Archaeology in the universe - 0 views
started by Sandra Flores on 30 Oct 14
started by Sandra Flores on 30 Oct 14
started by Sandra Flores on 30 Oct 14
started by Sandra Flores on 30 Oct 14
The elemental abundances of metal-poor star exhibit a striking and rare signature. She speaks for the enrichment by a supernova , which can take place only in stars with extremely high masses. Perhaps it is an indication of a progenitor star with more than 140 solar masses.
Adrian Kaminski
Massereiche Sterne im Galaxienhaufen
Researchers at the Japanese astronomers Wako Aoki from National Astronomical Observatory of Japan studied the chemical composition of a very metal-poor star, and came across a unique signature.
The star with the catalog name J001820.5-093939.2 SDSS (SDSS J0018-0939) is a relatively cool main sequence star with a temperature of less than 4600 degrees Celsius and about half a solar mass. The approximately 1000 light years distant celestial body was under a sky survey - the Sloan Digital Sky Survey discovered -.
With the help of the telescope Subaru on Hawaii, the scientists recorded on high-resolution spectra and determined the abundances of 13 different elements. They found that of those of other stars of similar metallicity distinguished the chemical signature of the star significantly. In particular, it was found that in the star both lighter elements such as carbon and magnesium, but also heavy strontium and Bariumkerne relative to iron are rarely unique.
Paarinstabilitätssupernova
While a pair instability supernova, the star is completely torn and there remains no core. It is a possible scenario for stars with masses greater than 100 solar masses.
The early universe contained no heavy elements. These are products of nuclear fusion processes in stars and the cosmos were only supplied by supernova explosions that accompany the stellar mass stars. Only then they stood for the formation of new stars are available. With the help of model calculations it is possible to simulate the resulting mixing ratios of elements in stars of later generations. However, the abundances of SDSS J0018-0939 not match the ideas of a typical core collapse of an old star.
Rather, the signature found for the enrichment speaks through a single special event: a so-called pair instability supernova. Theorists predict that such a case of very massive stars with more than 100 solar masses and low levels of elements heavier than helium, can cause the star is disrupted in its entirety. During the final phase of helium burning in its core high densities and temperatures lead to energies at which photons that contribute to a certain stabilization of the body can convert into electron-positron pairs are. Because of the lack of radiation pressure then drops the star uncontrolled collapse. The explosively incipient fusion processes can tear the body completely, so that no core remains.
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The mass of the core of the star helium in this type of collapse is crucial for the production of heavy elements during the process. Calculations show that a helium core of about 130 solar masses could generate a signature, as it was observed in SDSS J0018-0939. Despite some uncertainties, the researchers assume that the frequency element of the star could be an indication of such a pair instability supernova. Such was long regarded as purely speculative, because astronomers are not sure how often arisen stars with more than 100 solar masses.
Many simulations show that fragmentation processes during the development phase as well as a high radiation pressure can prevent the formation of very massive stars. In the recent past, however, there was already a first indication of this special type of supernovae. They make about 100 times more energy than ordinary supernova explosions and also differ somewhat in the time course of their radiation. Future direct evidence would be important to better understand the mechanisms involved in the formation of extremely massive stars. Furthermore, it could help to estimate how often such occurred in the early universe and how they contributed to the structure formation and element enrichment.