Calypso: the Immortal Wife
Poor Odysseus. For those unfamiliar with his story, we'll provide a brief synopsis. He was the King of Ithaca whose life would have likely been less eventful had he not been so fiendishly clever. His travails truly began when he joined the throng of eager suitors who besieged King Tyndareus' palace in order to win his daughter Helen's hand in marriage. As the world's most beguilingly beautiful woman, Helen would naturally be sought by all. Or, almost all. Odysseus was unique among these men in that he truly didn't wish to be Helen's husband. Instead, he desired her cousin Penelope, daughter of Tyndareus' brother Icarius. (Not to be confused with Icarus, the ill-fated son of Daedalus who fell to his death when venturing too close to the Sun while flying upon waxen-wings.) Being a sagacious sort, Odysseus knew that Penelope was the wiser, craftier and more loyal of the two women. He managed to win Penelope by assisting her uncle Tyndareus, who was worried that violence would ensue immediately after he chose the suitor to be Helen's husband. Odysseus advised the King to have all the suitors swear an oath to protect the sanctity of the marriage no matter whom he chose. The King heeded his advice and in gratitude persuaded his brother to allow Odysseus to marry Penelope. When Trojan prince Paris kidnapped Helen after she was married to Menelaus, the suitors were oath-bound to sail to Troy and retrieve her. By that time Penelope had already given birth to Telemachus and Odysseus wanted to remain at home. After all, an oracle warned him that if he went to fight the Trojans he would be gone twenty years. So, when Palamedes arrived in Ithaca to summon Odysseus, the latter pretended to be mad by plowing salt into his soil while babbling incoherently. Suspecting subterfuge, Palamedes placed the infant Telemachus in the plow's path. Odysseus' ruse was up when he diverted the plow away from his son. So, poor Odysseus joined the fight, which lasted ten years. After the war ended, thanks to the Trojan Horse trick that Odysseus, himself, had devised, he and his crew embarked immediately for Ithaca. Alas, they encountered one peril after another: the flesh-craving cyclops Polyphemus, Circe, the witch who transformed his men into swine, Scylla and Charybdis, sirens, and so many others. By the time Odysseus reached the island of Ogygia, all his crew members had perished. The nymph Calypso watched him step onto shore and fell madly in love with him. She enraptured him with her beauty and singing and kept him on the island for seven years. They spent their days roaming through the lush fields and crystalline caverns of Ogygia and spent their nights in close intimacy. Everyday Calypso fell more deeply in love with Odysseus. She promised Odysseus eternal youth if he would remain on the island forever as her husband. Yet, everyday Odysseus pinned more desperately for his wife Penelope. Though reluctant to confide these feelings to Calypso, he did pray to his matron goddess Athena to help him. Athena went to Zeus and pleaded on Odysseus' behalf. Zeus sent Hermes, the messenger god, to Ogygia to inform Calypso that she must release Odysseus for it was not his destiny to remain with her forever. Initially Calypso was furious and railed at the gods for not permitting goddesses to have affairs with mortals. Yet, she ultimately relented. Calypso prepared a raft and stocked it with enough provisions to enable Odysseus to reach Ithaca. (Of course, he experienced one more detour, to the island of the Phaeanians, before arriving home.) When Odysseus did reach Ithaca and was reunited with Penelope, he found that his wife had remained loyal and faithful. He, of course, well, didn't....
THE SOUTHWORTH PLANETARIUM
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2020-2021: II
THE DAILY ASTRONOMER
Tuesday, September 1, 2020
Tuesday, September 1, 2020
Remote Planetarium 80: Dark Matters
Why does astronomy work? How have astronomers managed to learn so much about the cosmos? Simple: celestial objects emit light, or, more accurately, electromagnetic radiation. This radiation disseminates through the Universe radially away from any luminous object. Astronomers study that light and from it they glean immense amounts of information related to the object that produced it. One can regard such light as being akin to a tapestry which astronomers have learned to decipher over the last few centuries. Astronomy is the art of interpreting light.
Yet, not all celestial objects emit such radiation. Dark matter, which astronomers believe comprises the vast majority of material within the Milky Way Galaxy and a substantial amount of material in the Universe, imparts no light into the Universe. It is not visible at all, hence the term "dark." According to the most recent estimates, dark matter makes up
- 84% of the Milky Way Galaxy
- 26% of the Universe
These estimates prompt the questions: how do astronomers know dark matter exists? Of what material does it consist?
KNOWING ABOUT DARK MATTER:
While the concept of "dark stars" and other invisible celestial objects dates back to the 17th century, when Newton developed his Law of Universal Gravitation, the first systematic study of dark matter didn't occur until Swiss astronomer Fritz Zwicky (1898-1974) observed the Coma Cluster of Galaxies.
