Category: red and dead

This One Distant, Red, Gas-Free Galaxy Defies Astronomers’ Expectations

“When two similarly-sized galaxies merge, it triggers a starburst: a massive formation of new stars. Under the right circumstances, some gas will form stars while the remainder is expelled, lost forever to the intergalactic medium. Once the gas for forming new stars is used up, the galaxy simply ages as the bluest, most massive stars die off. Over billions of years, only the redder, dimmer, lower mass stars remain.”

In astronomy, young galaxies actively form stars, and glow bright blue through the process. Only after many billions of years and at least one cataclysmic event do galaxies settle down into a gas-free, red state, once all the bluer stars have died out. “Red and dead” galaxies appear in the late Universe, normally as giant elliptical galaxies that lost their gas aeons ago.

Which is why this one galaxy is so puzzling: it’s red, dead, massive and compact, but it’s also sending us its light from 10.8 billion years ago!

How did this galaxy get so old-looking when it’s actually so young? The mystery continues, but here’s what we know so far.

Astronomers Discover Exactly How Galaxies Die

“Our Milky Way contains large star-forming regions, mostly along its spiral arms, indicating stellar life. But other, mostly elliptical galaxies, stopped forming stars many billions of years ago. These galaxies are called red-and-dead, because they don’t have any hot, young, blue stars associated with recent star formation. Since the hottest, bluest stars burn through their fuel the fastest, an intrinsic red color is evidence that no new stars have formed for a long time.”

With hundreds of billions of stars burning inside a typical galaxy, it seems like a stretch to call any such object already “dead.” But if you aren’t actively forming new stars, and you don’t have the material in you to form new stars in the future, “dead” is exactly what you are, whether you realize it or not. We’ve had a number of theories, for a long time, as to why a galaxy could lose its gas and burn out, but for the first time, we’ve discovered one in the nearby Universe. Just 240 million light years away, the galaxy NGC 1277 has a unique set of circumstances:

  • it’s moving very quickly through the intra-cluster medium,
  • it contains an ultra-massive black hole at its core,
  • and both its stars and globular clusters are overwhelmingly red.

It looks as though it hasn’t formed new stars in some 10 billion years, making it the oldest, deadest galaxy we’ve ever seen up close!

Come learn all about it, and what it means for the deaths of galaxies, on this edition of Mostly Mute Monday!