In the first example of strong gravitational lensing of a supernova, a galaxy that magnified a background, Type Ia supernova thirty-fold through gravitational lensing has been discovered, astronomers at Kavli IPMU announced.
The team has additionally shown how such discoveries of supernovae of Type Ia (SNIa) can be made far more common than was formerly believed possible.
SNIa seen through gravitational lenses can be used to make a direct measurement of the universe’s expansion rate, called the Hubble parameter, so this discovery could have a considerable influence on how cosmic expansion is studied in the future.
Measuring Cosmological Distance
Artists’ conception of Supernova PS1-10afx being gravitationally lensed. Credit: Anupreeta More/Kavli IPMU
Supernovae of Type Ia (SNIa) are tremendously valuable in the understanding of the Universe’s mysterious components like dark energy and dark matter.
SNIa have markedly similar peak luminosities, despite where they happen in the Universe. This characteristic allows astronomers to use SNIa as standard candles to measure cosmological distance independent of the Universe’s expansion.
Distance measurement with SNIa was key to the discovery of accelerating expansion of the Universe, which won the 2011 Nobel Prize in Physics.
A supernova named PS1-10afx was found in 2010 that displayed the same color and light curve, the change in brightness over time, as a Type Ia supernova, but its peak brightness was 30 times greater than expected.
That discovery was made using the Panoramic Survey Telescope & Rapid Response System 1, a telescope located in Hawaii that can image the entire visible sky several times each month. This anomaly led some to conclude that it was a completely new type of superluminous supernova.
“PS1-10afx looked a lot like a Type Ia supernova, but it was just too bright. Generally, the rare supernovae that have been found to shine brighter than Type Ia usually have higher temperatures (bluer colors) and larger physical sizes (and thus slower light curves). New physics would thus be required to explain PS1-10afx as an intrinsically luminous supernova,”
said team leader Robert Quimby.
Gravitational Lensing
Quimby’s team set out to find the hidden lens in 2013. Using the Low-Resolution Imaging Spectrograph on the 10 meter Keck-I telescope located in Hawaii, they spent 7 hours collecting light at the location of PS1-10afx, which had by then faded away itself.
“After carefully extracting the signal from the data, we had confirmation. Buried in the glare of the relatively bright host galaxy, we found a second, foreground galaxy. This second galaxy was faint enough to have previously gone unnoticed. But our analysis showed that it was still the right size to explain the gravitational lensing of PS1-10afx,”
said astronomer Anupreeta More.
Unexpected Discovery
Says Masamune Oguri from the Department of Physics at the University of Tokyo:
“We had existing predictions of what a gravitationally lensed Type Ia supernova would look like. But the small size of this lens galaxy and the large magnification it produced was not exactly what we were expecting for the first discovery. However, this system may very well prove typical of discoveries to come. Because more distant supernovae are more likely to be gravitationally lensed, lensed supernovae are typically highly magnified and located in the distant universe.”
One outcome of this is that most of the gravitationally lensed Type Ia supernovae that will be found with future surveys using instruments such as the coming Large Synoptic Survey Telescope can be identified by their colors. The higher redshift, gravitationally lensed supernovae are redder than the more nearby, un-lensed objects.
“Our new approach allows us to find unresolved strong lensing events produced by such low-mass galaxies. Thus, the expected number of gravitationally lensed Type Ia supernovae to be found in future surveys increases by an order of magnitude,”
says Oguri.
Study: R. M. Quimby, M. Oguri, A. More, S. More, T. J. Moriya, M. C. Werner, M. Tanaka, G. Folatelli, M. C. Bersten, K. Maeda, K. Nomoto. Detection of the Gravitational Lens Magnifying a Type Ia Supernova. Science, 2014; 344 (6182): 396 DOI:10.1126/science.1250903
