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Aula 1- Nosso Lugar No Universo Área 1, Aula 1 Aula 1- Nosso lugar no Universo Área 1, Aula 1. Alexei Machado Müller, Maria de Fátima Oliveira Saraiva e Kepler de Souza Oliveira Filho. Ilustração da Via Láctea e seus quatro braços maiores - Perseu, Norma, Crux- Scutum e Carina-Sagitário - e os braços menores de Órion e Cignus. Fonte: http://www.apolo11.com/imagens/etc/via_lactea_bracos_small.jpg. Introdução Prezado aluno em nossa primeira aula, da primeira área, vamos estudar o nosso lugar no Universo. Bom estudo! Objetivos Nesta aula vamos estudar a nossa localização no Universo, ao final esperamos que você esteja apto a: • identificar endereço da Terra no Universo; • diferenciar um planeta de uma estrela; • definir galáxia; • identificar quantos sóis têm em nossa galáxia; • estruturar o Universo em larga escala; • localizar a nossa galáxia no Universo; • conhecer a composição do Universo, partindo do nosso planeta, chegando ao Sistema Solar, a composição da Via Láctea, do Grupo Local, do Superaglomerado Local e, finalmente o Universo conhecido. Estamos no centro do Universo? Nosso lugar no Universo A Terra é um planeta, o que significa que ela é um corpo relativamente grande que orbita uma estrela - o nosso Sol. O sistema solar consiste do Sol e de todos os corpos que o orbitam: os oito planetas (incluindo a Terra), com seus satélites e anéis, os asteroides, os cometas e as incontáveis pequenas partículas que compõem o pó interplanetário. Nosso Sol é uma estrela, como outras estrelas que vemos no céu noturno. O Sol e todas as estrelas que podemos ver a olho nu fazem parte de um enorme conjunto de estrelas de forma discoidal chamado Via Láctea, a nossa galáxia. Uma galáxia é um enorme conjunto de estrelas no espaço, contendo de centenas de milhares a um trilhão ou mais estrelas. A Via Láctea é uma galáxia relativamente grande, com mais de 100 bilhões de estrelas. Figura 01.01.01: Representação artística da Via Láctea mostrando a localização do Sol. O sistema solar é localizado a aproximadamente 2/3 da distância entre o centro e a borda do disco galáctico. Área 1, Aula 1, p.2 Muitas galáxias se encontram agrupadas, formando Müller, Saraiva & Kepler aglomerados de galáxias. A Via Láctea pertence a um grupo de aproximadamente 50 galáxias, chamado Grupo Local. Em grande escala, o Universo tem a aparência de uma esponja na qual galáxias e aglomerados de galáxias são distribuídos esparsamente formando as "paredes" da esponja. Em alguns lugares as galáxias e aglomerados de galáxias estão mais condensados, formando estruturas gigantescas chamadas superaglomerados, eriam as partes ocas da esponja. O Grupo Local de galáxias pertence a um superaglomerado chamado Superaglomerado Local. Entre essas vastas superestruturas existem enormes vazios contendo poucas ou nenhuma galáxia, que na nossa analogia seriam as partes ocas da esponja. Finalmente, o Universo é a soma de toda matéria e energia, isto é, ele compreende os superaglomerados de galáxias e vazios, e tudo o que há dentro deles. Tradução livre de excertos do livro "The cosmic Perspective", de J. Bennet, M. Donahue, N. Schneider e M. Voit, 2002. Para finalizar essa introdução, acesse o vídeo O Universo Conhecido. Resumo O planeta Terra está localizado no Sistema Solar que, juntamente com mais de 100 bilhões de estrelas, formam a nossa galáxia, a Via Láctea. A nossa galáxia faz parte de um pequeno aglomerado de galáxias chamado Grupo Local, que por sua vez faz parte de uma região gigantesca em que há maior condensação de galáxias e de aglomerados de galáxias, chamado de Superaglomerado Local. Esse, por sua vez, juntamente com os demais superaglomerados de galáxias e de vazios, formam o Universo. Questões de fixação Agora que vimos o assunto previsto para a aula de hoje resolva as questões de fixação e compreensão do conteúdo a seguir, utilizando o fórum, comente e compare suas respostas com os demais colegas. Bom trabalho! 1. Qual o endereço da Terra no Universo? 2. Como um planeta se distingue de uma estrela? Qual o papel da massa nessa distinção? 3. O que é uma galáxia? Como é o nome da galáxia a que pertence o sistema solar? 4. Quantos "sóis" têm, aproximadamente, a nossa galáxia? Qual o lugar do nosso Sol nela? 5. Em larga escala, como o Universo está estruturado? 