Description: In this Apogee podcast, Cosmic discusses the discovery of a large ring (or bubble) structure in the Orion Molecular Complex
Bio: Cosmic is a self- and crowd-funded independent research astronomer and space musician.
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Hello! This is Cosmic, and welcome to the Apogee podcast! The format of this podcast is myself describing, discussing, and critiquing an article of my choice from an astronomical journal. Sometimes topics within these articles send me off on temporary tangents, but they’re always relevant to the overall topic. These podcasts will take place at or near the date of the apogee which is when, along its orbit around the Earth, the Moon is furthest away.
If you have any articles to suggest for future podcasts, I would be happy to take a look at them. I can be reached at cosmiclettuce AT gmail DOT com.
The music you hear in the background are my own compositions, which can be downloaded from my soundcloud channel ‘cosmiclettuce’. I hope you enjoy listening to space music as much as I do.
The apogee for this podcast will take place tomorrow, 12 December 2014, at 23:04 UTC. The lunar distance at that time will be 404583 km, which is 247 km further away than last apogee on 15 November, and 827 km closer than the next apogee on 9 January 2015.
I’d also like to wish everyone a wonderful solstice. This year, the solstice takes place on 21 December at 23:03 UTC. The solstices and equinoxes are my adopted holidays.
Ok, on with the paper!
Just like the previous two apogees, I’m taking a look at yet another discovery paper. This one is entitled “3D DUST MAPPING REVEALS THAT ORION FORMS PART OF A LARGE RING OF DUST”. There are 15 authors on this paper from 7 institutions including Max Plank, Harvard, Univ of Hawaii, Durham University, the Astronomical Observatory of Strasborg, and Priceton. The constellation of Orion, as many of you know, hosts one of the most active regions of star formation in our galaxy. If you’ve yet to see the Great Orion Nebula, or the Horsehead Nebula, or Barnard’s loop, or any of the other “diffuse nebulae” that make up the Orion Molecular Complex (OMC), I encourage you to find sometime with a telescope and heve them show these to you. They are all very beautiful.
This region is the nearest site of on-going star formation. As such, it is also the most studied. Astronomers more or less decided that they had this place pretty much figured out. Nevertheless, the authors of this paper claim that they have found a new structure in this region that’s never been detected before.
So how could they do that with such confidence? When we look at the night sky or take a photograph of it, it appears flat to us. We’re not able to discern distances simply by looking at an object. Now that’s not entirely true, as long as the object we’re looking at is nearby. Using parallax, astronomers can very accurately determine distances out to about 100 parsecs (326 light years). Unfortunately, the OMC is about 500 parsecs away — too far to use parallax.
When three dimensional objects are projected onto a two dimensional plane, the near stuff merges with the middle stuff which mearges with the background stuff. We loose our sense of depth and there’s no way to fix that with a measurement. So what these authors have done is applied a new technique of 3D mapping that allows them to regain a very rough idea of depth or distances. The technique is very complicated, but if you’re in the mood to blow your mind, you can check out the paper I have listed in the program notes.
The way that I came to understand this technique is that they’ve created two models. The first is a model of the stars in this region. They create model stars that have temperature and metalicity characteristics similar to observations. They also create a “reddening” model which is a model of the structure of the nebula. The idea here is that if you take a model nebula and put a model star at some distance in the same line of site as the nebula, you can calculate how bright that star is going to be as seen from Earth, which is a functon of how far away the star is and how much it is reddened.
Ok, so now they have a model. They’ll tweak this model in a couple of ways to best fit some actual data. This data comes, just like the last Apogee Podcast, from Pan-STARRS1 (the Panoramic Survey and Rapid Response System). Pan-STARRS1 has very excellent brightness measurements (photometry) of most of the stars in the OMC at several different wavelengths (colors). So what the authors did is they tweaked the nebula and star models in two ways: they varied the distances of the stars to Earth, and they varied the amount of reddening in the nebula. When the best match was made between model and actual, the authors found that they had the highest resolution 3D map of the OMC ever.
What this allowed the authors to do was to look at layers within the OMC. They could separate out the foreground and background stars and nebulae and show only those layers associated with the OMC, for example.
When looking at various layers, they discovered a very large and distinct ring of material that no one had ever seen before! They have named it the ‘Orion Dust Ring’. They’ve measured it to be about 14 degrees in diameter. To get a sense of how big that is, go out this evening and look at Orion. Stretch your index finger and little finger as far from each other as you can. At arm’s length, the span from tip to tip is about 15 degrees. That’s pretty big. Given that size, the authors have calculated the ring to be about 100 parsecs (326 light years) in diameter.
The authors decide, in haste I think, that “a ring of clouds in Orion strongly suggest a bubble origin” when a shock wave swept up gas and dust, and then later popped and collapsed. A shock wave produced by what? They propose a number of possible sources of the shock wave, none of which they’re happy with. The first is a number of large, hot, nearby stars. But given what they know about these stars, it’s admitted in the paper that none of these stars could be responsible for this ring/bubble. The second is an open cluster NGC 2232, but it’s about 100 parsecs closer to us and moving in a way that doesn’t indicate any association with the ring/bubble. A third possibility is a supernova, but they note that this too is unlikely given the nebula densities needed to create a ring of such size. So the answer to that question is: no one knows. The authors plan to keep looking.
How old is it? They compare it to a nearby known bubble (the one associated with Lamdba Orionis) and determine that the Orion Dust Ring is about 15 million years old. But they say that this should be a low limit because it’s possible that the bubble popped and has slowed or has stopped expanding.
The authors also discuss two alternative interpretations. The first is an admittance that this could be a chance alignment. How I interpret that is that our brains are very good at finding patterns. So when we see a pattern like a ring we automatically think it’s an actual structure caused by previous events, when it very well could be just a random collection of objects that just so happen to form a pattern. They then get into a long discussion about the fact that this region is very complex and maybe there are things they’re just not understanding.
I appreciate the fact that the authors of this paper admit several times that this technique is in its infancy at that their uncertainties are very very high — on the order of 10% at best. I’d like to see this 3D mapping method tested in the laboratory and on other astronomical objects. This is some very excellent and painstaking work. I like the fact that they’re working with actual telescope data to help them with their models. Finally, I’m hopeful that in the future this amazing technique can be refined and improved.
And until next apogee … I bid you Peace.
End of podcast:
365 Days of Astronomy
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