The dead star’s cannibalism of its planetary system is the most extensive ever seen

The diagram illustrates the slow destruction of the planetary system of G238-44, with the tiny white dwarf in the center surrounded by a faint accretion disk made up of broken body parts falling onto the dead star. The remaining asteroids form a thin net of material surrounding the star. Larger gas giant planets may still exist in the system, and much further out lies a belt of icy bodies such as comets. Credit: NASA, ESA, Joseph Olmsted (STScI)

The violent agony of a nearby star has so profoundly disrupted its planetary system that the dead star left behind, known as a white dwarf, is sucking in debris from both inside and outside the planet. system, astronomers and colleagues at UCLA report today.

This is the first case of cosmic cannibalism in which astronomers have observed a white dwarf consuming both metallic rocky 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’ve never seen these two types of objects pile up on a white dwarf at the same time,” said lead researcher Ted Johnson, a physics and astronomy specialist at UCLA who obtained his diploma last week. “By studying these white dwarfs, we hope to better understand the 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 about 86 light-years from Earth, using archival data from the Hubble Space Telescope and other satellites and observatories. from NASA. A white dwarf is the burnt-out core that remains after a star like our sun has lost its outer layers and stopped burning fuel through nuclear fusion.

As surprising as the white dwarf’s varied diet is, the findings are also intriguing because astronomers believe icy objects crashed in and were flushed dry, rocky planets in our solar system, including Earth. Billions of years ago, comets and asteroids are believed to have brought water to our planet, creating the conditions for life. The composition of detected material raining down on G238-44 implies that icy reservoirs could be common among planetary systems, said research co-author Benjamin Zuckerman, professor of physics and astronomy at UCLA.

“Life as we know it requires a rocky planet covered in a variety of volatile elements like carbon, nitrogen and oxygen,” Zuckerman said. “The abundance of elements we see on this white dwarf appear to come from both a rocky parent body and a volatile-rich parent body – the first example we found among studies of hundreds of white dwarfs.”

Chaos and destruction: from the living star to the red giant and the white dwarf

Theories of planetary-system evolution describes the disappearance of a star as a turbulent and chaotic event, which begins when it explodes exponentially into what is called a red giant, then rapidly loses its outer layers, collapsing into a dwarf white – a super dense star about the size of Earth, with a mass of our sun. The process greatly disrupts the orbits of the remaining planets, and smaller objects – asteroids, comets, moons – that venture too close to them can be scattered like pinballs and sent rushing towards the white dwarf.

This study confirms the true extent of the chaos, showing that within 100 million years of the start of its white dwarf phase, the star is capable of simultaneously capturing and consuming materials from its neighboring asteroid belt and its distant regions similar to the Kuiper belt. .

Although astronomers have listed more than 5,000 planets outside our solar system, the only planet whose interior composition we have direct knowledge of is Earth. Because the material accumulating on G238-44 is representative of the building blocks of the major planets, this white dwarf cannibalism provides a unique opportunity to take the planets apart and see what they were made of when they first formed. times around the star, said Beth, a UCLA astronomy researcher. Klein, team member.

The team measured the presence of nitrogen, oxygen, magnesium, silicon and iron, among other elements, in the atmosphere of the white dwarf. Their detection of iron in very high abundance is evidence for the metallic cores of terrestrial planets, such as Earth, Venus, Mars and Mercury, Johnson said. Unexpectedly high nitrogen abundances led them to conclude that icy bodies were also present.

“The best fit for our data was a nearly two-to-one mixture of mercury-like materials and comet-like materials, which are made up of ice and dust,” Johnson said. “Metallic iron and nitrogen ice each suggest wildly different conditions for planetary formation. There is no known solar system object with so many of the two.”

The researchers say the ultimate scenario for our own sun in about 5 billion years will likely be quite similar to what was observed with G238-44. During the red giant phase of the sun, the Earth could be completely vaporized with the interior planetsthey predict.

The orbits of many asteroids in our solar system’s main asteroid belt will be gravitationally perturbed by Jupiter and will also fall on the white dwarf remnant that the sun will become, he said.

For more than two years, the UCLA research group, along with colleagues from UC San Diego and the University of Kiel in Germany, worked to unravel the mystery of G238-44 by analyzing the elements detected on the white dwarf star.

Their analysis included data from NASA’s former Far-Ultraviolet Spectroscopic Explorer, the High-Resolution Echelle Spectrometer at the Keck Observatory in Hawaii, and the Hubble Space Telescope’s Cosmic Origins Spectrograph and Imaging Spectrograph. space telescope. The Hubble Space Telescope is an international cooperation project between NASA and the European Space Agency.

The team’s findings were presented at an American Astronomical Society press conference on June 15.

Final moments of planetary remnants seen for the first time

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