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Space News Update — January 10, 2020 —

Contents

In the News

Story 1: Hubble detects smallest known dark matter clumps

Story 2:

SOFIA Reveals New View of Milky Way’s Center

Story 3: First SLS core stage departs factory

Departments

The Night Sky

ISS Sighting Opportunities

Space Calendar

NASA-TV Highlights

Food for Thought

Space Image of the Week

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1. Hubble detects smallest known dark matter clumps

When searching for dark matter, astronomers must go on a sort of "ghost hunt." That's because dark matter is an invisible substance that cannot be seen directly. Yet it makes up the bulk of the universe's mass and forms the scaffolding upon which galaxies are built. Dark matter is the gravitational "glue" that holds galaxies as well as galaxy clusters together. Astronomers can detect its presence indirectly by measuring how its gravity affects stars and galaxies.

The mysterious substance is not composed of the same stuff that makes up stars, planets, and people. That material is normal "baryonic" matter, consisting of electrons, protons, and neutrons. However, dark matter might be some sort of unknown subatomic particle that interacts weakly with normal matter.

A popular theory holds that dark matter particles don't move very fast, which makes it easier for them to clump together. According to this idea, the universe contains a broad range of dark matter concentrations, from small to large.

Astronomers have detected dark matter clumps around large- and medium-sized galaxies. Now, using Hubble and a new observing technique, astronomers have found that dark matter forms much smaller clumps than previously known.

Each of these Hubble Space Telescope snapshots reveals four distorted images of a background quasar and its host galaxy surrounding the central core of a foreground massive galaxy. The gravity of the massive foreground galaxy is acting like a magnifying glass by warping the quasar’s light in an effect called gravitational lensing. Quasars are extremely distant cosmic streetlights produced by active black holes. Such quadruple images of quasars are rare because of the nearly exact alignment needed between the foreground

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galaxy and background quasar. Astronomers used the gravitational lensing effect to detect the smallest clumps of dark matter ever found. The clumps are located along the telescope's line of sight to the quasars, as well as in and around the foreground lensing galaxies. The presence of the dark matter concentrations alters the apparent brightness and position of each distorted quasar image. Astronomers compared these measurements with predictions of how the quasar images would look without the influence of the dark matter clumps. The researchers used these measurements to calculate the masses of the tiny dark matter concentrations. Hubble's Wide Field Camera 3 captured the near-infrared light from each quasar and dispersed it into its component colors for study with spectroscopy. The images were taken between 2015 and 2018. Credit: NASA, ESA, A. Nierenberg (JPL) and T. Treu (UCLA)

The researchers searched for small concentrations of dark matter in the Hubble data by measuring how the light from faraway quasars is affected as it travels through space. Quasars are the bright black-hole-powered cores of very distant galaxies. The Hubble images show that the light from these quasars images is warped and magnified by the gravity of massive foreground galaxies in an effect called gravitational lensing. Astronomers used this lensing effect to detect the small dark matter clumps. The clumps are located along the telescope's line of sight to the quasars, as well as in and around the foreground lensing galaxies.

Using NASA's Hubble Space Telescope and a new observing technique, astronomers have found that dark matter forms much smaller clumps than previously known. This result confirms one of the fundamental predictions of the widely accepted "cold dark matter" theory.

All galaxies, according to this theory, form and are embedded within clouds of dark matter. Dark matter itself consists of slow-moving, or "cold," particles that come together to form structures ranging from hundreds of thousands of times the mass of the Milky Way galaxy to clumps no more massive than the heft of a commercial airplane. (In this context, "cold" refers to the particles' speed.)

The Hubble observation yields new insights into the nature of dark matter and how it behaves. "We made a very compelling observational test for the cold dark matter model and it passes with flying colors," said Tommaso Treu of the University of California, Los Angeles (UCLA), a member of the observing team.

Dark matter is an invisible form of matter that makes up the bulk of the universe's mass and creates the scaffolding upon which galaxies are built. Although astronomers cannot see dark matter, they can detect its presence indirectly by measuring how its gravity affects stars and galaxies. Detecting the smallest dark matter formations by looking for embedded stars can be difficult or impossible, because they contain very few stars.

While dark matter concentrations have been detected around large- and medium-sized galaxies, much smaller clumps of dark matter have not been found until now. In the absence of observational evidence for such small-scale clumps, some researchers have developed alternative theories, including "warm dark matter." This idea suggests that dark matter particles are fast moving, zipping along too quickly to merge and form smaller concentrations. The new observations do not support this scenario, finding that dark matter is "colder" than it would have to be in the warm dark matter alternative theory.

