determine the size of the halo.
Because of its mass and proximity to the Milky Way, the LMC is a unique astrophysics laboratory. Seeing the LMC’s interplay with our galaxy helps scientists understand what happened in the early universe, when galaxies were closer together. It also shows just how messy and complicated the process of galaxy interaction is.
Looking to the Future
The team will next study the front side of the LMC’s halo, an area that has not yet been explored.
“In this new program, we are going to probe five sightlines in the region where the LMC’s halo and the Milky Way’s halo are colliding,” said co-author Scott Lucchini of the Center for Astrophysics | Harvard & Smithsonian. “This is the location where the halos are compressed, like two balloons pushing against each other.”
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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Last Updated Nov 14, 2024 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
Astrophysics Astrophysics Division Galaxies Hubble Space Telescope Irregular Galaxies Spiral Galaxies The Milky Way Keep Exploring Discover More Topics From NASA
Hubble Space Telescope
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
NASA’s X-59 quiet supersonic research aircraft sits in its run stall at Lockheed Martin’s Skunk Works facility in Palmdale, California, firing up its engine for the first time. These engine-run tests start at low power and allow the X-59 team to verify the aircraft’s systems are working together while powered by its own engine. The X-59 is the centerpiece of NASA’s Quesst mission, which seeks to solve one of the major barriers to supersonic flight over land by making sonic booms quieter.NASA/Carla Thomas NASA’s Quesst mission marked a major milestone with the start of tests on the engine that will power the quiet supersonic X-59 experimental aircraft.
These engine-run tests, which began Oct. 30, allow the X-59 team to verify the aircraft’s systems are working together while powered by its own engine. In previous tests, the X-59 used external sources for power. The engine-run tests set the stage for the next phase of the experimental aircraft’s progress toward flight.
The X-59 team is conducting the engine-run tests in phases. In this first phase, the engine rotated at a relatively low speed without ignition to check for leaks and ensure all systems are communicating properly. The team then fueled the aircraft and began testing the engine at low power, with the goal of verifying that it and other aircraft systems operate without anomalies or leaks while on engine power.
Lockheed Martin test pilot Dan Canin sits in the cockpit of NASA’s X-59 quiet supersonic research aircraft in a run stall at Lockheed Martin’s Skunk Works facility in Palmdale, California prior to its first engine run. These engine-run tests featured the X-59 powered by its own engine, whereas in previous tests, the aircraft depended on external sources for power. The X-59 is the centerpiece of NASA’s Quesst mission, which seeks to solve one of the major barriers to supersonic flight over land by making sonic booms quieter.NASA/Carla Thomas “The first phase of the engine tests was really a warmup to make sure that everything looked good prior to running the engine,” said Jay Brandon, NASA’s X-59 chief engineer. “Then we moved to the actual first engine start. That took the engine out of the preservation mode that it had been in since installation on the aircraft. It was the first check to see that it was operating properly and that all the systems it impacted – hydraulics, electrical system, environmental control systems, etc. – seemed to be working.”
The X-59 will generate a quieter thump rather than a loud boom while flying faster than the speed of sound. The aircraft is the centerpiece of NASA’s Quesst mission, which will gather data on how people perceive these thumps, providing regulators with information that could help lift current bans on commercial supersonic flight over land.
The engine, a modified F414-GE-100, packs 22,000 pounds of thrust, which will enable the X-59 to achieve the desired cruising speed of Mach 1.4 (925 miles per hour) at an altitude of approximately 55,000 feet. It sits in a nontraditional spot – atop the aircraft — to aid in making the X-59 quieter.
Engine runs are part of a series of integrated ground tests needed to ensure safe flight and successful achievement of mission goals. Because of the challenges involved with reaching this critical phase of testing, the X-59’s first flight is now expected in early 2025. The team will continue progressing through critical ground tests and address any technical issues discovered with this one-of-a-kind, experimental aircraft. The X-59 team will have a more specific first flight date as these tests are successfully completed.
