Low-energy gamma rays 'directly image' the center of the Milky Way — a world first from a balloon experiment
A research group including JAXA has announced that it has, for the first time in the world, directly imaged low-energy gamma rays coming from the center of the Milky Way, using the same principle as an optical telescope. As I read about it, it struck me as one of those stories that looks modest at first but is actually remarkable, so I'm sharing it.
The target is gamma rays in the 150–600 keV range, energies below 1 MeV. With no high-precision imaging method and heavy background noise, this band has been an unexplored frontier known as the "MeV gap." Until now, researchers apparently had to rely on indirect methods, modeling the noise across the whole sky along with the faint signal to make estimates.
The instrument used was an "Electron-Tracking Compton Camera (ETCC)," which can follow even the tracks of electrons. By analyzing about a day of observations from the large balloon experiment "SMILE-2+," launched from central Australia in 2018, the team captured a significant signal from the direction of the galactic center as an image. I found the explanation easy to follow: with a conventional Compton camera, even a point source spreads out into a ring, whereas with the ETCC it converges to a single point.
The positron-annihilation gamma rays they obtained agree with previous observations within the margin of error, yet are about twice as intense. With emission several times stronger than theoretical predictions now more firmly established, there are hopes it will help test unknown origins such as dark matter or primordial black holes. The results were published in August 2026 in a journal of the American Physical Society and were also featured in a Nature Research Highlight.
A more sensitive follow-up experiment, "SMILE-3," is reportedly being prepared as a candidate for the balloon campaign planned in Australia in 2028. The phrase "from a science of inference to a science of seeing" really stayed with me.
Source: JAXA (Japan Aerospace Exploration Agency)
The target is gamma rays in the 150–600 keV range, energies below 1 MeV. With no high-precision imaging method and heavy background noise, this band has been an unexplored frontier known as the "MeV gap." Until now, researchers apparently had to rely on indirect methods, modeling the noise across the whole sky along with the faint signal to make estimates.
The instrument used was an "Electron-Tracking Compton Camera (ETCC)," which can follow even the tracks of electrons. By analyzing about a day of observations from the large balloon experiment "SMILE-2+," launched from central Australia in 2018, the team captured a significant signal from the direction of the galactic center as an image. I found the explanation easy to follow: with a conventional Compton camera, even a point source spreads out into a ring, whereas with the ETCC it converges to a single point.
The positron-annihilation gamma rays they obtained agree with previous observations within the margin of error, yet are about twice as intense. With emission several times stronger than theoretical predictions now more firmly established, there are hopes it will help test unknown origins such as dark matter or primordial black holes. The results were published in August 2026 in a journal of the American Physical Society and were also featured in a Nature Research Highlight.
A more sensitive follow-up experiment, "SMILE-3," is reportedly being prepared as a candidate for the balloon campaign planned in Australia in 2028. The phrase "from a science of inference to a science of seeing" really stayed with me.
Source: JAXA (Japan Aerospace Exploration Agency)
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