It’s
easy to imagine the universe as an endless sea of stars, but that’s a
biased, Earthly perspective. If we could zoom very far out, we’d see
bright cosmic clusters like our Milky Way, and between them,
unimaginably vast stretches of empty intergalactic space.
Artist’s concept of a Type Ia supernova exploding in the region between galaxies.
Well, not
completely empty: Sometimes, an ill-fated star gets flung from its home
to wander that intergalactic void. That, at least, is what appears to
have happened to three supernovae imaged by the Hubble Space Telescope
several years ago, and more recently by a team of Berkeley researchers
using the Canada-France-Hawaii Telescope. Exiled from the galaxies that
birthed them, these curious cosmic orphans, which are described in a forthcoming paper in the Astrophysical Journal, spent eons living in unimaginable darkness, before finally exploding to smithereens.
“We have
provided the best evidence yet that intracluster stars truly do explode
as Type Ia supernovae,” said Berkeley astronomer and lead study author
Melissa Graham in a statement,
“and confirmed that hostless supernovae can be used to trace the
population of intracluster stars, which is important for extending this
technique to more distant clusters.”
While stars
typically live out their lives within a single galaxy, every now and
then, a gravitational disturbance will wrench a stellar body out of its
normal orbit and send it flying off at breakneck speeds. Indeed, this
process is thought to disrupt up to 15 percent of the stars within large
galactic clusters. In most cases, the displaced stars remain
gravitationally bound to the cluster as a whole, scattered throughout
the cosmic hinterlands. In densities about a millionth of what we see
from Earth, these wanderers are too faint for astronomers to observe
until they explode at the end of their lives.
The
scientists behind the recent study are now searching intragalactic
space for stellar entrails, in order to begin censusing the population
of unseen cosmic nomads. Rare as they may be, these lonely stars offer
important insights into the formation and evolution of galaxy clusters
throughout the universe.
If exiled
stars aren’t unsettling enough, consider that any of these cosmic nomads
could harbor worlds, perhaps even life. In his novel Against a Dark Background, science
fiction author Ian Banks described life on Golter, a planet whose star
lies a million light years from its nearest neighbor. Anyone standing on
the surface of Golter would have peered up at night into a completely
starless sky. It’s unsettling, to say the least, to imagine that an
advanced society living on such a world would have nowhere else to go
when its star eventually failed.
Suddenly, I find myself very grateful for our place in the universe.
Follow Maddie on Twitter or contact her at maddie.stone@gizmodo.com
