Harvard Astronomers Explain Milky Way’s Warped Shape and Dark Matter Halo
A new study conducted by astronomers at the Center for Astrophysics | Harvard and Smithsonian (CfA) sheds light on the mysterious warped shape of the Milky Way and provides insights into the nature of dark matter. The findings offer compelling evidence for the hypothesis that our galaxy experienced a past collision with another galaxy.
For years, scientists have been aware of the Milky Way’s distinctive warp, which gives it the appearance of a twisted vinyl LP when viewed from the edge. However, the cause of this phenomenon has remained elusive until now.
Led by Jiwon Jesse Han, a student at the Griffin Graduate School of Arts and Sciences affiliated with CfA, the Harvard astronomers performed calculations that explain the Milky Way’s warp. Their research suggests that the galaxy is enveloped in an irregular dark matter halo, which is off-kilter and gives rise to the warp effect. The dark matter halo, which makes up 80% of the galaxy’s mass, is invisible and does not interact with light, making its shape difficult to determine.
The team’s calculations were based on their previous groundbreaking work, which revealed that the stellar halo, a diffuse cloud surrounding our galaxy, is tilted and elliptical in shape. Building on this knowledge, they assumed a similar tilted and oblong shape for the dark matter halo. By modeling the orbits of stars within this tilted halo, the researchers were able to match their results with existing observations of the warped and flared Milky Way.
The implications of these findings go beyond explaining the Milky Way’s shape. They also provide insights into the nature of dark matter itself. The shape of the dark matter halo can offer clues about the properties and particle nature of dark matter, which remains a mystery in physics. The researchers believe that the fact that the galaxy is not perfectly spherical suggests limitations on how dark matter can interact with itself.
Charlie Conroy, a faculty member at both CfA and the Department of Astronomy, described the tilted dark halo as an elegant explanation for the magnitude and direction of the Milky Way’s wobbly disk. The team’s work strengthens the hypothesis that the Milky Way’s formation was influenced by a collision with another galaxy.
The discovery may open up new avenues for studying dark matter, which is essential to a better understanding of the universe. By gaining confidence in their findings, scientists might develop more effective methods to study the unobservable dark matter that constitutes most of the cosmos. This could include identifying kinematic signatures of miniature dark matter halos, known as dark sub-halos, that are present within the Milky Way.
The study, titled “A tilted dark halo origin of the Galactic disk warp and flare,” was published in the journal Nature Astronomy. The research was co-authored by Charlie Conroy and Lars Hernquist, both faculty members at CfA and in the Department of Astronomy.