[/caption]
About 13 million light-years away in the constellations Canes Venatici, there’s a cloud. No, it’s not the same clouds that most of us have been experiencing lately – but a cluster of galaxies which appear form a single large cloud-like structure. The one we’re focusing on is Canes Venatici I, just a small section of the Virgo Supercluster and just moving along with the expansion of the Universe. In it we see a galaxy that stands out from the crowd for a very good reason… it has very little or no dark matter. It’s name? Messier 94.
When the very gifted Pierre Mechain discovered this galaxy on March 22, 1781, it took two days before Charles Messier had the chance to confirm his observation and catalog it as object 94. From Messier’s notes: “`Nebula without star, above the Heart of Charles [alpha Canum Venaticorum], on the parallel of the star no. 8, of sixth magnitude of the Hunting Dogs [Canes Venatici], according to Flamsteed: In the center it is brilliant and the nebulosity [is] a bit diffuse. It resembles the nebula which is below Lepus, No. 79; but this one is more beautiful and brighter: M. Mechain has discovered this one on March 22, 1781. (diam. 2.5′)”.
While most observers and some reference guides refer to M94 as a barred spiral galaxy (Sb), the notable feature of all is a dual ring structure – evidence of a low-ionization nuclear emission-line region (LINER) galactic nucleus. The inner core is a starburst ring, where many stars form rapidly and undergo supernovae at an astonishing rate. These starbursts may also be accompanied by the formation of galactic jets as matter falls into the central black hole forming a resonance pattern. Says C. Munoz-Tunon: “The bulge and the inner bar drive disk gas motion, causing inward movements outside the H II ring and outward just inside, thereby accumulating material to trigger star formation on the ring. In the central part the bar drives the gas toward the center, which explains the substantial amount of gas in the nucleus in spite of the presence of a fossil starburst. The peculiar motions reported in the literature in reference to the ionized gas of the H II ring can be understood as infalling gas encountering the shock waves generated by the starburst knots on the H II ring and being raised above the galaxy disk. The scenario of star formation propagating from the nucleus outward used to explain the apparent expanding motion of the HI ring is not fully supported, in light of a comparison of the location of the HI ring with that of the FUV ring. The FUV ring peaks at about 45″-48″, which might point to an inward-propagating star formation scenario.”
But, the point is arguable. According to the work of John Kormendy and Robert Kennicutt, it’s possible that what we’re seeing is simply an illusion of starburst caused by our viewing angle. “The Universe is in transition. At early times, galactic evolution was dominated by hierarchical clustering and merging, processes that are violent and rapid. In the far future, evolution will mostly be secular the slow rearrangement of energy and mass that results from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos. Both processes are important now. This review discusses internal secular evolution, concentrating on one important consequence, the buildup of dense central components in disk galaxies that look like classical, merger-built bulges but that were made slowly out of disk gas. We call these pseudobulges.”
Regardless of what caused the dual ring structure and declining rotation curves – the true answer is still elusive. Oddly enough it was what was proposed in 2008 which made Messier 94 even more mysterious… the lack of dark matter.
So, why should dark matter “matter”? That’s easy. We know its gravitational effects on visible matter and thereby we can explain the flat rotation curves of spiral galaxies, not to mention dark matter has a central role in galaxy structure formation and galaxy evolution. We owe these findings to Fritz Zwicky who told us that a a high mass-to-light ratio indicates the presence of dark matter in galaxies – just as he taught us that dark matter plays a role in galaxy clusters as well. Dr. Zwicky’s line of thinking was radical for the time… But is there still room for radical thinking? Why not?
