The phenomenon in 774 A.D. may have been a previously unrecognized supernova explosion and could explain a mysterious spike in carbon-14 levels in that year's growth rings in Japanese cedar trees, Nature reported Wednesday. Jonathon Allen, a biochemistry major at the University of California, Santa Cruz, heard about research in Japan that found an odd spike in carbon-14 levels in tree rings, probably caused by a burst of high-energy radiation striking the upper atmosphere and increasing the rate at which carbon-14 is formed. However, the only known causes of such bursts are supernova explosions or gigantic solar flares, and there was no historical record of any such events in the dates indicated by the tree rings.
Allen, intrigued, went on the Internet. "I just did a quick Google search," he said. "I knew that going that far back, there's very limited written history," he said. "The only things I'd ever seen or heard of were religious texts and 'chronicles' that listed kings and queens, wars and things of that nature." His Internet search led to eighth-century entries in the Anglo-Saxon Chronicle in an online library of historical and legal documents hosted by Yale University, where he found a reference to a "red crucifix" that appeared in the heavens "after sunset." "It made me think it's some sort of stellar event," Allen said.
Astronomers say they are impressed by Allen's find. "The wording suggests that the object was seen in the western skies shortly after sunset," Geza Gyuk, an astronomer at Chicago's Adler Planetarium, said. "That would mean that it would have moved behind the Sun [where it could not be seen] as Earth orbited the Sun. That, along with the dimness of the 'new star' due to dust would go a long way to explaining why no one else would have seen or recorded the event." Numbers of supernovae now known to astronomers "are simply missing" in the historical record, Gyuk said. "The sky is a large place and the historical record is not very good."
Read more: Ancient text may solve cosmic mystery - UPI.com
Nicknamed "Mingus", it was described at the 221st American Astronomical Society meeting in the US. These lightshows of dying stars have been seen since ancient times, but modern astronomers use details of their light to probe the Universe's secrets. Ten billion light-years distant, Mingus will help shed light on so-called dark energy, the force that appears to be speeding up cosmic expansion. Formally called SN SCP-0401, the supernova was something of a chance find in a survey carried out in part by the Supernova Cosmology Project (SCP) using the Hubble space telescope, first undertaken in 2004. But the data were simply not good enough to pin down what was seen. As David Rubin of the University of California, Berkeley, lead author on the study, told the AAS meeting, "for a sense of brightness, this supernova is about as bright as a firefly viewed from 3,000 miles away".
Further news had to wait until astronauts installed the Wide Field Camera 3 on the Hubble telescope in 2009 and again trained it on the candidate, which had - in an SCP tradition of naming supernovae after composers - already been named after jazz musician Charles Mingus. "Unfortunately, it took the development of Wide Field Camera 3 to bring home what the  measurements meant," Mr Rubin told BBC News. "The sensitivity is a few times better, which makes a huge difference, and we have a much cleaner image." The team went on to confirm that the supernova was in fact a Type 1a - a particular class of exploded star whose light occurs in such a regular way that it is known as a "standard candle".
'Bit of history'
What interests astronomers trying to find ever more distant Type 1a supernovae - distant both in space and in time - is the chance to compare them to better-known, more local supernovae. "We were able to watch these changes in brightness and spectral features for an event that lasted just a few weeks almost 10 billion years ago," said Saul Perlmutter, who leads the Supernova Cosmology Project. Prof Perlmutter shared the 2011 Nobel prize in physics for work with Type 1a supernovae that proved our Universe is speeding up in its expansion.
Elucidating the mysterious force, "dark energy", which has been invoked as the cause of the expansion, will require careful study of supernovae all the way back to the epoch of the earliest stars. "We're seeing two-thirds of the way back to the beginning of the Universe, and we're getting a little bit of history where the physics of what makes a supernova explode have to all work out the same way there as they do near here," he told the meeting. The group's study is published online and will appear in the Astrophysical Journal on 20 January.
The international team found a supernova shock wave — or shock breakout — only in the larger supernova, a finding that will help them understand these complex explosions that create many of the elements that make up humans, the Earth and the Solar System. “It’s like the shockwave from a nuclear bomb, only much bigger, and no one gets hurt,” said Dr Brad Tucker, from ANU Research School of Astronomy and Astrophysics.
The brilliant flash of an exploding star’s shockwave — what astronomers call the “shock breakout” — has been captured for the first time in visible light by NASA’s planet-hunter, the Kepler space telescope. Simulation credit: NASA/STSci.
Supernovae like these — known as Type II — begin when the internal furnace of a star runs out of nuclear fuel causing its core to collapse as gravity takes over. Supernovae are so bright that they can be seen in distant galaxies, which has helped astronomers learn much about the large-scale structure of the universe. However, very little is known about the early stages of these explosions.
The research, published in the Astrophysical Journal, reports the explosions of two old-age stars, red supergiants. As the core of a supernova collapses to form a neutron star, energy bounces back from the core in the form of a shockwave that travels at 30,000 to 40,000 kilometres per second, and causes the nuclear fusion that creates heavy elements such as gold, silver and uranium.
In one study, based at the Technical University of Munich, scientists from Germany and the US who found the iron isotopes in samples found on both the lunar surface and the ocean floor say this provides provides evidence that they were produced by the same supernova. Based on their data the researchers say their findings confirm the star that produced the telltale isotopes was about 300 light years away from us – a relatively close distance – when it exploded about 2 million years ago.
When a star explodes it creates new chemical elements, such as 60Fe, that are then blasted into space. They say that while the 60Fe isotope is produced almost exclusively by a supernova, it’s also possible that lunar material bombarded with cosmic particles could have also created the radioactive iron. “But this can only account for a very small portion of the 60Fe found,” said Dr. Gunther Korschinek, physicist at TUM and scientist of the Cluster of Excellence Structure and Origin of the Universe in a press release.
Mosaic image captured by the NASA/ESA Hubble Space Telescope shows a detailed look of the a small section of the Veil Nebula, the remains of a massive star that exploded about 8,000 years ago.
The radioactive iron isotope is said to have a half-life (time it takes a particle to fall to half its original value) of 2.62 million years, which in comparison to the age of the solar system – about 4.6 billion years – is a pretty short time. The researchers say that because of its half-life it’s doubtful that these isotopes were created when the solar system was formed. To make their findings the research team analyzed lunar samples, gathered by several of the Apollo missions to the moon in the late 1960′s to early 1970’s with the high-sensitivity accelerator mass spectrometer of the Maier-Leibnitz Laboratory near Munich.
The other study by an international team of scientists led by Dr. Anton Wallner, a nuclear physicist at the Australian National University Research School of Physics and Engineering reveals evidence of not just one but a succession of massive nearby supernova explosions. As with the German based study, Wallner and his colleagues found evidence of stellar remains in 120 samples of the 60Fe isotope gathered from the sediment and crust gathered from the bottom of the Pacific, Atlantic and Indian Oceans.