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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
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ESA/NASA’s SOHO Spies Bright Comet Making Debut in Evening Sky
The tail of comet C/2023 A3 Tsuchinshan-ATLAS spanned the view of the Solar and Heliospheric Observatory (SOHO) on Oct. 10, 2024. ESA/NASA The ESA (European Space Agency) and NASA Solar and Heliospheric Observatory (SOHO) has captured images of the second-brightest comet to ever pass through its field of view during the spacecraft’s nearly 29-year career.
The bright comet is C/2023 A3 Tsuchinshan-ATLAS, which has been garnering a lot of attention from skywatchers recently, displaying a long, dusty tail in pre-dawn skies throughout late September and early October. (Comet McNaught, viewed in 2007, holds the record as the brightest comet SOHO has seen.)
Between Oct. 7 and 11, the comet blazed through the view of SOHO’s LASCO (Large Angle and Spectrometric Coronagraph Experiment) instrument, which uses a disk to block out the bright light of the Sun so it’s easier to see details and objects near the Sun. This image, taken by SOHO on Oct. 10, 2024, shows the comet and its bright tail streaming from the upper left to the right. Mercury appears as a bright dot on the left.
After crossing through SOHO’s field of view, the comet will begin putting on an evening show for skywatchers around the world just after sunset starting Saturday, Oct. 12. Each day throughout October, the comet will gradually rise higher and higher in the western sky as it moves farther away from the Sun. But as it does, it will become fainter and fainter. Eagle-eyed skywatchers may be able to spot it with the naked eye for a few days, but after that, observers will likely need binoculars or a telescope to see it as it grows fainter.
Even if you are unable to spot this comet yourself, you can help SOHO search for others. Scientists and members of the general public have discovered more than 5,000 comets in SOHO imagery, and you can help find even more by visiting the Sungrazer Project.
By Vanessa Thomas
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Oct 11, 2024 Related Terms
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Via NASA Plane, Scientists Find New Gamma-ray Emission in Storm Clouds
Tropical thunderstorm with lightning, near the airport of Santa Marta, Colombia. Credit: Oscar van der Velde There’s more to thunderclouds than rain and lightning. Along with visible light emissions, thunderclouds can produce intense bursts of gamma rays, the most energetic form of light, that last for millionths of a second. The clouds can also glow steadily with gamma rays for seconds to minutes at a time.
Researchers using NASA airborne platforms have now found a new kind of gamma-ray emission that’s shorter in duration than the steady glows and longer than the microsecond bursts. They’re calling it a flickering gamma-ray flash. The discovery fills in a missing link in scientists’ understanding of thundercloud radiation and provides new insights into the mechanisms that produce lightning. The insights, in turn, could lead to more accurate lightning risk estimates for people, aircraft, and spacecraft.
Researchers from the University of Bergen in Norway led the study in collaboration with scientists from NASA’s Marshall Space Flight Center in Huntsville, Alabama, and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the U.S. Naval Research Laboratory, and multiple universities in the U.S., Mexico, Colombia, and Europe. The findings were described in a pair of papers in Nature, published Oct. 2.
The international research team made their discovery while flying a battery of detectors aboard a NASA ER-2 research aircraft. In July 2023, the ER-2 set out on a series of 10 flights from MacDill Air Force Base in Tampa, Florida. The plane flew figure-eight flight patterns a few miles above tropical thunderclouds in the Caribbean and Central America, providing unprecedented views of cloud activity.
The scientific payload was developed for the Airborne Lightning Observatory for Fly’s Eye Geostationary Lightning Mapper Simulator and Terrestrial Gamma-ray Flashes (ALOFT) campaign. Instrumentation in the payload included weather radars along with multiple sensors for measuring gamma rays, lightning flashes, and microwave emissions from clouds.
NASA’s high-flying ER-2 airplane carries instrumentation in this artist’s impression of the ALOFT mission to record gamma rays (colored purple for illustration) from thunderclouds.Credit: NASA/ALOFT team The researchers had hoped ALOFT instruments would observe fast radiation bursts known as terrestrial gamma-ray flashes (TGFs). The flashes, first discovered in 1992 by NASA’s Compton Gamma Ray Observatory spacecraft, accompany some lightning strikes and last only millionths of a second. Despite their high intensity and their association with visible lightning, few TGFs have been spotted during previous aircraft-based studies.
“I went to a meeting just before the ALOFT campaign,” said principal investigator Nikolai Østgaard, a space physicist with the University of Bergen. “And they asked me: ‘How many TGFs are you going to see?’ I said: ‘Either we’ll see zero, or we’ll see a lot.’ And then we happened to see 130.”
However, the flickering gamma-ray flashes were a complete surprise.
“They’re almost impossible to detect from space,” said co-principal investigator Martino Marisaldi, who is also a University of Bergen space physicist. “But when you are flying at 20 kilometers [12.5 miles] high, you’re so close that you will see them.” The research team found more than 25 of these new flashes, each lasting between 50 to 200 milliseconds.
