At the heart of our galaxy lies a puzzling, diffuse glow of gamma rays that has intrigued scientists since its detection by NASA“s Fermi Gamma-ray Space Telescope shortly after its launch in 2008. This radiation, typically associated with high-energy phenomena such as rapidly spinning or exploding stars, has led to various hypotheses regarding its origin.
While some astronomers attribute this glow to pulsars—remnants of exploded stars—others propose that it could result from interactions involving dark matter, a mysterious and largely elusive substance believed to outnumber regular matter by a factor of five. Initial studies have supported both theories, but a complication arose: the shape of the gamma ray glow closely resembled that of the galactic bulge, an area densely populated with older stars, including pulsars. This observation seemed to lend credence to the pulsar hypothesis, as dark matter”s influence would likely produce a more uniform spherical glow.
Despite the challenge, researchers have struggled to identify sufficient pulsars that could account for the gamma rays, leaving the question of the glow”s source unresolved. Recent simulations conducted on supercomputers, however, have provided fresh insight, indicating that dark matter collisions might indeed generate the bulge-shaped glow.
“We are currently faced with two competing theories: one suggesting dark matter as a potential explanation for our observations, and the other pointing to old stars,” stated Joseph Silk, a physics and astronomy professor at Johns Hopkins University and co-author of a study published in the journal Physical Review Letters. “From my perspective, there is now a 50% likelihood that dark matter is the cause, rather than the more conventional explanation involving old stars.”
Establishing the existence of dark matter would represent a monumental advancement in physics. The notion of dark matter was first proposed by Swiss astronomer Fritz Zwicky in the 1930s, with confirmations from American astronomers Vera Rubin and W. Kent Ford in the 1970s. They observed that stars at the edges of spiral galaxies were orbiting at velocities too high to be accounted for by visible matter alone, leading to the hypothesis of a substantial, unseen mass keeping them in place. Despite ongoing investigations, scientists have yet to directly observe this elusive substance.
“The nature of dark matter remains one of the most significant unsolved issues in physics,” Silk remarked. “Its presence is ubiquitous, yet what it actually is continues to elude us.”
Various theories regarding dark matter”s composition range from primordial black holes to undiscovered particles. Much of the research has focused on the latter, particularly the search for a specific category of particles known as Weakly Interacting Massive Particles (WIMPs). These hypothetical particles are thought to interact weakly with normal matter and are undetectable by light, allowing them to pass through ordinary matter with ease. When WIMPs collide, they are predicted to annihilate each other, resulting in the emission of gamma rays, thus making them a compelling candidate for the source of the observed glow.
Silk”s recent study utilized advanced computer simulations to map the dark matter distribution within the Milky Way, considering the galaxy”s formation history. “Previous models treated dark matter as a uniform spherical mass, as it was the simplest approach,” he explained. “Our contribution was to create a more accurate simulation of dark matter distribution, revealing that the central region, where the gamma rays are emitted, is more flattened—resembling an egg shape.” This flattened structure aligns closely with the data gathered from the Fermi telescope.
Encouragingly, confirmation of a potential link between dark matter and the gamma ray glow may be on the horizon. The Cherenkov Telescope Array Observatory (CTAO), currently under construction in Chile and Spain, is expected to commence data collection by 2027. With its enhanced capability to detect gamma rays at higher resolutions than Fermi, the CTAO could determine whether the gamma rays emanating from the Milky Way”s center are indeed the result of dark matter collisions.
Should the CTAO fail to establish this connection, scientists may find themselves revisiting alternative explanations for the glow, with all hypotheses remaining viable. The study has reignited the possibility that dark matter could elucidate the enigmatic glow at the galactic core, although it does not provide definitive evidence for the dark matter theory. Tracy Slatyer, a physics professor at the Massachusetts Institute of Technology who was not involved in the study, commented, “I believed the dark matter hypothesis was reasonable even before this study.”
According to Chamkaur Ghag, a physics and astronomy professor at University College London and study outsider, the findings bolster the international pursuit of WIMPs, which are seen as an elegant solution to the enduring dark matter dilemma. “The ongoing development of additional WIMP detectors raises the possibility of detecting signals from these particles annihilating in space, potentially resolving the long-standing dark matter mystery,” he stated.
Nico Cappelluti, an associate professor at the University of Miami, asserted that the Fermi telescope has been transformative for NASA. He emphasized that this latest research reinforces the relevance of dark matter in explaining the mysterious glow at the Milky Way”s center. “This enigma persists, captivating scientists like me,” Cappelluti noted. “Understanding dark matter is one of the foremost scientific challenges of our time. Although no WIMP signatures have been detected thus far, the Fermi telescope offers hope. This study serves as a reminder not to discount WIMPs just yet; they may still illuminate the center of our galaxy.”
If validated, this finding could bring us closer to unraveling a fundamental secret of the universe.
