00:00A recent study has involved almost 200 huge stars that are reaching the end of their lives.
00:07It has given scientists more precise information about how the Sun will one day end.
00:13It turns out that the Sun will be about 200 to 300 times bigger than it is now by the time its game is over.
00:21For starters, let's begin with some basic information about star sizes.
00:26Giant ones reach this stage because they've run out of nuclear fuel and are no longer burning hydrogen in their core.
00:33Eventually, the core gets hot enough to trigger the next stage of fusion, which is helium burning.
00:39All the stars that were surveyed in this new study were either in this hydrogen shell burning or helium core burning phase.
00:48Even though giant and supergiant stars only make up less than 5% of all stars, or at least that we know of,
00:56they're actually really visible from a distance because they're so bright.
01:01In fact, according to scientists, about a third of all the stars you can see outside on a dark, moonless night are giant or supergiant stars.
01:12This study will eventually give astronomers really useful info about massive stars.
01:17They'll be able to figure out their size and temperature no matter where they are or their evolutionary stage.
01:24This means they can see a star's true color and use that to find out its radius. Pretty cool, right?
01:32It does raise the question, what will our Sun be like when it gets old and grumpy?
01:37To put it simply, it will expand when it starts burning its hydrogen shell, but then shrink a bit during its helium core burning phase.
01:46After a few hundred million years, it'll end up as a giant star about 200 to 300 times its current size.
01:54Eventually, the Sun will expand so much that it will simply evaporate.
01:59So, what will happen after the Sun fades away?
02:04Scientists actually have some predictions about what will go down, even though we won't be around to see it.
02:10They're pretty sure the Sun will turn into a planetary nebula.
02:14These planetary nebulae are chunks of gas and dust in space that come from a star that is fading away.
02:22They got their name because they looked like planets to people using telescopes back in the 18th century,
02:28even though we now know they have nothing to do with actual planets.
02:33And here's the crazy thing.
02:35Astronomers have found out they can use the level of brightness of these planetary nebulae to calculate their distance from us.
02:42In 2018, scientists also found out that the Sun is the smallest a star can be to still be able to produce a visible nebula.
02:51Any smaller and it would not be visible.
02:54Stars that are up to three times more massive than the Sun will produce brighter nebulae.
03:00The Sun is currently 4.6 billion years old, but it's estimated to have another 10 billion years until its end.
03:09The Sun is also getting brighter with each year.
03:13It doesn't seem like a lot now, but it's actually going to cause some big problems for Earth.
03:19In about a billion years, the Sun will be too bright for life on Earth to survive.
03:25Our oceans will evaporate and it will be too hot for water to form again.
03:30So unless we find a way to escape from this planet, humanity only has about a billion years left.
03:38Will Earth still be around by the time the Sun turns to dust?
03:42It's hard to know for sure the exact timeline.
03:46But even before that happens, Earth will most likely be scorched and lifeless, with no atmosphere or oceans left.
03:53It's not clear how close the Sun's outer layers will get to Earth.
03:57But if they get too close, it could cause Earth to spiral into the Sun and disappear altogether.
04:05Even if our planet does somehow manage to survive the Sun's giant phase, it will be orbiting a hot white dwarf.
04:13Or a star that has run out of its fuel.
04:16In that distant future, the Sun will be barely larger than our planet.
04:21Eventually, the Sun will cool and dim completely.
04:24It will move to another stage called a black dwarf.
04:27It will cause Earth's orbit to loosen up and our planet will spiral into the faded Sun.
04:33But interestingly, the Sun doesn't get the final say in what happens to Earth.
04:39Gravity keeps planets in orbit, but it also attracts them to each other.
04:43Which can cause their orbits to flex and drift.
04:46This could lead to the Solar System destabilizing and ejecting planets, including Earth.
04:52Basically, a lot might happen in the next 5 billion years before the Sun becomes a red giant.
05:00There's also another scenario.
05:03While most stars stay far away from our Solar System, there's a chance that one could come closer in the next billion years.
05:10Even a small star or black hole could mess up the orbit of our planet if it gets too close.
05:17But don't worry too much, the odds of that happening are low because of the amount of space between stars.
05:24Our Sun is a solitary star, so there's little to no chance we'll be able to catch a ride with another one nearby.
05:32However, many stars in our universe have companions.
05:35Among these stars is Castor, a stunning system that comprises 6 stars and is one of the brightest objects in the night sky.
05:45Although humans have been admiring Castor for ages, they were not aware of its true nature until the invention of telescopes and spectroscopes.
05:55Even with the help of a small telescope, it's evident that Castor is composed of two primary stars, Castor A and B A, that revolve around each other.
06:05These stars are larger than the Sun and need 467 years to complete one orbit.
06:12In total, Castor is composed of 6 different stars.
06:16The biggest one, called Castor AA, is roughly two times larger than the Sun, while the smallest has about 0.5 of the Sun's mass.
06:26If humans want to survive the next billions of years, we might need to set up camp somewhere else in the universe.
06:33It may seem like something out of a sci-fi movie, but it could be our reality one day.
06:39Thankfully, NASA is already looking at some options.
06:42They've discovered two new planets, TOI-700E and TOI-700D.
06:49That might be new hotspots for us humans.
06:53TOI-700E is the optimistic zone, which means it could have water and even an atmosphere.
07:00TOI-700D is in the conservative habitable zone, so scientists aren't too sure about it yet, but hey, we'll take what we can get.
07:10But hold on, before you start packing your bags, there's a little problem.
07:15How do we get there?
07:17It took John Glenn months of preparation just to circle Earth three times.
07:22So we might need to start working on our astronaut training.
07:26Well, at least we have some options for our future intergalactic vacation plans.
07:31Wouldn't it be nice if we could time travel so we could see what our solar system will look like in billions of years?
07:37An American physicist named Ron Mallett has proposed one interesting theory for time travel.
07:44It uses light, a resource that is abundant in the universe.
07:48His idea involves using a rotating cylinder of light, which could transport an object in both space and time, similar to how a bubble moves in a swirling liquid.
07:59Mallett suggests that a cylinder of the right shape could allow for travel to the past and the future.
08:05To test his theory, he has been trying to secure funding for an experiment.
08:10However, some scientists consider Mallett's theory to be impossible and unnecessary to test.
08:16We might also be able to travel through time if we move fast enough.
08:21According to Einstein, the way we experience time can change depending on how fast we're moving.
08:27If we go really fast, time slows down.
08:30For example, astronauts in space age a tiny bit more slowly than people on Earth.
08:36This is important for things like GPS, which would be incorrect without special adjustments because of how time is affected.
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