Astronomers discover quadruply-lensed supernova with cosmic magnifying glass

 

Astronomers have spotted a rare and spectacular sight in the distant universe: a supernova whose light was split into four images by the gravity of a galaxy in front of it. The supernova, named SN Zwicky, was a type Ia explosion, which occurs when a white dwarf star is destroyed by its companion star. Type Ia supernovas are important for measuring cosmic distances and studying the mysterious dark energy that is accelerating the expansion of the universe.

SN Zwicky was first detected by the Zwicky Transient Facility (ZTF) at Palomar Observatory in California on August 21, 2022. The ZTF is a survey telescope that scans the sky for transient objects, such as supernovas, asteroids and black hole mergers. The supernova appeared unusually bright, which prompted further observations by other telescopes, including the W.M. Keck Observatory, the Very Large Telescope, the Hubble Space Telescope and the Nordic Optical Telescope.

The follow-up observations revealed that SN Zwicky was actually four images of the same supernova, arranged in a cross-like pattern around a faint galaxy. This galaxy acted as a gravitational lens, bending and magnifying the light from the supernova as it passed by. This phenomenon was predicted by Albert Einstein more than a century ago, based on his theory of general relativity. According to this theory, massive objects can warp the fabric of space-time around them, creating a lens-like effect for distant light sources.

Gravitational lensing is a rare and powerful tool for astronomers, as it can reveal objects that would otherwise be too faint or too small to be seen. For example, gravitational lensing can help detect planets around other stars, reveal hidden galaxies and clusters of galaxies, and probe the distribution of dark matter in the universe.

However, finding a gravitationally lensed supernova is even rarer, as supernovas are short-lived events that last only a few weeks or months. Only a handful of such cases have been discovered so far, and SN Zwicky is the first one to be found by ZTF.

SN Zwicky is also special because it is a type Ia supernova, which has a consistent brightness that can be used as a standard candle to measure distances in the universe. By comparing the apparent brightness of SN Zwicky with its true brightness, astronomers can estimate how far away it is. In this case, SN Zwicky exploded more than 4 billion light-years away from us, while the lensing galaxy is about 2.5 billion light-years away.

Type Ia supernovas were also used to discover the accelerated expansion of the universe in 1998, which implies that there is an unknown force called dark energy that is pushing the universe apart faster and faster. By studying more type Ia supernovas, especially those that are gravitationally lensed, astronomers hope to learn more about the nature and origin of dark energy.

“Strongly lensed type Ia supernovas allow us to see further back in time because they are magnified. Observing more of them will give us an unprecedented chance to explore the nature of dark energy,” said Joel Johansson, co-author of a study on SN Zwicky published in Nature Astronomy on June 12, 2023.

The study was led by Ariel Goobar of Stockholm University in Sweden, who said that SN Zwicky is “the smallest resolved gravitational lens system found with optical telescopes.” The team also found that two of the four images of SN Zwicky were brighter than expected, which could be due to smaller microlensing events within the lensing galaxy that further amplified the supernova’s light.

The discovery of SN Zwicky is an example of how modern astronomical instruments can reveal new and exciting phenomena in the cosmos. “I was observing that night and was absolutely stunned when I saw the lensed image of SN Zwicky,” said Christoffer Fremling of Caltech, who was part of the ZTF team that detected the supernova. “The discovery showcases the remarkable capabilities of ZTF and its ability to find rare transients.”

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The secret of the amniotes: How live birth may have helped reptiles and birds conquer the land

 

We all know that chickens lay eggs, but did you ever wonder how their ancestors managed to survive on land without water? A new study suggests that the earliest reptiles and birds may have had a different strategy: they gave birth to live young.

The study, published in the journal Nature Ecology and Evolution, challenges the long-held view that hard-shelled eggs were the key to the success of amniotes, a group of vertebrates that includes mammals, reptiles and birds. Amniotes have a special membrane inside their eggs that protects the developing embryo from drying out.

The researchers analysed 51 fossil species and 29 living species of amniotes and found evidence that many of them were viviparous, meaning they directly gave birth to their young. They also found signs of extended embryo retention (EER), a flexible reproductive strategy where the mother can keep the young inside her body for varying periods of time, depending on the environmental conditions.

This means that instead of relying on a hard egg shell to protect their offspring, these ancient amniotes may have used EER as a way to adapt to different habitats and climates. EER could also allow the mothers to control the timing and location of birth, ensuring better chances of survival for their young.

Michael Benton, a co-author of the study from the Bristol’s School of Earth Sciences, explained that this finding overturns the traditional view of how amniotes evolved. “Before the amniotes, the first tetrapods to evolve limbs from fishy fins were broadly amphibious in habits. They had to live in or near water to feed and breed, as in modern amphibians such as frogs and salamanders,” he said in a press statement.

“When amniotes appeared around 320 million years ago, they were able to break away from the water by evolving waterproof skins and other characteristics that allowed them to control water loss. But the amniotic egg was key here. In a way, the amniotic was thought to be a ‘private pond’ in which a developing reptile was protected from drying out in warm climates. This was believed to be what allowed Amniota to move away from waterbodies and dominate the land.”

However, the new study shows that this classic model is not supported by the fossil and living evidence. Baoyu Jiang, leader of the project and a professor at Nanjing University, said that biologists had noticed that many lizards and snakes display flexible reproductive strategy across oviparity (egg-laying) and viviparity. “Sometimes, closely related species show both behaviours, and it turns out that live-bearing lizards can flip back to laying eggs much more easily than had been assumed,” he said in a press statement.

Armin Esler, co-author of the study, added that when they looked at fossils, they found that many ancient marine reptiles were live-bearers. Some other fossils showed the to-and-fro between oviparity and viviparity, not just lizards.

The researchers concluded that EER may have been an ancestral trait of amniotes that was lost or modified in some groups over time. EER may have also been an important factor in the evolution of mammals, which are mostly viviparous today.

The study sheds new light on the diversity and complexity of reproductive strategies among vertebrates, and how they may have influenced their evolutionary success. It also raises new questions about how EER affects the development and behaviour of the young, and how it is regulated by hormones and genes.

The next time you see a chicken laying an egg or a lizard giving birth to a baby, you may want to think about their ancient ancestors who may have done things differently.

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