A new study analyzes several sites where dead stars once exploded
The brilliant explosions of dead stars have been used for years to
illuminate the far-flung reaches of our cosmos. The explosions, called
Type Ia supernovae, allow astronomers to measure the distances to
galaxies and measure the ever-increasing rate at which our universe is
stretching apart.
But these tools aren't perfect. In the cosmic hardware store of our
universe, improvements are ongoing. In a new report, appearing March 27
in the journal Science, astronomers identify the best, top-of-the-line
Type Ia supernovae for measuring cosmic distances, pushing other, more
clunky tools to the back of the shelf.
Using archived data from NASA's Galaxy Evolution Explorer (GALEX),
scientists show that a particular class of Type Ia supernovae that occur
near youthful stars can improve these measurements with a precision of
more than two times that achieved before.
"We have discovered a population of Type Ia supernovae whose light
output depends very precisely on how quickly they fade, making it
possible to measure very exact distances to them," said Patrick Kelly of
the University of California, Berkeley, lead author of the new study.
"These supernovae are found close to populations of bright, hot young
stars."
The findings will help light the way to understanding dark energy,
one of the greatest mysteries in the field of cosmology, the study of
the origin and development of the universe. Dark energy is the leading
culprit behind the baffling acceleration of our cosmos, a phenomenon
discovered in 1998. The acceleration was uncovered when astronomers
observed that galaxies are pulling away from each other at increasing
speeds.
The key to measuring this acceleration -- and thus the nature of dark
energy -- lies with Type Ia supernovae, which work much like light
bulbs strung across space. Imagine lining up 60-watt light bulbs across a
field and standing at one end. The farthest light bulb wouldn't appear
as bright as the closest one due to its distance. Since you know how
bright the light bulb inherently is, you can use the extent of its
dimming to figure out the distance.
Type Ia supernovae, also referred to as "standard candles," work in a
similar way because they consistently shine with about the same amount
of light. While the process that leads to these explosions is still not
clear, they occur when the burnt-out core of a star, called a white
dwarf, blasts apart in a regular way, briefly lighting up the host
galaxy.
However, the explosions aren't always precisely uniform. They can
differ considerably depending on various factors, which appear to be
connected to the environments and histories of the exploding stars. It's
as if our 60-watt bulbs sometimes give off 55 watts of light, skewing
distance measurements.
Kelly and his team investigated the reliability of these tools by
analyzing the surroundings of nearly 100 previous Type Ia explosions.
They used data from GALEX, which detects ultraviolet light. Populations
of hot, young stars in galaxies will shine brightly with ultraviolet
light, so GALEX can distinguish between young and older star-forming
communities.
The results showed that the Type Ia supernovae affiliated with the
hot, young stars were significantly more reliable at indicating
distances than their counterparts.
"These explosions are likely the result of youthful white dwarfs," said Kelly.
By focusing on this particular brand of Type Ia tools, astronomers
will be able to, in the future, make even sharper measurements of the
size and scale of our universe. According to the science team, this
class of tools could work at distances up to six billion light-years
away, and perhaps farther.
"GALEX surveyed the entire sky, allowing past and future eruptions of
these high-quality standard candles to be identified easily," said Don
Neill, a member of the GALEX team at the California Institute of
Technology in Pasadena, not affiliated with the study. "Any improvement
in the standard candles will have a direct impact on theories of dark
energy, allowing us to home in on this mysterious force propelling the
acceleration of the universe."
Caltech led the Galaxy Evolution Explorer mission and was responsible
for science operations and data analysis. The mission ended in 2013
after more than a decade of scanning the skies in ultraviolet light.
NASA's Jet Propulsion Laboratory in Pasadena, California, managed the
mission and built the science instrument. The mission was developed
under NASA's Explorers Program managed by the Goddard Space Flight
Center, Greenbelt, Maryland. Researchers sponsored by Yonsei University
in South Korea and the Centre National d'Etudes Spatiales (CNES) in
France collaborated on this mission. ?
Graphics and additional information about the Galaxy Evolution Explorer are online at: http://www.nasa.gov/galex - http://www.galex.caltech.edu
Media Contact
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov
Source: JPL-Caltech/News
