A hiper estrela / Hyper star

A hiper-estrela R136a1, no plano de fundo, comparada ao nosso Sol - relativamente franzino - R136a1 (localizada no centro da imagem) tem uma massa detectada de 265 vezes a do Sol. Cientistas da Universdade de Sheffield encontraram o gigante estelar – nomeado R136a1 – usado o Ultra Grande Telescópio do Observatório Europeu do Sul, no Chile e dados do Telescópio Espacial Hubble.

A estrela localiza-se na Nebulosa da Tarântula, na Grande Nuvem de Magalhães, uma pequena galáxia "satéllite" que orbita a Via Láctea. Até então, as estrelas maiss pesadas conhecidas tinham cerca de 150 vezes a massa do Sol, e acreditava-se ser este próximo do tamanho-limite cósmico.

À medida que as estrelas tornam-se mais massivas, a quantidade de energia criada em seus núcleos aumenta a uma taxa mais rápida que a força da gravidade, que as mantém coesas. As torrentes de energia produzidas finalmente tornam-se tão poderosas que as estrelas se dividem.

Este é conhecido como o "Limite de Eddington", em homenagem ao físico britânico Arthur Eddington que, em 1919, provou a Teoria da Relatividade de Einstein ao mostrar que a luz é desviada pela gravidade.

It was believed that the Eddington Limit was reached at around 150 solar masses. However, R136a1 has been measured at 265 solar masses. Since heavy stars rapidly lose mass as they grow older by converting it into energy, R136a1 has already lost 20 per cent of its mass in its short million-year life. It is believed originally to have been a colossal 320 solar masses. The Sun, by comparison, has been burning for 4.57 billion years, and has converted only 0.03 per cent of its mass into energy.

O pesquisador-chefe da equipe de Sheffield, professor Paul Crowther, disse à Astronomy Now: "Devido à sua proximidade ao Limite de Eddington, elas perdem massa a uma taxa bem alta."

Isso significa que elas são incrivelmente brilhantes e quentes – acredita-se que a R136a1 tenha uma temperatura de superfície de mais de 40.000 graus Celsius, e que seja 10 mihões de vezes mais brilhante que o Sol.

Entre as maiores estrelas conhecidas até agora estão a Estrela Pistola, entre 80 e 150 vezes a massa solar, e Eta Carinae, em torno de 100 vezes a massa solar. A Estrela Pistola irradia tanta energia em 20 segundos quanto nosso Sol o faz em um ano. No entanto, ambas ficaram diminuídas com a nova descoberta.

Segundo a Astronomy Now, R136a1 libera mais energia que todas as estrelas da Nebulosa de Orion, e se estivesse em nosso sistema solar, seria tão mais brilhante que o Sol quanto esse o é do que a Lua.

Há quatro estrelas no aglomerado RCM 136a, onde fica a R136a1, com uma massa superior a 150 vezes a do Sol. Essas quatro estrelas sozinhas fornecem metade da energia do aglomerado inteiro, que contém 100.000 estrelas no total.

Hiper estrelas como a R136a1 devem ter-se formado a partir de várias jovens estrelas fundindo-se, e só são encontradas bem no coração dos aglomerados estelares.

Hyper-star R136a1, in the background, compared to our own - relatively puny - Sun.

R136a1 (located at the center of the image) has been found to have a current mass of 265 times that of the Sun.

The Tarantula Nebula with the cluster of stars named RMC 136a marked with a red box Scientists at the University of Sheffield found the stellar giant – named R136a1 – using the European southern Observatory's Very Large Telescope in Chile and data from the Hubble Space Telescope.

The star is located in the Tarantula Nebula in the Large Magellanic Cloud, a small "satellite" galaxy which orbits the Milky Way.

Previously, the heaviest known stars were around 150 times the mass of the Sun, and this was believed to be close to the cosmic size limit.

As stars get more massive the amount of energy created in their cores grows at a faster rate than the force of gravity which holds them together. The torrents of energy produced eventually become so powerful that the stars are torn apart.

This is known as the "Eddington Limit", after the British physicist Arthur Eddington who, in 1919, proved Einstein's theory of relativity by showing that light is bent by gravity.

It was believed that the Eddington Limit was reached at around 150 solar masses.

However, R136a1 has been measured at 265 solar masses. Since heavy stars rapidly lose mass as they grow older by converting it into energy, R136a1 has already lost 20 per cent of its mass in its short million-year life. It is believed originally to have been a colossal 320 solar masses. The Sun, by comparison, has been burning for 4.57 billion years, and has converted only 0.03 per cent of its mass into energy.

The chief researcher in the Sheffield team, Professor Paul Crowther, told Astronomy Now: "Because of their proximity to the Eddington Limit they lose mass at a pretty high rate." This means that they are incredibly bright and hot – R136a1 is believed to have a surface temperature of more than 40,000 degrees Celsius, and is 10 million times brighter than the Sun.

Among the largest known stars previously known were the Pistol Star, between 80 and 150 solar masses, and Eta Carinae, around 100 solar masses. The Pistol Star radiates as much energy in 20 seconds as our Sun does in a year. However, both are utterly dwarfed by the vast new discovery.

According to Astronomy Now, R136a1 gives off more energy than all the stars in the Orion Nebula, and if it were in our solar system would be as much brighter than the Sun as the Sun is than the Moon.

There are four stars in the cluster RCM 136a, where R136a1 sits, with a mass over 150 that of the Sun. Those four stars alone give off half the energy of the entire cluster, which contains 100,000 stars in total.

Hyper-stars like R136a1 are believed to be formed from several young stars merging together, and are only found in the very heart of stellar clusters.