Govert Schilling

This is exactly the kind of book I would have loved as a science-obsessed kid. It’s not a kids’ book, but it’s written by a skilled science journalist and is highly accessible. It is filled with facts and gorgeously designed. It can be dipped into at random, or read cover-to-cover. The introductory information on the history of the constellations is thorough without being overlong. And did I mention how absolutely stuffed with factual information it is? For each constellation there’s a detailed map and a table with information about the number of stars it contains, bordering constellations, and when it’s visible to skywatchers, at what latitudes. There’s a timeline of discoveries associated with the constellation, reproductions of classical representations of the constellation, a handful of lovely photos of sky phenomena within them, and/or an artist’s representation of an exoplanet found within it. Each photo has a short but detailed and informative caption right next to it, making the book easy to navigate. One thing I especially appreciate about the captions is how Schilling usually identifies the facility used to take the photo and whether it’s in natural color or some other wavelength, a rarity in popular books about space.… (más)

Like the best science books, this is just as much about what we know as how we know it, and as what we don't know. Schilling is especially good at describing problems in our cosmological models. The book is well written and engaging.

> the very first two-dimensional numerical simulations of rotating disk galaxies, published by astronomers Richard Miller, Kevin Prendergast, and Bill Quirk in 1970 and by Frank Hohl in 1971, showed just that: the initially circular disk turns into an elongated, bar-like structure, and the galaxy’s stars end up in wildly elliptical orbits—very different from the orderly circular motions observed in the Milky Way. With the help of Princeton’s Ed Groth, Peebles and Ostriker developed a program that would run on the university’s computer, while adding a third dimension to the simulations. Their results agreed very well with those of Miller, Prendergast, Quirk, and Hohl. As Ostriker and Peebles wrote in The Astrophysical Journal, “Axisymmetric, flat galaxies are grossly and irreversibly unstable.” … Spinning, low-mass galaxies are unstable; more mass would help. But if that additional mass is also located in the rotating disk, the galaxy would be just as unstable as before—after all, the simulations showed that it’s the disk shape itself that leads to instability. No, the extra mass needs to be distributed in a huge, more or less spherical halo, not taking part in the orderly rotation of the disk. … Later research has revealed that large, random stellar motions in the cores of galaxies can also stabilize flat, rotating disks

> The Andromeda galaxy may be the Milky Way’s nearest large neighbor, but it’s still 2.5 million light-years away. At that distance, it was flat-out impossible to record the spectrum of an individual star, even with Ford’s powerful device. Instead the two astronomers focused on so-called HII regions (pronounced aitch two): luminous clouds of hot, ionized hydrogen gas, akin to the famous Orion Nebula, but much larger. These, too, orbit a galaxy’s center at velocities determined by the total mass within their paths.

> Between 1971 and 1973, Shostak and his thesis advisor David Rogstad, who had moved to Groningen in the Netherlands to work with the new Westerbork telescope, published papers on a total of six galaxies, including NGC 2403, M101 (also known as the Pinwheel galaxy), and M33—the third major member of the so-called Local Group, to which our Milky Way and Andromeda belong. In each case, they found that clouds of cold hydrogen gas way beyond the optical edge of the galaxy were rotating much faster than expected, indicating the presence of “low-luminosity material in the outer regions of these galaxies,” as they wrote in a September 1972 paper in The Astrophysical Journal. Meanwhile, NRAO astronomer Morton Roberts was studying neutral hydrogen in the Andromeda galaxy, using the then-largest radio telescope in the world—the Green Bank Telescope, which had become operational in 1962. Improving on the pioneering Dwingeloo observations by van de Hulst, Raimond, and van Woerden, Roberts published his first results in 1966—just one year after Vera Rubin started to share an office with Kent Ford at Carnegie’s Department of Terrestrial Magnetism

> Whether or not Rubin, Ford, and Thonnard were also aware of the work by Rogstad and Shostak remains unclear—the trio did not reference it in their 1978 and 1980 publications. But Shostak just can’t imagine they didn’t know about it. “In 1972, thanks to Mort Roberts, I had a postdoc job at NRAO,” he says. “One of the summer students there was Vera’s twenty-year-old daughter Judy, who would later become an astronomer herself. I’m sure she must have discussed our work with her mother. Vera didn’t have flat rotation curves until a couple of years later; we had done it years before.”

> It all seemed to confirm the earlier, less precise, and less sensitive results of Rogstad and Shostak and of Roberts and Whitehurst. Eventually, no fewer than twenty-five galaxies turned out to have flat rotation curves out to very large distances from their cores, indicating the presence of large amounts of invisible mass way beyond the optical disk. Bosma presented initial results at conferences in 1976 and 1977, but the full extent of his work only became clear with the publication of his 1978 dissertation “The Distribution and Kinematics of Neutral Hydrogen in Spiral Galaxies of Various Morphological Types.” Later that year, Rubin, Ford, and Thonnard described their results for just ten galaxies, based on optical observations. So, is Albert Bosma frustrated?

