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There is significant evidence in the field of astronomy for the existence…

- - - - A black hole forms when a massive, dying star crumples under its own gravity. It shrinks until all of its mass is contained in an infinitely dense point, called a singularity
      - Its gravity is so intense that if anything ventures with an invisible border around the singularity, called the event horizon, it cannot escape. Just outside of this event horizon is high-temperature material, called the accretion disk, waiting to fall into the black hole. This disk emits x-rays, a high-energy form of light, because the matter moves so fast that its friction produces a great deal of heat. Jets of energy and matter, whose formations are unknown, can stretch away from the accretion disk for hundreds of thousands of light-years. A ring of photons are nudged up against the event horizon, surrounding the black hole. This loop of light, called the innermost stable circular orbit, outlines the edge of the black hole
    - - The feeling of being sucked into a black hole is known as spaghettification
      - As you approach the black hole, its gravity becomes bothersome, and you begin to feel a pull on your feet first. It soon pulls your feet much harder than the rest of your body and your feet begin to stretch away from your calves. This uncomfortable feeling grows as you’re strung out into a thin strand, like spaghetti
    - - Quantum mechanics suggest information can never be destroyed
      - One idea is that quantum physics dictates that information remains on the black hole’s edge, even while the object falls in
      - Another idea is that once a black hole has lost about half of itself to Hawking radiation, the event horizon can no longer store enough encoded information to tell the story of what’s inside. After that, nothing can go inside or else its information will be lost, and the singularity essentially collides with the event horizon. A “firewall,” or a wall of energetic particles born from collision, then lies just outside the horizon, incinerating anything that tries to cross it
      - Another idea is that as the object approaches the black hole’s edge, the edge’s gravitational field changes. That shifts the radiation in a way that encodes information about the object
      - The last idea is that as a 3-D object enters the event horizon, it leaves a 2-D stamp, or hologram, on the event horizon. As Hawking radiation leaves, an impression of the object’s identity is stamped on the hologram
    - - Stars orbit our galaxy’s central black hole, Sagittarius A (pronounced A star). In 2011, astronomers discovered G2, which they thought was a gas star, and it was headed toward the black hole. They believed the black hole would rip it apart. However, when it came in contact, G2 spaghettified a little bit and continued on its path. Scientists now believe the gas cloaks a secret star, whose gravity kept the clouds safe from total annihilation
    - - While we have solid evidence that black holes exist, many of the details are uncertain. Other possibilities are wormholes and white holes
      - Wormholes (Einstein-Rosen-Bridges) are shortcuts between two places in space. In this scenario, after you enter the black hole, you enter a “tunnel” and come out many light-years away through a white hole, the opposite of a black hole
      - You can leave a white hole, but you can never enter it. Although wormholes and white holes are mathematically possible, no one has ever found evidence of them.
  - - - The Gaia mission mapped the locations of over 1.1 billion stars across the Milky Way and beyond. It gives the position for a star in the sky with a precision of less than a microarc second for suns with as faint a magnitude as 20.7. To put that into perspective, it is equivalent to pinpointing the exact location of a grain of sand in San Francisco as seen from Boston
      - The main goal of Gaia is to create an extraordinarily precise 3-D star map. To complete this, the Gaia spacecraft will monitor each star about 70 times over five years
    - - Stars are born within the clouds of dust and scattered throughout most galaxies. The Orion Nebula is a dust cloud. Turbulence deep within these clouds causes the gas and dust to collapse under its own gravitational attraction. While collapsing, the central material heats up. Known as a protostar, this hot core will one day become a star. As the cloud collapses, the core forms and begins gathering dust and gas. Not all of this material ends up as part of a star, as some could become planets, asteroids, comets, or the material could not change at all
    - - A star the size of our sun requires about 50 million years to mature from the beginning of collapse to adulthood. Our sun will stay in the phase it is in now for approximately 10 billion years
      - Stars are fueled by the nuclear fusion of hydrogen to form helium in the core. The outflow of energy keeps the star from collapsing under its own weight and the energy for the star to shine. Main Sequence stars span a wide range of colors and brightnesses, and are able to be classified according to those qualities
      - Types and Sizes
        
        The smallest stars are red dwarfs, which contain as little as 10% the mass of the Sun and emit only 0.01% as much energy, glowing dimly at temperatures of 3000-4000K. They are by far the most numerous stars in the universe and have lifespans of tens of billions of years
        
