Why Our Sun Will Live Longer Than Our Galaxy | Unveiled

Why Our Sun Will Live Longer Than Our Galaxy

When we die, not all of our cells stop functioning. Many continue to work, outliving their host. In a similar way, when galaxies die that doesn’t mean the stars inside them do as well. Many times individual stars will outlive their host galaxy, and the same can be said of our sun.

This is Unveiled and today we’re answering the extraordinary question of Why Our Sun WIll Live Longer Than Our Galaxy

Our sun is a main-sequence star, meaning that it’s burning hydrogen into helium and releasing that energy in the form of heat and light. Main sequence stars are extremely common and make up 90% of all stars in the universe. Stars are born from clouds of gas and dust that collapse and eventually ignite. The life cycle varies from star to star, depending on how massive they are. Our sun is average-sized and will survive around 10 billion years in total, but other more massive stars can run out of fuel in a matter of millions of years. Our sun has already been around for 5 billion years, and in another 5 will run out of hydrogen and begin its transformation into a red giant.

It’s much harder to define our galaxy and its natural lifespan. Galaxies are collections of stars, and are constantly merging and changing as new stars are born or old ones go supernova or get ejected into interstellar space. Based on its oldest stars, we can estimate that the Milky Way is 13.5 billion years old, close to the age of the universe. A galaxy could be said to “die” by being absorbed into another, larger galaxy; or by “quenching”, when it stops forming new stars. It’s a relative mystery as to why some galaxies eventually quench, though it’s thought that they do so when they run out of cold gases that stars form from. Because of this, researchers group galaxies by color. Galaxies are said to move from Blue Cloud, which are active galaxies, to Red Sequence, to when they stop forming new stars.

If we don’t consider any other outside factors, our galaxy and sun will actually live relatively the same amount of time. If we think of the sun as “dead” when it runs out of its primary source of energy and turns into a red giant, then it has 5 billion years left. And if we pronounce the Milky Way dead when it quenches and ceases star formation, research suggests that that could happen in less than 5 billion years as well. Neither will actually disappear when this happens, however. Our galaxy would continue to exist in a state of inactivity, and our sun will continue to exist as a red giant. Eventually, it will collapse again into a white dwarf, and then, theoretically, a black dwarf. A black dwarf has never been seen in nature because it’s thought that white dwarfs have longer lifespans than the time that the universe has existed.

However, the reality is that the Milky Way won’t remain undisturbed for the next 5 billion years anyway. In only 4 billion years the Andromeda galaxy will collide with our own and the two will begin merging. The Andromeda Galaxy contains twice as many stars as our own Milky Way, and neither will retain any semblance of their original formations. The newly formed galaxy won’t even be a spiral galaxy anymore but an elliptical one. Despite this, our sun and our entire solar system will survive the encounter, likely unscathed. There’s only a one in ten million chance that a star will come anywhere near Neptune. Both galaxies contain trillions of stars, but the distance between each star is so massive that it’s unlikely any will collide - and the new galaxy will be a combination of both - nicknamed Milkdromeda.

From the viewpoint of Earth, any surviving life will see a massive display of stars filling the night sky as both galaxies weave in and out of each other like a swarm of bees or a flock of birds. Humanity would be met with an amazing spectacle and be completely safe on Earth, as it would all be happening a vast distance away. Our constellations would be forever changed as new patterns filled the night sky, and the newly formed galaxy will be around for some time after.

It’s unlikely that life will be on Earth when that happens, however. Despite our sun not going red giant for another 5 billion years, it grows in luminosity, and subsequently heat, by about 10% every billion years. It will grow hot enough in the next billion years to push Earth out of the habitable zone and potentially evaporate its oceans, beginning its transformation into another Venus. If we are still around, we’ll have had to flee to another planet, potentially Mars, to watch as the sun begins to turn into a red giant and fill our sky and burn the inner planets. If we haven’t mastered interstellar travel, we likely won’t survive the transformation.

As for the sun, it will cool and become a white dwarf, remaining in this state for tens of billions of years. However, that’s assuming that nothing happens to our sun in the meantime. When the Milky Way and Andromeda galaxies merge, the supermassive black holes at the centers will also begin circling each other. They will eventually merge, but will spend millions of years doing so because of a process called dynamical friction, where the surrounding stars alter the black holes’ paths. Eventually, they’ll merge, and there’s a chance that our sun will fall towards the center of the new galaxy and be catapulted out into interstellar space. Alternatively, it could get too close and end up being devoured by the supermassive black hole.

All in all, even if we pronounce the sun dead when it becomes a red giant and not when it runs out of fuel completely, our Milky Way Galaxy will be long gone by that point. It’s thought to have survived for almost as long as the universe itself, but all things must come to an end, and our galaxy only has 4 billion years left to live before it collides with the Andromeda galaxy and becomes completely intertwined with it. There’s a chance that this process will affect our sun, but the chances are extremely small, and it’s far more likely that our solar system won’t change at all, even if it ends up being catapulted and flung into interstellar space from the galactic forces. Humans probably won’t be around to see what happens either way, but our local neighborhood of planets will remain unscathed as they continue to orbit our sun, which will likely remain for billions of years more, albeit in a different form.

And that’s Why Our Sun Will Live Longer Than Our Galaxy.