A new star system discovered by the kilodegree survey

Astronomers have discovered a new star system on the outskirts of the Milky Way as part of the Kilo Degree Survey (KiDS). The newly discovered system, called Sextans II, is likely an extremely faint dwarf galaxy. The result was reported in a paper published November 10 on preprint server arXiv.

KiDS is a large-scale multi-scale survey using the VLT Survey Telescope (VST) at the Paranal Observatory of the European Southern Observatory in Chile. Since 2011, the survey has mapped 1,350 square degrees of the night sky in four broadband filters (u, g, r, i). Although KiDS focuses on collecting large-scale structures in the universe, it may also detect extragalactic star systems with low surface brightness.

That’s why a team of astronomers led by Massimiliano Gatto of the Capodimonte Astronomical Observatory in Naples, Italy, decided to conduct a large-scale search for faint, unknown star systems using KiDS. For this purpose, they looked for low-luminosity stellar density in the latest KiDS Data Release (DR4), which yielded promising results.

“We report the discovery of large, compact overdensities of old, metal-poor stars in the KiDS (Data Release 4) survey,” the researchers wrote in the paper.

The team identified a very promising hyperdensity of stars in the Sextans constellation with an absolute integral value of -3.9. Subsequent observations of this hyperdensity using the 8.2-meter Subaru telescope confirmed that it was a star system located about 473,000 light-years away.

Astronomers initially named the newly discovered system KiDS-UFD-1 and named it Sextans II. The collected data indicate that Sextance 2 is relatively small, with a half-light radius of about 629 light-years, while its mass is estimated at 4,910 solar masses. The system has a metallicity of -1.5 dex, an ellipticity of 0.46, and is at least 10 billion years old.

According to the authors of the paper, the results indicate that the Sextans II system is a faint, ancient, and metal-poor system. Gatto’s team concluded that the newly discovered star system is a faint spherical satellite of the Milky Way, most likely an ultra-faint dwarf (UFD) galaxy. In general, UFD galaxies are the least luminous, most dark matter-dominated, and least chemically evolved galaxies.

However, the researchers do not rule out the possibility that Sextans II is a malfunctioning globular cluster, adding that more research into this system is needed to confirm its true nature.

“The final word on the nature of the system can only be provided by appropriate spectroscopic follow-up of a reasonable sample of member stars, which may be challenging, given the size range spanned by the candidate RGB members,” the scientists wrote.