black holes

Black holes are some of the strangest and most fascinating objects found in outer space. They are objects of extreme density, with such strong gravitational attraction that even light cannot escape from their grasp if it comes near enough.

Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term "black hole" was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971.

There are three types: stellar black holes, supermassive black holes and intermediate black holes.

When a star burns through the last of its fuel, it may find itself collapsing. For smaller stars, up to about three times the sun's mass, the new core will be a neutron star or a white dwarf. But when a larger star collapses, it continues to fall in on itself to create a stellar black hole.

Black holes formed by the collapse of individual stars are (relatively) small, but incredibly dense. Such an object packs three times or more the mass of the sun into a city-size range. This leads to a crazy amount of gravitational force pulling on objects around it. Black holes consume the dust and gas from the galaxy around them, growing in size.

According the Harvard-Smithsonian Center for Astrophysics, "the Milky Way contains a few hundred million" stellar black holes.

Small black holes populate the universe, but their cousins, supermassive black holes, dominate. Supermassive black holes are millions or even billions of times as massive as the sun, but have a radius similar to that of Earth's closest star. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.

Scientists aren't certain how such large black holes spawn. Once they've formed, they can easily gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to enormous sizes.

Scientists once thought black holes came in only small and large sizes, but recent research has revealed the possibility for the existence of midsize, or intermediate, black holes (IMBHs). Such bodies could form when stars in a cluster collide in a chain reaction. Several of these forming in the same region could eventually fall together in the center of a galaxy and create a supermassive black hole.

In 2014, astronomers found what appeared to be an intermediate-mass black hole in the arm of a spiral galaxy.

"Astronomers have been looking very hard for these medium-sized black holes," co-author Tim Roberts, of the University of Durham in the United Kingdom, said in a statement.

"There have been hints that they exist, but IMBH's have been acting like a long-lost relative that isn't interested in being found."

The event horizon of a black hole marks the dark region in space where the escape velocity is higher than the speed of light. This region is typically considered the “black hole”. Nothing can escape it, both photons and matter is inevitably pulled into the singularity. The distance from the singularity to the event horizon is also known as the Schwarzschild radius.

black hole facts

• If you fell into a black hole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached singularity. But a 2012 study in Nature suggests that quantum effects would cause the event horizon to act much like a wall of fire, instantly burning anyone to death.

black hole facts

• Black holes do not "suck." Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them.

black hole facts

• If you replaced the sun with a black hole of equal mass, the Earth would not get sucked in -- it would continue orbiting the black hole as it orbits the sun, today.

black hole facts

• Black holes are the only objects in the universe that can trap light by sheer gravitational force. They’re thought to be what anchors galaxies — some of the largest objects in the universe.

black hole facts

• Astronomers estimate there are anywhere from 10 million to a billion stellar black holes, with masses roughly thrice that of the sun, in the Milky Way.

bibliography

• http://earthspacecircle.blogspot.com.au/p/sun.html
• http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k...
• hubblesite.org/explore_astronomy/black_holes/
• list25.com/25-crazy-facts-black-holes/
• www.businessinsider.com.au/what-black-holes-really-are-2014-10
• http://www.astronomysource.com/tag/event-horizon-definition/