Chapter 162 Nebula

Hua Feng gradually came to understand that the projection of the Milky Way across the night sky resembles a glowing river flowing through the firmament, hence its ancient names the Silver River or the Celestial River. It can be observed throughout all four seasons, though the brightest and most magnificent portion is visible between summer and autumn.

The most crucial point, as Sun Wukong told him, was that suspicious objects of various races had been detected heading toward Earth, with one of them originating from the direction of the constellation Sagittarius.

The primary constellations through which the Milky Way passes include: Cygnus, Aquila, Vulpecula, Sagitta, Ophiuchus, Scutum, Sagittarius, Scorpius, Ara, Norma, Lupus, Triangulum Australe, Circinus, Musca, Crux, Vela, Puppis, Monoceros, Orion, Taurus, Gemini, Auriga, Perseus, Cassiopeia, and Lacerta.

The Milky Way varies in brightness and width across the sky. Its narrowest points measure only 4° to 5°, while its widest spans approximately 30°. For the Northern Hemisphere, a vital landmark of the summer night sky is the band of light extending from the north-northeast horizon toward the southern horizon—the Milky Way—along with the "Summer Triangle," formed by three bright stars: Vega on one bank of the Milky Way, Altair on the other, and Deneb within it.

The summer Milky Way stretches northward from the eastern side of Scorpius, spanning the sky with breathtaking grandeur and majestic beauty. However, it can only be fully appreciated in the wild, free from light pollution (with a limiting visual magnitude of 5.5 or higher). The winter Milky Way is much dimmer (located around Orion and Canis Major), but the night sky features the brilliant constellation Orion, alongside the bright "Winter Triangle" formed by Sirius, Betelgeuse, and Procyon.

The 88 Constellations of the Sky:
Circumpolar Constellations (Northern Sky): Ursa Minor, Ursa Major, Cepheus, Cassiopeia, Draco
Northern Constellations: Andromeda, Perseus, Hercules, Lacerta, Camelopardalis, Vulpecula, Auriga, Boötes, Canes Venatici, Leo Minor, Coma Berenices, Corona Borealis, Lynx, Lyra, Cygnus, Sagitta, Delphinus, Pegasus, Triangulum
Zodiac Constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, Pisces
Equatorial Constellations: Equuleus, Canis Minor, Aquila, Ophiuchus, Serpens, Hydra, Sextans, Monoceros, Orion, Cetus
Southern Constellations: Ara, Apus, Grus, Columba, Lepus, Fornax, Pictor, Antlia, Caelum, Telescopium, Microscopium, Norma, Circinus, Horologium, Mensa, Indus, Volans, Dorado, Musca, Chamaeleon, Tucana, Corvus, Phoenix, Pavo, Hydrus, Lupus, Canis Major, Triangulum Australe, Crux, Piscis Austrinus, Octans, Corona Australis, Carina, Puppis, Pyxis, Reticulum, Vela, Sculptor, Centaurus, Eridanus, Scutum, Crater

One of the Satellite Galaxies: Large Magellanic Cloud
The Milky Way has two satellite galaxies: the Large Magellanic Cloud and the Small Magellanic Cloud. Galaxies situated outside the Milky Way are referred to as extragalactic galaxies.

The Milky Way, the Andromeda Galaxy, and the Triangulum Galaxy are the principal galaxies of the Local Group, which comprises a total of approximately 50 galaxies. The Local Group itself is a component of the Virgo Supercluster.

The Milky Way is surrounded by several dwarf galaxies belonging to the Local Group, the largest of which is the Large Magellanic Cloud with a diameter of 21,000 light-years, while the smallest are the Carina Dwarf, Draco Dwarf, and Leo II Dwarf, each measuring a mere 500 light-years in diameter. Other galaxies orbiting the Milky Way include the Small Magellanic Cloud, with the closest being the Canis Major Dwarf, followed by the Sagittarius Dwarf Elliptical Galaxy, Ursa Minor Dwarf, Auriga Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo Dwarf.

The Magellanic Clouds:
In January 2006, researchers reported that an unexplained warp previously discovered in the disk of the Milky Way is actually a ripple caused by the gravitational perturbations of the orbiting Large and Small Magellanic Clouds. As they pass through the outer edges of the Milky Way, they trigger vibrations at specific frequencies.

The mass of these two galaxies is approximately 2 percent of that of the Milky Way, which was previously deemed insufficient to affect our galaxy. However, when dark matter is taken into consideration, the movement of these two galaxies becomes substantial enough to impact the larger Milky Way. Calculations incorporating dark matter amplify the effect on the Milky Way twentyfold; these computations were derived from a computer model developed by Martin Weinberg of the University of Massachusetts Amherst. In his model, dark matter is distributed from the galactic disk all the way out to the farthest known boundaries, leading the model to predict that the gravitational shock wave would be magnified as the Magellanic Clouds pass through the Milky Way.

At the 222nd meeting of the American Astronomical Society held in June 2013, NASA released stunning new images of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) captured by the Swift spacecraft. These are the highest-resolution space images ever made public by NASA. These unprecedented high-definition images will assist scientists in further identifying and studying the stars, supernovae, and star cluster systems residing within the two nebulae.

