Twisted Magnetic Fields Can Reveal How Protobinary Systems, Tatooine Planets Form

by Anashe Bandari

Tatooine is real.

Well, sort of.

Circumbinary planets – planets that orbit around two stars, like the fictional Star Wars planet Tatooine and its two suns – exist in the universe, and are sometimes referred to as Tatooine planets. Systems in which two stars rotate around each other, called binary star systems, are incredibly common, comprising over half the stars in the Milky Way galaxy. But how does a binary system like this happen?

Researchers using the Stratospheric Observatory for Infrared Astronomy (SOFIA) saw a twisted magnetic field around a protobinary star system, a very young binary star system that is still growing. This provides a hint about how the system came to be.

As stars begin to form, they obtain most of their material from a disk of dust and gas surrounding them. A larger envelope of matter surrounds and feeds the disk. From here, binaries can emerge in one of two ways – far apart, where they grow in the envelope, or much closer to one another, where they form in the disk.

There’s a caveat, though: binaries that form in the envelope can move closer to each other over time, so even if they look near to one another now, they were not necessarily always that way.

That’s where magnetic fields come in.

In a recent study, SOFIA observations – supported by data from the Atacama Large Millimeter Array (ALMA), the Pico dos Dias Observatory, and archival data from the Herschel Space Observatory – found the magnetic field in the star-forming cloud Lynds 483 (L483) is oriented east-to-west in its outer regions, but twists 45 degrees counter-clockwise toward its center. ALMA confirmed that L483 contains two protostars and Herschel provided information about some of the region’s physical properties, while SOFIA and Pico dos Dias traced the magnetic field’s shape.

A subset of polarization vectors are overlain atop a Spitzer Space Telescope image of Lynds 483.
A subset of polarization vectors are overlain atop a Spitzer Space Telescope image of Lynds 483. The SOFIA data is shown in red, and the orange vectors were obtained by Pico dos Dias Observatory. The green vectors show data obtained by SHARC C-II Polarimeter at the Caltech Submillimeter Observatory in previous work, shown here as a comparison of scales. Near the center of the image is a small yellow dot indicating the location of the binary protostars. The combined fields show a twist as they approach the protostellar envelope, though they are parallel on larger scales. Credit: L483: NASA/JPL-Caltech/J. Tobin; Vectors: Cox et al. 2022, Chapman et al. 2013

“If we back up a little bit, we think these protostars formed far away, migrated, and twisted up their field in the process of coming toward each other,” said Erin Cox, a postdoctoral associate at Northwestern University in Evanston, Illinois, who led the study.

Because stars and their planets form around the same time, figuring out how the protobinary came together tells astronomers about the types of planets it can harbor.

“If we understand how the protobinary stars formed, we will get a better understanding of how much stuff is in the disk, which is the material that provides the planets with their masses,” Cox said. “We want to understand what our starting mass budget is for these planets.”

For example, the protobinaries’ inward migration can enhance the motion of the gas and dust around them, ejecting them out of the system. If too much material gets blown out, only Earth-like rocky planets can potentially form, rather than gas giants, like Jupiter.

Being able to see these magnetic fields helps decipher the formation of binary systems and, in turn, their associated Tatooine planets.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014, and the mission will conclude no later than Sept. 30, 2022. SOFIA will continue its regular operations until then.

SOFIA Finds More Water in the Moon’s Southern Hemisphere

by Anashe Bandari

In 2020, researchers using the Stratospheric Observatory for Infrared Astronomy (SOFIA) announced they had discovered water on the sunlit surface of the Moon. Now, they’ve confirmed it – and found even more.

The image shows flux data obtained by SOFIA’s FORCAST instrument overlaid on an orthographic projection of the Moon
The image shows flux data obtained by SOFIA’s FORCAST instrument overlaid on an orthographic projection of the Moon, creating a map of water abundances in the Moretus Crater region. Surface lunar features are clearly visible within the flux data. In this image, lighter colors correspond to a higher flux, and darker corresponds to a lower flux. Credit: Honniball et al. and Applied Coherent Technology Corp. The Moon reference image is constructed using the LRO-WAC albedo mosaic.

