Supernova caught "in the act"

Astronomers from Princeton observed a month-old supernova, and encountered a fresh explosion - a once-in-a-lifetime event, the first in the history of astronomy

Halvin Swift performed another interesting arson. This time, and this is also the first time this happens, astronomers managed to catch a star at the stage when it turns into a supernova. These stellar explosions have been seen before but only when the fireworks were already in full swing. "For years we dreamed of seeing a star right at the time of the explosion, but this is a once-in-a-lifetime event," said Alyssa Soderberg of Princeton University, who led the international team of scientists who studied the explosion. "This fresh supernova is going to be the Rosetta Stone of supernova research for years to come."

In January 2008, Soderberg made observations of a supernova that happened a month before and is in the process of spreading. However, she and her research student studied the X-rays that were picked up and transmitted from space by the Swift satellite, they saw a particularly bright light that seemed to jump from the sky. They didn't know it at the time but they became the first astronomers to catch a star as it exploded.

"In those days - until a year ago - people discovered supernovae in visible light and then began to study them to understand which star exactly exploded, what the mechanism was and what was created as a result of the explosion" says Robert Kirchner, professor of astronomy at Harvard University. "But here we are talking about something new - the X-rays arrived right at the beginning and provided us with an early warning of the event."

Soderbergh treated the discovery as an extremely discounted one (the nickname in English is serendipity and the late Yuval Na'eman translated this word into Hebrew as 'Athens' - according to Saul the king who went looking for Athens and found the monarchy). The satellite pointed to exactly the right place at the right time, she said. Due to the fact that she asked Swift's chief scientist at NASA's Goddard Center, Neil Gehrels, to point the telescope that way to observe another supernova and when she went outside the observatory to give lectures, she asked her colleague Ido Berger to keep an eye on the data for her.

"It's a cheap chain of events - a surprise," said Soderberg, who led the group investigating the explosion. "It was all over in minutes."

Other observers also pointed their telescopes at the stellar explosion and made detailed observations of the event. Among the observatories are the Hubble and Chandra space telescopes, two telescopes (60 and 200 inches) on Mount Plumer, the Gemini Observatory on Kitt Peak in Hawaii, and the very large array and Apache Point Observatory in New Mexico. These observations allowed a detailed study of the event.

A supernova event occurs when the core of a massive star exhausts its supply of nuclear fuel and collapses under its own gravity. The star becomes a compressed object - a neutron star. The new neutron star contracts and expands, creating shock waves that pass through the layers of gas. This process causes the star to explode into pieces. Until now, astronomers have been able to observe bright supernovae days or weeks after the event, when the supernova's debris envelope receives its energy from the radioactive elements created during the explosion.

A team from the Weizmann Institute is also involved in monitoring the supernova

This surprising discovery led to the mobilization of a research team, which was based on 51 research groups from different parts of the world, including Prof. Eli Waxman and Dr. Avishi Gal-Yam from the Weizmann Institute of Science. Dr. Gal-Yam performed measurements and calculations that allowed scientists to neutralize various disturbances, such as clouds of interstellar dust, which caused (by way of absorption) changes in the wavelengths of the exploding star's radiation. Thanks to these calculations, the scientists were able to extract valuable information about the explosion process. The data on the burst of the shock wave and the formation of X-rays in the explosion fully corresponded to a theoretical model of the supernova explosion process developed by Prof. Waxman together with Prof. Peter Mazarus from the University of Pennsylvania in the USA. In this way, the scientists were able to show that supernova 2008D is a normal supernova, and not a relatively rare explosion in which a jet burst of gamma radiation is also involved.

This observation has already given scientists new information about the dimensions of the exploding star, the structure of its mantle, and the properties of the shock wave that pushed the mantle out. These days, they continue to analyze the data, with the aim of solving some of the open questions in this field, and especially to perfect the model that describes the supernova explosion process. These new understandings of the explosion process may help scientists identify exploding stars at earlier stages of the explosion, allowing further observations and precise tracking of the explosion stages.