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A Snag-Bridge in Arp 102 A Snag-Bridge in Arp 286 A Snag Red Shift in NGC 4319 Cocorico !
It's forbidden to see this bridge of matter
With the WIYN telescope
Arp 102 - Source NOAO

ARP 102 or the Dynamics of Galaxies Clusters

In the night of the 23/06/95, the NOAO (WIYN Telescope) takes the photograph of the galaxy pair Arp 102. This exceptional quality photograph would not probably never have attracted our attention if we had not had in memory a previous picture appearing in "Atlas of Peculiar galaxies" of Halton Arp. We remembered a detail, that there is in the picture of the catalog two bridges of matter, whereas the picture of the NOAO shows only one (the one that we distinguishe on the right), but not the one of the left, that is yet visible in the picture of Arp.
We have first processed the picture of Arp to see if in this picture, the bridge of matter on the left could be an artifact. We didn't find anything abnormal. This failure is due, on the one hand, because it is a monochromatic picture and on the other hand because the resolution is certainly insufficient, whereas the picture of the NOAO is a trichromatic high resolution. picture.

California Institute of Technology.
Atlas of Peculiar Galaxies.
By Halton Arp
Arp 102 - Source: Atlas of Peculiar galaxies - Halton Arp
We processed then the picture of the NOAO. Below is the result:
Image of Arp 102 (NOAO) DP by B. Lempel

The two "bridges of matter" are perfectly visible. There is not any ambiguousness. And it confirms that which one hardly distinguishes in the picture of Halton Arp.


  1. Why the picture published by the NOAO doesn't show the left bridge of matter ?
  2. For what technical reason, with means that Arp didn't certainly have, doesn't this bridge appear here ? We cannot imagine that one made some Digital Processing to make it disappear. And we have difficulty again imagining that astronomers didn't "see" this bridge of matter.
Hypothese: We are in the presence of interacting galaxies. Bridges of matter are the result of mutual gravitational influences of galaxies upon each other. This hypothesis seems very probable.

 We have in this picture:

  1. Near the center of the photograph, a spiral galaxy whose right arm is strongly stretched and extended outwards, with the shape of a circular shape. One notices, at its extremity a frontal shock zone that seems to be the source of young stars.

  2. On the left, an elliptic galaxy, linked to the spiral galaxy by a straight matter bridge.It is impossible, with this one picture, to say from where is came this matter, nor to say of what it is made. Its direction movement is not obvious.

  3. We can already deduct that these two bridges of matter are not of the same kind. The fact that the left bridge is straight imposes, considering the distance separating the two galaxies, of the order of 500.000 ly, that these two galaxies didn't have, one in relation to the other, of perceptiblel angular motion during at least this time.

  4. The redshift of the spiral galaxy is 7182 km/s, The one of the elliptic galaxy is 7250 km/s (Source: Nigel Sharp - NOAO). These very similar redshiftses don't pose a particular problem. They demonstrate that these two galaxies are near close.

  5. The number of distant galaxies was considerably multiplied by the Digital processing. It is not trivial.

 Here is what the NOAO says about Arp 102

This interesting interacting spiral/elliptical pair of galaxies was first described in the Catalogue of Peculiar Galaxies, compiled by Halton Arp in 1966. It is also pair number 508 in Igor Karachentsev's catalog of binary galaxies. The large spiral galaxy (type SABb pec) shows long blue tidal tails caused by its interaction with the southerly elliptical. In fact, this "elliptical" is much the more interesting galaxy, despite its more nondescript appearance. It is a broad line radio galaxy with an unresolved core and a sub-parsec VLBI component at 6cm. It is also an intermediate type Seyfert, meaning it has an active nucleus, and it shows a double-peaked emission line profile (separation about 5000 km/s), which is considered to be strong evidence for the presence of an accretion disk, probably around a central supermassive black hole.
In this picture we also see the presence of numerous more distant background galaxies, showing as clusters of small, diffuse red objects and scattered diffuse blue objects. These objects are very difficult to detect and require excellent conditions and superb optics.

Location: 17 18 00 +49 04 (1950.0), constellation of Hercules (just!).
Distance: approximately 320 million light years


 The NOAO hardly extends to the spiral galaxy. It barely makes allusion to the gravitational interactions between the two galaxies. It stresses on the elliptic galaxy. That in itself is pretty strange. Is an elliptic galaxy, even a Seyfert, even with an active core, as exceptional that that? Why don't they ponder about the system in its whole, on the pair of galaxies with their filaments of matter, on "bridges of matter " as says Halton Arp ?
Would not the elliptic galaxy be "active" and "a Seyfert" because it is in an interactive system, in terms of gravitation and also in terms of matter exchanges ?
All the same we cannot limit Arp 102 to only one galaxy, and thus artificially isolate the elliptic galaxy from its global environment.
Let us also note the excessive rotational speed of the "accretion disk" in the elliptic galaxy (gap of 5000 km/s, i.e. 2500 km/s about). Would there not be in the core of this galaxy a lens effect, which would be due to the gradient of matter density, as we already met otherwise some in certain cores of galaxies (M 87, Einstein Cross) ?


For an unknown reason the two galaxies are, or were, immobilized in space since, or during, more than 500.000 years. The straight matter bridge, that links them, shows that. Let's note however that the axis of the jet is not oriented toward the center of the elliptic galaxy. It could mean that there exists nevertheless a very slow movement, or that the elliptic galaxy took regained mobility a while ago. 

  1. The Merger of the Milky Way and Andromeda Galaxies - One finds superb simulations of galaxy interactions there.

  2. Galaxies: Interactions and Induced Star Formation - R.C. Kennicutt,Jr. F. Schweizer & J.E. Barnes. - Springer (available also at amazon.com)

    Galaxies et cosmologie - Françoise Combes, Patrick Boissé, Alain Mazure & Alain Blanchard - Available in all the good bookshops (French)

  3. Dynamique des Galaxies - (Françoise Combes - Observatoire de Paris).

  4. Dynamics of Galaxy Interactions by Joshua E. Barnes. Very complete. High quality simulations.

  5. Introducing BAX: a database for X-ray clusters and groups of galaxies.

"When looking at this picture no amount of advanced academic education can substitute for good judgment; in fact it would undoubtedly be an impediment"  (Halton Arp - Seeing Red)
Created: 08/26/2010
Last release: 03/04/16
The Brigge of matter of Arp 286: Next