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Naines brunes et planètes </a> </li> <li class="list-group-item "> <a class="d-block" title="NAINES BRUNES, Autres caractéristiques des naines brunes" href="/encyclopedie/naines-brunes/6-autres-caracteristiques-des-naines-brunes/"> 6. Autres caractéristiques des naines brunes </a> </li> <li class="list-group-item "> <a class="d-block" title="NAINES BRUNES, Bibliographie" href="/encyclopedie/naines-brunes/7-bibliographie/"> 7. Bibliographie </a> </li> </ul> <button class="btn btn-sm btn-universalis" data-bs-toggle="collapse" data-bs-target="#free-toc" aria-expanded="false" title="Afficher / masquer le sommaire"> <i aria-hidden="true" class="fa fa-fw fa-eye"></i> Sommaire </button> </div> <h1 class="mb-1"> <strong>NAINES BRUNES</strong> </h1> <ul class="pagination justify-content-center public-links "><li class="page-item active"><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 1" class="page-link" title="Abonnez-vous" data-loaded="true">1</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 2" class="page-link" title="Abonnez-vous" data-loaded="true">2</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 3" class="page-link" title="Abonnez-vous" data-loaded="true">3</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 4" class="page-link" title="Abonnez-vous" data-loaded="true">4</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 5" class="page-link" title="Abonnez-vous" data-loaded="true">5</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 6" class="page-link" title="Abonnez-vous" data-loaded="true">6</a></li></ul><div class="content paged type-article" ><div class="block_1" data-ucode="yC070700_0"><i class="anchor" id="yC070700_0"></i><p>Prédites par les théoriciens dans les années 1960, longtemps recherchées, découvertes en 1995, les naines brunes, qui constituent le chaînon manquant entre le monde des <a data-bs-toggle="popover" data-bs-content="La majorité des astres visibles dans le ciel sont des étoiles. Elles sont souvent groupées en associations et amas de quelques centaines de milliers d'étoiles, ceux-ci se groupant à leur tour en unités beaucoup plus grandes, les galaxies . Une galaxie typique contient de 10 milliards à 100 milliards d'étoiles, et l'on dénombre des millions de galaxies sur les images acquises par les ..." title="Article : ÉTOILES" href="/encyclopedie/etoiles/">étoiles</a> et celui des <a data-bs-toggle="popover" data-bs-content="Les planètes du Système solaire sont connues depuis l’Antiquité. Leur nombre a évolué en fonction des découvertes successives et n’est peut-être pas définitif. Les huit planètes connues sont, en s’éloignant du Soleil : Mercure, Vénus, la Terre, Mars, Jupiter, Saturne, Uranus et Neptune. Elles se trouvent toutes à proximité du plan de l’orbite terrestre (l’écliptique). L..." title="Article : PLANÈTES" href="/encyclopedie/planetes/">planètes</a>, soulèvent des questions fondamentales sur la formation de ces deux grandes familles d'astres. Les naines brunes sont très répandues dans notre Galaxie, où elles sont trois fois moins nombreuses que les étoiles. Leur contribution totale en masse est cependant environ trente-cinq fois plus faible que celle de ces dernières. L'espoir d'expliquer la masse manquante galactique par les naines brunes s'est envolé lorsque les progrès des techniques de détection ont permis de faire un recensement précis de ces objets.</p><div class="clearfix"></div></div><div class="block_1" data-ucode="yC070700_1"><i class="anchor" id="yC070700_1"></i><h2>Qu'est-ce qu'une naine brune ?