Astronomers are always looking for answers to the mysteries of the universe by observing celestial objects and attempting to comprehend cosmic phenomena, but huge discoveries don't always come knocking in observatories.
After searching for over a decade, a team of researchers detected, identified, and captured a rare cosmic event that opens up new ways to understand the expansion of the universe and the mysterious dark matter — all thanks to a distant galaxy magnifying a supernova's brightness.
What Is A Type Ia Supernova?
Type Ia supernovas are dying stars that burn at a consistent brightness, allowing astronomers to measure their distance from Earth. This would, in turn, also allow scientists to precisely measure any celestial objects detected around them. However, the farther away a Type Ia supernova is, the more difficult it is for astronomers to actually find and study it.
This is why Professor Ariel Goobar from University of Stockholm's Oskar Klein Centre has spent the past 15 years searching for a gravitationally lensed type Ia supernova — and he found one by chance in 2016 when he spotted iPTF16geu.
iPTF16geu Supernova And Gravitational Lensing
Professor Goobar first noticed that iPTF16geu — a Type Ia supernova that has been identified earlier but was mostly ignored — seems to have increased in brightness in 2016. Astronomers originally thought that the supernova was just another Type Ia about 1 billion light-years away since that is the limit of the telescope in California's Palomar Observatory, but the recent discovery made things clearer and more exciting for astronomers.
iPTF16geu is, in fact, a Type Ia about 4 billion light-years away so the sudden magnification of its brightness to 50 times of what is expected baffled astronomers — at least until Prof. Goobar suggested that it was lensed.
"I've been looking for a lensed supernova for about 15 years. I looked in every possible survey, I've tried a variety of techniques to do this and essentially gave up ... One of the reasons I'm interested in studying gravitational lensing is that it allows you to measure the structure of matter — both visible and dark matter — at scales that are very hard to get," Prof. Goobar explains.
A rapid follow up with partner observatories that use more powerful telescopes showed that a galaxy was, at that time, in between Earth and iPTF16geu, causing the supernova to undergo gravitational lensing. That is to say, the galaxy bent the light coming from the supernova and made it appear 50 times brighter. Not only that, the galaxy also produced multiple images of iPTF16geu when seen from certain angles.
Take a look at the photo below showing multiple versions of the lensed supernova.
"I was baffled when I saw the initial data for iPTF16geu from the Palomar Observatory. It looked like a normal Type Ia supernova but it was much brighter than it should have been given its distance from us," study co-author and Caltech Assistant Professor for Astronomy Mansi Kasliwal said.
What This Means For Astronomy
Prof. Goobar and his team's discovery is significant for astronomy because it will allow scientists to measure the expansion of the universe and understand dark matter and the gravitational lensing phenomenon.
Not only this, two Lawrence Berkeley National Laboratory researchers have already come up with a possible method for identifying gravitationally lensed supernovas using the observations published by Prof. Goobar and his team.
"It is extremely difficult to find a gravitationally lensed supernova, let alone a lensed Type Ia ... [but] since the discovery of iPTF16geu, we now have some thoughts on how to improve our pipeline to identify more of these events," astrophysicist Peter Nugent from Berkeley Lab's Computational Research Division said.
Prof. Goobar and his team's observations have been published in the journal Science.