Do Galaxies Recycle Their Material?


It’s a great question that’s now been validated by the Hubble Space Telescope. Recent observations have shown how galaxies are able to recycle huge amounts of hydrogen gas and heavy elements within themselves. In a process which begins at initial star formation and lasts for billions of years, galaxies renew their own energy sources.

Thanks to the HST’s Cosmic Origins Spectrograph (COS), scientists have now been able to investigate the Milky Way’s halo region along with forty other galaxies. The combined data includes instruments from large ground-based telescopes in Hawaii, Arizona and Chile whose goal was determine galaxy properties. In this colorful instance, the shape and spectra of each individual galaxy would appear to be influenced by gas flow through the halo in a type of “gas-recycling phenomenon”. The results are being published in three papers in the November 18 issue of Science magazine. The leaders of the three studies are Nicolas Lehner of the University of Notre Dame in South Bend, Ind.; Jason Tumlinson of the Space Telescope Science Institute in Baltimore, Md.; and Todd Tripp of the University of Massachusetts at Amherst.

The focus of the research centered on distant stars whose spectra illuminated influxing gas clouds as they pass through the galactic halo. This is the basis of continual star formation, where huge pockets of hydrogen contain enough fuel to ignite a hundred million stars. But not all of this gas is just “there”. A substantial portion is recycled by both novae and supernovae events – as well as star formation itself. It not only creates, but “replenishes”.

The color and shape of a galaxy is largely controlled by gas flowing through an extended halo around it. All modern simulations of galaxy formation find that they cannot explain the observed properties of galaxies without modeling the complex accretion and "feedback" processes by which galaxies acquire gas and then later expel it after chemical processing by stars. Hubble spectroscopic observations show that galaxies like our Milky Way recycle gas while galaxies undergoing a rapid starburst of activity will lose gas into intergalactic space and become "red and dead." (Credit: NASA; ESA; A. Feild, STScI)

However, this process isn’t unique to the Milky Way. Hubble’s COS observations have recorded these recycling halos around energetic star-forming galaxies, too. These heavy metal halos are reaching out to distances of up to 450,000 light years outside the visible portions of their galactic disks. To capture such far-reaching evidence of galactic recycling wasn’t an expected result. According to the Hubble Press Release, COS measured 10 million solar masses of oxygen in a galaxy’s halo, which corresponds to about one billion solar masses of gas – as much as in the entire space between stars in a galaxy’s disk.

So what did the research find and how was it done? In galaxies with rapid star formation, the gases are expelled outward at speed of up to two million miles per hour – fast enough to be ejected to the point of no return – and with it goes mass. This confirms the theories of how a spiral galaxy could eventually evolve into an elliptical. Since the light from this hot plasma isn’t within the visible spectrum, the COS used quasars to reveal the spectral properties of the halo gases. Its extremely sensitive equipment was able to detect the presence of heavy elements, such as nitrogen, oxygen, and neon – indicators of mass of a galaxy’s halo.

So what happens when a galaxy isn’t “green”? According to these new observations, galaxies which have ceased star formation no longer have gas. Apparently, once the recycling process stops, stars will only continue to form for as long as they have fuel. And once it’s gone?

It’s gone forever…

Original Story Source: Hubble Space Telescope News Release.

16 Replies to “Do Galaxies Recycle Their Material?”

  1. Yo Tammy, referring to the second paragraph, in the third line: […] large ground-based telescopes in Hawaii, Arizona and Chili […]”

    That last one must be a really hot telescope! 😉

    Actually, that should be Chile.

  2. ‘In matters of galactic importance, mass, not fusion incineration, is the vital thing.’

    COS’s high sensitivity allows many galaxies that happen to lie in front of the much more distant quasars.

    Not to go Ivan on you on the incomplete sentence, but (modulo my insufficiency in english) this seems to confuse two or three different factual claims. One of ‘allowing seeing’ (“allows for”) which seems to be the intended one. But also another of being ‘allows having’ (“allows”), and yet another possibility is ‘allowed by (“allows by”).

    We can’t allow having that, can we?