> “It’s true that Vera came late to the party. All that talk about a Nobel Prize, and now a large telescope being named after her … it makes you feel kind of strange.” Then again, he adds, she never claimed priority herself. Indeed, as I have noted before, Bosma’s thesis is referenced in the 1980 publication by Rubin, Ford, and Thonnard. And in their 1978 paper, the authors make clear that “Mort Roberts and his collaborators deserve credit for first calling attention to flat rotation curves.” … Sandra Faber, who later became a distinguished professor at the University of California, Santa Cruz, believes that—contrary to what is usually the case—Rubin’s current record in history has actually been helped by the fact that she was a woman. It is a remarkable example of reverse gender inequality. “Bosma’s thesis is brilliant. Two hundred years from now,” she muses, “people will certainly realize how important his contributions have been.”

> In 1987 and 1988, they published three more papers—two in The Astrophysical Journal and one in Nature—in which they expanded on their earlier work. Taken together, the Gang’s five landmark publications—collectively known as the DEFW papers, for Davis, Efstathiou, Frenk, and White—firmly put nonbaryonic cold dark matter on the map as the sole candidate for the major constituent of the universe. CDM appeared to be able to explain just about everything.

> Observe hundreds (or thousands, or even millions) of faint background galaxies. Check for departures from random orientations. Use these departures to map the strength of the weak lensing effect that’s responsible for the minute distortions. Then derive the corresponding mass distribution in the foreground. Presto: you’ve just arrived at a mass map of part of the universe. And since most of the universe’s gravitating mass is dark matter, the map you’ve produced basically charts the dark matter along the line of sight—a feat first achieved (albeit with rather poor accuracy) by Anthony Tyson of AT&T Bell Laboratories and his colleagues in 1984.

> Luckily there are ways to make the distinction between microlensing and other sources of nonperiodic variation. One key characteristic of a microlensing event is the perfectly symmetrical shape of its light curve—the graph showing how brightness varies with time. If a star brightens at one rate and then dims at another, microlensing cannot be the cause. And there’s another important clue. An intrinsically variable star usually changes color, however subtly, because its surface temperature rises and falls. The result is that the star’s behavior as seen through a red filter is slightly different from what is seen through a blue filter. In contrast, microlensing events are expected to be “achromatic”: red light is amplified in exactly the same way as blue light

> within a couple of years, Aubourg and his coauthors had to retract each of their claims, much to their disappointment. Follow-up observations revealed that both of their suspect stars were weird variables after all, with long quiescent periods and occasional brightness changes that had all the symmetric and achromatic characteristics of microlensing events.

> Sixty satellite dwarfs swarming around the Milky Way may sound like a lot, but theorists predict there should be at least five hundred. And it’s not that astronomers haven’t searched hard enough. The current surveys should really have turned up many, many more. It’s called the missing-satellite problem,

> real dwarf galaxies do not show these prominent density cusps at their cores. The dark matter distribution, as derived from velocity observations, is always much flatter. This third mismatch between ΛCDM simulations and the real universe is called the core-cusp problem, or the cuspy halo problem

> Detailed supercomputer simulations of the growth of cosmic structure, like IllustrisTNG and EAGLE, show how large galaxies like our Milky Way end up being surrounded on all sides by huge numbers of dark matter subhalos, which become visible as dwarf galaxies. In the real universe, however, the dwarf companions are not only too few in number; they also do not surround their host galaxy equally in every direction. Instead, the majority of satellite galaxies are found in a flattened disk, which does not coincide with the central plane of the host. No matter how computational astrophysicists tweak their code, they are not able to reproduce this distribution in their simulations. It’s known as the planes-of-satellite-galaxies problem.

> the light from a remote quasar can be split into multiple images by the gravity of a massive foreground object, such as a huge elliptical galaxy. Importantly, brightness changes in the lensed quasar arrive at Earth at different moments, because each light path has its own associated travel time. So if one quasar image exhibits a certain pattern of flickers, the same pattern will be observed in another image of the same quasar with a delay of (usually) a couple of months. From this time delay—and a precise model of the mass distribution of the foreground lens—it is possible to calculate the distances traveled. Combining this with redshift measurements yields a value for the Hubble constant to a precision of a few percent. The international H0LiCOW project led by Suyu (H 0 Lenses in COSMOGRAIL’s Wellspring) kept track of brightness variations in six gravitationally lensed quasars to arrive at a value for the Hubble constant of 73.3 km / s / Mpc, with a precision of 2.4 percent—in almost perfect agreement with the SH0ES value

> How, then, to make sense of the divergence over the Hubble constant? Is it around 74.0 km / s / Mpc, as Riess, Suyu, and others have found, or is it 67.4 km / s / Mpc, as indicated by the cosmic back ground radiation?

> the results so far seem to indicate that cosmic matter is distributed more homogeneously than expected. Cosmologists use the parameter S 8 as a measure of the “lumpiness” of the universe, and the value of S 8 as measured by KiDS and DES (somewhere between 0.76 and 0.78) is some 8 percent lower than the value predicted from Planck’s observations of the cosmic microwave background (0.83). This significant discrepancy is known as the S 8 tension… (más)