00:00Tiny black holes, able to pierce entire planets, could cross terrestrial objects right now.
00:08Could these objects include your own body?
00:12Most likely.
00:13The key lies in the fact that, theoretically, black holes can vary considerably in size,
00:19ranging from those weighing billions of times the mass of the sun,
00:23to others, tiny, much lighter than a simple trombone.
00:27These tiny black holes, called primordial black holes,
00:30could precisely be those that cross your arm or your leg right now.
00:34The primordial black holes, being so tiny, have left no direct evidence of their existence.
00:41However, a group of physicists proposed an original method,
00:45looking for their traces in everyday objects.
00:48Although they are incredibly small, they would still be large enough to be observed with a microscope.
00:55The probability of detecting these traces remains small,
00:58but their research would require very little resources.
01:01What makes primordial black holes so unique?
01:04They could have formed shortly after the Big Bang, in the extreme conditions of the primordial universe.
01:09Even more fascinating, they could have constituted an essential part of black matter,
01:14this enigmatic substance representing 85% of all the matter in the universe.
01:20Contrary to black holes from the collapse of stars or gas clouds,
01:24primordial black holes would probably have been born from extremely dense areas of subatomic particles,
01:30such as protons, neutrons or electrons, during the first fractions of a second of the universe.
01:36These black holes could have the mass of a mountain,
01:39while being as small as a hydrogen atom,
01:42which makes them particularly difficult to detect.
01:45To better orient their research,
01:47scientists have established calculations,
01:49aiming to predict the clues that could leave these primordial black holes.
01:53An interesting hypothesis is that planets or asteroids could capture these black holes,
01:58which would then siphon inside their celestial bodies.
02:01If the core of a planet or an asteroid is liquid,
02:05a captured black hole could absorb this denser matter.
02:09After swallowing the core, the black hole could escape as a result of a shock or impact.
02:14The result would be an empty planetary shell.
02:17If the object is relatively small, about a tenth of the size of the Earth,
02:22it could remain intact long enough to be detected by astronomers.
02:26On the other hand, larger but empty planets would collapse under the effect of their own gravity.
02:32This offers another way to identify primordial black holes.
02:36If a small planet or a moon has a density much lower than normal,
02:41it could indicate that it is hollow and can be sculpted by a black hole.
02:45We may not even need to look for clues in space anymore.
02:49Scientists have also determined what would happen if a primordial black hole crossed an object on Earth.
02:56For example, a black hole of about one ton could dig a tunnel through matter,
03:01creating an opening about 700 times thinner than a human hair.
03:06What is even more fascinating,
03:08if an object moves at a speed greater than that of sound in a material,
03:13the molecules of this material do not have time to react.
03:16And the material does not tear.
03:18It's a bit like comparing the throw of a stone against a window, which breaks it,
03:22to the shot of a bullet, which leaves only a clear and precise hole.
03:26Researchers could analyze rocks dating back a billion years,
03:30or even structures dating back a few centuries,
03:32to find traces of these microscopic passages.
03:35However, there is a downside.
03:37The chances of finding such a tunnel are extremely low.
03:41According to researchers' calculations,
03:43the probability that a primordial black hole crosses a particular rock,
03:46one billion years old, is only 1 in 10,000.
03:49Despite this, the simplicity of the test justifies that we are interested in it.
03:53Now let's address the risks for you, or for your dog,
03:57if a primordial black hole were to cross you.
04:00Let's be clear.
04:01The chances of this happening during your life, or that of your dog,
04:06are astronomically low.
04:08But if it were to happen, no need to panic.
04:11Unlike planets or ancient rocks,
04:14human or animal bodies only suffer from a low internal tension.
04:18It seems difficult to believe that a primordial black hole
04:21can pass through you without you noticing it.
04:24However, while you are watching this video,
04:27thousands of billions of neutrinos cross your body at the speed of light,
04:31and you feel absolutely nothing.
04:33These particles are nicknamed ghost particles,
04:36and this nickname is not trivial.
04:38Maybe one day, we will also nickname the primordial black holes
04:42as ghost black holes.
04:44Although all this may seem highly speculative,
04:47research of this kind is crucial.
04:49Many ideas, which used to seem extravagant,
04:53are now an integral part of science.
04:56A creative thought is essential to solve the greatest mysteries of physics,
05:00like the exact nature of black matter.
05:03For 80 years, the brightest minds have been tackling these problems
05:07without finding a solution.
05:08Thus, it is not enough to bring small modifications to existing theories.
05:13We must completely rethink our way of addressing these questions.
05:16Let's go back to the subject of black holes.
05:18Astronomers have recently discovered a low-mass black hole
05:22that intrigues the scientific community.
05:24Indeed, there is a notable absence of black holes
05:28with a mass between 2 and 5 times that of the Sun.
05:32Scientists do not know if these small black holes are simply difficult to detect
05:36or if they are truly rare.
05:39This new discovery could well offer clues to solve the mystery.
05:43This black hole is located precisely at the heart of this gap,
05:47with a mass equivalent to about 3.5 times that of the Sun.
05:51Researchers have detected it thanks to its companion,
05:54a giant massive red star located at about 5,800 light-years from Earth.
06:00Although this star is only 2.5 times more massive than the Sun,
06:05it is about 13 times larger and shines 100 times more intensely.
06:10Astronomers made this discovery
06:12by relying on data from the Gaia spacecraft of the European Space Agency,
06:16which maps the movements of more than a billion stars in our galaxy.
06:20Gaia excels in the surveillance of movements in two dimensions of stars,
06:24lateral and vertical.
06:26However, observations using a terrestrial telescope
06:30were necessary to determine the movements of the red giant towards Earth.
06:35These observations revealed a surprising fact.
06:38Two objects were moving together in a large orbit, almost circular.
06:42This orbit aroused questions.
06:44The black hole should have formed following a supernova,
06:48the extremely bright explosion of a star,
06:51which would then have lost a large part of its mass very quickly.
06:54Such a loss should have disrupted the orbit.
06:57According to a fundamental rule of orbital mechanics,
07:00if a binary system loses half of its mass,
07:03the two objects should separate.
07:05Even if the loss of mass may not have been as drastic in this specific case,
07:09it should have produced an elongated and oval orbit,
07:12not an almost circular orbit, like the one observed.
07:16Another problematic point for this theory
07:18is the behavior of supernova explosions,
07:21which are not always perfectly symmetrical.
07:23If the explosion had been unbalanced,
07:25the residual black hole could have deviated from its trajectory
07:29and separated from its companion star.
07:32This could explain the rarity of small observed black holes.
07:35Many could land alone, in the galaxy, invisible and undetected.
07:40This is precisely what makes the discovery of this binary system so intriguing.
07:45Another hypothesis also deserves to be considered.
07:48It is possible that the black hole and the red giant
07:51initially belonged to a triple stellar system,
07:54with two massive stars in the center
07:57and the red giant orbiting more outside.
08:00The current black hole could then have formed
08:03after the fusion of the two central stars.
08:05It is not excluded either that the invisible object of the system
08:08is actually composed of two small compact objects,
08:11rather than one.
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