They capture a strange “echo of light” in a supernova

The explosion of a star, of the kind known as a supernova, sends an intense burst of light in all directions. However, on rare occasions, rings or ‘light echoes’ extend from the original position of the supernova, in the following months and years. The unusual phenomenon has been observed by astronomers recently.

The international team that has carried out the study is made up of astronomers from Dublin, Barcelona, ​​Aarhus, New York and Garching, among whom is Lluís Galbany, member of the Institute for Space Studies of Catalonia (IEEC) and the Institute of Space Sciences (ICE) attached to the Higher Council for Scientific Research (CSIC) in Spain.

The team has merged the images captured by the Hubble Space Telescope (HST) into a short GIF video. The animation first shows the supernova explosion in the center, followed by several rings of light that appear as the light from the explosion hits several nearby dust layers.

‘The data set is considerable and has enabled us to produce stunning color images and animations showing the evolution of light echoes over a five-year period. It is a rarely seen phenomenon that has previously only been documented in a few supernovae,” says lead author Maximillian Stritzinger of Aarhus University.

Astrophysicist Morgan Fraser says: “Although the James Webb Space Telescope has attracted a lot of attention, its predecessor, Hubble, continues to provide incredible images of the universe. The HST has been observing the sky for more than three decades, so we can discover things like this light echo that slowly evolves over the years.”

Color images of the light echo associated with the supernova SN 2016adj. The dashed line highlights the position of the main light echo ring as it expands from the supernova position between 300 and 580 days after the explosion, along with a predominant dust lane. The dust lane extends from east-northeast to west-southwest and clearly obscures both parts of the light echo and the background stars. (Images: ICE, IEEC, UCD, Aarhus University, Hofstra University, European Southern Observatory)

For his part, the researcher Lluís Galbany comments: “The shock wave of this strong supernova explosion propagates at more than 10,000 kilometers per second. Before this shock wave there is an intense flash of light emitted by the supernova, and this is what is causing the expanding rings that we can see in the images. Supernovae are of interest as these cosmic explosions produce many of the heavy elements, such as carbon, oxygen and iron, that make up our galaxy, stars and our planet.”

The supernova in question, called SN 2016adj, was first seen in 2016 and belongs to the well-known galaxy Centaurus A, located between 10 and 16 million light-years from Earth. For five and a half years, the team has watched the area around the supernova after it slowly faded away.

Centaurus A is full of dust lanes, and as light from the supernova spreads laterally it hits these dusty areas which, over time, light up further and further away from the supernova’s original position, creating a series of emission rings in expansion called light echoes.

Variations in these rings over the years of observation allow the team to track the distribution of dust lanes in the galaxy near the explosion. The data suggests that the dust is distributed in columns with large holes in the middle, creating an image similar to a piece of Swiss cheese.

Professor Stritzinger states: ‘Centaurus A is a huge elliptical galaxy. These are mostly quiet, dust-free, and without younger stars likely to explode as supernovae, but Centaurus A is clearly different. It is a strong radio astronomical source and contains prominent dusty regions with new stars forming within. This is a sign that it has ‘recently’ gobbled up another smaller spiral galaxy, and things haven’t calmed down yet, as they might in a couple of hundred million years. Observing the development of these light echoes will help us better understand these violent galaxy collisions.”

So far, four different light echoes produced by four different dust layers have been observed. The team plans to follow up on observations with the Hubble Telescope in the future, hoping that more rings of light will emerge.

The study is titled “Hubble Space Telescope Reveals Spectacular Light Echoes Associated with the Stripped-envelope Supernova 2016adj in the Iconic Dust Lane of Centaurus A.” And it has been published in the academic journal Astrophysical Journal Letters. (Source: IEEC / ICE / CSIC)