A recent study has unveiled the true shape of the diffuse cloud of stars surrounding the disk of our galaxy, known as the stellar halo. Previously thought to be largely spherical, like a beach ball, the new model, based on modern observations, shows that the stellar halo is oblong and tilted, simila
, provide insight into various astrophysical subjects, including the history and evolution of our galaxy and clues in the search for dark matter.accuracy. “There are a lot of important implications of the stellar halo not being spherical but instead shaped like a football, rugby ball, or zeppelin — take your pick!”
“The stellar halo is a dynamic tracer of the galactic halo,” says Han. “In order to learn more about galactic haloes in general, and especially our own galaxy’s galactic halo and history, the stellar halo is a great place to start.” Complicating matters further, the stellar halo has proven to be quite diffuse, containing only about one percent of the mass of all the galaxy’s stars. Yet over time, astronomers have succeeded in identifying many thousands of stars that populate this halo, which are distinguishable from other Milky Way stars due to their distinctive chemical makeup , as well as by their distances and motions across the sky.
Combining these data in a flexible model that allowed for the stellar halo shape to emerge from all the observations yielded the decidedly non-spherical halo — and the football shape nicely dovetails with other findings to date. The shape, for example, independently and strongly agrees with a leading theory regarding the formation of the Milky Way’s stellar halo.
“The tilt and distribution of stars in the stellar halo provide dramatic confirmation that our galaxy collided with another smaller galaxy 7-10 billion years ago,” says Conroy. Conroy’s latter point alludes to the multiple dark matter detector experiments now running and planned. These detectors could increase their chances of capturing an elusive interaction with dark matter if astrophysicists can adjudge where the substance is more heavily concentrated, galactically speaking. As Earth moves through the Milky Way, it will periodically encounter these regions of dense and higher-velocity dark matter particles, boosting the odds of detection.
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