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Stars die because they exhaust their nuclear fuel. Really massive stars use up their hydrogen fuel quickly, but are hot enough to fuse heavier elements such as helium and carbon. Once there is no fuel left, the star collapses and the outer layers explode as a ‘supernova’.
In collapsed stars, matter has been pushed to the limit. In the normal course of its life, this pressure is provided by the energy produced in nuclear reactions deep in the center of the star. When those nuclear reactions stop producing energy, the pressure drops and the star falls in on itself.
So, how long does a supernova take to explode? A few million years for the star to die, less than a quarter of a second for its core to collapse, a few hours for the shockwave to reach the surface of the star, a few months to brighten, and then just few years to fade away.
Left alone, black holes lose mass due to ‘Hawking radiation’, so that their event horizons are slowly shrinking. But, the interior of the black hole, or its ‘singularity’ (the point at which all the black hole’s matter is concentrated) has already reached the limit of its density and cannot ‘collapse’ any further.
When the cores collapse to form dense stellar objects called neutron stars, they blast off the outer layers of the star in a supernova. When the core collapses, the blast wave slams into the dense material above, which thwarts the explosion. Instead of creating a supernova, the star implodes, forming a black hole.
Naked eye supernova are far rarer. There was a naked eye gamma ray burst in 2008, but I don’t think anyone actually got outside in time to see it. If you have 50 years to look at the stars, you might see a supernova. If you have a small telescope, you can pick them up pretty regularly in nearby galaxies.
Probably not. All of the stars you can see with the unaided eye lie within about 4,000 light-years of Earth. But the most distant ones are intrinsically brighter, have more mass and are therefore likely to die in rare supernova explosions.
If black holes evaporate under Hawking radiation, a solar mass black hole will evaporate over 1064 years which is vastly longer than the age of the universe. A supermassive black hole with a mass of 1011 (100 billion) M ☉ will evaporate in around 2×10100 years.
For outside observers, a black hole is one solidary element, and there is no proper time inside the black hole, but there is only the observed coordinate time according to our spacetime coordinates.
An astroid named 16 Psyche, after Cupid’s wife, was found to be made almost entirely of iron and nickel. That means, in current US markets, 16 Psyche is worth somewhere around $10,000 quadrillion (the world’s economy is around $74 trillion).
International Space Station
Large Hadron Collider
Asking the International Space Station to justify its existence is a tall order. NASA estimates the station has cost U.S. taxpayers $50 billion since 1994 — and overall, its price tag has been pegged at $100 billion by all member nations.
It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada). The ownership and use of the space station is established by intergovernmental treaties and agreements.
The first rudimentary station was created in 1969 by the linking of two Russian Soyuz vehicles in space, followed by other stations and developments in space technology until construction began on the ISS in 1998, aided by the first reusable spacecraft ever developed: the American shuttles.
2.2 billion USD
The crew stayed in orbit with Skylab for 28 days. Two additional missions followed, with the launch dates of July 28, 1973, (Skylab 3) and November 16, 1973, (Skylab 4), and mission durations of 59 and 84 days, respectively. The last Skylab crew returned to Earth on February 8, 1974.
Skylab was made to go up but not to come back down. Because the project represented the next step toward wider space exploration, NASA threw itself into successfully putting Skylab in orbit.
The fall marked the official end for America’s first crewed orbital outpost — and famously prompted the Aussie town of Esperance to charge NASA $400 for littering. Skylab leveraged Apollo hardware that was left over after the final three missions of the moon program were canceled in the early 1970s.
Skylab program objectives were twofold: To prove that humans could live and work in space for extended periods, and to expand our knowledge of solar astronomy well beyond Earth-based observations. The program was successful in all respects despite early mechanical difficulties.
It’s actually moving 12 times faster than a jet fighter. If you shot anything at that speed on Earth, by the time it was about to hit the ground, it would miss! In the same way, the ISS isn’t floating in space, it’s falling towards Earth and missing!
Parts of Skylab, America’s first space station, come crashing down on Australia and into the Indian Ocean five years after the last manned Skylab mission ended. No one was injured.