00:00Viewed, it would seem that two giant stars have been surprised in full romantic kiss.
00:05Although it may seem to be only paparazzi swans at first glance,
00:10it is actually a fascinating cosmic phenomenon discovered by an international team of astronomers.
00:17The life cycle of a single star is relatively simple.
00:21They are born in huge gas regions of space, burning their fuel,
00:25then, at some point, they explode in supernovas.
00:29But when stars are born close to each other,
00:33their mutual gravitational attraction can captivate them in what seems to be an eternal dance.
00:40Sometimes, they get so close that they almost seem to touch each other.
00:45These stars can spend billions of years spinning around each other.
00:49But their kiss only lasts a few million years, which is only a wink at the scale of the cosmos.
00:56Leonardo Almeida, the main author of this study,
01:00set out to find binary stars trapped in this cosmic kiss.
01:05He focused his research on the Nebula of Tarantula,
01:08a magnificent region of star formation located in the Large Magellanic Cloud,
01:12160,000 light-years from our planet.
01:15And there, he discovered the sparkling binary star system,
01:18called VFTS 352, which stood out from the others.
01:24The two discovered stars were quite large and almost identical in size.
01:29Together, they form a mass about 57 times greater than that of our Sun.
01:34Before that, only three other large-mass binary systems had been discovered.
01:39Since these two stars were so close,
01:42they generated an intense gravitational attraction
01:46that made them orbit around each other at a stupefying rate of one revolution per day,
01:51separated by barely 12 km.
01:54With such proximity, they formed a bridge allowing their stellar fuel to mix,
02:00thus sharing nearly 30% of their total volume.
02:03The temperatures of this system were also unparalleled
02:06and reached 41,000 degrees.
02:10At first, it seems that the internal mixture of their energy
02:13could allow these stars to live longer,
02:16by burning more fuel over prolonged periods.
02:19But this benefit would only be temporary.
02:22Two probable scenarios are drawn for their fate.
02:26They could merge to form a giant star, which would explode into a supernova,
02:31or they could explode separately
02:34and end their days as black holes orbiting around each other.
02:41If they merged, this process would take about 600,000 years,
02:45while if they became a system of binary black holes,
02:48they could continue to burn for another 3 million years.
02:51However, the two scenarios would ultimately lead to their destruction,
02:55unless they turned into two distinct black holes,
02:59drifting in opposite directions through the vastness of space,
03:03a possibility that is also conceivable.
03:08Recently, astronomers from all over the world attended a stunning show.
03:12Jupiter and Venus, the two brightest planets in the night sky,
03:17were so close together that they seemed about to collide or kiss.
03:22At least, that's what it looked like from Earth.
03:25In reality, they are still separated by 643 million kilometers.
03:31Another fascinating subject for astronomers concerns the G objects.
03:35They are celestial objects that look like clouds of dust and gas
03:39but behave like stars.
03:43In the center of our galaxy, there is a supermassive black hole,
03:46Sagittarius A, with a mass 4 million times higher than that of our Sun.
03:51And recently, scientists discovered two mysterious objects,
03:55called G objects, close to this black hole.
03:58They are G1 and G2 objects.
04:02The most likely theory is that G2 is made up of two stars
04:06orbiting around the black hole in tandem
04:08before merging into a single huge star
04:11enveloped in an exceptionally thick cloud of gas and dust.
04:16When G2 approached the closest to the black hole,
04:19it emitted a strange signature, stretching and losing a large part of its gas.
04:24As it approached the black hole, it lost its outer envelope
04:29and became more compact.
04:33What particularly excites astronomers about G objects
04:37is the material that is ripped off by tidal forces
04:40when it passes near the central black hole.
04:43This material inevitably ends up being sucked by the black hole,
04:47creating a real pyrotechnic show.
04:51This happens because the material consumed by the black hole heats up
04:55and emits radiation before disappearing through the event horizon.
04:59This horizon is the formidable limit of a black hole,
05:02beyond which nothing can escape.
05:07It now seems that scientists have discovered four other G objects,
05:11G3, G4, G5 and G6.
05:14All are located less than 0.13 light years from the black hole.
05:18It could be that these six objects once belonged to binary systems
05:22that have come together until they merged
05:25due to the powerful gravity of this massive black hole.
05:28Usually, it takes more than a million years
05:31for the fusion process between two stars to end.
05:34We hope to discover more G objects,
05:36because it gives us one of the rare opportunities
05:38to study the behavior of matter close to a supermassive black hole
05:41without it being immediately swallowed.
05:44At least, for the moment.
05:47Have you heard of variable stars?
05:50When we look at the sky,
05:52we often imagine that stars are points of immutable and eternal light.
05:56But if some stars seem to be constant,
05:59others change their luminosity over time, hence their name variable stars.
06:04Some of them go out and come back on for periods
06:07ranging from a few days to several years.
06:09These variations are not visible to the naked eye.
06:12Only astronomers, thanks to their sophisticated equipment
06:15and their long-term observations, are able to detect them.
06:20And what about vampire stars?
06:22Imagine two stars in a binary system,
06:25a red giant and a white dwarf
06:27spinning around each other like cosmic ballet dancers.
06:32The red giant, formerly a vibrant star,
06:35has aged and weakened.
06:39Its external layers of hydrogen,
06:41formerly firmly held by its gravity,
06:43have relaxed, making it vulnerable to the greed of the small and dense white dwarf.
06:49The white dwarf, nicknamed vampire star,
06:52convoys the fuel of its big sister
06:54and sees an unexpected opportunity there.
06:58As they dance together,
07:00the vampire star uses its powerful gravitational force
07:03to siphon the hydrogen from the red giant's external layers.
07:07It then shines in a blue hue
07:10and seems to rejuvenate and overflow with energy
07:12as its rider turns gray.
07:17But there are more than vampire stars.
07:19There are also zombie stars.
07:22Sometimes, when a red giant explodes,
07:25it does not disintegrate completely.
07:28Instead, a remnant of the white dwarf subsists after it,
07:32comparable to a zombie star that was dead but has now come back to life.
07:38However, this zombie star does not have a brain like in the movies,
07:42but hydrogen itself that the vampire star has been stealing from it since the beginning.
07:46If the zombie star is close enough to its former partner,
07:50it will begin to suck up matter to resuscitate its nucleus.
07:55It will then become a hydrogen bomb,
07:57ready to explode in a formidable show of cosmic revenge.
08:04It is a fascinating phenomenon that we generally do not detect
08:07because these explosions are much weaker than the usual supernovas.
08:11But when they occur,
08:13the detonation that results from it is truly daunting
08:17and destroys both the vampire star and its zombie twin.
08:21It would seem that vampires and zombies
08:23are not just fictional characters after all.
08:27Not only are we made of star dust,
08:29but we also have more in common with stars than we thought.
08:34Thus, stars also like to stay in groups with their loved ones,
08:38and most stars prefer to travel through the universe in clusters.
08:42These stellar clusters are groups of stars gravitationally linked to each other.
08:47Those that are there are generally the same age and the same type,
08:51sharing the same hobbies and the same centers of interest.
08:54Perhaps they even have a more active social life than ours.
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