"Dark matter is colder than we knew at smaller scales," said Anna Nierenberg of NASA's Jet Propulsion Laboratory in Pasadena, California, leader of the Hubble survey. "Astronomers have carried out other observational tests of dark matter theories before, but ours provides the strongest evidence yet for the presence of small clumps of cold dark matter. By combining the latest theoretical predictions, statistical tools, and new Hubble observations, we now have a much more robust result than was previously possible."

Hunting for dark matter concentrations devoid of stars has proved challenging. The Hubble research team, however, used a technique in which they did not need to look for the gravitational influence of stars as tracers of dark matter. The team targeted eight powerful and distant cosmic "streetlights," called quasars (regions around active black holes that emit enormous amounts of light). The astronomers measured how the light

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emitted by oxygen and neon gas orbiting each of the quasars' black holes is warped by the gravity of a massive foreground galaxy, which is acting as a magnifying lens.

Using this method, the team uncovered dark matter clumps along the telescope's line of sight to the quasars, as well as in and around the intervening lensing galaxies. The dark matter concentrations detected by Hubble are 1/10,000th to 1/100,000th times the mass of the Milky Way's dark matter halo. Many of these tiny groupings most likely do not contain even small galaxies, and therefore would have been impossible to detect by the traditional method of looking for embedded stars.

The eight quasars and galaxies were aligned so precisely that the warping effect, called gravitational lensing, produced four distorted images of each quasar. The effect is like looking at a funhouse mirror. Such quadruple images of quasars are rare because of the nearly exact alignment needed between the foreground galaxy and background quasar. However, the researchers needed the multiple images to conduct a more detailed analysis.

The presence of the dark matter clumps alters the apparent brightness and position of each distorted quasar image. Astronomers compared these measurements with predictions of how the quasar images would look without the influence of the dark matter. The researchers used the measurements to calculate the masses of the tiny dark matter concentrations. To analyze the data, the researchers also developed elaborate computing programs and intensive reconstruction techniques.

"Imagine that each one of these eight galaxies is a giant magnifying glass," explained team member Daniel Gilman of UCLA. "Small dark matter clumps act as small cracks on the magnifying glass, altering the brightness and position of the four quasar images compared to what you would expect to see if the glass were smooth."

The researchers used Hubble's Wide Field Camera 3 to capture the near-infrared light from each quasar and disperse it into its component colors for study with spectroscopy. Unique emissions from the background quasars are best seen in infrared light. "Hubble's observations from space allow us to make these measurements in galaxy systems that would not be accessible with the lower resolution of ground-based telescopes—and Earth's atmosphere is opaque to the infrared light we needed to observe," explained team member Simon Birrer of UCLA.

Treu added: "It's incredible that after nearly 30 years of operation, Hubble is enabling cutting-edge views into fundamental physics and the nature of the universe that we didn't even dream of when the telescope was launched."

The gravitational lenses were discovered by sifting through ground-based surveys such as the Sloan Digital Sky Survey and Dark Energy Survey, which provide the most detailed three-dimensional maps of the universe ever made. The quasars are located roughly 10 billion light-years from Earth; the foreground galaxies, about 2 billion light-years.

The number of small structures detected in the study offers more clues about dark matter's nature. "The particle properties of dark matter affect how many clumps form," Nierenberg explained. "That means you can learn about the particle physics of dark matter by counting the number of small clumps."

However, the type of particle that makes up dark matter is still a mystery. "At present, there's no direct evidence in the lab that dark matter particles exist," Birrer said. "Particle physicists would not even talk about dark matter if the cosmologists didn't say it's there, based on observations of its effects. When we cosmologists talk about dark matter, we're asking, 'How does it govern the appearance of the universe, and on what scales?'"

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Astronomers will be able to conduct follow-up studies of dark matter using future NASA space telescopes such as the James Webb Space Telescope and the Wide Field Infrared Survey Telescope (WFIRST), both infrared observatories. Webb will be capable of efficiently obtaining these measurements for all known quadruply lensed quasars. WFIRST's sharpness and large field of view will help astronomers make observations of the entire region of space affected by the immense gravitational field of massive galaxies and galaxy clusters. This will help researchers uncover many more of these rare systems.

