Is Hoag’s Object a Dense Plasma Focus?

[StefanR]

What force swept away the stars and formed this 120,000 light-year-wide ring in space? This could be one of electrical energy’s protean forms.

There are places in the cosmos where stars form up into ranks that stretch in lines for thousands of light-years. Elsewhere, rings of stars can be found encircling compact structures that have been measured at over 10,000 light-years in diameter.

Art Hoag discovered the galaxy that bears his name in 1950 and by conventional redshift-equals-distance calculations, it is approximately 183 megaparsecs away in the constellation Serpens. The ring of “young” blue stars is notable, as is the dense core and the hovering swarm of globular clusters that lie in the center of the formation. There is an obvious swirling shape that radiates outward in the same way as that from the Cartwheel Galaxy in the constellation Sculptor. The filaments that connect the core with the ring in the Cartwheel Galaxy are missing in Hoag’s Object, although they could be radiating in dark current mode.

http://www.thunderbolts.info/tpod/2008/ ... object.htm

[StefanR]

What I also liked was the view of the Cartweel a little further of:

. Presented for your consideration: a composite showing a visual image of the Cartwheel galaxy (at left) and smaller galaxies of the Cartwheel group, superposed with high resolution radio observations of neutral hydrogen (traced by the green contours). The neutral hydrogen trail suggestively leads to the culprit galaxy at the far right, presently about 250,000 light years distant from the Cartwheel!
http://antwrp.gsfc.nasa.gov/apod/ap970224.html

3.1. Ring Galaxies (YDe0)

P. N. Appleton and the author have recently completed an extensive review of this subject (1996, henceforth AS96), so I will limit this to a brief summary. (References are minimal in this section, but the reader can find many sources of more detailed information in that review.) Collisional ring galaxies are rare. They are the product of a nearly head-on collision between a D-type primary and a substantial companion, i.e. one with mass in the range 10-100% of the primary. A companion with much less mass would not have much of an effect on the primary, while one more massive than the "primary" is possible, but evidently unusual. The basic theory was worked out by Lynds and Toomre (1976, also see Theys and Spiegel 1976, 1977, and Toomre 1978). As the companion approaches and passes through the primary disk, stars and gas clouds assumed to be in circular orbits before the collision, are drawn inward by the extra gravity. As the companion moves away, the unbalanced centripetal force drives an outward rebound. The response is faster in the inner disk and slower in the outer disk, so stars still moving inward meet rebounders moving out, producing a compression wave which propagates outward. If the impact parameter is small this wave is a circular ring.

The Cartwheel galaxy, mentioned above, was probably the first ring galaxy discovered, and still is regarded as a prototype. This despite the fact that its progenitor was an usually late-type galaxy. The outer disk shows no evidence of old stars, though there is plenty of gas. It is also unusual in having two prominent rings, and the so-called spokes - spiral segments between the two rings (see Figure 4). However, there are a couple dozen collisional ring galaxies that have been studied in some detail, with many more candidates awaiting further study. Their progenitors span the whole range of Hubble disk types, e.g., from the "Sacred Mushroom" system, AM 1724-622, studied by Wallin and Struck-Marcell (1994, see Fig. 1) with a very early-type progenitor (e.g. an S0 galaxy) to the Cartwheel.

http://nedwww.ipac.caltech.edu/cgi-bin/ ... _stamp=YES

http://nedwww.ipac.caltech.edu/level5/S ... 3.html#3.1

Some more at solstation about the Milky Ring and other ring galaxies:

Possibly 10 times thicker than the spiral disk of the Milky Way, the ring encircles the disk -- which has a diameter up to around 100,000 ly -- like a giant torus (or "doughnut"). In the Monoceros patch observed by the SDSS team, the ring appears to extend over 16,000 ly (5,000 parsecs or pc) above and below the galactic plane, with stars below the plane extending about 2,000 pc further from galactic center than those located above the plane; it also appear to be somewhat less than 13,000 ly (4,000 pc) wide. In the patch observed by the ING team, however, the ring appears to have a lower scale height of around 2,400 ly (750 pc) with a width around 6,500 ly (2,000 pc). Looking at the Milky Way from above, the ring is turning clockwise (prograde rotation) at about 68 +/- 16 miles (or 110 +/- 25 km) per second, assuming that its stars move on average in a circular orbit (Yanny et al, 2003). Our Sun, Sol, moves in the same direction at twice this speed but lies only about 26,000 ly from galactic center

According to McClure-Griffiths, the arc or arm could be a tendril that was once part of another spiral arm. Indeed, it is not be unusual for a medium-sized galaxy like the Milky Way to have arms that extend so far, as nearby Andromeda, a similar spiral, has long gaseous arms. On the other hand, another possibility is that the gas was drawn out of the Milky Way in a collision with a dwarf galaxy early in its evolution. In the near future, astronomers hope to characterise the make-up of the new arm in more detail, and to run computer simulations to determine whether it could have been created by the near collision of a small galaxy with the Milky Way.

As summarized by astronomers Ronald J. Buta and Françoise Combes in their paper on "Galactic Rings," about one-fifth of all spiral disk galaxies display a ring-shaped pattern, and an additional third appear to have broken or partial rings made up of spiral arms ("pseudo-rings"). In general, galactic rings are most often associated with galaxies that have central "bars" of stars (such as the one found in the Milky Way (now classified as a barred spiral galaxy) or other common non-axisymmetric perturbations such as ovals. In addition, most galactic rings are the sites of active star formation, and in some apparently old galaxies their rings are the only places where recent star formation can be found. A few rings are sites of the most spectacular "starbursts" of stellar formation known in "non-violently" interacting galaxies.

Although a small fraction of galactic rings observed do appear to be the result of collisions or mergers of galaxies, or of accretion of intergalactic gas, the vast majority of rings are probably created by simple resonance phenomena that are caused by the actions of a rotating bar or some other non-axisymmetric disturbance on the motions of gas clouds within a galactic disk. Evidence for the resonance hypothesis has been accumulating for two decades, so that many astronomers now believe that rings are a natural consequence of barred galaxy dynamics, perhaps more easily understood than the bars and ovals that created them. However, some barred galaxies lack rings, while others (such as Hoag's Object) display rings despite the apparent lack of a bar. Questions remain regarding the role of mild tidal interactions, the origin of the gas that fuels star formation in rings, the existence of intrinsic bar/ring misalignment, and the simultaneous existence of different ring types that may have been created during very different eras in the life of the host galaxy.

http://www.solstation.com/x-objects/gal-ring.htm