</h2><p>Une naine brune est une étoile « ratée » qui ne peut maintenir de façon stable les réactions de fusion nucléaire de l'<a data-bs-toggle="popover" data-bs-content="L'hydrogène est un gaz inodore et incolore ; c'est le plus léger de tous les éléments chimiques. Son numéro atomique est égal à 1. Il perd son électron unique dans ses combinaisons avec les éléments non-métalliques ; il s'unit également avec les métaux pour donner des hydrures dans lesquels il peut jouer le rôle d'anion (H - ). Enfin les composés les plus nombreux et notamment tou..." title="Article : HYDROGÈNE" href="/encyclopedie/hydrogene/">hydrogène</a> caractérisant les débuts de l'évolution stellaire. Les étoiles naissent de l'effondrement gravitationnel de nuages de gaz et de poussière interstellaires, essentiellement composés d'hydrogène et d'hélium. Lors de la contraction d'un nuage, la proto-étoile s'échauffe, permettant aux régions centrales d'atteindre éventuellement la température critique de 3 millions de degrés nécessaire à la fusion de l'hydrogène. L'énergie colossale qui est libérée par ces réactions nucléaires permet d'arrêter la contraction gravitationnelle de l'étoile, laquelle atteint alors un régime d'équilibre quasi parfait où l'essentiel de la perte d'énergie due au rayonnement en surface est contrebalancé par la production d'énergie nucléaire en son centre.</p><div class="clearfix"></div><div class="media-container float-md-start me-2 col-md-3 text-center"><figure class="figure text-center w-100 mb-0 p-1" style="position: relative"><a data-ucode="PA083300" data-showMediaPlayer="1" class="protected media-reference-copy " title="Média : Taille d'une naine brune" href="/media/taille-dune-naine-brune-pa083300/"><img id="PA083300" loading="lazy" src="/typo3temp/assets/_processed_/4/1/csm_pa083300_370015be54.webp" class="figure-img rounded mx-auto media_resized" alt="Taille d'une naine brune - crédits : NASA/ CXC/ SAO" data-description="Conception d'artiste montrant les tailles comparées du Soleil, de la naine brune TWA 5B et de la planète Jupiter, de gauche à droite." data-copyright="NASA/ CXC/ SAO" width="1024" height="791" /></a><figcaption class="figure-caption"><p class="m-0 mt-1 fw-bold text-gray-700 text-truncate"> Taille d'une naine brune </p><p class="m-0 copyright text-sm text-gray-700 text-truncate"> NASA/ CXC/ SAO </p></figcaption></figure></div><p>Si la masse de la proto-étoile est trop faible, la température critique de fusion de l'hydrogène ne peut être atteinte avant que la matière ne devienne dégénérée, au sens quantique du terme. Lors de la contraction gravitationnelle, la densité augmente, les électrons se rapprochent les uns des autres, et deviennent dégénérés. Une pression dite de dégénérescence s'instaure, qui va s'opposer à la contraction gravitationnelle. Cette pression possède une propriété remarquable : elle ne dépend pas de la température (en mécanique classique, la pression est proportionnelle à la température). La matière dégénérée a alors un comportement paradoxal : lors d'une compression où densité et pression augmentent, la température diminue. Une future naine brune ne peut atteindre, lors de sa contraction gravitationnelle initiale, la température critique qui la ferait basculer dans le monde des étoiles. La masse critique en deçà de laquelle la fusion de l'hydrogène ne peut s'amorcer est déterminée théoriquement : elle est d'environ 0,07 masse solaire, soit 70 masses de Jupiter.