These images were acquired by the Ultraviolet/Optical Telescope (UVOT) onboard the Swift spacecraft. Astrophysicists from NASA, the Goddard Space Flight Center, and Pennsylvania State University collaborated to photograph our two nearest neighboring galaxies from various angles using the Swift satellite's UVOT. They then stitched together tens of thousands of smaller photographs to create the clearest image to date, boasting a resolution exceeding 160 megapixels, a total file size of 457 megabytes, and stored in TIFF format.

The raw image of the Large Magellanic Cloud reaches an astounding 160 megapixels, assembled from 2,200 partial photographs captured over a total span of 5.4 days. Meanwhile, the raw image of the Small Magellanic Cloud consists of 57 megapixels, compiled from 656 partial frames taken over 1.8 days.

Scale of the Magellanic Clouds:
According to official NASA data, both the Large Magellanic Cloud and the Small Magellanic Cloud are the largest celestial systems closest to our Milky Way, classifying them as satellite galaxies of the Milky Way. Specifically, the Large Magellanic Cloud lies approximately 163,000 light-years from the Milky Way, with a scale roughly 20 percent that of the Milky Way and a mass equivalent to only 2 percent of it. The Small Magellanic Cloud is situated about 200,000 light-years from the Milky Way, with a mass equal to 50 percent of the Large Magellanic Cloud's mass.

Cosmic Origin:
When a galaxy possessing a galactic nucleus travels at high speed through the universe and overtakes another galaxy also equipped with a galactic nucleus, if their traveling speeds are comparable, they will mutually devour one another, eventually coalescing into a larger galaxy.

Should the galactic nuclei of these two galaxies meet, they will orbit one another and form an even more massive, rapidly rotating galactic nucleus. This high-speed rotating galactic nucleus functions much like a giant generator, erupting with powerful particle streams from its poles and jetting them far into the distance. The greater the energy of the galactic nucleus, the higher the volume of the jetted particle streams, and the farther they will travel.

We designate such a galactic nucleus as a bipolar jet galactic nucleus. While ejecting high-energy particle streams, a galactic nucleus expends its own energy; however, upon capturing other star clusters or galaxies, its energy is replenished. As the energy of the galactic nucleus undergoes cycles of fluctuation from high to low, it constructs two thick jet bands.

If the magnetic axis of the galactic nucleus revolves around another axis (known as the rotational axis of the galactic nucleus), the trajectory of the jet bands will curve, eventually evolving into the two spiral arms of a spiral galaxy.

Generally, the larger the angle (ranging from 0 to $pi/2$) between the magnetic axis and the rotational axis of the galactic nucleus, the flatter the resulting galactic disk will be; otherwise, it will be thicker.

The faster the magnetic axis of the galactic nucleus rotates around its rotational axis, the tighter the spiral arms will wind; otherwise, the looser they will be. The two spiral arms of a spiral galaxy are active regions of star formation.

Our Milky Way is precisely this type of spiral galaxy—a barred spiral galaxy.

Decreasing Mass:
When Alis Deaso recalibrated the instruments used to measure the mass of the Milky Way, she shockingly discovered that the mass of the Milky Way had decreased. "We found that the mass of the Milky Way is only half of what is commonly believed," stated Deaso. She is an astronomer at the University of California, Santa Cruz, and presented her measurement findings at the 221st meeting of the American Astronomical Society.

Measuring the mass of the Milky Way is complex, partly because the majority of its mass originates from unseen dark matter. Scientists typically measure the rotational velocity of the galaxy and combine it with theories regarding dark matter distribution to arrive at a conclusion.

Using this methodology, Mark Reid and his team at the Harvard-Smithsonian Center for Astrophysics calculated the total mass of the Milky Way to be tens of trillions of times the mass of the Sun, publishing their findings in 2009. Nevertheless, Reid acknowledged that "measuring the total mass of the Milky Way is exceedingly complicated" and fraught with numerous uncertainties.

Deaso and her colleagues adopted a different approach. In research published in the Monthly Notices of the Royal Astronomical Society, they searched for the very first time for stars located at extreme distances from the center within the stellar halo of the Milky Way—a spherical envelope measuring one billion light-years in diameter. Deaso explained that the dispersion velocity of these distant stars can reveal the true mass of the Milky Way.

The results demonstrated that the mass of the Milky Way is "merely" 500 billion to one trillion times the mass of the Sun—less than half of Reid's prior measurement.

Deaso cautioned that this conclusion was derived based on her assumptions concerning the size of the Milky Way's halo and the motion of stars orbiting the galactic center. Nonetheless, she maintains that these assumptions rest upon credible theoretical foundations.

Reid remarked that measuring the mass of the Milky Way "is crucial for understanding how our galaxy formed and predicting the evolutionary trajectory of galaxy clusters over the next several billion years," given the gravitational interactions existing between galaxy clusters. "The optimal method to determine the total mass of the Milky Way is to ascertain the complete three-dimensional velocities of its star clusters," he noted.

Current technology cannot yet provide such data, but Deaso hopes that observations from larger telescopes will soon substantiate her conclusions. "We require more stellar samples located even farther from the center of the Milky Way," she stated.

Regardless, life moves forward, and the mighty wheel of time never halts for anything.