Astronomers at Tel Aviv University’s Wise Observatory outside Mitzpe Ramon in the Negev have discovered evidence of a galaxy’s being gobbled up by its neighbors. They identified a heavenly body in the shape of a tadpole with an enormous tail about 500,000 light-years long and some 300 million light-years away from Earth. They said the “tadpole,” which had not been discovered until now because it shines in a very pale light, is composed of the remains of a dwarf galaxy created by swallowing two large nearby galaxies.
Their article has just been published in the Scientific Bulletin of the Royal Astronomical Society.
The researchers, led by Dr. Noah Brosch of the School of Physics and Astronomy, identified an unknown celestial body about 300 million light-years away. The “torso” has an elliptical ‘head’ with two galaxies in its center. They believe this is a new and concrete demonstration of a fascinating process in the universe – the absorption of a dwarf galaxy by the two large galaxies in its vicinity.
The study was conducted in collaboration with scientists at the University of California at Los Angeles (UCLA) and the Russian Academy of Sciences.
“We’re looking for ‘action’ in the sky,” explained Brosch. “We’re watching galaxies and nearby areas to detect evidence of change. Is the galaxy growing or shrinking? Is it interacting with other galaxies? Among other things, we observe dense clusters of galaxies, assuming that when the galaxies are close together, there will be more interactions between them,” added Brosch.
“This kind of dense galaxy group is called Hickson Compact Group (HCG), named after Canadian astronomer Paul Hickson, who identified them in 1982. Unlike galaxy clusters that include many thousands of galaxies, HCG groups include only a few galaxies, making it relatively easy for us to identify and understand interactions between them. The group of galaxies observed in this study is called HCG 98,” he said.
HCG 98 is a dense group of four galaxies, located 300 million light-years away. In comparison, the visible end of the universe is about 14 billion light-years away, so the HCG 98 group is actually a relatively close neighbor. In observations and experiments, astronomers used special technology, including a telescope that was acquired about five years ago, and a method of processing that combines many photographs of the same region and allows researchers to distinguish even very pale bodies that cannot be seen in any other way.
These observations of HCG 98 revealed a new and unusual finding – a giant celestial body shaped like a tadpole made up of two ordinary galaxies, followed by an enormous tail,” said Brosch, “We think this is concrete evidence of a process that is going on in the universe constantly: the dissolution of dwarf galaxies by larger galaxies. Such an event, which takes about a billion years, occurs when the stars of the dwarf galaxy are attracted by the gravitational force of the large galaxies.”
In this case, the head of the tadpole appears to have been created from the stars of the dwarf galaxy, which were close to the two predatory galaxies observed in the center of the head; the giant tail is composed of the remains of farther stars in the disintegrating galaxy. In fact, said concluded Brosch, “our observation has captured the liquidation process in full swing.”
Wise Observatory researchers are continuing their large-scale project using the special detection technology for nearly 100 galaxies across the universe.