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 …
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 …
The Gravity Tango
The image above shows two supermassive black holes orbiting each other. It is a composite image where the blue/white indicates x-rays and the pink indicates radio wavelengths. It may look like they are orbiting closely, but the black holes are about 25,000 light years apart, which is about the same distance the Sun is from the center of the Milky Way.
Yes, Virginia, There Are Black Holes
Recent headlines have proclaimed “Black Holes Don’t Exist!” They’re wrong. Black holes absolutely exist. We know this observationally. We know by the orbits of stars in the center of our galaxy that there is a supermassive black hole in its center. We know of binary black hole systems. We’ve found the infrared signatures of more than a million black holes. …
Big Bang Burger Bar
Lately there’s been news of a radical new theory proposing that the universe began from a hyper-dimensional black hole. Most of the reports seem to stem from an article posted a while back on the Nature blog, which references the original paper. So let’s have a little reality check.
Hole-y War
Yesterday I talked about black hole thermodynamics, specifically how you can write the laws of thermodynamics as laws about black holes. Central to the idea of thermodynamics is the property of entropy, which can be related to the amount of physical information a system has.