Possible Preview of the Ultimate Fate of Earth
Astronomers have found evidence of a dying star engulfing its planet — just as the Sun will likely end up swallowing up the Earth — in a system some 13,000 light years away. Evidence for the world-ending phenomenon was captured by the Gemini South telescope in Chile, which is operated by the US National Science Foundation’s NOIRLab. Astronomers said the “smoking gun” for the event came in the form of a long, low-energy outburst from the star caused by the planet skimming along the star’s surface.
At a modest 4.6 billion years old, our Sun is effectively middle-aged, and is kept burning by the fusion of hydrogen atoms into helium in the star’s core.
In around 5–6 billion years, however, the Sun will begin to run out of this fuel. At this point, as the outward pressure of thermonuclear fusion begins to wane, the star’s core will start to collapse in on itself.
This will cause the plasma surrounding the core to become hot enough to start up hydrogen fusion instead — the energy released by which will push out the Sun’s outer layers, which cool and take on a reddish hue as it becomes a “red giant”.
This process will see the Sun expand to several hundred times its original size — totally engulfing the orbits of Mercury, Venus and likely Earth as well.
Scientists have estimated that across our galaxy, the Milky Way, such “planetary engulfments” only occur a few times a year.
Astronomers have seen evidence for the aftermath of this phenomena — specifically, the resulting corpse of a star and the burnt-out husk of a planet.
However, the new study by NOIRLab astronomer Dr Ryan Lau and his colleagues is the first to detect an engulfment as it was happening.
Dr Lay said: “These observations provide a new perspective on finding and studying the billions of stars in our Milky Way that have already consumed their planets.”
The first hints of the planetary engulfment event — a short-lived, ten-day optical outburst were uncovered in images taken by the Zwicky Transient Facility, a sky survey being performed at the Palomar Observatory in California.
The event was then confirmed using archival observations made by NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which saw a long-lived signal in the infrared part of the spectrum.
Paper co-author and fellow NOIRLab astronomer Aaron Meisner said: “Our team’s custom reanalysis of all-sky infrared maps from NEOWISE exemplifies the vast discovery potential of archival survey data sets.”
Finally, high-resolution and long-term observations by Gemini South were used to distinguish the planetary engulfment from other types of outburst like a solar flare or coronal mass ejection.
Gemini Observatory program director Martin Still said: “These new observations support predictions for the future of our own planet.
“This discovery is a wonderful example of the feats we can accomplish when we combine world-class telescope operation and cutting-edge scientific collaboration.”
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According to the researchers, the outburst caused by the planet being swallowed up by its host star lasted for around 100 days.
Analysis of the outburst’s lightcurve — as well as the material ejected during the planet’s engulfment — allowed the team to gain insight into the mass of the star (some 0.8–1.5 solar masses) and the planet (at 1–10 times the mass of Jupiter).
The ejected material, meanwhile, was composed of around 33 Earth masses of hydrogen and about 0.33 Earth masses of dust.
Dr Lau said: “That’s more star- and planet-forming material being recycled, or burped out, into the stellar medium thanks to the star eating the planet.”
The findings of this study will help refine the searches for similar events in the future — such as by looking for signs of chemical pollution in the remnant star following the planet’s engulfments.
Dr Lau concluded: “I think there’s something pretty remarkable about these results that speaks to the transience of our existence.
“After the billions of years that span of our Solar System, our own end stages will likely conclude in a final flash that lasts only a few months.”
The full findings of the study were published in the journal Nature.
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