Hubble photos of "Tadpole galaxy"
Category: Science > Astronomy
Asked by: steveg-ga
List Price: $4.00
30 Apr 2002 11:42 PDT
Expires: 07 May 2002 11:42 PDT
Question ID: 8003
Nasa just released some new Hubble photos. One of them (http://oposite.stsci.edu/pubinfo/pr/2002/11/pr-photos.html) shows a long stream of stars strectching out from a large galaxy toward the lower right. The claim is that a small galaxy colliding with the large galaxy created the stream of stars. Further, it claims that the small galaxy is now in the upper left of the large galaxy which means that it entered from the lower right. My question is: How does a galaxy entering from the lower right create a stream of stars extending to the lower right?
Re: Hubble photos of "Tadpole galaxy"
Answered By: alexander-ga on 30 Apr 2002 15:01 PDT
Interesting question. :) First off, the "Tadpole" galaxy is properly named UGC 10214. I think the "Tadpole" moniker came up recently in relation to these Hubble photos. Knowing that, we can pull up a couple of references: "They noticed that a galaxy called UGC 10214 has a stream of material flowing out of it, as if it is interacting with another galaxy. But in this case, the stream of material is apparently flowing towards nothing." [ http://groups.google.com/groups?q=UGC10214&hl=en&safe=off&selm=3A54AB70.7867CAF1%40nova.astro.utoronto.ca&rnum=1 ] It's interesting to hear that this article discusses the possible presence of an invisible "dark galaxy" that is causing an interaction, but I don't believe this to be the case. I was also able to pull up another, far less detailed image: http://www.ast.cam.ac.uk/~trentham/ugc10214.html Keeping this and the new Hubble image visible, you should be able to see that there is a slight, but definite, "arc" to the stream of stars. How is this relevant, you ask? First, the official report reads "Its distorted shape was caused by a small interloper, a very blue, compact galaxy visible in the upper left corner of the more massive Tadpole." and "Strong gravitational forces from the interaction created the long tail of debris, consisting of stars and gas that stretch out more than 280,000 light-years." There is no evidence, in other words, of which direction the colliding galaxy originated from, nor is this particularly relevant. Here's my hypothesis: Each galaxy is getting pulled into the other's gravitational force, and matter is being "whipped" around the other galaxy's center. Much like the way space probes are "slingshot" around planets, this causes a substantial increase in velocity, and would cause the matter in question to be rapidly ejected out of the vicinity. The trail is still within the gravitational field of the two galaxies, however, and so is gradually pulled back in. Hence the arc -- the trail is question in actually in a very eccentric elliptical orbit. In fact, you can see that matter from the larger galaxy is also being influenced by the smaller galaxy's gravitational field -- on the left-hand side, an arm is being "pulled up" and spun around the smaller galaxy. Search terms used: "UGC 10214", others difficult due to timeliness of the subject.
rated this answer:
The answer was a hypothesis based on the available information on the web. However, I was hoping for an informed answer based on more innate knowledge.
Re: Hubble photos of "Tadpole galaxy"
From: dronak-ga on 13 Jun 2002 13:28 PDT
These references might be more technical than you want, but I'll provide them anyway. I did a quick look for some journal articles on this object, UCG 10214, and only found one recent one. A copy can be found online at http://arXiv.org/abs/astro-ph/?0110115 . The print version reference is Briggs, F.H., Moller, O., Higdon, J.L., Trentham, N., Ramirez-Ruiz, E. 2001, Astronomy and Astrophysics, 380, 418. It's titled "Did VV 29 collide with a dark Dark-Matter halo?". I'm not sure it has quite what you're looking for, but it contains a good reference in there to a long paper (44 pages) titled "Galactic Bridges and Tails" -- Toomre, A. and Toomre, J. 1972, Astrophysical Journal, 178, 623. An online version should be availble at http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1972ApJ...178..623T&db_key=AST&high=3d08f73d8625917 . I'm not sure if this web site requires your school/workplace to have electronic access to the journal normally. If you can't get it online and are interested, hopefully a local university/college library will carry it. The Astrophysical Journal is one of the major journals in astronomy research. It may be more technical than you want though, I'm not sure. I'm just skimming it, but it looks like it will explain a lot of the galactic dynamics involved in creating things like tidal tails for you if you don't mind reading a professional level journal article. There's quite a lot of physics involved in modelling things like UGC 10214 and unless we have some of the input parameters, we're going to have a difficult time making the models match reality with any level of confidence. As alexander-ga notes, there's really nothing in that Hubble press release that says the small galaxy had to come from the lower right. It might have, but it could have started in the upper left area and completed an orbit around the major galaxy already, too. It can be very difficult to determine these sorts of details and without them, it can be hard to know exactly what's going on. After all, we basically get a snapshot photo of a work in progress