On an interstellar scale, humanity is practically invisible. The radio signals that we transmit into outer space may extend over an impressive 200 light-years, but this is only a tiny fraction of the Milky Way (105,700 light-years in diameter). Even if someone were listening, after a few light-years our signals will decay into noise, impossible to identify as the source of an intelligent species.
Hypervelocity stars travel the galaxy at 1000 km/sec. They’re made when one star in a binary system gets sucked into the supermassive black hole in the middle of a galaxy, and its partner is flung out 100x faster than other stars, sometimes faster than the galactic escape velocity. One neutron star in particular (RX J0822-4300) was measured to be moving at a record speed of over 1,500 km/s (0.5% of the speed of light) in 2007 by the Chandra X-ray Observatory.
White holes are the hypothetical opposite of black holes. It is supposed to be a region of space-time that cannot be entered from the outside, although matter and light can escape from it. Some scientists suggest that 'The Big Bang' might have been produced by a supermassive white hole explosion. It theoretically exists as a result of Einstein’s field equations, but there is no physically known process for one to be made.
It is believed that one star goes supernova somewhere in the universe on average every single second and for the Milky Way galaxy this number is 3 stars every century. Humanity has only recently developed instruments like neutrino detectors that are sensitive enough to detect new supernovas. Neutrinos are emitted directly when the core collapses, so they arrive here earlier than the light. So if a neutrino detector picks up a supernova signal, they automatically send a message to various telescopes to watch that spot for the upcoming supernova. In fact, anyone can sign up to their early warning mailing list so you will get notified if they detect one. It's not reserved for just astronomers.
A Quasi-star is a type of (extremely) massive star that may have existed early in the universe. The matter in the early universe was so dense that quasi stars could grow to thousands of times the mass of our sun. The cores of these stars might have been crushed by their own weight so much to actually collapse into black holes while the star was still forming. Its energy would come from material falling into a central black hole, as opposed to nuclear fusion. These stars might explain the supermassive black holes that exist today as the universe is simply not old enough for these supermassive black holes to exist.
6Beyond the Solar System
Our solar system is surrounded by an 89,000 degree Fahrenheit orb of plasma created by the interaction between the sun and interstellar winds. This creates a 100 million miles wide sausage-shaped bubble known as the heliosphere and it protects the solar system from harmful cosmic rays. Outside the heliosphere begins the interstellar space, beyond which Oort cloud is theorized to exist. The solar system’s boundary is theorized to include Oort cloud from where long-period comets are thought to originate. Traveling at the speed of the fastest man-made object it would take 'Voyager 1' 300 years to reach it and it would take another 30,000 years to pass through it. Outside this, our solar system is currently in an area with only 5% of the average density of the galaxy. It was likely blasted clear by a supernova 20 million years ago.
When a star goes supernova, the rapidly expanding bubble of hot, metal-rich gas from it hits the edge of the galactic disk where it suddenly encounters much less resistance from a much lower density of the interstellar medium, allowing it to form a chimney perpendicular to the disk. After arcing well outside the disk, this material then cools and rains down over a large portion of the galaxy, seeding stellar nurseries with metals that will later become planets.
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8Stealing Black Hole's Energy
Due to angular momentum, when really massive spinning stars collapse to form black holes, they start spinning faster and faster. In fact, some black holes spin millions of times a second. This spinning creates a volume of dragged space-time called the ergosphere, which is escapable. Theoretically, any injected matter could capture some of the spinning black hole's angular momentum. British mathematician Roger Penrose hypothesized a way to steal some energy from a rotating black hole by injecting matter into the ergosphere and capturing some of the spinning black hole's angular momentum.
Turbulence in stellar nurseries will cause groups of stars from the same cloud to be scattered relatively quickly. There’s no reason to think that the current nearest stars to the sun are our siblings, though we probably do have sibling stars out there somewhere. Scientists have probably found a star (HD 162826) that formed from the same molecular cloud as our sun about 110 light-years away. This star might have shared the stellar nursery the sun was born in about 4.6 billion years ago. This star is 15 percent more massive than the sun, so it can’t be called a solar twin, just a solar sibling.
Our solar system revolves around a giant black hole in the middle of the galaxy in the constellation Sagittarius. This galactic orbit takes about 250 million years, so the last time the earth was on the other side of the galaxy, the dinosaurs were around. Dust clouds at the center of our galaxy however obscure this black hole from ever being visible from earth. If we could however remove those dust clouds, then we would be able to see a fireball rise every night rivaling the moon in brightness with a raging black hole in the center.