A team of Chinese and Japanese astronomers found that a strange star inside the galactic halo originated from a dwarf galaxy that was disrupted and swallowed by the Milky Way.
Small star systems like dwarf galaxies are considered the main building blocks of our galaxy. However, it is not clear how many and what stars in our galaxy come from satellite dwarf galaxies.
A research team led by Zhao Gang, an astronomer at the Chinese Academy of Sciences' National Astronomical Observatory, has discovered a chemically special star that has an unusually low amount of magnesium, but contains an abundance of heavy elements such as europium, gold, and uranium.
"This is the first galactic star discovery to have a very small amount of magnesium and excessive heavy elements," said Li Haining, a research team member.
"The stars keep chemical information about their birthplace in their outer layer. We can distinguish stars created in the Milky Way from those that originated in dwarf galaxies based on their chemical mass," Zhao said.
The chemical composition of a special star shows that it comes from a dwarf galaxy that has been disrupted by the interaction with the Milky Way.
The extreme amplification of this star's heavy elements suggests that this dwarf galaxy would be affected by the events of the fast neutron capture process, the dominant process through which elements heavier than iron are formed. Such a process could happen during the fusion of binary neutron stars in the dwarf galaxy.
The study will help astronomers better understand the creation of heavy elements in space and the evolution of the Milky Way and other galaxies.
Meanwhile, astronomers are only able to detect about 30 stars containing excessive heavy elements in our galaxy. The new study provides substantial evidence that these special stars may have originated from dwarf galaxies disturbed by the Milky Way.
Research, based on data obtained in the Chinese large-scale spectral telescope (LAMOST) and the Japanese Subaru telescope, has been published online in the latest issue of Nature Astronomy.
LAMOST is a spectroscopic reconnaissance telescope capable of capturing 4,000 spectra per exposure. LAMOST has earned more than 8 million stellar spectra to study the formation of the Milky Way.
"The massive spectrum provided by the LAMOST survey gives us a great opportunity to find chemically special stars," said Xing Qianfan, the first author of the article.
These types of stars can be used to explore the chemical development of various star systems, Xing said.
"This newly discovered star with large excesses of heavy elements provides a window for exploring the chemical development of disturbed dwarf galaxies. Star formation in dwarf galaxies is relatively slow compared to larger galaxies, leading to chemical differences between their star populations," Xing said. .
"Chemically wondrous stars will be good marks for exploring the history of the Milky Way," Zhao said.