</p><div class="clearfix"></div></div><div class="clearfix"></div></div><ul class="pagination justify-content-center public-links "><li class="page-item active"><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 1" class="page-link" title="Abonnez-vous" data-loaded="true">1</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 2" class="page-link" title="Abonnez-vous" data-loaded="true">2</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 3" class="page-link" title="Abonnez-vous" data-loaded="true">3</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 4" class="page-link" title="Abonnez-vous" data-loaded="true">4</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 5" class="page-link" title="Abonnez-vous" data-loaded="true">5</a></li><li class="page-item "><a href="/abonnement" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="page 6" class="page-link" title="Abonnez-vous" data-loaded="true">6</a></li></ul><div class="folio-block"><p class="folio-block-title text-center text-uc"><strong>La suite de cet article est accessible aux abonnés</strong></p><ul class="list-unstyled"><li><i class="fa fa-fw fa-check-circle"></i> Des contenus variés, complets et fiables</li><li><i class="fa fa-fw fa-check-circle"></i> Accessible sur tous les écrans</li><li><i class="fa fa-fw fa-check-circle"></i> Pas de publicité</li></ul><p class="text-center"><a href="/abonnement/" class="btn btn-cta text-uc" id="folio-button" data-matomo-category="Article" data-matomo-name="Folio" data-matomo-value="Block bottom">Découvrez nos offres </a></p><p class="text-center text-sm"> Déjà abonné ? <a href="/identification/" id="folio-login">Se connecter</a></p></div><div id="ad_mpuslot" class="pub-container text-center"><div class="pub-placeholder"></div></div><section class="mt-3 mb-5"><i class="anchor" id="C070700_AUTHORS"></i><p class="title-minor">Écrit par</p><ul class="list-group"><li class="list-group-item" data-dc-author="BARAFFE, Isabelle"><a title="Auteur : Isabelle BARAFFE" rel="author" href="/auteurs/isabelle-baraffe/"><strong>Isabelle BARAFFE</strong></a> : directrice de recherche au C.N.R.S., École normale supérieure, Lyon </li></ul></section><section class="mb-5"><div class="text-center mb-3 d-print-none"><a class="d-inline-flex flex-row justify-content-center align-items-center btn btn-light btn-large text-start" title="Carte mentale : NAINES BRUNES" href="/carte-mentale/naines-brunes/"><i class="fa fa-sitemap fa-rotate-270 me-1 fs-1 text-universalis"></i><p class="m-0"><strong class="fs-4">Carte mentale</strong><br /> Élargissez votre recherche dans Universalis </p></a></div></section> <section class="mb-5 article-classification" data-print-label="la classification" data-print-target=".article-classification"> <i class="anchor" id="yC070700_ROOT_LINES"></i> <p class="title-minor">Classification</p> <nav aria-label="Classification 1"> <ol class="breadcrumb"> <li class="breadcrumb-item"> <a title="Classification : Astronomie et astrophysique" href="/classification/astronomie-et-astrophysique/"> Astronomie et astrophysique </a> </li> <li class="breadcrumb-item active" data-dc-subject="Naines brunes"> <a title="Classification : Naines brunes" href="/classification/astronomie-et-astrophysique/naines-brunes/"> Naines brunes </a> </li> </ol> </nav> </section> <section class="mb-5 d-print-none"> <i class="anchor" id="yC070700_MEDIAS"></i> <p class="title-minor">Médias</p> <div class="row"> <div class="col-12 col-md-4 text-center p-1"> <figure class="figure text-center w-100 mb-0 p-1" style="position: relative"> <a data-ucode="PA083300" data-showMediaPlayer="1" class="protected media-reference-copy " title="Média : Taille d'une naine brune" href="/media/taille-dune-naine-brune-pa083300/"> <img id="PA083300" loading="lazy" src="/typo3temp/assets/_processed_/4/1/csm_pa083300_370015be54.webp" class="figure-img rounded mx-auto media_resized" alt="Taille d'une naine brune - crédits : NASA/ CXC/ SAO" data-description="Conception d'artiste montrant les tailles comparées du Soleil, de la naine brune TWA 5B et de la planète Jupiter, de gauche à droite." data-copyright="NASA/ CXC/ SAO" width="1024" height="791" /> </a> <figcaption class="figure-caption"> <p class="m-0 mt-1 fw-bold