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Oldest known star found by Australian astronomers

A TEAM LED BY ASTRONOMERS at The Australian National University has discovered the oldest known star in the Universe, which formed shortly after the Big Bang 13.7 billion years ago.

The discovery has allowed astronomers for the first time to study the chemistry of the first stars, giving scientists a clearer idea of what the Universe was like in its infancy.

“This is the first time that we’ve been able to unambiguously say that we’ve found the chemical fingerprint of a first star,” said lead researcher, Dr Stefan Keller of the ANU Research School of Astronomy and Astrophysics.

“This is one of the first steps in understanding what those first stars were like. What this star has enabled us to do is record the fingerprint of those first stars.”

The star was discovered using the ANU SkyMapper telescope at the Siding Spring Observatory, which is searching for ancient stars as it conducts a five-year project to produce the first digital map the southern sky.

Star SMSS J031300.36-670839.3

Astronomers have determined that star SMSS J031300.36-670839.3 is the oldest yet found.

A different star recipe

The ancient star is around 6,000 light years from Earth, relatively close in astronomical terms. It is one of the 60 million stars photographed by SkyMapper in its first year.

“The stars we are finding number one in a million,” says team member Professor Mike Bessell, who worked with Keller on the research.

“Finding such needles in a haystack is possible thanks to the ANU SkyMapper telescope that is unique in its ability to find stars with low iron from their colour.”

Dr Keller and Professor Bessell confirmed the discovery using the Magellan telescope in Chile.

The composition of the newly discovered star – known only as SMSS J031300.36-670839.3 – shows it formed in the wake of a primordial star, which had a mass 60 times that of our Sun.

“To make a star like our Sun, you take the basic ingredients of hydrogen and helium from the Big Bang and add an enormous amount of iron – the equivalent of about 1,000 times the Earth’s mass,” Dr Keller says.

Dr Stefan Keller with the SkyMapper telescope

Dr Stefan Keller with the SkyMapper telescope

“To make this ancient star, you need no more than an Australia-sized asteroid of iron and lots of carbon. It’s a very different recipe that tells us a lot about the nature of the first stars and how they died.”

No sign of iron

Dr Keller says it was previously thought that primordial stars died in extremely violent explosions that blasted their iron into huge volumes of space. But the ancient star shows signs of pollution with lighter elements such as carbon and magnesium, and no sign of pollution with iron.

“This indicates the primordial star’s supernova explosion was of surprisingly low energy. Although sufficient to disintegrate the primordial star, almost all of the heavy elements such as iron, were consumed by a black hole that formed at the heart of the explosion,” he says.

The result may resolve a long-standing discrepancy between observations and predictions of the Big Bang.

The discovery was published in the latest edition of the journal Nature.

Adapted from information issued by ANU.

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Hot star: don’t get too close!

WR 22 and the Carina Nebula

The hot, massive, young star in the centre of this image is WR 22, a member of the rare class of Wolf–Rayet stars, seen against the backdrop of the Carina Nebula. At the distance of the nebula, this image covers an area of 72 x 72 light-years.

A spectacular new image from the European Southern Observatory’s (ESO) Wide Field Imager at the La Silla Observatory in Chile shows the brilliant and unusual star WR 22 and its colourful surroundings.

WR 22 is a very hot and bright star that is shedding its atmosphere into space at a rate many millions of times faster than the Sun. It is located in the outer part of the dramatic Carina Nebula, a huge cloud of gas and dust from which it and many other stars formed.

Very massive stars live fast and die young. Some of them have such intense radiation passing through their thick atmospheres late in their lives that they shed gas into space many millions of times more quickly than relatively sedate stars such as our Sun.

These rare, very hot and massive objects are known as Wolf–Rayet stars, after the two French astronomers who first identified them in the mid-nineteenth century. Wolf-Rayet stars typically have surface temperatures between 25,000 and 50,000 degress Celsius. (The Sun’s surface temperature is only 5,500 degrees.)

WR 22 is one of the most massive examples yet measured, is one of many exceptionally brilliant stars associated with the beautiful Carina Nebula (also known as NGC 3372) in the southern Milky Way. The outer part of this huge region of star formation forms the colourful backdrop to this image.

See the full-size, high-resolution image here (0.7MB, will open in a new window)

The central part of nebula lies off to the left of WR 22, and can be seen in the wider view below.

A wider view of the Carina Nebula

A wider view of the Carina Nebula, showing WR 22 at right and a bright conglomeration at left that hides another huge and famous star, Eta Carinae.

See the full-size, high-resolution version of the wide-field image here (0.7MB, will open in a new window)

The subtle colours of the nebula are a result of the interactions between the intense ultraviolet radiation coming from hot massive stars, including WR 22, and the vast gas clouds, mostly hydrogen, from which they formed.

WR 22 is a part of a binary star system and has been measured to have a mass at least 70 times that of the Sun. Although it is over 5,000 light-years from Earth, it is so bright that it can just be faintly seen with the unaided eye under good conditions.

Adapted from information issued by ESO.

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