Posts Tagged ‘supernovas’
[LINK] “Did an 8th century gamma ray burst irradiate the Earth?”
A Royal Astronomical Society press release suggests that, in the 8th century, Earth was briefly irradiated by gamma rays. I’d mentioned the story in a links roundup back in June 2012, but the story got legs.
n 2012 scientist Fusa Miyake announced the detection of high levels of the isotope Carbon-14 and Beryllium-10 in tree rings formed in 775 CE, suggesting that a burst of radiation struck the Earth in the year 774 or 775. Carbon-14 and Beryllium-10 form when radiation from space collides with nitrogen atoms, which then decay to these heavier forms of carbon and beryllium. The earlier research ruled out the nearby explosion of a massive star (a supernova) as nothing was recorded in observations at the time and no remnant has been found.
Prof. Miyake also considered whether a solar flare could have been responsible, but these are not powerful enough to cause the observed excess of carbon-14. Large flares are likely to be accompanied by ejections of material from the Sun’s corona, leading to vivid displays of the northern and southern lights (aurorae), but again no historical records suggest these took place.
Following this announcement, researchers pointed to an entry in the Anglo-Saxon Chronicle that describes a ‘red crucifix’ seen after sunset and suggested this might be a supernova. But this dates from 776, too late to account for the carbon-14 data and still does not explain why no remnant has been detected.
Drs. Hambaryan and Neuhӓuser have another explanation, consistent with both the carbon-14 measurements and the absence of any recorded events in the sky. They suggest that two compact stellar remnants, i.e. black holes, neutron stars or white dwarfs, collided and merged together. When this happens, some energy is released in the form of gamma rays, the most energetic part of the electromagnetic spectrum that includes visible light.
In these mergers, the burst of gamma rays is intense but short, typically lasting less than two seconds. These events are seen in other galaxies many times each year but, in contrast to long duration bursts, without any corresponding visible light. If this is the explanation for the 774 / 775 radiation burst, then the merging stars could not be closer than about 3000 light years, or it would have led to the extinction of some terrestrial life. Based on the carbon-14 measurements, Hambaryan and Neuhӓuser believe the gamma ray burst originated in a system between 3000 and 12000 light years from the Sun.
Bad Astronomy’s Phil Plait thinks the story possible. Critically, it can be tested: is there a stellar remnant in the correct place?
[BRIEF NOTE] On the search for the sun’s birthplace
Progressive Download’s John Farrell had a brief post outlining the efforts of some astronomers to identify the cluster of stars where our sun formed. Our solar system formed 4.56 billion years ago in the aftermath of the forced condensation of interstellar gas by the shock wave of a supernova perhaps one light-year away; it stands to reason that other stars formed in the neighbourhood, too.
(I find the idea really, really cool. We Live In A Science-Fiction Future.)
A 2010 ScienceNOW article reported on a Russian study that suggested identifying sibling stars of the Sun would be a difficult task indeed.
[L]ast year astronomer Simon Portegies Zwart of Leiden University in the Netherlands claimed that scientists might be able to find the sun’s siblings. He calculated how the stars dispersed as they revolved around the galaxy’s center and estimated that between 10 and 60 of them should reside within 330 light-years of Earth. At that distance, a sunlike star is visible through binoculars. Such stars would share the sun’s age, chemical composition, and motion through space—and might give insight into the birth of the solar system.
Yury Mishurov of the Southern Federal University in Rostov-on-Don, Russia, was not convinced that the sun’s siblings would be so easy to find. “I thought that [Portegies Zwart’s] model was oversimplistic, because he did not take into account the effects of spiral arms,” which can fling stars far and wide with their gravity. So Mishurov and astronomer Irina Acharova, also of the Southern Federal University, ran computer simulations that modeled a cluster of stars orbiting the galaxy’s center. The simulations tracked the sun’s siblings as they passed in and out of the galaxy’s spiral arms over 4.6 billion years.
“The stars dispersed in a very broad space,” says Mishurov.
In some simulations, the stars spread along a full orbit around the galactic center. In these cases, just three or four of the thousand stars remained within 330 light-years of Earth. “We cannot say that it is absolutely impossible to find siblings, but it is a very difficult task,” says Mishurov, whose work will appear in an upcoming issue of Monthly Notices of the Royal Astronomical Society.
Still, I suppose that the steady impressive expansion of detailed knowledge of the environment of the Milky Way Galaxy at least allows for the list of candidates to be narrowed down. A January 2012 paper submitted at arXiv, “The Sun was not born in M 67”, suggests that our sun didn’t form in Messier 67, a cluster of stars currently between 2600 and 2900 light years away from our solar system in roughly the opposite direction from the core of the Milky Way Galaxy.
Using the most recent proper-motion determination of the old, Solar-metallicity, Galactic open cluster M 67, in orbital computations in a non-axisymmetric model of the Milky Way, including a bar and 3D spiral arms, we explore the possibility that the Sun once belonged to this cluster. We have performed Monte Carlo numerical simulations to generate the present-day orbital conditions of the Sun and M 67, and all the parameters in the Galactic model. We compute 3.5 \times 10^5 pairs of orbits Sun-M 67 looking for close encounters in the past with a minimum distance approach within the tidal radius of M 67. In these encounters we find that the relative velocity between the Sun and M 67 is larger than 20 km/s. If the Sun had been ejected from M 67 with this high velocity by means of a three-body encounter, this interaction would destroy an initial circumstellar disk around the Sun, or disperse its already formed planets. We also find a very low probability, much less than 10^-7, that the Sun was ejected from M 67 by an encounter of this cluster with a giant molecular cloud. This study also excludes the possibility that the Sun and M 67 were born in the same molecular cloud. Our dynamical results convincingly demonstrate that M67 could not have been the birth cluster of our Solar System.
A National Geographic News article by Dave Mosher covers the same terrain in non-professional detail.
