The last act of a dying star was to destroy all of its planets

The last act of a dying star was to destroy all of its planets

When white dwarfs run amok, their planets suffer from the resulting chaos. Evidence later emerges in and around the dying star’s atmosphere after it engulfed planetary and cometary debris. That’s the conclusion a team of UCLA astronomers came to after studying the nearby white dwarf G238-44 in detail. They found a case of cosmic cannibalism on this dying star, located about 86 light years from Earth.

If this star were in the place of our Sun, it would ingest the remains of planets, asteroids and comets up to the Kuiper Belt. This expansive buffet makes this act of stellar cannibalism one of the most widespread ever seen.

“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 UCLA physics and astronomy graduate. “By studying these white dwarfs, we hope to better understand the planetary systems that are still intact.”

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Artist's impression of a white dwarf (a dying star) siphoning debris from shattered worlds into its planetary system.  Courtesy of NASA/ESA, Joseph Olmstead (STScI)
An artist’s impression of a white dwarf siphoning debris from the shattered worlds of its planetary system. Courtesy of NASA/ESA, Joseph Olmstead (STScI)

Find Evidence of Chaos in a Dying Star

Johnson was part of a team from UCLA, UC San Diego and the University of Kiel in Germany working to study chemical elements detected in and around the atmosphere of white dwarfs. They used data from NASA’s former Far-Ultraviolet Spectroscopic Explorer, the High-Resolution Echelle Spectrometer from the Keck Observatory in Hawaii, and the Hubble Space Telescope’s Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph . The team found and measured the presence of nitrogen, oxygen, magnesium, silicon and iron, along with other elements.

Iron is particularly interesting since it constitutes the core of rocky planets such as Earth or Mars. Its presence is a clue that Earth-like worlds once revolved around G238-44. The presence of large amounts of nitrogen implies that the system also had a pool of icy bodies.

When the white dwarfs strike

When stars like the Sun enter a very old age, they leave behind scorched cores called white dwarfs. Over billions of years, these remnants of dying stars slowly cool. Before you get to that, however, the actual agony can be quite violent and messy. It is then that they cannibalize the worlds around them. The discovery of the “remains” of these planets, comets and asteroids, in the atmosphere of G238-44 paints a worrying picture of the future of our solar system.

The evolution of our Sun as a dying star to become a red giant, then form a planetary nebula, and eventually become a white dwarf.  Image credit: ESO/S.  Steinhofel
The evolution of our Sun as a dying star to become a red giant, then form a planetary nebula, and eventually become a white dwarf. This evolutionary process also affects the worlds and other objects in its system. Image credit: ESO/S. Steinhofel

We can expect our Sun to go through the process beginning in about five billion years. First, it will swell into a red giant, gobbling up planets eventually to Earth’s orbit. Then it will lose its outer layers, forming what we call a “planetary nebula.” After all that dissipates into space, what’s left is the massive but tiny white dwarf.

The whole process will tear the solar system apart, tearing planets to shreds and scattering comets and asteroids. Any of these objects that come too close to the white dwarf Sun will be sucked in and destroyed. The scale of the destruction is happening pretty quickly if the example of G238-44 is any clue. This study shows the shocking scale of the chaos. Less than 100 million years after entering its white dwarf phase, the dying star was able to capture and consume material from its nearby asteroid belt and distant Kuiper Belt-like regions.

The slow destruction of the planetary system of G238-44, with the tiny white dwarf in the center, surrounded by a faint accretion disk of broken body parts falling onto the dead star.  All remaining asteroids form a thin net of material surrounding the dying star.  Larger gas giant planets may still exist in the system, and much further out lies a belt of icy bodies such as comets.  The process of swallowing up the remnants of its worlds began shortly after the star entered the white dwarf phase.  Courtesy of: NASA, ESA, Joseph Olmsted (STScI)
The slow destruction of the planetary system of G238-44, with the tiny white dwarf in the center, surrounded by a faint accretion disk of broken body parts falling onto the dead star. All remaining asteroids form a thin net of material surrounding the dying star. Larger gas giant planets may still exist in the system, and much further out lies a belt of icy bodies such as comets. The process of swallowing up the remnants of its worlds began shortly after the star entered its white dwarf phase. Courtesy: NASA, ESA, Joseph Olmsted (STScI)

What else this white dwarf reveals

Not only does this discovery show what’s in our future, but it also provides interesting insight into how other systems are forming. It offers clues to what they contain and insight into our own solar system’s past. For example, astronomers believe icy objects crashed into dry, rocky planets in our own fledgling solar system. This is in addition to the rocky materials that helped create our planet. For G238-44, that means an interesting amalgamation of things from various regions and the evidence shows it.

“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.

A dying star gives further clues

The death of this sun-like star and its penchant for gobbling up debris has another interesting twist. Billions of years ago, comets and asteroids likely provided our planet with water, creating the conditions for life. According to Benjamin Zuckerman, professor of physics and astronomy at UCLA, the combination of icy and rocky material detected raining down on G238-44 shows that other planetary systems may have icy reservoirs (such as the Kuiper Belt and the Cloud d’Oort). This is in addition to rocky bodies such as Earth and asteroids.

“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 have found among studies of hundreds of white dwarfs. “

It’s fascinating to think that our own Sun could do the same in a few billion years. Perhaps a future astronomer on a planet a few decades away will do the same study as Johnson and his team – and spot the remains of Earth in the dying glow of the Sun’s white dwarf.

For more information

Dead Star’s cannibalism on its planetary system is the most extensive ever observed

Dead star caught tearing apart planetary system

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