‘Wimpy’ dwarf fossil galaxy reveals new facts about early universe


Faintest galaxy ever detected illuminates unusual aspects of the universe’s early evolution.

Out on the edge of the universe, 75,000 light years from us, a galaxy known as Segue 1 has some unusual properties: It is the faintest galaxy ever detected. It is very small, containing only about 1,000 stars. And it has a rare chemical composition, with vanishingly small amounts of metallic elements present.

Now a team of scientists, including an MIT astronomer, has analyzed that chemical composition and come away with new insights into the evolution of galaxies in the early stages of our universe — or, in this case, into a striking lack of evolution in Segue 1. Commonly, stars form from gas clouds and then burn up as supernova explosions after about a billion years, spewing more of the elements that are the basis for a new generation of star formation.

Not Segue 1: In contrast to all other galaxies, as the new analysis shows, it appears that Segue 1’s process of star formation halted at what would normally be an early stage of a galaxy’s development.

“It’s chemically quite primitive,” says Anna Frebel, an assistant professor of physics at MIT, and the lead author of a new paper detailing the new findings about Segue 1. “This indicates the galaxy never made that many stars in the first place. It is really wimpy. This galaxy tried to become a big galaxy, but it failed.”

But precisely because it has stayed in the same state, Segue 1 offers valuable information about the conditions of the universe in its early phases after the Big Bang.

“It tells us how galaxies get started,” Frebel says. “It’s really adding another dimension to stellar archaeology, where we look back in time to study the era of the first star and first galaxy formation.”

Metal-poor stars: a telltale sign

The paper, “Segue 1: An Unevolved Fossil Galaxy from the Early Universe,” has just been published by Astrophysical Journal. Along with Frebel, the co-authors of the paper are Joshua D. Simon, an astronomer with the Observatories of the Carnegie Institution, in Pasadena, Calif., and Evan N. Kirby, an astronomer at the University of California at Irvine.

The analysis uses new data taken by the Magellan telescopes in Chile, as well as data from the Keck Observatory in Hawaii, pertaining to six red giant stars in Segue 1, the brightest ones in that galaxy. The astronomers are able to determine which elements are present in the stars because each element has a unique signature that becomes detectable in the telescope data.

In particular, Segue 1 has stars that are distinctively poor in metal content. All of the elements in Segue 1 that are heavier than helium appear to have derived either from just one supernova explosion, or perhaps a few such explosions, which occurred relatively soon after the galaxy’s formation. Then Segue 1 effectively shut down, in evolutionary terms, because it lost its gas due to the explosions, and stopped making new stars.

“It just didn’t have enough gas, and couldn’t collect enough gas to grow bigger and make stars, and as a consequence of that, make more of the heavy elements,” Frebel says. Indeed, a run-of-the-mill galaxy will often contain 1 million stars; Segue 1 contains only about 1,000.

The astronomers also found telling evidence in the lack of so-called “neutron-capture elements” — those found in the bottom half of the periodic table, which are created in intermediate-mass stars. But in Segue 1, Frebel notes, “The neutron-capture elements in this galaxy are the lowest levels ever found.” This, again, indicates a lack of repeated star formation.

Indeed, Segue 1’s static chemical makeup even sets it apart from other small galaxies that astronomers have found and analyzed.

“It is very different than these other regular dwarf-type galaxies that had full chemical evolution,” Frebel says. “Those are just mini-galaxies, whereas [Segue 1 is] truncated. It doesn’t show much evolution and just sits there.”

“We would like to find more”

Dwarf galaxies, astronomical modeling has found, appear to form building blocks for larger galaxies such as the Milky Way. The chemical analysis of Segue 1 sheds new light on the nature of those building blocks, as Frebel notes.

Indeed, other astronomers suggest that the study of galaxies such as Segue 1 is a vital part of progress in the field. Volker Bromm, a professor of astronomy at the University of Texas, says the new paper is “very nice and important,” and “substantiates the idea” that analyzing faint dwarf galaxies produces new insight into the universe’s development.

As Bromm points out, when it comes to the chemical composition of early stars, any search for clues among stars closer to us in the Milky Way can be problematic; most such stars have had “a very complex assembly and enrichment history, where many generations of supernovae contributed to the abundance patterns [of elements] seen in those stars.” Dwarf galaxy stars do not come with that problem.

