Glossary term: Enana blanca
Description: Se espera que las estrellas con una masa de hasta ocho veces la del Sol terminen su vida como enanas blancas. Esto incluye a nuestro Sol. Las enanas blancas tienen densidades muy elevadas, y una enana blanca típica podría tener la masa del Sol comprimida en una bola ligeramente mayor que el tamaño de la Tierra. Una enana blanca ya no produce energía a partir de reacciones nucleares en su núcleo, sino que brilla gracias a la energía residual. Las más calientes parecen azules o blancas debido a la energía que irradian a causa de las altísimas temperaturas de su superficie. El núcleo de una enana blanca podría estar compuesto de helio o de carbono-oxígeno u oxígeno-neón-magnesio, dependiendo de la masa inicial de la estrella. No se contrae bajo su propia gravedad debido a la resistencia en su interior provocada por la presión de degeneración de los electrones, un fenómeno cuántico. La presión de degeneración solo puede sostener enanas blancas con masas de hasta 1.4 veces la masa del Sol. Los remanentes estelares con masas superiores a este límite (conocido como límite de Chandrasekhar) son estrellas de neutrones o agujeros negros.
Related Terms:
- Agujero negro
- Estrella de neutrones
- Evolución estelar
- Remanentes estelares
- Electrón
- Clase de luminosidad
See this term in other languages
Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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In Other Languages
- Árabe: الأقزام البيضاء
- Bengalí: সাদা বামন
- Alemán: Weißer Zwerg
- Inglés: White Dwarf
- Francés: Naine blanche
- Italiano: Nana Bianca
- Japonés: 白色矮星 (external link)
- Portugués de Brasil: Anã Branca
- Chino simplificado: 白矮星
- Chino tradicional: 白矮星
Related Media
Sirius A with his faint white dwarf companion Sirius B
Caption: This Hubble Space Telescope image highlights Sirius, the brightest star in Earth’s night sky, appearing as an intensely luminous object at the center with prominent cross-shaped diffraction spikes. These spikes, along with the saturated glow around the main star, are caused by the Sirius' light being spread out by the telescope and camera used to make this image. Slightly below and to the left of the main star, a tiny point of light marks Sirius B, a much dimmer object captured thanks to Hubble’s high sensitivity.
Sirius A is an A-type star, known for its high surface temperature and strong white-blue light, while Sirius B is a compact white dwarf, the dense remnant of a star that has exhausted its nuclear fuel. Together, they form a well-known Binary star system located about 8.6 light-years from Earth.
Sirius B was originally a higher mass and brighter star that burned through its hydrogen fuel more quickly than Sirius A. This led to Sirius B evolving into a red giant and eventually ending its life as a planetary nebula, leaving only the remains of its core as a white dwarf orbiting Sirius A.
Credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester)
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Related Diagrams
Diagrama Hertzsprung-Russell
Caption: Este diagrama muestra la temperatura y luminosidad de diferentes estrellas. El tamaño de cada punto representa el radio de la estrella y su color es el que vería el ojo humano. El color de las estrellas oscila entre un azul apagado y un naranja rojizo apagado. Ninguna estrella tiene un color puro como el rojo, el verde o el azul, ya que los espectros de las estrellas incluyen luz de muchos colores diferentes. Sin embargo, las estrellas más rojas suelen denominarse rojas y las más azules, azules. La muestra de estrellas utilizada para hacer este diagrama se eligió para mostrar una amplia gama de estrellas de diferentes tipos, por lo que el número relativo de cada tipo de estrella no es representativo de la frecuencia con la que cada tipo se encuentra.
Desde arriba a la izquierda hasta abajo a la derecha hay una larga línea de estrellas que queman hidrógeno en sus núcleos. Ésta es la llamada secuencia principal. En esta línea se encuentran las estrellas Mintaka, Achernar, Sirio A, el Sol y Próxima Centauri. Los objetos situados alrededor de Próxima Centauri, en el extremo inferior derecho de la secuencia principal, se denominan enanas rojas. En la parte inferior derecha de las enanas rojas se encuentran Teide 1 y Kelu-1 A. Estos dos objetos son enanas marrones, objetos de masa demasiado baja para tener núcleos lo suficientemente calientes como para fusionar hidrógeno durante un periodo de tiempo prolongado. Como no queman hidrógeno, las enanas marrones no se consideran estrellas de la secuencia principal. El nombre de enana marrón no está relacionado con su color.