6. A nossa galáxia ocupa um lugar especial no Universo? Área 1, Aula 1, p.3 Müller, Saraiva & Kepler A seguir, no ambiente virtual de aprendizagem, veja se há alguma atividade prevista para a conclusão dessa aula. Obrigado pela sua presença, em caso de dúvidas contate o tutor. Até a próxima aula! Área 1, Aula 1, p.4 Müller, Saraiva & Kepler Aula 2 - Estrelas Binárias Área 2, Aula 2 Alexei Machado Müller, Maria de Fátima Oliveira Saraiva & Kepler de Souza Oliveira Filho Ilustração do exoplaneta Kepler-16 com seus dois sóis. O planeta foi descoberto pela missão Kepler da NASA. Crédito: NASA/JPL- Caltech. Introdução Prezado aluno, em nossa segunda aula, da segunda área, vamos tratar das estrelas binárias. Primeiro devemos ter o cuidado para saber diferenciar estrelas binárias reais (duas estrelas próximas no céu que se encontram à mesma distância da Terra, formando um sistema físico) e binárias aparentes – ou estrelas duplas aparentes (duas estrelas próximas no céu, porém, que se encontram a distâncias diferentes da Terra, mas por projeção parecem duplas). Mais de 50% das estrelas do céu compõem sistemas com dois ou mais membros. Bom estudo! Objetivos Nesta aula trataremos de estrelas binárias e esperamos que ao final você esteja apto a: • definir o que é uma estrela binária; • diferenciar os tipos de sistemas binários; • calcular a massa das estrelas em sistemas binários; • entender a importância dos sistemas binários para conhecer as massas das estrelas. Por que estudar estrelas binárias? Estrelas binárias São duas ou mais estrelas próximas que estão praticamente a mesma distância da Terra, formam um sistema físico, orbitando mutuamente. Mais de 50% das estrelas do céu compõem sistemas com dois ou mais membros. Desde 1783 se tem registro de evidências de estrelas binárias. Estrelas binárias São duas estrelas próximas Figura 02.02.01: Sistema binário eclipsante Algol. que estão praticamente à mesma distância da Terra Um breve histórico das estrelas binárias e formam um sistema físico, orbitando Em 1783, John Goodricke viu a estrela Algol (β mutuamente. Persei) diminuir seu brilho em mais de uma magnitude por Estrelas binárias aparentes algumas horas,e calculou seu período em 2d 20 h 49min. Em 1804, William Herschel descobriu uma companheira São duas estrelas que fraca da estrela Castor (a Geminorum) e, usando uma parecem estar próximas medida que James Bradley havia feito em 1759, mediu o no céu, mas estão a distâncias diferentes da período como sendo de 342 anos. Herschel foi o primeiro a Terra e só parecem duplas estabelecer que se tratavam de corpos interagindo pelo efeito da projeção. gravitacionalmente, isto é, de binárias físicas. Em 1827, Felix Savary determinou, pela primeira vez, a órbita de uma estrela binária, ao mostrar que ξ Ursae Majoris tinha uma órbita elíptica, com um período de 60 anos. Em 1889, Edward Charles Pickering e Antonia Caetana de Paiva Área 2, Aula 2, p.2 Pereira Maury descobriram as binárias espectroscópicas, Müller, Saraiva & Kepler ao perceberem que a estrela Mizar A (ζ Ursae) apresentava linhas duplas que variavam com um período de 104 dias. Em 1908 Mizar B foi também detectada como uma binária espectroscópica por Edwin Brant Frost 1866 – 1935) e Friedrich Wilhelm Hans Ludendorff (1873 - 1941), com um período de 175,6 dias. Figura 02.02.02: O sistema binário Castor, a estrela mais brilhante da constelação de Gemeos (1,6 mag), que está a 45 anos-luz da Terra e é composto de duas estrelas separadas de 6 segundos de arco e com um período de 350 anos. Figura 02.02.03: Imagem atual obtida com o interferômetro ótico Navy Prototype Optical Interferometer no Arizona, com seis telescópios, compreendendo 15 minutos de arco, de Mizar A (2,27 mag), uma binária espectroscópica descoberta em 1889, Mizar B (3,95 mag), a 15 segundos de arco de distância, e a estrela variável Alcor (4,04 a 4,07 mag). Figura 02.02.04: Posição de Mizar na constelação de Ursa Major, também conhecida como Big Dipper, do hemisfério norte. Área 2, Aula 2, p.3 Müller, Saraiva & Kepler Tipos de Sistemas Binários Existem quatro tipos de sistemas binários e eles são classificados conforme as suas descobertas (histórico). - Binárias visuais São classificados como binárias visuais os pares de estrelas que estão associadas gravitacionalmente que se separam por dezenas e até centenas de unidades astronômicas. Ao serem observadas por telescópio são vistas como duas estrelas. (Exemplos nas figuras 02.02,05 e 02.02.06). Figura 02.02.05: Binárias visuais Mizar e Alcor. Figura 02.02.06: Sistema binário visual Sírius A e Sírius B. - Binárias astrométricas São assim classificadas quando um de seus componentes é muito tênue para ser observado ao telescópio, mas a sua detecção é obtida pelas ondulações no movimento da companheira mais brilhante. (Exemplo na figura 02.02.07). Figura 02.02.07: Movimento do sistema Sírius A e Sírius B medido entre 1980 e 1920. A linha pontilhada marca o movimento do centro de massa. Antes da descoberta de Sírius B, em 1862, apenas o movimento de Sírius A era detectado, e a estrela era classificada como binária astrométrica. Área 2, Aula 2, p.4 Müller, Saraiva & Kepler - Binárias espectroscópicas Nesse sistema a separação média entre as estrelas é na ordem de uma unidade astronômica (1 UA). Por apresentarem um período curto, a velocidade orbital é grande. Para determinar a natureza desse sistema de estrelas binárias faz-se a observação da variação da sua velocidade radial, estabelecida através da análise das linhas espectrais da estrela que variam de comprimento de onda com o passar do tempo.
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