The findings on Segue 1 also indicate that there may be a greater diversity of evolutionary pathways among galaxies in the early universe than had been thought. However, because it is only one example, Frebel is reluctant to make broad assertions.

“We would really need to find more of these systems,” she notes. “Or, if we never find another one [like Segue 1], it would tell us how rare it is that galaxies fail in their evolution. We just don’t know at this stage because this is the first of its kind.”

Frebel’s work often focuses on analyzing the chemical composition of unusual stars closer to us. However, she says she would like to continue this kind of analysis for any other galaxies like Segue 1 that astronomers may find. That process could take a while; she acknowledges that any such future discoveries will require “patience, and a little luck.”




Wimpy dwarf fossil galaxy reveals new facts about early universe

10 Responses to ‘Wimpy’ dwarf fossil galaxy reveals new facts about early universe

  1. Reder van Rooyen 14196663 May 2, 2014 at 7:51 am #

    I read that Segue 1 was originally found in 2007 and as stated may hold some key information in helping us understand the universe we live in, a topic which definitely has a lot of unanswered questions. Exciting indeed if you ask me. In the blog post it says that the discovery of a similar galaxy is going take some time and thus requires patience. So I was wondering whether this might halt the progress being made on this topic especially if someone new has to potentially take over the work done, each time. It is clear that this galaxy is an exception when it comes to galaxy formation, is it then conceivable to think that the state which Segue 1 is currently in might also be different than other galaxies at the same stage, thus making it difficult to use it in making inferences about the evolution of other galaxies and the universe as a whole? The post also states that the Segue 1 has poor metal content, what does this imply exactly? I read that the Square Kilometer Array telescope was mentioned in previous comments, I really hope it will positively contribute to these studies as it will further help South Africa’s involvement in complicated science and help put South Africa on the map. I really found this blog post very interesting and enjoyed reading up on some facts that I never knew before, and it has created a curiosity within me.

  2. Sedgeley (14053536) May 2, 2014 at 7:17 am #

    What a thought-provoking article! While reading it, a few questions came to mind:
    – Is 75 000 light years really the radius of the universe known to us? (Assuming that the distance to Segue 1 was measured in a straight line)
    – Could there be other life forms in this galaxy?
    Since the scope for SETI (Search for Extra Terrestrial Intelligence) is now broader, I would say that the possibility for finding other life forms is greater. It is said that Segue 1 is a surviving relic of the very first galaxies. It is also said that Segue 1 is 13 billion years old (Paul Wallis, 2014).
    I wonder that if it is so old and distant, maybe it is composed of entities unknown to us which may explain its chemical composure and characteristics. Since Segue 1 seems to be a galaxy frozen in time, we may use information gathered on the galaxy, and relate it to us, and thus get more insight on our galaxy, the Milky Way. It boggles my mind to think that such places and things actually exist, and that we would never have been aware of their existence had it not been for our technological advances. there is much more to the night sky than what we see with the naked eye.

  3. Keabetswe 14367310 May 2, 2014 at 5:45 am #

    Quite an interesting article. It means we are getting close to finding out answers about the formation of the universe because the the deeper we go,the trickier it becomes. Segue 1 might be an odd galaxy but it’s just another stepping stone and a fun puzzle that scientists are willing to tackle, hopefully, with the help of the SKA.

  4. Robyn (14110352) May 2, 2014 at 2:30 am #

    I was really curious about the fact that this galaxy just ”ran out” of energy. I mean it clearly had sufficient energy to being with, it had enough to form 6 of the brightest red giants so why did it just run out? Where did all the energy and gas go? Looking up segue 1 i saw that it contains a lot of dark matter, is that were all the energy could potentially go?
    I also looked up if galaxies can reach equilibrium thinking that perhaps this galaxy had no need to get bigger because it had reached a comfortable state? It sounds dumb but can galaxies reach equilibrium because I found some information similar called Heat Death of the Universe,”ultimate fate of the universe in which the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain processes that consume energy” http://en.wikipedia.org/wiki/Heat_death_of_the_universe.
    Is it possible that this galaxy is experiencing this and is ‘dying’?
    I find it interesting that from this ‘fossil’ galaxy we can look at conditions of the early universe and try to find if there are other galaxies that experienced the same effect. from this galaxy we can gain insight to supernovas and the after effects,”“This gives us clues about what those first supernovae looked like,” she added in a paper published in The Astrophysical Journal.”

