Astronomers² have confirmed that an exploding star spotted³ by Nasa's Swift satellite is the most distant cosmic object to be detected by telescopes.

天文学家已经证实，美国航空航天局的威夫特卫星拍摄到的一颗爆发星是天文望远镜探测到的最远的宇宙星体。

The redness of the afterglow is indicative of the event's distance

In the journal Nature, two teams of astronomers report their observations of a gamma-ray burst from a star that died 13.1 billion light-years away.

The massive star died about 630 million years after the Big Bang.

UK astronomer¹ Nial Tanvir described the observation as "a step back in cosmic time".

Professor Tanvir led an international team studying the afterglow（晚霞，夕阳） of the explosion, using the United Kingdom Infrared⁴ Telescope (UKIRT) in Hawaii.

He told BBC News that his team was able to observe the afterglow for 10 days, while the gamma ray burst itself lasted around 12 seconds.

The event, dubbed⁵ GRB 090423, is an example of one of the most violent explosions in the Universe.

It is thought to have been associated with the cataclysmic（洪水的，灾变的） death of a massive star - triggered by the centre of the star collapsing⁶ to form a "stellar（恒星的，星的）-sized" black hole.

"Swift detects something like 100 gamma ray bursts per year," said Professor Tanvir. "And we follow up on lots of them in the hope that eventually we will get one like this one - something really very distant."

Another team, led by Italian astronomer Ruben Salvaterra studied the afterglow independently with the National Galileo Telescope in La Palma.

Little red dot

He told BBC News: "This kind of observation is quite difficult, so having two groups have the same result with two different instruments makes this much more robust（强壮的，强健的）."

"It is not surprising - we expected to see an event this distant eventually," said Professor Salvaterra.

"But to be there when it happens is quite amazing - definitely something to tell the grandchildren."

The astronomers were able to calculate the vast distance using a phenomenon known as "red shift".

Most of the light from the explosion was absorbed by intergalactic（银河间的） hydrogen gas. As that light travelled towards Earth, the expansion of the Universe "stretches" its wavelength⁷, causing it to become redder.

"The greater that amount of movement [or stretching], the greater the distance." he said.

The image of this gamma ray burst was produced by combining several infrared images.

"So in this case, it's the redness of the dot that indicates that it is very distant," Professor Tanvir explained.

Before this record-breaking event, the furthest object observed from Earth was a gamma ray burst 12.9 billion light-years away.

"This is quite a big step back to the era（纪元，时代） when the first stars formed in the Universe," said Professor Tanvir.

"Not too long ago we had no idea where the first galaxies⁸ came from, so astronomers think this is a profound（深奥的，深厚的） moment.

"This is... the last blank bit of the map of the Universe - the time between the Big Bang and the formation of these early galaxies."

And this is not the end of the story.

Bing Zhang, an astronomer from the University of Nevada, who was not involved in this study, wrote an article in Nature, explaining its significance.

The discovery, he said, opened up the exciting possibility of studying the "dark ages" of the Universe with gamma ray bursts.

And Professor Tanvir is already planning follow-up studies "looking for the galaxy⁹ this exploding star occurred in."

Next year, he and his team will be using the Hubble Space Telescope to try to locate that distant, very early galaxy.