The testing is taking place at Lockheed Martin’s Skunk Works facility in Palmdale, California. During later phases, the team will test the aircraft at high power with rapid throttle changes, followed by simulating the conditions of an actual flight.
NASA’s X-59 quiet supersonic research aircraft sits in its run stall at Lockheed Martin’s Skunk Works facility in Palmdale, California, prior to its first engine run. Engine runs are part of a series of integrated ground tests needed to ensure safe flight and successful achievement of mission goals. The X-59 is the centerpiece of NASA’s Quesst mission, which seeks to solve one of the major barriers to supersonic flight over land by making sonic booms quieter.NASA/Carla Thomas “The success of these runs will be the start of the culmination of the last eight years of my career,” said Paul Dees, NASA’s deputy propulsion lead for the X-59. “This isn’t the end of the excitement but a small steppingstone to the beginning. It’s like the first note of a symphony, where years of teamwork behind the scenes are now being put to the test to prove our efforts have been effective, and the notes will continue to play a harmonious song to flight.”
After the engine runs, the X-59 team will move to aluminum bird testing, where data will be fed to the aircraft under both normal and failure conditions. The team will then proceed with a series of taxi tests, where the aircraft will be put in motion on the ground. These tests will be followed by final preparations for first flight.
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Last Updated Nov 06, 2024 EditorLillian GipsonContactMatt Kamletmatthew.r.kamlet@nasa.gov Related Terms
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By European Space Agency
An international team of astronomers has used the NASA/ESA/CSA James Webb Space Telescope to detect the first brown dwarf candidates outside the Milky Way in the star cluster NGC 602.
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By NASA
On Oct. 18, 1989, space shuttle Atlantis took off on its fifth flight, STS-34, from NASA’s Kennedy Space Center (KSC) in Florida. Its five-person crew of Commander Donald E. Williams, Pilot Michael J. McCulley, and Mission Specialists Shannon W. Lucid, Franklin R. Chang-Díaz, and Ellen S. Baker flew a five-day mission that deployed the Galileo spacecraft, managed by NASA’s Jet Propulsion Laboratory in Southern California, to study Jupiter. The astronauts deployed Galileo and its upper stage on their first day in space, sending the spacecraft on its six-year journey to the giant outer planet. Following its arrival at Jupiter in December 1995, Galileo deployed its atmospheric probe while the main spacecraft entered orbit around the planet, studying it in great detail for eight years.
Left: The STS-34 crew of Mission Specialists Shannon W. Lucid, sitting left, Franklin R. Chang-Díaz, and Ellen S. Baker; Commander Donald E. Williams, standing left, and Pilot Michael J. McCulley. Middle: The STS-34 crew patch. Right: The Galileo spacecraft in Atlantis’ payload bay in preparation for STS-34.
In November 1988, NASA announced Williams, McCulley, Lucid, Chang-Díaz, and Baker as the STS-34 crew for the flight planned for October 1989. Williams and Lucid, both from the Class of 1978, had each flown once before, on STS-51D in April 1985 and STS-51G in June 1985, respectively. Chang-Díaz, selected in 1980, had flown once before on STS-61C in January 1986, while for McCulley and Baker, both selected in 1984, STS-34 represented their first spaceflight. During their five-day mission, the astronauts planned to deploy Galileo and its Inertial Upper Stage (IUS) on the first flight day. Following the Galileo deployment, the astronauts planned to conduct experiments in the middeck and the payload bay.
Left: Voyager 2 image of Jupiter. Middle: Galileo as it appeared in 1983. Right: Illustration of Galileo’s trajectory from Earth to Jupiter.
Following the successful Pioneer and Voyager flyby missions, NASA’s next step to study Jupiter in depth involved an ambitious orbiter and atmospheric entry probe. NASA first proposed the Jupiter Orbiter Probe mission in 1975, and Congress approved it in 1977 for a planned 1982 launch on the space shuttle. In 1978, NASA renamed the spacecraft Galileo after the 17th century Italian astronomer who turned his new telescope toward Jupiter and discovered its four largest moons. Delays in the shuttle program and changes in the upper stage to send Galileo from low Earth orbit on to Jupiter resulted in the slip of its launch to May 1986, when on Atlantis’ STS-61G mission, a Centaur upper stage would send the spacecraft toward Jupiter.
