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Our solar system
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Our solar system seems to have been blown into existence by the winds of a nearby massive star.
Most astrophysicists think the solar system formed from a cloud of gas and dust squeezed by a nearby supernova blast.
Supernovae produce the isotope iron-60, so Bizzarro's team looked for it in meteorites that formed in the first million years of the solar system's history.

"There was no iron-60, ruling out the supernova trigger mechanism" - Martin Bizzarro,  University of Copenhagen in Denmark.

However, they found another isotope, aluminium-26, that suggests an alternative. Aluminium-26 only forms in stars about 30 times as massive as the sun, and such stars radiate energetic winds loaded with the isotope. These winds could have buffeted the gas and dust cloud, causing the solar system to form, he says.

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Solar System Formation
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It's an exciting time to be a cosmochemist. State-of-the-art laboratory techniques for analysing traces of elemental isotopes are now so good that the "born on" date for billion-year-old rocks and minerals can be pinpointed to well within a million years. This kind of precision has opened dramatic new windows on how our solar system came to exist 4,567,200,000 years ago.

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GEOCHEMISTRY: Isotopes Suggest Solar System Formed in a Rough Neighbourhood

Astrophysicists have long assumed that a supernova played midwife to the solar system. An exploding star could have collapsed wispy interstellar gas and dust into a dense swirling disk to get things started and loaded it with the intensely radioactive aluminium that cooked up chunks of the nascent solar system. But a group of cosmo-chemists presents evidence that the sun was born into an even more brutal environment.
The evidence for our violent beginnings comes from some of the most precise isotopic measurements yet of nickel in samples of Earth, Mars, and meteorites. Martin Bizzarro of the University of Copenhagen in Denmark and colleagues had gone looking for signs of radioactive iron-60 in the oldest meteorite from an asteroid that had melted in the earliest solar system. The iron-60 itself wouldn't be there. It was forged in the heart of a star and spewed into the material that would become the solar system after the star went supernova. Then the iron-60 promptly decayed away into nickel-60. So the researchers looked for the nickel "ash" using a type of mass spectrometer that can ionise all the nickel in a sample. That allows sensitive detection of the isotopes following magnetic separation. They also analysed each sample many times to drive down the analytical error.
To their surprise, Bizzarro and colleagues did not find the expected extra dose of the iron-60 marker. Instead, the samples contained less nickel-60 than found in younger meteorites. Apparently, the solar system's shot of iron-60 had not arrived when this old meteorite solidified about a million years after the solar system's start. Yet radioactive aluminum-26--also made in stars--had been there all along.

"Iron-60 and aluminum-26 don't seem to be coming into the solar system at the same time. There's only one stellar environment that can do that: very, very massive stars" - Martin Bizzarro.

The bigger the star, the faster it burns its hydrogen fuel. If it has more than 30 times the mass of the sun, a star will blow away much of its outer layers--including its aluminum-26--in the last million years of its brief life of 4 million years or so. That stellar wind could have driven the collapse of interstellar gas and dust to form our sun and the protoplanetary disk that once surrounded it. Later, the massive star exploded, spewing iron-60 from its deep interior.

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RE: Solar supernova
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Observations of the Rosette nebula revealed that, beyond 10 trillion miles of an O-star, about 45 percent of the stars had disks - about the same amount as there were in safer neighbourhoods free of O-stars. Within this distance, only 27 percent of the stars had disks, with fewer and fewer disks spotted around stars closest to the O-star. In other words, an O-star's danger zone is a sphere whose damaging effects are worst at the core. For reference, our sun's closest star, a small star called Proxima Centauri, is nearly 30 trillion miles away.
The new study indicates that a protoplanetary disk will boil off faster in the zone's perilous core. For example, a disk two times closer to an O-star than another disk will evaporate twice as fast.

"The edges of the danger zone are sharply defined. It is relatively safe for protoplanetary disks outside it, whereas a disk that gets dragged along by its star to be really close to an O-star could disappear in as fast as a hundred thousand years" - Zoltan Balog, University of Arizona, Tucson.

