Mass is a basic quantity. How much stuff does an astronomical object contain?

A common objection to MOND is that it does not entirely reconcile the mass discrepancy in clusters of galaxies. This can be seen as an offset in the acceleration scale between individual galaxies and clusters.

This title is an example of what has come to be called Betteridge’s law. This is a relatively recent name for an old phenomenon: if a title is posed as a question, the answer is no . This is especially true in science, whether the authors are conscious of it or not.

This post simply announces that I will be giving a Golden Webinar at 3pm EST Friday 15 January 2021 courtesy of the Instituto de Astrofisica of the Pontifica Universidad Catolica de Chile. The seminar is free and open to all but you need to register in advance if you want to hear it. There are many excellent speakers in previous episodes of this series that you can hear on Youtube.

“Galaxies are made of stars.” Bob Schommer, quoted by Dave Silva in his dissertation on stellar populations This tongue-in-cheek quote is a statement of the obvious, at least for the 90+ years since Hubble established that galaxies are stellar systems comparable to and distinct from the Milky Way.

People seem to like to do retrospectives at year’s end. I take a longer view, but the end of 2020 seems like a fitting time to do that. Below is the text of a paper I wrote in 1995 with collaborators at the Kapteyn Institute of the University of Groningen. The last edit date is from December of that year, so this text (in plain TeX, not LaTeX!) is now a quarter century old. I am just going to cut & paste it as-was;

A unique prediction of MOND One curious aspect of MOND as a theory is the External Field Effect (EFE). The modified force law depends on an absolute acceleration scale, with motion being amplified over the Newtonian expectation when the force per unit mass falls below the critical acceleration scale a ₀ = 1.2 x 10 ^-10 m/s/s. Usually we consider a galaxy to be an island universe: it is a system so isolated that we need

This post is a recent conversation with David Garofalo for his blog. Today we talk to Dr. Stacy McGaugh, Chair of the Astronomy Department at Case Western Reserve University. David : Hi Stacy. You had set out to disprove MOND and instead found evidence to support it. That sounds like the poster child for how science works. Was praise forthcoming?

The following is a guest post by Indranil Banik, Moritz Haslbauer, and Pavel Kroupa (bios at end) based on their new paper Modifying gravity to save cosmology Cosmology is currently in a major crisis because of many severe tensions, the most serious and well-known being that local observations of how quickly the Universe is expanding (the so-called ‘Hubble constant’) exceed the prediction of the standard cosmological

This post is adopted from a web page I wrote in 2008, before starting this blog. It covers some ground that I guess is now historic about things that were known about WIMPs from their beginnings in the 1980s, and experimental searches therefore. In part, I was just trying to keep track of experimental limits, with updates added as noted since the first writing.

I have been busy teaching cosmology this semester. When I started on the faculty of the University of Maryland in 1998, there was no advanced course on the subject. This seemed like an obvious hole to fill, so I developed one.