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Journey Inside A Bok Globule

NGC281/IC1590 Hubble Heritage Parallel Vision - Jukka Metsavainio

NGC281/IC1590 Hubble Heritage Parallel Vision - Jukka Metsavainio

You asked for more? You got it. This time our dimensional visualization is going to take us 9500 light years away from where you’re sitting now and deep into the Perseus spiral arm of the Milky Way Galaxy. Buckle your seat belt and relax your eyes, because we’re heading into two versions of a 132 light year expanse known as NGC 281 and the central core called IC 1590…

Just like last time, this dual image requires a little bit of a challenge on your part to create a 3D effect. Thanks to the wizardry of Jukka Metsavainio, we’ve gone even one better. There’s two! The first version you see on this page are for those of you who have success relaxing your eyes and being a certain distance from the screen to get the images to merge. The one below is for those of you who have better luck crossing your eyes and catching dimension in the center image. Are you ready for your journey? Then have a look and let’s learn…

NGC281/IC1590 Hubble Heritage Cross Vision - Jukka Metsavainio

NGC281/IC1590 Hubble Heritage Cross Vision - Jukka Metsavainio

The whole gigantic region of nebulosity is known as NGC 281 and most commonly referred to as the “Pac Man Nebula”. Visible to small telescopes and located in the constellation of Cassiopeia (RA 00:42:59.35 Dec +56:37.18.8), this cloud of high density hydrogen gas is being ionized by an incredible output of ultraviolet radiation from the hot, neophyte stars which coalesced there. Deep in the center of this HII region is a open area called IC 1590 – home to a young galactic star cluster – and several dark patches known as “Bok Globules”.

If that sounds like something you might expel when you have a cold, you’re right. They are cold… Cold pockets of dense dust, molecular hydrogen and gas. Bok globules are the brain child of astronomer Dr. Bart Jan Bok – who, among other things, loved to study the paranormal. When Bok proposed their existence in the 1940’s, he knew what was going on. These dark regions were acting like interstellar cocoons – protecting their inner stars from being stripped by the radioactive stellar winds of nearby companions and blocking visible light. When stellar metamorphosis had occurred, the new star then begins to send out its own winds and radiation to evaporate the globule – but this isn’t always the case. Sometimes the cocoon gets destroyed before the life inside ignites.

In our image you will see bright blue stars, members of the young open cluster IC 1590, near the globules. Meanwhile, the cluster’s partially revealed core in the upper right hand corner is filled with a tight grouping of extremely hot, massive stars emitting visible and ultraviolet light, causing those incredible pink clouds. When these star forming dust clouds were first imaged by Hubble, we thought we knew a lot about them. But what have we learned since?

According to research done by T.H. Henning (et al): “The exciting star HD 5005 of the optical nebulosity is a Trapezium system… and emission shows that the molecular cloud NGC 281 A consists of two cloud fragments. The western fragment is more compact and massive than the eastern fragment and contains an NH3 core. This core is associated with the IRAS source 00494+5617, an H2O maser, and 1.3 millimeter dust continuum radiation. Both cloud fragments contain altogether 22 IRAS point sources which mostly share the properties of young stellar objects. The maxima of the 60 and 100 micrometers HIRES maps correspond to the maxima of the (12)CO (3 to 2) emission. The NGC 281 A region shares many properties with the Orion Trapezium-BN/KL region the main differences being a larger separation between the cluster centroid and the new site of star formation as well as a lower mass and luminosity of the molecular cloud and the infrared cluster.”

Great! It’s confirmed! It’s a star forming region, very much like what we can observe when we see M42. But, maybe… Maybe there’s just a little bit more to it than that? Hubble observations shows the jagged structure of the dust clouds as if they are being stripped apart from the outside. What could have caused that? Only the radiation from the nearby stars? Hmmm…. Not everyone seems to think so.

