It is Black Hole Friday! Instead of getting lost in the darkness of of black Friday shopping madness, NASA offers us an alternative — since 2013, the day after Thanksgiving has been celebrated as a day to learn about cosmic Black holes, 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.com/…
Also, NASA TV at www.nasa.gov/… is streaming black hole content all day.
Here is a sample of the tweets and some background on black holes.
Black Hole Pairs
Using a suite of different observatories including NASA’s Chandra X-ray Observatory, the Wide-field Infrared Survey Explorer (WISE), and the ground-based Large Binocular Telescope in Arizona, researches discovered five pairs of supermassive black holes, each containing millions of times the mass of the Sun. These black hole couples formed when two galaxies collided and merged with each other, forcing their supermassive black holes close together.
Black Hole Dinner
On March 28, 2011, NASA's Swift satellite detected intense X-ray flares thought to be caused by a black hole devouring a star. In one model, illustrated here, a sun-like star on an eccentric orbit plunges too close to its galaxy's central black hole. About half of the star's mass feeds an accretion disk around the black hole, which in turn powers a particle jet and high-energy radiation.
A Star is Spaghettified — a rapidly spinning black hole ripping apart a passing star that wandered too close.
Black Holes on the Move
The following image shows a possible renegade black hole, which contains about 160 million times the mass of our Sun, and is located in an elliptical galaxy about 3.9 billion light years from Earth.
This black hole may have “recoiled,” in the terminology used by scientists, when two smaller supermassive black holes collided and merged to form an even larger one. At the same time, this collision would have generated gravitational waves that emitted more strongly in one direction than others. This newly formed black hole could have received a kick in the opposite direction of those stronger gravitational waves. This kick would have pushed the black hole out of the galaxy’s center, as depicted in the artist’s illustration.
Sagittarius A* — The Black Hole at the Center of our Galaxy
Sagittarius A* is thought to be the location of a supermassive black hole, containing the mass of 4 million Suns.
Of the estimated 100M black holes in our Milky Way galaxy, we have detected signs of only about 30 of them.
The Chandra X-ray Observatory
Many of the black holes have been discovered using the Chandra X-ray Observatory (CXO), a Flagship-class space observatory launched on STS-93 by NASA on July 23, 1999. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2017.
What are Black Holes?
A black hole is a region of space where matter has collapsed in on itself. 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.
Black Hole Event Horizon
The boundary of the region 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, forming 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.
The Event Horizon Telescope
The Event Horizon Telescope (EHT) is an international collaboration aiming to capture the first image of a black hole by creating a virtual Earth-sized radio telescope.
At present, the EHT team is processing observations from a week-long observing campaign in April 2017 that linked together eight telescopes in Hawaii, Arizona, Spain, Mexico, Chile, and the South Pole via the technique of very-long-baseline interferometry (VLBI). This global array targeted two supermassive black holes, one at the center of the Milky Way and the other in M87, a giant elliptical galaxy about 50 million light-years away in Virgo.
Results have not been shared or published yet.
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 — twitter.com/…
- NASA Twitter page — twitter.com/…
- 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/...
- A Star is Spaghettified — www.dailykos.com/…
- Galaxies and Nebulae by Hubble — www.dailykos.com/…
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The Best Black Friday 2017 Deals for Space Fans — www.space.com/… ;-)