Does HD 190412 C white dwarf turn into a diamond? Discover the first observational evidence of crystallization! | sorae universe portal site

「white dwarfIt is sometimes referred to as the “largest diamond in the universe.” Strictly speaking, white dwarfs found in the current universe do not crystallize like diamonds, so strictly speaking, the research team of Alexander Wiener et al. said a white dwarf at a distance of 104 light-years.HD 190412 cWe noticed evidence that crystallization had begunThis is the first time that crystallization of a white dwarf has been confirmed from direct observations.He is (※ 1) 。

*1 … In 2004, research results were published that estimated that about 90% of the white dwarf “BPM 37093 (V886 Centauri)” had crystallized, but this was based on stellar earthquake data. It is a modeling study based on indirect evidence. In contrast, the current study of HD 190412 C was extrapolated from direct observations of the light emitted by the white dwarf.

A white dwarf is a celestial body that originated from a star as light as the Sun and does not explode as a supernova during the red giant phase. It is a compressed star in which gas and dust are ejected from the outer layer, leaving only a solid core (the nucleus, the central nucleus), and the nuclear fusion reaction stops in the center. Since the mass of the sun is confined to the size of the Earth, the white dwarf is compressed by the great gravity, and the carbon atoms shrink and oxygen, which are the two main components, to the max. (※ 2) 。

* 2 … The composition of the “elements” that make up a white dwarf changes depending on the mass of the parent star. The most common composition of a white dwarf is carbon and oxygen, but white dwarfs of light stars are mostly composed of helium, while white dwarfs of heavy stars are said to be composed mostly of neon and magnesium.

A white dwarf is a “dead star” that only retains residual heat when the star’s core is stationary and does not generate new heat. As the temperature decreases, the arrangement of the atoms that make up the white dwarf changes from the center outward in order, from a random state to an aligned state, which is thought to cause crystallization. White dwarfs are called “diamonds” because they are believed to form crystals of carbon atoms under pressure. and high temperature. (※ 3) 。

* 3 … However, since the environment of the white dwarf is extremely high in temperature and pressure, it is not known whether the inner part is really a diamond or the appearance of another crystal structure.

It is said that it will take 1,000 trillion years for the entire white dwarf to cool down. Our universe is only 0.001% of its age, so a white dwarf that has fully crystallized into a diamond does not yet exist in our universe. However, since there are white dwarfs in the early stages of cooling in the current universe, it is not surprising that they would start some crystallization.

So how do we find evidence that crystallization has begun in white dwarfs? Fenner and his colleagues found evidence of a relationship between HD 190412 C and the celestial bodies around it.

HD 190412 C is one of the objects in the quadruple star system HD 190412, the other three of which are all stars. Stars and white dwarfs have independent methods for calculating age, and several methods can be used to narrow down the age difference. The age of a white dwarf can be estimated based on its surface temperature, or “coolness”.

However, when crystallization occurs inside the white dwarf, heat from the crystallization (latent heat) is released and the white dwarf is heated up. The heat of crystallization displaces the estimated age from the surface temperature, making the white dwarf appear “younger” than it actually is. This discrepancy in the estimated age could be concrete evidence that crystallization has occurred.

As a result of the observations, the entire HD 190412 star system is estimated to be about 7.3 billion years old, while HD 190412 C is estimated to be about 4.2 billion years old, including the time it was a star before becoming a star. A white dwarf. The large gap of 3.1 billion years in the age of the entire star system is thought to be caused by the reheating of HD 190412 C, which makes it appear younger than it actually is. (※ 4) . This is strong evidence that crystallization has begun within. Based on our observations, HD 190412 C is estimated to have crystallized in about 65% of the central part.

*4… The original star that produced HD 190412 C was very massive, estimated to have lived about 290 million years. For this reason, the time before it becomes a white dwarf is considered to be roughly within the 3.1 billion year gap.

However, the estimated age of the entire star system varies depending on the calculation method used, leaving a wide margin of plus or minus 1.9 billion years from an estimate of 3.1 billion years. In order to speculate in detail about the interior of a white dwarf, the uncertainty in the age of the star system HD 190412 must be within a billion years. You can’t. In addition, the effect of separating a secondary component (Neon-22) present in the interior of the white dwarf as it crystallizes is said to further decrease the cooling rate for about a billion years. The implications of this are also noted.

However, the fact that there is evidence of crystallization in a white dwarf at a short distance of about 104 light-years from Earth indicates that similar phenomena occur in other white dwarfs. By observing a large number of white dwarfs, we may be able to learn more specific things about the phenomena that occur inside white dwarfs.

source

• Alexander Viner and others. A crystallized white dwarf in a Sirius-like quadruple system. (arXiv)
• Bob Yerka. “A White Dwarf’s Journey to Crystallization into a Celestial Diamond”. (Phys.org)
• Michelle Star. “The white dwarf star enters the age of crystallization and turns into a “cosmic diamond.” (Science alert)
• HM Van Horn. “Crystallization of white dwarfs”. (The Astrophysical Journal)
• Kanaan et al. “Whole Earth Telescope observations of BPM 37093: A seismic test of the crystallization theory in white dwarfs”. (astronomy and astrophysics)

Text: Rare Aya