Tag: 苏州唐人阁九品2019

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First Galaxies Fast and Compact

first_imgThe old picture: after the big bang, matter is diffuse.  Out of the darkness, stars slowly begin to form, as the first galaxies take shape.  Galaxies start out large and slowly grow more dense and structured over billions of years.  The new picture: the first galaxies are very compact and dense, spinning rapidly, with stars forming at a prodigious rate.  The compact galaxies spin twice as fast as “mature” galaxies closer to us.    This change in thinking was expressed by reports found on Science Daily and Space.com.  A look at the original paper in Astrophysical Journal Letters puts the surprises in context.1  Pieter van Dokkum et al made observations with the Hubble Space Telescope and the Keck Observatory at redshift z=2.3 in near-infrared light.  They found nine galaxies that seemed more compact than usual and did not find any of the large galaxies common at lower redshifts.  They deduced that the distant galaxies are 0.9 kiloparsecs in diameter (compared to 5 kpc for nearby galaxies), and that the compact galaxies rotate twice as fast.  They did, however, list 5 possible sources of error.  Their field of view was limited, for instance, and “the stellar ages and masses of the galaxies have large uncertainties.”  Most important, they said, studies at redshifts greater than 2 are “typically based on photometric redshifts, which are poorly calibrated for faint, red galaxies.”    Nevertheless, they felt confident that their survey rules out “monolithic” models of galaxy evolution (i.e., “in which early-type galaxies are assembled at the same time as their stars”).  They viewed their results as “the most direct evidence to date for an essentially hierarchical assembly history for massive galaxies.”    One of the unsolved problems in the paper was how to get large mature galaxies out of early compact ones.  How would a dense, compact object grow outward by a factor of six?  Galaxy mergers seem insufficient to do the trick.  Another problem is how they formed in the first place.  For that, the astronomers invoked one of their favorite fudge factors – dark matter:Van Dokkum speculated on how these small, crowded galaxies formed.  He said, one way could have involved an interaction in the emerging universe between hydrogen gas and dark matter — an invisible form of matter that accounts for most of the universe’s mass.  Shortly after the Big Bang, the universe contained an uneven landscape of dark matter.  He said that hydrogen gas could have been trapped in puddles of the invisible material which began spinning rapidly in dark matter’s gravitational whirlpool, forming stars at a furious rate.1.  van Dokkum et al, “Confirmation of the Remarkable Compactness of Massive Quiescent Galaxies at z~2.3: Early-Type Galaxies Did not Form in a Simple Monolithic Collapse,” Astrophysical Journal Letters,677:L5�L8, 2008 April 10, DOI: 10.1086/587874.You gotta love the imagination of some scientists.  Nobody has a clue what dark matter is, or whether it even exists.  This guy has the imaginary stuff forming puddles and whirlpools.  Let him connect his “mysterious unknown stuff” (02/28/2008) with empirical observations before telling us it will make stars form at a furious rate.    Claims like the ones in this paper should always be taken with a grain of salt.  Many laymen read such things on Science Daily or other popular news sources and have no idea what the astronomers are talking about, let alone what it means.  Something to watch for is the element of surprise.  Why were the astronomers surprised by what they found?  What did they actually find?    Measurements such as this are extremely difficult to make.  Astronomers are trying to interpret very faint objects near the limit of observability.  It becomes hard to establish where the noise stops and the signal begins.  The team was honest enough in the original paper to list five major sources of error that could invalidate the claims that these galaxies are unusually compact.  To us, each source of error seemed significant.    Another caution is that observations at cosmological distances are very much tied into the theories employed to make the observations.  What does an infrared blob with a redshift of 2.3 (inferred to represent something at a given distance and age) actually represent?  Why were they focusing on these things instead of other things?  In the 1920s, recall, Edwin Hubble thought that galaxies began as ellipticals and evolved into spirals.  In later years some astronomers reversed the sequence.  Lately astronomers have been finding more structure, more density, and more “maturity” the farther back they look.    It appears that this team was somewhat eager to substantiate the hierarchical model of galaxy evolution over the monolithic model.  But how do they know there are not other possibilities?  And how do they know other sources of error, unknown to us today, might confuse what they think they saw?  Consider that about 20 years ago, many astronomers were caught off guard by the discovery of gravitational lensing.  The bending of light by intervening galaxies, they realized, can seriously compromise the interpretation of distant objects.  It was something few had ever considered.  No one knows whether another phenomenon might be introducing systematic errors into the observations today.    That being said, let’s assume they are correct, and that these distant galaxies are in fact more compact than expected.  It is noteworthy that the astronomers were surprised to see tight and dense structures so close to the assumed big bang.  Simplistic models would have predicted otherwise.  Creation astronomers might want to consider how this survey might fit a “top-down” model for galaxy formation.  Humphreys’ “white hole cosmology” predicted, for example, that distant galaxies would appear from earth to be changing rapidly due to gravitational time dilation.  We’ll leave such considerations to those interested.  The lesson for our purposes is that different assumptions allow for different interpretations consistent with the very same empirical observations.  Things are not always what they seem.  Some cosmologists have their scientific method backward.  They work according to the inverted principle, “No observation should be considered legitimate until confirmed by theory.”    Observation should trump theory in science.  It may not be possible to observe something completely free of bias, but a good first step would be to state one’s biases up front as far as one is aware of them.(Visited 10 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img read more

