sábado, 3 de junho de 2017

Tycho Brahe e a Supernova por ele observada, em 1572


A Estrela Explodida
- uma Supernova -
que Tycho Brahe presenciou,
em 1572,
- e que continou observando 
ao longo de dezoito meses,
escrevendo um livro 
(De Stella Nova)
descrevendo este objeto
que tomou seu Nome! -
e o Remanescente dessa mesma Explosão,
nos dias de hoje.




Créditos:
Tycho Brahe 

Tycho's Supernova Remnant 
 Credit: X-ray: NASA/CXC/SAOInfrared: NASA/JPL-CaltechOptical: MPIA, Calar AltoO. Krause et al.

https://apod.nasa.gov/apod/ap090317.html





Olá!

Caro Leitor,
todos nós, amantes das estrelas,
ansiamos pelo dia
em que possamos presenciar
uma Supernova
simplesmente 
surgindo diante de nossos olhares embevecidos,
não é verdade?

E mais ainda
se acaso este Supernova fosse tão brilhante, 
tão brilhante
que poderia ser observada também durante o dia
- pelo menos por cerca de duas semanas!
E melhor ainda:
que pudesse continuar apresentando-se
nos céus estrelados
durante quase um ano e meio!

Será que isso já aconteceu?
Sim!
Aconteceu durante a vida de Tycho Brahe,
no outono/inverno de 1572,
quando enfrentava o frio da noite
para chegar em casa e então jantar....

O astrônomo dinamarquês ficou tão extasiado
diante daquele espetáculo inesperado
- uma estrela explodindo num lugar 
onde ele nunca havia visto qualquer estrela...
(na constelação Cassiopeia) -,
que chegou a chamar alguns de seus serviçais 
bem como alguns camponeses que voltavam da lida no campo...,
para lhes dizer que tudo aquilo era verdade,
para testemunharam tal realidade fantástica!





Descrição: Gravura que surge no livro Astronomie Populaire, de Camille Flammarion (1872), e que ilustra Tycho Brahe a observar a supernova pela primeira vez. (©Astronomie Populaire - Camille Flammarion (1872))



https://www.astro.up.pt/divulgacao/imagem.php?WID=462&CID=2&ID=89&NIID=173&Lang=pt








Durante os dezoitos meses seguintes, 
Tycho Brahe trabalhou intensamente
na escrita de seu livro
- De Stella Nova 
(Sobre a Estrela Nova) -
trazendo suas observações
sobre esta Supernova,
este presente dos céus estrelados
que brindou sua vida de astrônomo
apaixonado por seu trabalho!





http://www.professorelian.com.br/downloads/CRONOLOGIA%20ASTRON%C3%94MICA.pdf



Tycho_Cas_SN1572
http://www.astropt.org/2014/11/26/a-estrela-nova-de-1572/



https://www.astro.up.pt/divulgacao/imagem.php?WID=462&CID=2&ID=89&NIID=174&Lang=pt





..................................


Tycho reports (from Burnham's Celestial Handbook):


``On the 11th day of November in the evening after sunset, I was contemplating the stars in a clear sky. I noticed that a new and unusual star, surpassing the other stars in brilliancy, was shining almost directly above my head; and since I had, from boyhood, known all the stars of the heavens perfectly, it was quite evident to me that there had never been any star in that place of the sky, even the smallest, to say nothing of a star so conspicuous and bright as this. I wqs so astonished of this sight that I was not ashamed to doubt the trustworthyness of my own eyes. But when I observed that others, on having the place pointed out to them, could see that there was really a star there, I had no further doubts. A miracle indeed, one that has never been prevoiously seen before our time, in any age since the beginning of the world.''
.........................................................

http://spider.seds.org/spider/Vars/sn1572.html


Tycho reportou (a partir de Burnham's Celestial Handbook):
" No décimo primeiro dia de novembro, na noitinha após o por-do-sol, estava eu contemplando as estrelas no céu transparente.  Percebi uma nova e não-usual estrela, ultrapassando as demais estrelas em brilho, estava brilhando praticamente por cima de minha cabeça: e desde então eu venho, desde minha adolescência, conhecendo perfeitamente todas as estrelas do céu, até as menores, e mais ainda sobre umaestrela tão chamativa e brilhante como esta! Eu fiquei tão estupefato com esta visão que fiquei envergonhado por duvidar da verdade testemunhada por meus próprios olhos. Porém, quando observei que outras pessoas também apontaram para o mesmo lugar, pude acreditar que havia realmente uma estrela lá, sem dúvida alguma.  Um milagre, certamente, um que nunca teria antes sido visto antes de nosso tempo ou em outra época desde o começo do mundo."



SN 1572, Tycho's Supernova

B Cassiopeiae, Supernova Type I (?) in Cassiopeia
[SN 1572 Tycho]
Right Ascension00 : 25.3 (h:m)
Declination+64 : 09 (deg:m)
Distance10,000 (ly)
Visual brightness-4 (mag)


When Tycho Brahe was on his way home on November 11, 1572, his attention was attracted by a star in Cassiopeia which was shining at about the brightness of Jupiter and which had not been seen in this place before. Tycho reports (from Burnham's Celestial Handbook):
``On the 11th day of November in the evening after sunset, I was contemplating the stars in a clear sky. I noticed that a new and unusual star, surpassing the other stars in brilliancy, was shining almost directly above my head; and since I had, from boyhood, known all the stars of the heavens perfectly, it was quite evident to me that there had never been any star in that place of the sky, even the smallest, to say nothing of a star so conspicuous and bright as this. I wqs so astonished of this sight that I was not ashamed to doubt the trustworthyness of my own eyes. But when I observed that others, on having the place pointed out to them, could see that there was really a star there, I had no further doubts. A miracle indeed, one that has never been prevoiously seen before our time, in any age since the beginning of the world.''
Tycho was so impressed by this event that he devoted the rest of his professional life to astronomy only. Nevertheless, Tycho had not been the first to discover this "new" star; according to Burnham, it was probably first seen by W. Schuler on November 6, 1572. Tycho found it at about as brilliant as Jupiter, and it became soon equal to Venus. For about two weeks the star could be seen in daylight. At the end of November it began to fade and change color, from bright white over yellow and orange to faint reddish light, finally fading away from visibility in March, 1574, having been visible to the naked eye for about 16 months.

The image in this page is from Tycho Brahe's "Stella Nova", taken from the online edition at the Danish National Library of Science and Medicine.


