O pulsar é um tipo de estrela de nêutrons que emite energia eletromagnética a intervalos periódicos. As estrelas de nêutrons são os corpos celestes mais parecidos com os buracos negros que astrônomos conseguem observar diretamente, concentrando 500 mil vezes mais massa do que a de todo o planeta Terra, em uma esfera cujo tamanho não ultrapassa o de uma cidade. A matéria é tão concentrada que uma colher de chá pesa tanto quanto o Monte Everest.
"Com este novo grupo de pulsares, o Fermi já detectou até agora mais de 100 desses objetos, o que é um marco importante, considerando-se que, antes do lançamento do Fermi, em 2008, sabia-se que apenas sete deles emitiam raios gama," diz Pablo Saz Parkinson, astrofísico do Instituto Santa Cruz de Física de Partículas da Universidade da California, Santa Cruz, e coautor de dois artigos com os detalhes das descobertas.
Um grupo de pulsares combina densidade enorme e rotação extrema. Os mais veloz desses chamados pulsares de milissegundos gira ao ritmo de 43.000 revoluções por minuto.
Um grupo de pulsares combina densidade enorme e rotação extrema. Os mais veloz desses chamados pulsares de milissegundos gira ao ritmo de 43.000 revoluções por minuto.
Acredita-se que pulsares de milissegundos atinjam tais velocidades por estarem gravitacionalmente presos a sistemas binários com estrelas normais. Durante parte de suas vidas estelares, gás flui da estrela normal para o pulsar. Com o tempo, o impacto desse gás em queda gradualmente acelera a rotação do pulsar.
Os fortes campos magnéticos e a rápida rotação dos pulsares faz com que eles emitam potentes feixes de energia, de ondas de rádio até raios gama. Como a estrela transfere energia rotacional ao pulsar, o giro dele diminui depois que essa transferência termina.
Normalmente, pulsares de milissegundos têm em torno de 1 bilhão de anos de idade. No entanto, na edição de 3 de novembro da revista Science, a equipe do Fermi revela a existência de um pulsar brilhante e energético de milissegundos com apenas 25 milhões de anos de idade.
O objeto, designado PSR J1823−3021A, fica em NGC 6624, um agrupamento esférico de velhas estrelas, chamado aglomerado globular, um dos cerca de 160 objetos semelhantes que orbitam nossa galáxia. O aglomerado tem cerca de 10 bilhões de anos de idade, e está localizado a aproximadamente 27.000 anos-luz da Terra, na direção da constelação de Sagitário.
O Telescópio de Grande Área do Fermi (LAT) mostrou como onze aglomerados globulares emitem raios gama, a emissão cumulativa de dezenas de pulsares de milissegundos, fraca demais até mesmo para o Fermi detectá-las individualmente. Mas não é o caso de NGC 6624.
"É surpreendente que todos os raios gama que vemos desse aglomerado venham de apenas um objeto. Ele deve ter-se formado recentemente, considerando-se a rapidez com que emite energia. É mais ou menos como um bebê chorando em uma silenciosa casa de repouso," disse Paulo Freire, autor principal do estudo, no Instituto Max Planck de Radioastronomia, em Bonn, Alemanha.
O J1823−3021A foi identificado anteriormente como um pulsar por suas emissões de rádio, ainda que dos nove novos pulsares, nenhum seja de milissegundos, e somente um foi posteriormente identificado como emissor de ondas de rádio.
A pulsar is a type of neutron star that emits electromagnetic energy at periodic intervals. A neutron star is the closest thing to a black hole that astronomers can observe directly, crushing half a million times more mass than Earth into a sphere no larger than a city. This matter is so compressed that even a teaspoonful weighs as much as Mount Everest.
"With this new batch of pulsars, Fermi now has detected more than 100, which is an exciting milestone when you consider that, before Fermi's launch in 2008, only seven of them were known to emit gamma rays," said Pablo Saz Parkinson, an astrophysicist at the Santa Cruz Institute for Particle Physics at the University of California Santa Cruz, and a co-author on two papers detailing the findings.
One group of pulsars combines incredible density with extreme rotation. The fastest of these so-called millisecond pulsars whirls at 43,000 revolutions per minute.
Millisecond pulsars are thought to achieve such speeds because they are gravitationally bound in binary systems with normal stars. During part of their stellar lives, gas flows from the normal star to the pulsar. Over time, the impact of this falling gas gradually spins up the pulsar's rotation.
The strong magnetic fields and rapid rotation of pulsars cause them to emit powerful beams of energy, from radio waves to gamma rays. Because the star is transferring rotational energy to the pulsar, the pulsar's spin slows after this transfer is completed.
Typically, millisecond pulsars are around a billion years old. However, in the Nov. 3 issue of Science, the Fermi team reveals a bright, energetic millisecond pulsar only 25 million years old.