The team of researchers led by Casey Honniball, a postdoctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, found molecular water in the Moretus Crater region, located near the Moon’s Clavius Crater, where the original finding took place. This confirmation that water is indeed present outside of Permanently Shadowed Regions on the Moon’s southern hemisphere allowed the researchers to begin decoding where this water comes from. Additionally, with the new observations, the researchers were able to create a map of the water abundances in the crater, which they could not do for the Clavius Crater due to insufficient data. Because the Moretus study included a much larger number of observations, the map helped determine that the abundance of water on the Moon varies with both temperature and latitude – in particular, there is more water at the poles and at lower temperatures.

“Water on the Moon is exciting because it allows us to study the processes that occur not only on the Moon, but also on other airless bodies. It is of extreme importance as a resource for human exploration,” said Honniball. “If you can find [sufficiently] large concentrations of water on the surface of the Moon – and learn how it’s being stored and what form it’s in – you can learn how to extract it and use it for breathable oxygen or rocket fuel for a more sustainable presence.”

When looking at the Moon, it is, in general, difficult to differentiate between water and hydroxyl – a molecule composed of oxygen bound to a single hydrogen atom (OH), as opposed to water’s two hydrogen atoms (H2O). With its Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), SOFIA can look at 6.1-micron emission features from the Moon, a wavelength of emission unique to water. And by flying above 99% of the water vapor in Earth’s atmosphere, SOFIA can see what ground-based telescopes cannot.

Because SOFIA is capable of distinguishing water from hydroxyl, the astronomers found evidence for a theory about how water came to be on the Moon in the first place, ruling out several previous hypotheses.

“The Moon is constantly being bombarded by solar wind, which is delivering hydrogen to the lunar surface,” Honniball said. “This hydrogen interacts with oxygen on the lunar surface to create hydroxyl.”

Then, when the Moon is hit by micrometeorites – which happens surprisingly often – the high temperature of the impact causes two hydroxyl molecules to combine, leaving behind a water molecule and an extra oxygen atom. A lot of this water is likely lost to space, while some is trapped within glass formed on the Moon’s surface by the impact.

More SOFIA data about lunar water is forthcoming: The group made additional observations to understand how water varies with the Moon’s latitude, composition, and temperature to corroborate the strong indications of increased water toward the poles in the current work.

NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) will arrive on the South Pole of the Moon in late 2024 to map water in different forms and other volatiles. The SOFIA observations provide an idea of how one form of water is distributed in sunlit regions, helping to place VIPER’s future measurements into a broader context.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014, and the mission will conclude no later than Sept. 30, 2022. SOFIA will continue its regular operations until then.

SOFIA Returns from New Zealand Deployment

The Stratospheric Observatory for Infrared Astronomy (SOFIA) has returned to its usual base of operations after a month of science observations in the Southern Hemisphere. The observatory was temporarily based out of Christchurch International Airport in New Zealand.

SOFIA is seen in front of Building 703 with crew going down the stairs
The Stratospheric Observatory for Infrared Astronomy (SOFIA) returns to NASA’s Armstrong Flight Research Center Building 703 on Aug. 11 after a productive month of science flights out of Christchurch International Airport in New Zealand. Credit: NASA/Joshua Fisher

SOFIA arrived Thursday, Aug. 11 at NASA Armstrong Flight Research Center’s Building 703 in Palmdale, California, and plans to resume science flights Monday, Aug. 22.

SOFIA had been scheduled to remain longer in New Zealand before severe weather caused damage to the aircraft, requiring the mission to adjust its science observation plans and cancel the remainder of the deployment. During its time in the Southern Hemisphere, SOFIA observed and studied a wide range of celestial objects and phenomena, like cosmic magnetic fields, the structure of the Milky Way, and the origin of cosmic rays.

An inspection and assessment of the aircraft determined SOFIA may safely return to science flights for the remainder of the mission, following minor repairs and a safety checkout flight conducted in New Zealand. The mission will conclude no later than Sept. 30.

SOFIA Adjusts Science Planning Following Damage to Aircraft

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is adjusting its science observation plans and canceling the remainder of its Southern Hemisphere deployment following damage to the aircraft caused by severe weather on Monday, July 18. SOFIA is currently operating out of Christchurch International Airport in New Zealand to better observe celestial objects in the southern skies.

SOFIA at Christchurch Airport, NZ at night
SOFIA at Christchurch International Airport, New Zealand. Credit: NASA/SOFIA/G. Perryman

The SOFIA team has determined the needed repairs will take at least three weeks, eliminating the possibility of conducting the remaining science observation flights that were planned from New Zealand through August 7.