The January 1986 Challenger accident not only halted shuttle flights for 31 months but also canceled the Centaur as an upper stage for the orbiter. Remanifested onto the less powerful IUS, Galileo would require gravity assist maneuvers at Venus and twice at Earth to reach its destination, extending the transit time to six years. Galileo’s launch window extended from Oct. 12 to Nov. 21, 1989, dictated by planetary alignments required for the gravity assists. During the transit, Galileo had the opportunity to pass by two main belt asteroids, providing the first closeup study of this class of objects. Upon arrival at Jupiter, Galileo would release its probe to return data as it descended through Jupiter’s atmosphere while the main spacecraft would enter an elliptical orbit around the planet, from which it would conduct in depth studies for a minimum of 22 months.
Left: The Galileo atmospheric probe during preflight processing. Middle: The Galileo orbiter during preflight processing. Right: Space shuttle Atlantis arrives at Launch Pad 39B.
The Galileo atmospheric probe arrived at KSC on April 17 and the main spacecraft on May 16, following which workers joined the two together for preflight testing. Meanwhile, Atlantis returned to KSC on May 15, following the STS-30 mission that deployed the Magellan spacecraft to Venus. The next day workers towed it into the Orbiter Processing Facility to prepare it for STS-34. In KSC’s Vehicle Assembly Building (VAB), workers began stacking the Solid Rocket Boosters (SRB) on June 15, completing the activity on July 22, and then adding the External Tank (ET) on July 30. Atlantis rolled over to the VAB on Aug. 22 for mating with the ET and SRBs. Galileo, now mated to its IUS, transferred to Launch Pad 39B on Aug. 25, awaiting Atlantis’ arrival four days later.
The next day, workers placed Galileo into Atlantis’ payload bay and began preparations for the Oct. 12 launch. The Terminal Countdown Demonstration Test took place on Sept. 14-15, with the astronauts participating in the final few hours as on launch day. A faulty computer aboard the IUS threatened to delay the mission, but workers replaced it without impacting the planned launch date. The five-member astronaut crew arrived at KSC Oct. 9 for final preparations for the flight and teams began the countdown for launch. A main engine controller problem halted the countdown at T minus 19 hours. The work required to replace it pushed the launch date back to Oct. 17. On that day, the weather at the pad supported a launch, but clouds and rain at the Shuttle Landing Facility several miles away, and later rain at a Transatlantic (TAL) abort site, violated launch constraints, so managers called a 24-hour scrub. The next day, the weather cooperated at all sites, and other than a brief hold to reconfigure Atlantis’ computers from one TAL site to another, the countdown proceeded smoothly.
Left: STS-34 astronauts pose following their Sept. 6 preflight press conference. Middle: Liftoff of Atlantis on the STS-34 mission. Right: Controllers in the Firing Room watch Atlantis take to the skies.
Atlantis lifted off Launch Pad 39B at 12:53 p.m. EDT on Oct. 18. As soon as the shuttle cleared the launch tower, control shifted to the Mission Control Center at NASA’s Johnson Space Center in Houston, where Ascent Flight Director Ronald D. Dittemore and his team of controllers, including astronaut Frank L. Culbertson serving as the capsule communicator, or capcom, monitored all aspects of the launch. Following main engine cutoff, Atlantis and its crew had achieved orbit. Forty minutes later, a firing of the two Orbital Maneuvering System (OMS) engines circularized the orbit at 185 miles. The astronauts removed their bulky Launch and Entry Suits (LES) and prepared Atlantis for orbital operations, including opening the payload bay doors.
Left: Galileo and its Inertial Upper Stage (IUS) in Atlantis’ payload bay, just before deployment. Middle: Galileo and its IUS moments after deployment. Right: Galileo departs from the shuttle.