text-gray-700 text-truncate"> Taille d'une naine brune </p> <p class="m-0 copyright text-sm text-gray-700 text-truncate"> NASA/ CXC/ SAO </p> </figcaption> </figure> </div> <div class="col-12 col-md-4 text-center p-1"> <figure class="figure text-center w-100 mb-0 p-1" style="position: relative"> <a data-ucode="DE072320" data-showMediaPlayer="1" class="protected media-reference-copy " title="Média : Évolution de la luminosité de différentes étoiles et d'une naine brune" href="/media/evolution-de-la-luminosite-de-differentes-etoiles-et-dune-naine-brune-de072320/"> <img id="DE072320" loading="lazy" src="/typo3temp/assets/_processed_/0/8/csm_de072320_cd600a7523.webp" class="figure-img rounded mx-auto media_resized" alt="Évolution de la luminosité de différentes étoiles et d'une naine brune - crédits : Encyclopædia Universalis France" data-description="Évolution de la luminosité L (normalisée à la luminosité solaire actuelle L&odot;) d'étoiles de différentes masses (exprimées en masse solaire M&odot;) et d'une naine brune." data-copyright="Encyclopædia Universalis France" width="2000" height="1668" /> </a> <figcaption class="figure-caption"> <p class="m-0 mt-1 fw-bold text-gray-700 text-truncate"> Évolution de la luminosité de différentes étoiles et d'une naine brune </p> <p class="m-0 copyright text-sm text-gray-700 text-truncate"> Encyclopædia Universalis France </p> </figcaption> </figure> </div> <div class="col-12 col-md-4 text-center p-1"> <figure class="figure text-center w-100 mb-0 p-1" style="position: relative"> <a data-ucode="DE072321" data-showMediaPlayer="1" class="protected media-reference-copy " title="Média : Relation masse-rayon des étoiles et des naines brunes" href="/media/relation-masse-rayon-des-etoiles-et-des-naines-brunes-de072321/"> <img id="DE072321" loading="lazy" src="/typo3temp/assets/_processed_/a/e/csm_de072321_d92e4e796b.webp" class="figure-img rounded mx-auto media_resized" alt="Relation masse-rayon des étoiles et des naines brunes - crédits : Encyclopædia Universalis France" data-description="La courbe présente, pour les étoiles et les naines brunes, la relation théorique entre masse et rayon, en excellent accord avec les mesures de rayons stellaires, matérialisées par les points noirs. Rayons et masses sont exprimés en unités solaires. Les planètes géantes Jupiter et Saturne sont…" data-copyright="Encyclopædia Universalis France" width="2000" height="1485" /> </a> <figcaption class="figure-caption"> <p class="m-0 mt-1 fw-bold text-gray-700 text-truncate"> Relation masse-rayon des étoiles et des naines brunes </p> <p class="m-0 copyright text-sm text-gray-700 text-truncate"> Encyclopædia Universalis France </p> </figcaption> </figure> </div> </div> </section> <section class="mb-5 d-print-none learn-more"> <i class="anchor" id="yC070700_REFERENCES"></i> <p class="title-minor">Autres références</p> <ul class="list-group"> <li class="list-group-item"> <h3 class="fs-5 m-0 mt-1"> <a href="/encyclopedie/exoplanetes/#c23616"> <span class="rg">EXOPLANÈTES - </span><span class="rm">Méthodes de détection</span> </a> </h3> <ul class="list-inline list-inline-bullet mb-1 text-muted"> <li class="list-inline-item text-sm">Écrit par <span rel="author">Anne-Marie LAGRANGE</span> </li> <li class="list-inline-item text-sm">2 917 mots</li> <li class="list-inline-item text-sm">7 médias </li> </ul> <div class="d-none d-md-inline-block float-start me-3"> <a class="protected" title="Article : EXOPLAN&Egrave;TES - M&eacute;thodes de d&eacute;tection" href="/encyclopedie/exoplanetes/"> <img class="rounded shadow" loading="lazy" alt="Système formé du Soleil (ou autre étoile) et d’une planète (ou d’une exoplanète) - crédits : Encyclopædia Universalis