SOFIA arrived in New Zealand on June 18 and had a successful and productive month of science flights. Using two instruments, HAWC+ and GREAT, SOFIA observed and studied a wide range of celestial objects and phenomena, like cosmic magnetic fields, structure of the Milky Way, and the origin of cosmic rays.

During the deployment, the SOFIA team also took part in multiple outreach events, sharing information about the observatory and its science with students in grades K-12, youth groups, museum attendees, and members of the aerospace industry.

The aircraft will return to its usual base of operations in Palmdale, California, and resume science flights after repairs are complete.

SOFIA Down for Maintenance in Christchurch

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is down for maintenance after being damaged by a storm that affected the area around Christchurch International Airport in New Zealand on Monday, July 18.

During the severe weather event, high winds caused the stairs outside the aircraft to shift, causing light damage to the front of the aircraft, as well as the stairs themselves. There were no injuries to any staff. The aircraft damage is being assessed, repair plans are moving forward, and new stairs are being delivered. During this time, the mission’s science observation schedule will be reassessed, as SOFIA is unable to continue normal operations until the repairs are complete and stairs are available.

SOFIA currently is operating out of Christchurch International Airport to better observe celestial objects in the Southern Hemisphere. Updates to the status of SOFIA will be shared once available.

Orion’s Veil Comes Out of Its Shell

by Anashe Bandari

Orion’s Veil might be breaking.

Within the Orion Nebula is a massive set of stars known as the Trapezium stars. The winds from the Trapezium stars blow a bubble of dust and gas in the area in front of them, called Orion’s Veil. The majority of Orion’s Veil is sparse, with most of its gas lying in the bubble’s wall. The wall, or Orion’s Veil shell, is about a light-year thick and expanding toward us – and recent observations by the Stratospheric Observatory for Infrared Astronomy (SOFIA) German REceiver for Astronomy at Terahertz Frequencies (GREAT) have identified some unexpected features in it.

A 3D model of the Orion Nebula shows Orion’s Veil shell as a bluish gas surrounding the nebula depicted in red and yellow
A 3D model of the Orion Nebula shows Orion’s Veil shell as a bluish gas surrounding the nebula depicted in red and yellow. Researchers using SOFIA found a protrusion in the shell, which could allow gas and dust to escape beyond the shell. Credit: NASA, ESA, Frank Summers (STScI), Greg T. Bacon (STScI), Lisa Frattare (STScI), Zolt G. Levay (STScI), K. Litaker (STScI). Acknowledgment: Axel Mellinger, Robert Gendler, Rogelio B. Andreo

“The bubble – with a diameter of approximately seven light-years – should be an almost sphere-like structure, but we found a protrusion in its northwestern part,” said Ümit Kavak, a postdoctoral researcher at SOFIA based out of NASA’s Ames Research Center in California’s Silicon Valley, who is the lead author on a recent paper describing the studies.

The SOFIA observations show ionized carbon emission in this protrusion, which Kavak used to determine its size, structure, and how it is expanding, in hopes of uncovering its origins and future.

Shaped like a “U” lying on its side, the protrusion extends well beyond Orion’s Veil shell. It is a likely spot for the shell to pierce, and the protrusion’s chimney-like top seems to imply it already has.

Infrared image of Orion Nebula with curved and dashed lines over it showing outflows, rims, lobes, shells, and protrusion along with location of Trapezium stars.
Schematic picture of the protrusion (green lines, center right) and outflows of ionized carbon extending beyond the protrusion — where the shell has likely been pierced — overlaid on a Wide-field Infrared Survey Explorer image of the region. Credit: NASA/JPL-Caltech/WISE Team; Kavak et al.

“When you breach the Veil shell, you effectively start stirring a cosmic soup of gas and dust by adding turbulence,” Kavak said.

“This isn’t the most appetizing soup, but it’s one of the ways to form new stars or limit future star formation,” added Alexander Tielens, a researcher at Leiden University and another author on the paper.

This turbulence affects the density, temperature, and chemistry of its surrounding region, which may ultimately lead to the creation or destruction of star formation sites.

The group also identified a second, weaker protrusion, which they plan to investigate further in a future publication. Together, these protrusions affect the entire morphology of the Orion Nebula.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014, and the mission will conclude no later than Sept. 30, 2022. SOFIA will continue its regular operations until then, including science flights and a deployment to New Zealand this summer.

