“We have found a giant, exceptional remnant of a disturbed galaxy,” says the observational astronomer Noah Brosch at The Florence and George Wise Observatory at Tel Aviv University, om 2018 discovery of a disturbed galaxy resembling a giant tadpole, complete with an elliptical head and a long, straight tail, about 300 million light-years from Earth. The galaxy is a million light-years long from end to end, ten times larger than the Milky Way.
“Would reach a fifth of the way from Andromeda to our own Milky Way”
“What makes this object extraordinary is that the tail alone is almost 500,000 light-years long,” says Prof. R. Michael Rich at the University of California, Los Angeles. “If it were at a distance from the Andromeda Galaxy, which is about 2.5 million light-years from Earth, it would reach a fifth of the way to our own Milky Way.”
Brosch and Rich collaborated in the study with Dr. Alexandr Mosenkov from St. Petersburg University and Dr. Shuki Koriski from TAU’s Florence and George Wise Observatory and School of Physics and Astronomy.
A giant tadpole from the disturbance of a dwarf galaxyy
According to the study, the giant “tadpole” was created by the disturbance of a small, previously invisible dwarf galaxy that mostly contains stars. As the gravitational force from two visible galaxies pulled on stars in this vulnerable galaxy, the stars formed closer to the pair “the head” of the tadpole. Stars that lingered in the sacrificial galaxy formed the “tail”.
System of two very close disk galaxies
“The extragalactic frog fry contain a system of two very close to ‘normal’ disk galaxies, each about 40,000 light-years in diameter,” says Brosch. “Together with other nearby galaxies, the galaxies form a compact group.” small group of galaxies called HCG098 that will merge into a single galaxy over the next billion years.
Compact Galaxy groups
Such compact galaxy groups were first identified in 1982 by astronomer Paul Hickson, who published a catalog of 100 such groups. Hickson Compact Groups investigates environments with high galaxy densities that are not at the core of a “cluster” of galaxies (clusters themselves contain thousands of galaxies). The “Tadpole Galaxy” is listed as No. 98 in the Hickson Compact Group catalog.
“In compact group environments, we believe we can study ‘pure’ examples of galaxy-galaxy interactions, learn how matter is transferred between members and how new matter can modify and affect the growth and development of the galaxy,” says Dr. Brosch.
For the research, the researchers collected dozens of images of the targets, each exposed through a wide filter that selects red light while virtually eliminating foreign light pollution. “We used a relatively small 70 cm telescope at the Wise Observatory and an identical telescope in California, both of which were equipped with state-of-the-art CCD cameras,” says Brosch. The two telescopes are collaborating on a project called the Halos and Environments of Nearby Galaxies (HERON) Survey.
The study was part of a long-term project at TAU’s Florence and George Wise Observatory, which explores the sky at low light levels to discover the smallest details of studied galaxies.
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