kottke.org posts about black holes
How massive are they? The Sun is 1 solar mass and as wide as 109 Earths. Sagittarius A, the black hole at the center of the Milky Way, weighs 4.3 million solar masses and is as wide as Mercury is far from the Sun. The black hole at the center of the Phoenix Cluster is one of the largest known black holes in the Universe; it's 73 billion miles across, which is 19 times larger than our entire solar system (from the Sun to Pluto). As for how much it weighs, check this out:
I also like that if you made the Earth into a black hole, it would be the size of a peanut. (thx, reidar)
What would happen if a tiny black hole the size of a marble were placed at the center of the Earth? Rest assured, the Earth won't completely be swallowed up by the black hole but that's really the only good news to offer.
First of all, not all of the Earth would simply be sucked into the black hole. When the matter near the black hole begins to fall into the black hole, it will be compressed to a very high density that will cause it to be heated to very high temperatures. These high temperatures will cause gamma rays, X-rays, and other radiation to heat up the other matter falling in to the black hole. The net effect will be that there will be a strong outward pressure on the outer layers of the Earth that will first slow down their fall and will eventually ionize and push the outer layers away from the black hole. So some inner portion of the core will fall into the black hole, but the outer layers, including the crust and all of us, would be vaporized to a high temperature plasma and blown into space.
This would be a gigantic explosion -- a significant fraction of the rest of the mass of the Earth matter that actually fell into the black hole will be converted into energy.
FYI, that marble-sized black hole would have about the same mass as the Earth. Not that they exist, mind you. Maybe, maybe not. Blackish holes? Dark grey holes? Anyway, really heavy.
In an "only Nixon can go to China" moment in physics, Stephen Hawking now says "there are no black holes".
Most physicists foolhardy enough to write a paper claiming that "there are no black holes" -- at least not in the sense we usually imagine -- would probably be dismissed as cranks. But when the call to redefine these cosmic crunchers comes from Stephen Hawking, it's worth taking notice. In a paper posted online, the physicist, based at the University of Cambridge, UK, and one of the creators of modern black-hole theory, does away with the notion of an event horizon, the invisible boundary thought to shroud every black hole, beyond which nothing, not even light, can escape.
In its stead, Hawking's radical proposal is a much more benign "apparent horizon", which only temporarily holds matter and energy prisoner before eventually releasing them, albeit in a more garbled form.
Were you to be close to a black hole, this program shows you what you might observe.
The optical appearance of the stellar sky for an observer in the vicinity of a black hole is dominated by bending of light, frequency shift, and magnification caused by gravitational lensing and aberration. Due to the finite apperture of an observer's eye or a telescope, Fraunhofer diffraction has to be taken into account. Using todays high performance graphics hardware, we have developed a Qt application which enables the user to interactively explore the stellar sky in the vicinity of a Schwarzschild black hole. For that, we determine what an observer, who can either move quasistatically around the black hole or follow a timelike radial geodesic, would actually see.
For Linux and Windows only, although there are sample videos for non-downloaders or those on other machines.
As black holes evaporate, they release Hawking radiation. Named after the legendary Stephen, who first argued for its existence in 1974, Hawking radiation emitted is measured by the mass, angular momentum, and charge of the black hole. Hawking radiation has been predicted to be part of the eventual catalyst for the heat death of the universe, and recent findings suggest that it's possibly closer than astronomers originally calculated. Don't max out your credit cards or adopt a Twinkie diet just yet. Scientists believe that it takes roughly 10^102 years for a supermassive black hole to evaporate, and chances are that global warming, war, or Twinkies will have done in humanity long before then.
A list of 15 uses of tiny black holes, including hazardous waste disposal, cheap transport, and hanging posters without tacks.
It looks like black holes can grow to be as massive as 50 billion suns. How massive is that? It's approximately 99 duodecillion kilograms....which is a 99 followed by 39 zeros. (Put another way, if you had 99 duodecillion dollars, you could buy as many PlayStation 3s as you wanted. Blows your mind, right?)
How to survive a black hole. If you're in a rocket ship about to fall into a black hole, you might live a bit longer if you turn on your engines. "But in general a person falling past the horizon won't have zero velocity to begin with. Then the situation is different -- in fact it's worse. So firing the rocket for a short time can push the astronaut back on to the best-case scenario: the trajectory followed by free fall from rest."
Scientists want to build an array of submillimeter telescopes across the whole earth to peer "inside" the massive black hole at the center of the galaxy.
Update: Many people wrote in to correct me in saying that "submillimeter" referred to the size of the telescopes...it of course referred to the EM wavelength. Me brain not working right.
Astronomers may have detected the formation of a black hole. "A faint visible-light flash moments after a high-energy gamma-ray burst likely heralds the merger of two dense neutron stars to create a relatively low-mass black hole."