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Researchers Capture Rare ‘Light Echo’ From Star Explosion

When a star bursts (a supernova), it transmits its strong eruption of light in various directions. On exceptional occasions, ‘light echoes’ or rings of light disperse from the initial supernova location in the months and years that follow, as illustrated recently in an article published in the journal Astrophysical Journal Letters.

Researchers Capture Rare ‘Light Echo’ From Star Explosion

Animation of colored images exhibiting the light echoes of SN 2016adj over a 5.5-year period. The images are centered on the position of the supernova which is observed in the first two epochs and then fades away. Image Credit: Hubble Space Telescope

The research is based on observations made using the Hubble Space Telescope (HST) by a group of astronomers from the Institute of Space Sciences and the Institute of Space Studies of Catalonia in Barcelona (Spain), the Hofstra University (New York, USA), the Aarhus University (Denmark), the University College Dublin (UCD) School of Physics (Republic of Ireland), and the European Southern Observatory (Garching, Germany).

The researchers combined the HST images in a brief .gif video, illustrating primarily the supernova blast at the very center, trailed by light rings that appeared when light from the blast hit different layers of dust in the neighborhood.

The data set is remarkable and enabled us to produce very impressive colored images and animations that exhibit the evolution of the light echoes over a five-year period. It is a rarely seen phenomenon previously only documented in a handful of other supernovae.

Professor Maximillian Stritzinger, Study Lead Scientist, Aarhus University

Dr. Morgan Fraser, a Dublin-based astrophysicist from UCD School of Physics, explained, “While the James Webb Space Telescope has drawn much attention, its predecessor Hubble continues to provide incredible images of the universe. HST has now been observing the sky for over three decades, so we can find things like this light echo that evolve slowly over many years.

The blast wave from this powerful supernova explosion is racing outwards at over 10,000 kilometers per second. Ahead of this blastwave is an intense flash of light emitted by the supernova, and this is what is causing the expanding rings 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, which make up our galaxy, stars, and our planet.

Dr. Lluis Galbany, Study Co-Author, Institute of Space Sciences and Institute of Space Studies in Catalonia

Co-author Dr. Stephen Lawrence of Hofstra University in Hempstead, New York, notes that “a good everyday analogy is to imagine the finale of a fireworks show—the bright burst of light from a shell at the end of the show will light up the smoke from earlier shells that is still lingering in the area.

By comparing a series of photographs taken over several minutes, you could measure all sorts of information that is not directly related to the most recent explosion that is lighting up the scene, things like how many shells had previously exploded, how opaque is the smoke from a given shell, or how fast and in what direction was the wind blowing.

Dr. Stephen Lawrence, Study Co-Author, Hofstra University

The supernova under exploration, christened SN 2016adj, was first spotted in 2016 and is a part of the prominent strange galaxy Centaurus A, located between 10 and 16 million lightyears from Earth. For 5.5 years, astronomers observed the region surrounding the supernova after it gradually disappeared.

Centaurus A is filled with dust lanes, and when the sideways scattering light from the supernova touches these dusty regions over time, they irradiate further and further away from the initial supernova location, forming a series of expanding rings of emission known as light echoes.

The differences in these rings during the years of exploration allow scientists to investigate the layout of the dust lanes in the galaxy close to the blast. The information proposes that they have columns of dust with large holes in between, somewhat like a piece of Swiss cheese.

Centaurus A is a huge elliptical galaxy. These are mostly quiet, dust free, and without younger stars prone to go off as supernovae, but Centaurus A is obviously different. It is a strong radioastronomical source and it contains prominent dust lanes with new stars forming within.

Professor Maximillian Stritzinger, Study Lead Scientist, Aarhus University

“This is a sign that it has ‘recently’ gobbled up another smaller spiral galaxy, and matters have not yet settled down, as it might in a couple of hundreds of millions of years. Observing the development of these light echoes will help us gain more insight into these violent galaxy collisions,” Professor Stritzinger added.

Thus far, four individual light echoes formed by four diverse sheets of dust have been witnessed. Going forward, the researchers plan to pursue the observations using the HST, anticipating that additional light rings will arise. Additionally, it could be possible to find a range of the light echoes, demonstrating in effect the range of the fundamental supernova.

Journal Reference

Stritzinger, M. D., et al. (2022) Hubble Space Telescope Reveals Spectacular Light Echoes Associated with the Stripped-envelope Supernova 2016adj in the Iconic Dust Lane of Centaurus A. Astrophysical Journal Letters.


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