Por encima de la secuencia principal se encuentran las subgigantes, gigantes y supergigantes. Se trata de estrellas que han terminado de quemar hidrógeno en su núcleo y han evolucionado hasta convertirse en objetos de mayor tamaño. El brillo de una estrella depende de su temperatura y tamaño, de modo que las gigantes son más brillantes que las estrellas de radio más pequeño pero con la misma temperatura. Con el tiempo, estos objetos se acercarán al final de su vida y atravesarán una fase de nebulosa planetaria o se convertirán en supernovas. Las estrellas que terminan su vida con una fase de nebulosa planetaria se convierten en un tipo de remanente estelar denominado enana blanca. Estos objetos son mucho más pequeños que las estrellas de la misma temperatura, por lo que son más débiles y se encuentran muy por debajo de la secuencia principal. Las estrellas que terminan su vida como supernovas se convierten en agujeros negros o estrellas de neutrones. Éstas no se muestran en este gráfico.
Credit: IAU OAE/Niall Deacon
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Stellar Evolution
Caption: This diagram shows the life cycle of stars of different masses. The mass of the different types of star increases from bottom to top with time going from left to right.
The life cycle of a star depends on its mass, with lower mass stars have longer lifetimes. All stars form from clouds of gas that collapse under their own gravity. As the star collapses, its core becomes hotter and denser. If the star has a mass greater than 0.08 solar masses (0.08 times the mass of the Sun), the pressure of the star’s mass pushing down on its core creates a high enough core temperature for hydrogen fusion to ignite. This burns hydrogen into helium in the star’s core, providing a heat source to power the star and to stop its core from collapsing further. If the collapsing object has a mass below 0.08 solar masses then it does not ignite hydrogen fusion in its core. It continues to cool and slowly contract. Such substellar objects are known as brown dwarfs, shown here in the lowest row.
After stars have formed, they burn hydrogen in their cores and begin their so-called main sequence phase. The most massive stars (>25 solar masses, shown here at the top) have very high core temperatures and thus burn through their hydrogen fuel more quickly. This means they may only spend a few million years on the main sequence burning hydrogen in their cores. Once the hydrogen in the core is exhausted the star’s core contracts, becomes hotter and helium burning starts in the core. While the core contracts, the outer layers of the star expand and it becomes a supergiant. For the most massive stars strong stellar winds strip off the cooler outer layers, leading to the star being very large and very hot, a blue supergiant. Once helium is exhausted in the core, carbon is burned, and then heavier elements. Eventually the star ends with an iron core. Fusing iron into heavier elements does not generate energy so at this point fusion stops in the core. Once this core of iron is massive enough, it and the surrounding matter suddenly collapses to form a black hole and the outer layers are flung off in a supernova explosion.
Slightly lower mass stars (between 8 and 25 solar masses, seen here second top) evolve in a similar way although they do not have strong enough winds to push their outer layers away and become blue supergiants, instead it evolves into a red supergiant. While such stars also collapse and create supernova explosions. The remnant of the star’s core is not massive enough to collapse into a black hole. Instead, its electrons and protons combine to form neutrons and it is supported by a quantum mechanical effect called neutron degeneracy pressure. This results in the remnant of the star being a tiny neutron star, several solar masses in mass but only a few kilometres across.
For stars similar in mass to the Sun (between 0.4 and 8 solar masses, seen here in the middle row), the star burns hydrogen in its core until the hydrogen in its core is exhausted. At this point a hydrogen burning shell forms around the core. Eventually the core will become hot enough to burn helium into carbon and oxygen. After this the star is left with a carbon and oxygen core surrounded by shells burning helium and hydrogen. These shells are unstable producing thermal pulsations that convulse the star. Eventually these pulsations become so extreme that the star’s outer layers are thrown off. This leaves the carbon and oxygen core as a white dwarf supported by electron degeneracy pressure. The outer layers of the star form what is known as a planetary nebula (which doesn’t actually have anything to do with planets despite the name).
The lowest mass stars (seen here in the second bottom row) are so low in mass that their evolutionary timescales are much longer than the age of the universe. This means that none have evolved beyond the main-sequence. Low mass stars are fully convective meaning material in the core is constantly being mixed with material above. This means that all the hydrogen in the star would eventually be burned in the core, but this will take trillions of years.
Credit: Danielle Futselaar/IAU OAE
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