There is still much debate about black hole singularities, even though it’s pretty clear black holes exist.
Little Bang
In the center of our galaxy there is a supermassive black hole known as Sgr A*. Through observations of stars orbiting the black hole, we know it has a mass of about 4 million Suns. Normally this black hole is pretty quiet, but in 2013 there was an unexpected x-ray burst.
Matter of Scale
One of the fascinating things about black holes is their scale. In principle, black holes are determined by density. If matter reaches a critical density, then it will collapse under its own weight. It’s a collapse nothing can prevent, not even the strongest repulsive forces in the nucleus of an atom.
When You’re a Jet
The evidence for black holes often seems confusing to the general public. On the one hand scientists say that a black hole is an object of such great density that not even light can escape it. This leads to the question of how we can observe such a thing if it doesn’t emit light? The answer scientists give is that black holes are a source of intense energy, driving things such as quasars and galactic jets. This apparent contradiction has led some people to reject that there is any evidence for black holes at all. Supporters of the electric universe models go even further, and claim that things like quasars and jets are due to pinched electric currents or similar phenomena. But in fact a black hole being both dark and bright isn’t contradictory.
Weft and Warp
Gravitational lensing is a well-known effect where the mass of an object such as a galaxy deflects the light from more distant objects. It was first observed by Arthur Eddington in 1916, and affects the observed position stars. With distant quasars it can produce an effect known as an Einstein cross. Even dark matter can gravitationally lens distant objects, which is one of the ways we know of its existence. But where gravitational lensing would be the strongest is in the vicinity of a black hole.
Recoil Effect
Most galaxies have a supermassive black hole in their centers, but some don’t. The Triangulum galaxy (also known as M33) doesn’t have one, despite being a pretty standard looking spiral galaxy. The general thought is that such galaxies did have a supermassive black hole at one time, but it was ejected by some mechanism. One mechanism is through collisions with …
Black Hole Sun
We know that supermassive black holes exist in the center of most galaxies, and they can become quite massive (upwards of billions of solar masses). What we aren’t sure about is just how they come to be.
Sphere of Influence
Suppose you were to flash a light where you are at this moment. The light would speed away from you at about 300,000 kilometers per second, which is known as the speed of light. In general you could point the light in any direction, so flash of light would in general be an expanding sphere of light.
Hungry Hungry Hippo
In an earlier post I talked about ultraluminous x-ray sources, and how they are typically powered by stellar-mass black holes. The source of these intense x-rays is the superheated material surrounding the black hole. By observing the intensity of the x-rays, we can get a handle on just how much mass a black hole is actively accumulating. The x-ray intensity has …