If you think life on earth is strange, you are right. But life - and death - are even stranger in outer space. What happens when a star dies? Does a cosmic priest perform last rites, sprinkling star dust on the feverish forehead of the doomed star? Not exactly. If the dead star is big enough it turns into a most intriguing phenomenon: a black hole.
But even though a black hole has never been seen, and scientific consensus on its existence is just a theory, letâ€™s run with it and see where we end up.
Weâ€™ll start with stars. Our Sun is a star. We think our Sun is huge and, relatively speaking, it is. One million earths could fit inside the Sun. For us that is plenty big. But our Sun is one of the smaller, newer stars in the Milky Way galaxy. It is only 4.5 billion years old. Â There are more than one hundred billion other stars living and dying in the universe. Some we see, most we do not.
Our Sun has a magnetic core 27 million degrees hot.Â Although quite small, the core contains most of the Sunâ€™s total mass. The Sunâ€™s gravitational core makes the planets of our solar system orbit around it. It takes Earth a year to orbit the Sun. The Sun is also on an orbit, a much longer orbit - it lasts about 250 million years. What does our Sun orbit around? The magnetic core of the Milky Way galaxy: an incredibly large and powerful black hole. More about that soon. Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
When a star burns, the heat in the star pushes out and balances the internal pull of gravity. In about 5 billion years â€“ give or take a few million â€“ our Sun will burn through the last of its hydrogen fuel. The outer layers will dissolve or float away. It will begin to die.
When the Sunâ€™s fuel is finally spent there will be no outward movement to counteract the pull of gravity. The star will collapse in on itself and downsize to a ball of intensely compacted matter about the size of the Earth. Our Sun will become a â€˜white dwarf,â€™ an ember glowing from leftover heat; when the heat is gone the Sun will be a black dwarf star.
Because the Sun is a smaller star it cannot compress its matter enough to form a black hole. It takes the death of a star with (at least) three times the mass of our Sun to create one. The majority of stars are much bigger than the Sun. Some stars are twenty times (or more) larger. The death of a huge star is noticed by the entire universe.
The outer layers of a huge star do not simply dissolve or fall away like our Sun. The outer layers of a large star fall inward but then bounce off the core with a shock wave effect. This creates a supernova explosion of incomprehensible force, causing a flash of light seen throughout the universe. National Geographic explains:
â€œDetonate a Hiroshima-like bomb every millisecond for the entire life of the universe and you will still fall short of the energy released in the final moments of a giant star collapse.â€
Collapse is the key word. After the supernova explosion of the outer layer, the body of the star collapses inward with unstoppable, ferocious momentum that creates temperatures of 100 billion degrees. Everything within the gravitational pull is immediately crushed to microscopic size.
Weâ€™re talking violence on a monstrous, unbelievable scale. Shards of iron the size of mountain ranges are instantly pulverized into grains of sand, which are pulverized into atoms and neutrons, which are in turn pulverized into smaller and smaller particles. If Earth collapsed into a black monster its diameter would be about two thirds of an inch, but its weight would be unchanged.
It is suspected that a gigantic black hole is at the center of the Milky Way galaxy. Scientists call it SgrA* (Sagittarius A-star) because it can be â€˜seenâ€™ in the constellation Sagittarius. Being seen for a black hole consists of observing the stars or planets that orbit around it.
SgrA* is 26,000 light years away. Its estimated mass is 4 million times the mass of the Sun. That is big. Yet our monster of the Milky Way is totally punked by its cousin in the Andromeda galaxy the size of 100 million suns. How did it get that big? Overeating.
Right now SgrA* is pulling a gas cloud towards it at 1800 miles per second. Sometime later this year the cloud of gas will approach the event horizon of SgrA*m, which will trigger scrutiny from scientists all over the world. It is hoped we will be able to measure the event horizon by seeing a line of debris from the gas cloud disappearing forever into the hungry mouth of SgrA*. Stay tuned! By the end of this year we may have conclusive proof black holes really exist.