This may be remembered as one of the more important physics images of this generation.
Credit: Tomonori Totani, The University of Tokyo
Physicists from Japan’s University of Tokyo have published a new paper in the Journal of Cosmology and Astroparticle Physics, claiming to show the first direct imagery of dark matter. It’s a finding that will surely generate some controversy, and it needs to be examined by the world’s leading experts. But for now, it seems as though dark matter might not be so dark, after all.
Put simply, dark matter is supposed to be totally invisible. It should interact with regular matter through gravity alone, and so while it might bend light very slightly, it really shouldn’t be visible in any other way. This has created a complex problem for astrophysicists investigating dark matter, who have had to make do with studying the large-scale distribution and motion of mass in the universe; this can yield some information at the cosmic scale, but none in the way of fine detail.
Still, a proposed mechanism called dark matter annihilation has been theorized to produce light directly. Specifically, the annihilation of dark matter particles and antiparticles should produce faint but measurable gamma-ray emissions.
This full version of the dark-matter render. Grey bar explained, below.
Credit: Tomonori Totani, The University of Tokyo
This study used the Fermi Gamma-ray Space Telescope to observe the center of the galaxy, where gravity should cause dark matter to cluster, increasing the frequency of annihilation events. What they saw, when calibrating the telescope to the exact specifics of theoretical dark-matter-annihilation gamma rays, was the image above: the first direct image of dark matter, rendered from gamma-ray detections.
The gray bar simply covers the area of the picture where the radiation of the galactic core is too strong, and muddies up the signal to the point that it’s unusable. Sort of an odd choice to just blank it out, but whatever.
The Japanese team states that the image they generated appears to show a halo-like pattern, a shape that dark matter has previously been theorized to form.
If the finding is accepted, it would also help to settle the debate about the fundamental nature of dark matter, since the annihilation concept is based on the theory of dark matter as based on Weakly Interacting Massive Particles, or WIMPs. If dark matter annihilation can be proven to exist, that constitutes strong evidence for the WIMPy nature of dark matter.
A simulation of the formation of dark matter structures from the early universe until today.
Credit: NASA/SLAC National Accelerator Laboratory
The finding is already getting some pushback from physicists around the world, however. Many point out that these gamma ray detections could be due to events other than dark matter annihilation, in particular, certain behaviors of neutron stars.
We’ll have to wait and see how it plays out. If confirmed, this image would be a real game-changer for astrophysics. The ability to directly image dark matter means the ability to image the substance that has, perhaps, more to do with the formation of galaxies, stars, and planets than even regular matter itself.
If this really is a way to look at dark matter directly, it could be a skeleton key that lets astronomers unlock untold secrets of the cosmos.