Today is Black Hole Friday! Instead of getting lost in the darkness of Black Friday shopping, join NASA and researchers in celebrating Black Hole Friday. Since 2013, the day after Thanksgiving has been celebrated by NASA as a day to learn about Black holes, the singularities in space, so incredibly dense that nothing nothing can escape the clutches of their gravity, not even light. It is a celebration guaranteed to excite our brain cells without lightening up our wallets. Also, to tickle our funny bone :-)
Throughout the day, NASA and researchers from around the world, will be posting images, articles and humor about black holes. Look for #BlackHoleFriday on twitter.
Here is a sample of the tweets, artistic images and some background on black holes.
A Short Primer on Black Holes
A black hole is a region of space where matter has collapsed in on itself, due to the force of gravity. This collapse results in a huge amount of mass being concentrated in an extremely small volume. The gravitational pull of this region is so great that nothing can escape – not even light.
As a star ages, its nuclear fusion reactions stop because the fuel for these reactions gets depleted. At the same time, the star's gravity pulls material inward and compresses the core. As the core compresses, it heats up and eventually creates a supernova explosion in which the outer layers of material and radiation blasts out into space. What remains is the highly compressed and extremely massive core.
After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.
The observable universe is estimated to contain 1019 black holes. hubblesite.org/...
Black holes come in various sizes and need not be super massive -
Note that the smallest black hole that can be formed by natural processes at the current stage of the universe has over twice the mass of the Sun.
Check out the video below and the one at www.pbs.org/… called Black Hole Apocalypse.
Follow the twitter chain below for another concise description of Black Holes.
Black Hole Event Horizon
The boundary of the region around a black hole from which no escape is possible is called the event horizon. Particles, including photons, that pass through the event horizon are swallowed by the black hole. Inside the event horizon, all "events" (points in space-time) stop, and nothing (not even light) can escape. Our current theories of physics do not apply inside a black hole.
The radius of the event horizon is called the Schwarzschild radius, named after astronomer Karl Schwarzschild, whose work led to the theory of black holes. The Schwarzschild radius = 2GM/c2, where G is the gravitational constant, M is the object mass and c is the speed of light.
Types of Black Holes
There are two types of black holes:
- Schwarzschild - Non-rotating black hole
- Kerr - Rotating black hole
Black Hole Observation
Blacks holes cannot be directly observed since they do not generate or reflect electromagnetic radiation. The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter that falls onto a black hole can form an external accretion disk heated by friction, from which the jets – ultra-powerful beams of energy – are shot out into space, perpendicular to the plane of the disk, creating some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location.
A black hole, due to its massive gravity, creates the gravitational lens effect, which bends electromagnetic waves, including light, from other celestial objects that pass near the black hole. The following gif shows an animated simulation of gravitational lensing caused by a Schwarzschild black hole going past a galaxy in the background. A secondary image of the galaxy can be seen within the black hole Einstein ring on the opposite direction of that of the galaxy. The secondary image grows (remaining within the Einstein ring) as the primary image approaches the black hole.
Does Nothing Escape a Black Hole?
Hawking radiation is blackbody radiation that is predicted to be released by black holes, due to quantum effects near the event horizon. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974.
An explanation of the process is that vacuum fluctuations cause a particle–antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole while the other escapes. In order to preserve total energy, the particle that fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). This causes the black hole to lose mass, and, to an outside observer, it would appear that the black hole has just emitted a particle. In another model, the process is a quantum tunnelling effect, whereby particle–antiparticle pairs will form from the vacuum, and one will tunnel outside the event horizon.
Rotating black holes can lose energy as described by the Penrose process; the black hole loses some of its angular momentum in the process. The energy loss is made possible because the rotational energy of the black hole is located not inside the event horizon, but on the outside of it in the ergosphere, in which a particle is propelled with the rotating spacetime. See en.wikipedia.org/… for details.
Closing Remarks
The Universe is a marvelous place. There is so much we do not understand yet, there is so much more to explore. Understanding the Universe, finding our place in it and searching for life is our destiny, not flipping hamburgers, driving delivery trucks or digging for coal.
There is a lot of fascinating information on black holes and other exotic celestial objects; I recommend browsing through some of the references, searching for other articles and watching some of the excellent videos on YouTube. The movie Interstellar is worth a watch too.
For today, let’s share our knowledge and humor on the subject of Black Holes.
References
- #BlackHoleFriday
- NASA Black Hole page — www.nasa.gov/…
- Black hole wiki — en.wikipedia.org/...
- How Black Holes Work - science.howstuffworks.com/…
- Hawking Radiation — en.wikipedia.org/…
- Black Hole Apocalypse — www.pbs.org/…
- A Star is Spaghettified — www.dailykos.com/…
- Galaxies and Nebulae by Hubble — www.dailykos.com/…
- Astronomy Roundup - We are made of Star-Stuff — www.dailykos.com/...