The remnant of this supernova had to wait for its discovery until the 1960s, when extremely faint nebulosity was identified on Mt. Palomar photo plates near the position, and gaseous remainders were identified by their radio emission; a stellar remnant has not been found. The radio source has been cataloged as 3C 10, the SNR as G 120.1+1.4 in Dave Green's catalogue of galactic SNRs. The gas shell is now expanding at about 9000 km/s (compare with the Crab Nebula's about 1000 only), and has reached an apparent diameter of 3.7 arc minutes. Tycho's supernova remnant appears to be the more typical representative of these class of objects of the two.

http://spider.seds.org/spider/Vars/sn1572.html



https://library.sydney.edu.au/collections/rare-books/online-exhibitions/modernity/images/brahe1-1.jpg




Learned: 
Tico Brahae, His Astronomicall Coniectur 
of the New and Much Admired [Star].







Learned: 
Tico Brahae, His Astronomicall Coniectur of the New and Much Admired [Star].


http://lhldigital.lindahall.org/cdm/compoundobject/collection/astro_early/id/283/rec/11


Learned: 

Tico Brahae, His Astronomicall Coniectur of the New and Much Admired [Star].





TitleLearnedTico Brahae, His Astronomicall Coniectur of the New and Much Admired [Star].
Alternative TitleLearnedTico Brahae, his astronomicall coniectur of the new and much admired [star] which appered in the year 1572.;Brahe on the comet of 1572.
Reference TitleBraheTycho1632Learned.
CreatorBraheTycho1546-1601.
SubjectStars, New.
Astronomy -- Early works to 1800.
Keywordsnova
supernova
DescriptionTycho Brahe's 'De Nova Stella' was originally published in Copenhagen in 1573. In the book, he described observations of a new star that appeared in the constellation Cassiopeia in 1572. With careful measurementsTycho discovered that the new star did not shift position with respect to the other stars, and therefore was really a starSince conventional opinion held that the heavens were perfect and unchangingTycho's evidence marked the beginning of the end of the doctrine of the immutability of the heavens. In 1632 an English printer issued this translation.
PublisherLondon : Printed by BA[lsop] and TF[awcet], for M[Sparke] and SNealand.
Date original1632
Extent19 cm.
Identifier58
Call NumberQB841.B78 1632
LanguageEnglish
CollectionAstronomy - Early Works
Rightshttp://www.lindahall.org/imagerepro/
Data contributorLinda Hall Library, LHL Digital Collections.
Typeimage
OCLC number692360164
http://lhldigital.lindahall.org/cdm/compoundobject/collection/astro_early/id/283/rec/11
.........................................................



The sixteenth century was a time of turmoil on Earth, but one thing that was assured was the unchanging nature of the heavens. The seasons changed, the Moon and planets moved against the background of stars, but everything was orderly, predictable. The stars were eternal. They did not come or go. The nova must be earthly, perhaps something high in the atmosphere, just as comets were believed to be. Tycho set about measuring the distance to the nova. He could not tell how far away it was, but he could tell it was further than the Moon, and probably the planets as well. Tycho's nova shattered the myth that the heavens were unchanging with time, and began a revolution in cosmology that is still ongoing.

.........................................................

https://www.nasa.gov/audience/forstudents/postsecondary/features/F_Tycho_Nova.html



O Século XVI foi um tempo tumultuado na Terra, porém uma questão que era bem assegurada era o fato da natureza sempre imutável dos céus.  As estações mudavam, a Lua e os planetas movimentação contra o pano de fundo das estrelas, porém tudo era ordenado e previsível.  As estrelas eram eternas.  Elas não vinham ou iam. A Nova deveria ser terrena, talvez alguma coisa em um plano mais alto da atmosfera, assim como se acreditava que eram os cometas. Tycho pôs-se a medir a distância da Nova. Ele não podia dizer o quão distante ela estava, porém ele podia dizer que estaria mais distante do que a Lua e provavelmente também dos planetas.  A Nova de Tycho havia destruído o mito de que os céus eram imutáveis no tempo e deu início a uma revolução na cosmologia, que continua acontecendo.






Hoje em dia
e com o tempo passando,
sua "nova estrela"
foi transformando-se
e se nos apresentando
através seus remanescentes
e vem sendo denominada
como
A Supernova Remanescente de Tycho
Tycho's supernova remnant (SNR).


Créditos:
Tycho Brahe 


Tycho's Supernova Remnant 
 Credit: X-ray: NASA/CXC/SAOInfrared: NASA/JPL-CaltechOptical: MPIA, Calar AltoO. Krause et al.

https://apod.nasa.gov/apod/ap090317.html





Certamente existem dois astrônomos mais recentes
que tiveram a imensa boa oportunidade
de observarem uma Supernova:
Tycho Brahe, em 1572, e Johannes Kepler, em 1604
- e ambos escreveram livros
detalhando suas observações sobre as mesmas.

Um bom tempo antes,
uma outra Supernova foi observada ,
em 1054
(por astrônomos chineses que a denominram
como Estrela Visitante, Guest Star,
assim como povos vivendo
no atual Arizona e Novo Mexico)
- e hoje em dia é conhecida como 
A Nebulosa do Caranguejo, M1,
próxima ao Chifre mais ao sul, do Touro.

Aparentemente, 
somente cerca de 11 supernovas explodiram
na Via Lactea nos últimos 20.000 anos.

Quer dizer,
a visão fantástica e o testemunho
da explosão de uma estrela
- uma Supernova -
é um fato realmente raro,
raríssimo!

O que nos resta, então,
é nos determos na observação
e nos estudos
dos Remanescentes dessas Supernovas 
do passado.

Hoje em dia,
conhecemos alguns tipos de Supernovas
e aquela observada e detalhada
por Tycho Brahe
é denominada de Supernova Tipo Ia.




supernova Explosive death of a star, caused by the sudden onset of nuclear burning in a white dwarf star (Type Ia), or gravitational collapse of the core of massive star followed by a shock wave that disrupts the star(Type II, Type Ib, Ic). A supernova is one of the most energetic events of the universe and may temporarily outshine the rest of the galaxy in which it resides. [More Info: Field Guide]
supernova remnant The expanding glowing remains from a supernova. [More Info: Field Guide]


Supernova - 
Morte explosiva de uma estrela causada pelo súbito início de queima nuclear em uma estrela anã branca (Tipo Ia), ou um colapso gravitacional do núcleo de uma estrela massiva seguido por uma onde de choque que despedaça a estrela (Tipo II, Tipo Ib, Tipo Ic).  Uma supernova é um dos mais energéticos eventos do universo e pode temporariamente ofuscar o resto da galáxia na qual reside.

Remanescente de Supernova -
 A expansão incandescente que permanece a partir de uma supernova.





Tycho's observations, made decades before the invention of the telescope, were so good that modern astronomers know his "new" star was a supernova of this type. It would surely make Tycho very happy to see that his discovery in the winter of 1572 is so intimately linked to the cutting edge astrophysics of the 21st century.