The abundance of fast bursts and the discovery of intermediate-duration flashes could be among the most important thundercloud discoveries in a decade or more, said University of New Hampshire physicist Joseph Dwyer, who was not involved in the research. “They’re telling us something about how thunderstorms work, which is really important because thunderstorms produce lightning that hurts and kills a lot of people.”
More broadly, Dwyer said he is excited about the prospects of advancing the field of meteorology. “I think everyone assumes that we figured out lightning a long time ago, but it’s an overlooked area … we don’t understand what’s going on inside those clouds right over our heads.” The discovery of flickering gamma-ray flashes may provide crucial clues scientists need to understand thundercloud dynamics, he said.
Turning to aircraft-based instrumentation rather than satellites ensured a lot of bang for research bucks, said the study’s project scientist, Timothy Lang of NASA’s Marshall Space Flight Center in Huntsville, Alabama.
“If we had gotten one flash, we would have been ecstatic — and we got well over 100,” he said. This research could lead to a significant advance in our understanding of thunderstorms and radiation from thunderstorms. “It shows that if you have the right problem and you’re willing to take a little bit of risk, you can have a huge payoff.”
By James Riordon
NASA’s Earth Science News Team
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Last Updated Oct 02, 2024 EditorJenny MarderContactJames RiordonLocationMarshall Space Flight Center Related Terms
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By NASA
3 Min Read October’s Night Sky Notes: Catch Andromeda Rising!
Hot stars burn brightly in this new image from NASA’s Galaxy Evolution Explorer, showing the ultraviolet side of a familiar face. At approximately 2.5 million light-years away, the Andromeda galaxy, or M31, is our Milky Way’s largest galactic neighbor. Credits:
NASA If you’re thinking of a galaxy, the image in your head is probably the Andromeda Galaxy! Studies of this massive neighboring galaxy, also called M31, have played an incredibly important role in shaping modern astronomy. As a bonus for stargazers, the Andromeda Galaxy is also a beautiful sight.
Spot the Andromeda Galaxy! M31’s more common name comes from its parent constellation, which becomes prominent as autumn arrives in the Northern Hemisphere. Surprising amounts of detail can be observed with unaided eyes when seen from dark sky sites. Hints of it can even be made out from light polluted areas. Use the Great Square of Pegasus or the Cassiopeia constellation as guides to find it. Credit: Stellarium Web Have you heard that all the stars you see at night are part of our Milky Way galaxy? While that is mostly true, one star-like object located near the border between the constellations of Andromeda and Cassiopeia appears fuzzy to unaided eyes. That’s because it’s not a star, but the Andromeda Galaxy, its trillion stars appearing to our eyes as a 3.4 magnitude patch of haze. Why so dim? Distance! It’s outside our galaxy, around 2.5 million light years distant – so far away that the light you see left M31’s stars when our earliest ancestors figured out stone tools. Binoculars show more detail: M31’s bright core stands out, along with a bit of its wispy, saucer-shaped disc. Telescopes bring out greater detail but often can’t view the entire galaxy at once. Depending on the quality of your skies and your magnification, you may be able to make out individual globular clusters, structure, and at least two of its orbiting dwarf galaxies: M110 and M32. Light pollution and thin clouds, smoke, or haze will severely hamper observing fainter detail, as they will for any “faint fuzzy.” Surprisingly, persistent stargazers can still spot M31’s core from areas of moderate light pollution as long as skies are otherwise clear.
Generated version of the Andromeda Galaxy and its companion galaxies M32 and M110. Stellarium Web Modern astronomy was greatly shaped by studies of the Andromeda Galaxy. A hundred years ago, the idea that there were other galaxies beside our own was not widely accepted, and so M31 was called the “Andromeda Nebula.” Increasingly detailed observations of M31 caused astronomers to question its place in our universe – was M31 its own “island universe,” and not part of our Milky Way? Harlow Shapley and Heber Curtis engaged in the “Great Debate” of 1920 over its nature. Curtis argued forcefully from his observations of dimmer than expected nova, dust lanes, and other oddities that the “nebula” was in fact an entirely different galaxy from our own. A few years later, Edwin Hubble, building on Henrietta Leavitt’s work on Cepheid variable stars as a “standard candle” for distance measurement, concluded that M31 was indeed another galaxy after he observed Cepheids in photos of Andromeda, and estimated M31’s distance as far outside our galaxy’s boundaries. And so, the Andromeda Nebula became known as the Andromeda Galaxy.
This illustration shows the location of the 43 quasars scientists used to probe Andromeda’s gaseous halo. These quasars—the very distant, brilliant cores of active galaxies powered by black holes—are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars’ light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo’s material. NASA, ESA, and E. Wheatley (STScI) These discoveries inspire astronomers to this day, who continue to observe M31 and many other galaxies for hints about the nature of our universe. One of the Hubble Space Telescope’s longest-running observing campaigns was a study of M31: the Panchromatic Hubble Andromeda Treasury (PHAT). Dig into NASA’s latest discoveries about the Andromeda Galaxy, on their Messier 31 page.
Originally posted by Dave Prosper: September 2021
Last Updated by Kat Troche: September 2024
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