Source: Phys.org Return to Contents

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2. SOFIA Reveals New View of Milky Way’s Center

NASA has captured an extremely crisp infrared image of the center of our Milky Way galaxy. Spanning a distance of more than 600 light-years, this panorama reveals details within the dense swirls of gas and dust in high resolution, opening the door to future research into how massive stars are forming and what’s feeding the supermassive black hole at our galaxy’s core.

Among the features coming into focus are the jutting curves of the Arches Cluster containing the densest concentration of stars in our galaxy, as well as the Quintuplet Cluster with stars a million times brighter than our Sun. Our galaxy’s black hole takes shape with a glimpse of the fiery-looking ring of gas surrounding it.

The new view was made possible by the world’s largest airborne telescope, the Stratospheric Observatory for Infrared Astronomy, or SOFIA. Flying high in the atmosphere, this modified Boeing 747 pointed its infrared camera called FORCAST – the Faint Object Infrared Camera for the SOFIA Telescope – to observe warm, galactic material emitting at wavelengths of light that other telescopes could not detect. The image combines SOFIA’s new perspective of warm regions with previous data exposing very hot and cold material from NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory.

An overview paper highlighting initial results has been submitted for publication to the Astrophysical Journal. The image was presented for the first time at the American Astronomical Society annual meeting this week in 2020 in Honolulu.

“It’s incredible to see our galactic center in detail we’ve never seen before,” said James Radomski, a Universities Space Research Association scientist at the SOFIA Science Center at NASA’s Ames Research Center in California’s Silicon Valley. “Studying this area has been like trying to assemble a puzzle with missing pieces. The SOFIA data fills in some of the holes, putting us significantly closer to having a complete picture.”

Birth of Stars

The Milky Way’s central regions have significantly more of the dense gas and dust that are the building blocks for new stars compared to other parts of the galaxy. Yet, there are 10 times fewer massive stars born here than expected. Understanding why this discrepancy exists has been difficult because of all the dust between Earth and the galactic core getting in the way – but observing with infrared light offers a closer look at the situation.

The new infrared data illuminates structures indicative of star birth near the Quintuplet Cluster and warm material near the Arches Cluster that could be the seeds for new stars. Seeing these warm features in high resolution may help scientists explain how some of the most massive stars in our entire galaxy managed to form so close to each other, in a relatively small region, despite the low birthrate in the surrounding areas.

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“Understanding how massive star birth happens at the center of our own galaxy gives us information that can help us learn about other, more distant galaxies,” said Matthew Hankins, a postdoctoral scholar at the California Institute of Technology in Pasadena, California and principal investigator of the project. “Using multiple telescopes gives us clues we need to understand these processes, and there’s still more to be uncovered.”

Ring Around the Black Hole

Scientists can also more clearly see the material that may be feeding the ring around our galaxy’s central supermassive black hole. The ring is about 10 lightyears in diameter and plays a key role in bringing matter closer to the black hole, where it may eventually be devoured. The origin of this ring has long been a puzzle for scientists because it may be depleted over time, but the SOFIA data reveal several structures which could represent material being incorporated into it.

The data were taken in July 2019 during SOFIA’s annual deployment to Christchurch, New Zealand, where scientists study the skies over the Southern Hemisphere. The full, calibrated dataset is currently available to astronomers worldwide for further research via the SOFIA Legacy Program.

The Spitzer Space Telescope will be decommissioned on January 30, 2020 after operating for more than 16 years. SOFIA continues exploring the infrared universe by studying wavelengths of mid- and far-infrared light with high resolution light that are not accessible to other telescopes, and helping scientists understand star and planet formation, the role magnetic fields play in shaping our universe, and the chemical evolution of galaxies. Some of the very faint points and dark regions revealed in SOFIA’s image can help plan targets for the telescopes of the future, like the James Webb Space Telescope.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR.

Source: NASA Return to Contents

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3. First SLS core stage departs factory

The heart of NASA’s first flight-ready Space Launch System heavy-lift rocket emerged from its factory in New Orleans Wednesday morning for a barge trip to the Stennis Space Center in Mississippi for an eight-minute test-firing of its space shuttle-era hydrogen-fueled engines.

The 212-foot-long (64.6-meter), 27.6-foot-wide (8.4-meter) core stage of the Space Launch System rolled out of its factory at the Michoud Assembly Facility, signaling a significant, but long-delayed milestone in the SLS program’s eight-year history.