As Observações de Tycho, realizadas décadas antes da invenção do telescópio, foram tão consistentes que astrônomos modernos souberam
que sua "Nova" estrela era uma supernova desse tipo.  Certamente, isso teria feito Tycho sentir-se bem feliz em ver que sua descoberta no inverno de 1572 é tão intimamente fusionada ao mais moderno desenvolvimento na astrofísica do Século XXI.




Nesta Postagem, Caro Leitor,
encontre alguma informação
sobre Tycho Brahe e seu momento de vida
quando estêve diante de sua Nova Estrela
e seu trabalho devotado à mesma;
alguma informação
sobre 
A Supernova Remanescente Tycho;
sobre o que são Supernovas
e suas catalogações;
e, finalmente, 
sobre o Tipo Ia de Supernova.

Com um abraço estrelado,
Janine Milward


P.S.  Caro Leitor,
Estamos trazendo a você
uma série de Postagens
sobre Tycho Brahe.  
Confira:

- Tycho Brahe trabalhando em seu Uraniburgo, 
o Castelo de Urânia, a Musa das Estrelas, 
e seu Encontro com Kepler, ao final de sua vida.

-  Tycho Brahe e a Cratera com seu Nome, no Umbigo da Lua

- Tycho Brahe e a Supernova por ele observada, em 1572

- Tycho Brahe e o Grande Cometa de 1577

- Tycho Brahe e o protótipo de uma Espaçonave com seu Nome, 
na Dinamarca



2001 January 7
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.
Tycho Brahe Measures the Sky 
 Credit: Tycho Brahes Glada V„nner
Explanation: Tycho Brahe was the most meticulous astronomical observer of his time. Brahe, who lived between 1546 and 1601, set out to solve the day's most pressing astronomical problem: to determine whether the Earth or the Sun was at the center of the Solar System. To do this Brahe and his assistants created the first major astronomical observatory where they devised and used the most accurate pre-telescopic astronomical instrumentsTycho Brahe thus compiled tables of precise measurements of the positions and brightnesses of planets and stars. Brahe never solved the Solar System problem himself - but left data so impressively accurate his assistant Johannes Kepler was able to develop definitive laws. Brahe is also remembered for witnessing a supernova in 1572, showing that the Great Comet of 1577 was not an atmospheric phenomena, and for his metal nose.




Tycho Brahe era o mais meticuloso observador astronômico de seu tempo.  Brahe, que viveu entre 1546 e 1601, saiu em busca de resolver o problema astronômico mais impositivo: determinar se a Terra ou o Sol era o centro do Sistema Solar. Para fazer isso, Brahe e seus assistentes criaram o primeiro maior observatório astronômico onde eles inventaram e usaram os mais acurados instrumentos astronômicos anteriores ao telescópio.  Tycho Brahe, então, compilou tabelas de medição precisa das posições e brilhos dos planetas e estrelas.  Brahe nunca resolveu o problema do Sistema Solar - porém deixou dados tão impressionante acurados que seu assistente, Johannes Kepler, pôde desenvolver leis definitivas.  Brahe também é lembrado por testemunhar uma supernova, em 1572, e de mostrar que o Grande Cometa de 1577 não era um fenômeno atmosférico; e sempre lembrado por seu nariz metálico.




Observe, Caro Leitor,
na Ilustração Stellarium abaixo,
a constelação de Cassiopeia
onde eu marquei a proximidade da Supernova.


Stellarium



Explosão de uma Estrela e um Mito

Uma estrela que explodiu.  Para a mente dos seres vivenciando o Século Dezesseis, isso era tão absurdo como um elefante voando.  Isso não podia acontecer.  Isso era contrário à ordem da natureza de acordo com o fato de que estrelas pertencem a "..... região etérea do mundo celestial o qual é livre de mudança ou de corrupção".  As estrelas eram símbolos do eterno e do imutável, parte de um sistema de posição permanente e além do mundo mundo sempre mutável e sempre corruptível mais abaixo.

Então, em novembro de 1572, uma estrela ainda mais brilhante do que Vênus apareceu, de repente, na constelação Cassiopeia. Todos na Europa e no Oriente distante a observaram.  A Nova Estrela ou Nova de 1572 deveria quebrar para sempre a crença humana sobre a incorruptibilidade das estrelas.  O homem mais responsável por esse rearranjo do cenário cósmico foi Tycho Brahe.

.................................................................


EXPLOSION OF A STAR AND A MYTH

[89] An exploding star. To the sixteenth century mind this was as absurd as a flying elephant. It just did not happen. It was contrary to the order of nature according to which stars belong to the ". . . ethereal region of the celestial world which is free from change or corruption." The stars were symbols of the eternal and unchangeable, part of a system of permanence standing above the ever-changing, ever-corruptible world below.

Then, in November 1572, a star brighter than the planet Venus appeared suddenly in the constellation of Cassiopeia. It was noticed throughout Europe and in the Far East. The New Star or Nova of 1572 would shatter forever man's belief in the incorruptibility of the stars. The man most responsible for this rearrangement of the cosmic landscape was Tycho Brahe, a stormy, roisterous astronomer known for his acid tongue and silver nose.
Tycho, who wore a prosthetic silver nose to replace the one he had lost in a duel at age twenty, made accurate measurements of the position of the star relative to the other stars in Cassiopeia. For 18 months, though the brightness of the star declined steadily until it became invisible, its position remained fixed. This proved that the new star, or Stella Nova, belonged to the "eighth sphere" of the fixed stars.

Today, more than 400 years later, we use the word supernova to describe Tycho's object, even though we now know that it was not a new star at all. It had been there for tens of millions of years or more, invisible to the naked eye because of its distance of more than 6000 light years. It became visible at the end rather than the beginning of its evolution, as it underwent a catastrophic explosion.

The remnant of Tycho's supernova was singled out for study by the HEAOs because it is relatively young and is still glowing brightly in X-rays. We know when the supernova explosion occurred, and, thanks to Tycho, we know a good deal of its early history. It presents one of the best opportunities to study the interaction of the exploded star with the interstellar gas around it and to determine the mass and composition of the ejected material. Only through such comparisons can we check the theories that purport to explain the mechanisms of supernova explosions, the origin of the elements, and the origin of cosmic rays.

Most of the energy emitted by Tycho's supernova remnant falls in the X-ray band. There it gives off several billion times more X-rays than does the Sun and more energy than several hundred suns would emit at all...


[
90]
Tycho Brahe
Tycho Brahe

...wavelengths. Relatively little energy comes from the supernova remnant in the form of optical radiation, and even less in radio waves.

That is not to say that the radio waves are unimportant. On the contrary, the sensitivity of giant radio telescopes is such that the remnant of Tycho's supernova was first discovered in 1952, using the Jodrell Bank radio telescope. Shortly thereafter, faint optical wisps in the same location were discovered using the 200-inch telescope at Mt. Palomar.

