Brown dwarf WISEA J155349.96+693355.2 linked to ancient galaxy collision

The brown dwarf WISEA J155349.96+693355.2 is a low-temperature, metal-poor object identified as the first of its kind to be associated with the Gaia-Enceladus substructure. This group of stars was once part of a separate dwarf galaxy that collided with our Milky Way billions of years ago. Observations have confirmed that this brown dwarf follows a distinct, highly eccentric orbit consistent with objects that originated outside the Milky Way and were later absorbed into its outer halo.

Spectroscopic analysis using the James Webb Space Telescope revealed an atmosphere containing water, methane, and ammonia. The relative absence of carbon monoxide and carbon dioxide, combined with a low metallicity—a term indicating a lower concentration of elements heavier than hydrogen and helium—confirms its ancient, metal-poor nature.

The findings were gathered using the telescope’s instruments to measure light across a wide range of wavelengths from 0.6 to 12 micrometers. By analyzing the radial velocity and movement patterns of the brown dwarf, the data showed it possesses a high-velocity, elongated orbit.

Key findings
- Identified as the first brown dwarf chemically and kinematically linked to the Gaia-Enceladus Milky Way substructure.
- Confirmed an effective temperature of approximately 960 Kelvin.
- Detected H2O, CH4, and NH3 absorption features in the object's atmosphere.
- Measured a radial velocity of -163 kilometers per second.
- Confirmed a highly eccentric galactic orbit consistent with an accreted halo object.

Scientific study

JWST Observations of the Metal-poor T Dwarf WISEA J155349.96+693355.2: The First Brown Dwarf Associated with the Gaia-Enceladus Milky Way Substructure (external link)