Predicted powerful outflows ofcold gases from galaxies were predicted and have now been discovered andconfirmed. There is plenty more to thisstory but this is at least a glimpse into the sheer power of the flows andconfirmation that we appear to live in a pretty quiet zone.
At the moment galactic theory istheory piled on top of theory with little means of actual proof of anything. It hangs together as a good story, butbelieving any of it should be 0put on hold.
I also think that so-called blackholes are discharged as photon jets that eventually coalesce as atomicparticles and the resultant gases. However we work it up, a lot of mass escapesany galaxy to be recovered by other galaxies. The best model for the universe of galaxies is an assemblage of super galacticcells in which most of the content is recycling through the core.
I should also mention that the dominanttime function for a galaxy will be slightly different than that of the universeitself. This could be rather significantin terms of comparing galaxies.
Caught in the act by Herschel
by Staff Writers
ESA's Herschel Space Observatory has detected massive amounts of molecular gasgusting at high velocities - in some cases in excess of 1000 kilometres persecond - from the centres of a set of merging galaxies. Driven by star formationand central black holes, these powerful storms are strong enough to sweep awaybillions of solar masses of molecular gas and to interfere with global galacticprocesses.
These observations indicate that, in the galaxies hosting the brightestActive Galactic Nuclei, outflows can clear the entire supply for creating starsand feeding the black hole. This finding provides long-sought-after evidence ofhighly energetic feedback processes taking place in galaxies as they evolve.
Massive outflows of gas from galactic centres are tell-tale signs thatpowerful, storm-like processes affecting the global galactic balance of massand energy are underway. Within a galaxy, these storms can be generated in theregions of active star formation, stirred by stellar winds and shock waves fromsupernova explosions.
They can also be triggered close to the central black hole, whereradiation pressure from the accretion disc drivesthe surrounding gas away. When powerful enough, outflows can sweep away thegalaxys entire reservoir of gas, depleting it of the raw material that createsstars and feeds the central black hole. This inhibits further star formationepisodes and additional black hole growth.
Thus, galactic outflows cause negative feedback, halting the samemechanisms that produced them in the first place.
"Outflows are key features in models of galactic formation andevolution, but prior to our work no decisive evidence of their active role insuch processes had been gathered," explains Eckhard Sturm from theMax-Planck-Institut fur extraterrestrische Physik (MPE) in Germany
While there have been other detections of galactic outflows, almost allprevious observations dealt only with neutral and ionised gas. "Bydetecting outflows in the cold molecular gas from which stars are born, we canfinally witness their direct impact on star formation," he adds.
The team observed a number of Ultra-Luminous InfraRed Galaxies(ULIRGs): galaxies enshrouded in gas and dust that shine brightly in the infrared.They were observed with the spectrometer of Herschel's PACS instrument as partof the Survey with Herschel of the ISM in Nearby INfrared Galaxies (SHINING), aguaranteed-time key programme of the PACS consortium.
Elliptical galaxies are thought to arise from the merger ofgas-rich spiralgalaxies, a process in which ULIRGs represent an intermediate stage. Gasoutflows develop naturally within this scenario, and they are crucial toexplaining some observed characteristics of elliptical galaxies. Ellipticalgalaxies contain old stellar populations, relatively small amounts ofgas and almost no sign of ongoing star formation.
This is in contrast with spiral galaxies, which are dominated by youngstars and are rich in gas necessary for intense star formation. For ellipticalgalaxies to derive from spiral galaxies, something must drain the cold gas andhalt the production of stars, and outflows such as those observed by Herschelappear as ideal candidates for the job.
Another property that finds a natural explanation in galactic outflowsis the strong correlation observed between the mass of black holes and thestellar mass of the spheroidal component of the galaxies hosting them: blackholes that are relatively more massive appear to reside in galaxies withspheroids that contain more stars.
This empirical relation suggests that black hole growth and starformation are intertwined, both initially drawing from the gas reservoir, andcreating feedback mechanisms such as outflows that eventually suppress them.
"Herschel's sensitivity enabled us to detect these giganticgalactic storms, and to demonstrate, for the first time, that they may bestrong enough to shut down stellar production entirely," says co-authorAlbrecht Poglitsch, also from MPE and the Principal Investigator of PACS. Theoutflows were traced via spectral lines of the hydroxyl molecule (OH). Theexcellent spectral resolution of PACS allowed astronomers toclearly identify the characteristic blue- and red-shifted profile caused by thesystem geometry.
"With velocities of 1000 kilometres per second and higher, theoutflows we detected are 10,000 times faster than any terrestrial hurricane andare able to strip galaxies of gas amounting to several hundred solar massesevery year," he adds.
The data set suggests that slower outflows may be initiated by starformation regions, whereas those with higher velocity appear to be related tothe activity of Active Galactic Nuclei (AGN) powered by central black holes:brighter AGN seem to sweep gas away faster than their less luminouscounterparts.
However, it will be necessary to analyse a larger sample of galaxies inorder to verify this claim that the measured velocity can be used as anindicator of the main mechanism driving the outflow.
"Although it is early to draw general conclusions, it appears thatthe galaxies hosting the most luminous AGN are releasing gas at a much higherpace than their star formation rates. We expect that they will exhaust theirreservoir of cold molecular gas rather quickly," notes team memberJacqueline Fischer from the Naval Research Laboratory in the USA
This will produce galaxies with characteristics that match thoseobserved in ellipticals: poor in cold gas, populated by old stars andharbouring black holes with masses strongly correlated with the galaxy'sstellar mass.
"By catching molecular outflows 'in the act', Herschel has finallyyielded long-sought-after evidence that powerful processes with negativefeedback do take place in galaxies and dramatically affect theirevolution," adds Goran Pilbratt, ESA's Herschel Project Scientist.
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