ASTRONOMERS FROM ANTIQUITY PPAGEage 164 MARCH/APRIL 2019 $5 Probing for Planets Space agencies prepare next generation of exoplanet hunters THE UNIVERSITY OF TEXAS AT AUSTIN Mc DONALD OBSERVATORY STARDATE STAFF MARCH/APRIL • Vol. 47, No. 2 EXECUTIVE EDITOR Damond Benningfield EDITOR Rebecca Johnson ART DIRECTOR C.J. Duncan EATURES EPARtmENts TECHNICAL EDITOR F D Dr. Tom Barnes CONTRIBUTING EDITOR Alan MacRobert 4 Poets, Philosophers, Queens, Astronomers MERLIN 3 MARKETING MANAGER Casey Walker Early women astronomers drafted MARKETING ASSISTANT calendars, plotted eclipses, built SKY CALENDAR MARCH/APRIL 10 Joanne Duffy observatories, and helped shape humanity’s early understanding of the THE STARS IN MARCH/APRIL 12 universe For information about StarDate or other programs of the McDonald Observatory By Jasmin Fox-Skelly Education and Outreach Office, contact ASTROMISCELLANY 14 us at 512-471-5285. For subscription orders only, call 800-STARDATE. 16 Kepler Passes the Torch ASTRONEWS 20 StarDate (ISSN 0889-3098) is published As a successful planet-hunting bimonthly by the McDonald Observatory Resetting the Clock on Saturn’s Rings Education and Outreach Office, The Uni- spacecraft came to the end of its mission, versity of Texas at Austin, 2515 Speedway, Chasing Away Planet Nine Stop C1402, Austin, TX 78712. © 2019 a successor took flight. Several others are The University of Texas at Austin. Annual expected to follow in the next decade Chillin’ Under the Sun subscription rate is $26 in the United States. Subscriptions may be paid for using By Rebecca Johnson Birth of a Black Hole, or Death by Black Hole? credit card or money orders. The University of Texas cannot accept checks drawn on Gaia Spies Galaxy-Hopping Stars foreign banks. Direct all correspondence to StarDate, The University of Texas at Austin, 2515 Speedway, Stop C1402, Austin, TX 78712, or call 512-471-5285. POSTMAS- TER: Send change of address to StarDate, The University of Texas at Austin, 2515 Speedway, Stop C1402, Austin, TX 78712. Periodicals Postage Paid at Austin, TX. On The Cover StarDate is a registered trademark of The University of Texas McDonald Observatory. Artist’s concept of Kepler-62f, the smallest planet the Kepler spacecraft has found orbiting in a star’s habitable zone. Kepler’s mission Visit StarDate Online at stardate.org or on: recently ended, but its successors will continue to probe exoplanets for their secrets. For more, see Page 16. NASA AMES/JPL-CALTECH/T. PYLE AMES/JPL-CALTECH/T. NASA This Page Coming Up Hydrogen gas glows red in the Ghost Nebula, Our May/June issue brings you excerpts from seen by Hubble Space Telescope 550 light- new books in astronomy and space science years away in the constellation Cassiopeia. to spice up your summer reading. We’ll also The gas is heated by blasts of ultraviolet bring you summer skywatching notes and StarDate radiation from the nearby blue giant star charts, Merlin’s answers, and more. StarDate Magazine Frank N. Bash Visitors Center Gamma Cassiopeiae (not shown), which is 34,000 times more powerful than the Sun. I/H. ARAB (UNIV. OF STRASBOURG) ARAB (UNIV. I/H. c 2 MARCH/APRIL 2019 NASA/ESA/STS MERLIN Dear Merlin, tional force. Presumably they Celestial bodies (planets, as- continue to draw in matter (and teroids, comets, etc.) obey the grow larger and gravitation- laws of gravitational physics. ally stronger) until all the Is it possible to have a celestial nearby matter is absorbed. object that travels askew to the Is it possible, then, that gravitational forces of the solar the galaxies we observe system — something that plays — billions of light-years by rules that transcend our local distant, and therefore bil- forces? lions of years in the past Bill Dockery — have been consumed Knoxville, Tennessee by a giant black hole and no longer even exist in M Ö R T Following the laws of phys- our time frame? S D N U L ics isn’t just recommended, it’s Owen Daniel E N AY L required. There is no way for Fort Worth any object to break those laws. That’s a comforting thought, Possible, but highly unlikely. because otherwise scientists Black holes in the centers would have no way of knowing of galaxies can grow to mon- where any object was going, so strous proportions. The larg- give birth to new stars.) Kuiper Belt, which is a dough- they might never know if an est yet measured top 10 bil- Also, keep in mind that while nut-shaped region beyond the object endangered Earth. lion times the mass of the Sun, 10 billion solar masses is a lot, realm of the major planets. Having said that, Merlin will which certainly produces a it’s insignificant compared to The calculations aren’t precise add that