Monday, February 26

Student-built super pressure balloons search Earth’s sky for dark matter 2023

High-altitude balloons are under fire. In February, the US military shot down a Chinese spy balloon and a “unidentified aerial phenomenon” that was presumably a hobbyist balloon.

In early May, another enormous balloon was spotted in the southern hemisphere, raising concerns it was a surveillance device. Instead, balloon-borne telescopes that view deep into space from the stratosphere are the future of astronomy.

“We’re looking up, not down,” explains Princeton University physics professor William Jones, director of NASA’s Super Pressure Balloon Imaging Telescope (SuperBIT) team. The roughly 10-foot-tall telescope, launched from Wānaka, New Zealand, on April 15, has circled the southern hemisphere four times on a football stadium-sized polyethylene balloon.

Its three cameras captured Hubble Space Telescope-like photos of the Tarantula Nebula and Antennae galaxies. SuperBIT may help scientists understand dark matter, a supposedly unseen element only known via its gravitational impacts on observable things.

Next-generation observatories like the James Webb Space Telescope can provide clear images of distant astronomical objects to study dark matter. But building and deploying a space telescope is costly. Hubble cost $1.5 billion to launch, while JWST cost approximately $10 billion to reach Lagrange point 2.

SuperBIT cost $5 million to launch.

“Students run everything. “That’s what makes projects like these so nimble and able to do so much with limited resources,” Jones says of the SuperBIT collaboration involving Princeton, Durham University in the UK, and Toronto University in Canada. “Only the grad students can work on this full-time—no professional engineers or technicians.”

Another Princeton astronomy group created Stratoscope I in 1957, the first balloon-borne telescope. 20 years of NASA research into super pressure balloons made SuperBIT one of several new observatories. 2015 saw the first SuperBIT launch and test flights.

Traditional balloons expand when the sun heats them and air pressure fluctuates with altitude. That alters the envelope volume and balloon buoyancy, making it hard to maintain a consistent height.

Superpressure balloons pressurize helium inside a primary envelope to maintain volume and buoyancy day and night. The balloon then employs a smaller balloon—a ballonet—inside or under the main envelope as a ballast to fill or empty the compressed air pocket to alter height and maneuver the ship.

SuperBIT’s super pressure balloon can deliver a 3,500-pound scientific payload to 108,000 feet, higher than 99.2% of Earth’s atmosphere. The SuperBIT telescope does not discover exoplanets or view deeper into the cosmos like JWST. Instead, it seeks a more pervasive and mysterious entity.

“Dark matter is not made of any of the elements or particles we are familiar with through everyday observations,” Jones explains. It’s everywhere: Possibly 27% of the universe. Jones says, “We know this through the gravitational influence that it has on the usual matter—stars and gas, and the like—that we can see,” which makes up 5% of the universe.

Scientists believe that dark energy makes up about 67 percent of the cosmos.

Gravitational lensing is used to detect dark matter by examining huge galaxy clusters that bend light from distant objects. JWST can utilize this method to magnify galaxies to observe more distant objects. It can show the mass and dark matter around the “lens” galaxy clusters.

“After measuring how much dark matter there is and where it is, we’re trying to figure out what dark matter is,” explains SuperBIT scientific team member and Durham University physics professor Richard Massey. “We look at the few special places in the universe where lumps of dark matter are smashing into each other.”

The Antennae galaxies, 60 million light-years from Earth, are colliding. Hubble “gives it a field of view too small to see the titanic collisions of dark matter,” Massey adds. “We built SuperBIT.”

NGC 4038 and NGC 4039, the Antennae galaxies, collide 60 million light-years distant toward the southern constellation Corvus. Hubble, Chandra, and Spitzer have photographed the galaxies.

SuperBIT, like Hubble, observes 300- to 1,000-nanometer wavelengths. SuperBIT’s half-degree field of vision allows it to survey larger areas of the sky than Hubble’s tenth degree. Its half-meter mirror is smaller than Hubble’s 1.5 meters.

SuperBIT also outperforms space telescopes. The SuperBIT team used more modern camera sensors than current space telescopes since it took less time to create and did not need complex accessories to protect it from radiation, severe temperatures, and space debris. Jones said SuperBIT has a 60-megapixel sensor, unlike Hubble’s Wide Field Camera 3’s 8-megapixel sensors. Scientists can update the balloon-carried telescope from the ground since it floats down on a parachute after each trip.

Massey said they’re talking to SuperBIT 24/7 for 100 days. “It has just finished its fourth trip around the world, experiencing the southern lights, turbulence over the Andes, and quiet cold above the middle of the Pacific Ocean.” Jones anticipates retrieving the system in southern Argentina in late August.

SuperBIT may be the start. NASA is developing a Gigapixel class Balloon Imaging Telescope (GigaBIT) with a Hubble-sized mirror. Jones thinks GigaBIT will be cheaper and more powerful than any satellite telescope sensing the same range of light.

It’s unclear if SuperBIT will solve dark matter’s identity. Grad students will analyze project results after a few flights.

What will data reveal? Who knows! “That’s the excitement—and the guilty secret,” Massey adds. After 2,000 years of research, we still don’t know what the universe’s two most prevalent substances are or how they function.

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