by A dead star that eats its own planets is like a raging cosmic zombie destroyed by planetary debris.
The imprintable metal scar sits on the surface of this white dwarf star; this kind of stellar remnant will be left behind when the sun dies too, and indicates that there is an “afterlife” for planetary systems.
The scar on the surface of the white dwarf, known as WD 0816-310, was spotted by a team of astronomers using the Very Large Telescope (VLT) located in the Atacama desert region of Northern Chile. It represents the first unique signature seen on a white dwarf star due to the cannibalization of planets and asteroids.
“It is well known that some white dwarfs – slowly cooling down on stars like our sun – are cannibalizing pieces of their planetary systems,” Armagh Observatory team leader and astronomer Stefano Bagnulo said in a statement. “Now we have discovered that the magnetic field of the star plays a central role in this process, leaving a scar on the surface of the white dwarf.”
Related: These supernovas are kicking up a storm, fueling cosmic life and death
The team of astronomers was able to use the VLT to determine the origin of the metal scar thrown by WD 0816-310, which is about the size of Earth and about the mass of the Sun.
“We have shown that these metals come from a planetary fragment as large as or possibly larger than Vesta, which is about 500 kilometers (311 miles) across and the second largest asteroid in the solar system,” Jay Farihi, team member discovery and professor at University College London, said in the statement.
Dead star and its metal scar
White dwarfs are born when stars around the size of the sun exhaust the fuel supply necessary for nuclear fusion to occur in their hearts. As this process ends, so does the outflow of energy that has supported each star against the inward pressure of its own gravity for billions of years.
This causes the core of the star to collapse and its outer layers, where nuclear fusion proceeds, “puff out” to tens, or hundreds, of the original width of the dying star. This is called the red giant phase of the star’s life, and is a phase that the sun will reach in about 5 billion years. When it becomes a red giant, the sun will ascend to the orbit of Mars and engulf the inner planets, including Earth.
The red giant phase is short-lived, and the outer layers of the star are still dissipating and cooling. This eventually leaves a planetary nebula of gas and dust. This nebula would be made of stellar material that surrounded the core of a smoldering star that had turned into a cosmic dwarf: a white dwarf.
These white dwarfs can then go on to accrete the remaining bodies in their systems, such as planets and asteroids, that were not destroyed during the red giant phase.
Astronomers have previously observed white dwarfs contaminated by metals from accreting bodies. The idea is that such pollution occurs when the bodies are too close to these dead stars.
The team’s new observation is different, however, as material found for WD 0816-310 appears to be concentrated in one scar-like region.
The strength of the signal from metals on WD 0816-310 appears to vary as the dead star rotates. This shows that the metals are concentrated in a specific area rather than being spread evenly across the star’s surface. Furthermore, the observed changes are synchronized with changes in the magnetic field of WD 0816-310, suggesting that its metal scar is located at one of its poles.
“Surprisingly, the material was not evenly mixed over the star’s surface, as theory predicted. Instead, this scar is a concentrated patch of planetary material, which possesses the same magnetic field that guided the infalling fragments,” staff. Western University member and professor John Landstreet said in the statement. “Nothing like this has been seen before.”
RELATED STORIES:
— Just before this star exploded, this star emitted the mass value of the sun
— An extremely dense star could be in the strange wake of a supernova explosion
— An extremely dense star could be in the strange wake of a supernova explosion
To reach these conclusions, the team used a VLT instrument known as the Focal Reducer and Low Dispersion Spectrograph (FORS2). FORS2 is described as the “Swiss Army knife” of the instruments at the Paranal Observatory because of its ability to study many different astronomical objects in many different ways.
FORS2 was sensitive enough to allow the team to observe this small white dwarf and measure its magnetic field. That indicated that the star has a scar.
In addition to showing how planetary systems remain dynamically active after death, the results show the power of FORS2 to probe things like the mass composition of planets orbiting other stars outside the solar system.
The team’s research was published on February 26 in the Astrophysical Journal Letters