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Precautionary Pruning of Trees Urged for the Hurricane Season

first_img Director of the Metrological Service of Jamaica, Evan Thompson, projects that the 2017 season will be very active with the formation of 11 to 17 tropical systems, up to nine are expected to develop into hurricanes, with at least four likely to reach the dangerous category three strength or greater. Story Highlights Overhanging trees are often regarded as an enhancement to the beauty, luxury and comfort of homes and business places, both as rich sources of fruits as well providing welcome shading from the sun.However, these extended limbs can become dangerous elements during a storm or hurricane.Director of the Meteorological Service of Jamaica, Evan Thompson, projects that the 2017 season will be very active with the formation of 11 to 17 tropical systems, of which up to nine are expected to develop into hurricanes, with at least four likely to reach the dangerous category three strength or greater.Forest Technician at the Department, Deon Brown, emphasizes that doing reduces wind resistance within the canopy of  trees and the likelihood of limbs breaking and being tossed, given the erratic nature of strong winds accompanying a storm or hurricane.“One of the impacts on trees in a hurricane is that it can topple over. So if the tree is in close proximity (to a building), you can lessen the damage by removing some of the branches because sometimes they might get entangled in electric wires and could cause all kinds of problems,” she points out.Miss Brown urges persons not to resort to willy-nilly hacking of trees, but rather to consult with qualified tree-care professional to ensure that proper pruning methods are employed.She emphasises that incorrect methods can affect the overall health and lifespan of trees.Miss Brown advises that when pruning, care must be taken to protect the sections of trees where cuts or incisions have been made to avoid exposure to fungus or termite infestation which could compromise it by causing decay, thereby rendering it vulnerable in extreme weather.President of the Incorporated MasterBuilders Association, Humphrey Taylor, also underscores the importance of pruning trees and doing so properly.While arguing that trees should not be planted close to buildings, he says where this is the case, pruning must be a foremost safety consideration.Mr. Taylor acknowledges that some homeowners resist the idea of cutting trees because they think it may lose its beauty. However, he assures that “it will grow back.”Meanwhile, the Forestry Department has issued guidelines which it says should be followed when pruning a tree.These include not making cuts that are flush with the tree trunk or main branches to which they are attached. Additionally, incisions should be slightly slanted from the upper to the lower side of the branch.The Department further recommends that, where feasible, a fungicidal tincture (or plain paint) be applied to the area of the incision to retard or prevent rot or termite infestation.Additionally, is says where large branches overhang buildings or other infrastructure, incremental removal of small, manageable pieces of limbs will decrease the potential threat of damage.For further information, persons may contact the Forestry Department at 173 Constant Spring Road in Kingston or call them at 924-2667 or consult the nearest tree care professional or company.center_img Overhanging trees are often regarded as an enhancement to the beauty, luxury and comfort of homes and business places, both as rich sources of fruits as well providing welcomed shading from the sun. However, these extended limbs can become dangerous elements during a storm or hurricane.last_img read more

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