"Hubble V1" -- The Star that Exploded the Size of the Observable Universe

"Hubble V1" -- The Star that Exploded the Size of the Observable Universe

The NASA's Hubble Space Telescope has been focused in the image above on a single variable star that in 1923 altered the course of modern astronomy. V1 is a special class of pulsating star called a Cepheid variable that can be used to make reliable measurements of large cosmic distances. Though the Universe is filled with billions upon billions of stars, the discovery of this single variable star in 1923 altered the course of modern astronomy. And, at least one famous astronomer of the time lamented that the discovery had shattered his world view.

The star goes by the inauspicious name of Hubble variable number one, or V1, and resides in the outer regions of the neighboring Andromeda galaxy, or M31. But in the early 1900s, most astronomers considered the Milky Way a single "island universe" of stars, with nothing observable beyond its boundaries. Andromeda was cataloged as just one of many faint, fuzzy patches of light astronomers called "spiral nebulae."
Were these spiral nebulae part of the Milky Way or were they independent island universes lying outside our galaxy? Astronomers didn't know for sure, until Edwin Hubble found a star in Andromeda that brightened and faded in a predictable pattern, like a lighthouse beacon, and identified it as V1, a Cepheid variable. This special type of star had already been proven to be a reliable distance marker within our galaxy.