View Full Version : APOD: can you tell me what these are?

2008-Apr-18, 02:01 PM
Hey everyone.

First, I'm new to these forums, so I apologize if this isn't the correct place to post a question.

I'm wondering if anyone can tell me what the dark objects in the upper right portion of the frame in this picture (http://antwrp.gsfc.nasa.gov/apod/image/0804/ic2948_crouch.jpg) are?

My guess is that it they must be abberations of some kind because they don't look like gaps in the emission nebula. Could it be space debris at a relatively close range compared to the nebula itself?

Thanks for any input!

2008-Apr-18, 07:48 PM
They are explained in the text that went with the image.

They are also known as Bok Globules. No difference that I'm aware of.


2008-Apr-20, 04:33 PM
Archived Image (http://antwrp.gsfc.nasa.gov/apod/ap080418.html)

Seen in silhouette near the top of the view are small, dark clouds of obscuring cosmic dust. Called Thackeray's Globules for their discoverer, they are potential sites for the formation of new stars, but are likely being eroded by the intense radiation from the nearby young stars.

2008-Apr-20, 04:45 PM
In the meantime, Welcome to BAUT AndrewS. You found the right place and it's a good question too. APOD puts out some amazing pictures, I wish they had much longer and descriptive narratives at times...

2008-Apr-20, 04:56 PM
I'm wondering if anyone can tell me what the dark objects in the upper right portion of the frame in this picture (http://antwrp.gsfc.nasa.gov/apod/image/0804/ic2948_crouch.jpg) are?

Have you read: Thackeray's globules in IC 2944 (http://adsabs.harvard.edu/abs/1997A&A...327.1185R)?

I'm not inlcined to, but it looks like there is much information to be had there.

We have studied the complex of small globules discovered by A.D. Thackeray in the southern HII region IC 2944. They are located precisely on the line-of-sight to the luminous OB stars in the region, and thus appear as shadows against the bright HII region. Thanks to this geometry, exceptionally fine details can be discerned on CCD images, which show that the globules are generally sharp-edged and highly structured, and that the complex contains a multitude of fragments in all sizes down to the resolution element of about one arcsec (1800 AU). CO millimeter observations reveal that the largest globule consists of two kinematically separate entities, with masses of about 11 and 4 M_sun. Very large velocity differences exist between the various globules, suggesting that the globules comprise a highly dynamic system perhaps one million years old. We believe that the globules are the remnants of an elephant-trunk observed from behind, originating as a Rayleigh-Taylor instability in an expanding neutral shell powered by the hot HII region. The globule complex is now in an advanced stage of disintegration. We have found no evidence for star formation in any of the globules.

10 pages.