Astronomers Baffled to Detect the Smallest Known Case of 'Galactic Cannibalism' in the Universe
The universe remains a big mystery for astronomers despite decades of research. Something new continues to come up in the world beyond that shakes all the core assertions of astronomy. In 2018, research came out claiming that a phenomenon typically observed in massive galaxies also happened in small galaxies, stated Live Science. Findings regarding this discovery were published in the journal Monthly Notices of the Royal Astronomical Society.
Canibalism in galaxies has been detected before in large galaxies. Scientists speculate that large galaxies like the Milky Way become humongous over time by gobbling up stars from neighboring galaxies. This behavior was not seen in small galaxies, but the study claims that they also follow this practice. Researchers associated with the study claimed that they spotted this 'cannibalism' in one of the Milky Way's satellite galaxies, Sextans dwarf spheroidal. This satellite galaxy has been determined to be 12 billion years old, and is also considerably smaller than the typical massive galaxies like the Milky Way. Data imply that Sextans dwarf spheroidal has 100,000 times less solar mass than the Milky Way.
Researchers believe that the present size of Sextans dwarf spheroidal came into being due to it consuming a smaller galaxy in comparison. The study took into consideration several previous sky surveys for the examination of the Sextans dwarf spheroidal. The surveys gave them insights regarding orbital speeds, colors, and brightness of stars in this galaxy. Experts noted some intriguing patterns in these stars.
The Sextans dwarf spheroidal has two kinds of stars- blue and red stars. The blue stars have less metal composition, while the red ones exhibit more metal composition. Both these groups follow a different arrangement. The blue stars come together in a round cluster and are arranged in an orderly fashion. On the other hand, red stars are more scattered in the galaxy. The fact that these two stars are so distinct in features, despite being part of the same galaxy, implied to researchers that Sextans dwarf spheroidal was made out of two smaller galaxies. "The most reasonable explanation of this phenomenon is that two galaxies merged, and had different metallicities," lead study author Luis Cicuéndez said.
Velocity data revealed that there is a "ring-like substructure" made of stars in the galaxy. These stars have a lower metal composition than other stars around them, and orbit with a much higher velocity. Researchers claim that the substructure was a consequence of the Sextans dwarf spheroidal eating up another metal-poor galaxy. Experts are yet to figure out if the substructure was part of the older galaxy or came into being during the merger. Estimates of this possible cannibalism by Sextans dwarf spheroidal, if true, is the smallest case of intergalactic cannibalism ever observed.
Researchers claimed that the findings showcase that the hierarchical theory of galaxy formation applies even to small galaxies. "This finding appears to show that the hierarchical theory of galaxy formation, in which small galaxies merge to form larger ones, can explain the formation of even the smallest known galaxies," said study co-author Giuseppina Battaglia, a physicist at the Instituto de Astrofísica de Canarias.