WD J2147–4035

Lore & Background

WD J2147–4035 was first identified from Gaia data as a white dwarf candidate in 2019. In 2021 it was pointed out as an unusual faint white dwarf in the solar neighbourhood, with researchers suggesting it could be extremely old (about 10 Gyrs). In 2022, observations with X-shooter on the Very Large Telescope confirmed it as a white dwarf, likely with a helium-dominated atmosphere, and detected metal pollution including sodium, lithium, potassium, and possibly carbon. The lithium line shows Zeeman splitting, indicating a magnetic white dwarf with a measured magnetic field strength of 0.55 ±0.03 Megagauss. The magnetism can lead to inhomogeneous brightness distribution, and TESS light curve data show a rotation period of around 13 hours. The nature of the accreted parent body remains unclear as of September 2024.

Reader's Guide

WD J2147–4035 is significant as a very cold white dwarf that challenges typical expectations: despite being a white dwarf, its low temperature gives it a reddish appearance, and its extreme age of about 10.7 Gyrs makes it one of the oldest known white dwarfs. Its magnetic field and metal pollution from planetary debris provide direct evidence of past planetary system activity. The object's very red color (r-z=2.29 mag) is attributed to a low hydrogen-to-helium ratio, resulting in mild collision induced absorption, which gives it a distinct orange color. This contrasts with many cold white dwarfs that are IR-faint due to strong CIA. The detection of lithium, sodium, potassium, and possible carbon in its atmosphere, along with the measured rotation period and magnetic field, offer a rare window into the late-stage evolution of planetary systems around aging stars.

Did You Know?

• WD J2147–4035 has a temperature of about 3,050 Kelvin, making it appear reddish despite being a white dwarf.
• It is a magnetic white dwarf with a field strength of 0.55 ±0.03 Megagauss.
• The white dwarf has a rotation period of around 13 hours, inferred from TESS light curve data.
• Its total age is estimated at 10.7 ±0.3 Gyrs, including a progenitor lifetime of about 500 Myrs.