Despite this doomsday scenario, there is a chance some planets could survive a close encounter with an O-star. According to one alternative theory of planet formation, some gas giants like Jupiter might form in less than one million years. If such a planet already existed around a young star whose disk is blown away, the gas giant would stay put while any burgeoning rocky planets like Earth would be forever swept away.
Some astronomers think our sun was born in a similarly violent neighbourhood studded with O-stars before migrating to its present, more spacious home. If so, it was lucky enough to escape a harrowing ride into any danger zones, or our planets, and life as we know it, wouldn't be here today.

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Interaction of Supernova Ejecta
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Title: Interaction of Supernova Ejecta with Nearby Protoplanetary Disks
Authors: N. Ouellette, S. J. Desch, J. J. Hester

The early Solar System contained short-lived radionuclides such as 60Fe (t1/2 = 1.5 Myr) whose most likely source was a nearby supernova. Previous models of Solar System formation considered a supernova shock that triggered the collapse of the Sun's nascent molecular cloud. We advocate an alternative hypothesis, that the Solar System's protoplanetary disk had already formed when a very close (< 1 pc) supernova injected radioactive material directly into the disk. We conduct the first numerical simulations designed to answer two questions related to this hypothesis: will the disk be destroyed by such a close supernova; and will any of the ejecta be mixed into the disk? Our simulations demonstrate that the disk does not absorb enough momentum from the shock to escape the protostar to which it is bound. Only low amounts (< 1%) of mass loss occur, due to stripping by Kelvin-Helmholtz instabilities across the top of the disk, which also mix into the disk about 1% of the intercepted ejecta. These low efficiencies of destruction and injectation are due to the fact that the high disk pressures prevent the ejecta from penetrating far into the disk before stalling. Injection of gas-phase ejecta is too inefficient to be consistent with the abundances of radionuclides inferred from meteorites. On the other hand, the radionuclides found in meteorites would have condensed into dust grains in the supernova ejecta, and we argue that such grains will be injected directly into the disk with nearly 100% efficiency. The meteoritic abundances of the short-lived radionuclides such as 60Fe therefore are consistent with injection of grains condensed from the ejecta of a nearby (< 1 pc) supernova, into an already-formed protoplanetary disk.

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RE: Solar supernova
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The dust that condensed to form the sun, the Earth and the stuff of human bodies has long been thought to have originated in violent explosions of giant stars. But observations with NASA's Spitzer Space Telescope have found cosmic dust where it had never been found before.

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The dust that condensed to form the sun, the Earth and the stuff of human bodies has long been thought to have originated in violent explosions of giant stars. But these explosions--called supernovae--can’t account for all the dust in the cosmos. Now, observations with NASA’s Spitzer Space Telescope, led by University of Minnesota astrophysicists, have found cosmic dust where it had never been found before. The finding implies that the deaths of smaller, humbler stars may have supplied the early dust that seeded the myriad stars like our sun, and produced dust more efficiently than the big guns. The work is published in the October issue of the Astrophysical Journal.
Though less spectacular than supernova explosions, the formation and release of dust into space by stars that die relatively quietly is a pivotal event in the evolution of new stars like the sun. Identifying sources of dust not only helps researchers draw a picture of how our solar system formed but can help in searches of the cosmos for events that may lead to the formation of new sunlike stars and planets.
Led by the university’s Martha Boyer, a graduate student in astronomy, and astronomy professor Charles “Chick” Woodward, the research team found dust deep within an ancient pack of stars called a globular cluster. Known by its astronomical designation M15, the cluster contains hundreds of thousands of stars and is probably 12.5 billion years old, dating back to the early days of our Milky Way galaxy. Its stars are similar to the sun, but some of them are undergoing the death throes that the sun will experience one day. In that process, the stars swell up into huge, relatively cool stars known as red giants and give off a strong stellar wind containing the seeds of dust grains.

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-- Edited by Blobrana at 20:35, 2006-11-13

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The Sun had sisters when it was born. In fact, according to new research, it had hundreds of thousands of siblings.
And at least one was a supernova, providing further support for the idea that there could be lots of planets around other stars since our solar system emerged in such an explosive environment.

