The last cries of light emitted by a dying star have been preserved in a series of eerily beautiful images, slowly echoing through the cosmos.
The Hubble Space Telescope captured in spectacular detail the flash of light that followed a massive supernova star in 2016 as the glow spread outward over a period of more than five years.
The resulting animation of stitched images is a treasure trove of evolutionary information about dying stars and dust surrounding the supernova in its home galaxy, Centaurus A.
“A good everyday analogy is to imagine the finale of a firework display – the bright burst of a shell at the end of the show will ignite the smoke from previous shells that still lingers in the area,” says the astronomer Stephen Lawrence. from Hofstra University in the United States.
“By comparing a series of photographs taken over several minutes, you can measure all sorts of information that is not directly related to the most recent explosion illuminating the scene, things like the number of shells that have already exploded , the smoke opacity of a given shell, or how fast and in what direction the wind was blowing.”
Light echoes are a truly amazing phenomenon that can only really be seen from a distance. They occur when something produces a flash of light that radiates out into space. If this light encounters a physical barrier, such as clouds of cosmic dust, it will reflect and arrive at a different time than the initial burst. It’s much the same as a sound echo, but with light. We can use these light echoes to map and understand space and the objects in it.
When a supernova was observed in 2016, astronomers took notice and repeatedly returned to the host galaxy, Centaurus A, located more than 12 million light-years away, to see if they could observe any changes over time. This perseverance paid off. Not only were they able to collect data on the fading light from the supernova, named SN 2016adj, but they managed to capture its light echoes.
“The shock wave from this powerful supernova explosion is traveling at more than 10,000 kilometers (over 6,200 miles) per second,” said astronomer Lluis Galbany from the Institute of Space Sciences in Spain.
“Before this shock wave is an intense flash of light emitted by the supernova, and this is what causes the expanding rings that we can see in the images. Supernovae are interesting because these cosmic explosions produce many heavy elements such as carbon, oxygen and iron, which make up our galaxy, the stars and our planet.”
Centaurus A is a bit quirky. It is classified as an elliptical galaxy, which are usually smooth oval-shaped galaxies with very little dust and very old stars. However, Centaurus A is very dusty, brimming with star formation and somehow 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 headed towards Earth, it would have encountered several clouds of dust. From our position, we would see this as a sequence of rings growing in size. Four distinct light echoes were observed over the five-year observation period, which meant four clouds of dust, each large and dense enough to produce a light echo.
These bright echoes allowed 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 a material whose density is too low to produce a detectable light echo.
While we’re excited to see an image of Centaurus A from JWST, which will cut through the dust to see the galaxy’s enigmatic heart, research shows that there are certain sightings where 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 some very impressive colorful images and animations that show the evolution of light echoes over a five-year period,” says Stritzinger. “This is a previously rarely seen phenomenon only documented in a handful of other supernovae.”
The research has been published in Letters from the Astrophysical Journal.