Preparations for Galileo’s deployment began shortly thereafter. In Mission Control, Flight Director J. Milton Heflin and his team, including capcom Michael A. Baker, took over to assist the crew with deployment operations. The astronauts activated Galileo and the IUS, and ground teams began checking out their systems, with the first TV from the mission showing the spacecraft and its upper stage in the payload bay. Lucid raised Galileo’s tilt table first to 29 degrees, McCulley oriented Atlantis to the deployment attitude, then Lucid raised the tilt table to the deploy position of 58 degrees. With all systems operating normally, Mission Control gave the go for deploy.
Six hours and 20 minutes into the mission, Lucid deployed the Jupiter-bound spacecraft and its upper stage, weighing a combined 38,483 pounds. “Galileo is on its way to another world,” Williams called down. The combination glided over the shuttle’s crew compartment. Williams and McCulley fired the two OMS engines to move Atlantis a safe distance away from the IUS burn that took place one hour after deployment, sending Galileo on its circuitous journey through the inner solar system before finally heading to Jupiter. The primary task of the mission accomplished, the astronauts prepared for their first night’s sleep in space.
STS-34 crew Earth observation photographs. Left: The Dallas-Ft. Worth Metroplex. Middle left: Jamaica. Middle right: Greece. Right: The greater Tokyo area with Mt. Fuji at upper left.
For the next three days, the STS-34 astronauts focused their attention on the middeck and payload bay experiments, as well as taking photographs of the Earth. Located in the payload bay, the Shuttle Solar Backscatter Ultraviolet experiment, managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, measured ozone in the Earth’s atmosphere and compared the results with data obtained by weather satellites at the same locations. The comparisons served to calibrate the weather satellite instruments. Baker conducted the Growth Hormone Concentrations and Distributions in Plants experiment, that investigated the effect of the hormone Auxin in corn shoot tissue. Three days into the mission, she placed plant canisters into a freezer to arrest plant growth and for postflight analysis. Chang-Díaz and Lucid had prime responsibility for the Polymer Morphology experiment, developed by the 3M Company. They used a laptop to control experiment parameters as the hardware melted different samples to see the effects of weightlessness. Baker conducted several medical investigations, including studying blood vessels in the retina, changes in leg volume due to fluid shifts, and carotid blood flow.
Left: The Shuttle Solar Backscatter Ultraviolet experiment in Atlantis’ payload bay. Middle: Ellen S. Baker, right, performs a carotid blood flow experiment on Franklin R. Chang-Díaz. Right: Chang-Díaz describes the Polymer Mixing experiment.
Left: The STS-34 crew poses on Atlantis’ fight deck. Middle: Atlantis touches down at Edwards Air Force Base in California. Right: The STS-34 astronauts pose in front of Atlantis.
On Oct. 23, the astronauts awakened for their final day in space. Because of high winds expected at the primary landing site at Edwards Air Force Base (AFB), managers moved the landing up by two revolutions. In preparation for reentry, the astronauts donned their orange LESs and closed the payload bay doors. Williams and McCulley oriented Atlantis into the deorbit attitude, with the OMS engines facing in the direction of travel. Over the Indian Ocean, they fired the two engines for 2 minutes 48 seconds to bring the spacecraft out of orbit. They reoriented the orbiter to fly with its heat shield exposed to the direction of flight as it encountered Earth’s atmosphere at 419,000 feet. The buildup of ionized gases caused by the heat of reentry prevented communications for about 15 minutes but provided the astronauts a great light show. The entry profile differed slightly from the planned one because Atlantis needed to make up 500 miles of cross range since it returned two orbits early. After completing the Heading Alignment Circle turn, Williams aligned Atlantis with the runway, and McCulley lowered the landing gear. Atlantis touched down and rolled to a stop, ending a 4-day 23-hour 39-minute flight, having completed 79 orbits of the Earth. Following postlanding inspections, workers placed Atlantis atop a Shuttle Carrier Aircraft, a modified Boeing-747, and the combination left Edwards on Oct. 28. Following refueling stops at Biggs Army Airfield in Texas and Columbus AFB in Mississippi, Atlantis and the SCA arrived back at KSC on Oct. 29. Workers began to prepare it for its next flight, STS-36 in February 1990.
