by Our Sun is both our best friend and our worst enemy. On the one hand, we need our star to have its own life. Earth and the other planets in the Solar System were formed from the same cloud of gas and dust as the Sun.
And without its light, there could be no life on this planet. On the other hand, a day will come when the Sun ends all life on Earth and, in the end, the Earth will destroy itself.
A new study published in Nature highlights the risks that stars may pose to their planets. The authors looked at stars similar to our Sun and found that at least one in 12 stars has a trace of metals in its atmosphere. These are thought to be the scars of the planets and stars that have swallowed the stars.
Planets should never get too comfortable orbiting their parent star, as there are at least two ways their star can betray their trust and meet their violent demise.
Tidal interference
The first is through a process known as “tidal intrusion”. As a planetary system forms, some planets will orbit their star along paths that are not quite circular or are slightly inclined relative to the star’s plane of rotation. When that happens, the gravitational force exerted by the star on the planet will slowly correct the shape or alignment of the planet’s orbit.
In extreme cases, the gravitational force exerted by the star will destabilize the planet’s orbit, slowly pulling it closer and closer. If the hapless planet gets too close, it will be torn apart by the star’s gravity. This happens because the side of the planet facing the star is slightly closer than the side facing away (the difference is the diameter of the planet).
The strength of the star’s pull depends on the distance between it and the planet, so the side of the planet facing the star feels a slightly stronger pull than the side facing away.
On Earth, this difference in the strength of the force of gravity creates tides and the daily flow of tides. Basically, the Sun is trying to deform the Earth, but it’s long enough that it only pulls on the waters of its oceans. But a planet dangerously close to its star will have its crust and core pulled apart by these tides.
If the planet is not too close to the star, its shape will only be deformed into an egg shape. Just a little closer to the star, and the difference in the gravitational pull on its various sides is enough to tear it apart completely, reducing it back to a cloud of gas and dust that spirals into the star and vaporises it into hellfires.
The process of tidal intrusion was first proposed about 50 years ago. Over the past few decades, astronomers – including my group – have observed many tidally-ignited flares caused by stars being shredded by supermassive black holes at the center of galaxies.
Last year, for the first time, a group of astronomers reported observing a similar, dimmer flare consistent with a planet being engulfed and consumed by its star.
Planetary tidal interference may be quite common, as shown by the new finding that at least 1 in 12 stars show signs of ingesting planetary material.
Other studies have found that between a quarter and a half of all white dwarfs – the remnants of stars up to twice the size of our Sun – sport similar scars. As their name suggests, white dwarfs are white hot. With surface temperatures of thousands of degrees, the hottest white dwarfs emit ultraviolet and X-ray light energetic enough to vaporize their orbiting planets.
The End of the World
Don’t be in any doubt; The world will not be destroyed by a tidal wave. The end of our planet will come in about five billion years, when the Sun will turn into a red giant.
Stars are powered by a process called fusion, where two light elements are combined to make a heavier one. All stars begin their lives with the desire to fuse hydrogen in their cores into the element helium. This fusion process stabilizes them both against explosion, due to the unrestrained pull of gravity, and creates the light that makes them settle. Our Sun has been fusing hydrogen into helium for about 4.5 billion years.
But 4.5 billion years from now, the hydrogen in the Sun’s core will run out. All fusion will stop in the core, and gravity will unexpectedly force the star to contract. As the core contracts, it will heat up until the temperature is high enough to fuse helium into carbon.
Fusion will stabilize the star again. Meanwhile, however, the star’s outer envelopes will expand and cool, giving the massive star a redder hue. As the Sun grows red giant, it will pass Mercury, Venus and Earth – perhaps even reaching all the way out into the orbit of Mars.
The Earth may have another five billion years to go, but we will not be here to become extinct. As the Sun burns through its stores of hydrogen, it grows progressively brighter: every billion years, its luminosity increases by about 10%.
A billion years from now, the Sun will be bright enough to boil the Earth’s oceans. So the next time you bask in the sun’s warm rays, remember: we’ve got it covered for us.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Or Graur receives funding from the UKRI Science and Technology Facilities Council.