Returning to New Zealand: SOFIA Travels to Christchurch for a Seventh and Final Time

By Maggie McAdam

After a two-year hiatus, SOFIA has returned to Christchurch, New Zealand, for a long deployment. About once a year, SOFIA temporarily moves its operating home to better observe celestial objects in the Southern Hemisphere.

SOFIA at Christchurch International Airport
SOFIA taxiing on the ramp at Christchurch International Airport in 2017. Image Credit: NASA/SOFIA/Waynne Williams

There is always a high demand from the SOFIA scientific community to observe the southern skies, and SOFIA has been working to meet those needs. This year, we already deployed once to Santiago, Chile, for a quick, two-week deployment to observe the Large Magellanic Cloud. Now SOFIA is heading back to New Zealand for the seventh and final time.

“We are thrilled to be returning to Christchurch to continue to study and discover the infrared universe,” said Naseem Rangwala, the SOFIA project scientist.

SOFIA has made 12 deployments over its operational lifetime, generally leaving Palmdale, California, to observe celestial objects and phenomena not visible from its home skies. We observed occultations in Florida and New Zealand, as well as atomic oxygen in Earth’s atmosphere, stellar feedback, and magnetic fields from German soil.

Christchurch is often SOFIA’s home-away-from-home when deploying overseas. This time, SOFIA plans to conduct 32 flights to observe a wide range of celestial objects and phenomena, like cosmic magnetic fields, stellar feedback, and cosmic rays, using two instruments, HAWC+ and GREAT.

Probing the Magnetic Universe

Milky Way galactic center, looking like a band of red clouds against a starry background.
While in New Zealand, SOFIA will observe magnetic fields in our galaxy, the Milky Way, pictured here from a previous study with another SOFIA instrument. Image credit: NASA/SOFIA/JPL-Caltech/ESA/Herschel.

Sticking relatively close to our cosmic home, SOFIA will start by investigating our galaxy, the Milky Way. A team of researchers is mapping the magnetic fields within the Milky Way’s central regions. These data will complement a previous Legacy Program that made mid-infrared images of the Milky Way. This work is similar to other cosmic magnetic field studies that map the shape and strength of this invisible force in other galaxies. SOFIA can detect cosmic magnetic fields on many scales, including star formation scales, especially along filaments.

SOFIA will also be looking at magnetic fields in filaments of material in our galaxy. These filaments are thread-like structures full of cold gas and dust. Most stars form in these dark rivers of material. A team of scientists will be investigating how magnetic fields play a role in star formation in filaments.

Stars Blowing Bubbles and a Barometer for Cosmic Rays

Deployment crew and staff stand in front of the SOFIA aircraft, all wearing neon yellow high-vis vests and jackets.
SOFIA in Christchurch, New Zealand, during its 2019 deployment with the staff and crew of the observatory. Image credit: NASA/Waynne Williams.

After HAWC+ finishes up probing the magnetic universe, SOFIA’s operations team will swap the instrument for the German PI-led GREAT instrument. GREAT does a wide variety of studies including looking at stellar feedback – how some stars can affect the regions around them. Young massive stars create huge winds that blow out into the surrounding dusty material, sometimes blowing celestial bubbles. As they do this, the stellar winds plow into the material and sometimes can trigger or quench star formation. Scientists want to understand when and why star formation is turned on or off.

GREAT, like the radio in your car, can be tuned to be sensitive to specific signals. During the New Zealand deployment, it will be set to register hydride molecules. These molecules were some of the first types that formed in our universe, and, even now, they are sometimes created in other environments. When scientists detect hydrides, they can use them as sensitive barometers for the presence of cosmic rays, high energy particles that travel close to the speed of light.

Hydride molecules form in very specific circumstances, and, usually, scientists can determine their production rate. At the same time, these molecules are quite delicate and can easily be destroyed by passing cosmic rays. Understanding the balance between their production and destruction can provide clues to the abundance of cosmic rays.

Scientists have measured the cosmic rays produced by our Sun and understand them very well, but do not fully understand cosmic rays that originate from outside our solar system. Using hydride molecules, researchers will investigate how abundant cosmic rays are in environments outside our solar system.

