Little Galaxies Are Big on Dark Matter

Article written: 29 Dec , 2011
Updated: 24 Dec , 2015
by

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Dark matter… It came into existence at the moment of the Big Bang. Within its confines, galaxies formed and evolved. If you add up all the parts contained within any given galaxy you derive its mass, yet its gravitational effects can only be explained by the presence of this mysterious subatomic particle. It would be easy to believe that the larger the galaxy, the larger the amount of dark matter should be present, but new research shows that isn’t so. Dwarf galaxies have even higher proportions of dark matter than their larger counterparts. Although the dwarfs are the most common of all, we know very little about them – even when they consume each other. Enter the star stream…

“Several of my previous images feature the fossil remnants of these ancient mergers as faint stellar rivers called tidal streams. These stellar streams are the table crumbs from small dwarf galaxies that were gravitationally dismembered as they were devoured by the larger galaxy they orbited.” says astrophotographer, R. Jay Gabany. “The theory implies dwarf galaxies also merged and are still merging with each other. But, there has never been clear photographic evidence or a close investigation of dwarf galactic mergers until now.”

The target is NGC 4449, a small, irregular dwarf galaxy much like the Milky Way’s Large Magellanic Cloud. What makes it interesting to astronomers is the presence of thousands of hot blue stars and massive red regions interspaced with thick dust clouds. It isn’t just forming new stars… it’s experiencing an explosion of star birth! According to current theory, dwarf galaxies such as this one could be undergoing a merger event, but there hasn’t been photographic proof until now.

“The picture I am sharing is of a small, dwarf galaxy known as NGC 4449 that’s located about 12.5 million light years from Earth towards the northern constellation of Canes Venatici, the Hunting Dogs. This galaxy is about the size of our Milky Way’s largest satellite galaxy, the Magellanic Cloud. But, NGC 4449 is much farther away and it is experiencing a major star burst event- an episode characterized by the production of new stars at a furious rate.” says Gabany. “This image is unique because it captures the first dwarf galaxy known to have its own tidal stream of stars. Therefore, it represents the first closely studied example of a dwarf galaxy merging with an even smaller dwarf star system! The professional astronomers with whom I work also suspect the merger may have contributed to the ferocious production rate of new stars inside NGC 4449.”

The research done by the team led by Dr. David Martinez-Delgado has some very interesting ramifications and their paper has been accepted for publication in the Astrophysical Journal Letters.. As so well put in Jay’s photographic explanation in his webpage; “Although the cold dark matter theory predicts mergers and interactions between dwarf galaxies, there is scant observational evidence that these types of mergers are still happening in the nearby local Universe. Interactions between dwarf galaxies invoke the possibility of exploring a very different merger regime. For example, research has shown that multiple dwarf galaxies with different stellar masses may exist in similar sized dark matter halos, hence what appears as a minor merger of stars could be a major dark matter merger. Studying interactions on a small scale, such as NGC 4449, provides unique insights on the role of stars versus dark matter in galactic merger events.”

Where once amateur astrophotographers painted beautiful portraits of what lay just beyond human perception in deep space, they are now crafting images capable of true science. The eyes of their telescopes are being combined with professional instruments and producing amazing results.

“We live in an age where science has become unfettered from examining the Universe with only our physical six senses.” concludes Gabany. “This has unlocked a profound new level of understanding, resolved ancient mysteries and unlatched a Pandora’s chest filled with new questions begging for answers. We still have much to learn.”

For Further Reading: Dwarfs Gobbling Dwarfs: A Stellar Tidal Stream Around NGC 4449 and Hierarchical Galaxy Formation On Small Scales and The Big Deal About Dwarf Galaxies.

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16 Responses

  1. Anonymous says

    That image of a night’s starry stream is fantastic.

