SOFIA’s Infrared View of the Skies

The Stratospheric Observatory for Infrared Astronomy, SOFIA, studies the universe with infrared light.
That’s a range of wavelengths on the infrared spectrum, from those measuring about 700 nanometers, too small to see with the naked eye, to about 1 millimeter, which is about the size of the head of a pin. Other observatories, such as the Spitzer Space Telescope and Herschel Space Observatory, also studied infrared light. But each telescope observes different wavelengths of infrared light, filling in puzzle pieces that are essential to learning what makes the universe tick.

Spitzer studied exoplanets (planets outside our solar system), distant galaxies, and cold matter found in the space between stars using infrared wavelengths between 3.6-160 microns until 2009 when it ran out of coolant. After the coolant was depleted, it studied wavelengths between 0.3-0.9 microns, which are primarily near infrared wavelengths, during its so called “warm mission.”

SOFIA studies wavelengths of mid- and far-infrared light between 0.4-612 microns, letting scientists tackle big questions of how previously unseen forces shape the cosmos. With its 45,000-foot-high view of the night skies, the formation of planets and stars, the strange behavior of magnetic fields, and the chemistry of galaxies are all becoming clearer.

The discoveries from SOFIA often build on what previous observatories learned and illustrate the distinct yet complementary infrared perspective provided by different telescopes.

Diving into Star Formation

SOFIA found many newborn massive stars that had not been seen before in the largest star forming region in our galaxy, called W51A. Massive stars can weigh more than eight times our Sun, but it’s not well understood how they form and how they affect the birth of their stellar neighbors.

“Seeing regions like W51A in great detail gives us a better understanding of how stars actually form — surrounded by many others,” said James De Buizer a senior scientist at the SOFIA Science Center at NASA’s Ames Research Center in California’s Silicon Valley. “We can learn how the presence of nearby stars, or environmental differences, change how a cluster of massive stars forms and evolves over time.”

But seeing these massive stars is not easy. They are hidden deep inside celestial clouds. SOFIA’s infrared camera called FORCAST, the Faint Object Infrared Camera for the SOFIA Telescope, can peer inside the obscuring clouds, revealing how these enormous stars are changing their surroundings.

Using the new details, researchers calculated the age of W51A’s different regions and found that many of the stellar clusters are each made of multiple generations of star birth. Moreover, some of the objects that had previously been identified as massive newborn stars by other telescopes, including Spitzer, had been misclassified. SOFIA’s new view indicates that some are actually older or smaller, less massive stars.

Areas like W51A are so intensely bright at far-infrared wavelengths that many details could not be seen by most space telescopes because their detectors were saturated, like an overexposed photo. Near-infrared observations by Spitzer were contaminated by bright emission from smoke-like carbon molecules present in star-forming environments, which made it difficult to determine the stars’ properties. But SOFIA’s detectors work at wavelengths that are free from this smoky environmental contamination, revealing previously hidden details — including those needed to accurately classify the stars’ sizes and ages.

Combining the data from both SOFIA and space telescopes like Spitzer and the Herschel Space Observatory is helping researchers understand the complete star formation history of W51A. In some areas, the most massive stars have triggered the birth of younger generations, but in others they have slowed it. Based on all the data, they expect the next generation of stars to form near the center of W51A.

The team created the image by combining new SOFIA data with existing data from Spitzer and Herschel Space Observatory. It shows arcs and bubbles blown by adolescent massive stars, as the intense radiation pressure from the largest stars pushes dust from their natal cocoons out in all directions. The heat from the dust in these features glows brightly at infrared wavelengths of 37 and 70 microns, which are green and red. Although the adolescent stars have cleared dust from inside the bubbles, there is still hot and excited gas inside, which can be seen in the 20-micron infrared view that is traced in blue. Together, the multifaceted infrared view gives scientists a more complete understanding of how the most massive stars in our galaxy are born and how they affect their neighbors.

Uncovering Magnetic Fields

SOFIA newest instrument, the High-resolution Airborne Wideband Camera-Plus (HAWC+), can study celestial magnetic fields. The Cigar galaxy, Messier 82, is famous for its extraordinary speed in making new stars, something astronomers call the “starburst phenomenon.” The high rate of star birth is generating a stellar wind flowing out of the galaxy that drags material with it.

Spitzer’s wide view found that the wind is blowing dust 20,000 light-years around the galaxy — far beyond where stars are forming. But scientists were not sure why the dust reached so far. Subsequent observations with SOFIA peered closed to the galaxy’s core, revealing that the wind is also dragging the galaxy’s magnetic field.

Magnetic fields are usually parallel to the plane of the galaxy, but the wind is dragging it so it’s perpendicular. Generally, magnetic fields are powerful enough to resist stellar winds, but the Cigar galaxy’s wind is so strong that it’s dragging the magnetic field with it. This supports Spitzer’s initial findings that the starburst-driven wind is transporting a huge amount of material and shows that it’s an ongoing route for material to escape from inside the galaxy.

Together with other, complementary telescopes, SOFIA’s infrared view of the skies is expanding scientists’ understanding of the universe by revealing more than human eyes can see.

The Spitzer Space Telescope was decommissioned on Jan. 30, 2020, after operating for more than 16 years. NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Space operations are based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.

Herschel is a European Space Agency mission, with science instruments provided by consortia of European institutes and with important participation by NASA. While the observatory stopped making science observations in April 2013, after running out of liquid coolant as expected, scientists continue to analyze its data. NASA’s Herschel Project Office is based at NASA’s Jet Propulsion Laboratory, Pasadena, California. JPL contributed mission-enabling technology for two of Herschel’s three science instruments. The NASA Herschel Science Center, part of IPAC, supports the U.S. astronomical community. Caltech manages JPL for NASA.

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. 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 (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA’s Armstrong Flight Research Center Hangar 703, in Palmdale, California.