Galactic bars and bulges Galaxy Zoo

-


a hst image of ngc 1300, typical barred spiral


spiral galaxies have central bar-shaped structures composed of stars. these galaxies called barred spirals , have been investigated galaxy zoo in several studies. unclear why spiral galaxies have bars , not. galaxy zoo research has shown red spirals twice host bars blue spirals. these colours significant. blue galaxies hue hot young stars contain, implying forming stars in large numbers. in red galaxies, star formation has stopped, leaving behind cooler, long-lived stars give them red colour.



a mlo image of bulgeless galaxy ngc 4536.


karen masters, scientist involved in studies, stated: time data have hinted spirals more old stars more have bars, such large number of bar classifications re more confident our results. s not yet clear whether bars side effect of external process turns spiral galaxies red, or if alone can cause transformation.


spiral galaxies have bulges @ centers. these bulges huge, tightly packed groups of stars. however, using galaxy zoo volunteer classifications, has been found spiral galaxies not have bulges. many galactic bulges thought host supermassive black hole @ centers: pure disk galaxies no bulges growing central black holes found. pure disk galaxies , central black holes may consistent relation derived elliptical , bulge-dominated galaxies different formation histories implies details of stellar galaxy evolution , dynamics may not fundamental co-evolution of galaxies , black holes. seems these bulgeless galaxies have formed in environments isolated other galaxies. hypothesised black hole mass may more tightly tied overall gravitational potential of galaxy , therefore dark matter halo, rather dynamical bulge component.


in september 2014, paper titled: galaxy zoo: candels barred disks , bar fractions accepted publication mnras. first set of results hubble space telescope candels survey part of galaxy zoo 4. study reports discovery of strong barred structures in massive disk galaxies @ z ≈1.5 in deep rest-frame optical images candels . within sample of 876 disk galaxies identified visual classification in galaxy zoo 4, 123 barred galaxies examined. found bar fraction across redshift range 0.5 < z < 2 not evolve.








Comments

Post a Comment

Popular posts from this blog

Early forms Nasal helmet

-
helmet of saint wenceslaus, prague the nasal helmet characterised possession of nose-guard, or nasal , composed of single strip of metal extended down skull or browband on nose provide facial protection. helmet appeared throughout western europe late in 9th century, , became predominant form of head protection, replacing previous types of helmet design based on late roman types such ridge helmet , helmets of spangenhelm construction. nasal helmets universally conical in shape. skull raised single sheet of iron or of composite, segmented (spangenhelm) construction. spangenhelm variety was, in general, earlier method of construction. single-piece skulls, being technically more difficult produce, became more common increase in metallurgical skill on time. though nasals had been used on earlier helmets, , on contemporary helmets found in byzantium, slavic eastern europe , middle east, characteristic of nasal helmet in general larger , integrated either skull or browband of helmet. nasal...
Read more

History Fixed exchange-rate system

-
1 history 1.1 chronology 1.2 gold standard 1.3 bretton woods system 1.4 current monetary regimes history the gold standard or gold exchange standard of fixed exchange rates prevailed 1870 1914, before many countries followed bimetallism. period between 2 world wars transitory, bretton woods system emerging new fixed exchange rate regime in aftermath of world war ii. formed intent rebuild war-ravaged nations after world war ii through series of currency stabilization programs , infrastructure loans. 1970s saw breakdown of system , replacement mixture of fluctuating , fixed exchange rates. chronology timeline of fixed exchange rate system: gold standard the earliest establishment of gold standard in united kingdom in 1821 followed australia in 1852 , canada in 1853. under system, external value of currencies denominated in terms of gold central banks ready buy , sell unlimited quantities of gold @ fixed price. each central bank maintained gold reserves official reserve asset. example, du...
Read more

Early years .281995.E2.80.931999.29 History of D.C. United

-
1 years (1995–1999) 1.1 d.c. awarded inaugural mls franchise 1.2 immediate success (1996–99) 1.2.1 1996: debut double 1.2.2 1997: back-to-back league titles 1.2.3 1998: international glory 1.2.4 1999: rongen steps in early years (1995–1999) d.c. awarded inaugural mls franchise prior 1994 fifa world cup, united states soccer federation fulfilled promises fifa aiding in foundation of new professional league. on june 15, 1994, major league soccer selected washington, d.c. out of twenty-two applicants host 1 of first 7 franchises, 3 more added before league s launch. once mls franchise awarded washington, new management had name it. in keeping sports naming conventions in united states, earliest efforts entailed area s name followed mascot. ideas included spies , americans , eagles . eventually, however, new team s operators decided name team d.c. united . name united alluded well-known european club names such leeds , manchester united, , reflected team s location in capital of uni...
Read more