Saviez-vous qu'il existe dans notre galaxie des étoiles qui se déplacent si rapidement qu'elles peuvent en fait échapper à la Voie lactée ? Ces étoiles ultra-rapides, connues sous le nom d'« étoiles hypervéloces », voyagent à des millions de miles à l'heure ! Elles atteignent cette vitesse incroyable grâce à des événements cosmiques intenses, comme une explosion de supernova ou le fait d'être catapultées par le trou noir supermassif au centre de notre galaxie. Une fois que ces étoiles atteignent une vitesse suffisante, elles peuvent se libérer de l'attraction gravitationnelle de la Voie lactée. Les scientifiques ont découvert quelques-unes de ces étoiles fugitives, et il est fascinant de penser qu'elles s'élancent vers l'espace intergalactique. Qui sait où elles finiront par atterrir ensuite ! Animation créée par Sympa. ---------------------------------------------------------------------------------------- Musique par Epidemic Sound https://www.epidemicsound.com Pour ne rien perdre de Sympa, abonnez-vous!: https://goo.gl/6E4Xna ---------------------------------------------------------------------------------------- Nos réseaux sociaux : Facebook: https://www.facebook.com/sympasympacom/ Instagram: https://www.instagram.com/sympa.officiel/ Stock de fichiers (photos, vidéos et autres): https://www.depositphotos.com https://www.shutterstock.com https://www.eastnews.ru ---------------------------------------------------------------------------------------- Si tu en veux encore plus, fais un tour ici: http://sympa-sympa.com
Category
😹
FunTranscript
00:00At first glance, it looks like any other star.
00:04Until you look away for just a second.
00:07You look again.
00:09And it is unobtainable.
00:10The reason is that it is probably the fastest of the stars.
00:15Listen a little.
00:16Astronomers have recently discovered a new amazing star class.
00:20They have received the name of hypervelocity stars.
00:23They have spotted about a dozen.
00:26And it turns out that they are so fast
00:28that one day they may leave our galaxy, the Milky Way,
00:32to embark on an intergalactic journey.
00:35You see, the stars are constantly moving through the arms
00:38in a spiral of our Milky Way
00:40like pressed cars in the middle of high-speed traffic.
00:45But when you look at the night sky,
00:47it seems to you that these luminous points
00:50are as immobile as the monumental pyramids of Giza.
00:54Now, among these 200 to 400 billion stars
00:57that consider the Milky Way as their home,
01:00a tiny fraction stands out from the others.
01:03Gravitational interactions have accelerated these massive stars
01:06to the point that they move two or three times faster than our sun.
01:11Yes, these are the famous hypervelocity stars
01:14whose destiny is to free themselves
01:16one day from the gravitational constriction of our galaxy.
01:19It looks like they are trying to reach unprecedented speeds.
01:23They move at more than 126,000 km per hour.
01:28A hypervelocity star could cross the distance
01:31that separates the Moon from our planet in just 20 minutes.
01:36These stars are solitary
01:38and very different from the hypervelocities we have known so far.
01:41The original hypervelocities were large and blue
01:44and seemed to be born in the heart of the galaxy.
01:47But these new stars, they are quite small,
01:50not bigger than our sun,
01:52and do not seem to come from the center of the Milky Way,
01:55which is surprising.
01:57They are most often discovered escaping from relatively young stars.
02:01Most of the hypervelocity stars
02:03are in the outer halo of the galaxy,
02:06about 150,000 light years from the center of it.
02:10It is interesting to note that an astronomer
02:12from the National Laboratory of Los Alamos in New Mexico
02:16predicted the existence of hypervelocity stars in 1988,
02:20but scientists only began to discover them in 2005.
02:25The first star spotted was 350,000 light years from the heart of the Milky Way
02:30and was 2.4 million km away from its center per hour.
02:36Astronomers say it is extremely difficult
02:39to chase a star out of the galaxy.
02:42When it happens,
02:43it is most of the time because of a supermassive black hole.
02:47And according to experts,
02:48it is probably Sagittarius A-star
02:52that accelerates hypervelocity stars,
02:54or at least some of them.
02:57To reach the speed of evasion,
02:59a star must receive an impulse of an unimaginable force for us.
03:03And as the central black hole of the Milky Way
03:06has a mass of 4 million suns,
03:08it probably has enough power
03:10to produce something of this kind.
03:12In the most common scenario,
03:14we have a binary star,
03:16a system made up of two gravitationally linked stars
03:20orbiting each other.
03:22Suppose these stars are caught in the core of our black hole.
03:26As one of the stars goes in a spiral towards the black hole,
03:30its sister is projected outward at a phenomenal speed.
03:34This is what is called a three-body exchange.
03:38Astronomers have already discovered 18 giant stars
03:41that could have been made hypervelocity by this process.
03:44There is also a theory
03:46according to which hypervelocity stars
03:48could have been ejected from their stellar masses
03:51by supernova explosions.
