Cosmology: Milky Way gobbles up satellites (Introduction)

by David Turell , Thursday, November 05, 2020, 18:15 (1480 days ago) @ David Turell

Small spherical galaxies orbiting the Milky Way feel its effects and give up gas to us:

https://www.sciencenews.org/article/milky-way-little-dwarf-galaxies-gas-stars

"Some 60 known galaxies orbit the Milky Way. About a dozen of these satellite galaxies are dim dwarf spheroidals, which each emit just 0.0005 to 0.1 percent as much light as the Milky Way. Their few stars are spread out from one another, giving the galaxies such a ghostly appearance that the first one found was initially suspected to be only a fingerprint on a photographic plate.

"But these ghostly galaxies once sparkled with young stars. A new study finds that most of these galaxies lit up when they first crossed into our galaxy’s gravitational domain as fresh stars arose. But then, in most cases, the little galaxies stopped making stars soon afterward, because the Milky Way stripped the dwarf galaxies of gas, the raw material for star formation.

***

"Dwarf galaxies that kept their distance also kept their gas longer, the researchers found. The galaxies that came closest to the Milky Way’s center, such as Draco and Leo I, ceased all star formation soon after crossing the Milky Way’s frontier. However, the galaxies that entered our galaxy’s domain but remained farther out, such as Fornax and Carina, fared better.

“'Those two galaxies kept their interstellar gas inside them, so that the star formation still continued,” Chiba says. Both galaxies managed to eke out new stars for many billions of years after crossing into the Milky Way’s realm. Today, however, neither galaxy has any gas left."

Comment: This all makes good sense. The Milky Way is a giant which allows the Earth to find a place two-thirds of the way out on the second spiral arm, safely distant from all the galaxies' fireworks.