        The most massive stars, known as hypergiants, may be 100 or more times more massive than our sun, and have surface temperatures of more than 30,000K. They emit hundreds of thousands of times more energy than the sun, but have lifetimes of only a few million years. Today, these are extremely rare, as the Milky Way only contains a handful of hypergiants
    - - The larger a star, the shorter its life. All but the most massive stars live for billions of years
      - When a star has fused all the hydrogen in its core, nuclear reactions stop and the core begins to collapse onto itself, while becoming much hotter. Hydrogen fusion still continues in a shell surrounding the core. The core pushes outer layers of the star outward, causing them to expand and cool and the star turns into a red giant. Average stars like the sun will eject its outer layers until the stellar core is exposed. This is called a white dwarf. They are roughly the size of our earth, but contain the mass of a star
      - Pressure from fast moving electrons keeps the star from collapsing completely. This fate awaits only stars with a mass up to about 1.4 times the mass of our sun. Above that mass, electron pressure cannot support the core against further collapse. White dwarfs may become novae. Nova is Latin for “new,” as they were once thought to be new stars. However, they are actually very old stars. If a white dwarf is close enough to another star, its gravity may attract matter (mostly hydrogen) from the outer layers of that star onto itself. When enough hydrogen accumulates on the surface, a burst of nuclear fusion occurs, causing the white dwarf to brighten greatly and expel the remaining material
      - Within a few days, the glow dims and the cycle starts again. Sometimes, extremely massive white dwarfs may attract so much mass that they collapse and explode completely, becoming a supernova. A supernova is not merely a bigger nova, as in a nova, only the star’s surface explodes, while in a supernova, the star’s core collapses and then explodes
      - In massive stars, nuclear reactions lead to the production of iron in the core. After this, the star has used all the energy it can out of nuclear fusion. The star no longer has a way to support its own mass, and the iron core collapses. In just seconds, the core shrinks from 5000 miles in diameter to just a dozen, and the temperature spikes 100 billion degrees or more. The outer layers begin to also collapse, but then bounce back and release a tremendous amount of energy
      - Supernovae release an unimaginable amount of energy. For some days or weeks, a supernova could be brighter than an entire galaxy. These explosions occur about once every hundred years in the typical galaxy
      - If the collapsing stellar core at the center of a supernova contains between about 1.4 and 3 solar masses, the collapse continues until electrons and protons combine to form neutrons, producing a neutron star. These are incredibly dense, similar to the density of an atomic nucleus. The gravitation at the surface is immense due to the density. They have powerful magnetic fields which can accelerate atomic particles around its magnetic poles producing powerful beams of radiation
      - If the collapsed stellar core is larger than three solar masses, it collapses completely and forms a black hole, an infinitely dense object whose gravity is so high that nothing can escape. The dust and debris left behind by novae and supernovae eventually mix with the interstellar gas and dust, enriching it with heavy elements and chemical compounds. These materials are recycled and provide the building blocks for new stars
  - - - Another explanation for how space acquires energy is the quantum theory of matter. In this theory, empty space is full of virtual particles that continually form and then disappear. However, when physicists tried to find out how much energy this theory would give empty space, the number came out 10^120 times too big
      - One explanation for dark energy is that it is a property of space. Einstein discovered a property of space that it is possible for more space to come into existence. A version of his gravity theory with a “cosmological constant” makes a prediction that empty space can contain its own energy. Since this is a property of space itself, then it would not be diluted as space expands
      - Another explanation for dark energy is that it is a new energy fluid or field, which is something that fills all of space but whose effect on the expansion of the universe is the opposite of normal matter and normal energy. Some have named this “quintessence,” of the fifth force, but if this is true, we still don’t know what it is like, what it interacts with, or why it exists
      - The last possibility is that Einstein’s theory of gravity is not correct, but this would affect the way that normal matter galaxies behave
    - - First, it is dark and is not in the form of stars and planets, which are visible
      - Second, it is not dark clouds of normal matter
        
