White dwarfs shed light on the structural disarray that results after star death.

University of California, Los Angeles (UCLA) astronomers and colleagues report that the violent death throes of a nearby star caused such a severe disruption to its planetary system that the dead star left behind — known as a white dwarf — is sucking in debris from both the system’s inner and outer reaches.

This is the first time astronomers have seen evidence of cosmic cannibalism, where a white dwarf star is seen chowing down on both rocky-metallic material, likely from a nearby asteroid, and icy material, likely from a body similar to those found in the Kuiper belt at the edge of our own solar system.

Lead researcher Ted Johnson, a UCLA physics and astronomy major who recently graduated, said, “We have never seen both of these kinds of particles accreting onto a white dwarf at the same time.” We intend to learn more about still-functioning planetary systems by investigating these white dwarfs.

The findings are based on a review of elements collected by the atmosphere of white dwarf G238-44, which is around 86 light-years away from Earth. This review used archived data from the Hubble Space Telescope and other NASA satellites and observatories. The burned-out core of a star like our sun that has shed its outer layers and has stopped fusing fuel is known as a white dwarf.

Because scientists think icy objects crashed into and irrigated dry, rocky planets in our solar system, including Earth, the findings are as intriguing as the white dwarf’s diverse diet. It is believed that comets and asteroids brought water to our planet billions of years ago, creating the conditions for life. According to study co-author and UCLA professor of physics and astronomy Benjamin Zuckerman, the composition of the material found to be falling onto G238-44 suggests that frozen reservoirs may be prevalent throughout planetary systems.

Credit: NASA, ESA, Joseph Olmsted (STScI)

According to Zuckerman, “life as we know it needs a rocky planet covered in a variety of volatile components like carbon, nitrogen, and oxygen.” The first instance has been discovered amid examinations of hundreds of white dwarfs: “The abundances of the components we find on this white dwarf appear to have come from both a stony parent body and a volatile-rich parent body.”

From a living star to a red giant to a white dwarf, there is chaos and destruction.
According to theories of planetary-system evolution, a star’s death is a violent, chaotic process that starts when it exponentially expands into a red giant, loses its outer layers, and collapses into a white dwarf, a super-dense star the size of Earth with the mass of our sun. Smaller objects like asteroids, comets, and moons that approach them too closely risk having their orbits severely perturbed and being sent hurtling in the direction of the white dwarf.

The star can simultaneously gather and eat material from its surrounding asteroid belt and its distant Kuiper belt-like areas within 100 million years of the start of its white dwarf phase, confirming the full scope of the chaos.

The only planet whose interior we have some direct knowledge of is Earth, despite the fact that astronomers have listed more than 5,000 planets outside of our solar system. This white dwarf cannibalism offers a rare opportunity to disassemble planets and see what they were made of when they first formed around the star, according to team member and UCLA astronomy researcher Beth Klein. This is because the materials accreting onto G238-44 are representative of the building blocks of major planets.

In addition to other elements, the scientists measured the amount of nitrogen, oxygen, magnesium, silicon, and iron in the white dwarf’s atmosphere. According to Johnson, their discovery of iron in extremely high abundance is proof that terrestrial planets like Earth, Venus, Mars, and Mercury have metallic cores. They came to the conclusion that frozen bodies were also present because of unexpectedly large nitrogen abundances.

Credit: NASA, ESA, Joseph Olmsted (STScI)

According to Johnson, a mixture of Mercury-like material and comet-like material, which is composed of ice and dust, provided the greatest fit for the data. “Iron metal and nitrogen ice each imply radically distinct planetary creation conditions. No other known object in the solar system has as much of both.

According to the experts, the final scenario for our sun will probably resemble what has been observed with G238-44 quite a bit in about 5 billion years. They believe that the Earth and the inner planets may both be fully destroyed during the red giant phase of the solar.

Many asteroids in the main asteroid belt of our solar system will have their orbits gravitationally altered by Jupiter and some of them may crash onto the white dwarf remnant that the sun will become, according to him.

The UCLA scientific team has been examining the elements found on the white dwarf star for more than two years, along with collaborators from UC San Diego and the University of Kiel in Germany. Their goal is to solve the enigma of G238-44.

Data from the Hubble Space Telescope’s Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph, the decommissioned NASA Far Ultraviolet Spectroscopic Explorer, the High Resolution Echelle Spectrometer at the Keck Observatory in Hawaii, and other observatories were used in their research. NASA and the European Space Agency collaborated internationally on the Hubble Space Telescope project.

The team’s findings were revealed on June 15 at a press conference held by the American Astronomical Society.

Ted Johnson’s route to the stars: UCLA undergrad research

Ted Johnson on the UCLA campus. Credit: Bella Bertaud

Lead researcher Ted Johnson, whose work was supported during his senior year by the UCLA Undergraduate Research Scholars Program, remarked, “Conducting research as an undergraduate was the single most essential thing I could accomplish at UCLA.” It has confirmed for me that I want to continue pursuing a career in research. I started this project two years ago, and I am now an entirely different scientist. I was so ignorant at the time.

Johnson attributed his growth as an astronomer throughout his undergraduate period to his research group, in particular the “excellent mentorship” of UCLA researcher Beth Klein.

“I was very lucky to have found a research group that had so much time for its undergraduates,” he said. “Everyone in our group wanted us undergrads to be the best scientists we could be. In group meetings, they are always ready to give feedback and suggestions on our work and were always extremely constructive. We have an amazing community here at UCLA, and I am grateful for the time I was able to spend on this campus.”

Klein said that Johnson was “one of the best students I have ever had the privilege to teach and work with” — a sentiment echoed by Johnson’s co-author and UCLA professor Benjamin Zuckerman.

“It has been a special pleasure for me as a longtime astronomer to be associated with this exciting research project led by Ted, who is an outstanding undergraduate,” he said.

Johnson, who graduated June 10, has now accepted a position as a full-time predoctoral research assistant at NASA’s Goddard Space Flight Center and will be applying to graduate programs in astronomy.