Fritz Zwicky Located about 300 million light years from our solar system, the Coma Cluster of Galaxies consists of more than 1000 member galaxies distributed over a region ten million light years in radius. In 1933, Zwicky announced that the cluster's component galaxies were moving far too swiftly than they should have been according to the physical laws relating a cluster's mass and the velocities of the galaxies within it. Zwicky employed the Virial Theorem, which states that within a self-gravitating distribution of equal mass objects such as galaxies, the total kinetic energy of the objects relates to the entire gravitational potential energy of the entire system. He hypothesized the existence of invisible material he dubbed "dunkle Materie."
The astronomical community largely ignored Zwicky's work for nearly half a century. The concept of "dark matter" came to the fore later in the twentieth century when astronomers such as Vera Rubin (1928-2016) studied the galactic rotation rates and the velocities of stars within the Milky Way.
Vera RubinBy analyzing the structures of distant galaxies, astronomers determined that the masses of galaxies seemed to be concentrated in and around the galactic nuclei (centers). Consequently, they assumed that the speeds of stars would decrease with increasing distance from the galactic center as the amount of material within the galaxy determines these velocities. (On a smaller scale, the Sun's mass relates directly to the orbital speeds of its attendant planets. The more massive the Sun, the quicker the revolutionary velocity.
They were astonished to have observed that the velocities of stars toward the galaxy's outer regions were moving much more quickly than they expected. The above graph shows the difference between the calculated velocity curve (red) and the observed velocity curve (white). The most plausible theory to explain this discrepancy involves dark matter. Much more material must be present within the Milky Way than we can directly observe. In fact, the majority of the galaxy must consist of dark matter.
The extensive observations of galaxies within various clusters and the stars within our galaxy has led to development of the "dark matter theory." Although this matter doesn't emit visible radiation, it does interact gravitationally with visible matter and so is indirectly detectable. It is possible that other WIMPS (Weakly Interacting Massive Particles) could be responsible, but haven't yet been identified.
WHAT IS DARK MATTER?
Astronomers don't know, actually. Although the nature of dark matter remains mysterious, many possibilities have been suggested to explain dark matter. Some have suggested that dark matter consists of neutrinos, nearly massive particles generated in nuclear reactions such as the fusion processes powering the Sun. Scientists have identified three neutrino types: electron, muon and tau: the names of the elementary particles with which they are associated. It was once thought that neutrinos were "fixed." An electron neutrino always remained the same and could not alter form. However, studies of electron neutrinos emitted by the Sun showed that neutrinos can, indeed, change form, a process known as "oscillation." These oscillations are only possible if the neutrino contains at least some mass. Indeed, a neutrino is massive, but only just. While scientists have yet to ascertain a neutrino's true mass, they do know that the three neutrino types have different masses and the sum of these three masses is about one millionth that of an electron. Just as a reminder, an electron is a wraith of a thing: it is 1835 less massive than a proton, the positively charged particle within an atomic nucleus. Although neutrinos are lightweights even in the ghostly realm of the sub-microscopic, they exist in a vast abundance. Every second, billions of neutrinos pass harmlessly through your body and then move through Earth without the least impediment. These neutrinos originate in the Sun, the cores of other stars and some date back to the Universe's infancy. Is it possible that the octillions of neutrinos roaming about the galaxy could be contributing to its mass? The problem with this notion is that many neutrinos might still be massless. Also, it is difficult to imagine that these neutrinos could account for 84% of the galaxy's missing matter.
Neutrinos! Despite this artistic depiction, neutrinos are not luminous. Instead, they are nearly massive particles produced by nuclear reactions.
Other possible dark matter candidates could be MACHOS (Massive Compact Halo Objects). These are objects such as brown dwarfs (protostars that lacked the sufficient mass to produce fusion-inducing core temperatures), planets and even other non-luminous materials such as comets and asteroids. While these objects could possibly represent a small fraction of dark matter, it is difficult to imagine that all these extraneous bodies could amount to the majority of galactic material. In our own solar system, the Sun accounts for 99.8% of the material within it. (A sobering reminder of how minuscule even our entire planet is relative to the Sun.)
These are two of the leading contenders. Many others have been suggested, even the notion that dark matter is caused by the gravitational influence of a parallel Universe. The true problem with that hypothesis is that it doesn't lend itself to direct or even indirect observational evidence.
We mention dark matter today because we are exploring the galaxy. This exploration would be incomplete without an examination of dark matter, which accounts for most of the material comprising the Milky Way. Its true nature remains one of astrophysics' most confounding mysteries.
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