APOD: The Gum Nebula Expanse (2018 May 24)

[APOD Robot]

The Gum Nebula Expanse

Explanation: Named for a cosmic cloud hunter, Australian astronomer Colin Stanley Gum (1924-1960), The Gum Nebula is so large and close it is actually hard to see. In fact, we are only about 450 light-years from the front edge and 1,500 light-years from the back edge of this interstellar expanse of glowing hydrogen gas. Covered in this 40+ degree-wide monochrome mosaic of Hydrogen-alpha images, the faint emission region stands out against the background of Milky Way stars. The complex nebula is thought to be a supernova remnant over a million years old, sprawling across the Ship's southern constellations Vela and Puppis. This spectacular wide field view also explores many objects embedded in The Gum Nebula, including the younger Vela supernova remnant.

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[HunterofPhotons]

Exquisite.
Wonderfully planned and executed and the processing is spot on.
Well done, John.

dan kowall

[neufer]

Multiple kinematical populations in Vela OB2 from Gaia DR1 data
F. Damiani1, L. Prisinzano1, R. D. Jeffries2, G. G. Sacco3, S. Randich3 and G. Micela1

<<The Vela OB2 association spans a wide sky region inside the Gum nebula (Pettersson 2008) and has been subject to an increasing number of studies in recent years..., as we describe below, the Gaia proper-motion data show clear evidence of a double population in Vela OB2, with intriguing analogies with those from the Gaia-ESO survey data.

Using their well-defined mean proper motions, we may trace back in time the apparent average positions of populations C and D over a few Myr.The arrows in Fig. 4 show the positions of γ² Vel and NGC 2547 extrapolated back 1.1 Myr, using the(error-weighted) mean proper motions of concentrated populations C and D.This shows that their (sky-projected) distance is now slowly increasing,while it reached a minimum value of 0.65 degrees (4.04 pc) 1.1 Myr ago. This is a small enough value, compared to the apparent sizes of both γ² Vel and NGC 2547 clusters, to expect a significant dynamical interaction between them, provided that also their distances from the Sun are (or were at that time) coincident within a few pc. An intriguing possibility is therefore that population B in the γ² Vel cluster originates from a tidal stripping event during a close encounter with the (denser) cluster NGC 2547. One difficulty with this hypothesis lies in the offset of the RV distribution of population B with respect to that of population A, whereas tidal stripping may be expected to create two symmetric (leading and trailing) tails.

To summarise, the Gaia DR1 data indicate that populations C and D had the highest probability of a mutual interaction in the past 1−1.5 Myr. Determining if this has actually taken place depends on a more accurate determination of the populations’ respective parallaxes, which are expected from future Gaia data releases. Future Gaia data releases will permit a more accurate determination of its properties.>>

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[GoshOGeeOGolly]

https://www.google.ca/search?q=does+you ... e&ie=UTF-8

[De58te]

Only 450 light years away? That's closer than the star Betelgeuse. And farthest away 1,500 light years. The star in Orion's belt, Alnilam is 1,340 ly away. [Wikipedia's Orion Belt article. When clicking on Alnilam's main article, it says Alnilam is 2,000 ly away.] So basically if we change the Gum's 450 light years to 600 ly of Betelgeuse, the Gum Nebula would fit into the space between Betelgeuse and Alnilam in the constellation Orion.