April 09, 2019
from Space Website
shows how positrons behave near the event horizon
rotating black hole.
But what exactly is an "event
The closer someone came to a black hole, the greater the speed they would need to escape that massive gravity.
According to Einstein's theory of special relativity, nothing can travel faster through space than the speed of light. This means a black hole's event horizon is essentially the point from which nothing can return.
The name refers to the impossibility of witnessing any event taking place inside that border, the horizon beyond which one cannot see.
When an item gets near an event horizon, a witness would see the item's image redden and dim as gravity distorted light coming from that item.
At the event horizon,
this image would effectively fade to invisibility.
This means the fabric of space and time around the singularity has also curved to an infinite degree, so the laws of physics as we currently know them break down.
The size of an event horizon depends on the black hole's mass:
The supermassive black holes that the Event Horizon Telescope is observing are far larger:
The strength of a black hole's gravitational pull depends on the distance from it - the closer you are, the more powerful the tug.
But the effects of this
gravity on a visitor would differ depending on the black hole's
mass. If you fell toward a relatively small black hole a few times
the mass of the sun, for example, you would get pulled apart and
stretched out in a process known as spaghettification, dying
well before you reached the event horizon.
You would not die
of spaghettification before you crossed the event horizon
(although numerous other hazards around such a black hole might kill
you before you reached that point).
Recent findings suggest
that black holes can rotate at speeds greater than 90 percent that
of light, Loeb said.
This leads the event
horizons of rotating black holes, also known as
Kerr black holes, to appear oblong
- squashed at the poles and bulging at their equators.
(In a non-rotating black
hole, also known as a
Schwarzschild black hole, the inner
and outer horizons coincide.)
Frame dragging is
also seen around other massive bodies, including Earth.
Matter falling into the
ergosphere can get enough speed to escape the black hole's
gravitational pull, taking some of the black hole's energy with it.
In this manner, black holes can have powerful effects on their
A non-rotating black hole would convert about 5.7 percent of an in-falling object's mass into energy, following Einstein's famous equation,
In contrast, a rotating black hole could convert up to 42 percent of an object's mass into energy, scientists have determined
Recent work has greatly upset the conventional view of black holes.
In 2012, physicists suggested that anything falling toward a black hole might encounter "firewalls" at or in the vicinity of the event horizon that would incinerate any matter falling in.
This is because when
particles collide, they can become invisibly connected through a
link called entanglement, and black holes could break such links,
releasing incredible amounts of energy.
Some physicists suggest
that instead of abysses from which nothing can return, what we
currently think of as black holes may actually be a range of
black-hole-like objects that lack event horizons, such as so-called
fuzzballs, Loeb said.