Two galaxy clusters, each a quadrillion times the mass of the Sun, collided to form the system formally known as Macs J0025.4-1222.

This image of the mammoth spiral galaxy M81, located about 12 million light years away, contains data from four different NASA satellites.

The brightest supernova ever recorded on Earth, this spectacular light show was documented in China, Japan, Europe, and the Arab world. It was brighter than Venus, and visible during the day for weeks.

There is nothing subtle about the black hole in the galaxy Centaurus A. First off, it's about 10 million times more massive than the sun, and Chandra's X-ray image shows it's not just sitting quietly as a bright point in the middle.

A composite image of NGC 4258, about 25 million light-years from Earth, shows an X-shaped pattern when seen in different types of light.

About a hundred and forty years ago, the light from a supernova explosion in our galaxy reached the Earth, but no one saw it. The discovery of this supernova remnant helps astronomers better understand how often these stellar time-bombs go off in our galaxy.

In 3C321, a jet from a black hole in one of the galaxies is pummeling its neighbor galaxy, the first time this type of galactic violence has ever been seen. The jet could bring big trouble for any planets in its path, but could also trigger a burst of star formation in its wake.

Like the Milky Way, Sombrero is a spiral galaxy. However, we see Sombrero edge-on from our vantage point from Earth, rather than the face-down perspective that is more familiar.

The supernova explosion that created this object was witnessed on Earth about 400 ago years by many skywatchers, including the astronomer Johannes Kepler. This object, which now bears Kepler's name, is the remains of a massive star's demise.

When seen in visible light from the Hubble Space Telescope, M82 looks like an ordinary spiral galaxy.