Was the Milky Way once an active galaxy?

Two bubbles 50,000 light-years across may hold the answer.

How did Hoag’s Object form?

We normally think of galaxies as falling into two main morphological types, spiral and elliptical. Spiral galaxies have spiral arms, which wind about a central nucleus, all embedded in a halo containing stars, globular clusters, and dark matter. Elliptical galaxies are…

Andromeda’s double nucleus

Most galaxies only have one nucleus at their center. Why does Andromeda have two?

The centers of galaxies are often extremely turbulent places. They usually contain supermassive black holes — weighing…

A tale of two redshifts

How did 3C 186 eject its supermassive black hole? With gravitational waves.

The Lynx Arc: A starburst 12 billion years ago

Want to take a peek at 25,000 of the most violent stars in the universe? Look no further than the Lynx Arc.

N6946-BH1: The disappearing star

Throughout history, supernovae have been noticed for their sudden appearances and disappearances. Chinese astronomers in the second century were the first to call them “guest stars”, because they stayed visible in the sky for months, slowly fading to become too dim for…

What is a Lyman-alpha blob?

Giant clouds of gas billions of light-years away are emitting radiation…

Sagittarius A East: A supernova remnant or a star torn apart?

The galactic center’s a busy place — and…

M33 X-7 is way too massive. Here’s why.

The most massive stars in the local universe often form in…