Reading- ages 9 light gray13 dark grayand 17 black. Debate on the origins of the racial achievement gap[ edit ] Researchers have not reached consensus about the causes of the academic achievement gap ; instead, there exists a wide range of studies that cite an array of factors, both cultural and structural, that influence student performance in school. Annette Lareau suggested that students who lack middle-class cultural capital and have limited parental involvement are likely to have lower academic achievement than their better resourced peers. Based on the National Center for Educational Statistic about half of African American male students grew up in single-parent households.
This was an unexpected identification, because models of high mass stellar evolution at the time did not predict that blue supergiants are susceptible to a supernova event. Some models of the progenitor attributed the color to its chemical composition rather than its evolutionary state, particularly the low levels of heavy elements, among other factors.
This was likely due to neutrino emission, which occurs simultaneously with core collapse, but before visible light was emitted. Visible light is transmitted only after the shock wave reaches the stellar surface.
Approximately three hours earlier, the Mont Blanc liquid scintillator detected a five-neutrino burst, but this is generally not believed to be associated with SN A.
The first pulse started at A second pulse of three neutrinos arrived between 9. Although only 25 neutrinos were detected during the event, it was a significant Project c math 533 from the previously observed background level.
This was the first time neutrinos known to be emitted from a supernova had been observed directly, which marked the beginning of neutrino astronomy. The data suggest that the total number of neutrino flavors is at most 8 but other observations and experiments give tighter estimates.
Many of these results have since been confirmed or tightened by other neutrino experiments such as more careful analysis of solar neutrinos and atmospheric neutrinos as well as experiments with artificial neutrino sources.
However, since the supernova first became visible, astronomers have been searching for the collapsed core but have not detected it.
The Hubble Space Telescope has taken images of the supernova regularly since Augustbut, so far, the images have shown no evidence of a neutron star. A number of possibilities for the 'missing' neutron star are being considered. Another is that a pulsar was formed, but with either an unusually large or small magnetic field.
It is also possible that large amounts of material fell back on the neutron star, so that it further collapsed into a black hole. Neutron stars and black holes often give off light as material falls onto them. If there is a compact object in the supernova remnant, but no material to fall onto it, it would be very dim and could therefore avoid detection.
Other scenarios have also been considered, such as if the collapsed core became a quark star. Although the luminous emission consists of optical photons, it is the radioactive power absorbed that keeps the remnant hot enough to radiate light.
Without radioactive heat it would quickly dim. The radioactive decay of 56Ni through its daughters 56Co to 56Fe produces gamma-ray photons that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times several weeks to late times several months.
Later measurements by space gamma-ray telescopes of the small fraction of the 56Co and 57Co gamma rays that escaped the SNA remnant without absorption   confirmed earlier predictions that those two radioactive nuclei were the power source. That is currently powered by the radioactive decay of 44Ti with a half life of about 60 years.
With this change, X-rays produced by the ring interactions of the ejecta began to contribute significantly to the total light curve. This was noticed by the Hubble Space Telescope as a steady increase in luminosity 10, days after the event in the blue and red spectral bands.
Sequence of HST images from toshowing the collision of the expanding remnant with a ring of material ejected by the progenitor 20, years before the supernova  The three bright rings around SN A that were visible after a few months in images by the Hubble Space Telescope are material from the stellar wind of the progenitor.
These rings were ionized by the ultraviolet flash from the supernova explosion, and consequently began emitting in various emission lines.Do you really want to delete this prezi?
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on the domain. While statisticians and mathematicians uniformly use the term "normal distribution" for this distribution, physicists sometimes call it a Gaussian distribution and, because of its curved flaring shape, social scientists refer to it as the "bell curve." Feller () uses the symbol.