and are trying to determine the history and future of it from that one photo. Not an easy task I can assure you. I can give you a basic idea of how you can get a tidal tail on the side away from the object though. Tidal effects like this and ocean tides on the Earth are caused by the difference in the gravitational pull on the object. The small galaxy in the upper left exerts a gravitational pull on the larger galaxy that goes as 1/(distance^2). So it pulls harder on the side of the big galaxy near it than the center. That pulls the near side away from the center. However, in similar fashion it pulls on the center of the big galaxy harder than it does the far side of it. This pulls the center away from the far side. This is why we have tides on opposite sides of the Earth at once -- the Moon pulls on the near side harder than the center pulling the water up there, but also pulls harder on the center than the far side making the center pull away from the water which lags behind to form the other tide. Depending on the orbital parameters of the galaxies involved in the merger, this same general effect can create tidal tails on both sides of the larger galaxy. Different orbital parameters have different effects on the merger remnants and getting those parameters from a single snapshot isn't easy. That's why we don't always know exactly what's going on in situations like this. Does that help answer your original question? The galaxies are obviously going to evolve as the merger progresses, but that's the basic idea on how you can get a tail on the side the smaller object entered from. That Toomre and Toomre paper has many figures showing galaxies in different orbits and how that effects the way the merger evolves. Something like their Figure 4 shows an example of a tidal tail forming on the side of the large galaxy that the smaller one entered from. I hope this helps and the journal articles aren't too technical for you.
Re: Hubble photos of "Tadpole galaxy"
From: neiltren-ga on 08 Jul 2002 20:23 PDT
Hello, I appreciate this is all a bit late for this discussion but I think you might find some of our current thoughts in Cambridge interesting. What happened is that my colleagues and I were working on ways to find galaxies made only of dark matter -- something for which I believe is strongly motivated by theoretical astrophysics -- and simultaneously I came upon whis galaxy in an image for a project where I was studying the little background galaxies. So we wondered if a dark galaxy could be pulling the plume (we call this VV29b) out of the main galaxy (called VV29a). We though this was possible since we didn't see evidence for a second galaxy (the little blue galaxy -- VV29c, that is probably taking part in the interaction wasn't very clear in the images we had at the time). The idea was plausible but I didn't like it too much since the hypothesized dark galaxies are small and you need quite a big thing too pull this much material out of a regular galaxy like VV29a. Now I don't really believe this idea, due to more recent data. Following this, radio imaging of this galaxy was done at the Westerbork Telescope in the Netherlands. This is what is described in the article by Frank Briggs. This data told us two main things -- [what the radio HI data measures is the gas -- loose atoms -- not stars in the galaxies so we one other main component of the galaxies] 1) There is very little velocity gradient *along* the plume VV29b. This doesn't look to me to be material being pulled out of VV29a at speed or anything else. 2) In the HI gas image, VV29c is a big galaxy and has the potential to do quite a bit of damage to VV29a. You couldn't tell that if you just looked at the stars and not the gas We hardly noticed VV29c at all in the original optical data, and even in the new Hubble Space Telescope data -- one of the deepest and most impressive images ever taken -- you have to look pretty hard to see it. But in the radio image it's obviously a major galaxy. Armed with this information, and some velocity information from the radio data, we're now trying to piece together a description of what actually happened to produce this odd system. The problem to me seems one of uniqueness -- we know from Toomre & Toomre's 1972 article -- a result confirmed by big computer simulations -- that interactions between two galaxies can produce shapes a bit like this. A couple scenarios are described in this forum and by Briggs, based on the plume VV29b resulting from an interaction between the galaxies VV29a and VV29c. Another idea I like is that we are looking at an interaction between what was originally *three* galaxies, and VV29b started out as a regular galaxy, just like VV29a and VV29c that somehow got flattened by gravitational forces during the interaction. I have no idea as to details -- this is something we need to simulate with computers. So in my opinion the bottom line is that at present the data are not really good enough to tell us exactly what is going on. Lots of models might work -- based on 2 or 3 interacting galaxies -- but we can't really say which is the right one. Mostly what seems to be needed is very-high resolution spectroscopy so we know exactly what each bit of each of the 3 components is doing. We can then use a computer simulation to go back in time and figure out all this. Hope this of interest, Neil Trentham, firstname.lastname@example.org
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