Teams loaded the core stage into NASA’s Pegasus barge to be ferried on a half-day journey to the Stennis Space Center in Mississippi.

Spaceflight Now was at Michoud for Wednesday’s rollout ceremony, which occurred with festive New Orleans flair. Some SLS team members wore shiny bead necklaces, and a “second line” New Orleans drum and brass band accompanied the rocket on the trek out of the factory.

Built by Boeing, the core stage is covered in insulating foam, similar to the thermal insulation used on the space shuttle’s external tank. The core stage has the same diameter as the shuttle fuel tank and was built in the same factory in east New Orleans.

The huge first stage of NASA’s Saturn 5 moon rocket was also manufactured at Michoud.

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Another piece of technology borrowed from the space shuttle for the SLS core stage is its use of RS-25 main engines. Four Aerojet Rocketdyne-built RS-25 engines, each a veteran of multiple space shuttle launches, are affixed to the chrome-colored aft end of the SLS core stage.

Those four engines are upgraded with modernized electronics and rated for slightly higher throttle settings than they were in the shuttle program. The RS-25 engines will be ignited later this year on a test stand at the Stennis Space Center in southern Mississippi during a “green run” test series designed to confirm the rocket works as designed when loaded with more than 700,000 gallons of super-cold liquid hydrogen and liquid oxygen propellants.

The four RS-25 engines will power up to full throttle to generate nearly 2 million pounds of thrust during the hotfire test.

Once the green run test is complete in Mississippi, NASA will ship the core stage to the Kennedy Space Center in Florida, where it will join two side-mounted solid-fueled boosters — also using modified space shuttle technology — and an upper stage derived from United Launch Alliance’s Delta 4-Heavy rocket.

The SLS will blast off from pad 39B at the Florida spaceport some time in 2021. A target launch date is still under review after a series of delays have pushed back the SLS’s inaugural test flight from its original schedule in 2017.

The first launch, designated Artemis 1, will carry NASA’s Orion crew capsule on an unpiloted flight into lunar orbit and back to Earth. Boeing teams at Michoud are building a second SLS core stage for the Artemis 2 mission, which could blast off in 2022 or 2023 to carry another Orion vehicle with four astronauts around the moon and back.

The Artemis program’s third mission, planned for 2024, could include an attempt to land astronauts on the moon, a five-year goal set by the Trump administration last year.

Read our earlier story for the details on completion of manufacturing on the SLS core stage.

Source: Spaceflight Now Return to Contents

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The Night Sky Friday, Jan. 10 • Full Moon (exact at 2:21 p.m. EST). This evening spot Pollux and Castor to the Moon's upper left, as shown below. Procyon shines farther to the Moon's lower right.

• Penumbral eclipse of the Moon for Europe, Africa, Asia, and Australia, as the Moon skims through the pale outer fringe of Earth's shadow. The eclipse is pretty deep as penumbral ones go: the Moon's edge misses the shadow's dark umbra by only about 10% of the Moon's diameter. Therefore the shading will be pretty obvious around the event's mid-time, 19:10 January 10th UT (GMT). The shading will be on the Moon's southern side. Full details. Live video stream (starts at 17:00 UT).

Saturday, Jan. 11 • Here it is the coldest very bottom of the year, but the Summer Star, Vega, still hangs in there. Look for it twinkling in the northwest during and shortly after nightfall. The farther north you are the higher it will be. If you're north of latitude 51° (Calgary, central Ontario and Quebec, London, Berlin), Vega is actually circumpolar. But if you're too far south, it's already gone.

Sunday, Jan. 12 • The waning gibbous Moon rises in the east about an hour after dark. As it climbs, watch below it for Regulus to creep up in its wake. For North America they're about 6° or 7° apart.

Monday, Jan. 13 • Dimmed Betelgeuse. The red supergiant Betelgeuse marking Orion's shoulder has always been slightly variable, but lately it has been in an unusually low dip: As of January 9th it was around visual magnitude +1.4 instead of its more typical +0.5. That's actually fainter than Aldebaran, with which it's often compared, magnitude +0.9. Where do you judge it? See Bob King's What’s Up With Betelgeuse?

And no, this does not mean Betelgeuse is about to go supernova, despite the overinflated hype going around (friends and relatives keep asking me). Yes, it's nearing the end of its life — but on an astronomical timescale! Expect to wait something like 100,000 years.

