My six-year old daughter is a question asking machine. We were driving home from school a couple of days ago, and she was grilling me about the nature of the Universe. One of her zingers was this, “What’s the Biggest Star in the Universe”? I had an easy answer, the Universe is a big place, and there’s no way we can possibly know what the biggest star is. That didn’t go over so well. So she refined the question. What’s the biggest star that we know of?
Of course, I was stuck in the car, and without access to the Internet. But now I’m back at home, doing some research, and I thought I’d share the answer with the rest of you too.
Before we jump straight to the answer, let’s take a look at our own Sun for a sense of scale. Our familiar star is a mighty 1.4 million km across (870,000 miles). That’s such a huge number that it’s hard to get a sense of scale. The Sun accounts for 99.9% of all the matter in our Solar System. In fact, you could fit one million planet Earths inside the Sun.
Astronomers say colossal star known as R136a1 is more than 265 times more massive than the sun
Click to enlarge Visible-light image of the Tarantula nebula (left), zoomed-in image from the Very Large Telescope (centre), and the R136 cluster in near-infrared (right) with the cluster itself lower right. Photograph: ESO/PA
Astronomers say they have discovered the most colossal star on record, in a region of space known as the Tarantula nebula in a neighbouring galaxy to our own.
The record-breaking star has a mass 265 times greater than the sun and is millions of times brighter, they said.
The discovery has astonished scientists, who thought it was impossible for stars to exceed more than 150 times the mass of the sun.
When the star was born it could have been more than twice as massive. Because it is so far away – about 165,000 light-years – it can only be seen with the use of powerful telescopes in the southern hemisphere.
If the star, known as R136a1, took the place of the sun in our solar system, its gravitational attraction would pull our planet in so close that the length of an "Earth year" would shrink to three weeks.
"It would bathe the Earth with incredibly intense ultraviolet radiation, rendering life on our planet impossible," said Raphael Hirschi, a researcher at Keele University.
A team led by Paul Crowther, an astrophysicist at Sheffield University, used the Very Large Telescope (VLT) in the Atacama desert of northern Chile and archival material from the Hubble space telescope to study two young clusters of stars called NGC 3603 and RMC 136a.
The first group of stars, NGC 3603, lies about 22,000 light-years away, while stars in the RMC136a cluster are in a neighbouring galaxy called the Large Magellanic Cloud.
The astronomers found a clutch of monster stars, including several that are tens of times larger than the sun and several million times brighter. Some have surface temperatures of more than 40,000C – seven times hotter than our own sun.
These enormous stars churn out vast quantities of material, and, close up, would look fuzzy compared with the sun. "Unlike humans, these stars are born heavy and lose weight as they age," said Crowther. "Being a little over a million years old, the most extreme star, R136a1, is already 'middle-aged' and has undergone an intense weight-loss programme, shedding a fifth of its initial mass over that time, or more than 50 solar masses."
Such heavyweight stars are extremely rare, forming only within the densest star clusters. Distinguishing the individual stars was made possible by the use of infra-red instruments on the telescope.
"Owing to the rarity of these monsters I think it is unlikely that this new record will be broken any time soon," said Crowther.
A short but intense life
Lightweight stars, such as our sun, live a long and quiet life. Massive stars, on the other hand, are very rare, and have a short but intense existence before exploding as supernovas.
Star R136a1, discovered thousands of light years away from the solar system, the most massive star found to date. It has a mass about 265 times that of our own sun and would have been over 320 solar masses when it was born a million or so years ago.
R136a1 has now overtaken the likes of Eta Carinae and the Pistol Star as the most massive and luminous known star in existence. Like these other giants it has a large radius for its mass and surface temperature, over 40,000C. Its brightness is hundreds of thousands of times greater than that of the sun.
While still a young star, R136a1's size eclipses other categories: red dwarfs, which weigh in at about 0.1 solar masses, low-mass yellow dwarfs such as the sun, and massive blue dwarf stars weighing eight times more than the sun.
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