Left: An illustration of Galileo in orbit around Jupiter. Right: Galileo’s major mission events, including encounters with Jupiter’s moons during its eight-year orbital study.
One hour after deployment from Atlantis, the IUS ignited to send Galileo on its six-year journey to Jupiter, with the spacecraft flying free of the rocket stage 47 minutes later. The spacecraft’s circuitous path took it first to Venus on Feb. 10, 1990, back to Earth on Dec. 8, 1990, and again on Dec. 8, 1992, each time picking up velocity from the gravity assist to send it on to the giant planet. Along the way, Galileo also passed by and imaged the main belt asteroids Gaspra and Ida and observed the crash of Comet Shoemaker-Levy 9 onto Jupiter. On Dec. 7, 1995, the probe plummeted through Jupiter’s dense atmosphere, returning data along the way, until it succumbed to extreme pressures and temperatures. Meanwhile, Galileo entered orbit around Jupiter and far exceeded its 22-month primary mission, finally plunging into the giant planet on Sept. 21, 2003, 14 years after leaving Earth. During its 35 orbits around Jupiter, it studied not only the planet but made close observations of many of its moons, especially its four largest ones, Ganymede, Callisto, Europa, and Io.
Left: Galileo image of could formations on Jupiter. Right: Closeup image of terrain on Europa.
Of particular interest to many scientists, Galileo made 11 close encounters with icy Europa, coming as close as 125 miles, revealing incredible details about its surface. Based on Galileo data, scientists now believe a vast ocean lies beneath Europa’s icy crust, and heating from inside the moon may produce conditions favorable for supporting life. NASA’s Europa Clipper, launched on Oct. 14, 2024, hopes to expand on Galileo’s observations when it reaches Jupiter in April 2030.
Enjoy the crew narrated video of the STS-34 mission. Read Williams‘ recollections of the STS-34 mission in his oral history with the JSC History Office.
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By NASA
The study of X-ray emission from astronomical objects reveals secrets about the Universe at the largest and smallest spatial scales. Celestial X-rays are produced by black holes consuming nearby stars, emitted by the million-degree gas that traces the structure between galaxies, and can be used to predict whether stars may be able to host planets hospitable to life. X-ray observations have shown that most of the visible matter in the universe exists as hot gas between galaxies and have conclusively demonstrated that the presence of “dark matter” is needed to explain galaxy cluster dynamics, that dark matter dominates the mass of galaxy clusters, and that it governs the expansion of the cosmos.
X-ray observations also enable us to probe mysteries of the Universe on the smallest scales. X-ray observations of compact objects such as white dwarfs, neutron stars, and black holes allow us to use the Universe as a physics laboratory to study conditions that are orders of magnitude more extreme in terms of density, pressure, temperature, and magnetic field strength than anything that can be produced on Earth. In this astrophysical laboratory, researchers expect to reveal new physics at the subatomic scale by conducting investigations such as probing the neutron star equation of state and testing quantum electrodynamics with observations of neutron star atmospheres. At NASA’s Marshall Space Flight Center, a team of scientists and engineers is building, testing, and flying innovative optics that bring the Universe’s X-ray mysteries into sharper focus.
