White dwarf star siphoning debris

Dead star caught violently tearing apart planetary system

White dwarf star siphoning debris

This illustration shows a white dwarf star siphoning debris from broken objects in a planetary system. The Hubble Space Telescope detects the spectral signature of vaporized debris that revealed a combination of rocky-metallic and icy materials, the ingredients of planets. The findings help describe the violent nature of evolved planetary systems and the composition of their disintegrating bodies. Credit: NASA, ESA, Joseph Olmsted (STScI)

Rocky, icy bodies have been identified among the debris on the surface of a white dwarf star

“Bring out your dead! rings in the air in the classic film “Monty Python and the Holy Grail”, a joyous parallel to what happens around a[{” attribute=””>white dwarf star in a nearby planetary system. The dead star is “ringing” its own bell, calling out to the “dead” to collect at its footsteps. The white dwarf is all that remains after a Sun-like star has exhausted its nuclear fuel and expelled most of its outer material – decimating objects in the planetary system that orbit it. What’s left is a band of players with unpredictable orbits that – despite protests that they “aren’t dead yet!” – will ultimately be captured by the central star.

How do we know? The bodies consumed by the star leave telltale “fingerprints” – caught by the Hubble Space Telescope and other NASA observatories – on its surface. The spectral evidence shows that the white dwarf is siphoning off both rocky-metallic and icy material – debris from both its system’s inner and outer reaches. Uncovering evidence of icy bodies is intriguing, since it implies that a “water reservoir” might be common on the edges of planetary systems, improving the chances for the emergence of life as we know it.

A star’s agony has disrupted its planetary system so violently that the dead star left behind, called a white dwarf, siphons debris both inside and outside the system. It’s the first time astronomers have observed a white dwarf star that consumes both metallic and icy rocky material, the ingredients of planets. Archival data from NASA’s Hubble Space Telescope and other NASA observatories were key to diagnosing this case of cosmic cannibalism. The findings help describe the violent nature of evolved planetary systems and can inform astronomers about the composition of newly formed systems. Credit: NASA Goddard Space Flight Center; Main producer: Paul Morris

Dead star caught tearing apart planetary system

A star’s agony has disrupted its planetary system so violently that the dead star left behind, called a white dwarf, siphons debris both inside and outside the system. It’s the first time astronomers have observed a white dwarf star that consumes both metallic and icy rocky material, the ingredients of planets.

Archival data from NASA’s Hubble Space Telescope and other NASA observatories were key to diagnosing this case of cosmic cannibalism. The findings help describe the violent nature of evolved planetary systems and can inform astronomers about the composition of newly formed systems.

The findings are based on analysis of material captured from the atmosphere of nearby white dwarf star G238-44. A white dwarf is what remains of a star like our Sun after it has lost its outer layers and stopped burning fuel through nuclear fusion. “We have never seen these two types of objects accumulate on a white dwarf at the same time,” said Ted Johnson, principal investigator and recent graduate of the University of California, Los Angeles (UCLA). “By studying these white dwarfs, we hope to better understand the planetary systems that are still intact.”

Planetary system G238-44

This illustrated diagram of the planetary system G238-44 traces its destruction. The small white dwarf star is at the center of the action. A very faint accretion disk is made up of broken body parts falling onto the white dwarf. The remaining asteroids and planetary bodies constitute a reservoir of matter surrounding the star. Larger gas giant planets may still exist in the system. Much further out is a belt of icy bodies such as comets, which also eventually feed the dead star. Credit: NASA, ESA, Joseph Olmsted (STScI)

The findings are also intriguing because small, icy objects are credited with crashing into and “irrigating” dry, rocky planets in our solar system. Billions of years ago, comets and asteroids are thought to have brought water to Earth, creating the conditions necessary for life as we know it. The composition of detected bodies raining down on the white dwarf implies that ice reservoirs could be common among planetary systems, Johnson said.

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

demolition derby

Theories of planetary system evolution describe the transition between the phases of a red giant star and a white dwarf as a chaotic process. The star is rapidly losing its outer layers and the orbits of its planets are changing dramatically. Small objects, such as asteroids and dwarf planets, can venture too close to giant planets and be sent plummeting towards the star. This study confirms the true magnitude of this violent chaotic phase, showing that within 100 million years of the start of its white dwarf phase, the star is capable of simultaneously capturing and consuming material from its asteroid belt. and Kuiper belt-like regions.

The estimated total mass ultimately engulfed by the white dwarf in this study may not be greater than the mass of an asteroid or small moon. Although the presence of at least two objects that the white dwarf consumes is not directly measured, it is likely that one is rich in metals like an asteroid and the other is an icy body similar to what we found on the outskirts of our solar system in the Kuiper belt. .

Although astronomers have cataloged more than 5,000 exoplanets, the only planet of which we have direct knowledge of its interior composition is Earth. White dwarf cannibalism provides a unique opportunity to disassemble planets and see what they were made of when they formed around the star.

The team measured the presence of nitrogen, oxygen, magnesium, silicon and iron, among other elements. The detection of iron in very great abundance is proof of the metallic cores of telluric planets, such as the Earth,[{” attribute=””>Venus, Mars, and Mercury. Unexpectedly high nitrogen abundances led them to conclude the presence of icy bodies. “The best fit for our data was a nearly two-to-one mix of Mercury-like material and comet-like material, which is made up of ice and dust,” Johnson said. “Iron metal and nitrogen ice each suggest wildly different conditions of planetary formation. There is no known solar system object with so much of both.”

Death of a Planetary System

When a star like our Sun expands into a bloated red giant late in its life, it will shed mass by puffing off its outer layers. One consequence of this can be the gravitational scattering of small objects like asteroids, comets, and moons by any remaining large planets. Like pinballs in an arcade game, the surviving objects can be thrown into highly eccentric orbits.

“After the red giant phase, the white dwarf star that remains is compact – no larger than Earth. The wayward planets end up getting very close to the star and experience powerful tidal forces that tear them apart, creating a gaseous and dusty disk that eventually falls onto the white dwarf’s surface,” Johnson explained.

The researchers are looking at the ultimate scenario for the Sun’s evolution, 5 billion years from now. Earth might be completely vaporized along with the inner planets. But the orbits of many of the asteroids in the main asteroid belt will be gravitationally perturbed by Jupiter and will eventually fall onto the white dwarf that the remnant Sun will become.

For over two years, the research group at UCLA, the University of California, San Diego, and the Kiel University in Germany, has worked to unravel this mystery by analyzing the elements detected on the white dwarf star cataloged as G238-44. Their analysis includes data from NASA’s retired Far Ultraviolet Spectroscopic Explorer (FUSE), the Keck Observatory’s High Resolution Echelle Spectrometer (HIRES) in Hawaii, and the Hubble Space Telescope’s Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS).

The team’s results were presented at an American Astronomical Society (AAS) press conference on Wednesday, June 15, 2022.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

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