Over two-thirds of the spiral galaxies we see have an elongated nearly featureless bar-like structure across the middle. The bars can appear long or short, thin or squat. They are smooth and featureless compared with beclotted spiral arms. Our own Milky Way has a bar, though we cannot see it visually or in most astro-images because of star and dust clouds in the way.
Yet for all their ubiquity, bars are relatively recent. They do not begin to appear until the universe was about half its current age. Why are bars such latecomers? Why did they begin in the first place? What is their function?
The answers to these questions are not found in objects we can see — stars, nebulae, galactic structures. Instead, galaxy bars are shaped by things we cannot see — gravity, turbulent winds, magnetic fields, and globs of dark matter that does not shine.
This issue of Sky Candy simplifies the complexities of recent astrophysical research about barred galaxies into language any astronomy enthusiast can read.
