The light from the supernova iPTF16geu and of its host galaxy is warped and amplified by the curvature of space mass of a foreground galaxy. In the case of the point-like supernova, the light is split into four images. These have been resolved with the Hubble Space Telescope. Original image by ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al, edited and modified by Joel Johansson
An international team led by Ariel Goobar at Stockholm University has detected for the first time multiple images from a gravitationally lensed Type Ia supernova iPTF16geu. The new observations suggest promising new avenues for the study of the accelerated expansion of the Universe, gravity and distribution of dark matter in the universe. Type Ia supernovae, nature’s own “standard candles,” have been used for many years by astronomers to measure cosmological distances. These studies led to the discovery of the accelerated expansion of the Universe, a sensational discovery that won the 2011 Nobel prize in Physics.
In this special case, the supernova appeared magnified, but also multiplied. The new observations provide a promising new tool to test key cosmological theories about the accelerating expansion of the universe and the distribution of a mysterious substance known as dark matter. Type Ia supernovae are abundant and frequently used by astronomers to accurately measure distances in the universe. Gravitational lensing – the curving of space due to gravity – has also been observed many times since the early 20th century when it was predicted by Einstein. Yet, imaging a gravitationally lensed Type Ia supernova had proven formidably difficult, until now.
Goobar and his group are partners in two Caltech-led international scientific collaborations – iPTF (intermediate Palomar Transient Factory) and GROWTH (Global Relay of Observatories Watching Transients Happen). The iPTF takes advantage of the Palomar Observatory and its unique capabilities to scan the skies and discover, in near real time, fast-changing cosmic events such as supernovae. GROWTH manages a global network of researchers and telescopes that can swiftly perform follow-up observations to study these transient events in detail.
Within 2 months of detection, the team observed iPTF16geu supernova with Hubble and the adaptive-optics instruments on the Keck Observatory atop Mauna Kea, Hawaii, and the VLT telescopes in Chile. Apart from producing a striking visual effect, capturing the image of the strongly lensed Type Ia supernova such as iPTF16geu is extremely useful scientifically. Astronomers can now measure very accurately how much time it takes for the light from each of the multiple images of the supernova to reach us. The difference in the time of arrival can then be used to estimate with a high precision the expansion rate of the universe known as the Hubble constant. Currently, the different methods to measure the Hubble constant produce slightly different results but even these small changes can result in significantly different scenarios for the predicted evolution and expansion of the universe.
Observing an event such as iPTF16geu is rather improbable. Moreover, using data from Keck and Hubble the team finds that the lensing galaxy needs a great deal of substructure to account for the observed differences in the 4 supernova images, and the total lens magnification. This may introduce new questions about the way matter clumps in the universe and challenge astronomers’ understanding of gravitational lensing at small scales. http://www.su.se/english/research/profile-areas/astrophysics-cosmology-and-particle-physics/light-rays-from-a-supernova-bent-by-the-curvature-of-space-time-around-a-galaxy-1.329459
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