    1. Let’s not allow it, but you should’ve pointed out where the sentence happens to be. It took me a few maddening seconds to find it, and it was in the first photo caption, not in the text of the report. It should be something like “allows THE WEIGHING OF many galaxies that etc.” because the next sentence goes on to explain what it is that allows galaxies to be weighed: ” The ionized heavy elements serve as proxies for estimating how much mass is in a galaxy’s halo.”

      That’s as far as GALACTIC (in other words, merely local) ecology is concerned, which is part of the “COSMIC ecology”, the proper title for the report at the website of the Nat’l. Maritime Museum, Greenwich, not “Galactic Ecology”. (The entire Cosmos is a single ecosystem, with galaxies as lesser ecosystems. Everything ends up in “the Cosmic Ash Heap” at the bottom of the diagram.) Moreover, in the diagram included with that report, where it says “Type I” it should read “Ia”, and also it should be “Types II and Ib” instead of “Type II”, as they acknowledged when I complained back in December of 2004: “The (…) diagram does indeed suffer from considerable simplification so you are quite right to point out that etc.” See

      Also, the arrow that is labeled “Type I” and should be labeled “Type Ib”, which issues from the bubble that says “Some Double Stars”, is in need of the following explanation that I also got from them in the same reply: “All Type Ia arise from low mass binary stars, but whether from merger or mass transfer or both is not clear.”

      However, they warned: “As more supernovae are discovered the range of types grows.” I guess the range of types went on growing in the course of the next seven years or will do so to the point that the diagram is or will be even more outdated than now. What a mess! Who is man or woman enough to clean it up?

      There’s even more to it since what we see and call the Universe could be just one in a huge number of tiny, rhythmically expanding and contracting cells that would be like the alveoli of a lung, following the breathing of a parent Universe, the Lung Universe or Breathing Universe. This agrees with Hindu mythology, with Brahma bringing forth All That Is by exhaling and extinguishing it by inhaling, in an endless cycle.

      The relevant question here right now is whether or not matter leaks from one cell to the neighboring cells, which would mean that there is an even bigger ecosystem. The hierarchy of ecosystems would be thus: galaxies-pulsating cell-Lung Universe…but this could go on indefinitely, with the Lung being just one unit in a greater unit, the Lung of Lungs, and so on, like a fractal, as we now suspect.

      There would be no end to it, and likewise at the opposite end: the infinitely small. First they said that the atom was indivisible, then they smashed it and found smaller things, but then they smashed these and found quarks, and now they think that eventually they will be able to crack quarks and find even tinier things, etc. etc.

      1. [Y]ou should’ve pointed out where the sentence happens to be. It took me a few maddening seconds to find it, […].

        The easiest way to locate any text on your computer screen is by pressing “Ctrl” + “F” on your computer’s keyboard, and then copy & paste the text into the search box that appears.

      2. unfortunately since we switched servers, it has been amazingly difficult for me to just do a “quick correct” on a grammatical error. so… please forgive if i am slow to fix something, or just get too frustrated to do it. sorry… 🙁

      3. Not on my Dell Inspiron laptop. The procedure elicits no response.

        It’s frustrating to see how mistakes pop up no matter how careful one tries to be. On the first line of my third paragraph it should be “Type Ia” (one ay), not “Type Ib”. Also, it’s a picture caption, not a photo caption.

        What about the odd sentence? Surely there’s something missing there.

        Sorry about the (unavoidable) delay.This is all for the record since no one will ever read this, probably.

      4. …but yes, it does work. It’s that I didn’t notice the Find bar that appeared up there. Thank you. By the way, you ought to tell people about the mistake in the report titled “Do-It-Yourself Guide to Measuring the Moon’s Distance”, where it says that “Amy Shira Teitel is an historian of spaceflight”. That used to be the correct way, centuries ago, when the letter aitch was mute, but not in our days, when it’s just a presumptuous use of the language, apart from being a mistake. It must be “a historian”.

      5. Thanks for this too! I had always, um, presumed, that it was remaining as a weak-strong difference of pronunciation, hence “an historian” in modern language without silent “h”.

        [I have to presume a lot since I learn languages by “monkey see, monkey do”. They are too unstructured for my liking. :-/]

        So it is gradually passing into oblivion as the OD implies? That is both sad and encouraging (a living language).

      6. I had noticed that as well, and you’re correct, but some people (Cockneys) still drop their H’s; here is the Oxford Dictionaries opinion.

