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Re-Thinking the Magellanic Clouds

Centauri Dreams has always been captivated with the Magellanic Clouds, two galaxies that are the Milky Way’s nearest neighbors in space. The fascination is in many respects visual. Knowing that they’re a beautiful sight to those below the equator, the counter-thought came quickly to mind — what would the Milky Way look like from one of these small satellite galaxies? How bright would it be, how much of the sky would it fill? While pondering such questions, have a look at the Large Magellanic Cloud below, and be sure to click to enlarge this gorgeous image.

Pondering such things, I wrote a story called “Magellanic,” a sort of Weird Tales-era fantasy (I realize that Weird Tales still exists, but I refer to the fabled issues of the 20’s and 30’s). Mixing in a first contact scenario in 1920’s Tibet, a mountain-climbing adventurer at the end of his career, a bit of intelligence agency intrigue and throwing in Edwin Hubble for good measure, I thought I had a winner, but the story remained sadly unpublished, reminding me that my talents lie in other directions.

The Large Magellanic Cloud

Image: The Large Magellanic Cloud, a fixture in my imagination since childhood. New observations indicate that many of our previous theories about the Magellanics must be radically revised. Credit: Copyright Robert Gendler and Josch Hambsch 2005.

The latest news about the Magellanics is that they may not be satellites at all, but independent galaxies that have approached comparatively recently. Astronomers from the Harvard-Smithsonian Center for Astrophysics have measured anomalously high velocities for the duo, implying that they are not bound to the Milky Way. Thus we throw out many previous theories about the Magellanics and their presumed effects.

For one thing, the Milky Way’s gaseous disk is known to be warped, a fact hitherto explained by gravitational tides due to the Magellanics. The new theory has the Clouds arriving between one and three billion years ago, making it unlikely they are the cause of the warp. And the long hydrogen trail called the Magellanic Stream that extends behind the Clouds was thought to be formed from similar interactions. Knowing that the Magellanics are only passing by tends to rule out this scenario as well.

“We have known about the Clouds since the time of Magellan, and a single measurement has thrown out everything we thought we understood about their history and evolution,” says Gurtina Besla (Center for Astrophysics).

And that’s what makes astrophysics in our era so exciting. For that matter, consider the changes in perspective just since 1998, with the discovery of the universe’s continuing acceleration in expansion. As I keep saying (wishing I was young enough to do it myself, though realizing I was never any good at math), what a time to embark on a career in astrophysical research! In this case, add to the Magellanics mystery that star formation within them must now be completely re-thought and you’ll see that we have another example of reassessment that pushes existing theory to the limit.

The paper is Besla et al., “Are the Magellanic Clouds on their First Passage about the Milky Way?” (abstract).

Comments on this entry are closed.

  • ljk September 18, 2007, 9:34
  • Athena September 18, 2007, 20:03

    Very pretty images, Larry.

    Paul, why not publish your story here? After all, it’s your site!

  • Administrator September 18, 2007, 20:13

    I appreciate that thought, Athena, and thanks, but I think that particular story is best left retired. One day, if I get time and get back to doing some fiction, I may see if I can revitalize it. In fact, your comment gives me a boost in that regard.

  • Adam September 19, 2007, 3:44

    Hi Paul

    My maths is better than my writing, but I’m not patient enough to do astrophysics – years getting experiments, mining data, etc etc. Whew! But it’d be cool to see your efforts sometime.


  • Jay Lake September 19, 2007, 7:08

    Hey Paul, that actually sounds like an interesting story. Drop me a line, I’d be curious to read it.

    Jay Lake, SFWA

  • george scaglione September 19, 2007, 9:29

    paul,if you ever do want to write some sf count me in as a reader by all means!! and please keep me advised !! all the very best, george

  • me andi September 19, 2007, 15:25

    Yes, as Athena says publish it here. We would appreiate it.

