The Hubble Space Telescope (HST) has been used to image three rare supernovae that were torn from their host galaxies long ago. The lonesome dying stars shine roughly one billion light years away from our own home planet, and hundreds of light years away from their nearest stellar companions.
These Type 1a supernovae result when a white dwarf star collects gas and dust that falls onto the surface. When the material reaches a critical mass, it erupts in a massive explosion that can temporarily outshine a galaxy. In a typical family of stars like the Milky Way, such events happen about once every 100 years.
Any planets that once orbited the stars before they exploded in their death throes would have experienced night skies with few visible stars.
A fourth supernova seen by Hubble likely had plenty of neighbors — astronomers believe it may be the first such even seen within a globular cluster. These collections of stars feature thousands of stellar bodies huddled in close quarters — resembling a dandelion gone to seed. Although stars in these groupings are found close together, there aren't many members in each globular cluster — fewer than 10,000.
"Since there are far fewer stars in globular clusters, only a small fraction of the supernovae are expected to occur in globular clusters. This might be the first confirmed case, and may indicate that the fraction of stars that explode as supernovae is higher in either low-mass galaxies or globular clusters," said Melissa Graham of the University of California, Berkeley.
The supernovae were discovered between 2008 and 2010, by astronomers using the Canada-France-Hawaii Telescope located on Mauna Kea in Hawaii. Examination of Hubble data revealed that the three isolated supernovae exploded while the bodies were far from their parent galaxies.
University of California astronomers believe their research will provide new information about the material found in the vast spaces between the galaxies. This data could lead to explanations about how and why galaxies collect together in clusters, separated by vast bubbles. These clusters are in turn found within superclusters of galaxies, which are the largest formations in the known universe.
Type 1a supernovae usually occur in binary systems, where a white dwarf is paired with a larger companion that pours material onto the smaller stellar body, resulting in the massive eruption. This phenomenon suggests that these isolated supernovae were once members of double star systems.
An article describing the discovery and analysis of the four distant supernovae was published in the Astrophysical Journal and is available online.
