When the Sun reaches the end of its main sequence, approximately 5 billion years from now, it will enter what is known as its Red Giant Branch (RGB) phase, during which it will expand and potentially consume Mercury, Venus, and possibly Earth. Not long after, it will undergo gravitational collapse and blow off its outer layers, leaving behind a dense remnant known as a white dwarf. While this is how planet Earth will eventually meet its end, it will not mark the end of the Solar System, as the white dwarf remnant of our Sun surrounded by clouds of trace elements.
Such is the nature of the Universe, where the only constant is change and nothing goes to waste. Nevertheless, an international team of astronomers was surprised when they were studying an ancient white dwarf that was actively accreting material from its former planetary system. Using the W. M. Keck Observatory on Maunakea in Hawaii, the team obtained spectroscopic evidence of 13 chemical elements commonly associated with rocky bodies. This discovery challenges our current understanding of the late stages of stellar evolution.
The team consisted of astronomers from the Trottier Institute for Research on Exoplanets and the Department of Physics at the Université de Montréal, the Centre de Recherche en Astrophysique du Québec (CRAQ), the Earth and Planets Laboratory at the Carnegie Institution for Science, the Gemini Observatory/NOIRLab, the Space Telescope Science Institute (STScI), and multiple universities. Their findings were presented in a paper published in *The Astrophysical Journal Letters* on Oct. 22nd.
*LSPM J0207+3331 is a particularly old white dwarf star, located 145 light-years from Earth in the constellation Triangulum. Credit: Université de Montréal*
The system in question was LSPM J0207+3331, a white dwarf system located 145 light-years from Earth. This stellar remnant is extremely ancient, estimated at 3 billion years old, and is surrounded by a hydrogen-rich envelope. Based on the spectra they obtained using the High Resolution Echelle Spectrometer (HIRES) on the Keck I telescope, the team detected a host of minerals, including sodium (Na), magnesium (Mg), aluminum (Al), Silicon (Si), Calcium (Ca), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and strontium (Sr).
According to the team’s analysis, these minerals were once part of a differentiated rocky body measuring at least 200 km (120 mi) in diameter that was torn apart by the star’s gravity. The resulting debris disk is the oldest and most metal-rich ever observed around a hydrogen-rich white dwarf. “This discovery challenges our understanding of planetary system evolution,” said lead author Érika Le Bourdais of the iREX Institute. “Ongoing accretion at this stage suggests white dwarfs may also retain planetary remnants still undergoing dynamical changes.”
The system is an example of a “polluted white dwarf,” which refers to stellar remnants surrounded by clouds of material. Nearly half of those observed showed signs of accreting heavy elements, but these are typically concealed by their hydrogen-rich atmospheres, making this detection especially significant. The presence of heavy elements suggests that these stars still had planetary systems, which were dynamically disturbed (possibly by a passing star or rogue planet) at some point in their long histories.
In the case of LSPM J0207+3331, the team estimates that the perturbation was likely recent (occurring within the last few million years), which likely sent the rocky body spiraling inward towards its star. This is based in part on the amount of rocky material they detected, which is unusually high for a 3-billion-year-old white dwarf. From this, the team concluded that the system may be an example of delayed instability involving multi-planet interactions that gradually destabilize their orbits over billions of years.
Co-investigator John Debes of the STScI explained:
Something clearly disturbed this system long after the star’s death. There’s still a reservoir of material capable of polluting the white dwarf, even after billions of years. This suggests tidal disruption and accretion mechanisms remain active long after the main-sequence phase of a star’s life. Mass loss during stellar evolution can destabilize orbits, affecting planets, comets, and asteroids. Future observations may help distinguish between a planetary shakeup or the gravitational effect of a stellar close encounter with the white dwarf.
Artist’s impression of a planet orbiting a white dwarf star. Credit: W.M. Keck Observatory.
The next step will be to investigate what may have disrupted the system, which could include a Jupiter-sized planet still orbiting LSPM J0207+3331. Such a planet will be difficult to detect visually, but could be found by measuring the gravitational influence it has on its star. In this respect, the ESA’s Gaia Observatory may be sensitive enough to indirectly detect the presence of any outer planets. Infrared observations using NASA’s *James Webb Space Telescope* (JWST) could also aid in the search for outer planets in this system.
These findings not only challenge current assumptions about late-stage stellar evolution but also provide a clearer picture of what will become of the Solar System someday.
Further Reading: STScI, The Astrophysical Journal