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Entries in gravity (41)


Black holes

Black holes are the most extreme and violent objects of the universe... They push our understanding of Nature to its limits. A black hole is basically a star that has exhausted all its nuclear fuel and has collapsed under its own weight. If our Sun were to form a black hole (which it won't because it is not heavy enough), all its stuff would collapse into a ball of radius about 3 km (that's around 2 miles) - its current size is 200,000 times more... The surface of a black hole is known as the black hole horizon. If you were falling into a black hole, as you approach its horizon, the rate at which you age will slow down as seen by your worried relatives far away: time gets severly warped near a black hole. You may survive crossing the horizon, but, once you do, you are doomed forever... you will never ever be able to escape - at least not in your preferred form... This is what happens to entire planets and stars when they come too close to a black hole: they get sucked in! A black hole is basically an engine that devours and consumes large amounts of mass as it roams around the universe. It is a drain hole in space that gets larger as it sucks more stuff. In recent years, we have discovered that there are billions of black holes in the universe! more dramatically, some are supermassive: they have devoured billions and billions of stars - that's billion with a 'b'... they typically sit at the center of galaxies as the stars in the galaxy spiral into it - sort of like water flushing down the toilet... Our own galaxy has a supermassive black hole at its center and we are on our way down the drain... I'll write more about this subject in time, specially from the perspective of string theory. For now, check out this amazing video about black holes... a bit long but worth every minute:


Black Hole Destroying a Star

A very well done artist's depiction of a star being eaten alive by a black hole...


Is this the face of God?

Is this the face of God? At least this is how this image was portrayed in the media when it was announced in 2000, described by some as the greatest scientific discovery in human history. The discovery process took roughly from 1965 to 2000, until physicists were finally able to pin down the details. The story goes as follows: About 14 billion years ago, the universe was at some point a small spec of hot opaque plasma plus dark energy (see my previous post about the dark side...). Because of the dark energy, space expanded violently and the plasma cooled down. At around 100,000 years since this initial explosion, the plasma condensed and became transparent, like milk turning into water. This image is an actual real picture of that moment of condensation, the deepest in space and time we are able to look. It is simply the closest we can get to imaging the beginning of time... The colors indicate temperature of the plasma, blue for colder, red for hotter. Every tiny temperature fluctuation ends up seeding stars and galaxies in the next 14 billion years as the transparent universe continues to expand. And here we are, miserable but a bit more enlightened.


The Dark Side Of Things

In recent years, astrophysicists (who were ridiculed for decades for good reasons...) have finally pinned down the most amazing fact about the universe: the stuff we and the stars are made of and that we can see all around us is a tiny fraction of what the whole universe is really made of... about 95% of the universe is built from an unknown type of "stuff" that we cannot see. If that is not freaky enough, most of this dark stuff, about 70% of the whole mass of the universe, is something totally beyond our grasp: it antigravitates, repels... This dark stuff is everywhere around us, and because of it, the universe is undergoing a violent explosive expansion. Lots of cool stuff to write about this that we now know; for now, check out this video: a bit sensationalist, but the content is basically correct:


Billions of galaxies

One of the most profound human discoveries of recent times is a snapshot of the "edge" of the universe... In the late 1990s, the Hubble telescope took a couple of images looking deep into the dark sky, a picture of the universe when it was only 500 million years old (the full age is around 14 billion years...). The result was simply astounding. If you want to feel very very (very) insignificant, watch this great video (and ignore the corny background music...):


The M87 mega black hole


The M87 mega black hole... taken by the Hubble space telescope. This is an entire galaxy, with an obscenely huge black hole at its center, devouring the stars in it in the millions! The intense light is the scream from the stars falling into the black hole...the jet in the picture is spit out by the ongoing process ofstars being eaten alive... the length of the jet is several hundred thousand light-years... who said physics can't be violent.


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