Yesterday I wrote about how we test whether unitless constants such as alpha (α) change over the history of the universe. You might also have noticed that I said if such constants did change, then it would mean either fundamental physical constants change or there is some exotic physics going on. We looked at the physical constants yesterday, so today let’s look for exotic physics.
The Great Escape
Earlier this week I talked a bit about black holes. In particular, one of the properties of a black hole known as the event horizon. The event horizon is the point of no return for matter entering a black hole. Once you cross the event horizon, you can never escape. Not even light can escape a black hole because of the warping of space at the event horizon. Of course this means that the mass of a black hole can only increase. Over time material crosses the event horizon, and in so doing forever adds its mass to that of the black hole.
Point of No Return
If you toss a ball up into the air, it will fall back to the ground. Toss one faster, and the ball will travel higher before returning to the ground. Of course this raises the question of just how fast you would have to throw a ball for it to never fall back down. Put another way, could you throw …
Monkey in the Middle
One of the mysteries about black holes is that they only seem to come in two sizes: stellar mass black holes formed from the collapse of a star, and supermassive black holes at the centers of galaxies. The former are typically around 5 – 10 solar masses, while the latter can be millions or billions of solar masses. What we don’t see are black holes of a few hundred to several thousand solar masses, and we aren’t sure why.
Blurred Lines
One of the challenges with observing black holes is that they don’t emit light. Except for the theoretical Hawking radiation, black holes don’t radiate any light because they are simply and extreme warping of space and time. That doesn’t mean we can’t see black holes. Usually there is a great deal of material in the region around a black hole, so we can observe the light coming from this material. For example, we can observe x-rays, radio waves and visible light emitted by the heated plasma in the accretion disk. We can also see jets of material streaming away from the black hole. This tells us a great deal about black holes, but it doesn’t tell us about the specific structure of warped space and time. For that we still need to rely a lot on relativity theory.
Not So Fast
Supermassive black holes in the center of galaxies rotate at very high speeds. Typically the rotation speed of a galactic black hole is measured by looking at x-rays reflected off the accretion disk of the black hole.
Behind the Veil
Last September a planet-massed gas cloud known as G2 will made a close approach to the supermassive black hole at the center of our galaxy. At minimum distance it will pass within about 260 AU of the black hole, which is about a third as close as any other object so observed. It will be close enough that it will enter the hot accretion region of the black hole, and may provide the first observation of matter as it is absorbed by the black hole.
Down the Rabbit Hole
Black holes are interesting objects, because we know they exist but we don’t know what they are. That isn’t quite true. We know that they are formed from the gravitational collapse of matter, either as supermassive black holes in the centers of galaxies, or as stellar mass black holes from the collapse of a star. We know that they power quasars and radio galaxies, that they can form accretion disks of matter around their equators, and that they can produce powerful jets of matter when they are active. But buried within our understanding of black holes is a fundamental contradiction that we have yet to resolve.
Two of a Kind
A new paper in Nature has announced the discovery of a close binary of supermassive black holes. Known as J1502SE and J1502SW, the two black holes are estimated to have a mass of about 100 million solar masses each, and they are separated by only 450 light years. This means they orbit each other once every 4 million years. For …