* To be precise, black holes have been proposed as a possible dark matter candidate—a topic we will get to later. Observational constraints and theoretical issues now make this scenario very unlikely.

* Admittedly, this analogy goes only so far. Unlike disgruntled exiles, heavy elements—once distributed around the Universe—won’t spur further instabilities. Better still, they contribute to the formation of stellar systems and even to life.

† In fact, this picture—though widely accepted—is currently disputed by experts. On the one hand, predictions for the spectra and light curves of exploding white dwarfs match the observations very well. On the other hand, no one has seen the expected companion binary star to the white dwarfs. Astronomers therefore suggest that it might instead be the merging of two white dwarfs that gives rise to the explosion. Some data support this conclusion—mostly having to do with measuring the difference in time between the binary’s formation and its explosion—but the detailed predictions for the single white dwarf explosion scenario are yet to be confirmed, so the matter remains unresolved.

* Temperature differences in kelvin are identical to differences measured in degrees Celsius, but the minimum possible temperature is 0, rather than −273.15, as it is in Celsius units, or −459.67, as it is in Fahrenheit ones.

* Note that dark here has the usual meaning of absorbing light. This is not “dark matter”

* The George E. Brown, Jr. Near-Earth Object Survey section of the NASA Authorization Act of 2005 (Public Law 109-155)

* The International Commission on Stratigraphy (ICS), which is responsible for naming these time frames, also tried to eliminate the fourth subdivision—the Quaternary—but the International Union for Quaternary Research protested. So in 2009 the ICS restored the term. The Tertiary period—with its less ardent defenders—is no longer an official term, which is why K-T was replaced with K-Pg.

* Technically there were constraints due to precision measurements of other processes but generally these were neglected in the presentations based purely on direct searches for the Higgs boson itself.

* Some dark matter particles are their own antiparticle, in which case they can annihilate with other similar particles.

* electronvolts (eV), the unit of energy most used by particle physicists. keV, kiloelectron volts represents one thousand eV, whereas GeV, gigaelectron volts—a unit frequently used in discussions of physics at today’s high-energy accelerators—is one billion electron volts.