A composite X-ray/Optical/Infrared image of the Crab Pulsar. The X-ray image from the Chandra X-ray Observatory (blue and white), reveals exquisite details in the central ring structures and gas flowing out of the polar jets. Optical light from the Hubble Space Telescope (purple) shows foreground and background stars as pinpoints of light. Infrared light from the Spitzer Space Telescope (pink) traces cooler gas in the nebula. Finally, magnetic field direction derived from X-ray polarization observed by the Imaging X-ray Polarimetry Explorer is shown as orange lines. Magnetic field lines: NASA/Bucciantini et al; X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech Unlike optical telescopes that create images by reflecting or refracting light at near-90-degree angles (normal incidence), focusing X-ray optics must be designed to reflect light at very small angles (grazing incidence). At normal incidence, X-rays are either absorbed by the surface of a mirror or penetrate it entirely. However, at grazing angles of incidence, X-rays reflect very efficiently due to an effect called total external reflection. In grazing incidence, X-rays reflect off the surface of a mirror like rocks skipping on the surface of a pond.
A classic design for astronomical grazing incidence optics is the Wolter-I prescription, which consists of two reflecting surfaces, a parabola and hyperbola (see figure below). This optical prescription is revolved around the optical axis to produce a full-shell mirror (i.e., the mirror spans the full circumference) that resembles a gently tapered cone. To increase the light collecting area, multiple mirror shells with incrementally larger diameters and a common focus are fabricated and nested concentrically to comprise a mirror module assembly (MMA).
Focusing optics are critical to studying the X-ray universe because, in contrast to other optical systems like collimators or coded masks, they produce high signal-to-noise images with low background noise. Two key metrics that characterize the performance of X-ray optics are angular resolution, which is the ability of an optical system to discriminate between closely spaced objects, and effective area, which is the light collecting area of the telescope, typically quoted in units of cm2. Angular resolution is typically measured as the half-power diameter (HPD) of a focused spot in units of arcseconds. The HPD encircles half of the incident photons in a focused spot and measures the sharpness of the final image; a smaller number is better.
Schematic of a full-shell Wolter-I X-ray optic mirror module assembly with five concentrically nested mirror shells. Parallel rays of light enter from the left, reflect twice off the reflective inside surface of the shell (first off the parabolic segment and then off the hyperbolic segment), and converge at the focal plane. NASA MSFC NASA Marshall Space Flight Center (MSFC) has been building and flying lightweight, full-shell, focusing X-ray optics for over three decades, always meeting or exceeding angular resolution and effective area requirements. MSFC utilizes an electroformed nickel replication (ENR) technique to make these thin full-shell X-ray optics from nickel alloy.
X-ray optics development at MSFC began in the early 1990s with the fabrication of optics to support NASA’s Advanced X-ray Astrophysics Facility (AXAF-S) and then continued via the Constellation-X technology development programs. In 2001, MSFC launched a balloon payload that included two modules each with three mirrors, which produced the first focused hard X-ray (>10 keV) images of an astrophysical source by imaging Cygnus X-1, GRS 1915, and the Crab Nebula. This initial effort resulted in several follow-up missions over the next 12 years, and became known as the High Energy Replicated Optics (HERO) balloon program.
In 2012, the first of four sounding rocket flights of the Focusing Optics X-ray Solar Imager (FOXSI) flew with MSFC optics onboard, producing the first focused images of the Sun at energies greater than 5 keV. In 2019 the Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) instrument on the Spectr-Roentgen-Gamma Mission launched with seven MSFC-fabricated X-ray MMAs, each containing 28 mirror shells. ART-XC is currently mapping the sky in the 4-30 keV hard X-ray energy range, studying exotic objects like neutron stars in our own galaxy as well as active galactic nuclei, which are spread across the visible universe. In 2021, the Imaging X-ray Polarimetry Explorer (IXPE), flew and is now performing extraordinary science with an MSFC-led team using three, 24-shell MMAs that were fabricated and calibrated in-house.
Most recently, in 2024, the fourth FOXSI sounding rocket campaign launched with a high-resolution MSFC MMA. The optics achieved 9.5 arcsecond HPD angular resolution during pre-flight test with an expected 7 arcsecond HPD in gravity-free flight, making this the highest angular resolution flight observation made with a nickel-replicated X-ray optic. Currently MSFC is fabricating an MMA for the Rocket Experiment Demonstration of a Soft X-ray (REDSoX) polarimeter, a sounding rocket mission that will fly a novel soft X-ray polarimeter instrument to observe active galactic nuclei. The REDSoX MMA optic will be 444 mm in diameter, which will make it the largest MMA ever produced by MSFC and the second largest replicated nickel X-ray optic in the world.