The radio discovery of Tycho's supernova remnant was a watershed in astronomy. It demonstrated the usefulness of radio telescopes in searching for the remnants of supernova explosions. The technique developed rapidly, until today no nebula is considered to be a certified supernova remnant unless it possesses the characteristic signature of radio emission of high energy electrons.

Observations show that the radio waves in supernova remnants are produced by the synchrotron process, named after a phenomenon first observed in synchrotron particle accelerators, namely, the emission of strongly polarized radiation by very energetic electrons spiraling along a magnetic field. The shells of supernova remnants are filled with magnetic energy and enormous numbers of charged particles bouncing around the shell at speeds very near the speed of light. This situation is not unique to Tycho's supernova remnant. Every supernova remnant somehow produces large quantities of extremely high energy particles. Clearly, supernova remnants are efficient particle accelerators and play an important role in producing the high energy particles, or cosmic rays, that constantly bombard Earth. How do they do it?

 https://history.nasa.gov/SP-466/ch9.htm


2009 March 17
See Explanation.  Clicking on the picture will download
 the highest resolution version available.
Tycho's Supernova Remnant 
 Credit: X-ray: NASA/CXC/SAOInfrared: NASA/JPL-CaltechOptical: MPIA, Calar AltoO. Krause et al.


Explanation: What star created this huge puffball? Pictured above is the best multi-wavelength image yet of Tycho's supernova remnant, the result of a stellar explosion first recorded over 400 years ago by the famous astronomer Tycho Brahe. The above image is a composite of an X-ray image taken by the orbiting Chandra X-ray Observatory, an infrared image taken by the orbiting Spitzer Space Telescope, and an optical image taken by the 3.5-meter Calar Alto telescope located in southern Spain. The expanding gas cloud is extremely hot, while slightly different expansion speeds have given the cloud a puffy appearance. Although the star that created SN 1572, is likely completely gone, a star dubbed Tycho G, too dim to be easily discerned here, is being studied as the possible companion. Finding progenitor remnants of Tycho's supernova is particularly important because the supernova was recently determined to be of Type Ia. The peak brightness of Type Ia supernovas is thought to be well understood, making them quite valuable in calibrating how our universe dims distant objects.






In the winter of 1572, a Danish nobleman admired the chill night sky as he walked home for supper. His attention fell immediately upon a dazzling star, brighter than Venus, where there had been no star before. He was so shocked that he asked his servants to tell him he wasn't dreaming. Then he asked some passing peasants if they too saw the star. For the next eighteen months, the nobleman was obsessed with the new star, or nova, for its appearance would change humanity's view of the universe forever. The nobleman's name was Tycho Brahe, and he was the greatest astronomer of his age.


Em uma gelada noite do inverno de 1572, um nobre dinamarquês admirava o céu enquanto dirigia-se para sua casa e ansiando por seu jantar.  Sua atenção foi imediatamente atraída por um estrela ofuscante, mais ainda brilhante do que Vênus e em lugar onde não existia estrela anteriormente.  Ele ficou tão chocado que pediu aos seus serviçais para lhe dizerem que não estava dormindo.  Então perguntou a alguns camponeses que passavam se estes haviam também visto a estrela.  Ao longo dos seguintes dezoito meses, o nobre estêve obcecado pela nova estrela, ou Nova, porque sua aparição deveria mudar para sempre a visão da humanidade sobre o universo.  O nobre era Tycho Brahe e ele era o maior astrônomo de sua época.





When the star that created this supernova remnant exploded in 1572, it was so bright that it was visible during the day. And though he wasn't the first or only person to observe this stellar spectacle, the Danish astronomer Tycho Brahe wrote a book about his extensive observations of the event, gaining the honor of it being named after him.

Quando a estrela que criou esta remanescente de supernova explodiu em 1572, era tão brilhante que podia ser vista durante o dia. E, apesar de que não fosse a primeira ou mesmo a única pessoa a observar este espetáculo estelar, o astronômo dinamarquês Tycho Brahe escreveu um livro acerca suas extensivas observações do evento, ganhando a honra de ter seu nome aliado ao objeto.





Tycho's supernova remnant (SNR) is located around 7,500 light-years (ly) from Sol in the north central part (0:25:17+64:8:37, J2000; and 0:25:13+64:8.7, ICRS 2000.0) of Constellation Cassiopeia, the Lady of the Chair -- north of Kappa Cassiopeiae and Shedar (Alpha Cassiopeiae); northeast of Caph (Beta Cassiopeiae); northwest of Gamma CassiopeiaeRuchbah (Delta Cassiopeiae), Achird (Eta Cassiopeiae), M103, and theDouble Cluster, and southeast of Errai (Gamma Cephei). Useful catalogue numbers and designations for this supernova remnant include: Tycho'S SN, Tycho SNR, SN 1572, SNR 021.0+63.0, SNR 120.1+01.4, SNR 120.2+01.4, NOVA Cas 1572, X Cep X-1, B Cas, GRS 120.10 +01.40, and BD+63 39a.






March 7, 1999
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.
Tycho's Supernova Remnant in X-ray 
 Credit: ROSATMPENASA
Explanation: How often do stars explode? By looking at external galaxies, astronomers can guess that these events, known as a supernovae, should occur about once every 30 years in a typical spiral galaxy like our MilkyWay. However, the obscuring gas and dust in the disk of our galaxy probably prevents us from seeing many galactic supernovae -- making observations of these events in our own galaxy relatively rare. In fact, in 1572, the revered Danish astronomer, Tycho Brahe, witnessed one of the last to be seen. The remnant of this explosion is still visible today as the shockwave it generated continues to expand into the gas and dust between the stars.Above is an image of the X-rays emitted by this shockwave made by a telescope onboard the ROSAT spacecraft. The nebula is known as Tycho's Supernova Remnant.




Tycho's Nova

07.22.04
In the winter of 1572, a Danish nobleman admired the chill night sky as he walked home for supper. His attention fell immediately upon a dazzling star, brighter than Venus, where there had been no star before. He was so shocked that he asked his servants to tell him he wasn't dreaming. Then he asked some passing peasants if they too saw the star. For the next eighteen months, the nobleman was obsessed with the new star, or nova, for its appearance would change humanity's view of the universe forever. The nobleman's name was Tycho Brahe, and he was the greatest astronomer of his age.


