Supernovae Used To Gauge The Power Of Cosmic Lenses
May 2, 2014

Researchers Discover First Ever Gravitationally Lensed Type Ia Supernova

redOrbit Staff & Wire Reports - Your Universe Online

Two teams of astronomers have used the Hubble Space Telescope to observe distant exploding stars, and their research could help determine the power of naturally-occurring “cosmic lenses” than can be used to magnify objects in the far-off universe, NASA officials announced on Thursday.

The scientists, who are working independently, have studied three supernovae using the phenomenon of gravitational lensing, which causes the light from the stars to be amplified by the immense gravity of massive foreground galaxy clusters. The gravitational lensing effect is used by astronomers to search for distant objects that are typically too faint to see, even with the most powerful modern telescopes, the US space agency added.

According to the ESA’s Hubble website, the results of these two studies mark the first advances towards the most precise prescription to date of gravitational lenses. The degree to which a gravitationally lensed object is magnified is based on the amount of matter and dark matter in a cluster.

Scientists try to create maps estimating the location and amount of invisible dark matter each one contains. These maps are essentially the lens prescriptions of a galaxy cluster, the agency added, and they predict how much the distant objects locate behind a cluster will be magnified once their light passes through it.

Typically, astronomers have struggled to determine whether or not this prescription is accurate. However, research teams from the Supernova Cosmology Project and the Cluster Lensing And Supernova survey with Hubble (CLASH) have devised new methods to double-check a gravitational lens’s prescription.

They analyzed a trio of supernovae (identified as Tiberius, Didius and Caracalla), each of which was lensed by a different massive galaxy cluster (Abell 383, RXJ1532.9+3021 and MACS J1720.2+3536, respectively). At least two of those exploding stars appeared to be a special type known as a Type Ia supernovae, which are highly sought-after because they possess a consistent level of peak brightness that make them a reliable distance-estimating tool.

“Here, for the first time, we have found Type Ia supernovae that can be used like an eye chart for each lensing cluster,” explained CLASH team member and Rutgers University associate professor Saurabh Jha. “Because we can estimate the intrinsic brightness of the Type Ia supernovae, we can independently measure the magnification of the lens, which is not possible with other background sources.”

The supernovae were initially discovered in the CLASH survey – a Hubble census investigating dark matter distribution in 25 galaxy clusters - by Jha and his colleagues, who published their findings in the May 1 issue of The Astrophysical Journal. They exploded between seven and nine billion years ago, when the universe was just over half of its current age of 13.8 billion years old, NASA said.

Both Jha’s team and the Supernova Cosmology Project team, whose findings appear in Thursday’s edition of the Monthly Notices of the Royal Astronomical Society, used Hubble’s Advanced Camera for Surveys to conduct observations in visible light, and the telescope’s Wide Field Camera 3 to do so in infrared light. Both teams then compared their results with independent theoretical models of the dark matter content of the clusters.

They were able to conclude that their predictions fit the models, thus proving that this method of cosmic magnification can be effective. The astronomers now plan to search for additional Type Ia supernovae that are hidden behind large galaxy clusters, with the hopes that they can find approximately 20 exploding stars spread out behind one lone cluster in order to successfully complete an entire cluster of galaxies, the US space agency said.

“It is encouraging that the two independent studies reach quite similar conclusions,” said lead author Jakob Nordin, a member of the Supernova Cosmology Project and the Lawrence Berkeley National Laboratory. “These pilot studies provide very good guidelines for making future observations of lensed supernovae even more accurate.”

“Building on our understanding of these lensing models also has implications for a wide range of key cosmological studies,” added Supernova Cosmology Project leader Saul Perlmutter. “These lens prescriptions yield measurements of the cluster masses, allowing us to probe the cosmic competition between gravity and dark energy as matter in the Universe gets pulled into galaxy clusters.”