It is there, but cannot be seen. Yet, it has been found. MSNBC.com reports that astronomers have discovered an invisible galaxy called VIRGOHI21. Located in Virgo (50 million light years away) the galaxy has no visible stars. Astronomers used radio telescopes to detect the galaxy since regular telescopes cannot see it. Scientists believe the galaxy may be made of up dark matter, which cannot be seen with the naked eye. Space.com offers an explanation of dark matter in this article.