    “ If you add up all the parts contained within any given galaxy you derive its mass, yet its gravitational effects can only be explained by the presence of this mysterious subatomic particle. “ Is that an assumption? Could it be, for example, a “property of space”? Or something else altogether?
    ____

    I have never, and will never like these persistent analogies to carnivorous predation: devouring, consuming, eating, swallowing-up ( and worst of all, cannibalism! ), etc. It seems to project the ugly, violent system of Nature that presently reigns on Earth to the heavens. In my mind, these commonly used metaphorical references only diminish the grandeur of the celestial realm in the sight of man and woman – shadow its radiance with our world’s darkness.
    ____

    There is a theory, maybe no longer valid, that the continents were built-up, or renewed, perhaps, through a kind of accretion process via Earth’s Plate Tectonic Mechanism: a constructive, renewing, mass-adding process; one that is accompanied with a burst of intense geologic activity.
    ____

    Could it be these Dwarf Galaxies serve some beneficial – constructive – role in the life stories of large, heavy-weight Galaxies? Like small islands of rock being added to larger continental masses over movements of time? A dynamic process – unlike that involving a Lion capturing a Gazelle, destroying its life, as the poor beast is ripped apart and devoured!

    Stars are not destroyed in “collisions” and “dinners”; they either interact with, or are added to the Galaxy – merging and enriching(?) them. But the Dwarf Galaxy’s stars shine on in a new brilliant – revitalized? – setting!

    ( The poor Gazelle is no more, as the Lion sleeps tonight. )
    _______________________________________

    “Where once amateur astrophotographers painted beautiful portraits of what lay just beyond human perception in deep space, they are now crafting images capable of true science. The eyes of their telescopes are being combined with professional instruments and producing amazing results.

    “We live in an age where science has become unfettered from examining the Universe with only our physical six senses.” concludes Gabany. “This has unlocked a profound new level of understanding, resolved ancient mysteries and unlatched a Pandora’s chest filled with new questions begging for answers. We still have much to learn.”

    Man today, thanks to generations of pianeers past, seems to be standing on a summit of profoundly expanded view, from where horizons recede into infinity, or phase into another, higher realm of existence:

    Oh! I have slipped the surly bonds of Earth
    And danced the skies on laughter-silvered wings;
    Sunward I’ve climbed, and joined the tumbling mirth
    Of sun-split clouds, — and done a hundred things
    You have not dreamed of — wheeled and soared and swung
    High in the sunlit silence. Hov’ring there,
    I’ve chased the shouting wind along, and flung
    My eager craft through footless halls of air. . . .

    Up, up the long, delirious burning blue
    I’ve topped the wind-swept heights with easy grace
    Where never lark, or ever eagle flew —
    And, while with silent, lifting mind I’ve trod
    The high untrespassed sanctity of space,
    Put out my hand, and touched the face of God.

    John Gillespie Magee Jr
    American Spitfire pilot who
    fought in the Battle of Britain

  2. Anonymous says

    This puts models of DM abundance to task. Most models have DM increasing its abundance with the observed mass up to a ratio of about 5:1 over luminous matter with standard sized galaxies. This observation puts these models under some question.

    LC

    • Dan Bernitt says

      I don’t suppose it could be some kind of mysterious effect that throws Einstein’s constant way off? Wouldn’t that screw up gravity calculations?

      • Torbjörn Larsson says

        Yes, but the cc seems constant.

        In any case its an expression of large scale negative pressure that doesn’t behave like particulate matter. It is difficult (for me) to see how it would screw up gravity locally.

      • Torbjörn Larsson says

        Yes, but the cc seems constant.

        In any case its an expression of large scale negative pressure that doesn’t behave like particulate matter. It is difficult (for me) to see how it would screw up gravity locally.

  3. Anonymous says

    Around the time the paper describing observations of this stellar stream were published another paper appeared detailing a possible second dwarf galaxy cannabalized by NGC 4449. In this case, a globular cluster in the galaxy appears flattened and displays two short tails of stars on either side of the cluster, similar to some gravitationally distorted globular clusters in the Milky Way. These and other clues point to this cluster (CL 77=B15) being the surviving nucleus of a dwarf galaxy almost totally consumed by NGC 4449: http://arxiv.org/PS_cache/arxiv/pdf/1111/1111.5861v1.pdf

    Jay GaBany, who acquired the deep 0.5m telescope images for this study also features the fantastic 8-meter Subaru image of NGC 4449 on his website (definitely worth a look!): http://www.cosmotography.com/images/interactive_ngc4449.html

    The globular cluster CL 77, the putative nucleus of a dwarf galaxy consumed by NGC 4449, is also visible in this Subaru image (see Fig 1 in the linked paper for a finder chart).