According to the work of Joanna Jalocha, Lukasz Bratek and Marek Kutschera, ordinary luminous stars and gas account for all the material in M94 – with no room for dark matter. “The comparison of mass functions and rotation laws at the end of the previous section, illustrates the fact that the models with flattened mass distributions are more efficient than the commonly used models assuming spherical halo. The former are better in accounting both for high rotational velocities as well as for low scale structure of rotation curves and with noticeably less amount of matter than the latter (the relation between rotation and mass distribution in the disk model is very sensitive for gradients of a rotation curve). The use of the disk model is justified for galaxies with rotation curves violating the sphericity condition. This is necessary (although not sufficient) condition for a spherical mass distribution. Rotation of the spiral galaxy NGC 4736 can be fully understood in the framework of Newtonian physics. We have found a mass distribution in the galaxy that agrees perfectly with its high-resolution rotation curve, agrees with the I-band luminosity distribution giving low mass-to-light ratio of 1.2 in this band at total mass of 3.43 × 1010M, and is consistent with the amount of HI observed in the remote parts of the galaxy, leaving not much room (if any) for dark matter. Remarkably, we have achieved this consistency without invoking the hypothesis of a massive dark halo nor using modified gravities.
There exist a class of spiral galaxies, similar to NGC 4736, that are not dominated by spherical mass distribution at larger radii. Most importantly, in this region rotation curves should be reconstructed accurately in order not to overestimate the mass distribution. For a given rotation curve it can be easily determined whether or not a spherical halo may be allowed at large radii by examining the Keplerian mass function corresponding to the rotation curve (the so called sphericity test). By using complementary information of mass distribution, independent of rotation curve, we overcame the cutoff problem for the disk model, that for a given rotation curve, a mass distribution could not be found uniquely as it was dependent on the arbitrary extrapolation of the rotation curve.”
More explanation? Then step into MOND – Modified Newtonian dynamics where a modification of Newton’s Second Law of Dynamics (F = ma) is used to explain the galaxy rotation problem. It simply states that acceleration is not linearly proportional to force at low values. But will it work here? Who knows? Says Jacob Bekenstein: “The modified newtonian dynamics (MOND) paradigm of Milgrom can boast of a number of successful predictions regarding galactic dynamics; these are made without the assumption that dark matter plays a significant role. MOND requires gravitation to depart from Newtonian theory in the extragalactic regime where dynamical accelerations are small. So far relativistic gravitation theories proposed to underpin MOND have either clashed with the post-Newtonian tests of general relativity, or failed to provide significant gravitational lensing, or violated hallowed principles by exhibiting superluminal scalar waves or an {a priori} vector field.”
So next time you’re out observing galaxies, have a look at the “Cat’s Eye” Galaxy. Even a small telescope will reveal its bright, controversial nucleus and wispy shape. And thanks to outstanding astrophotographers like Roth Ritter we’re allowed to see a whole lot more…
Our thanks go to Roth Ritter of Northern Galactic for sharing his incredible work!
Have you noticed the paired pattern of stars to the lower left of the galaxy? The image needs to be rotated, but viewed as a stereo pair (though it would need to be verified with matching spectra) they are duplicated. Gravitational lens anyone?
Bink: Im having trouble seeing this stereo pair at the bottom left of the image…there is a similarity in the pattern, but there is no true symmetry here that I can see?
The theory of Dark Matter was rejected by a hostile scientific community that suppressed publication of Fritz Zwicky’s work during his lifetime. Fritz Zwicky correctly identified the existence of Dunkle Materie, coining the term itself. He pointed out that the universe as they understood it was only a fraction of the whole, and that his colleagues were only looking at the dust bunnies in front of the door. Bitter resentment remains even today, as the scientific community has continued to fail in explaining Dark Matter, even with the aid of supercomputers and millions of dollars that my father could not avail himself. It is unfortunate, that the unacceptable literary assaults continue by many following such egregious, errant compass, while seeking credit for his work.
Barbarina Zwicky
Rotate your screen left 30 to 45 degrees so that the two groups of three stars that are vertical in the original are side by side. Those three bright ones, plus the one bright one directly left of the bottom one of the three plus four dim ones, overlay.
Two groups that look like this.
(there is no preview or re-edit, so I hope they render)
*
*
* *
They did not. The white space compressed.
Let’s see if this works.
……………………*
……………………*
*………………..*
Hey Barbarina.
http://en.wikipedia.org/wiki/Fritz_Zwicky
Also read the article in Discovermagazine.