03:53Hypervelocity stars,
03:55recently discovered,
03:56seem to have the same composition as normal stars.
04:00This is why astronomers do not think
04:02they come from an exotic place
04:04located outside the galaxy
04:06or in the outer halo of the Milky Way.
04:09This halo is actually a lifeless region
04:12filled with old poor metal stars
04:15and very weak masses.
04:17It is unlikely that a hypervelocity star is found there,
04:20unless it has been ejected in this direction.
04:23Hypervelocity stars remain a mystery,
04:26but they are not the only ones to behave strangely.
04:30For example, in 2017,
04:32astronomers spotted a bright star
04:35rushing out of the Milky Way.
04:37It was moving incredibly fast,
04:39at a speed of 3.2 million km per hour,
04:42almost four times faster than the sun in orbit
04:45around the center of the galaxy.
04:47The main problem with this wandering star
04:50was that it was moving in the opposite direction
04:52compared to most of the other stars
04:54orbiting the center of our galaxy.
04:57But this is not the only strangeness about it.
05:00Its appearance also raised many questions.
05:04Was it a hypervelocity star?
05:06Was it even a star?
05:08This wanderer seemed to be made up of
05:11a totally different stellar matter from its congeners.
05:14Astronomers managed to identify its composition.
05:17It was made up of heavy and metallic atoms.
05:20Most of the other stars are made up of much lighter elements.
05:24This star was called LP40-365.
05:28It was moving so fast
05:30that it literally left our galaxy.
05:33Scientists therefore thought
05:35that it had been ejected by a cosmic disaster.
05:38For example, a supernova.
05:40Today, astronomers claim that the star,
05:43which was previously considered a white dwarf,
05:46was actually a stellar fragment,
05:48a kind of residue caused by a supernova explosion.
05:52The explosion must have been so powerful
05:54that it pushed LP40-365 very far out of the galaxy.
06:00This star fragment continues to turn slowly around its axis.
06:04Thanks to this observation,
06:06astronomers can confirm the fact that LP40-365
06:11is actually only a space debris,
06:13and not an entire star.
06:15But such a conclusion means
06:17that it would have been a witness to a supernova.
06:20Even if this event occurred at the speed of light,
06:23it is the entire composition of this space object that has been modified.
06:27Most stars are mainly composed of helium and hydrogen,
06:31but LP40-365 is different.
06:35It contains heavy elements,
06:37magnesium, oxygen and neon.
06:39It is undoubtedly the supernova
06:41that added its atoms to the composition of this star.
06:44Astronomers also consider
06:46that all the heavier elements than helium are metals.
06:49This means that after being a witness to the supernova,
06:53LP40-365 has become metallic.
06:57Our space traveler lights up
06:59and then darkens every 8 or 9 hours.
07:02This could mean that it emits pulsations.
07:04But in general,
07:06stellar pulsations are much less regular.
07:09A more plausible explanation
07:11is that the surface of the star is irregular.
07:13It is the rotation of the star
07:15that would cause these differences in brightness.
07:17Now let's move on to another curious space corse.
07:21This is the 18th brightest star in the night sky,
07:24called Fomalhaut.
07:26If you observe it with a telescope,
07:29you will be confronted with a terrifying spectacle.
07:32It is not surprising that it is nicknamed
07:34the Eye of Sauron.
07:35A ring of dust and debris surrounds it,
07:38which gives it the appearance of a giant eye
07:40that looks straight into your soul.
07:42This intimidating star
07:44has a mass more than twice that of our sun
07:47and is 25 light-years from Earth,
07:50which is not so far
07:52if we consider the distances in space.
07:54There is also a star that tears itself apart.
07:57It has a beautiful name,
07:59Vega.
08:00At first glance, it seems normal.
08:02Big, bright and quite young.
08:05But the more we advance in time,
08:07the more it becomes bizarre.
08:09For example, it is not really round.
08:11It looks like an egg.
08:13The reason may be that it rotates so fast
08:15that it ends up deforming.
08:17This has led to temperature variations on its surface.
08:21In addition, it reaches 93% of the maximum speed
08:25that a star of this size can tolerate,
08:27i.e. 273 km per second.
08:31Astronomers do not know exactly
08:33why Vega rotates so fast
08:35that it almost tears itself apart.
08:37Mira is sometimes one of the weakest stars
08:40and sometimes one of the brightest in the night sky.
08:43This system is actually made up of two stars.
08:46One of them is a red giant
08:48that once looked like our sun.
08:51The other is a white dwarf.
08:53The red giant constantly gets rid of its external layers,
08:57creating a cloud of debris around the system.
09:00This phenomenon could be the cause
09:02of the regular darkening of the stars.
09:04It could also explain why the intervals
09:06between these periods of darkening are not regular.
09:09But the most interesting thing is
09:11that this binary star has a tail
09:13similar to that of comets.
09:15Transcribed by ESO. Translated by —