Recycling galaxies caught in the act

March 30, 2012, W. M. Keck Observatory
One of the six galaxies that has been found by the Keck I telescope to have significant inflows of gas, which together with outflows create a galactic juggling act. Credit: NASA/STScI

( -- When astronomers add up all the gas and dust contained in ordinary galaxies like our own Milky Way, they stumble on a puzzle: There is not nearly enough matter for stars to be born at the rates that are observed. Part of the solution might be a recycling of matter on gigantic scales – veritable galactic fountains of matter flowing out and then back into galaxies over multi-billion-year timescales. 

Now, a team of astronomers led by Kate Rubin of the Max Planck Institute for Astronomy in Germany has used the W. M. Keck Observatory to find evidence of just such fountains in distant spiral .

In the , it’s estimated that every year about one solar mass (an amount of equal to that of our Sun) worth of dust and gas is turned into stars. Yet a survey of the available raw materials shows that our galaxy could not keep up this rate of for longer than a couple of billion years. Star ages and comparisons with other spiral galaxies show that one solar mass per year is a typical star formation rate. So the puzzle appears to be universal.

Images of the six galaxies with detected inflows, detected by the Keck I telescope. Most of these galaxies have a disk-like, spiral structure, similar to that of the Milky Way. Star formation activity occurring in small knots is evident in several of the galaxies' spiral arms. Because the spirals appear tilted in the images, Rubin et al. concluded that we are viewing them from the side, rather than face-on. This orientation meshes well with a scenario of 'galactic recycling' in which gas is blown out of a galaxy perpendicular to its disk, and then falls back at different locations along the edge of the disk. These images were taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Credit: NASA/STScI

This means additional matter must find its way into galaxies. One possible source is an inflow from huge low-density gas reservoirs filling the intergalactic voids. There is, however, little evidence that this is happening.

Another possibility, closer to home, involves a gigantic cosmic matter cycle. Gas is observed to flow away from many galaxies, and may be pushed by several different mechanisms, including violent supernova explosions (which are how massive stars end their lives), and the sheer pressure exerted by light emitted by bright stars on gas in their cosmic neighborhood.

As this gas drifts away, it is pulled back by the galaxy’s gravity, and could re-enter the same galaxy on timescales of one to several billion years. This process might solve the mystery. If so, then the gas we find inside galaxies may only be about half of the raw material that ends up as fuel for star formation. Large amounts of gas are caught in transit, but will re-enter the galaxy in due time. It’s a gigantic juggling act, in other words, with some of the balls in the galactic hands and others in the air. Added all together, there is a sufficient amount of raw matter to account for the observed rates of star formation.

Until now, however, there was a great deal of uncertainty about the idea of cosmic recycling. Would such gas indeed fall back, or would it more likely reach the galaxy’s escape velocity, flying ever further out into space, never to return? For local galaxies out to a few hundred million light-years in distance, there had been studies showing evidence for inflows of previously-expelled gas. But what about more distant galaxies, where outflows are known to be much more powerful? Would gravity still be sufficient to pull the gas back? If no, astronomers might be forced to radically rethink their models for how star formation is fueled on galactic scales.

To sort this out, Rubin and her team examined gas associated with a hundred galaxies at distances between 5 and 8 billion light-years with the Keck I telescope’s Low Resolution Imaging Spectrogtaph (LRIS). They found in six of those galaxies the first direct evidence that gas adrift in intergalactic space does indeed flow back into star-forming galaxies.

Even more encouraging, the inflow which can be detected by with the Keck I telescope might well depend on the angle at which we observe the galaxy. As Rubin and her team can only measure average motion, the real proportion of galaxies with this kind of inflow is likely to be higher than the six percent suggested by their data. It could, in fact, be as high as 40 percent. This is a key piece of the puzzle and important evidence that cosmic recycling could indeed solve the mystery of the missing star-making matter.

Explore further: Stars made from galactic recycling material

More information: The results described here have been published as Kate H. R. Rubin et al., “The Direct Detection of Cool, Metal-Enriched Gas Accretion onto Galaxies at z ~ 0.5” in the journal Astrophysical Journal Letters, Vol. 747 (2012), p. 26ff. The co-authors are Kate H. R. Rubin (Max Planck Institute for Astronomy), J. Xavier Prochaska (MPIA and UCO/Lick Observatory, University of California), David C. Koo (UCO/Lick Observatory), and Andrew C. Phillip (UCO/Lick Observatory).

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1 / 5 (3) Mar 30, 2012
Gas is observed to flow away from many galaxies..... Would such gas indeed fall back, or would it more likely reach the galaxys escape velocity?
Here's an explanation of what is going on. http://www.presto...ndex.htm
not rated yet Mar 30, 2012
The ultra large black holes in the middle of practically all galaxies tear and rip matter to its core essentially refreshing the matter to its original star building state.

All matter is made of the same essential components, so it stands to reason that the black holes of galaxies would be the ultimate force that causes this cycle.
1 / 5 (5) Mar 30, 2012
Or consider the much simpler explanation common to all galaxies with a massive core: that new matter enters our universe in the core of that supermassive star and is ejected into the surrounding galaxy, providing the raw material to sustain the star formation rates observed. Duh.....

2 & 2=.... I am beginning to loose faith in the intelligence of astronomers...