A Strong Finish

Arc-shaped patch with gold border and SOFIA text in gold with the telescope mirror in place of the O. The patch reads "New Zealand 2022, NASA, DLR, USRA, DSI" and shows SOFIA flying over New Zealand with the Milky Way and the fours stars of the Southern Cross constellation in the background sky.
2022 Deployment patch graphic. Image credit: NASA/SOFIA/Cheryse Triano.

Many of the key celestial objects for astronomers, like the center of the Milky Way, are either visible only from the Southern Hemisphere or more easily observed from these latitudes. Three years after SOFIA achieved first light in 2010, the observatory made its first trip to New Zealand. Now, nine years later and with six previous trips to Christchurch, this will be SOFIA’s last international deployment.

NASA and DLR recently announced the conclusion of the SOFIA mission. SOFIA will operate for the rest of fiscal year 2022, before entering an orderly shutdown process on October 1, 2022.

“We are committed to delivering a strong finish for this unique astrophysics mission, from a place of strength and pride, by giving our scientific community as much data as possible from the Southern Hemisphere,” Dr. Rangwala said. Moving forward, SOFIA’s data will be available in NASA’s public archives for astronomers worldwide to use.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.

Are Magnetic Fields Moving the Clouds in Cygnus-X?

by Anashe Bandari

Hidden behind a dark band of dust known as the Great Rift, the Cygnus-X star formation region is more than a bit of a mystery. Astronomers haven’t quite figured out what the molecular clouds in Cygnus-X are doing, and why, but observations from the Stratospheric Observatory for Infrared Astronomy (SOFIA) may help.

These mysteries relate to the fact that Cygnus-X is a difficult region to study. Two of its clouds – DR21 and W75N – clearly have separate gas velocities, but which cloud is in front of the other, and whether or not the two clouds are colliding, are open questions. Dan Clemens, an astronomer at Boston University, is the principal investigator on a project using SOFIA to examine Cygnus-X and the effects of magnetic fields on its clouds and cloud filaments. Details of these studies were presented at the June 2022 meeting of the American Astronomical Society.

Cygnus-X northeast region with segments showing the magnetic field orientations and curves highlighting filaments and sub-filaments.
Cygnus-X northeast region. Background image was constructed from Herschel SPIRE 250um in red, Herschel PACS 70um in green, and Spitzer MIPS 24um in blue. Red polygon indicates region surveyed for near-infrared, H-band (1.6um) stellar polarizations. Cyan segments indicate the magnetic field orientations derived from those NIR polarizations. Dashed white curves highlight filaments and sub-filaments cataloged by Hennemann et al. (2012) and new filaments and subfilaments from this study. The green polygon shows the DR21 Ridge region surveyed using SOFIA HAWC+ E-band (214um) polarization and the inscribed smaller magenta polygon shows the corresponding HAWC+ A-band (52um) polarization surveyed region. Credit: Herschel/Spitzer/SOFIA/Hennemann et al./Clemens et al.

“You can think of it as a pasta bowl with all these threads going in,” said Clemens. “Which pasta is in front of which pasta? Are there separate piles of pasta, or are they interacting piles of pasta that cause stars to form?”

On top of this, the presence of magnetic fields adds further complexity. What these magnetic fields are doing – whether they are passive participants in the clouds’ dynamics or helping to direct mass flows – is a question the SOFIA data may help answer by looking at small-scale filaments within the clouds.

Using SOFIA’s High-resolution Airborne Wideband Camera Plus (HAWC+), Clemens and his team zoomed in on Cygnus-X to look at the polarizations of the filaments at far-infrared wavelengths. These polarizations indicate the directions of the small-scale magnetic fields in the region, which the researchers use to determine the role the fields are playing.

“We want to ascertain the nature of the magnetic fields along these filaments, where they begin, and where they end,” Clemens said.  “This will help test our best star formation models and notions.”

Most modern theories of star formation hint that magnetic fields may be channeling gas flows within molecular clouds toward a central hub, where massive star formation occurs. The SOFIA observations will reveal the magnetic fields in filaments within the clouds, helping to verify the idea that fine, weak magnetic fields can control how stars form.

According to the team’s analysis, there appear to be four distinct layers of gas and dust between us and the northern region of Cygnus-X. Whether or not these layers are interacting will affect their understanding of SOFIA’s magnetic field data. As such, Clemens and his collaborators will need to determine which cloud is in front of the other, and if they are going to collide, before the SOFIA data – and supporting wider-field, ground-based, near-infrared data – describing the magnetic fields can be effectively interpreted.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014, and the mission will conclude no later than Sept. 30, 2022. SOFIA will continue its regular operations until then, including science flights and a deployment to New Zealand this summer.