the motions of objects powerful gravitational pull. the mass of a major galaxy. enough to pinpoint the possible in the solar system can be af- Yet several things conspire The Milky Way, for example, planet’s location, though, so fected by objects outside the to prevent a black hole from has a mass of more than a tril- astronomers must scan large solar system. A passing star, for devouring its entire host gal- lion Suns, and its disk spans regions of the sky — far from example, can stir up the Oort axy. For one thing, as a black 100,000 light-years or more. the ecliptic — to try to find it. Cloud, which is a vast shell of hole “feeds,” it surrounds itself All of that material exerts its Even though the planet is comet-like bodies that extends a with a spinning disk of gas. As own gravitational pull, keep- estimated to be several times light-year or more from the Sun. the gas gets closer to the black ing stars and gas clouds from Earth’s diameter, it is hun- These objects can get enough of hole it moves faster, so it pro- falling toward the central dreds of times farther from the a push to fall toward the Sun, duces friction. That heats the black hole. Sun than Earth is, so sunlight where they could possibly run gas to millions of degrees, so it So while astronomers can’t would be only a tiny fraction into Earth or another body. produces a lot of radiation. The be sure that black holes haven’t as strong as at Earth. It the Such encounters strictly fol- radiation produces pressure sucked up their entire galactic planet is at its farthest pro- low the laws of physics, how- that pushes away the material homes, they know that it’s not jected distance, in fact, sun- ever — no cheating allowed! that’s trying to fall toward the likely. light would be less than one- black hole. That acts as a tidy millionth as strong as at Earth, Dear Merlin, regulator, preventing the black Dear Merlin, which means there would be As I understand black holes, hole from overindulging. (The Why is Planet 9 so difficult little to illuminate it. Objects they tend to exist in the centers of outward-moving pressure also to track down, especially if it is in that part of the solar sys- galaxies, and that nothing (even can cause clouds of gas around as large as presumed? Is it too tem typically are darkened by light) can escape their gravita- the black hole to collapse and far away from the Sun? Would it long exposure to cosmic radia- be found on the ecliptic with the tion, too, so a possible Planet 9 other planets? would be quite dark. SEND QUESTIONS TO Corrin Gani The planet might shine Merlin Austin brighter in the infrared, but StarDate still would be a faint target. So, Merlin is unable to send University of Texas at Austin personal replies. Answers to 2515 Speedway, Stop C1402 Astronomers have inferred as with the discovery of Pluto many astronomy questions are Austin, TX 78712 the presence of Planet 9 from almost a century ago, if Planet available through our web site: [email protected] the alignment and motions of 9 exists it will take a lot of pa- I/H. ARAB (UNIV. OF STRASBOURG) ARAB (UNIV. I/H. c stardate.org/astro-guide stardate.org/magazine a group of iceballs outside the tient searching to find it. NASA/ESA/STS S TAR D ATE 3 POETS, PHILOSOPHERS, QUEENS, ASTRONOMERS Early women astronomers drafted calendars, plotted eclipses, built observatories, and helped shape humanity’s early understanding of the universe By Jasmin Fox-Skelly 4 MARCH/APRIL 2019 Visitors check out Cheomseongdae, the observatory created by Sonduk. Opposite page, from left: Sonduk; a modern depiction of Hypatia POETS, PHILOSOPHERS, QUEENS, ASTRONOMERS TOP6BIN/WIKIPEDIA; LEFT PAGE, FROM LEFT: WIKIMEDIA, NASA/CXRO/CFA WIKIMEDIA, LEFT: FROM LEFT PAGE, TOP6BIN/WIKIPEDIA; S TAR D ATE 5 enrietta Swan Leavitt helped make the expanding universe possible. She discovered that a class of bright pulsating stars made perfect “standard candles” for determining the scale of the universe: Measure such a star’s maximum brightness and the length of its pulses and you could determine its distance. Edwin Hubble used those stars to discover that swirling,H spiral-shaped motes of matter are far outside the Milky Way galaxy, greatly increasing the size of the known universe. He also used them as a first step in determining that the universe is expanding. Leavitt’s discovery helped revolutionize humanity’s concept of the universe. She wasn’t the first woman to do so, however. History is full of examples of female astronomers whose work changed the way we think about the cosmos. In fact, some of the very first astronomers were female, and women have been studying the stars since antiquity.