Researchers at UCLA, UC San Diego, and the University of Kiel in Germany, led by Tom Johnson, have studied the elements found in the atmosphere of the white dwarf star G238-44 for more than two years. This white dwarf is about 86 light-years away from Earth.
Johnson is currently a full-time predoctoral research assistant at NASA’s Goddard Space Flight Center and hopes to apply to graduate programs in astronomy. UCLA researcher Beth Klein and UCLA professor Benjamin Zuckerman have both endorsed Johnson as a very talented student.
The researchers used information from NASA’s now-defunct Far Ultraviolet Spectroscopic Explorer, the High-Resolution Echelle Spectrometer at the Keck Observatory in Hawaii, and the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph on the Hubble Space Telescope.
On June 15, the results of Johnson’s team’s work was presented at a press conference by the American Astronomical Society.
Planets are slowly falling apart in planetary system G238-44
Johnson has observed that the planets in the planetary system G238-44 are slowly falling apart. Johnson has reported that the violent death of a star in G238-44 has caused so much damage to its planetary system that the dead star left behind (a white dwarf) is sucking in debris from both the inner and outer parts of the system.
A white dwarf is the burned-out core of a star like our Sun that has lost its outer layers and stopped using nuclear fusion to burn fuel.
The atmosphere of G238-44
At the center of G238-44 is a tiny white dwarf, and around it is a faint accretion disk made up of pieces of broken planets falling onto the dead star. The asteroids still there form a thin stream of material around the star.
Astronomers have now seen with their own eyes what happens when a star like our Sun dies. A star that dies can cannibalize the planetary systems around it.
What is interesting about Johnson’s research is not so much that the dead star cannibalizes other planets but rather the slow breakup of planets and asteroids feeding the star. Astronomers can learn a lot about the composition of planets as they observe them break up.
Sucking in debris from both the inner and outer parts of the system.
When a star dies, the system is thrown into disarray. This is the first observation of a white dwarf star accreting both rocky-metallic material, most likely from a nearby asteroid, and icy material, most likely from a body like those found in our solar system’s Kuiper belt.
What we learn about planets when they fall apart before being consumed by a white dwarf:
- Icy reservoirs might be common in planetary systems: Even though the white dwarf’s varied diet is surprising, the findings are also interesting because astronomers think that icy objects crashed into dry, rocky planets in our solar system, like Earth, and rained water on them.
- It is considered that comets and asteroids brought water to Earth billions of years ago, creating the right conditions for life. Professor of physics and astronomy Benjamin Zuckerman at UCLA and co-author of the study, said that the nature of the rain falling on G238-44 suggests that icy reservoirs might be common in planetary systems.
First observation of its kind
Zuckerman said, “Life as we know it needs a rocky planet with many volatile elements on it, like carbon, nitrogen, and oxygen.” “The abundances of elements we see on this white dwarf seem to have come from both a rocky parent body and a volatile-rich parent body. This is the first time we’ve seen this in our studies of hundreds of white dwarfs.”
Chaos when a star dies
Theories of how planetary systems evolve say that a star’s death is a chaotic, tumultuous event. A star gets bigger and bigger until it becomes a red giant. Then, it quickly loses its outer layers and collapses into a white dwarf, which is a super dense star about the size of Earth and has the same mass as our Sun. The process messes up the orbits of the remaining planets in a big way, and asteroids, comets, and moons that get too close to them can be thrown around like pinballs and sent hurtling toward the white dwarf.
How far away can a dying star pull objects?
Think a black hole is scary? When it died, astronomers observed that this star could pull in material from its nearby asteroid belt and its outlying Kuiper belt-like regions within 100 million years of the start of its white dwarf phase.
An interesting case study of what other planets are made of
Astronomers have found more than 5,000 planets outside our solar system. Still, Earth is the only one whose interior we know something about.
The materials falling onto G238-44 are like the building blocks of giant planets. Watching the process of this white dwarf accretion is an opportunity for astronomers to see what planets are made of when they are taken apart.
Proof that planets like Earth, Venus, Mars, and Mercury have metal cores
The team looked for nitrogen, oxygen, magnesium, silicon, and iron in the white dwarf’s atmosphere, among other things. Unexpectedly high amounts of nitrogen made them think that there were also icy bodies around. Johnson said they found a lot of iron, proving that planets like Earth, Venus, Mars, and Mercury have metal cores.
“The best fit for our data was a mix of almost two parts material like Mercury and one-part material like a comet, which is made up of ice and dust,” Johnson said. “Iron metal and nitrogen ice point to very different ways that planets were made. No other known object in the solar system has so much of both.”
What do these findings mean for Earth?
The scientists say that the final situation for our Sun in 5 billion years will probably be a lot like what has been seen with G238-44. They think that during the red giant phase of the Sun, the Earth and the inner planets could be completely vaporized.
Johnson said that Jupiter’s gravity would change the paths of many of the asteroids in the main asteroid belt of our solar system. Some will also crash into the white dwarf that the Sun will become.
Feature image credit: NASA