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kottke.org posts about black holes

A 20-year time lapse of stars orbiting a massive black hole

posted by Jason Kottke   Jul 31, 2018

The European Southern Observatory’s Very Large Telescope in Chile has been watching the supermassive black hole in the center of our galaxy and the stars that orbit it. Using observations from the past 20 years, the ESO made this time lapse video of the stars orbiting the black hole, which has the mass of four million suns. I’ve watched this video like 20 times today, my mind blown at being able to observe the motion of these massive objects from such a distance.

The VLT was also able to track the motion of one of these stars and confirm for the first time a prediction made by Einstein’s theory of general relativity.

New infrared observations from the exquisitely sensitive GRAVITY, SINFONI and NACO instruments on ESO’s Very Large Telescope (VLT) have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometres from the black hole and moving at a speed in excess of 25 million kilometres per hour — almost three percent of the speed of light.

S2 has the mass of about 15 suns. That’s 6.6 × 10^31 pounds moving at 3% of the speed of light. Wowowow.

How to harvest nearly infinite energy from a spinning black hole

posted by Jason Kottke   Apr 23, 2018

Well, this is a thing I didn’t know about black holes before watching this video. Because some black holes spin, it’s possible to harvest massive amounts of energy from them, even when all other energy sources in the far far future are gone. This process was first proposed by Roger Penrose in a 1971 paper.

The Penrose process (also called Penrose mechanism) is a process theorised by Roger Penrose wherein energy can be extracted from a rotating black hole. That extraction is made possible because the rotational energy of the black hole is located not inside the event horizon of the black hole, but on the outside of it in a region of the Kerr spacetime called the ergosphere, a region in which a particle is necessarily propelled in locomotive concurrence with the rotating spacetime. All objects in the ergosphere become dragged by a rotating spacetime. In the process, a lump of matter enters into the ergosphere of the black hole, and once it enters the ergosphere, it is forcibly split into two parts. For example, the matter might be made of two parts that separate by firing an explosive or rocket which pushes its halves apart. The momentum of the two pieces of matter when they separate can be arranged so that one piece escapes from the black hole (it “escapes to infinity”), whilst the other falls past the event horizon into the black hole. With careful arrangement, the escaping piece of matter can be made to have greater mass-energy than the original piece of matter, and the infalling piece has negative mass-energy.

This same effect can also be used in conjunction with a massive mirror to superradiate electromagnetic energy: you shoot light into a spinning black hole surrounded by mirrors, the light is repeatedly sped up by the ergosphere as it bounces off the mirror, and then you harvest the super-energetic light. After the significant startup costs, it’s basically an infinite source of free energy.

Black holes could delete the Universe

posted by Jason Kottke   Aug 25, 2017

In their latest video, Kurzgesagt takes a look at black holes, specifically how they deal with information. According to the currently accepted theories, one of the fundamental laws of the Universe is that information can never be lost, but black holes destroy information. This is the information paradox…so one or both of our theories must be wrong.

The paradox arose after Hawking showed, in 1974-1975, that black holes surrounded by quantum fields actually will radiate particles (“Hawking radiation”) and shrink in size (Figure 4), eventually evaporating completely. Compare with Figure 2, where the information about the two shells gets stuck inside the black hole. In Figure 4, the black hole is gone. Where did the information go? If it disappeared along with the black hole, that violates quantum theory.

Maybe the information came back out with the Hawking radiation? The problem is that the information in the black hole can’t get out. So the only way it can be in the Hawking radiation (naively) is if what is inside is copied. Having two copies of the information, one inside, one outside, also violates quantum theory.

So maybe black holes holographically encode their information on the surface?

Supermassive black holes are *really* massive

posted by Jason Kottke   Aug 19, 2015

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)

There’s a tiny black hole in my heart

posted by Jason Kottke   Feb 11, 2014

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.

Hawking backtracks on black holes

posted by Jason Kottke   Jan 27, 2014

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.

Black hole simulation

posted by Jason Kottke   Feb 11, 2010

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.

The death of the universe

posted by Ainsley Drew   Oct 09, 2009

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.

Useful black holes

posted by Jason Kottke   Oct 13, 2008

A list of 15 uses of tiny black holes, including hazardous waste disposal, cheap transport, and hanging posters without tacks.

Big black holes

posted by Jason Kottke   Sep 12, 2008

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

posted by Jason Kottke   May 23, 2007

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

posted by Jason Kottke   Oct 07, 2005

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

posted by Jason Kottke   May 10, 2005

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.”