I happened to visit this blog as a visitor from a computer not mine. Seeing it that way made me realize how obnoxious the ads had become. So WordPress’s extortion worked; I’ve agreed to send them a few $ every month to get rid of the ads. With it comes a new domain name: tritonstation.com. Bookmarks to the previous website (tritonstation.wordpress.com) should redirect here. Let me know if a problem arises, or the barrage of ads fails to let up.

Britain and America are two nations divided by a common language. attributed to George Bernard Shaw Physics and Astronomy are two fields divided by a common interest in how the universe works. There is a considerable amount of overlap between some sub-fields of these subjects, and practically none at all in others.

I haven’t written here since late January, which not coincidentally was early in the Spring semester. Let’s just say it was… eventful. Mostly in an administrative way, which is neither a good way, nor an interesting way. Not that plenty interesting hasn’t happened. I had a great visit to Aachen for the conference Dark Matter & Modified Gravity. Lots of emphasis on the philosophy of science, as well as history and sociology.

There is a tendency when teaching science to oversimplify its history for the sake of getting on with the science.

This Thanksgiving, I’d highlight something positive. Recently, Bob Sanders wrote a paper pointing out that gas rich galaxies are strong tests of MOND. The usual fit parameter, the stellar mass-to-light ratio, is effectively negligible when gas dominates. The MOND prediction follows straight from the gas distribution, for which there is no equivalent freedom.

In the last post, I noted some of the sociological overtones underpinning attitudes about dark matter and modified gravity theories. I didn’t get as far as the more scientifically  interesting part, which  illustrates a common form of reasoning in physics. About modified gravity theories, Bertone & Tait state Leaving aside just which observations need to be mimicked so precisely (I expect they mean power spectrum;

A colleague points out to me a recent preprint by Bertone & Tait titled A New Era in the Quest for Dark Matter . Most of the narrative is a conventionalist response to the failure of experimental dark matter searches, posing a legitimate question in this context. Where do we take it from here?

Like the Milky Way, our nearest giant neighbor, Andromeda (aka M31), has several dozen dwarf satellite galaxies. A few of these were known and had measured velocity dispersions at the time of my work with Joe Wolf, as discussed previously. Also like the Milky Way, the number of known objects has grown rapidly in recent years – thanks in this case largely to the PAndAS survey.

I have been wanting to write about dwarf satellites for a while, but there is so much to tell that I didn’t think it would fit in one post. I was correct. Indeed, it was worse than I thought, because my own experience with low surface brightness (LSB) galaxies in the field is a necessary part of the context for my perspective on the dwarf satellites of the Local Group.

A quick note to put the acceleration discrepancy in perspective. The acceleration discrepancy, as Bekenstein called it, more commonly called the missing mass or dark matter problem, is the deviation of dynamics from those of Newton and Einstein. The quantity D is the amplitude of the discrepancy, basically the ratio of total mass to that which is visible.

The Milky Way and its nearest giant neighbor Andromeda (M31) are surrounded by a swarm of dwarf satellite galaxies. Aside from relatively large beasties like the Large Magellanic Cloud or M32, the majority of these are the so-called dwarf spheroidals. There are several dozen examples known around each giant host, like the Fornax dwarf pictured above.