Dead star seen feeding
Researchers have observed a dead star cannibalising its planetary neighbours.
A new report shows the violent death throes of a nearby star that thoroughly disrupted the planetary system it left behind.
The star, known as a white dwarf, is sucking in debris from both the system’s inner and outer reaches.
It is the first case of cosmic cannibalism in which astronomers have observed a white dwarf consuming both rocky-metallic material, likely from a nearby asteroid, and icy material, presumed to be from a body similar to those found in the Kuiper belt at the fringe of our own solar system.
“We have never seen both of these kinds of objects accreting onto a white dwarf at the same time,” said lead researcher Ted Johnson from UCLA.
“By studying these white dwarfs, we hope to gain a better understanding of planetary systems that are still intact.”
The findings are based on an analysis of materials captured by the atmosphere of G238-44, a white dwarf some 86 light-years from Earth, using archival data from the Hubble Space Telescope and additional NASA satellites and observatories.
A white dwarf is the burned-out core that remains after a star like our sun sheds its outer layers and stops burning fuel through nuclear fusion.
As surprising as the white dwarf’s wide-ranging diet is, the findings are also intriguing because astronomers believe icy objects crashed into and irrigated dry, rocky planets in our solar system - including Earth.
Billions of years ago, comets and asteroids are thought to have delivered water to our planet, sparking the conditions necessary for life.
The makeup of the material detected raining onto G238-44 implies that icy reservoirs might be common among planetary systems, said research co-author Benjamin Zuckerman, a UCLA professor of physics and astronomy.
“Life as we know it requires a rocky planet covered with a variety of volatile elements like carbon, nitrogen and oxygen,” Dr Zuckerman says.
“The abundances of the elements we see on this white dwarf appear to have come from both a rocky parent body and a volatile-rich parent body — the first example we’ve found among studies of hundreds of white dwarfs.”
Theories of planetary-system evolution describe the demise of a star as a turbulent, chaotic event.
The new study confirms the true scale of the chaos, showing that within 100 million years after the beginning of its white dwarf phase, the star is able to simultaneously capture and consume material from its nearby asteroid belt and its far-flung Kuiper belt–like regions.
Though astronomers have catalogued more than 5,000 planets outside our solar system, the only planet whose interior makeup we have some direct knowledge of is Earth.
Because the materials accreting onto G238-44 are representative of the building blocks of major planets, this white dwarf cannibalism provides a unique opportunity to take planets apart and see what they were made of when they first formed around the star.
The team’s results were presented at an American Astronomical Society press conference on June 15.