  • ljk December 17, 2007, 11:55

    An Interaction of a Magellanic Leading Arm High Velocity Cloud with the Milky Way Disk

    Authors: N. M. McClure-Griffiths, L. Staveley-Smith, F. J. Lockman, M. R. Calabretta, H. A. Ford, P. M. W. Kalberla, T. Murphy, H. Nakanishi, D. J. Pisano

    (Submitted on 14 Dec 2007)

    Abstract: The Leading Arm of the Magellanic System is a tidally formed HI feature extending $\sim 60\arcdeg$ from the Magellanic Clouds ahead of their direction of motion. Using atomic hydrogen (HI) data from the Galactic All Sky-Survey (GASS), supplemented with data from the Australia Telescope Compact Array, we have found evidence for an interaction between a cloud in the Leading Arm and the Galactic disk where the Leading Arm crosses the Galactic plane. The interaction occurs at velocities permitted by Galactic rotation, which allows us to derive a kinematic distance to the cloud of 21 kpc, suggesting that the Leading Arm crosses the Galactic Plane at a Galactic radius of $R\approx 17$ kpc.

    Comments: 14 pages, 5 figures, accepted to Astrophysical Journal Letters. Full resolution version available at this ftp URL

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0712.2267v1 [astro-ph]

    Submission history

    From: Naomi McClure-Griffiths [view email]

    [v1] Fri, 14 Dec 2007 00:51:16 GMT (668kb)


  • ljk May 7, 2008, 22:37

    The scattered debris of the Magellanic Stream

    Authors: T. Westmeier, B. S. Koribalski

    (Submitted on 7 May 2008)

    Abstract: Searching the HI Parkes All-Sky Survey (HIPASS) and its northern extension, we detected a population of very compact high-velocity clouds (HVCs) with similar velocities in the Galactic standard-of-rest frame which appear to be arranged in several filaments aligned with the nearby Magellanic Stream.

    A comparison with published OVI/CaII absorption and HI emission line measurements suggests that the HVCs are condensations within an extended and mainly ionised component of the Magellanic Stream. They coincide in position with a faint gas stream predicted in numerical simulations of the Magellanic Clouds by Gardiner & Noguchi (1996). Consequently, the Magellanic Stream could be much more extended than generally believed.

    Comments: 5 pages, 4 figures, accepted for publication in MNRAS

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.0820v1 [astro-ph]

    Submission history

    From: Tobias Westmeier [view email]

    [v1] Wed, 7 May 2008 01:15:49 GMT (271kb)


  • ljk July 1, 2008, 12:24

    Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function

    Authors: Erik J. Tollerud, James S. Bullock, Louis E. Strigari, Beth Willman

    (Submitted on 26 Jun 2008)

    Abstract: We correct the observed Milky Way satellite luminosity function for luminosity bias using published completeness limits for the Sloan Digital Sky Survey DR5. Assuming that the spatial distribution of Milky Way satellites tracks the subhalos found in the Via Lactea LambdaCDM N-body simulation, we show that there should be between ~300 and ~600 satellites within 400 kpc of the Sun that are brighter than the faintest known dwarf galaxies, and that there may be as many as ~1000, depending on assumptions. By taking into account completeness limits, we show that the radial distribution of known Milky Way dwarfs is consistent with our assumption that the full satellite population tracks that of subhalos.

    These results alleviate the primary worries associated with the so-called “Missing Satellites Problem” in CDM. We show that future, deep wide-field surveys like SkyMapper, the Dark Energy Survey (DES), PanSTARRS, and the Large Synoptic Survey Telescope (LSST) will deliver a complete census of ultra-faint dwarf satellites out to the Milky Way virial radius, offer new limits on the free-streaming scale of dark matter, and provide unprecedented constraints on the low-luminosity threshold of galaxy formation.

    Comments: 13 pages, 10 figures, ApJ submitted

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.4381v1 [astro-ph]

    Submission history

    From: Erik Tollerud [view email]

    [v1] Thu, 26 Jun 2008 23:54:33 GMT (561kb)