Predicted powerful outflows of
cold gases from galaxies were predicted and have now been discovered and
confirmed. There is plenty more to this
story but this is at least a glimpse into the sheer power of the flows and
confirmation that we appear to live in a pretty quiet zone.
At the moment galactic theory is
theory piled on top of theory with little means of actual proof of anything. It hangs together as a good story, but
believing any of it should be 0put on hold.
I also think that so-called black
holes are discharged as photon jets that eventually coalesce as atomic
particles and the resultant gases. However we work it up, a lot of mass escapes
any galaxy to be recovered by other galaxies.
The best model for the universe of galaxies is an assemblage of super galactic
cells in which most of the content is recycling through the core.
I should also mention that the dominant
time function for a galaxy will be slightly different than that of the universe
itself. This could be rather significant
in terms of comparing galaxies.
Caught in the act by Herschel
by Staff Writers
ESA's Herschel Space Observatory has detected massive amounts of molecular gas gusting at high velocities - in some cases in excess of 1000 kilometres per second - from the centres of a set of merging galaxies. Driven by star formation and central black holes, these powerful storms are strong enough to sweep away billions of solar masses of molecular gas and to interfere with global galactic processes.
These observations indicate that, in the galaxies hosting the brightest
Active Galactic Nuclei, outflows can clear the entire supply for creating stars
and feeding the black hole. This finding provides long-sought-after evidence of
highly energetic feedback processes taking place in galaxies as they evolve.
Massive outflows of gas from galactic centres are tell-tale signs that
powerful, storm-like processes affecting the global galactic balance of mass
and energy are underway. Within a galaxy, these storms can be generated in the
regions of active star formation, stirred by stellar winds and shock waves from
supernova explosions.
They can also be triggered close to the central black hole, where
radiation pressure from the accretion disc drives
the surrounding gas away. When powerful enough, outflows can sweep away the
galaxys entire reservoir of gas, depleting it of the raw material that creates
stars and feeds the central black hole. This inhibits further star formation
episodes and additional black hole growth.
Thus, galactic outflows cause negative feedback, halting the same
mechanisms that produced them in the first place.
"Outflows are key features in models of galactic formation and
evolution, but prior to our work no decisive evidence of their active role in
such processes had been gathered," explains Eckhard Sturm from the
Max-Planck-Institut fur extraterrestrische Physik (MPE) in Germany
While there have been other detections of galactic outflows, almost all
previous observations dealt only with neutral and ionised gas. "By
detecting outflows in the cold molecular gas from which stars are born, we can
finally 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 part
of the Survey with Herschel of the ISM in Nearby INfrared Galaxies (SHINING), a
guaranteed-time key programme of the PACS consortium.
Elliptical galaxies are thought to arise from the merger of
gas-rich spiral
galaxies, a process in which ULIRGs represent an intermediate stage. Gas
outflows develop naturally within this scenario, and they are crucial to
explaining some observed characteristics of elliptical galaxies. Elliptical
galaxies contain old stellar populations, relatively small amounts of
gas and almost no sign of ongoing star formation.
This is in contrast with spiral galaxies, which are dominated by young
stars and are rich in gas necessary for intense star formation. For elliptical
galaxies to derive from spiral galaxies, something must drain the cold gas and
halt the production of stars, and outflows such as those observed by Herschel
appear as ideal candidates for the job.
Another property that finds a natural explanation in galactic outflows
is the strong correlation observed between the mass of black holes and the
stellar mass of the spheroidal component of the galaxies hosting them: black
holes that are relatively more massive appear to reside in galaxies with
spheroids that contain more stars.
This empirical relation suggests that black hole growth and star
formation are intertwined, both initially drawing from the gas reservoir, and
creating feedback mechanisms such as outflows that eventually suppress them.
"Herschel's sensitivity enabled us to detect these gigantic
galactic storms, and to demonstrate, for the first time, that they may be
strong enough to shut down stellar production entirely," says co-author
Albrecht Poglitsch, also from MPE and the Principal Investigator of PACS. The
outflows were traced via spectral lines of the hydroxyl molecule (OH). The
excellent spectral resolution of PACS allowed astronomers to
clearly identify the characteristic blue- and red-shifted profile caused by the
system geometry.
"With velocities of 1000 kilometres per second and higher, the
outflows we detected are 10,000 times faster than any terrestrial hurricane and
are able to strip galaxies of gas amounting to several hundred solar masses
every year," he adds.
The data set suggests that slower outflows may be initiated by star
formation regions, whereas those with higher velocity appear to be related to
the activity of Active Galactic Nuclei (AGN) powered by central black holes:
brighter AGN seem to sweep gas away faster than their less luminous
counterparts.
However, it will be necessary to analyse a larger sample of galaxies in
order to verify this claim that the measured velocity can be used as an
indicator of the main mechanism driving the outflow.
"Although it is early to draw general conclusions, it appears that
the galaxies hosting the most luminous AGN are releasing gas at a much higher
pace than their star formation rates. We expect that they will exhaust their
reservoir of cold molecular gas rather quickly," notes team member
Jacqueline Fischer from the Naval Research Laboratory in the USA
This will produce galaxies with characteristics that match those
observed in ellipticals: poor in cold gas, populated by old stars and
harbouring black holes with masses strongly correlated with the galaxy's
stellar mass.
"By catching molecular outflows 'in the act', Herschel has finally
yielded long-sought-after evidence that powerful processes with negative
feedback do take place in galaxies and dramatically affect their
evolution," adds Goran Pilbratt, ESA's Herschel Project Scientist.
No comments:
Post a Comment