  5. Dean Herbig (14069882) May 2, 2014 at 2:11 am #

    Why did Segue 1 lose all of its gas due to explosions and why did all of the other galaxies that are known at present retain their gas? Why did all the other galaxies that are known at present evolve into bigger galaxies, except Segue 1? These are the questions that scientists are probably trying to answer and when scientists can answer all of these questions, we will be able to understand how our galaxy formed.

  6. 14143471(Tebogo koza) May 1, 2014 at 1:46 pm #

    Sheer intricacy I tell you!, I’ve been studying about such stellar formations and how stars in galaxies tend to deviate away from the main sequence on the H-R Diagram(well it depends on their mass anyway) but this really baffles me, Segue 1 acts really strangely because to think of it in due time, all of the stars will succumb to their own mass and fall to their gravity that is plunged towards their centres to violently explode(supernova) living behind remnants such as the white dwarf, but due to much of its gas being barren no stars will be formed, thus in time it will be a faint galaxy and a shadow of what was, I guess Einstein was right,God indeed doesn’t play dice with the universe.
    On the issue raised by Anna Frebel, I believe the galaxy wasn’t really attempting to become big,rather see it as it exhausted most of its energy in a short period of time, and couldn’t recover…however ridiculous its life ended, the galaxy is a beauty and an exception because so much about the big bang theory can be traced from studying its failure to evolve, and being a fossil it is, it will prove handy in the field of AstroA rcheology…hhmmm SKA, I think someday i’m going to derive results from you.

  7. Jana Muller 14007402 May 1, 2014 at 12:34 pm #

    Understanding the development and evolution is critical in understanding the evolution of stars as well. Through new technology such as the SKA radiotelescope it will become easier to detect more of these faint galaxies and will make it easier for scientists to compare the evolutionary track galaxies follow. What I find really interesting is that the Segue 1 galaxy stopped evolving and developing. Which also poses the question to whether their are even fainter galaxies still undetected. It would be good to be able to compare other galaxies to see if there are any significant differences in their evolution and how the chemicals in and surrounding the galaxy have an effect on whether or not the galaxy continues to expand or if it stops evolving. Can chemical reactions with chemicals that are already in the galaxy alter the way the stars in it form?

  8. Boitshoko(14172209) May 1, 2014 at 9:17 am #

    Galaxy evolution is very wide field of study even concluding on a result is laborious work and the immense testing that goes in such findings is inspiring, the is no doubt about it that the galaxy evolves in different ways such in hierarchical formation but to find a galaxy that tried to be bigger galaxy is fascinating and that the findings were done with pre-new equipment. New technology like the SKA program will help discover such galaxies ,the SKA will heighten our understanding of our universe by helping scientists and radio astronomers understand the process of star formation .There is evidence to suggest that present day galaxies have been formed by a number of smaller galaxies over a vast time span. In order to probe the cold gas content of the galaxies the radio continuum emission is used and the SKA is used to probe the star formation rates in the galaxy ( Baugh et al 2004).

  9. 14011736 (Dawid Wolhuter) May 1, 2014 at 7:47 am #

    I have always found the universe intriguing. It is weird reading that a galaxy “failed” in becoming a big galaxy. How do the scientist know that the galaxy failed in becoming a big galaxy? Isn’t the galaxy maybe just in the early stages of development? Might the galaxy not expand further in years to come? If not, it is really interesting since, it is the first of it’s kind to be discovered.

  10. 14015278 May 1, 2014 at 6:27 am #

    This is so great!! I personally think that galaxies and other solar systems are most interesting! However disturbing some may see it, I have always wondered and read about other potentially exciting planet with always some hope that one day scientists, if not me, would finally be able to find some sort of habitable planet other than Earth. Many studied and found that the moon or Mars might be pretty good with a few adjustments, but nothing could ever get as close as the incredible living conditions we experience on Earth. I was always convinced they were too narrow minded and one should try investigate other galaxies and solar systems. They finally did!! So although this planet is much smaller than the one we are used too and is a mere 75000 light years away, it still stirs my imagination and lets make me wonder… Many positive factors of this newly discovered planet include the presence of water and an similar climate due to a layer resembling our current ozone layer and atmosphere. The sun it orbits is much smaller but considering that the planet it self is rather small this does not really pose a real problem. Very, very interesting and a “must continue” research!

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