Tuesday, Jan. 14 • Sirius twinkles brightly after dinnertime below Orion in the southeast. Around 8 or 9 p.m., depending on your location, Sirius shines precisely below fiery Betelgeuse in Orion's shoulder. How accurately can you time this event for your location, perhaps using the vertical edge of a building? Of the two, Sirius leads early in the evening; Betelgeuse leads later.

Source: Sky & Telescope Return to Contents

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ISS Sighting Opportunities

For Denver:

Date Visible Max Height* Appears Disappears Fri Jan 10, 6:12 AM 4 min 32° 22° above W 10° above SSE Sat Jan 11, 5:26 AM 2 min 44° 44° above SSE 11° above SE Sun Jan 12, 4:41 AM < 1 min 11° 11° above ESE 11° above ESE Sun Jan 12, 6:14 AM 1 min 10° 10° above WSW 10° above SW Mon Jan 13, 5:28 AM < 1 min 12° 12° above S 10° above S Sighting information for other cities can be found at NASA’s Satellite Sighting Information NASA-TV Highlights (all times Eastern Daylight Time) January 10, Friday 10:30 a.m. – NASA Astronaut Candidate Class Graduation Ceremony (All Channels) 1 p.m. – International Space Station Expedition 61 In-Flight Event with the World Surf League and NASA astronaut Christina Koch (All Channels) 1:45 p.m. – Live Interview with Fox News and NASA Administrator Jim Bridenstine – Johnson Space Center (All Channels) 2 – 6 p.m. – Live Interviews with NASA’s Astronaut Candidate Graduates – Johnson Space Center (All Channels) 7 p.m. – Replay of the NASA Astronaut Candidate Class Graduation event (All Channels)

January 11, Saturday 7 a.m., 2 p.m., 8 p.m. – Replay of Introducing Five Airborne Science Campaigns to Study Our Home Planet (All Channels) 8 a.m., 3 p.m., 9 p.m. – Replay of the NASA Astronaut Candidate Class Graduation Event (All Channels

January 12, Sunday 9 a.m., 4 p.m., 9 p.m. - Replay of Introducing Five Airborne Science Campaigns to Study Our Home Planet (All Channels) 10 a.m., 5 p.m., 10 p.m. - Replay of the NASA Astronaut Candidate Class Graduation Event (All Channels)

Watch NASA TV on the Net by going to the NASA website. Return to Contents

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Space Calendar

• Jan 10 - [Jan 03] Penumbral Lunar Eclipse • Jan 10 - Comet 73P-AW/Schwassmann-Wachmann At Opposition (3.547 AU) • Jan 10 - Asteroid 708 Raphaela Occults HIP 40388 (6.2 Magnitude Star) • Jan 10 - Asteroid 16054 (1999 JP55) Occults HIP 52120 (6.5 Magnitude Star) • Jan 10 - Apollo Asteroid 2019 YF4 Near-Earth Flyby (0.010 AU) • Jan 10 - [Jan 08] Apollo Asteroid 2020 AL2 Near-Earth Flyby (0.016 AU) • Jan 10 - Apollo Asteroid 2019 UO Near-Earth Flyby (0.030 AU) • Jan 10 - Apollo Asteroid 2019 YV Near-Earth Flyby (0.044 AU) • Jan 11 - Comet 289P/Blanpain Near-Earth Flyby (0.091 AU) • Jan 11 - Comet 384P/Kowalski At Opposition (0.605 AU) • Jan 11 - Hyperbolic Object A/2019 G2 Closest Approach To Earth (1.445 AU) • Jan 11 - Comet 306P/LINEAR Closest Approach To Earth (2.113 AU) • Jan 11 - Comet 243P/NEAT Closest Approach To Earth (2.788 AU) • Jan 11 - Apollo Asteroid 2019 WC5 Near-Earth Flyby (0.016 AU) • Jan 11 - Apollo Asteroid 2019 YV5 Near-Earth Flyby (0.043 AU) • Jan 11 - Asteroid 1539 Borrelly Closest Approach To Earth (1.967 AU) • Jan 11 - Kuiper Belt Object 230965 (2004 XA192) At Opposition (34.590 AU)