"We know that the majority of stars in our galaxy were born in star clusters. Now we also know that the newborn solar system not only arose in such a cluster, but also survived the impact of an exploding star. This suggests that planetary systems are impressively rugged and may be common in even the most tumultuous stellar nurseries" - Leslie Looney, who arrived at the solar sibling finding along with his colleagues at the University of Illinois at Urbana-Champaign.

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In a paper accepted for publication in the Astrophysical Journal, astronomy professors Leslie W. Looney and Brian D. Fields, and undergraduate student John J. Tobin take a close look at short-lived radioactive isotopes once present in primitive meteorites. The researchers' conclusions could reshape current theories on how, when and where planets form around stars.
Short-lived radioactive isotopes are created when massive stars end their lives in spectacular explosions called supernovas. Blown outward, bits of this radioactive material mix with nebular gas and dust in the process of condensing into stars and planets. When the solar system was forming, some of this material hardened into rocks and later fell to Earth as meteorites.
The radioisotopes have long since vanished from meteorites found on Earth, but they left their signatures in daughter species. By examining the abundances of those daughter species, the researchers could calculate how far away the supernova was, in both distance and time.

"The supernova was stunningly close; much closer to the sun than any star is today. Our solar system was still in the process of forming when the supernova occurred" - Brian D. Fields

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The Local Bubble
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Title: A Cold Nearby Cloud Inside the Local Bubble
Authors: David M. Meyer, J.T. Lauroesch, Carl Heiles, J.E.G. Peek, Kyle Engelhorn

The high-latitude Galactic H I cloud toward the extragalactic radio source 3C 225 is characterised by very narrow 21 cm emission and absorption indicative of a very low H I spin temperature of about 20 K. Through high-resolution optical spectroscopy, we report the detection of strong, very narrow Na I absorption corresponding to this cloud toward a number of nearby stars. Assuming that the turbulent H I and Na I motions are similar, we derive a cloud temperature of 20 (+6, -8) K (in complete agreement with the 21 cm results) and a line-of-sight turbulent velocity of 0.37 ±0.08 km/s from a comparison of the H I and Na I absorption linewidths. We also place a firm upper limit of 45 pc on the distance of the cloud, which situates it well inside the Local Bubble in this direction and makes it the nearest-known cold diffuse cloud discovered to date.

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RE: Solar supernova
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Title: Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster
Authors: Leslie W. Looney, John J. Tobin, Brian D. Fields (Univ. of Illinois at Urbana-Champaign)

We construct a simple model for radioisotopic enrichment of the protosolar nebula by injection from a nearby supernova, based on the inverse square law for ejecta dispersion. We find that the presolar radioisotopes abundances (i.e., in solar masses) demand a nearby supernova: its distance can be no larger than 66 times the size of the protosolar nebula, at a 90% confidence level, assuming 1 solar mass of protosolar material. The relevant size of the nebula depends on its state of evolution at the time of radioactivity injection. In one scenario, a collection of low-mass stars, including our sun, formed in a group or cluster with an intermediate- to high-mass star that ended its life as a supernova while our sun was still a protostar, a starless core, or perhaps a diffuse cloud. Using recent observations of protostars to estimate the size of the protosolar nebula constrains the distance of the supernova at 0.02 to 1.6 pc. The supernova distance limit is consistent with the scales of low-mass stars formation around one or more massive stars, but it is closer than expected were the sun formed in an isolated, solitary state. Consequently, if any presolar radioactivities originated via supernova injection, we must conclude that our sun was a member of such a group or cluster that has since dispersed, and thus that solar system formation should be understood in this context. In addition, we show that the timescale from explosion to the creation of small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0 to 2.2 Myr), and thus the temporal choreography from supernova ejecta to meteorites is important. Finally, we can not distinguish between progenitor masses from 15 to 25 solar masses in the nucleosynthesis models; however, the 20 solar mass model is somewhat preferred.

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