The balloon carried a stack of radioactive pancake-shaped films through the air, taking the world's most precise photos of the gamma ray beam of a neutron star. This pioneering work was accomplished by researchers from Kobe University, who combined the earliest radioactive radiation detection technology with advanced data acquisition technology and innovative time recording devices.
Stars shine at us in the full spectrum of light, from infrared to gamma rays. For each band, different sensing equipment is required. The most challenging of these are gamma rays, which are famous for being the high-energy product of nuclear fission because their very short wavelength means they don't interact with matter like other forms of light, so they can't be deflected with lenses and cannot be detected by standard sensors. As a result, there is a gap in our ability to detect light from fascinating stellar objects such as supernovae and their remnants.
To solve this problem, Kobe University astrophysicist Shigeki Aoki and his team turned their attention to the earliest material used to detect radioactivity - photosensitive film. "Our research group has been focusing on emulsion film's remarkable ability to track gamma rays with high precision and proposed that emulsion film could become an excellent gamma-ray telescope by introducing some modern data capture and analysis capabilities," Aoki explained.
Based on the high sensitivity of these films and a novel, automated, high-speed process for extracting data from the films, the idea is to stack several films to accurately capture the trajectories of particles produced when gamma rays hit them. Just like a pancake might capture where you poke a straw in, but recording the direction of the straw would require an entire stack of pancakes.
To reduce atmospheric interference, they then mounted the stack of films on a scientific observation balloon and raised it to an altitude of 35 to 40 kilometers. However, because the balloon swayed and twisted in the wind, the direction of the "telescope" was unstable, so they added a set of cameras to record the gondola's position relative to the starry sky at all times.
But this creates another problem, because as anyone who has taken photos with long exposures knows, photographic film cannot record the passage of time, so there is no direct way to know when the gamma ray impact occurred. To overcome this problem, they made the bottom three layers of film move back and forth at fixed but different speeds, like the hands of a clock. Based on the relative misalignment of the marks on the underlying film, they were able to calculate the precise time of impact and correlate it with the camera footage.
Now, they have published the first image produced by the device in The Astrophysical Journal. This is the most accurate image of the Vela pulsar ever taken. The Vela pulsar is a rapidly spinning neutron star that projects a beam of gamma rays into the sky like a beacon at night. "In total, we captured trillions of trajectories with an accuracy of 1/10,000 of a millimeter. By adding timing information and combining it with attitude monitoring information, we were able to determine the 'when' and 'where' of the event with great precision, at a resolution more than 40 times that of conventional gamma-ray telescopes."
While these results are already impressive, new techniques offer the possibility of capturing even more detail in this band of light. Researchers from Kobe University explained: "Through scientific balloon experiments, we can try to contribute to many fields of astrophysics, especially applying gamma-ray telescopes to 'multi-messenger astronomy,' where simultaneous measurements of the same event captured by different techniques are required. Based on the successful data generated by the balloon experiment in 2018, we will expand the observation area and time in the following balloon flights, and look forward to making scientific breakthroughs in the field of gamma-ray astronomy."
Compiled source: ScitechDaily