• Jan 12 - [Jan 05] Royal Astronomical Society's 200th Birthday (1820) • Jan 12 - Comet C/2019 K8 (ATLAS) Closest Approach To Earth (3.148 AU) • Jan 12 - Comet 73P-AY/Schwassmann-Wachmann At Opposition (3.395 AU) • Jan 12 - Comet 73P-AZ/Schwassmann-Wachmann At Opposition (3.397 AU) • Jan 12 - Comet P/2013 YG46 (Spacewatch) At Opposition (3.793 AU) • Jan 12 - [Jan 07] Aten Asteroid 2020 AB2 Near-Earth Flyby (0.010 AU) • Jan 12 - [Jan 06] Apollo Asteroid 2020 AO1 Near-Earth Flyby (0.022 AU) • Jan 12 - Apollo Asteroid 4486 Mithra Closest Approach To Earth (1.315 AU) • Jan 12 - Apollo Asteroid 3752 Camillo Closest Approach To Earth (1.552 AU) • Jan 12 - Asteroid 101432 Adamwest Closest Approach To Earth (1.828 AU) • Jan 12 - Asteroid 18499 Showalter Closest Approach To Earth (2.013 AU) • Jan 12 - Asteroid 48300 Kronk Closest Approach To Earth (2.075 AU) • Jan 12 - 15th Anniversary (2005), Deep Impact Delta 2 Launch • Jan 12 - 110th Anniversary (1910), Discovery of the Great January Comet of 1910 • Jan 12 - Joseph Helffrich's 130th Birthday (1890) • Jan 13 - Hyperbolic Object A/2019 G2 At Opposition (1.447 AU) • Jan 13 - Comet 131P/Mueller Closest Approach To Earth (2.243 AU) • Jan 13 - Comet P/2019 A3 (PANSTARRS) Closest Approach To Earth (2.478 AU) • Jan 13 - Comet 371P/LINEAR-Skiff Closest Approach To Earth (2.944 AU) • Jan 13 - Comet 359P/LONEOS At Opposition (4.034 AU) • Jan 13 - Asteroid 75 Eurydike Occults HIP 115945 (6.0 Magnitude Star) • Jan 13 - [Jan 06] Apollo Asteroid 2020 AE1 Near-Earth Flyby (0.017 AU) • Jan 13 - [Jan 10] Apollo Asteroid 2020 AX2 Near-Earth Flyby (0.026 AU) • Jan 13 - Aten Asteroid 2020 AE Near-Earth Flyby (0.030 AU) • Jan 13 - [Jan 06] Apollo Asteroid 2020 AS1 Near-Earth Flyby (0.040 AU) • Jan 13 - Amor Asteroid 3988 Huma Closest Approach To Earth (1.026 AU) • Jan 13 - Asteroid 2343 Siding Spring Closest Approach To Earth (1.380 AU) • Jan 13 - Amor Asteroid 4957 Brucemurray Closest Approach To Earth (1.911 AU) • Jan 13 - Asteroid 4446 Carolyn Closest Approach To Earth (4.089 AU) • Jan 13 - Astro2020 Teleconference: Panel on Cosmology Report Development • Jan 13 - 40th Anniversary (1980), Discovery of EETA 79001 (Mars Meteorite)

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• Jan 14 - Jilin 1/NuSat 7-8 CZ-2D Launnch • Jan 14 - Comet 114P/Wiseman-Skiff Perihelion (1.579 AU) • Jan 14 - Comet 218P/LINEAR At Opposition (1.882 AU) • Jan 14 - Comet 101P/Chernykh Perihelion (2.342 AU) • Jan 14 - [Jan 04] Apollo Asteroid 2020 AO Near-Earth Flyby (0.024 AU) • Jan 14 - Apollo Asteroid 38086 Beowulf Closest Approach To Earth (0.822 AU) • Jan 14 - Asteroid 9957 Rafaellosanti Closest Approach To Earth (1.552 AU) • Jan 14 - Asteroid 37530 Dancingangel Closest Approach To Earth (1.875 AU) • Jan 14 - Asteroid 17062 Bardot Closest Approach To Earth (2.256 AU) • Jan 14 - Asteroid 6639 Marchis Closest Approach To Earth (2.599 AU) • Jan 14 - Amor Asteroid 5324 Lyapunov Closest Approach To Earth (3.591 AU)

Source: JPL Space Calendar Return to Contents

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Food for Thought

First sighting of hot gas sloshing in galaxy cluster

ESA's XMM-Newton X-ray observatory has spied hot gas sloshing around within a galaxy cluster—a never-before-seen behaviour that may be driven by turbulent merger events.