  4. Torbjörn Larsson says

    It would be easy to believe that the larger the galaxy, the larger the amount of dark matter should be present, but new research shows that isn’t so. Dwarf galaxies have even higher proportions of dark matter than their larger counterparts.

    [Ivan] Yo’ Tammy, amount is not the same as proportion! [/Ivan]

    Maybe my physical intuition is skewed, but I would assume that “light” matter would more efficiently aggregate the more dark matter there is. Hence the ratio LM/DM would increase with LM, no surprise there.

    • Member
      IVAN3MAN_AT_LARGE says

      Nice catch there, Torbjörn! I missed that when I had read the article late last night – and not had enough coffee! – before e-mailing Tammy about a few other minor errors. 😉

  5. Torbjörn Larsson says

    It would be easy to believe that the larger the galaxy, the larger the amount of dark matter should be present, but new research shows that isn’t so. Dwarf galaxies have even higher proportions of dark matter than their larger counterparts.

    [Ivan] Yo’ Tammy, amount is not the same as proportion! [/Ivan]

    Maybe my physical intuition is skewed, but I would assume that “light” matter would more efficiently aggregate the more dark matter there is. Hence the ratio LM/DM would increase with LM, no surprise there.

  6. Damian says

    Quote: “Dark matter… It came into existence at the moment of the Big Bang”

    Is that a fact? Can you provide proof for this statement?

    Its amazing that science has managed to extrapolate such a solid factual account of the universe from anthropocentric deterministic theories.

    In 2012 it seems that coherentism is the ‘lingua franca’ of cosmology.

    The first line and the last line of this article are at odds with each other, as it finishes with: “…We still have much to learn.”

    http://en.wikipedia.org/wiki/Regress_argument

    Happy new year. !

    • Torbjörn Larsson says

      Oy. Fractal error warning:

      – The reheating after inflation ends that is responsible for creating the primordial particles in the universe is predicted by the standard cosmology, which has no environmental (anthropic) reasoning in it.

      – A prediction is not an extrapolation in the sense of uninformed construction of new data points. For example, reheating is not extrapolated directly from any observation of it, but predicted out of theory.

      Likewise, we do observe properties of reheating in the CMB, the amount of resulting adiabatic and isocurvature anisotropy for example.

      – Most anthropic hypotheses have to be recast to environmental, say a preponderance of galaxies (stars) or dust (stars and planets), so they are not exactly anthropocentric.

      – Quantum mechanics which is our only “theory of everything” to date is deterministic, but also stochastic.

      Is that a fact? Can you provide proof for this statement?

      It is a fact, so we can’t provide mathematical proof, only empirical evidence. See above.

      The first line and the last line of this article are at odds with each other, as it finishes with: “…We still have much to learn.”

      The reason we know facts is because science method means learning facts. There is no conflict, and nothing of regress as we also learn universal facts with the specifics.

      For example, The Laws Underlying The Physics of Everyday Life Are Completely Understood.

      As a reflection in the face of the turning of the year, I don’t know how anyone would like to continue live with such a fragmented world view that is causes fractal errors. It is my understanding that in most cases it results from the Dunning-Kruger effect.

      Nothing personal, mind. As a note in case anyone afflicted reads this, the remedy then is first learning how to learn. Cooking by recipe and with help is accepted as a great way to start understand practices of learning! The New Year festivities is an excellent opportunity to get into the kitchen.

  7. jeff says

    “Much like the Milky Way’s Large Magellanic Cloud”… wait… wasnt it reported that the LMC WASN’T an orbiting galaxy of the Milky Way, but an independent galaxy? I could’ve sworn that i read that… but perhaps im wrong?

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