France" width="125" height="125" src="/typo3temp/assets/_processed_/f/4/csm_de161182_f689cb3179.webp"/> </a> </div> <div class="snippet-content mt-3"> ...3,6 mètres de l’ESO au Chili. Ils ont permis de résoudre, c’est-à-dire séparer, des étoiles formant un système double très serré, puis de détecter des <a data-bs-toggle="popover" data-bs-content="Prédites par les théoriciens dans les années 1960, longtemps recherchées, découvertes en 1995, les naines brunes, qui constituent le chaînon manquant entre le monde des étoiles et celui des planètes , soulèvent des questions fondamentales sur la formation de ces deux grandes familles d'astres. Les naines brunes sont très répandues dans notre Galaxie, où elles sont trois fois moin..." title="Article : NAINES BRUNES" href="/encyclopedie/naines-brunes/">naines brunes</a> – astres de masse intermédiaire entre celle d’une étoile et celle d’une planète – en orbite autour d’étoiles. Leur successeur, plus perfectionné,... </div> </li> <li class="list-group-item"> <h3 class="fs-5 m-0 mt-1"> <a href="/encyclopedie/masse-cachee-masse-manquante-matiere-noire/#c23616"> <span class="rg">MASSE CACHÉE </span><span class="rm">ou </span><span class="rg">MASSE MANQUANTE </span><span class="rm">ou </span><span class="rg">MATIÈRE NOIRE</span> </a> </h3> <ul class="list-inline list-inline-bullet mb-1 text-muted"> <li class="list-inline-item text-sm">Écrit par <span rel="author">Marc LACHIÈZE-REY</span> </li> <li class="list-inline-item text-sm">3 644 mots</li> </ul> <div class="snippet-content mt-3"> ...presque étoiles » qui n'auraient jamais atteint une température suffisante pour que s'amorcent les réactions nucléaires caractérisant une véritable étoile. De tels objets, baptisés« naines brunes », auraient pu se former en abondance. Les planètes extrasolaires rentrent dans la même catégorie. </div> </li> <li class="list-group-item"> <h3 class="fs-5 m-0 mt-1"> <a href="/encyclopedie/trappist-1-systeme-planetaire/#c23616"> <span class="rg">TRAPPIST-1, </span><em class="it">système planétaire</em> </a> </h3> <ul class="list-inline list-inline-bullet mb-1 text-muted"> <li class="list-inline-item text-sm">Écrit par <span rel="author">Franck SELSIS</span> </li> <li class="list-inline-item text-sm">1 775 mots</li> <li class="list-inline-item text-sm">3 médias </li> </ul> <div class="d-none d-md-inline-block float-start me-3"> <a class="protected" title="Article : TRAPPIST-1, syst&egrave;me plan&eacute;taire" href="/encyclopedie/trappist-1-systeme-planetaire/"> <img class="rounded shadow" loading="lazy" alt="Système planétaire Trappist-1 - crédits : Encyclopædia Universalis France" width="125" height="125" src="/typo3temp/assets/_processed_/f/b/csm_de170359_0331b38e6b.webp"/> </a> </div> <div class="snippet-content mt-3"> ...mesurer. Les transits sont bien plus accessibles autour d’astres plus petits et plus froids appelés naines ultrafroides. Ce terme regroupe les étoiles et <a data-bs-toggle="popover" data-bs-content="Prédites par les théoriciens dans les années 1960, longtemps recherchées, découvertes en 1995, les naines brunes, qui constituent le chaînon manquant entre le monde des étoiles et celui des planètes , soulèvent des questions fondamentales sur la formation de ces deux grandes familles d'astres. Les naines brunes sont très répandues dans notre Galaxie, où elles sont trois fois moin..." title="Article : NAINES BRUNES" href="/encyclopedie/naines-brunes/">naines brunes</a> – nom donné aux astres dont la masse, inférieure à 0,07 masse du Soleil, ne permet pas la fusion de l’hydrogène – et dont la température... </div> </li> <li class="list-group-item"> <h3 class="fs-5 m-0 mt-1"> <a href="/encyclopedie/univers/#c23616"> <span class="rg">UNIVERS</span> </a> </h3> <ul class="list-inline list-inline-bullet mb-1 text-muted"> <li