The last screams of light emitted by a dying star have been preserved in a series of hauntingly beautiful images, slowly reverberating throughout the universe.
The Hubble Space Telescope has captured in stunning detail the flare of light that followed a massive star that went supernova in 2016, as the flare spread outward over a period of more than five years.
The resulting animation of the stitched images is a treasure trove of information about the evolution of dying stars and the dust surrounding the supernova in the Centaurus A galaxy.
“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 ignite the smoke from previous shells still in the area,” says astronomer Stephen Lawrence. of Hofstra University in the USA.
“By comparing a series of photographs taken over a few minutes, you could measure all kinds of information not directly related to the most recent explosion to light the scene, things like how many shells had previously exploded, how opaque the smoke from a given shell is, or how fast and which way the wind was blowing.’
Light echoes are a truly amazing phenomenon that can only really be seen from a distance. They appear when something produces a flash of light that radiates into space. If this light encounters a physical barrier, such as clouds of cosmic dust, it will be reflected, arriving at a different time from the original explosion. It’s pretty much the same thing as sound echo, but with light. We can use these light echoes to help map and understand space and the objects within it.
When a supernova was observed in 2016, astronomers noted it and repeatedly returned to the host galaxy, Centaurus A, more than 12 million light-years away, to see if they could observe changes over time. This persistence paid off. Not only were they able to collect data on the fading light of the supernova, named SN 2016adj, but they were able to capture its luminous echoes.
“The blast wave from this powerful supernova explosion is racing outward at over 10,000 kilometers (more than 6,200 miles) per second,” says astronomer Lluis Galbany of the Institute of Space Sciences in Spain.
“In front of this blast wave is an intense flash of light emitted by the supernova, and this is what causes the expanding rings we can see in the images. Supernovae are of interest because these cosmic explosions produce many of the heavy elements such as carbon, oxygen and iron, which make up our galaxy, our stars and our planet.”
Centaur A is a little weird. It is classified as an elliptical galaxy, which are typically smooth, oval-shaped galaxies with very little dust and very old stars. However, Centaurus A is very dusty, bursting with star formation and somewhat distorted. These are all signatures of a cosmically recent collision with another galaxy, the effects of which have not yet subsided.
It is believed that when the light from the supernova traveled towards Earth, it would have encountered many clouds of dust. From our position, we would see this as a sequence of rings that expand in size. Four distinct bright echoes were observed in the five-year observation period, which meant four dust clouds, each large enough and dense enough to produce a light echo.
These bright echoes allowed the researchers, led by astronomer Maximilian Stritzinger of Aarhus University in Denmark, to map the dust next to the supernova. Their analysis suggests that the dusty structures contain spaces filled with material that is too low-density to produce a detectable light echo.
While we’re very excited to see an image of Centauri A from JWST, which will cut through the dust to see the galaxy’s enigmatic heart, the research shows that there are some observations for which Hubble is still king. Since Hubble has been in space for decades, it was able to capture a multi-year observation that provides detailed information about the structure of another galaxy.
“The data set is remarkable and allowed us to produce very impressive color images and animations showing the evolution of light echoes over a period of five years,” says Stritzinger. “It’s a rare phenomenon that has only previously been documented in a handful of other supernovae.”
The research has been published in The Astrophysical Journal Letters.