00:00Look at this flamboyant monster. It's a white dwarf.
00:04These stars are known to swallow objects that pass by them.
00:07And, one day, these objects could well be the planets of our own solar system.
00:12According to a new study, some regions of the solar system will be attracted by a white dwarf,
00:17then crushed and finally reduced to a fine dust, like coffee beans in a blade mill.
00:22Do you like this analogy?
00:24The state of a white dwarf corresponds to the last stage of the life of a star.
00:28It is a small and very dense object, usually the size of a planet,
00:33the result of a low mass and the exhaustion of all the available nuclear fuel in its core,
00:38and the loss of its outer layers.
00:41When our sun turns into a white dwarf, which will not be long in coming,
00:46it will destroy the asteroids and the moons around Mars and Jupiter.
00:50They will be pulverized by its gravity.
00:53The Earth, it, will be swallowed before the sun even turns into a white dwarf.
00:57But this will not happen before 6 billion years.
01:01Researchers working on this subject have come to these conclusions
01:04by observing what happened to space bodies, asteroids, moons and planets
01:09that passed near three white dwarfs.
01:12For 17 years, they observed and analyzed transits,
01:15that is, the moment when the luminosity of a white dwarf decreases
01:19because a stable-orbit object passes in front of it.
01:22In the case of white dwarfs, we can predict these transits
01:25and use them to study the stars themselves
01:28and the celestial objects that pass in front of them.
01:32Thus, when an object approaches too close to a white dwarf,
01:35the immense gravity of the star tears it into increasingly smaller fragments.
01:39The scientific team has also discovered that the transits of these debris are chaotic.
01:44In addition, they usually have a strange shape,
01:47which means that they do not cease to disintegrate.
01:50The first white dwarf used to study this process
01:54seemed stable and relatively calm over the past few years.
01:58But scientists have discovered evidence of a major catastrophic event
02:02that occurred around 2010.
02:05The next star darkens irregularly every few months,
02:09before lighting up again.
02:11The behavior of the third white dwarf was close to theoretical predictions.
02:15Its transits varied in number, shape and depth.
02:18But the latest study has shown researchers
02:21that these transits have now completely ceased.
02:24This is evidence of the unpredictable nature of transits.
02:27One minute, you see them.
02:29The next moment, they have disappeared.
02:31The reason could be the chaotic environment in which they occur.
02:35As for our solar system, and our planet in particular,
02:38its destiny is rather dark.
02:40The Earth will be swallowed up by the sun in expansion
02:43before our star even turns into a white dwarf.
02:46In the rest of the solar system, further from the sun,
02:49some asteroids located between Mars and Jupiter,
02:52as well as some of Jupiter's moons, will also be destroyed.
02:55They may indeed be displaced and get too close to the white dwarf.
03:01However, astronomers are not 100% sure
03:04that this is exactly what should happen in our solar system.
03:08We just have to wait and see how things evolve
03:11over the next 6 billion years.
03:13As for the white dwarfs,
03:15scientists have recently discovered one
03:18whose surface has a strange metallic scar.
03:21This spot could be formed when the star has crumbled
03:25and swallowed up a tiny planet revolving around it.
03:28The white dwarfs, which have traces of metal in their atmosphere,
03:32are not uncommon.
03:33These traces are caused by planets falling on the stars
03:36due to their immense gravity.
03:38Experts have long thought that these metals
03:40should be evenly distributed on the surface of these polluted white dwarfs.
03:44But a new study has led to the discovery of a white dwarf
03:47with a strange concentrated metal spot.
03:50This star was observed for two months
03:52using the Very Large Telescope installed in Chile.
03:55Researchers have discovered an opaque metal spot.
03:58It was located above one of the magnetic poles of the star
04:01and blocked part of its light during its rotation.
04:04Based on this observation,
04:06astronomers concluded that the material
04:08could have been attracted to the star
04:10by the powerful magnetic field of the latter.