A speckled purple, brown and white ball against a black background.  The image shows what is left of a star that exploded over 400 years ago.  The outer edge of the circle is purple and quite smooth, whereas the interior is a mish-mash of color showing its turbulent history.
Image to right: This Chandra image reveals fascinating details of the turbulent debris created by a supernova explosion that was observed by the Danish astronomer Tycho Brahe in the year 1572. The colors show different X-ray energies, with red, green and blue representing low, medium and high energies, respectively. The image is cut off at the bottom because the southernmost region of the remnant fell outside the field of view of the detector. Credit: NASA/CXC/SAO

The sixteenth century was a time of turmoil on Earth, but one thing that was assured was the unchanging nature of the heavens. The seasons changed, the Moon and planets moved against the background of stars, but everything was orderly, predictable. The stars were eternal. They did not come or go. The nova must be earthly, perhaps something high in the atmosphere, just as comets were believed to be. Tycho set about measuring the distance to the nova. He could not tell how far away it was, but he could tell it was further than the Moon, and probably the planets as well. Tycho's nova shattered the myth that the heavens were unchanging with time, and began a revolution in cosmology that is still ongoing.

Tycho's Nova would today be called a supernova, the explosive death of an old star. There are different sorts of supernova, but the one Tycho saw requires a special set of circumstances.

A large orange star against a black background.  The right side of the star is distorted and drawn out into a white cone that joins onto a blue-white disc.  This disc turns from blue to white in its center, and represents hot gas spinning towards a tiny white dwarf star.
Image to left: An artist's rendering of a supernova in the making. Here one of a pair of stars has become a white dwarf, and is drawing material from its companion, the red star on the left. The white dwarf is very small in comparison to the red star, and is hidden within the white hot disc of hydrogen gas it has acquired. Credit:CXC/M.Weiss

When a star like our Sun runs out of nuclear fuel, it will go through a beautiful death ritual, shedding its outer layers while its inside squeezes down into a dense white-hot ball about the size of the Earth. This ball, aptly named a White Dwarf, is where the story will end for the Sun, but not so for other White dwarfs. This is because most stars live in pairs, a union that becomes dangerous when one of the pair turns into a white dwarf. The white dwarf is greedy - its strong gravity begins to tug at the outer layers of hydrogen gas from its companion and wraps the gas around itself, in the process creating a ticking time bomb. The hydrogen layer grows, getting hotter and hotter until at critical temperature the bomb goes off; a thermonuclear explosion as bright as a billion stars, and a flash that can be seen across the universe.

A valuable property of this type of supernova is that they are all similar sized explosions. So if one supernova looks fainter than another, it must be further away. This property makes them the most accurate tool for measuring the huge distances between galaxies. For when a star in a particular galaxy explodes, we can tell how far the galaxy is by how faint the supernova looks. Measuring distance using this type of supernova gave astronomers the first hint that the expansion of our universe is actually speeding up (see the link below to find out how).

Three pairs of images, showing three galaxies before and after a supernova explosion within them.  First galaxy is a blue-white blob with a faint blue crescent-shaped fuzz running north-south.  The supernova appears as a red blob just below the center of the galaxy, in the middle of the southern fuzz.  Second galaxy is a faint misshapen spiral, with orange-red core and blue-purple arms.  The supernova is a white blob just below the galaxy’s core.  The third galaxy is an orange-red ball, with the supernova appearing as a smaller orange-red blob just above it.
Image above: "Before and After" Images of galaxies taken by the Hubble Space Telescope show very distant supernovae that exploded when the universe was less than half its current age. The apparent brightness of this type of supernova gives cosmologists a way to measure the expansion rate of the universe at different times in the past. Credit: NASA and A. Riess (STScI)
Tycho's observations, made decades before the invention of the telescope, were so good that modern astronomers know his "new" star was a supernova of this type. It would surely make Tycho very happy to see that his discovery in the winter of 1572 is so intimately linked to the cutting edge astrophysics of the 21st century.

https://www.nasa.gov/audience/forstudents/postsecondary/features/F_Tycho_Nova.html






Uma supernova tipo Ia é uma sub-categoria das estrelas variáveis cataclísmicas, resultado de uma violenta explosão de uma estrela anã branca. Uma anã branca é o resíduo de uma estrela que completou o seu ciclo de vida normal e cessou sua fusão nuclear. Entretanto, anãs brancas do tipo comum de carbono-oxigênio são capazes de futuras reações de fusão, que liberam uma grande quantidade de energia se sua temperatura estiver alta o suficiente.
Fisicamente, as anãs brancas de baixo índice de rotação[1] são limitadas a massas que estão abaixo do limite de Chandrasekhar, de cerca de 1,38 massas solares.[2] Essa é a massa máxima que pode ser suportada pela pressão de degenerescência dos elétrons. Além desse limite, a anã branca entraria em colapso. Se uma anã branca gradualmente acresce da massa de uma companheira binária, acredita-se que seu núcleo atinge a temperatura de ignição da fusão do carbono, uma vez que esta alcança o limite. Se a anã branca fundir-se com outra estrela (um fato muito raro), ela irá momentaneamente ultrapassar o limite e entrar em colapso, mais uma vez elevando sua temperatura anterior ao ponto de ignição de fusão nuclear. Dentro de poucos segundos após o início da fusão nuclear, uma fração substancial de matéria da anã branca sofre uma reação nuclear que libera energia suficiente (1-2 × 1044 joules)[3]para liberar a estrela em uma explosão de supernova.[4]

Essa categoria de supernovas produz um consistente pico de luminosidade por causa da massa uniforme das anãs brancas que explodem pelo mecanismo de acresção. A estabilidade desse valor permite que essas explosões sejam usadas como velas padrão para medir a distância de suas galáxias hospedeiras porque a magnitude aparente das supernovas depende sobretudo da distância.


type Ia supernova (type one-a) is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.[1]
Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses (M).[2][3] Beyond this, they re-ignite and in some cases trigger a supernova explosion. Somewhat confusingly, this limit is often referred to as the Chandrasekhar mass, despite being marginally different from the absolute Chandrasekhar limit where electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf gradually accretes mass from a binary companion, the general hypothesis is that its core will reach the ignition temperature for carbon fusion as it approaches the limit. If the white dwarf merges with another white dwarf (a very rare event), it will momentarily exceed the limit and begin to collapse, again raising its temperature past the nuclear fusion ignition point. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy (1–2×1044 J)[4] to unbind the star in a supernova explosion.[5]
This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance.
In May 2015, NASA reported that the Kepler space observatory observed KSN 2011b, a Type Ia supernova in the process of exploding. Details of the pre-nova moments may help scientists better judge the quality of Type Ia supernovae as standard candles, which is an important link in the argument for dark energy.[6]

