Astronomers spot white dwarf star with two rings of planetary debris

WASHINGTON, Nov 7 : Billions of years from now, the sun is expected to run out of fuel and greatly expand into what is called a red giant, eventually shedding its outer layers and leaving behind its dense core, a white dwarf. Some of the planets in our solar system would be destroyed while others might survive.

Researchers have now spotted a white dwarf with planetary debris swirling around it in an unusual configuration that may offer a peek into one possible outcome for our solar system in the distant future.

Unlike in similar systems previously observed, the debris disc surrounding this white dwarf appears to consist of two distinct rings. The researchers said the disc may have been shaped by two planetary or smaller rocky bodies that are embedded in the rings after managing to survive the star's violent death throes.

The white dwarf, named J1328−1450, is located in the Milky Way roughly 1,600 light-years from Earth, in the constellation Virgo. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). The observations were made using the European Southern Observatory's Chile-based Very Large Telescope.

Prior to this discovery, astronomers had identified 21 white dwarfs with debris surrounding them, all of which had a single disc and not a double ring of material as the new observations reveal.

"It shows that the remnants of a planetary system can have a much more complex structure than we previously thought, and provides further support to the idea that planetary rocky bodies may survive the transformation of a star into a white dwarf," said astronomer Felipe Lagos-Vilches of Universidad Técnica Federico Santa María in Chile, one of the authors of the study published in the journal Nature Astronomy.

The white dwarf has a mass about 47 per cent that of the sun, jam-packed into a diameter roughly the same as that of Earth.

The surviving planetary bodies may be remnants of larger and heavily disrupted planets. One of them may be around the size of the dwarf planet Pluto, with the other one smaller than that.

Lagos-Vilches said the original star may have hosted a planetary system before it expanded dramatically into a red giant, engulfing some of the innermost planets while ones with more distant orbits survived.

"The planetary system did not completely disappear. Some surviving rocky bodies may have been gravitationally perturbed onto highly eccentric orbits that brought them close to the white dwarf," Lagos-Vilches said.

"Objects that came sufficiently close were disrupted by the white dwarf's gravitational force. Their material was spread into a debris disc containing dust and gas. However, two relatively large rocky bodies may have survived within this debris," Lagos-Vilches said. 

The presence of the two bodies may help explain the distribution of the surrounding material into a pair of concentric gaseous rings, Lagos-Vilches said. 

"The outer ring is strongly depleted in magnesium compared with the inner ring. This suggests that they may originate from different parent bodies, or possibly from different layers of a rocky body that was disrupted when it went too close to the white dwarf due to its strong gravitational field," Lagos-Vilches said.

A GLIMPSE OF THE FUTURE

In about 5 billion years, the sun will become a red giant, Lagos-Vilches said.

"It will eventually lose its outer layers and become a white dwarf. The inner solar system will be dramatically affected. Mercury and Venus are expected to be engulfed by the expanding sun, while there is still no clear consensus on whether Earth will also be engulfed during this phase. The fate of the outer planets is different. Jupiter, Saturn and the more distant bodies should have a much better chance of surviving," Lagos-Vilches said.

After the sun becomes a white dwarf, surviving planetary remnants, moons and asteroids could potentially be drawn close enough to the white dwarf to be torn apart by gravitational forces.

"A debris disc like the one around J1328−1450 could therefore represent one possible stage in the very distant future of our own planetary system," Lagos-Vilches said.