Galaxy clusters are the largest systems in the universe bound together by gravity. They contain hundreds to thousands of galaxies and large quantities of hot gas known as plasma, which reaches temperatures of around 50 million degrees and shines brightly in X-rays.

Very little is known about how this plasma moves, but exploring its motions may be key to understanding how galaxy clusters form, evolve and behave.

"We selected two nearby, massive, bright and well-observed galaxy clusters, Perseus and Coma, and mapped how their plasma moved—whether it was moving towards or away from us, its speed, and so on—for the first time," says Jeremy Sanders of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and lead author of the new study.

"We did this over large regions of sky: an area roughly the size of two full Moons for Perseus, and four for Coma. We really needed XMM-Newton for this, as it'd be extremely difficult to cover such large areas with any other spacecraft."

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Jeremy and colleagues found direct signs of plasma flowing, splashing and sloshing around within the Perseus galaxy cluster—one of the most massive known objects in the universe, and the brightest cluster in the sky in terms of X-rays. While this kind of motion has been predicted theoretically, it had never been seen before in the cosmos.

By looking at simulations of how the plasma moved within the cluster, the researchers then explored what was causing the sloshing. They found it to be likely due to smaller sub-clusters of galaxies colliding and merging with the main cluster itself. These events are energetic enough to disrupt Perseus' gravitational field and kickstart a sloshing motion that will last for many millions of years before settling.

Unlike Perseus, which is characterised by a main cluster and several smaller sub-structures, the Coma cluster contained no sloshing plasma, and appears to instead be a massive cluster made up of two major sub-clusters that are slowly merging together.

"Coma contains two massive central galaxies rather than a cluster's usual single behemoth, and different regions appear to contain material that moves differently," says Jeremy. "This indicates that there are multiple streams of material within the Coma cluster that haven't yet come together to form a single coherent 'blob', like we see with Perseus."

The finding was made possible by a new calibration technique applied to XMM-Newton's European Photon Imaging Camera (EPIC). The ingenious method, which involved mining two decades of archival EPIC data, improved the accuracy of the camera's velocity measurements by a factor of over 3.5, raising XMM-Newton's capabilities to a new level.

"The EPIC camera has an instrumental background signal—the so-called 'fluorescent lines' which are always present in our data, and can sometimes be annoying as they're usually not what we're looking for," adds co-author Ciro Pinto, an ESA research fellow at the European Space Research and Technology Centre in Noordwijk, The Netherlands, who recently moved to Italy's National Institute for Astrophysics.

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"We decided to use these lines, which are a constant feature, to compare and align EPIC data from the past 20 years to better determine how the camera behaves, and then used this to correct for any instrumental variation or effects."

This technique made it possible to map the gas in the clusters more accurately. Jeremy, Ciro and colleagues used the background lines to recognise and remove individual variations between observations, and then eliminated any subtler instrumental effects identified and flagged up by their 20 years of EPIC data mining.

EPIC comprises three CCD cameras designed to capture both low- and high-energy X-rays, and is one of a trio of advanced instruments aboard XMM-Newton.

Exploring the dynamic X-ray sky since its launch in 1999, XMM-Newton is the biggest scientific satellite ever built in Europe, and carries some of the most powerful telescope mirrors ever developed.

"This calibration technique highlights newfound capabilities of the EPIC camera," says Norbert Schartel, ESA XMM-Newton Project Scientist.

"High-energy astrophysics often entails comparing X-ray data at different points in the cosmos for everything from plasma to black holes, so the ability to minimise instrumental effects is key. By using past XMM-Newton observations to refine future ones, the new technique may open up inspiring opportunities for new research and discovery."

These XMM-Newton observations will also remain unparalleled until the launch of ESA's Advanced Telescope for High-ENergy Astrophysics (Athena) in 2031. Whereas covering such large areas of sky will largely be beyond the capabilities of telescopes such as the upcoming JAXA/NASA X-ray Imaging and Spectroscopy Mission, or XRISM, Athena will combine a large X-ray telescope with state-of-the-art scientific instruments to shed new light on the hot, energetic universe.

Source: Phys.org Return to Contents

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Space Image of the Week

A waxing crescent Moon A waxing crescent Moon is pictured as the International Space Station orbited 260 miles above the north African country of Algeria. Source: NASA Return to Contents