A team of astronomers has made a remarkable discovery of a 3 billion-year-old white dwarf that is actively accreting material from its former planetary system. This finding, which was detailed in a paper published on October 22 in The Astrophysical Journal Letters, challenges existing notions about the evolution of stellar remnants.
As our Sun approaches the end of its main sequence phase in approximately 5 billion years, it will expand into a Red Giant Branch and may engulf the inner planets, including Mercury, Venus, and potentially Earth. Following this phase, it will shed its outer layers, resulting in a dense remnant known as a white dwarf. While Earth”s fate is sealed in this process, the white dwarf remains, surrounded by remnants of its former planetary system, indicates the ongoing cycle of cosmic material.
Using the W. M. Keck Observatory on Maunakea in Hawaii, the research team, which included experts from the Université de Montréal, the Centre de Recherche en Astrophysique du Québec, and the Carnegie Institution for Science, discovered spectroscopic evidence of 13 chemical elements typically associated with rocky bodies. This significant observation was made using the High Resolution Echelle Spectrometer (HIRES) on the Keck I telescope.
The white dwarf, designated LSPM J0207+3331, is situated 145 light-years from Earth in the constellation Triangulum. It is one of the oldest white dwarfs known, with an estimated age of 3 billion years, and is enveloped in a hydrogen-rich atmosphere. The analysis revealed a range of minerals, including sodium, magnesium, aluminum, silicon, calcium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and strontium. These elements are believed to originate from a differentiated rocky body, measuring at least 200 km in diameter, which was disintegrated by the gravity of the white dwarf.
According to lead author Érika Le Bourdais from the iREX Institute, this discovery has implications for our understanding of planetary system evolution. “Ongoing accretion at this stage suggests white dwarfs may also retain planetary remnants still undergoing dynamical changes,” she stated.
Within the context of white dwarfs, those that exhibit signs of accretion are referred to as “polluted white dwarfs.” Nearly half of the observed white dwarfs show evidence of accumulating heavy elements, though these indicators are often obscured by their hydrogen-rich atmospheres. The presence of these heavy elements implies the possible existence of planetary systems that have experienced significant disturbances, potentially due to a passing star or a rogue planet.
In the case of LSPM J0207+3331, the research team posits that the gravitational disturbance likely occurred recently, within the past few million years, leading to the inward spiral of the rocky body towards the star. This conclusion is supported by the unusually high amount of rocky material detected around this ancient white dwarf.
Co-investigator John Debes from the Space Telescope Science Institute noted that the next phase of research will focus on uncovering what may have disrupted the system. There is a possibility that a Jupiter-sized planet is still orbiting LSPM J0207+3331, which could be challenging to observe directly. However, its gravitational influence on the star could be detectable. The ESA”s Gaia Observatory may offer the sensitivity needed to identify any outer planets indirectly, and infrared observations from NASA”s James Webb Space Telescope could further aid in the exploration of this intriguing system.
This discovery not only redefines our understanding of the late stages of stellar evolution but also provides insights into the eventual fate of our own Solar System.