Scientists Wayne Baumgartner (left, crouched) and Nick Thomas (left, standing) calibrate an IXPE MMA in the MSFC 100 m Beamline. Scientist Stephen Bongiorno (right) applies epoxy to an IXPE shell during MMA assembly. NASA MSFC The ultimate performance of an X-ray optic is determined by errors in the shape, position, and roughness of the optical surface. To push the performance of X-ray optics toward even higher angular resolution and achieve more ambitious science goals, MSFC is currently engaged in a fundamental research and development effort to improve all aspects of full-shell optics fabrication.
Given that these optics are made with the Electroformed Nickel Replication technique, the fabrication process begins with creation of a replication master, called the mandrel, which is a negative of the desired optical surface. First, the mandrel is figured and polished to specification, then a thin layer of nickel alloy is electroformed onto the mandrel surface. Next, the nickel alloy layer is removed to produce a replicated optical shell, and finally the thin shell is attached to a stiff holding structure for use.
Each step in this process imparts some degree of error into the final replicated shell. Research and development efforts at MSFC are currently concentrating on reducing distortion induced during the electroforming metal deposition and release steps. Electroforming-induced distortion is caused by material stress built into the electroformed material as it deposits onto the mandrel. Decreasing release-induced distortion is a matter of reducing adhesion strength between the shell and mandrel, increasing strength of the shell material to prevent yielding, and reducing point defects in the release layer.
Additionally, verifying the performance of these advanced optics requires world-class test facilities. The basic premise of testing an optic designed for X-ray astrophysics is to place a small, bright X-ray source far away from the optic. If the angular size of the source, as viewed from the optic, is smaller than the angular resolution of the optic, the source is effectively simulating X-ray starlight. Due to the absorption of X-rays by air, the entire test facility light path must be placed inside a vacuum chamber.
At MSFC, a group of scientists and engineers operate the Marshall 100-meter X-ray beamline, a world-class end-to-end test facility for flight and laboratory X-ray optics, instruments, and telescopes. As per the name, it consists of a 100-meter-long vacuum tube with an 8-meter-long, 3-meter-diameter instrument chamber and a variety of X-ray sources ranging from 0.25 – 114 keV. Across the street sits the X-Ray and Cryogenic Facility (XRCF), a 527-meter-long beamline with an 18-meter-long, 6-meter-diameter instrument chamber. These facilities are available for the scientific community to use and highlight the comprehensive optics development and test capability that Marshall is known for.
Within the X-ray astrophysics community there exist a variety of angular resolution and effective area needs for focusing optics. Given its storied history in X-ray optics, MSFC is uniquely poised to fulfill requirements for large or small, medium- or high-angular-resolution X-ray optics. To help guide technology development, the astrophysics community convenes once per decade to produce a decadal survey. The need for high-angular-resolution and high-throughput X-ray optics is strongly endorsed by the National Academies of Sciences, Engineering, and Medicine report, Pathways to Discovery in Astronomy and Astrophysics for the 2020s.In pursuit of this goal, MSFC is continuing to advance the state of the art in full-shell optics. This work will enable the extraordinary mysteries of the X-ray universe to be revealed.
Project Leads
Dr. Jessica Gaskin and Dr. Stephen Bongiorno, NASA Marshall Space Flight Center (MSFC)
Sponsoring Organizations
The NASA Astrophysics Division supports this work primarily through the Internal Scientist Funding Model Direct Work Package and competed solicitations. This work is also supported by the Heliophysics Division through competed solicitations, as well as by directed work from other government entities.
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Last Updated Oct 15, 2024 Related Terms
Astrophysics Astrophysics Division Marshall Astrophysics Marshall Space Flight Center Science-enabling Technology Technology Highlights Explore More
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