READ: Gallery — Structure in the Universe

This busy region of space in the constellation Ursa Major is called the "Lockman Hole." Each tiny dot in this tapestry of color is an entire galaxy, many of them containing hundreds of billions or more stars.

This image from the Hubble Deep Field (HDF) represents a narrow "keyhole" view stretching almost to the visible horizon of the Universe. This HDF image covers a speck of the sky, only about the width of a dime 75 feet away. Although the "field" is a very small fraction of space, it is considered representative of the typical distribution of galaxies in the Universe.

Looking at distant objects is like looking back in time. This large cluster of galaxies (red dots in center), an early galactic metropolis, appears as it was 9.6 billion years ago, only about 4 billion years after the Big Bang. Astronomers were surprised to find such a well-populated cluster at an era when other clusters tended to be smaller.

The spiral galaxy of Andromeda is one of the Milky Way's most prominent neighbors, about 2.5 million light years away. Andromeda is thought to contain up to a trillion stars while our Milky Way has an estimated 200 billion to 400 billion stars.

The dramatic collision of these two galaxies in the constellation Cetus, collectively called ARP 147, has created an unusual wave of star formation. Young stars race through their life cycles in a few million years or less and explode as supernovae, leaving black holes and neutron stars behind (seen as pinkish blobs).

This image of the Cat's Eye Nebula in the constellation Draco, also known as NGC 6543, may resemble a creature embryo or a cocoon. But this planetary nebula represents a late stage of stellar evolution that our Sun should experience several billion years from now. When a star like the Sun begins to run out of fuel it becomes a red giant, eventually leaving behind a hot core that collapses to form a dense white dwarf star. In this case, a fast wind emanating from the hot core rams into the ejected atmosphere, pushed it outward, and creates the cocoon-like structure seen here. In less than a million years, NGC 6543 will collapse, becoming a less dramatic white dwarf.

The ejection of gas from this dying Sun-sized star in the constellation Norma, called the Ant Nebula or mz3, shows symmetrical patterns that scientists would not expect from an ordinary explosion. One possibility is that the central star has a closely orbiting companion whose gravitation forces shape the outflowing gas. A second possibility is that as the dying star spins, its strong magnetic fields are wound up into complex shapes.

A star's violent death in the constellation Taurus was observed on Earth as the supernova of 1054 CE. Now, almost a thousand years later, an extremely dense neutron star at the center of the supernova remnant is spewing out a blizzard of extremely high-energy particles into the expanding debris field known as the Crab Nebula.

The ongoing collision of the Antennae galaxies, which began hundreds of millions of years ago, has triggered the formation of millions of stars in the galactic clouds of dust and gas. The largest of these young stars have already raced through their evolution in a few million years and exploded as supernovae. The bright, point-like sources in this image are produced by material falling onto black holes and neutron stars that are remnants of the massive stars.

This surreal Hubble image shows a mountain of dust and gas rising in the Carina Nebula. The top of the three-light-year-tall pillar of cool hydrogen is being worn away by the radiation of nearby stars, while stars within the pillar unleash jets of gas that stream from the peaks.

The flower-shaped Rosette Nebula in the constellation Monoceros (The Unicorn) is also known by the less romantic name NGC 2237. It is a huge star-forming cloud of dust and gas in our own Milky Way galaxy.