1 / 5 (2) Mar 30, 2012
Interesting that all the photographs illustrating the article are small, blurry, indistinct pictures, indicating galaxies far away. Nothing like the pictures of the Whirpool Galaxy or the Sombrero. And the article suggests these processes of star formation are still ongoing, so this should be visible in nearby galaxies. Why, then, are only distant galaxies used for the demonstration?
5 / 5 (5) Mar 30, 2012
"And the article suggests these processes of star formation are still ongoing, so this should be visible in nearby galaxies. Why, then, are only distant galaxies used for the demonstration?"

The article notes that previous studies of local galaxies have already shown that inflows occur and that researchers wanted to see if such inflows may exist in more distant galaxies where, it is noted, outflows are observed to be more vigorous.

Btw, a preprint of the paper can be found here:
1 / 5 (4) Mar 30, 2012
veritable galactic fountains of matter flowing out and then back into galaxies over multi-billion-year timescales
This model I (and many other "crackpots") presented before years. The flat shape of galaxies is apparently the product of tossing the matter in their center. But this model violates the contemporary theory of black holes. The matter falling into black holes is wasted in accretion radiation, it cannot be recycled. In this perspective is significant the flat shape of galaxies is characteristic for mature, but not too young or very old galaxies. Too young galaxies are too radiative and their matter is repelled with pressure of radiation (antigravity). The old galaxies have black hole region inactive: the black holes at their center are actually evaporated. Such an evaporation is impossible in Einsteinian relativity, but its enabled in the models, accounting to superluminal neutrinos, which can escape the event horizon a way faster, than the Hawking mechanism allows.
1 / 5 (1) Mar 30, 2012
I think the orthogonal, polar jets in SMBH in galaxies may be much more massive than previously believed, as in comprising a significant fraction of the galaxy's entire mass.

These jets aren't going to be as dense as a Star obviously, but they might be as dense as a nebula, certainly more dense than ordinary inter-stellar space, so the overall mass could be very high relative to galactic averages.

Even the Milky Way has gigantic lobes and plumes of ordinary matter above and below the disk, it just isn't seen in the visible spectrum, but rather in X-ray, gamma, and other spectra.

It would seem to me that these jets and lobes could extend out into space, spread out very thin, and then whip back around some sort of magnetic field line until they are back in the plane of the disk, where gravity might be able to re-capture them...that is, if these gases are not colliding with other nearby galaxies before they have time to get re-captured.
1 / 5 (2) Mar 30, 2012
They could have included illustrations of nearby galaxies to show the contraat. For all they claim such star forming is taking place close in, there seems no real sign of such active regions, or even a fraction of them, in the Andromeda Galaxy, M33, M81. There are dutiful references to star formation and false color images of supposed young blue stars along the edges, but no massive regions of such significant formation. And apparently, if the article is to be accepted, all only for galaxies in excess of 5 billion light years away. Perhaps they are planning to try to draw a connection with the mythical "acceleration of expansion" of the universe at 5 billion years ago.
1 / 5 (1) Mar 30, 2012
They could have included illustrations of nearby galaxies to show the contraat.

Don't let it get to you.

With the amount of hypothesized stars in the Milky Way alone, they couldn't possibly do a half-assed survey of even 1 per thousand of them, never mind proto-stars and brown dwarfs and such to actually get some sort of baseline for how stars and nebulas actually behave, even under "typical" circumstances.

And as for deep, extra-galactic space, there have actually only been an almost insignificant portion of it ever looked at.

The Hubble Deep Field and Ultra-deep field only covers a region of space behind the equivalent of a stamp held at arm's length, and there's only been a few surveys done at that distance.

It would take something like 100 billion years for the Hubble telescope to complete a map of the entire sky at deep field resolutions, and you can't see much of anything of star formation in that anyway...
1 / 5 (1) Mar 30, 2012
Anyway, point is, a lot of the stuff that passes for "fact" is little more than conjecture based on one or two samples, taken from a field of unknown size and composition.

It would be like polling one college football fan on saturday, and then reporting his results as a "majority" or "consensus" opinion.
1 / 5 (1) Mar 31, 2012
As Scryer relates, the black holes at the centre of galaxies are involved in the recycling of matter on a constant basis, stripping it down to its bare neutrons, which then transform into protons and finally into hydrogen-1 (all in under twenty minutes) before eventually accreting back to the galactic plane. This could also explain why the Hawking radiation emitted from galactic black holes is difficult to measure; because it's not really energy at all. Note: This process also finds ready application in steady-state theory.
1 / 5 (1) Mar 31, 2012
before eventually accreting back to the galactic plane
1) Accretion is process of falling into black hole, not escaping from it. 2) Black hole already sits at galactic plane.
The ultra large black holes in the middle of practically all galaxies tear and rip matter to its core essentially refreshing the matter to its original star building state
The tidal effects are definitely capable to rip the constituents of matter - but under swallowing at least portion of them at the price. In this way the matter wouldn't be only recycled, but gradually consumed with central black hole. But the mass of central holes in galaxies is not so high - what worse, it decreases with time gradually.
1 / 5 (1) Mar 31, 2012
Before some time I realized, the object falling into black hole will actually never reach it: it will evaporate in vacuum and only very minute portion of it can reach the surface of event horizon. And this is just an insight, which we should apply for explanation of the recyclation of the galactic matter with central black holes.
1 / 5 (1) Mar 31, 2012
Or maybe the dark matter halo condenses sub-atomic particles from space fabric along the perimeter of galaxies. Space is not just the volume in which matter resides. We are so limited by our humanness.

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