00:00Have you ever just stared up at the night sky and wondered exactly how chaotic the universe really is?
00:06Well, welcome to This Explainer.
00:08Today, we're taking a wild journey right through the fascinating life cycle of stars.
00:12We're going to explore the entire cosmic zoo,
00:15starting from the quietest, most everyday dwarfs that silently fill our galaxies,
00:20all the way up to the most terrifying, massive cosmic remnants
00:23that literally challenge our very understanding of physics.
00:27To kick things off, ask yourself this.
00:29What actually determines a star's fate?
00:31Like, what happens when a star dies?
00:33And why is it that the biggest, brightest, most powerful stars in our universe are actually the most doomed?
00:40Well, the answer comes down to one simple thing.
00:43Mass.
00:43And as you'll see, mass dictates absolutely everything we are about to explore.
00:48Here is our roadmap for navigating this vast cosmic zoo.
00:52First, we'll look at the everyday dwarf stars.
00:54Two, we'll scale up to giants and supergiants.
00:57Three, we'll check out some strange stellar remnants.
01:00And finally, part four, the most extreme objects in existence.
01:04All right, let's dive into part one, the everyday dwarf stars.
01:09It's really fascinating to compare our own sun, which, by the way, is a yellow dwarf,
01:14to the much smaller, cooler red and orange dwarfs out there.
01:17Our sun sits around 5,000 to 6,000 Kelvin and is going to live for roughly 10 billion years.
01:23But consider the orange dwarfs.
01:25These stars are slightly smaller, sure, but they can live for 15 to 30 billion years.
01:31Because they're so incredibly stable and produce far fewer dangerous flares,
01:35they are actually considered fantastic candidates for hosting habitable planets.
01:40And here's a mind-blowing stat.
01:42Red dwarfs completely dominate the cosmos.
01:44We're talking a staggering 75% of all stars in existence.
01:49They're small, holding somewhere between 8% and 50% the mass of our sun.
01:53And they burn through their hydrogen fuel incredibly slowly.
01:57So slowly, in fact, that their lifespans can exceed a trillion years.
02:01Since our universe is only about 13.8 billion years old,
02:04that means not a single red dwarf in the history of the universe has ever had enough time to die
02:09yet.
02:09Think about that.
02:11Now, beyond the standard dwarfs, we do have some strange outliers on the smaller end.
02:16Take brown dwarfs.
02:16They're basically failed stars.
02:18They formed just like stars,
02:20sitting right in that weird middle ground between a heavy gas giant and a light red dwarf.
02:24But they just never accumulated enough mass to sustain ordinary hydrogen fusion.
02:29So they just slowly cool and dim.
02:31Then we have sub-dwarfs.
02:33These are ancient stars with super low metal content.
02:36They're often found out in the galactic halo,
02:38which tells us they formed very early in the universe's history,
02:41back before a lot of heavy elements even existed.
02:44To really understand how this all works,
02:46let's look at our own sun's timeline.
02:48Right now, it's about 4.6 billion years old,
02:51sitting perfectly in the middle of its yellow dwarf face.
02:54But in about 5 billion years, it's going to run out of hydrogen fuel in its core.
02:59When that happens, it's going to expand dramatically into a red giant,
03:03swelling up so much that it'll likely engulf the orbits of Mercury and Venus.
03:07Eventually, it sheds those outer layers entirely and collapses into a slowly cooling white dwarf,
03:13before theoretically, way, way in the future, becoming a completely cold, pitch black dwarf.
03:20Giants and Supergiants
03:22There's a real stark irony here.
03:25We just learned that a tiny, dim red dwarf can live for over a trillion years.
03:30But massive blue giants?
03:32These are intensely hot stars, easily exceeding 10,000 Kelvin,
03:36and shining tens of thousands of times brighter than our sun.
03:40But that brightness?
03:41It comes at a deadly cost.
03:43They aggressively burn through their fuel and die in just a few million years.
03:47In the stellar world, living large literally means dying very, very young.
03:52When we scale up to the supergiant variants, the sheer size becomes almost incomprehensible.
03:58Imagine taking a red supergiant, like the famous star Betelgeuse,
04:01and dropping it right at the center of our solar system.
04:04Its massive volume would swallow absolutely everything past the orbit of Mars,
04:10and maybe even reach Jupiter.
04:12They're absolutely enormous, but relatively cool.
04:15And that is a wild contrast to blue supergiants, which are immensely massive,
04:19we're talking 10 to 100 solar masses,
04:22and blisteringly hot, reaching up to 50,000 Kelvin
04:25before inevitably exploding in a violent supernova.
04:29Right at the very top of the mass scale,
04:31we find the absolute behemoths,
04:34the hypergiants and Wolf-Rea stars.