Small Molecules Have Big Impacts in Interstellar Clouds

by Anashe Bandari

“One of the key goals, when you think about modern astronomy, considers the life cycle of molecular material,” said Arshia Jacob, an astronomer at Johns Hopkins University. Diffuse atomic gas becomes dense molecular gas, which ultimately forms stars and stellar systems, and continues to evolve over time. Though astronomers understand much of this process, there are a lot of missing pieces.

Jacob is the lead author on a recent paper characterizing the interstellar medium in the Milky Way using SOFIA, the Stratospheric Observatory for Infrared Astronomy, to fill in some of these missing pieces. By studying six hydrides, which are molecules or molecular ions in which one or more hydrogen atoms are bound to a heavier atom through shared electron pairs, Jacob and her collaborators hope to better understand how molecular clouds form and evolve.

Green and red swirls of nebulae are seen over a field of bright blue stars with W3 glowing white. Two spectra are laid over the background image, one green, one red.
W3, one of the 25 Milky Way regions the HyGAL project will study, is seen as the glowing white area in the upper right of this image of the Heart and Soul Nebulae, taken by NASA’s Wide-field Infrared Survey Explorer (WISE). SOFIA looked at the abundances of six hydride molecules in W3, the spectra of two of which are shown in the box at left. Image credit: Nebulae: NASA/JPL-Caltech/UCLA; Spectra: Jacob et al.

Hydrides are useful to astronomers because they are very sensitive tracers of different phases of the interstellar medium, and their chemistry is relatively straightforward. Moreover, hydride observations provide measurements of the amount of material present.

The multi-investigator SOFIA project Hydrides in the Galaxy (HyGAL) uses a diverse selection of hydride molecules, allowing different processes to be monitored while complementing other observations. For example, one of the hydrides studied, argonium, can only form in regions that are almost purely atomic gas, so detecting argonium is indicative of a low molecular content in its surrounding environment. Other hydride molecules can indicate the presence of dense gas, intense cosmic radiation, turbulence, and more.

“Hydrides are small, but we can understand so much from them. Small molecules, big impact,” Jacob said.

In the first stage of the project, the group compared the hydride abundances in three regions of the Milky Way: two star-forming regions, W3(OH) and W3 IRS5, and a young stellar object, NGC 7538 IRS1. Though the average properties of these first three sources are similar, the full HyGAL project plans to study a total of 25 regions. With the remaining 22 sources covering distances from the inner galaxy all the way to the outer galaxy, they expect vastly different results.

“The sources are very different: Some of them are older, some have more chemical enrichment, some are younger and still forming stars,” Jacob said. “All of these will affect the nature of molecules that are formed, like their abundances, for example.”

Moving away from the galactic center, the transitions from atomic to molecular gas change, and the cosmic ray ionization rates vary vastly, which will result in differences in the ratios of molecules present and other properties. This will help astronomers understand the diversity of environments within the Milky Way.

“Imagine you’re moving into a cloud. At each stage, you’re seeing different molecules, reflecting changes in the cloud properties as it gets denser,” Jacob said. “Through this project, we’re filling in the properties of this transition.”

Currently, there have only been a handful of bright sources emitting a broad range of radiation that have been studied in this way, all concentrated in the inner galaxy. The SOFIA data will more than double the existing data, providing additional answers about the structure, dynamics, and chemistry of these clouds and where the dense material comes from.

SOFIA is the only facility presently capable of accessing the frequency range necessary for these observations at the required resolution. The German REceiver Astronomy at Terahertz Frequencies (GREAT) instrument aboard SOFIA allows five frequencies to be monitored simultaneously, each tuned to five of the six hydrides in question to determine the makeup of the cloud sources. These are complemented by studies at radio wavelengths with observatories such as the Karl G. Jansky Very Large Array near Socorro, New Mexico.

“The idea is to give us not only information about the sources themselves, but also information about the different spiral arms they cross, making this truly a study over galactic scales,” Jacob said.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014, and the mission will conclude no later than Sept. 30, 2022. SOFIA will continue its regular operations until then, including science flights and a deployment to New Zealand this summer.