      7. …which makes me wonder about Aussies, who get mad when they’re told they have a Cockney accent. The word “easy”, for example: they say “eye-zee”, not “ee-zee”.

      8. Ha, I did that mistake the first time I met a pair. “From England right, I can hear it on the accent?”

        At least I survived, it was outside any pub.

      9. Passing into oblivion?? Ivan3man has found a place where you find proof of the fact that Oxford does not believe in oblivion. It keeps hanging on to a letter enn for reasons that it ought to reveal to the world. Maybe it has something to do with the peculiar logic of the “Oxfudd oxunt” (note: that’s the phonetic spelling).

        The lowly, humble Cockneys that are scorned seem to be the sole guardians of a distant past (I think they always pronounce the H in Australia now). They’re giving scholarly Oxfoadd a lesson: retain the past in full. Don’t pronounce the H if you keep saying “an”, but you can’t have it both ways: use the obsolete article (an) and at the same time use the modern pronunciation. Cockneys are reasonable and consistent, Oxfudd is illogical.

        The space for replies gets ever thinner and I wonder what happens when you take it to the limit. I guess that at the limit it’s a column that’s one letter thick. Reading something squeezed into such a space would be hard but still possible. What happens if you try to go beyond the limit???!!! I suppose nobody has ever done this. Maybe the website implodes, gets lost and vanishes somewhere in cyberland, and you run the risk of being (mis)treated like a hacker and sent to jail for several years, if they manage to find you.

      10. Let’s not allow it, but you should’ve pointed out where the sentence happens to be.

        [daniel_rey_m commentary, first sentence.]

        Then I would go Ivan, right? =D Sorry about that.

        There’s even more to it since what we see and call the Universe could be just one in a huge number of tiny, rhythmically expanding and contracting cells

        No, it can’t be so. The universe is forever expanding in standard cosmology.

        That also means it has a cosmological horizon which is the maximum distance from which particles ever will reach an observer. So no exchange of mass-energy over larger distances.*

        And pattern search on religion signifies nothing. An expanding universe agrees with my breakfast loaf as they both expanded at some time.

        and likewise at the opposite end: the infinitely small.

        No, for whatever reason, likely to keep physics regulated from an UV-catastophe, particles hit the Planck energy limit. That gives, observably, a discrete measure to entropy. And if you go through the numbers there are only so many particles and so many interactions (fields).

        First they said that the atom was indivisible,

        That was a testable hypothesis, yes, and it was hence invalidated by observation. The success of reduction once doesn’t mean there are turtles all the way down; and as noted above such hypotheses have also been invalidated.

        * Except possibly under inflation. At least it left structures larger than the observable universe, even if there is no later dynamics (except expansion, natch) on these inflated scales.

      11. Nine years ago a physicist at a lecture amazed us by telling about the possibility that beyond quarks there could be a neverending succession of ever smaller elementary particles. Either this has now been unanimously rejected or it’s no longer part of the mainstream and maybe no more than the opinion of a tiny group of rebels.

        (He has a Ph.D. after his name and was part of one of the two international teams at the Fermilab that discovered the top quark. His university had made a big financial contribution to the enterprise and this had given him the right to go around claiming to be a co-discoverer of that quark, as another physicist explained to me years later. However, the two teams had a total of more than 400 members, and not all of them had that privilege because the universities that had sent them to the lab hadn’t made any grants. This shows that THERE IS A SHAMEFUL PRESTIGE MARKET in the international scientific community that almost nobody seems to be aware of. Prestige is sold to universities and professors like so much rice or beans at a commodity market. I was rather shocked. In 1969-70 I’d studied three semesters of Biology in that same university before dropping out. More autobiographic data are irrelevant unless I win the Nobel Prize for Dilettantism before I die.)

        There’s an additional complication in the background. What if there is something like an Uppsala school of thought??!!

        So let’s forget about subquarks, subsubquarks and subsubsubquarks. That argument against their existence (and the one against matter leaks between the little expanding cells) is convincing. May we assume that there is as yet no opposition to the idea of a possible, infinitely large fractal Universe that would be like a set of Matrioshka dolls (dolls within dolls within dolls…)?

        Why has nobody pointed out that in the natural sciences a capital “E” and a lower-case “e” stand for two very different things?

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