The thing is, if you read the tenure of the comments here, im sure you will discover on-going skepticism about Dark Matter. (for obvious as yet un-testable reasons). However I was unaware that your father was the first to propose the theory and that he suffered ridicule for doing so.
Now I am, so thanks for your comment.
However, our unseen matter will continue to attract detractors until it can be accounted for by observation. I fear you still have some time to kill until that happens.
Regards
Damian K
That was interesting. I’ve heard of Zwicky but I didn’t realize he was such a controversial figure before pouring over some of the web material. Not to poison the well but illustrating the difficulties with theory, he also proposed the failed “tired light” hypothesis I see.
I don’t know if he was suppressed, there are no references indicating it but that he “was not taken very seriously at first, until some forty years later [Wikipedia]”, and at least the obituaries I see acknowledges his efforts. Seems galaxy cluster data was the first observation, but the field waited for the problems to reconcile star motion within individual galaxies before accepting that dark matter predicts them both. Perhaps it was a matter of observation, it must be much more difficult to miss standard matter in the later case when the luminosity of the galaxies themselves isn’t a problem?
I don’t know about that. Several realistic candidates have been proposed and some rejected (say, ordinary matter as in brown dwarfs), so it is a live field AFAIU. That isn’t “fail” by any realistic measure of science. (One must never forget that there is “search” in research. :-))
Blink:
I don’t think this is gravitational lensing, as the lensing object, such as a galaxy should in front of the lensed object, such as a background galaxy or a quasar.
The stars are probably in our own galaxy. I suppose a lone black hole could be acting as the lense, but I would expect some distortion in the galaxy image as well.
Why are observations of the cosmos so often mysterious?
Does this indicate basic flaws in the assumptions of astronomy, cosmology, and astrophysics?
With kind regards,
Oliver K. Manuel
http://www.omatumr.com
Dark Gnat:
I agree with the theory of where the gravitational object would have to be, thus the reason why I put it in the form of a question.
On the other hand, 8 objects in a pattern that seems duplicated is quite the coincidence.
Without the spectra, though, to determine if they are the same objects seen twice, it could well be the bunny in the clouds effect.
Continued . . .
But what if this is an example of a real lensing effect, and what if we do indeed have an invisible close gravitational object to explain it, and what if it happens more than we have been noticing?
Would that perhaps account for our missing matter?
@Bink
I’m sorry, but since these are foreground stars a “dark object” that distorts them should also distorts some other parts of the picture (like the background galaxy). I think this is just coincidence.
If you mean black holes with “invisible close gravitational objects”, there have been some studies concerning the possibility of black holes being responsible for dark matter. And AFAIK the possibilities are very low.
About Fritz Zwicky
There are some funny stories about him. For example he “invented” a way to correct for the atmospheric disturbances during observeations (today we use “adaptive optics”). But he never was able to test his invention. For good reasons as I must say. He wanted to blow up some explosives outside the telescope dome 😀
barbarina,
i appreciate your taking the time to comment and to read. while i don’t even come close to belonging in the league of understanding all the implications of his work, i felt his ideas were absolutely brilliant.
when researching articles to accompany good astrophotography, i perhaps take more care and time than most would. for a three minute read, there are times when 5 or 6 hours of research goes into what the reader sees. why? because there is more of a story behind it than what simply meets the eye.
or what you can quickly find on google, eh?
once again, your father’s work played a major role in how we understand these things today. perhaps if we continue to stress his contributions and say it loud enough and long enough that finally it will be recognized!
I would add that Dr. Zwicky, while obtaining data that would later prove to validate his hypothesis, did hold some beliefs that did not on later analysis hold up. But, hey, scientists are humans after all, and are usually never correct 100% of the time. Dr Zwicky was certainly ahead of his time in suggesting the existence of “Dunkle Materie”. I think that this is a good example of a well known astronomer challenging the ‘status quo’, and eventually being vindicated by many other researchers . Brings to mind other ‘ignored’ scientists being vindicated (i.e. Birkeland and Alfven) in regards to their SPECIFIC assertions. Other controversial opinions held by Arp, Burbidge, Hoyle, Narlikar, Gibson, Schild & Milgrom, etc. have yet to put forth indisputable evidence of the validity of their models.
