As Einstein's theory of general relativity first predicted, matter has a strange effect on the very fabric of spacetime—it literally warps it. The consequence of this warping is gravity, which is rather apparent here on Earth. In space, however, the effects are mostly negligible. That is, until you look to the most massive, large-scale formations in the universe: Galaxy clusters.
Indeed, these galactic groups, which usually contain anywhere between 50 and 10,000 galaxies, are so massive, and warp spacetime to such a high degree that they essentially become magnifying glasses. This phenomenon, called gravitational lensing, presents astronomers with the opportunity to zero in on background objects that are normally way too distant to resolve clearly.
How Gravitational Lensing Works:
More specifically, when light from a background object encounters a gravity well, the rays are deflected. When this happens relative to our vantage point (that is, when the gravity well obstructs the background source from our line of sight), the object's light is both brightened and magnified.
Furthermore, because the light is redirected through multiple channels, we (the observers) usually don't see one image of it, but several different copies of the same source—some more prominent than the others, depending on the exact configuration of the pair in respect to Earth. If they perfectly align, the lensing generates a circular pattern of images, if they are off-center, twin copies are arranged in an arc-like formation.
Similarly, but on a much smaller scale, a form of lensing happens when rays of light from a background object travel close to the Sun. Instead of traveling in a straight, unobstructed line from their location to Earth, they are deflected by the Sun's gravity. Consequently, the object's apparent position differs from its true position, which could be several degrees away.
A Surprising Find:
Now, two teams of international researchers from the Australian National University (ANU) have truly witnessed something no other human being has seen before, despite their best efforts.
In a distant expanse of space, a star on the precipice of death has exploded. Only, this ancient star's light encountered a large galaxy cluster on its journey to Earth, resulting in the gravitational lensing we mentioned above. Only instead of two copies, there are four.
This discovery was made on accident, when a team from the University of California, Berkeley (UCB) was scouring the universe in search of previously-unknown galaxies. The UCB astronomer who embarked on the search, Dr. Patrick Kelly—who is the lead author of the study, and a member of the Grism Lens Amplified Survey from Space (GLASS) collaboration—then stumbled upon an Einstein Cross, with what appeared to be a prominent supernova glow.
Followup observations were conducted by the W. M. Keck Observatory, which helped confirm that the light was indeed that of a supernova, one that's about 20 times brighter than it would be in a traditional environment.
Its brightness stems from the fact that two lenses from the same galaxy cluster overlap. The strongest of the two projects three of the four images, while the secondary lense is generated by a monster elliptical galaxy. They are aligned in such a manner that one of the projected images falls right into its path. “The dark matter of that individual galaxy then bends and refocuses the light into four more paths,” Rodney explained, “generating the rare Einstein Cross pattern we are currently observing," according to one of the researchers.
Keck was also able to establish the background object's distance—about 9.3 billion light-years from Earth. That means that not only did this star explode when the universe was only 4 billion years old, but that the light itself has traveled billions of light-years before arriving at Earth. As such, we are seeing it as it appeared long, long ago.
“The LRIS spectrograph on Keck I was used to measure a spectrum at the location of the supernova and was used to measure the distance to the supernova host galaxy,” Tommaso Treu, the principal investigator on the GLASS project and Professor of Physics and Astronomy at the University of California, Los Angeles. “Furthermore, the spectrum was used to determine the intrinsic duration of the event: as a result of the expansion of the universe, distant events appeared stretched in time to us. For example an NBA basketball game in the supernova host galaxy would appear to us to last 120 minutes, instead of the standard 48 minutes it does on Earth. Finally, the non-detection of emission from the supernova itself allowed the team to rule out some potential contaminants and provides clues as to the type of supernova.”
Brad Tucker, one of the researchers from ANU's Research School of Astronomy and Astrophysics, notes:
“It’s perfectly set up, you couldn’t have designed a better experiment,” he continues, “You can test some of the biggest questions about Einstein’s theory of relativity all at once—it kills three birds with one stone.”
What's more, the finding could help us better understand the distribution of dark matter and dark energy, which are believed to be far more abundant than normal matter, along with their concentrations.
“It’s a relic of a simpler time, when the universe was still slowing down and dark energy was not doing crazy stuff,” Tucker said.
13.7 Billion Channels, & Something Good is On:
The team's groundbreaking research may not be the first time astronomers have ever seen magnified galaxies, but it is the first time a supernova has been part of the package. The surprises don't end there either.
Like all supernovae, the glow will inevitably dim before barely registering on our luminosity scale. Only, when the time comes, the supernova image will still be projected in the other displays. The Keck team compares this to a form of cosmic reruns, saying in their press release:
Putting dark matter and dark energy aside, if additional follow-up observations manage to capture the supernova's time-delayed reappearance, it will help garner insight into the medium through which the light traversed to reach our telescopes. That, in turn, will allow astronomers to make any necessary revisions to the models that describe mass of the cluster, called MACS J1149.6+2223. At 5 billion light-years distant, it's much closer to Earth than the progenitor galaxy
“We will measure the time delays, and we’ll go back to the models and say your prediction says the track would be this long and the hill would be this high,” Kelly said. “The lens modelers, such as Adi Zitrin (California Institute of Technology) from our team, will then be able to adjust their models to more accurately recreate the landscape of dark matter, which dictates the light travel time.”
On a final note, the researchers have decided to call the supernova 'Refsdal.' after the Norwegian astrophysicist who first suggested supernovae in lensed galaxies could yield clues about the expansion of the universe. Indeed, Sjur Refsdal—who passed away in 2009—would surely be thrilled to know that his concept actually panned out.
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