Now, 10 billion years later, they don’t make new stars at all. Full of old, rose-colored suns, they are “red and dead.” Theorists thought they’d become barren in their old age, lacking the cool gas that condenses into new stars. But in February, another team of astronomers discovered that some have plenty of cold gas — they just can’t use it. These galaxies’ supermassive black holes work against them, devouring nearby gas and exhaling powerful jets that either heat the remaining cold material or push it out of the galaxy entirely.
But not all the news this year focused on ellipticals; spiral galaxies showed up, too. This branch of the galactic family comes in different shapes: Some spirals have flat disks, while others are fat. In February, a third team of astronomers discovered the lifestyle difference: spin speed. As with pizza dough, the faster you twirl it, the thinner the crust becomes. Our own svelte galaxy spins at a speedy 600,000 mph.
Disks thin out or don’t, stars form or don’t, and galaxies grow gigantic but geriatric. As any astro-anthropologist would attest, making sense of our galaxy requires making sense of others that are younger, older, fatter, thinner and differently hued.