Consensus model


Spectrum of SN1998aq, a Type Ia supernova, one day after maximum light in the B band[7]
The Type Ia supernova is a sub-category in the Minkowski-Zwicky supernova classification scheme, which was devised by American astronomer Rudolph Minkowski and Swiss astronomer Fritz Zwicky.[8] There are several means by which a supernova of this type can form, but they share a common underlying mechanism. Theoretical astronomers long believed the progenitor star for this type of supernova is a white dwarf and empirical evidence for this was found in 2014 when a Type Ia supernova was observed in the galaxy Messier 82.[9] When a slowly-rotating[2] carbon-oxygen white dwarf accretes matter from a companion, it can exceed the Chandrasekhar limit of about 1.44 M, beyond which it can no longer support its weight with electron degeneracy pressure.[10] In the absence of a countervailing process, the white dwarf would collapse to form a neutron star, in an accretion-induced non-ejective process,[11] as normally occurs in the case of a white dwarf that is primarily composed of magnesium, neon, and oxygen.[12]
The current view among astronomers who model Type Ia supernova explosions, however, is that this limit is never actually attained and collapse is never initiated. Instead, the increase in pressure and density due to the increasing weight raises the temperature of the core,[3] and as the white dwarf approaches about 99% of the limit,[13] a period of convection ensues, lasting approximately 1,000 years.[14] At some point in this simmering phase, a deflagration flame front is born, powered by carbon fusion. The details of the ignition are still unknown, including the location and number of points where the flame begins.[15] Oxygen fusion is initiated shortly thereafter, but this fuel is not consumed as completely as carbon.[16]

G299 Type Ia supernova remnant.
Once fusion has begun, the temperature of the white dwarf starts to rise. A main sequence star supported by thermal pressure would expand and cool which automatically counterbalances an increase in thermal energy. However, degeneracy pressure is independent of temperature; the white dwarf is unable to regulate the fusion process in the manner of normal stars, so it is vulnerable to a runaway fusion reaction. The flame accelerates dramatically, in part due to the Rayleigh–Taylor instability and interactions with turbulence. It is still a matter of considerable debate whether this flame transforms into a supersonic detonation from a subsonic deflagration.[14][17]
Regardless of the exact details of this nuclear fusion, it is generally accepted that a substantial fraction of the carbon and oxygen in the white dwarf is converted into heavier elements within a period of only a few seconds,[16] raising the internal temperature to billions of degrees. This energy release from thermonuclear fusion (1–2×1044 J[4]) is more than enough to unbind the star; that is, the individual particles making up the white dwarf gain enough kinetic energy to fly apart from each other. The star explodes violently and releases a shock wave in which matter is typically ejected at speeds on the order of 5,000–20000 km/s, roughly 6% of the speed of light. The energy released in the explosion also causes an extreme increase in luminosity. The typical visual absolute magnitude of Type Ia supernovae is Mv = −19.3 (about 5 billion times brighter than the Sun), with little variation.[14]
The theory of this type of supernovae is similar to that of novae, in which a white dwarf accretes matter more slowly and does not approach the Chandrasekhar limit. In the case of a nova, the in-falling matter causes a hydrogen fusion surface explosion that does not disrupt the star.[14] This type of supernova differs from a core-collapse supernova, which is caused by the cataclysmic explosion of the outer layers of a massive star as its core implodes.[18]

Formation

Formation process
Gas is being stripped from a giant star to form an accretion disc around a compact companion (such as a white dwarf star). NASA image
Four images of a simulation of Type Ia supernova
Simulation of the explosion phase of the deflagration-to-detonation model of supernovae formation, run on scientific supercomputer.

Single degenerate progenitors

One model for the formation of this category of supernova is a close binary star system. The progenitor binary system consists of main sequence stars, with the primary possessing more mass than the secondary. Being greater in mass, the primary is the first of the pair to evolve onto the asymptotic giant branch, where the star's envelope expands considerably. If the two stars share a common envelope then the system can lose significant amounts of mass, reducing the angular momentum, orbital radius and period. After the primary has degenerated into a white dwarf, the secondary star later evolves into a red giant and the stage is set for mass accretion onto the primary. During this final shared-envelope phase, the two stars spiral in closer together as angular momentum is lost. The resulting orbit can have a period as brief as a few hours.[19][20] If the accretion continues long enough, the white dwarf may eventually approach the Chandrasekhar limit.
The white dwarf companion could also accrete matter from other types of companions, including a subgiant or (if the orbit is sufficiently close) even a main sequence star. The actual evolutionary process during this accretion stage remains uncertain, as it can depend both on the rate of accretion and the transfer of angular momentum to the white dwarf companion.[21]
It has been estimated that single degenerate progenitors account for no more than 20% of all Type Ia supernovae.[22]

Double degenerate progenitors

A second possible mechanism for triggering a Type Ia supernova is the merger of two white dwarfs whose combined mass exceeds the Chandrasekhar limit. The resulting merger is called a super-Chandrasekhar mass white dwarf.[23][24] In such a case, the total mass would not be constrained by the Chandrasekhar limit.
Collisions of solitary stars within the Milky Way occur only once every 107-1013 years; far less frequently than the appearance of novae.[25] Collisions occur with greater frequency in the dense core regions of globular clusters[26] (cf. blue stragglers). A likely scenario is a collision with a binary star system, or between two binary systems containing white dwarfs. This collision can leave behind a close binary system of two white dwarfs. Their orbit decays and they merge through their shared envelope.[27]However, a study based on SDSS spectra found 15 double systems of the 4,000 white dwarfs tested, implying a double white dwarf merger every 100 years in the Milky Way. Conveniently, this rate matches the number of Type Ia supernovae detected in our neighborhood.[28]
A double degenerate scenario is one of several explanations proposed for the anomalously massive (2 M) progenitor of the SN 2003fg.[29][30] It is the only possible explanation for SNR 0509-67.5, as all possible models with only one white dwarf have been ruled out.[31] It has also been strongly suggested for SN 1006, given that no companion star remnant has been found there.[22] Observations made with NASA's Swift space telescope ruled out existing supergiant or giant companion stars of every Type Ia supernovae studied. The supergiant companion's blown out outer shell should emit X-rays, but this glow was not detected by Swift's XRT (X-Ray telescope) in the 53 closest supernova remnants. For 12 Type Ia supernovae observed within 10 days of the explosion, the satellite's UVOT (Ultraviolet/Optical Telescope) showed no ultraviolet radiation originating from the heated companion star's surface hit by the supernova shock wave, meaning there were no red giants or larger stars orbiting those supernova progenitors. In the case of SN 2011fe, the companion star must have been smaller than the Sun, if it existed.[32] The Chandra X-ray Observatory revealed that the X-ray radiation of five elliptical galaxies and the bulge of the Andromeda galaxy is 30-50 times fainter than expected. X-ray radiation should be emitted by the accretion discs of Type Ia supernova progenitors. The missing radiation indicates that few white dwarfs possess accretion discs, ruling out the common, accretion-based model of Ia supernovae.[33] Inward spiraling white dwarf pairs are strong sources of gravitational waves.
Double degenerate scenarios raise questions about the applicability of Type Ia supernovae as standard candles, since total mass of the two merging white dwarfs varies significantly, meaning luminosity also varies.