04:36The heaviest stars out there, like the red hypergiant U.I. Scuti,
04:40emit millions of times more light than our sun.
04:42But they are incredibly unstable.
04:45Wolf-Rea stars, for instance, are so insanely hot,
04:48sometimes over 200,000 Kelvin,
04:51that they've entirely blown away their outer hydrogen layers,
04:54just exposing their helium-burning cores.
04:56They violently blast away their mass through powerful stellar winds,
05:00traveling up to 2,000 kilometers per second,
05:02speeding toward a catastrophic supernova or even a hypernova explosion.
05:07Let's move to Section 3, Strange Stellar Remnants.
05:11Remember earlier when we talked about the ultimate fate of our sun?
05:14When an average star sheds its layers, it leaves behind a white dwarf.
05:19It isn't a living star anymore.
05:20It's not producing any new energy.
05:22It's just a leftover core, roughly the size of Earth,
05:25but somehow still packing the mass of the sun.
05:28Because that matter is compressed so intensely,
05:31just a single teaspoon of white dwarf material would weigh approximately 5.5 tons here on our planet.
05:37But watch what happens to the math when a much more massive star dies.
05:41If a large star goes supernova and its core collapses into a neutron star,
05:46it packs up to two entire solar masses into a tiny sphere only about 20 kilometers in diameter.
05:52Protons and electrons are literally crushed together to form pure neutrons.
05:56Because of this extreme density, that exact same teaspoon of material we just talked about
06:02suddenly weighs an astounding 6 billion tons.
06:06The gravitational field on its surface is 2 billion times stronger than on Earth.
06:11These neutron stars can also spin at absolutely breathtaking speeds,
06:16emitting these lighthouse-like beams of radiation.
06:18We call these pulsars.
06:20When astrophysicist Jocelyn Bell Burnell first discovered pulsars back in 1967,
06:25the pulses sweeping across space were so incredibly precise,
06:29like better than atomic clocks,
06:31that researchers genuinely didn't know what to make of it.
06:34They actually briefly nicknamed the signal LGM-1, or Little Green Men,
06:39seriously considering the wild possibility that it might be an artificial beacon from an alien civilization.
06:45Okay, into our final section, part 4, the most extreme objects.
06:50Let's start with magnetars.
06:52These are a super rare type of neutron star with magnetic fields up to a quadrillion times stronger than Earth's.
06:59To put that into perspective for you,
07:01a magnetar located halfway between the Earth and the Moon
07:04would instantly wipe every single magnetic stripe on every credit card on our planet.
07:09They are so overwhelmingly powerful that back in 2004,
07:13a flare from a magnetar located 50,000 light-years away
07:16emitted more energy in a tenth of a second than our Sun does in 100,000 years,
07:22literally disturbing Earth's upper atmosphere.
07:24Now, for the absolute largest stars in existence,
07:27those with more than 20 solar masses,
07:30death means something even more extreme.
07:32The gravitational force becomes so entirely overpowering
07:36that the core collapses completely on itself,
07:39creating a black hole.
07:40This forms a boundary called an event horizon,
07:43which is a point of no return where absolutely nothing,
07:46not even light, can escape.
07:48We used to only know them by their gravitational effects,
07:51until 2019,
07:52when humanity famously captured the very first image
07:55of a supermassive black hole at the center of the galaxy M87.
08:00But physics never stops throwing curveballs, does it?
08:03Astronomers are actually hunting for objects right now
08:05that might exist perfectly between neutron stars and black holes.
08:09Enter the theoretical quark star.
08:12The idea here is that if the pressure inside a neutron star
08:15gets extreme enough,
08:16the neutrons themselves could shatter apart
08:18into their raw component quarks,
08:20creating a completely new state of matter called quark matter.
08:24In 2002, the Chandra X-ray Observatory
08:26spotted potential candidates that were too small to be neutron stars,
08:30but too large to be black holes,
08:32though they do remain unconfirmed for now.
08:34And that brings us to a really profound realization
08:37to wrap up this explainer.
08:38Earlier, we talked about theoretical blue dwarfs,
08:41which is what red dwarfs might turn into
08:43trillions of years from now.
08:44And we just looked at theoretical quark stars.
08:47Knowing that our universe is only 13.8 billion years old,
08:50it's essentially just an infant.
08:52It is still rapidly evolving.
08:54So we really have to ask ourselves,
08:57what other bizarre,
08:58mathematically predicted celestial bodies
09:00are simply waiting in the wings
09:02for the universe to age enough to finally be born?
09:04It makes you realize
09:06we have barely even scratched the surface of the cosmic zoo.
09:09That's all.
09:09You
