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New research reveals exact shape of halo of stars in our galaxy

The shape of the stellar halo is a very fundamental parameter that we've just measured to greater accuracy than was possible before

New research reveals exact shape of halo of stars in our galaxy

Sentinel Digital DeskBy : Sentinel Digital Desk

  |  21 Nov 2022 6:44 AM GMT

MASSACHUSETTS: The actual shape of the cloud-like diffusion of stars surrounding the disk of our milky-way galaxy has finally been discovered. It was believed to be spherical for decades. However, with the rise in modern observatory techniques, a new model is established that showcases that the stellar halo, as this cloudy diffusion is called, is oblong and tilted.

The findings – published in this month's The Astronomical Journal – offer insights into a host of astrophysical subject areas. The results, for example, shed light on the history of our galaxy and galactic evolution, while also offering clues in the ongoing hunt for the mysterious substance known as dark matter. "The shape of the stellar halo is a very fundamental parameter that we've just measured to greater accuracy than was possible before," says study lead author Jiwon "Jesse" Han, a PhD student at the Centre for Astrophysics | Harvard & Smithsonian. "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!"

"For decades, the general assumption has been that the stellar halo is more or less spherical and isotropic, or the same in every direction," adds study co-author Charlie Conroy, Han's advisor, and a professor of astronomy at Harvard University and the Center for Astrophysics. "We now know that the textbook picture of our galaxy embedded within a spherical volume of stars has to be thrown out."

The Milky Way's stellar halo is the visible portion of what is more broadly called the galactic halo. This galactic halo is dominated by invisible dark matter, whose presence is only measurable through the gravity that it exerts. Every galaxy has its own halo of dark matter. These halos serve as a sort of scaffold upon which ordinary, visible matter hangs. In turn, that visible matter forms stars and other observable galactic structure. To better understand how galaxies form and interact, as well as the underlying nature of dark matter, stellar haloes are accordingly valuable astrophysical targets.

"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."

Fathoming the shape of the Milky Way's stellar halo, though, has long challenged astrophysicists for the simple reason that we are embedded within it. The stellar halo extends out several hundred thousand light years above and below the star-filled plane of our galaxy, where our Solar System resides.

"Unlike with external galaxies, where we just look at them and measure their halos," says Han, "we lack the same sort of aerial, outside perspective of our own galaxy's halo."

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 (gaugeable by studies of their starlight), as well as by their distances and motions across the sky. (ANI)

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