Type Iax

It has been proposed that a group of sub-luminous supernovae that occur when helium accretes onto a white dwarf should be classified as Type Iax.[34][35] This type of supernova may not always completely destroy the white dwarf progenitor.[36]

Observation


Supernova remnant N103B taken by the Hubble Space Telescope.[37]
Unlike the other types of supernovae, Type Ia supernovae generally occur in all types of galaxies, including ellipticals. They show no preference for regions of current stellar formation.[38] As white dwarf stars form at the end of a star's main sequence evolutionary period, such a long-lived star system may have wandered far from the region where it originally formed. Thereafter a close binary system may spend another million years in the mass transfer stage (possibly forming persistent nova outbursts) before the conditions are ripe for a Type Ia supernova to occur.[39]

A long-standing problem in astronomy has been the identification of supernova progenitors. Direct observation of a progenitor would provide useful constraints on supernova models. As of 2006, the search for such a progenitor had been ongoing for longer than a century.[40] Observation of the supernova SN 2011fe has provided useful constraints. Previous observations with the Hubble Space Telescope did not show a star at the position of the event, thereby excluding a red giant as the source. The expanding plasma from the explosion was found to contain carbon and oxygen, making it likely the progenitor was a white dwarf primarily composed of these elements.[41] Similarly, observations of the nearby SN PTF 11kx,[42] discovered January 16, 2011 (UT) by the Palomar Transient Factory (PTF), lead to the conclusion that this explosion arises from single-degenerate progenitor, with a red giant companion, thus suggesting there is no single progenitor path to SN Ia. Direct observations of the progenitor of PTF11kx were reported in the August 24 edition of Science and support this conclusion, and also show that the progenitor star experienced periodic nova eruptions before the supernova - another surprising discovery. [43][44] However, later analysis revealed that the circumstellar material (CSM) is too massive for the single-degenerate scenario, and fits better the core-degenerate scenario.[45]

Light curve


This plot of luminosity (relative to the Sun, L0) versus time shows the characteristic light curve for a Type Ia supernova. The peak is primarily due to the decay of nickel (Ni), while the later stage is powered by cobalt (Co).
Type Ia supernovae have a characteristic light curve, their graph of luminosity as a function of time after the explosion. Near the time of maximal luminosity, the spectrum contains lines of intermediate-mass elements from oxygen to calcium; these are the main constituents of the outer layers of the star. Months after the explosion, when the outer layers have expanded to the point of transparency, the spectrum is dominated by light emitted by material near the core of the star, heavy elements synthesized during the explosion; most prominently isotopes close to the mass of iron (iron-peak elements). The radioactive decay of nickel-56 through cobalt-56 to iron-56 produces high-energy photons, which dominate the energy output of the ejecta at intermediate to late times.[14]

The use of Type Ia supernovae to measure precise distances was pioneered by a collaboration of Chilean and US astronomers, the Calán/Tololo Supernova Survey.[46] In a series of papers in the 1990s the survey showed that while Type Ia supernovae do not all reach the same peak luminosity, a single parameter measured from the light curve can be used to correct unreddened Type Ia supernovae to standard candle values. The original correction to standard candle value is known as the Phillips relationship[47] and was shown by this group to be able to measure relative distances to 7% accuracy.[48] The cause of this uniformity in peak brightness is related to the amount of nickel-56 produced in white dwarfs presumably exploding near the Chandrasekhar limit.[49]
The similarity in the absolute luminosity profiles of nearly all known Type Ia supernovae has led to their use as a secondary standard candle in extragalactic astronomy.[50]Improved calibrations of the Cepheid variable distance scale[51] and direct geometric distance measurements to NGC 4258 from the dynamics of maser emission[52] when combined with the Hubble diagram of the Type Ia supernova distances have led to an improved value of the Hubble constant.

In 1998, observations of distant Type Ia supernovae indicated the unexpected result that the Universe seems to undergo an accelerating expansion.[53][54] Three members from two teams were subsequently awarded Nobel Prizes for this discovery.[55]

Types


It has been discovered that Type Ia supernovae that were considered the same are in fact different; moreover, a form of the Type Ia supernova that is relatively infrequent today was far more common earlier in the history of the universe. This could have far reaching cosmological significance and could lead to revision of estimation of the rate of expansion of the universe and the prevalence of dark energy.[56][57]

https://en.wikipedia.org/wiki/Type_Ia_supernova












There’s controversial evidence for the presence of an ex-companion star in Tycho’s supernova remnant. The explosion happened in 1572. (NASA/CXC/Chinese Academy of Sciences/F. Lu)
 
There's controversial evidence for the presence of an ex-companion star in Tycho's supernova remnant. The explosion happened in 1572. (NASA/CXC/Chinese Academy of Sciences/F. Lu)
http://phenomena.nationalgeographic.com/2014/08/28/type-1a-supernovas-cosmic-candle-mystery/






Supernova é um evento astronômico que ocorre durante os estágios finais da evolução de algumas estrelas, que é caracterizado por uma explosão muito brilhante. Por um curto espaço de tempo, isto causa um efeito similar ao surgimento de uma estrela nova, antes de desaparecer lentamente ao longo de várias semanas ou meses.
Em apenas alguns dias o seu brilho pode intensificar-se em 1 bilhão de vezes a partir de seu estado original, tornando a estrela tão brilhante quanto uma galáxia, mas, com o passar do tempo, sua temperatura e brilho diminuem lentamente.
A explosão de uma supernova de tipo II pode expulsar para o espaço até 90% da matéria da estrela progenitora. O núcleo remanescente tem massa superior a 1,5 massas solares, a pressão de degenerescência dos elétrons não é mais suficiente para manter o núcleo estável; então os elétrons são capturados pelos prótons, originando nêutrons: o resultado é uma estrela composta de nêutrons, com aproximadamente 15 km de diâmetro e extremamente densa, conhecida como estrela de nêutrons ou pulsar. Mas, quando a massa desse núcleo ultrapassa 3 massas solares, nem mesmo a pressão de degenerescência dos nêutrons consegue manter o núcleo estável; então a estrela continua a colapsar, o que dá origem a uma singularidade no espaço-tempo, conhecida como buraco negro, cuja velocidade de escape é maior do que a velocidade da luz.

Uma supernova foi descoberta 20 vezes mais brilhante em seu pico do que a luz combinada de 100 bilhões de estrelas da galáxia Via Láctea, tornando-a a supernova mais brilhante já observada até 2016[1]. Atualmente, as supernovas tipo Ia são utilizadas como velas padrão para estudos da expansão do universo, técnica similar à utilizada por Edwin Hubble com cefeidas, mas, com eficiência muito maior, pois o brilho das supernovas é bem maior.

