Astronomers have discovered a planetary system that resembles how our solar system will look long after the sun dies. The system consists of a large gas giant, similar to Jupiter, orbiting a dead white dwarf star.
Located close to the center of the Milky Way galaxy, the system represents the first time astronomers have definitively confirmed the existence of a planet surviving the violent expansion of a star that occurs during its death throes.
The white dwarf at the center of this newly discovered planetary system is the kind of stellar remnant that stars with the mass of our sun leave behind when they run out of fuel.
“This evidence confirms that planets orbiting at a large enough distance can continue to exist after their star’s death,” said astronomy postdoctoral researcher at the University of Tasmania in Australia Joshua Blackman in a press release. “Given that this system is an analog to our own solar system, it suggests that Jupiter and Saturn might survive the Sun’s red giant phase when it runs out of nuclear fuel and self-destructs.”
Bennett pointed out that while this system implies Saturn and Jupiter may survive our star’s eventual fiery demise when it runs out of nuclear fuel at the end of its life, Earth will probably not be so fortunate.
Bennett added: “If humankind wanted to move to a moon of Jupiter or Saturn before the Sun fried the Earth during its red supergiant phase, we’d still remain in orbit around the Sun, although we would not be able to rely on heat from the Sun as a white dwarf for very long.”
Astronomers call stars that are burning hydrogen in their cores creating helium, main-sequence stars. When average mass stars run out of nuclear fuel, they can no longer support themselves against gravitational collapse.
As gravity wins over the star and the core collapses, the energy released heats the outer layers causing them to glow red and blowing outward this shell of material.
This results in a red giant, a compact stellar core with expanded puffy outer layers. When our star reaches this phase, these layers will probably reach out as far as the orbit of Mars. This is far enough to consume the inner planets, including Earth.
For the sun, this process will begin in about 5 billion years. But, despite the fact the Earth, Venus, and Mercury will be gone, our star will continue to change.
When its helium fuel is exhausted, the sun will no longer be able to support itself against gravity, and will collapse again.
The next stage in its evolution, and its last, will be a white dwarf, a cooling exposed stellar core surrounded by gas and dust that once constituted its outer layers. These cores are incredibly dense, usually around the size of Earth with about half the mass of the sun.
These white dwarf stars only glow dimly as they have run out of fuel to burn, which makes spotting them difficult. In order to do this, Blackman and Bennett used high-resolution images captured by the Keck Observatory in Hawaii.
They relied on the laser guide star adaptive optics system and a Near-Infrared Camera (NIRC2) at the observatory, located on the volcano Mauna Kea.
The team found the Jupiter-like planet first and were shocked when searching for its host star, they discovered that it wasn’t bright enough to be an ordinary main-sequence star.
“We have also been able to rule out the possibility of a neutron star or a black hole host. This means that the planet is orbiting a dead star, a white dwarf,” said coauthor and professor Jean-Philippe Beaulieu, Warren chair of Astrophysics at the University of Tasmania and National Center for Scientific Research (CNRS) director at the Institut d’Astrophysique de Paris. “It offers a glimpse into what our solar system will look like after the disappearance of the Earth, whipped out in the cataclysmic demise of our Sun.”
With this white dwarf and its gas giant planet discovered, the team predicts that around half of all white dwarfs could have similar planetary companions. Their next step will be to search for more of these dead stars that have planets orbiting them.
To do this, they will turn to the Nancy Grace Roman Telescope, set to launch later this decade. Part of the telescope’s mission will be to directly image giant planets, and it will be better equipped to spot such worlds around dead stars.
With this wider survey, astronomers should be able to determine if gas giants like Jupiter often escape the explosive final days of their parent stars.
“This is an extremely exciting result,” said chief scientist at Keck Observatory, John O’Meara. “It’s wonderful to see today an example of the kind of science Keck will be doing en masse when Roman begins its mission.”