Hubble captures rare 'light echo' from star explosion.

Host-subtracted F555W-band HST image of SN 2016adj on +1991 days, with the positions of LE1, LE2, LE3, and LE4 highlighted by colored rings and labeled. Credit: The Astrophysical Journal Letters (2022).
Host-subtracted F555W-band HST image of SN 2016adj on +1991 days, with the positions of LE1, LE2, LE3, and LE4 highlighted by colored rings and labeled. Credit: The Astrophysical Journal Letters (2022).

 A supernova, or star explosion, releases an enormous blast of light in all directions. Rarely, from the initial supernova spot, rings of light or "light echoes" stretch out in the months and years that follow.

A group of astronomers from Dublin, Barcelona, Aarhus, New York, and Garching just published a study in The Astrophysical Journal Letters based on observations made with the Hubble Space Telescope (HST) during that time. This week saw the release of the study titled "Hubble Space Telescope Reveals Spectacular Light Echoes Associated with the Stripped-envelope Supernova 2016adj in the Iconic Dust Lane of Centaurus A."

The HST photos were combined to create a brief gif-video that initially showed the supernova explosion at the very center, then light rings that developed as light from the explosion struck different layers of dust around.

Credit: University College Dublin
Credit: University College Dublin

Professor Maximillian Stritzinger, the lead researcher, from Aarhus University in Denmark stated, "The data set is exceptional and allowed us to create stunning colorful pictures and animations that show how the light echoes have changed over the course of five years. It is a seldom seen event that has only been studied in a few other supernovae."

Astrophysicist Dr. Morgan Fraser of the UCD School of Physics, a co-author and resident of Dublin, remarked, "Even though the James Webb Space Telescope has received a lot of attention, Hubble is still producing amazing photos of the cosmos. We can now identify objects like this light echo that slowly change over many years since HST has been studying the sky for more than three decades."

Dr. Lluis Galbany, a co-author from Barcelona's Institute of Space Sciences, stated, "This strong supernova explosion is sending a blast wave outward at a speed of more than 10,000 kilometers per second. The bright burst of light that the supernova released before to this blastwave is what is producing the expanding rings that can be seen in the photographs. Supernovae are fascinating because many of the heavy components that make up our galaxy, stars, and planet, such carbon, oxygen, and iron, are produced by these cosmic explosions."

Dr. Stephen Lawrence, a co-author from Hofstra University in New York, stated, "Imagine the finale of a fireworks display. The intense blast of light from a shell at the conclusion of the show would illuminate any remaining smoke from previous shells in the vicinity. It is possible to count the number of shells that have burst prior to the most recent explosion that is lighting up the picture, determine how impenetrable the smoke from a particular shell is, and determine the speed and direction of the wind by comparing a series of images taken over a period of time."

The SN 2016adj supernova in issue, which is located in the well-known odd galaxy Centaurus A and is 10 to 16 million light years away from Earth, was first seen in 2016. The researchers observed the region surrounding the explosion as it slowly dissipated for five and a half years.

There are several dust lanes in Centaurus A, and when the supernova's sideways spreading light struck these dusty places over time, it lighted them up more and farther away from the supernova's initial location, producing a series of expanding emission rings known as light echoes.

Researchers can examine the layout of the dust lanes in the galaxy close to the explosion thanks to changes in these rings throughout the years of monitoring. According to the data, they seem to be made up of dust columns with big gaps between them, like a slice of Swiss cheese.

remarked Professor Stritzinger "A massive elliptical galaxy called Centaurus A. The majority of them are calm, dust-free, and devoid of younger stars that may explode as supernovae, but Centaurus A is definitely unique. It has notable dust lanes with young stars growing within and is a potent radioastronomical source. The fact that things haven't yet calmed down, as they would in a few hundreds of millions of years, indicates that it "recently" ate up another smaller spiral galaxy. We will learn more about these ferocious galaxy collisions by watching the evolution of these light echoes."

Four separate light echoes created by four different dust sheets have so far been seen. The earliest observation of light echo emission linked to a supernova is provided by the data set for SN 2016adj. While earlier light echoes detected by HST, including SN 2014J, started only hundreds of days after explosion, the team was able to quantify these emissions 50 days after the star's demise. These are also the first light echoes discovered in the vicinity of a type Ic supernova.

Dr. Ferdinando Patat of the European Southern Observatory in Garching, Germany is a member of the team that intends to continue its observations with the HST in the future in the hopes that further light rings would manifest. Additionally, it could be able to retrieve the light echoes' spectra, which would essentially display the supernova's spectrum below.

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