@barbarina: have you read Freeman and McNamara’s book, In Search of Dark Matter?
It’s aimed at a general readership, rather than professional astronomers or physicists, and given its subject, Fritz Zwicky and his work is mentioned frequently.
If you have read it, I’d be interested to know what you think of the way it depicts Zwicky’s astronomical research and his published work.
Just a shout out to Tammy for the time she does take to research an object being featured. Your diligence does not go unnoted. I greatly appreciate the time taken to research a featured object, and, depending on the object, I like to download and read the papers you refer to. Often you will comment on less well-known papers on an object that may cast the object in a new light for me (such as the MOND reference in this article). Keep up the good work! 🙂
Reader’s of this story may be interested in two preprints: [http://arxiv.org/abs/0805.4163] and [http://arxiv.org/abs/0806.1131].
I have read Fritz Zwicky’s “Morphological Astronomy” some years ago, and was fascinated by the book. I remember also that he was one of the few astronomers to take gravitational lensing seriously very much ahead of its time. His term “Dunkle Materie” is now standard (viz., “dark matter”), but became so only after the somewhat misleading one “missing mass” for many years, and then the somewhat better (but still not quite hitting the nail on its head) “missing light” for a few more years. Please see the beginning of [http://arxiv.org/abs/astro-ph/0703430].
Also related is [http://arxiv.org/abs/0809.1972].
Briefly, the last word on whether dark matter is necessary on single galaxy scale and smaller is yet to be said. On larger scale, binary galaxies and groups, and still larger ones, clusters, it does seem necessary, as Zwicky was the first to discover. Please see [http://arxiv.org/abs/0901.3892] for something on this.
I am quite prepared to write a short article on this topic, or answer any specific questions any reader may have.
Thank you, Tammy, Damian, Torbjorn and Nereid for your insightful comments. As of yet, I have not been able to review the suggested materials, but I will do so.
Fritz Zwicky was the Father of Gravitational Lensing as well.
There are many embellished, partial truths and direct falsehoods in the oral histories. My father’s memory and the sciences would be better served if those were confirmed before being repeated. My father never used explosives, ever, and in fact disliked Jack Parsons tremendously because he brought explosives to Aerojet and endangered the entire facility. He called Jack Parsons “a dangerous man,” and in the end this proved tragically true, when Parson’s blew himself up in his own home.
Ben Traxler was my father’s night assistant on Mt. Palomar, and they conducted a valid experiment comparing the speed of a bullet in measuring the speed in which one could capture an image on the photographic plate. Ben Traxler was furious that this particular experiment had been falsely distorted by many and has now taken on a life of its own. The anecdote is now so twisted, that it no longer reflects any semblance of the truth, but has become a complete falsehood. I have a letter in my possession from Mr. Traxler to one such sensationalist author, written shortly before his passing. The author joked that he was not sure if the story were legend, but printed it anyway because it made good copy.
It is unfortunate, that such anecdotes continue.
Clear skies!
Barbarina
In this case, I’m sorry!
Rumors are spread easily – one can see that all the time!
However your father has been an extrodinary man (no doubt) and definitly had his “follies”. This is meant positively, because a physicist without being a little crazy wouldn’t be a real physicist in my opinion. And the experiance at my university teaches me this fact all the time – and many colleagues confirm that they are “proud” of it; so am I.
A trailblazer leads the way in unchartered territory, where others fear to go. It takes great courage and a bold spirit to research the unknown, and to present amazing theories such as Dark Matter, to members of a hostile scientific community, who still remain in the dark regarding his work.
I always respect and accept a sincere apology, although none was needed in this case. I am more than happy to clear up any confusion regarding my father in the future.
Clear skies,
Barbarina