Because of gravitational lenses, astronomers have seen the identical supernova thrice. And in twenty years, they assume they may see it another time

It is difficult for humans to realize that there are galaxies that are so far away that the light emanating from them can be so distorted that they actually experience some kind of time lag. But that is exactly what happens with extreme forms of the gravitational lensing effect, as they give us the beautiful pictures of Einsteinringen. In fact, the time dilation around some of these galaxies can be so extreme that the light from a single event, such as a supernova, can actually appear on Earth at dramatically different times. This is exactly what a team led by Dr. Steven Rodney from the University of South Carolina and Dr. Gabriel Brammer from the University of Copenhagen found out. Only three copies of this supernova have surfaced – and the team believes it will show up again in 20 years.

Finding such a supernova is important not only because of its mind-altering properties – it also helps resolve an important debate in the cosmological community. The speed of expansion of the universe has exceeded the expected speed calculated from the cosmic microwave background radiation. The most common way to solve this cosmological puzzle is to conjure up “dark energy” – a shadowy force supposedly responsible for accelerating the acceleration. But scientists don’t really know what dark energy is, and to figure it out they need a better model of the physics of the early universe.

UT video describing the cosmic microwave background radiation used to partially compute the rate of expansion of the universe.

One way to get this better model is to find an event that is actively distorted by a gravitational lens. What is important is that the same event must occur at two different, different times in order to provide inputs for a calculation of the ratio of the distance between the galaxy that is taking the lens image and the background galaxy that was the source of the event.

This ratio is an important component in calculating some of the variables associated with dark energy. And the supernova candidate Drs. Rodney and Brammer found is one of the best-defined so far. It is only the third such example of a multi-lens supernova. Quasars have also been caught with their own time delays, but the variable nature of the quasars themselves makes them less than ideal for the kind of angular distance calculations needed by cosmologists.

UT video describing the gravitational lensing effect.

The new supernova, known as AT2016jka, was broken down from Hubble data collected in 2016. It is located in “the most spectacular galaxy that REQUIEM has targeted”. [the observational program at Hubble that captured the data]“, It resides in the galaxy known as MRG-M0138.

MRG-M0138 has a “quadruple lens” which means that four copies of the galaxy can be seen scattered around a cluster of galaxies closer to our own galaxy known as MAC J0138.02155. When the team examined data in the region in July 2019, it found that the three point sources of light that were present in the July 2016 data were no longer there. Most likely, the July 2016 data captured a supernova with three different lenses.

UT video on the topology of the universe showing how matter clumps together and can affect time.

However, the expected fourth lens flare did not show up in the Hubble data. Using their lens model for the system, the team determined that the fourth image should appear sometime around 2037, plus or minus a couple of years. With such a long base time between the occurrence of the same event, this supernova would provide valuable data for the debate about time dilation in gravitational lens events.

Unfortunately, that also means that scientists have to wait almost 20 years to get their hands on this data. It also means that you need to keep an eye on that part of the sky in the 2 year window in which the calculations predict the fourth image of the supernova. It probably wouldn’t be a bad idea to keep half an eye there the rest of the time, too, just in case it shows up earlier than expected.

UT video about dark energy and how we know it exists.

If all goes well, this final piece of data regarding the exact date of the supernova’s peak brightness will be well monitored by a new fleet of cosmological instruments. Telescopes like the Vera Rubin and Nancy Grace promise to observe hundreds of these supernovae with lenses that can provide even more data to further constrain dark energy. Hopefully they can capture the last breath of the supernova in MRG-M0138 as well, to top off some great detective work and prove just how incredible gravitational time dilation really is.

Learn more:
arXiv – A gravitational lens supernova with an observable time lag of two decades
Sci-News – Astronomers discover twelve new quadruple quasars
Forbes – Eight new quadruple lenses are not only beautiful, they also show the temperature of the dark matter matte

Mission statement:
Image of cluster MAC J0138.02155 and galaxy MRG-M0138 with gravitational lens showing the positions of the three observed instances of the supernova (SN1-3) and the expected position of the fourth instance (SN4), which is expected to appear around 2037.
Credit – Rodney, Brammer et al.

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