        Matter is made up of particles called baryons. We know dark matter is not dark clouds of normal matter because we would be able to detect baryonic clouds when they absorb radiation
      - Third, dark matter is not antimatter, because there are no unique gamma rays produced as in antimatter
  - - - The most distant galaxy is 13.2 billion light years away, and the universe was created 13.8 billion years ago
      - It was discovered by a telescope that detected photons emitted from the galaxy’s clouds of hydrogen when the universe was less than 600 million years old. Such photons rarely make it to telescopes on Earth. They found that the wavelength of the photons had been stretched while on the way to Earth
      - Seeing hydrogen emission from such a distant galaxy might challenge the current understanding of the evolution of the universe.
    - - Two-thirds of the known galaxies, including the Milky Way, are spiral-shaped. At the center of the spiral, a lot of energy is being generated. Because of the immense gravity required to explain the movement of stars and the energy expelled, it is concluded that the center of the Milky Way is a supermassive black hole
      - Other galaxies have elliptical shapes, and a few have unusual shapes like toothpicks or rings
      - The shapes of galaxies are influenced by their neighbors, and galaxies collide often
  - - - The nature of dust and particle collisions, as well as some other factors, led to the progressive break-up of the dust cloud into increasingly larger clumps of materials and the formation of planets
  - - - The Giant Impact Hypothesis says that an interloping world called Theia, about the size of Mars, slammed into the Earth. Our planet recovered, while the Moon formed out of the remnant debris
    - - Last year, scientists reported that some of the Moon’s chemical signatures were suspiciously identical to Earth’s. Their ratios of isotopes should be distinct of one another, however, they are not
      - Scientists had thought the original impact of Earth and Theia was a sideswipe, but one solution to their similar isotopic ratios is that they smashed into each other like wrecking balls, creating a dense cloud of material 500 times the size of the Earth. Formed out of this violent cloud of debris, the Moon would surely share Earth’s chemical fingerprints
      - Another solution is that even in the less violent collision, an extended atmosphere could allow material to flow between the tattered Earth and still-forming Moon, bringing their chemistry into close alignment
- - - - Solutions
        
        On one hand, the solution is that the physics allow our universe is the only possible outcome
        
        On the other hand, we may be just one universe of many, part of a megaverse, where all possibilities exist among the landscape of neighboring universes
        
        A third possibility is that a deity created a life-friendly universe
  - - - The first multiverse candidate is the eternal inflation scenario which tells us that an infinite number of universes will randomly spring out, meaning that a life-permitting universe will eventually appear as part of a cosmologic thing called “inflation.” At the beginning of our universe, it inflated from the size of something infinitesimal to something a quarter of a billion light years across in the matter of a fraction of a second
      - The second multiverse explanation is the cosmological natural selection model, which suggets that each universe creates more universes through its black holes, and that the universes with superior black hole-making abilities will spawn new universes, while the other universes die off, eventually bringing about a universe that is fit for life
      - The third explanation is the cyclic model, which suggests that a cycle of big bangs happens
        
        Cyclic Models
        
        An early cyclic model proposed that a universe would expand for part of its life, then contract again and another big bang would happen
        
        Other cyclic models predict that, based on string theory, there are membranes that both contain and form universes
        
        One of these models says that another universe resides within millimeters of our own, which we cannot see because it is in a fifth dimension, and it has for an infinite time caused a series of big bangs when the universes collided
        
        Another model predicts that the membranes function much like a sheet when the sheet is vigorously shaken
  - - - To use an analogy, say that your body was covered with little growths that eventually turn into new, slightly different versions of you. Then, those growths begin to have a multitude of growths growing on them as well. How long would it take to run out of room to grow because they were bashing into another new version of you
        
        Under such theoretical constructs, cosmologists imagine that the new universes would look like a series of ever-growing, ever-multiplying soap bubbles in a giant mass. And the contents of each universe don’t slam into each other because the empty space around each universe is large enough so that the universes grow next to each other. Considering that our universe came from an unimaginably violent explosion, and if a universe formed along-side ours by this method, the two universes should logically collide with such astronomic power and dazzling releases of light and energy that they should be noticable by those living in a universe at the very least. Logically, it would be equal to a stick of dynamite exploding amidst soap bubbles
        
        Since there is no evidence of universes colliding, cosmologists are left postulating that not only must the expansion of a universe create more space, but that the regions between the universes must also expand exponentially and seamlessly so that the universes don’t touch one another
    - - Since the first offspring resemble their parents, you first need suitable parents. In other words, universes that are likely to give off life-allowing universes are universes that themselves were likely to allow life — and where did these universes come from?