Review: June 2021

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The lives of stars are secret because, to start with, only about 3,000 of the billions of trillions of stars in the universe are visible to the unaided eye. Most are undetectably faint unless they are really close, and most emit radiation our eyes cannot see, even through binoculars or a small telescope.  Take Proxima Centauri, the closest neighbor to our Sun. A red dwarf star, emitting only a thousandth the output of our Sun, primarily at infrared wavelengths, it is, in Lisa Harvey-Smith’s flamboyant phrasing, “barely bright enough to serve as a night-light for your toilet, let alone to light up the vast expanses of space.”  
    Astrophysicists like Lisa Harvey-Smith spend their careers deciphering the coded signals from stars, using an impressive array of ultra-high-tech tools—huge telescopes sensitive to a variety of wavelengths, gravitational wave detectors, and arrays of radio dishes that span the globe. Sparing readers the procedural details, Harvey-Smith presents readers with a sampling of bizarre astronomical objects, a rogues’ gallery of some of the most striking characters unmasked by current research.     
    Some are worthy of inclusion in the record books, such as WISE 0855-0714, a “sub-brown dwarf” and one of the coolest stars known. Its surface hovers around –25 degrees Celsius,  so chilly that crystals of ice float about in its atmosphere. Is this WISE guy a wimpy star or a pudgy planet? Then there is S5-HVS1, unremarkable in its size and temperature (it is about twice as hot as our Sun), but notable as the “fastest star ever discovered in the universe,” speeding along at more than a thousand miles a second. Astronomers trace its origin to the core of our Milky Way, where it was accelerated, like stone out of a slingshot, by the intense gravitational pull of our galaxy’s central black hole, itself a notable object 4 million times more massive than the Sun.
    Other members of this stellar menagerie are just plain quirky: Tabby’s star, named after astrophysicist Tabetha Boyajian, who discovered it, dims sporadically and unpredictably “as if ‘power save’ mode has engaged.” It can fade by as much as a fifth of its average brightness as irregular clouds of dust around the star—otherwise invisible—drift through our line of sight. Przybylski’s star pulses more rapidly and more regularly, every twelve minutes or so, but is distinguished by a surprisingly large abundance of radioactive elements, such as strontium and plutonium. Since these atoms decay too rapidly to have survived the millions of years since the star formed, nuclear reactions in the center of the star must be continuously creating them and then somehow burping them up to the surface where we see them. “It’s probably just indigestion,” quips the author.
    Harvey-Smith has a gift for the rhetorical flourish. She tags one spinning neutron star as “a magnet so strong that it could wipe a billion credit cards at a distance of 180,000 kilometers.” Kapteyn’s star, whose composition indicates great age and whose orbit indicates it came from outside our galaxy, is “an ancient invader” and “a wise old traveler.” “Don’t you just love science?” the author remarks, catching a breath. After reading her enthusiastic exposition, it is easy to concur. --LAM