00:00Well, it turns out black holes might not be as elusive as we once thought.
00:05They might be hiding within stars.
00:07In this case, the extra mass of some of these space slanders
00:11could explain weird gravitational effects in the universe.
00:15Previously, dark matter was the cause of these phenomena.
00:18The black holes I'm talking about might be those itty-bitty ones
00:22that appeared at the dawn of time when the universe was just a baby.
00:26And they may still be lurking in the hearts of giant stars.
00:30A team of scientists say the idea might be quite plausible.
00:34Astronomers could detect such trapped black holes
00:37by the vibrations they produce on their star's surfaces.
00:40And if there are many of them out there in the cosmos,
00:43they might function as the very dark matter that holds the universe together.
00:49Almost any black hole was once a massive star
00:52that collapsed in on itself and became incredibly dense.
00:56Black holes have immense gravitational pull.
00:58Even light can't escape their clutches.
01:01People often think that black holes work like vacuums, pulling space inside.
01:06But that's not the case.
01:08Black holes can only swallow stuff that is extremely close,
01:12usually space objects venturing into their event horizon.
01:15That's a black hole's point of no return.
01:18Once you cross this border, there's no escape.
01:20In 1971, renowned physicist Stephen Hawking suggested another origin of black holes.
01:28If we took the thick soup of particles that appeared moments after the Big Bang and the birth of the universe,
01:35we'd be bound to find some spots dense enough to collapse and create black holes.
01:40Such holes, which got the name of primordial black holes, could range in size from microscopic to gigantic.
01:48If they were pervasive and numerous enough, primordial black holes could act as dark matter,
01:54knitting the cosmos together with their enormous gravity.
01:57And dark matter is believed to make up 85% of all the matter in the universe.
02:02So what's the matter?
02:05Astronomers have been searching for primordial holes by looking for flashes
02:09that would occur when they pass in front of distant bright objects,
02:13magnifying their light like a lens.
02:15But they haven't spotted even one yet.
02:18On the other hand, if a primordial black hole was tiny enough,
02:22with a mass like that of an asteroid,
02:24and a diameter as minuscule as a hydrogen atom,
02:27the flashes wouldn't be bright enough to be detected by such surveys.
02:31Then the team, researching the phenomenon of primordial black holes,
02:36decided to consider the consequences of a universe
02:38where dark matter was made entirely out of tiny black holes.
02:43They concluded that one of such teensy holes
02:46could be dashing through the solar system at any given time.
02:49Some might occasionally get trapped within gas clouds,
02:52giving birth to new stars, ending up in their centers.
02:56The next step of the researchers was to build a model of a black hole
03:00existing in the very core of a star,
03:02where hydrogen atoms undergo fusion and produce light and heat.
03:06At first, they didn't see anything unusual.
03:09Even a super-dense stellar core is mostly empty space.
03:13And it wouldn't be easy for a microscopic black hole
03:16to find matter to consume there.
03:18That's why its growth would be incredibly slow.
03:21It could take longer than the lifetime of the universe
03:23for this tiny hole to eat a star.
03:27But what if a larger hole,
03:29as massive as the dwarf planet Pluto or asteroid Ceres,
03:33appeared at the center of a star?
03:35Then it would get bigger in a matter of a few hundred million years.
03:39The material would keep spiraling into the black hole,
03:43creating a disk that would heat up because of friction,
03:46emitting radiation.
03:47Once the black hole grew to the size of Earth,
03:49it would start emitting even more radiation,
03:53shining extremely brightly.
03:55It would also be churning up the star's core.
03:57And the star itself would turn into a black hole-powered
04:00rather than a fusion-powered object.
04:03Such entities were dubbed Hawking stars.
04:07To cool off,
04:08the exterior of a Hawking star would form a red giant.
04:11That's what our Sun is likely to turn into as it gets older.
04:15But a red giant star with a primordial black hole at its center
04:19would be cooler than the stars that have reached this stage
04:22through regular means.
04:24Such stars are known as red stragglers.
04:28To find out whether they indeed host a black hole,
04:32astronomers might need to tune into the frequencies
04:34at which stars vibrate.
04:36Since a Hawking star would mostly affect the interior of the star
04:40rather than its topmost layers,
04:42the star would thrum with a certain combination of frequencies.
04:46The waves created in the process
04:48could be detected in a way the star's light would pulse and thrum.
04:52So all scientists need to do now
04:54is study the already known red stragglers
04:57and figure out whether any of them
04:59show the characteristic vibrations of a black hole.
05:03Now, should we worry about the Sun?
05:05Since our star hasn't reached its red giant stage yet,
05:08we can't know whether it'll turn into a cool red straggler.
05:12What we know, though,
05:14is that our star might contain those tiny black holes
05:17that formed in the Big Bang.
05:18But now, we have no means to check whether they're indeed there.
05:22Currently, our star is around the midpoint of its existence.
05:29Middle-Aid.
05:30Hmm.
05:31It creates energy non-stop by fusing hydrogen atoms within its core.
05:36Once it runs out of hydrogen in its core,
05:38it will enter its red giant phase and begin to collapse.
05:42It'll happen in about 5 billion years.
05:44Don't hold your breath.
05:45And the phase itself will last for a billion years or so
05:48before our star depletes its fusible materials
05:51and loses its outer layers.
05:53It will leave behind a tiny white dwarf star
05:56half as massive as the Sun
05:58and around the size of our planet.
06:01In some cases,
06:02when the gravitational collapse of a star's core is complete,
06:06the star remnants turn into a black hole.
06:09But that's not the fate awaiting our Sun.
06:11You see, our star just doesn't have what it takes
06:14to become a black hole.
06:16It's not heavy enough.
06:17There are a few conditions that can affect
06:20whether a star can turn into a black hole,
06:23including its composition, rotation,
06:25and the processes that lead to its evolution.
06:28But the main requirement is still the right mass.
06:32Stars with 20 to 25 times the mass of the Sun
06:35can potentially experience the gravitational collapse
06:38needed to form black holes.
06:40In other words,
06:41the Sun is simply too small to form a black hole.
06:44But what would happen to us if it did?
06:49You might assume that if the Sun turned into a black hole,
06:52our planet would be doomed to be pulled into it.
06:55But do you remember the basics?
06:57Black holes aren't giant space vacuum cleaners,
07:00just sitting there and waiting for a new planet or star
07:03to get their hands on.
07:04Mwah!
07:05But black holes don't have enough gravitational force
07:08beyond that created by their incredible mass.
07:11And if the Sun were to turn into a black hole,
07:14which will not happen,
07:16this hole would still have the same mass as our former star.
07:19And Earth's orbit around this newly formed black hole
07:22wouldn't change.
07:24But all other things would change dramatically.
07:27The Sun, which is currently around 432,000 miles in radius,
07:32would shrink to a mere 1.9 miles in radius.
07:35But you wouldn't be concerned with the absence of the bright yellow sphere in the sky,
07:40since you have many more pressing issues on your hands.
07:43Our planet's main heat source would be gone,
07:46leaving us frozen in the dark.
07:48Without this source of energy,
07:49photosynthesis would immediately stop,
07:52disrupting entire food chains.
07:54Eventually, all life on Earth would be extinguished.
07:57But rest assured,
07:59our hard, barren rock of a planet would continue in its orbit.
08:03Oh well.
08:03Thank you very much.
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