The object, named PSR J1823−3021A, lies within NGC 6624, a spherical collection of ancient stars called a globular cluster, one of about 160 similar objects that orbit our galaxy. The cluster is about 10 billion years old and lies about 27,000 light-years away toward the constellation Sagittarius.
Fermi's Large Area Telescope (LAT) showed that eleven globular clusters emit gamma rays, the cumulative emission of dozens of millisecond pulsars too faint for even Fermi to detect individually. But that's not the case for NGC 6624.
"It's amazing that all of the gamma rays we see from this cluster are coming from a single object. It must have formed recently based on how rapidly it's emitting energy. It's a bit like finding a screaming baby in a quiet retirement home," said Paulo Freire, the study's lead author, at the Max Planck Institute for Radio Astronomy in Bonn, Germany.
J1823−3021A was previously identified as a pulsar by its radio emission, yet of the nine new pulsars, none are millisecond pulsars, and only one was later found to emit radio waves.
One group of pulsars combines incredible density with extreme rotation. The fastest of these so-called millisecond pulsars whirls at 43,000 revolutions per minute.
Millisecond pulsars are thought to achieve such speeds because they are gravitationally bound in binary systems with normal stars. During part of their stellar lives, gas flows from the normal star to the pulsar. Over time, the impact of this falling gas gradually spins up the pulsar's rotation.
The strong magnetic fields and rapid rotation of pulsars cause them to emit powerful beams of energy, from radio waves to gamma rays. Because the star is transferring rotational energy to the pulsar, the pulsar's spin slows after this transfer is completed.
Typically, millisecond pulsars are around a billion years old. However, in the Nov. 3 issue of Science, the Fermi team reveals a bright, energetic millisecond pulsar only 25 million years old.
The object, named PSR J1823−3021A, lies within NGC 6624, a spherical collection of ancient stars called a globular cluster, one of about 160 similar objects that orbit our galaxy. The cluster is about 10 billion years old and lies about 27,000 light-years away toward the constellation Sagittarius.
Fermi's Large Area Telescope (LAT) showed that eleven globular clusters emit gamma rays, the cumulative emission of dozens of millisecond pulsars too faint for even Fermi to detect individually. But that's not the case for NGC 6624.
"It's amazing that all of the gamma rays we see from this cluster are coming from a single object. It must have formed recently based on how rapidly it's emitting energy. It's a bit like finding a screaming baby in a quiet retirement home," said Paulo Freire, the study's lead author, at the Max Planck Institute for Radio Astronomy in Bonn, Germany.
J1823−3021A was previously identified as a pulsar by its radio emission, yet of the nine new pulsars, none are millisecond pulsars, and only one was later found to emit radio waves.
A pulsar is a type of neutron star that emits electromagnetic energy at periodic intervals. A neutron star is the closest thing to a black hole that astronomers can observe directly, crushing half a million times more mass than Earth into a sphere no larger than a city. This matter is so compressed that even a teaspoonful weighs as much as Mount Everest.
One group of pulsars combines incredible density with extreme rotation. The fastest of these so-called millisecond pulsars whirls at 43,000 revolutions per minute.
Millisecond pulsars are thought to achieve such speeds because they are gravitationally bound in binary systems with normal stars. During part of their stellar lives, gas flows from the normal star to the pulsar. Over time, the impact of this falling gas gradually spins up the pulsar's rotation.
The strong magnetic fields and rapid rotation of pulsars cause them to emit powerful beams of energy, from radio waves to gamma rays. Because the star is transferring rotational energy to the pulsar, the pulsar's spin slows after this transfer is completed.
Typically, millisecond pulsars are around a billion years old. However, in the Nov. 3 issue of Science, the Fermi team reveals a bright, energetic millisecond pulsar only 25 million years old.
The object, named PSR J1823−3021A, lies within NGC 6624, a spherical collection of ancient stars called a globular cluster, one of about 160 similar objects that orbit our galaxy. The cluster is about 10 billion years old and lies about 27,000 light-years away toward the constellation Sagittarius.
Fermi's Large Area Telescope (LAT) showed that eleven globular clusters emit gamma rays, the cumulative emission of dozens of millisecond pulsars too faint for even Fermi to detect individually. But that's not the case for NGC 6624.
"It's amazing that all of the gamma rays we see from this cluster are coming from a single object. It must have formed recently based on how rapidly it's emitting energy. It's a bit like finding a screaming baby in a quiet retirement home," said Paulo Freire, the study's lead author, at the Max Planck Institute for Radio Astronomy in Bonn, Germany.
J1823−3021A was previously identified as a pulsar by its radio emission, yet of the nine new pulsars, none are millisecond pulsars, and only one was later found to emit radio waves.
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