Active planetary systems orbit a significant fraction of hot, dense remnants of stars known as white dwarfs. These stars usually exhibit surface metals accumulated from debris disks. However, a planetesimal's entire journey, from a star-grazing orbit to final dissolution, remains poorly understood.
In a deep region of space, a strange star has been left with a metallic scar across its surface after devouring one of its planets. The unique ingestion of star ingestion was discovered by a team of scientists and was described in the paper "Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf."
Known as WD 0816-310, the star is a white dwarf located about 63 light-years away from Earth. Although believed to be a cool metal-polluted body, WD 0816-310 is a superdense husk of a dead star.
What are White Dwarfs?
White dwarfs refer to the stellar core, which remains when stars between 1/10 and eight times the mass of the Sun get exhausted and run out of fuel for nuclear fusion. When this happens, the stars remove their outer layers, exposing a compact, dense, white-hot core that cools slowly over time.
According to a 2001 study, around 97% of the stars in the Milky Way galaxy, including our own Sun, are destined to become white dwarfs. Still, the capabilities and compositions of these ultradense cosmic balls remain mysterious in so many ways.
Just like our own Sun, white dwarfs are slowly cooling embers of stars. It is well known that these stellar remnants cannibalize pieces of their planetary systems. However, astronomers used to believe that the bits of planets and asteroids shredded and engulfed by white dwarfs are evenly spread across their surfaces.
Some of the properties of white dwarf stars can be fairly determined directly from observations. These include analyses of their energy distribution and their optical and ultraviolet spectra. For cooler white dwarfs, however, the spectral properties have all vanished, and spectroscopic estimates are no longer available. With the recent advancements in astrophysics, scientists had renewed interest in the cooling and model atmosphere calculations of white dwarfs.
Cannibal White Dwarf Star
To gain more information about WD 0816-310, astronomers used the Very Large Telescope in Chile to monitor the stellar remnant for two months. They found that as the white dwarf rotated on its axis, the metals quickly changed and matched up with changes in its magnetic field.
The observations revealed that the polar magnetic field of WD 0816-310 had funneled the metallic leftovers from one of its meals onto one of its magnetic poles. This resulted in the creation of a dark metallic streak across its surface.
The scar was also found to be a concentrated patch of planetary material, locked in place by the same powerful magnetic fields that have guided the infalling fragments. Astronomers believe that by detecting more of the scarred husks, they can gain more unique insight into star systems beyond our own. Observations can also be made long after the demise of these systems.
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