Scientists can't directly observe black holes with telescopes that detect x-rays, light, or other forms of electromagnetic radiation. We can, however, infer the presence of black holes and study them by detecting their effect on other matter nearby.
By detecting the gravitational ripples when they collide.
We can also detect black holes by detecting the ripples in space-time created when two of them crash into each other. From that signal, we can tell how massive the black holes were, how far away they were, and how fast they were traveling when they collided.
Black holes have gravitational fields so strong that even light cannot escape, so they are defined by the shell of a black, featureless sphere called an event horizon. But the holes can nevertheless be seen.
Eventually, in theory, black holes will evaporate through Hawking radiation. But it would take much longer than the entire age of the universe for most black holes we know about to significantly evaporate.
Black holes are, by far, the most mysterious objects in the universe. They are objects in the cosmos where all of our knowledge of physics completely breaks down. And yet, despite their apparent impossibility, they exist.
This poses a tricky problem for scientists, whose instruments typically rely on light-whether it is visible light, radio waves, X-rays or infrared-to observe objects in space. Astronomers currently spot black holes by detecting the high-energy radiation emitted by swirling matter falling into them.
The Sun would need to be about 20 times more massive to end its life as a black hole. Stars that are born this size or larger can explode into a supernova at the end of their lifetimes before collapsing back into a black hole, an object with a gravitational pull so strong that nothing, not even light, can escape.
No supernova, no black hole
Our sun isn't massive enough to trigger a stellar explosion, called a supernova, when it dies, and it will never become a black hole either. In order to create a supernova, a star needs about 10 times the mass of our sun.
Contrary to popular belief, the Solar System would not be sucked in: a solar-mass black hole would exert no more gravitational pull than our Sun. As this computer simulation shows, the planets would actually continue on in their orbits as if nothing had happened.
After just a few minutes more — 21 to 22 minutes total — the entire mass of the Earth would have collapsed into a black hole just 1.75 centimeters (0.69”) in diameter: the inevitable result of an Earth's mass worth of material collapsing into a black hole. When matter collapses, it can inevitably form a black hole.
Black holes are so massive that they severely warp the fabric of spacetime (the three spatial dimensions and time combined in a four-dimensional continuum). For this reason, an observer inside a black hole experiences the passage of time much differently than an outside observer.
Black holes sound like objects from a science fiction story. These objects are dark, dense regions in the universe, and their gravitational pull is so strong that nothing can escape them—not even light! This is why black holes are so black: without light, we cannot see them.
Around a black hole, the distortion of spacetime is extreme. At the event horizon of a black hole, the spacetime curves into itself and as a result, light cannot escape from a black hole.
A black hole is a region where spacetime is so curved that every possible path which light could take eventually curves and leads back inside the black hole. As a result, once a ray of light enters a black hole, it can never exit. For this reason, a black hole is truly black and never emits light.
Scientists have discovered the only space object – a lone star, that has managed to escape the force of a supermassive black hole. This is unique because the gravitational pull in a black hole is supposed to be so strong that nothing can escape from it, not even light.
Dark energy can escape a black hole, no matter what size the black hole is and no matter how close the dark energy is to the center of the black hole. This is because dark energy is not affected by gravity at all.
It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The telescope is named after the “event horizon”, the boundary of the black hole beyond which no light can escape.
Black holes, even the one at the center of our galaxy, are very small. Only if you get very close to a black hole's event horizon does it start pulling everything in. So no, most of the galaxy will not eventually fall into the hole. Whether black holes have empty space around them or not depends on their environment.
In fact, recent estimates put dark matter as five times more common than regular matter in our universe. But because dark matter does not interact electromagnetically, we can't touch it, see it, or manipulate it using conventional means. You could, in principle, manipulate dark matter using gravitational forces.
One hour for a black hole observer would equate to 100,000,000 years for a person on Earth. Therefore one minute in a black hole would be roughly 1,700,000 years.
Time travel is possible – theoretically, for elementary particles with an accelerator one billion kilometres long. Teleportation and travelling forwards through time may be possible through wormholes, the bipolar black holes that link different regions of the universe.
Over time they shrink down to nothing and simply pop away in a flash of energy. It's not exactly fast. A good size black hole — say, a few times more massive than the sun — will take about 10^100 years to eventually evaporate through this process, known as Hawking Radiation.
It is possible for two black holes to collide. Once they come so close that they cannot escape each other's gravity, they will merge to become one bigger black hole. Such an event would be extremely violent.
Despite their abundance, there is no reason to panic: black holes will not devour Earth nor the Universe. It is incredibly unlikely that Earth would ever fall into a black hole. This is because, at a distance, their gravitational pull is no more compelling than a star of the same mass.
Scientists have debunked this perception. Earth is facing no threat because no black hole is close enough to the solar system for our planet. According to NASA, even if a black hole the same mass as the sun replace the sun, Earth still would not fall in.