Looking at the Sun now as it blazes in all its glory, it’s hard to remember that it is just a hot, glowy ball of gas. But there’s only so much gas it can burn. And like all good things must come to an end, someday the Sun too, will turn into a red giant before it becomes a white dwarf.
But when the Sun transitions into a red giant, life on Earth will be wiped out completely, and our planet will become little more than a scorched rock. The possibility of the Sun destroying our planet, even if the fated day is more than 5 billion years away, is daunting. This is why astronomers have been on the lookout for other solar systems to know more about our system’s doom.
Recently, using the W. M. Keck Observatory on Hawaii’s Mauna Kea, astronomers uncovered the first confirmed planetary system that closely resembles our solar system’s projected fate when the Sun dies. The planetary system consists of a Jupiter-like planet that revolves around a white dwarf star near the galaxy’s centre, in a Jupiter-like orbit.
The planet was identified using gravitational microlensing. This method allows planets to be found using light from a distant star. The path of the light from this star will be altered by the presence of a massive lens—in our case, a star and a planet. Thus, for a short period, the distant star will appear brighter.
“This evidence confirms that planets orbiting at a large enough distance can continue to exist after their star’s death. Given that this system is an analogue 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,” said Joshua Blackman, lead author of the study.
While this discovery bodes well for planets far from the Sun, the Earth’s future isn’t as promising. If humankind moved 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. However, we would not be able to rely on the heat from a white dwarf Sun for very long, believes David Bennett, a co-author of the study.
So what happens when the Sun dies?
The absence of a sequence star like our Sun led the researchers to discover that the Jupiter-like planet was orbiting a white dwarf.
When main sequence stars like our Sun die, they become white dwarfs. A star burns off all of the hydrogen in its core and expands into a red giant star in the latter stages of its life cycle. It then collapses in on itself, shrinking into a white dwarf, leaving just a hot, dense core roughly the size of Earth and half the mass of the Sun. White dwarfs are incredibly dim and compact, and they no longer have the nuclear fuel to shine brightly, making them hard to detect.
The newly-discovered white dwarf is about 60% the mass of the Sun, and its exoplanet survivor is a giant gas world about 40% more massive than Jupiter, according to high-resolution near-infrared images obtained with Keck Observatory’s laser guide star adaptive optics system paired with its Near-Infrared Camera (NIRC2).
“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,” said co-author Jean-Philippe Beaulieu, Professor.
The researchers intend to use statistical analysis to determine how many other white dwarfs have intact planetary survivors. The Nancy Grace Roman Telescope, a NASA mission that intends to photograph giant planets directly, will aid their investigation. It will allow scientists to establish if Jupiter-like planets are common in the latter phases of their host stars’ lives, or if a significant fraction of them are destroyed by the time their hosts become red giants.
The study was recently published in Nature and can be accessed here.
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