A pancake stack of radioactivity-sensitive films carried into the sky by a balloon was able to capture the world’s most accurate picture of the gamma ray beam of a neutron star. To achieve this, researchers at Kobe University combined the oldest method of capturing radioactive radiation with the latest data acquisition techniques and a smart time recording device.
The stars shine their light on us in the entire range of the light spectrum, from infra-red to gamma rays. For each of these bands, different sensing equipment is required. The most challenging are gamma rays, famous for being a high-energy product of nuclear fission, because their very short wavelength means they don’t interact with matter in the same way as other forms of light. and thus cannot be deflected. with lenses or detected by standard sensors. Thus, there is a gap in our ability to detect light coming from interesting stellar objects such as supernovae and their remnants.
To solve this issue, Kobe University astrophysicist Aoki Shigeki and his team turned to the earliest material used to detect radioactivity, photographic films.
“Our group pointed out the excellent capability of emulsion film to track gamma rays with high precision and suggested that it could become an excellent gamma-ray telescope by introducing more modern data acquisition and analysis. parts,” Aoki explained.
Based on the high sensitivity of these films and a novel, automatic, fast process of extracting data from them, the idea of physicists is to gather some of them in order to accurately capture the path of the particles produced by the gamma rays. effect, like a pancake you can get where you stick a straw into it, but it takes a whole stack to record the direction of the straw.
To reduce atmospheric interference, they placed the stack of films in a scientific observation balloon to raise it to a height between 35 and 40 kilometers. However, since a balloon shakes and rotates in the air, the direction of the “telescope” is not stable, so they added a set of cameras to record the orientation of the gondola in relation to the stars at any time. But this creates another issue, because as anyone who has taken a photo with a long exposure knows, photographic film does not record the passage of time and therefore it is not directly possible to know what time even what given effect of gamma ray occurred.
To overcome this problem, they made the bottom three layers of the film go back and forth at a regular but varying speed, like the hands of a clock. From the relative dislocation of the signs on the bottom plates they can calculate the exact time of the impact and thus correlate it with the footage of the cameras.
They have now published the first image resulting from this setup in the journal The Astrophysical Journal. This is the most precise image ever made of the Vela pulsar, a fast-spinning neutron star that shines a beam of gamma rays into the sky like a lighthouse at night.
“We obtained a total of several trillion tracks with an accuracy of 1/10,000 millimeters. By adding time information and combining it with behavior monitoring information, we were able to determine ‘when’ and ‘where’ the events originate with such precision that the The resulting resolution is more than 40 times higher than conventional gamma-ray telescopes,” Aoki summarized the achievements of his group.
Although these results are already impressive, the new technique opens up the possibility of obtaining more details in this frequency band of light than before.
The Kobe University researcher explained, “Through the balloon-borne scientific experiments, we can try to contribute to many areas of astrophysics, and especially to the opening of gamma-ray telescopes in ‘multi-messenger astronomy’ where the simultaneous measurements of the same phenomenon obtained through different techniques are necessary. Based on the success of the 2018 balloon experiment that these data were generated, we will expand the observation area and time of future balloon flights and look forward to scientific achievements in the field of gamma-ray astronomy .”
First emulsion-ray telescope imaging of the Vela pulsar by the GRAINE 2018 balloon-borne experiment, The Astrophysical Journal (2023). DOI: 10.3847/1538-4357/ad0973
Provided by Kobe University
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