Black Holes Supermassive stars (> 25 M☉), will collapse under a force

of gravity which is so strong that nothing can escape its pull -

not even light. They become black holes.Black Holes come in a variety of sizes, ranging from mini-

black holes with event horizons no larger than an atomic

nucleus to regular black holes with event horizons 10 - 50 km

across, to supergiant black holes with event horizons billions

of miles across (found at the core of many galaxies).

Around a Black Hole If no light can escape from a black hole, how can we “see”

them to know that they really exist??

Black holes pull in swirling clouds of gas from neighboring

stars.

These gases are moving so fast that they become very hot.

Very hot objects give off streams of X-Rays.

When astronomers see a strong X-ray source but no star is

visible at that location (using a regular light telescope), they

figure that it must be a black hole - a massively huge star that has collapsed under its own weight and

“winked out” of visibility.

Approaching a Black Hole Tidal forces are caused by gravity pulling with different degrees of force on objects which are different distances from the gravity source (Ex:: the center of the earth is 4,000 miles farther from the moon than the oceans, moon’s gravity pulls harder on the ocean, creating tides). Black holes have an incredibly huge masses packed into an incredibly tiny point called a singularity. This causes the force of gravity to skyrocket. As a result, the distance needed to create a noticeable tidal force is very small. A 6 foot tall human approaching a black hole would have much greater gravity pulling on his feet than on his head. The tidal forces would stretch him like Gumby. This would actually pull the person apart (as well as his spacecraft) as he approached the event horizon:

The Event Horizon The event horizon is the “edge” or boundary of the black hole - the “point of no return” (and no escape). All matter which passes the event horizon is trapped inside the black hole forever . If a spaceship reached this point intact, it would not be able to send signals back - the radio waves and microwaves would be pulled back by the black hole’s immense gravity. From a distance, the space- ship would appear to be permanently hovering on the event horizon. Once inside the event horizon, all matter is shredded and compressed down to a single point called the singularity. Beyond Black Holes... What if somebody could actually survive entering a black hole? The black hole could become a wormhole, a passageway meandering across space/time and connecting with a black hole in another universe (and possibly with another time as in “Bill & Ted’s Excellent Adventure” and “Contact”). Another possibility is a white hole, spewing out cosmic debris in another corner of the universe. These odd features are all mathematically possible, but may not actually exist. Black holes, on the” other hand, do exist and are quite common throughout the universe.

Black Hole with accretion disk (flat disk) and plasma jet (vertical funnel-shaped structure)