SOFIA Watches a Binary Star System’s Eclipse

by Anashe Bandari

With its observations of a special pair of stars at a special moment in their lives, the Stratospheric Observatory for Infrared Astronomy (SOFIA) is shedding new light on stardust.

Over an interval of 387 days, a giant star in the constellation Aquarius periodically has a dramatic change in its brightness. This is because the star falls into a category called Mira variables, which pulsate over long periods and surround themselves in a shell of dust.

But this isn’t just any Mira variable. The star is one of two in a binary star system known as R Aquarii, where it has a companion white dwarf. The two orbit one another, and the white dwarf crosses in front of the Mira variable every 43.6 years, causing an eclipse from the perspective of a viewer on Earth.

This composite image of R Aquarii resembles a ring of fire over a black field, with a glowing purple “S” flowing through it. Near the center of the image, in the middle of the ring and the “S” wave, is a twinkle of bright white, which is the Mira variable in R Aquarii.
This composite image of R Aquarii resembles a ring of fire over a black field, with a glowing purple “S” flowing through it. Near the center of the image, in the middle of the ring and the “S” wave, is a twinkle of bright white, which is the Mira variable in R Aquarii. The white dwarf is very faint and contributes very little to the optical emission. However, the purple wave is the result of a jet that is powered by the white dwarf accreting dust produced by the Mira variable. The smokey red circles are evidence of explosive events that occurred several hundred years ago. Overlain atop the composite image of R Aquarii is a set of five plots indicating the energy emitted by the system. SOFIA acquired four of the data sets, while the strong purple plot is data from the Infrared Space Observatory from 1996, when R Aquarii’s emission was strongest. The strength also depends on the phase of the binary star system’s eclipse, so it does not increase each successive year, exactly: the flux fell between 2018 and 2019. Credit: NASA/CSC/SAO/STScI/Palomar Observatory/DSS/NSF/NRAO/VLA/LCO/IMACS/MMTF/Sankrit et al.

There’s another thing that’s special about R Aquarii: The periastron, or the point in the orbit where the two stars are closest to each other, happens during the eclipse. This means that as the eclipse occurs – and the pair gets dimmer and dimmer, overall – the white dwarf and the Mira variable get closer and closer together. The white dwarf accretes more and more of the dust surrounding the Mira variable, and, because of this optimal geometry, we get to watch this process occur.

Since 2016, SOFIA, a joint project of NASA and the German Space Agency at DLR, has been monitoring the onset of the eclipse, which started in 2018, with periastron expected to occur in 2023. The flow of dust can be inferred at mid-infrared wavelengths, and SOFIA’s infrared camera, FORCAST, has just the right angular resolution to watch.

By combining what they know about the system – the distance between the two stars, the fact that an eclipse is ongoing, and predictions of how much dust there is – astronomers can figure out the balance between the amount of dust escaping the Mira variable and how much is being accreted by the white dwarf. These are “both very big questions,” said Ravi Sankrit, an astronomer at the Space Telescope Science Institute in Baltimore and first author on a recent paper about SOFIA’s 2018 and 2019 observations of R Aquarii.

“It’s an opportunity to see it in a unique way, because the material that’s being accreted isn’t obscured by the Mira, it’s right out in front,” added Steven Goldman, a scientist with Universities Space Research Association, based at NASA’s Ames Research Center in California’s Silicon Valley. Goldman is a co-author on the paper, which looks at how the onset of the eclipse is beginning to affect the dust surrounding the system.

Since the two stars move from being very far apart to very close to one another, their dust is constantly changing. Continued mid-infrared monitoring is required to fully understand how the dust is affected by the stars’ orbit.

“Binarity, winds, jet formation, mass loss, and accretion are fundamental astrophysics,” Sankrit said. “So, the real excitement here is that you’re getting something that is on a human timescale probing very fundamental aspects of astrophysics.”

The physics Sankrit, Goldman, and their team are uncovering is applicable to more than just R Aquarii. There are hundreds of other similar binaries, and those are just the ones we know of. These other binary systems are likely experiencing the same phenomenon but aren’t oriented correctly for us to be able to see their periastron and the changes in their surrounding dust.

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014, and the mission will conclude no later than Sept. 30, 2022. SOFIA will continue its regular operations until then, including science flights and a deployment to New Zealand this summer.