00:00At first sight, it looks like any other star, until you glance away just for a second.
00:06You look back, but the star is nowhere to be seen.
00:09All because it's likely the fastest star out there.
00:13Now hear me out.
00:15Astronomers have recently discovered an astonishing new class of stars.
00:18They got the name hypervelocity stars.
00:22Scientists have spotted around a dozen of such stars.
00:26And it turns out that they're so speedy that they can leave our home Milky Way galaxy one
00:31day and set off on an intergalactic journey.
00:35You see, stars do weave in and out of the Milky Way galaxy's spiral arms all the time.
00:41Like hurrying cars speeding through rush hour traffic.
00:44But when you look at the night sky, it may seem that these bright spots are as stationary
00:50as the monumental pyramids of Giza.
00:53Now among those 200 to 400 billion stars that call the Milky Way their home, there
00:59is a tiny, tiny fraction that stands out.
01:03Gravitational interactions have sped those massive stars up so much that they started
01:07moving twice or even three times faster than our Sun.
01:12Yep, these are the very hypervelocity stars bound to break free of the gravitational embrace
01:18of our galaxy.
01:20They seem to be trying to take speeds to a new level.
01:24They move at a speed of more than 700,000 miles per hour.
01:28A hypervelocity star could zip from the Moon to our planet in a mere 20 minutes.
01:34They are solitary stars, very different from previously discovered ones.
01:40The original hypervelocity stars are large and blue, and seem to be born in the core
01:46of the galaxy.
01:47As for the new stars, they are quite small, not bigger than our Sun, and don't seem
01:52to come from the galactic center, which is surprising.
01:55Instead, they are often caught fleeing youthful clusters.
02:00Most hypervelocity stars are in the Milky Way galaxy's outer halo, about 150,000
02:06light-years away from the galactic center.
02:09Interestingly, an astronomer at the Los Alamos National Laboratory in New Mexico predicted
02:15the existence of hypervelocity stars in 1988, but scientists didn't find any of them until
02:232005.
02:24The first star to be spotted was 350,000 light-years away from the core of the Milky Way and moved
02:31away from the center of the galaxy at about 1.5 million miles per hour.
02:39Astronomers say that it's extremely difficult to kick a star out of the galaxy.
02:43One of the most common mechanisms for doing so is some kind of interaction with a supermassive
02:49black hole at the galactic core.
02:52So Sagittarius A, which might be the very black hole we're looking for, at the center
02:57of the Milky Way probably accelerates hypervelocity stars, or at least some of them.
03:03To reach escape velocity, a star must get a more than a million-mile-per-hour kick.
03:09And since the Milky Way's central black hole has a mass of 4 million suns, it has enough
03:14power to produce something like that.
03:17The most typical scenario involves a binary pair of stars.
03:22This is a system of two stars that are gravitationally bound to and in orbit around each other.
03:29So let's say these stars get caught in the grip of our black hole, and as one of the
03:33stars is spiraling inward towards the black hole, its sibling is flung outward at a tremendous
03:40speed.
03:41This is called a three-body exchange.
03:44Astronomers have already found 18 giant hypervelocity stars that could have been produced by this
03:51mechanism.
03:54There's also a theory that hypervelocity stars might be ejected from dense stellar clusters
03:59by supernova explosions.
04:02The newly discovered hypervelocity stars seem to have the same composition as regular stars.
04:09That's why astronomers don't think that their birthplace could be some exotic place outside
04:13the galaxy or in the outer halo of the Milky Way.
04:17The thing is, it's a lifeless region full of old, metal-poor, and low-mass stars, and
04:23it's impossible to see a hypervelocity star there unless it was ejected in that direction.
04:30So hypervelocity stars still remain a mystery for us, but they're not the only stars out
04:36there that act weird.
04:38For example, in 2017, astronomers spotted a bright star hurtling out of the Milky Way.
04:45It was moving incredibly fast, at a speed of 2 million miles per hour, which is almost
04:50four times as fast as the Sun orbits around the center of the Milky Way galaxy.
04:56Anyway, the main issue with the wandering star was that it was moving against the direction
05:01in which most stars travel around the center of our galaxy.
05:06And it wasn't the only bizarre thing about it.
05:08Its appearance evoked a lot of questions.
05:11Was it a hypervelocity star?
05:14Was it even a star?
05:15The space traveler consisted of totally different star stuff.
05:20Astronomers managed to identify its composition.
05:23It was made up of heavy metallic atoms.
05:26Most other stars consist of way lighter elements.
05:30The wandering star got its name LP40-365.
05:35It was moving so fast that it literally dashed out of our galaxy.
05:40This made scientists believe that it was pushed out of its place by some kind of cosmic disaster,
05:46like a supernova.
05:48These days, astronomers claim that the star, which was previously considered to be a white
05:53dwarf, is actually a piece of star shrapnel.
05:57Kind of a leftover after a more massive star experienced a supernova.
06:02The explosion must have been so powerful that it pushed LP40-365 into interstellar space.
06:10This piece of a previously glorious star keeps slowly rotating around its axis.
06:17This is more proof astronomers need to claim LP40-365 is indeed just a chunk of space debris
06:24and not a full-fledged star.
06:27But such a conclusion means that it has witnessed a supernova.
06:31Even though this event happened lightning fast, the entire makeup of this space object
06:36was changed.
06:39You see, most stars consist mainly of helium and hydrogen.
06:43But LP40-365 is different.
06:46It contains such heavy elements as magnesium, oxygen, and neon.
06:51It must have been the supernova that added these atoms to the star's composition.
06:56By the way, astronomers considered all elements that are heavier than helium to be metals.
07:01This means that after witnessing the supernova, LP40-365 became metallic.
07:08Our space traveler brightens and then dims again every 8.9 hours.
07:13It might mean that the star pulsates, but usually stellar pulsations are much less regular.
07:19A more plausible explanation is that the star's surface is uneven, and as it spins, sunspots
07:25are brought into and out of view.
07:28Let's move to another unusual space body.
07:31It's the 18th brightest star in the night sky, and it's called Fomalhaut.
07:36If you look at it through a telescope, you'll be met by a terrifying sight.
07:41No wonder it's dubbed the Eye of Sauron.
07:44A ring of dust and debris circles it, making it look like a giant eye staring straight
07:50into your soul.
07:51The intimidating star is more than twice the mass of our sun and is 25 light-years away
07:56from Earth, which isn't that far away considering distances in space.
08:01Then there's a star that is tearing itself apart.
08:04It has a beautiful name, Vega.
08:07At first sight, it seems to be normal, large, bright, and pretty young.
08:12But the deeper you go, the weirder it gets.
08:16For example, it's not actually round, it looks like an egg.
08:21It might be because the star rotates so fast that its shape gets distorted, causing temperature
08:26variations across Vega's surface.
08:30It's also going 93% of the maximum velocity a star this big can handle, and I mean a mind-boggling
08:37170 miles per second!
08:41Astronomers aren't sure why Vega is rotating so fast that it's almost tearing itself apart.
08:47Mira is sometimes one of the faintest and sometimes one of the brightest stars in the
08:52night sky.
08:53This system actually consists of two stars.
08:56One of them is a red giant that once resembled our sun.
09:00The other is a white dwarf.
09:02The red giant is constantly shredding its outer layers, creating clouds of debris around
09:07the whole system.
09:09This phenomenon might be the reason for the regular dimming of the stars.
09:13It can also explain why the intervals between these periods of dimming aren't regular.
09:18But the coolest thing?
09:19It gives the stars a comet-like tail!
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