A 2007 study done by Mayumi Sato (et al) states: “Our new results provide the most direct evidence that the gas in the NGC 281 region was blown out from the Galactic plane, most likely in a superbubble driven by multiple or sequential supernova explosions in the Galactic plane.” Supernova? Yeah, you bet. And someone else thinks so, too…

Says S.T. Megeath (et al): “We suggest that the ring has formed in a superbubble blowout driven by OB stars in the plane of the Galaxy. Within the cloud complex, combined optical, NIR, mm and cm data detailing the interaction of a young O star with neighboring molecular cores, provide evidence of triggered star formation inside the cloud complex on a few parsec scale. These data suggest that two modes of triggered star formation are operating in the NGC 281 complex – the initial supernovae triggered formation of the entire complex and, after the first generation of O stars formed, the subsequent triggering of star formation by photoevaporation-driven molecular core compression.”

You’ve got it. This type of research suggests the cores were created within the molecular cloud. When they were exposed to direct UV radiation, the low density gas was stripped. This increase in pressure then caused a rippling shockwave which triggered star formation – first in the compressed regions and then in the HII areas. Says Megeath, “The total kinetic energy of the ring requires the energy of multiple supernovae. Both the high Galactic latitude and large expansion velocity may be explained if the NGC 281 complex originated in the blowout of an expanding superbubble. The loop of HI seen extending from the Galactic plane may trace the edge of a superbubble powered by supernovae near the Galactic plane. The expansion of a superbubble into the increasingly rarefied Galactic atmosphere can lead to a runaway expansion of the shell and the blowout of the bubble into the Galactic atmosphere. NGC 281 could have formed in the gas swept up and compressed in a blowout. Hence, NGC 281 maybe an example of the supernovae-driven formation of molecular clouds (and consequently, supernovae-triggered star formation).”

What incredible region! Hope you enjoyed your journey… And be sure to tip your hat to Bart Jan Bok who told the IAU (when they named Asteroid Bok for him in 1983) “Thanks for a little plot of land that I can retire to and live on.”

Our many, many thanks to Jukka Metsavainio of Northern Galactic for creating this unique image for Universe Today Readers! We look forward to more…


Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

Comments on this entry are closed.

  • btw February 3, 2009, 3:02 PM

    I still can’t get it. My eyes are just too old.

    Those 3D pictures that were popular a few years ago were easy, but this…

  • Astrofiend February 3, 2009, 5:37 PM

    1. btw Says:
    February 3rd, 2009 at 3:02 pm

    ” I still can’t get it. My eyes are just too old.

    Those 3D pictures that were popular a few years ago were easy, but this…”

    If you can stare at your finger 6 inches in front of your face, you can easily get this. Do the second ‘crossed eyes’ one. Now put your head about 30 or 40 cm from the screen. Stick a finger about 6 or so inches in front of your face so it appears just below the images in the background, and look at it. This will make you a bit cross eyed because you are looking at your finger so close to your face. Move your finger towards and away from the screen a bit and continue to watch it. As you do this, notice what happens to the images behind. There will be the two images – the left and right stereo ones. These will begin to overlap and cross over each other, and, at some point when your finger is at a certain distance, the images will cross over to a point where you have three perfect images – the left stereo, the right stereo, and sitting between them is the full stereo image. Note they have to be aligned almost perfectly.

    Now you have to shift your focus from your finger to the full stereo image behind without losing your cross eyed gaze, which would de-merge the image. With a bit of practice, the third image should all of a sudden ‘snap out’ at you, and it should almost be natural to hold that gaze.

    Hope this helps a bit!

  • Billy February 3, 2009, 6:32 PM

    Try copying and pasting the image into a program like Microsoft Paint. Save it as a jpg image, and open it in a resizeable program like Windows Picture and Fax Viewer. The center to center distance between the images should be same as your eyeballs.

  • Alex February 3, 2009, 8:40 PM

    Both images worked well for me, but they produce slightly different images. The first example looks the best, most realistic. The second one looks good in part, while other parts of the second one look visually confusing to a degree.

  • Brad February 4, 2009, 6:14 PM

    Wow that’s amazing! How does this work- are the left and right images different? Is it simply an optical illusion or are the stars “really” in those orientations?

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