This image was created using data from the NASA Hubble Space Telescope, and it reveals complex loops and clusters of cosmic dust within the giant elliptical galaxy NGC 1316. These intricate patterns of dust are somewhat similar to dust bunnies that hide in the corners and under beds in a household. They provide evidence that NGC 1316 was formed through the merger of two gas-rich galaxies in the past.
The Hubble Space Telescope’s exceptional spatial resolution and the sensitivity of the Advanced Camera for Surveys (ACS), which was installed on Hubble in 2002, allowed for highly accurate measurements of a specific class of red star clusters within NGC 1316. Astronomers studying these star clusters have concluded that they are clear indicators of a major collision between two spiral galaxies that occurred billions of years ago. This collision and merger ultimately shaped NGC 1316 into the galaxy we observe today, with its distinctive dust lanes and star clusters.
NGC 1316, also known as Fornax A, is located on the outskirts of a nearby cluster of galaxies in the southern constellation of Fornax. It’s situated at a distance of about 75 million light-years from Earth and stands out as one of the brightest elliptical galaxies within the Fornax galaxy cluster. Remarkably, NGC 1316 is also one of the most powerful and expansive radio sources in the sky, with its radio emissions extending over several degrees of the celestial sphere, which is beyond what is visible in the Hubble image.
The history of NGC 1316 has been tumultuous, leaving behind various visible signs of its past. Wide-field observations from the Cerro Tololo Interamerican Observatory in Chile have revealed a diverse array of ripples, loops, and plumes in the outer regions of the galaxy. These features are often referred to as “tidal” effects and are believed to be the remnants of other spiral galaxies that merged with NGC 1316 over the past several billion years.
In the inner regions of NGC 1316, as depicted in the Hubble image, you can see a complex system of dust lanes and patches. These are thought to be the remnants of the interstellar medium associated with one or more of the spiral galaxies that were absorbed or “swallowed” by NGC 1316 during its tumultuous history. This rich history of mergers and interactions has left its mark on the galaxy, creating a fascinating and intricate astronomical object.
A team of U.S. scientists, led by Dr. Paul Goudfrooij from the Space Telescope Science Institute in Baltimore, Maryland, conducted a study using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. They focused on studying star clusters in several nearby giant elliptical galaxies, with NGC 1316 being one of their primary subjects. The specific star clusters they examined are known as globular clusters, which are compact groups of hundreds of thousands to millions of stars formed simultaneously.
The remarkable sensitivity of the Hubble ACS data allowed the team to detect faint globular clusters that were previously challenging to observe. By counting the number of globular clusters detected based on their brightness, they were able to provide the first evidence of the gradual disruption of star clusters that originated from a past merger of gas-rich galaxies. Their findings showed that the proportion of low-mass clusters is notably lower in the inner regions of NGC 1316 compared to the outer regions, aligning with theoretical predictions.
The images captured by the Hubble ACS in March 2003 were then combined to create a color composite, incorporating data from different filters. The blue, yellow-green, and infrared filters represented by F435W, F555W, and F814W respectively, allowed the team to gather valuable insights.