Etimologia

Em Latim, “Nova” quer dizer “Novo”, ou seja, referindo-se astronomicamente para o que parece ser uma nova estrela temporária. Adicionando o prefixo “super-“, difere das “Novas” comuns, que são muito menos luminosas. A palavra “supernova” foi inventada por Walter Baade e Fritz Zwicky em 1931.[2]

Descoberta

Os primeiros trabalhos sobre o que inicialmente acreditava ser simplesmente uma nova categoria de “novas” foi realizado durante os anos 1930 por Walter Baade e Fritz Zwicky no Observatório Mount Wilson[3]. O nome  super-novas foi usado pela primeira vez em 1931, durante palestras realizadas no Caltech (Instituto de Tecnologia da Califórnia) por Baade e Zwicky, em seguida, utilizada publicamente em 1933 em uma reunião da Sociedade Americana de Física[2].  
Em 1938, o hífen tinha sido perdido e o nome moderno “supernovas” estava em uso[4].  Porque supernovas são eventos relativamente raros dentro de uma galáxia, que ocorrem cerca de três vezes por século na Via Láctea,[5]  a obtenção de uma boa amostra de supernovas para ser estudado requer um acompanhamento regular de muitas galáxias.   
Supernovas em outras galáxias não podem ser previstas com exatidão significativa. Normalmente, quando são descobertas, elas já estão em andamento.[6]  A maioria dos interesses científicos em velas de supernovas, como padrão para medir a distância, por exemplo, exigem uma observação de seu pico de luminosidade. Portanto, é importante descobrir-las bem antes que eles atinjam o seu máximo.
Astrônomos amadores, que muitas vezes ultrapassam os astrônomos profissionais, têm desempenhado um papel importante na busca de supernovas, normalmente, olhando para algumas das galáxias mais próximas através de um telescópio óptico e comparando-as com fotografias anteriores.[7] 

Ocorrência e catalogação

Por ser um fenômeno relativamente raro em uma galáxia, as supernovas são catalogadas, segundo o ano e a ordem da ocorrência, às vezes imediatamente "quando a lâmina de luz chega à Terra" como foi o caso da supernova de fevereiro de 1987, inicialmente denominada SN 1987. Se descobrissem outra (em arquivos fotográficos), adquire o nome de Sn 1987 B. Como, até agora, em nenhuma chapa fotográfica fez-se registro de igual ocorrência naquele ano, quer nessa ou em outra galáxia, ficou dispensada a letra A. De modo que, em nossa própria galáxia, só foram observadas, até agora, apenas 3 supernovas: em 1054, 1572, 1604, as quais, devido à data, não foram bem estudadas. E, além destas três, parecem ter sido cerca de 11 as supernovas que explodiram na Via Láctea nos últimos 20.000 anos, sempre em locais inobserváveis devido à poeira interestelar.
A supernova SN 1987A, ocorrida na galáxia satélite da Via Láctea chamada Grande Nuvem de Magalhães, foi a explosão estelar recente mais próxima da Terra, tendo sido observada com equipamentos de duas gerações ou seja os telescópios terrestres e os espaciais.

Supernova 1987
Diante desses números e o observado em todo o universo, calcula-se que ocorram, em média, 3 supernovas por milênio, em cada lado de galáxia (só vemos um lado) que tenha 200.000.000.000 de estrelas. Comparando com o número de estrelas que formam uma galáxia, os cosmólogos podem estimar alguns valores, como a idade das galáxias ou, se quiserem, a idade do universo observável. Compare-se esse número com a média de 30.000 novas comuns no mesmo período. Ou seja, para cada 10.000 novas, há uma supernova.
Partindo do pressuposto que ocorram 3 supernovas por milênio em nossa galaxia e, considerando que a idade da Via Láctea seja de entre 13 a 13,8 bilhões de anos, matematicamente podem ter ocorrido cerca de 39 milhões de explosões de supernovas em nossa própria galáxia.

Impacto no meio interestelar

Fontes de elementos pesados

As supernovas, são as principais fontes de elementos mais pesados que o oxigênio. Esses elementos são produzidos por fusão entre núcleos (fusão nuclear).

Tipos atuais

Tipo Ia

Ver artigo principal: Supernova tipo Ia
Há vários meios pelo quais uma supernova desse tipo pode se formar, mas eles compartilham um mecanismo interno comum. Se uma anã branca de carbono-oxigênio agregar bastante matéria para alcançar o limite de Chandrasekhar, de cerca de 1.38 massas solares [8] (para uma estrela que não gire), ela poderá não ser mais capaz de suportar a carga do seu plasma, através da pressão de degeneração eletrônica, e entrar em colapso por isto. Contudo, a visão atual do fenômeno é que este limite não é normalmente atingido; aumentando a temperatura e a densidade no interior do núcleo detonando a fusão nuclear do carbono quando a estrela aproxima deste limite (em cerca de 1%) antes do colapso ter iniciado.[8] Em poucos segundos, uma fração substancial da matéria da anã branca é consumida pela fusão nuclear, liberando bastante energia (1–2 × 1044 joules). Uma onda de choque, expandindo-se externamente, é gerada, com a matéria atingindo velocidades da ordem de 5,000–20,000 km/s ou, aproximadamente, 3% da velocidade da luz. Haverá, também, um aumento significativo da luminosidade, alcançando uma magnitude absoluta de -19.3 (ou 5 bilhões de vezes mais brilhante do que o Sol), com pequenas variações.

Tipo Ib e Ic

Ver artigo principal: Supernova tipo Ib e Ic

SN 2008D, uma supernova do tipo Ib[9], mostrada no espectro de raio X (a esquerda) e em luz visivel (a direita). foto da NASA.[10]
Estes eventos, tais como supernovas do Tipo II, são provavelmente estrelas massivas esgotadas de combustíveis em seus centros; contudo, os progenitores dos Tipos Ib e Ic perderam a maior parte de seu envoltório externo de hidrogênio, devido a seu forte vento solar ou devido à interação com uma companheira.[11]. Supernovas do tipo lb são tidas como resultantes do colapso de uma maciça estrela Wolf-Rayet. Existem algumas evidências de que uma pequena porcentagem das supernovas do tipo Ic podem ser a fonte de erupção de raios gama

https://pt.wikipedia.org/wiki/Supernova








Descrição: Gravura que surge no livro Astronomie Populaire, de Camille Flammarion (1872), e que ilustra Tycho Brahe a observar a supernova pela primeira vez. (©Astronomie Populaire - Camille Flammarion (1872))