04:13This process is similar to the one
04:15that causes the auroras of Boreal on Earth,
04:17where charged particles follow the magnetic field to the surface.
04:23The planet destroyed by the white dwarf
04:25was very likely small,
04:27the same size as the asteroid Vesta in the solar system,
04:30which is only 525 km in diameter.
04:33These debris are now clearly visible at the surface of the high star.
04:36It is therefore easier for researchers
04:38to examine the geochemistry of the planet
04:40before it is devoured.
04:42Such a study could even turn out
04:44to be one of the best ways to observe
04:46the small worlds located beyond the solar system,
04:48even if they have already disappeared.
04:50There could be many other bright stars like this one.
04:53The star in question was the first,
04:55but probably not the last.
04:57Even better, astronomers have already discovered
05:00two white dwarfs that seem to have similar scars.
05:04The repeated observation of these stars
05:06could help us to dig even more secrets
05:08and make other discoveries.
05:10Another strange white dwarf,
05:12discovered not so long ago,
05:14seems to have ceased to cool
05:16due to the formation of internal crystals.
05:20This discovery questions existing theories
05:23about the aging of stars
05:25as well as the methods of estimating their age.
05:27But scientists may have understood
05:29the reason for this phenomenon.
05:32White dwarfs are considered dead stars,
05:35that is, they do not cease to cool
05:38and that this process can generally
05:40not be reversed or interrupted.
05:42But in 2019, the Gaia satellite
05:45of the European Space Agency
05:47discovered a certain number of white dwarfs
05:49that had ceased to cool
05:51for more than 8 billion years.
05:53This could mean that some white dwarfs
05:55can generate a lot of additional energy
05:58and this goes against the classic theory
06:00of the dead star.
06:02At first, astronomers could not understand
06:05how this could happen.
06:07More than 97% of the stars of the Milky Way
06:10turn into white dwarfs.
06:12Astronomers have long thought
06:14that these stars were at the end of their lives.
06:16After exhausting their nuclear energy reserves,
06:18they cease to produce heat
06:20and cool down.
06:22The dense plasma they contain
06:24ends up freezing and the star solidifies from the inside.
06:26The whole process can take
06:28billions of years.
06:30But new data indicates
06:32that in some white dwarfs,
06:34this dense plasma does not cease to freeze.
06:36On the contrary,
06:38the solid crystals that form during the cooling
06:40become less dense
06:42and begin to float upwards.
06:44And so they move the liquid,
06:46heavier, downwards.
06:48The movement of this matter towards the center of the white dwarf
06:50releases gravitational energy.
06:52This energy is enough
06:54to interrupt the cooling process
06:56of the star for billions of years.
06:58This explanation actually corresponds
07:00to the properties of the white dwarfs
07:02that we have observed.
07:04But this is the first time
07:06that such a process is identified
07:08in a completely different type of star.
07:10And this is incredibly fascinating.
07:12We have here a completely new astrophysical phenomenon.
07:14But why does this happen
07:16in some stars and not in others?
07:18This probably depends
07:20on the composition of the object.
07:22Indeed, some white dwarfs
07:24come from the fusion of two different stars.
07:26When they collide
07:28and form a white dwarf,
07:30the composition of the star changes,
07:32and the formation of these floating crystals occurs.
07:34This discovery
07:36could force astronomers
07:38to review the methods they used
07:40until now to determine the age of the stars.
07:42Nowadays,
07:44we often use the state of a white dwarf
07:46as an age indicator.
07:48The colder a star is,
07:50the older we think it is.
07:52But today, we know that the cooling process
07:54of some dwarfs can be delayed.
07:56And this vacillates the certainties
07:58concerning the methods used.
08:00Some stars could be much older
08:02than we thought,
08:04with a gap of several billion years.
08:06This phenomenon recently discovered
08:08means that some of these stars
08:10are able to shine almost normally
08:12for billions of additional years.
08:14This complicates the measurements
08:16and questions the use of white dwarfs
08:18in the reconstruction of galactic history.
08:20Stay tuned.
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