class="list-inline-item text-sm">Écrit par <span rel="author">Jean AUDOUZE</span> et <span rel="author">James LEQUEUX</span> </li> <li class="list-inline-item text-sm">6 652 mots</li> <li class="list-inline-item text-sm">18 médias </li> </ul> <div class="snippet-content mt-3"> ...massives que le Soleil : certaines peuvent avoir des masses cent fois supérieures. Les étoiles les moins massives ont une masse de 0,08 masse solaire. Certains astres très peu lumineux, les <a data-bs-toggle="popover" data-bs-content="Prédites par les théoriciens dans les années 1960, longtemps recherchées, découvertes en 1995, les naines brunes, qui constituent le chaînon manquant entre le monde des étoiles et celui des planètes , soulèvent des questions fondamentales sur la formation de ces deux grandes familles d'astres. Les naines brunes sont très répandues dans notre Galaxie, où elles sont trois fois moin..." title="Article : NAINES BRUNES" href="/encyclopedie/naines-brunes/">naines brunes</a>, ont une masse encore inférieure à celle-ci ; les réactions thermonucléaires ne peuvent pas s'y produire,... </div> </li> </ul> </section> </div> <div class="col-lg-4 col-xl-3 px-0 d-none d-lg-block side-bar position-relative"> <div id="ad_rightslot" class="pub-container text-center"> <div class="pub-placeholder"></div> </div> <div id="ad_rightslot2" class="pub-container text-center"> <div class="pub-placeholder"></div> </div> <a class="wrapper cta" href="/abonnement" title="Abonnez-vous à Universalis pour 1 euro" data-matomo-category="CTA" data-matomo-name="Clic" data-matomo-value="Col right"> <img src="/typo3temp/assets/_processed_/b/6/csm_abo-3_f303c484f7.webp" class="full-height" loading="lazy" width="290" height="476" alt="Abonnez-vous à Universalis pour 1 euro"> </a> <div id="newsletter_subscription" class="wrapper p-3"> <p class="fs-3 fw-bold text-center text-light mb-1">Rejoignez-nous</p> <p class="text-center"> Inscrivez-vous à notre <strong>newsletter</strong></p> <div class="input-group mb-3"> <input type="text" class="form-control" placeholder="votre email"> <div class="input-group-append"> <button id="newsletter_subscription_button" class="btn btn-primary text-uppercase" type="button"> <strong>S'inscrire</strong></button> </div> </div> </div> </div> </div> </main> <div id="bandeau-footer"> <div class="container"> <p><a href="/abonnement" title="Abonnez-vous à Universalis pour 1 euro">Accédez à l'intégralité d'Universalis.fr <strong>sans publicité</strong></a></p> </div> </div> <footer class="container footer text-center d-print-none"> <ul class="list-inline list-inline-bullet mb-2"> <li class="list-inline-item"> <a href="http://www.encyclopaedia-universalis.fr/" title="Encyclopædia Universalis" rel="noopener" target="_blank">Encyclopædia Universalis </a> </li> <li class="list-inline-item"> <a href="https://www.encyclopaedia-universalis.fr/nous-contacter/infos/" title="Contactez-nous" rel="noopener nofollow" target="_blank">Contact</a></li> <li class="list-inline-item"> <a title="Mentions légales" rel="nofollow" href="/mentions-legales/">Mentions légales et politique de confidentialité</a> </li> <li class="list-inline-item"> <a href="https://abonnement.universalis.fr/typo3conf/ext/mailer/Resources/Public/Pdf/cgv.pdf" rel="noopener nofollow" target="_blank" title="Conditions générales de vente">CGV</a> </li> <li class="list-inline-item d-none d-md-inline-block"> <a href="javascript:" id="rgpd" rel="nofollow" title="Consentement RGPD">RGPD</a> </li> </ul> <p class="mb-2">Consulter le <a title="Dictionnaire de l'Encyclopædia Universalis" href="/dictionnaire/"> dictionnaire de l'Encyclopædia Universalis </a> </p> <p class="mb-3">© 2024 Encyclopædia Universalis France. 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