Astronomers have discovered an invisible galaxy that could be the first of many that will help unravel one of the universe's greatest mysteries.  Theorists have long said most of the universe is made of dark matter. Its presence is required to explain the extra gravitational force that is observed to hold regular galaxies together and that also binds large clusters of galaxies.

The theory suggests that pockets of pure dark matter ought to remain sprinkled across the cosmos.  In a cluster of galaxies known as Virgo, some 50 million light-years away, scientists looked for radio-wavelength radiation coming from hydrogen gas. They found a well of it that contains a hundred million times the mass of the Sun. It is now named VIRGOHI21. The well of material rotates too quickly to be explained by the observed amount of gas. Something else must serve as gravitational glue.

For those of you not in the know, "dark matter," is material of an unknown nature that can't be seen. 

Doctor Thalamo's Space Factoids:
- Radio telescopes detect the dark matter.
- Dark matter makes up about 23 percent of the universe's mass-energy budget
- Normal matter, the stuff of stars, planets and people, contributes just 4 percent
- The rest of the universe is driven by an even more mysterious thing called dark energy.