It's hard to imagine that someday, the Milky Way galaxy will cease to exist. Looking up at the stars, it feels as though Earth, and even the solar system that it belongs to, is infinite. But our sun is one of billions inside of this galaxy, and there's much more to the universe than that. Like anything else, stars die, although it takes billions of years to do so. At some point, though, catastrophe awaits, and it won't be just for us. So will the Milky Way galaxy last forever? The answer is more complicated than you might think.
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00:00When staring up at the nighttime stars, it's easy to forget that they, too, will die.
00:05In comparison to the brief dust of a single human life, with a very visible beginning,
00:09middle, and end, bound to an Earth defined by interwoven ecological cycles, the stars
00:14do indeed seem eternal.
00:16But let's put that in perspective.
00:18It's taken 13.8 billion years since the Big Bang to reach the point where we can even
00:23make such an observation.
00:25The Milky Way galaxy is a 100,000-light-year-wide spiral galaxy with a supermassive black hole
00:31at its center.
00:32Our sun is merely one of 100 billion stars in its expanse, and our single galaxy is but
00:37one of two trillion within the observable universe.
00:41And the observable universe?
00:42It's a mere 1,250th of the entirety of the cosmos, a 23-trillion-light-year-wide reality
00:49over 15 million times greater in volume than anything we will ever see or visit.
00:54The universe is expanding at a rate faster than the speed of light.
00:58The relatively short-term fate of the Milky Way, though, isn't bound to the death of its
01:02stars, but the collision between us and our neighbor, the Andromeda galaxy.
01:06There's no point in acting all surprised about it.
01:09The plans and demolition orders have been on display at your local planning office in
01:13Alpha Centauri from the 50th on Earth year.
01:16Before we dive into the fate of our Milky Way galaxy, we've got to take a little foray
01:20into the life cycle of stars themselves.
01:23Like humans, like that totally adorable little corgi that lives down the street, like the
01:27seemingly ancient redwood forests, or in fact, just like any other terrestrial life form,
01:32stars are born, pass through phases, and then die.
01:36Sorry, nothing can escape the inevitable, not even entire galaxies or the universe itself.
01:41Our own sun is a good reference point.
01:44In a 13.8-billion-year-old universe, the sun is a modestly-sized, modestly-hot yellow dwarf
01:50star about 4.5 billion years old.
01:52Its core is 15 million degrees Celsius, or 27 million degrees Fahrenheit, and its gravitational
01:59pull extends beyond Pluto for up to two light-years.
02:01Sure, that's impressive, but it faces the same end as every single star in the Milky
02:06Way and beyond, going quietly into the good night in a shrunken, white-dwarfed, fuel-burning
02:12fizzle, or explode into a supernova and scatter its remnants everywhere.
02:16But here's the thing.
02:18There will eventually be no new suns anywhere.
02:21This is the only era of the universe, the second era of five, when stars can be born.
02:26In this era, the stelliferous era is nearly ending.
02:29We're about 13.8 billion years in, and we've got about 200 million years to go.
02:34After that, stars will only die, and occasionally form new specks of light in the sky when they
02:39collide with each other.
02:40So how long does a star live?
02:43It depends on the mass.
02:45Very large stars can go supernova in only a few million years, a relative blip in the
02:49cosmic night.
02:51Smaller stars like our sun, however, can run on their fusion tanks up to 10 billion years.
02:55The Milky Way is full of a variety of such stars that will all continue to age.
03:00About 5 billion years from now, our sun will start to transition to its red giant phase.
03:04By about 8 billion years in the future, it'll consume the inner planets, Mercury, Venus,
03:10and yes, Earth.
03:11Our solar system's habitable zone will be Jupiter and Saturn and their moons.
03:16Before then, and about 2 billion years from now, the Andromeda Galaxy, a spiral galaxy
03:20about 2.5 million light-years away, will start to grow larger and larger in our night sky.
03:26Eventually, it'll crash with our own galaxy and swirl into a new nebula of gases and intermingled
03:32star systems to form the fused New Galaxy.
03:35That's when the Milky Way technically will cease to exist.
03:38While it's possible that collisions might happen, it's unlikely because of the amount
03:42of emptiness in space.
03:43So that's some good news in all of this.
03:46It's only after that whoever is left behind will see our sun set for the final time, shrinking
03:51into a white dwarf and eventually a black dwarf, the end of a star's life cycle and
03:55fizzled-out companion to a black hole, which forms when a sun goes supernova.
04:00Beyond that, all stars will wink out one by one.
04:04Black holes will consume everything, including other black holes, and grow bigger and bigger
04:08until they too eventually expel all the energy they've captured and leave in their place
04:13absolutely nothing at all.
04:15The entire universe will be locked, permanently, in a state of absolute zero.
04:20There will be no more heat because there will be no more energy difference between anything.
04:23Our chilled, starless cosmos will look like a dark dream of peace fulfilled.
04:28So to answer the question, will the Milky Way galaxy live forever?
04:32Of course not.
04:33This can be a terrifying thought, sure, but it can also be a very good reason to gaze
04:37up into the sky and appreciate the one brief epoch when such wonder is possible.
04:42In the meantime, don't sweat the small stuff.