Astronomers have found a pair of black holes that are in close proximity to each other. This is a rare beast, but what makes this even more amazing is that if they are correct, these two monsters are doomed to spiral together in a matter of thousands of years.
If this is true, these black holes are the closest pair of black holes ever seen, and will merge much sooner than any other system.
We know that every big galaxy has a black hole that is millions to billions of times the mass of the Sun. Sgr A*, the black hole in the center of our Milky Way, is napping at the moment. Some of them have a lot of gas and dust in them. The material forms a disk that can be many light years across, and the matter in it gets so hot it can glow fiercely.
This motion and the spin of the black hole can cause the formation of two beams of matter and energy that blast away from the disk. The jets emit light across the entire spectrum. If one of the jets is aimed at us, or very nearly so, we see super-high-energy gamma rays from it, and we call it a blazar.
Blazars can erupt in huge flares or show quiet periods that can last for a long time. A big flare can be caused by a sharp increase in material. We think that a lot of these black holes should be in systems where they can be in close proximity to each other.
Astronomers use radio telescopes to look for changes in brightness or behavior that could indicate a second black hole.
The blazar is PKS. It is part of a list of thousands of blazars that are monitored. It stuck out from the sample due to the fact that it looked like a periodic variation in its brightness. It is difficult to say if the survey was real or not because it has only been going on for a little more than a decade.
A team of astronomer hit paydirt after digging through old observations. Observations were made at different radio observatories over a period of time. They found that the variations seen decades ago match the period of the variations seen in the more recent data.
That is pretty weird, given how chaotic blazars are. The astronomer says that the black holes are moving away from each other, and sometimes towards us. The jet gets brighter when it moves toward us because of an effect called relativistic beam.
There is an effect called relativistic beam. If you hold a light bulb in front of you, the light expands in a sphere, in all directions, but if that light bulb is moving near the speed of light, the light we see is beamed, like a flashlight, aimed into the direction it is moving. An object headed toward you at close to the speed of light appears brighter, because more of its light is focused toward you, and something moving away appears darker, because its light is focused away from you.
If the astronomer is correct, the two people will be in contact with each other every 2.1 years, because the Universe is expanding, and at a distance of 9 billion light years.
If they are at the higher end of the scale, then they would be about 0.2 light years apart. 300 billion kilometers is about 70 times the distance from the Sun to Neptune.
That is close to a black hole. The black holes are ten times farther apart than the nearest contender.
These two black holes are doomed. Einstein predicted that they would create ripples in the fabric of spacetime called gravitational waves. The two black holes drop closer together over time. As the distance between the two drops increases, the strength of the waves increases. It is possible that the two will collide in 10,000 years, causing ripples in the Universe.
It usually takes hundreds of millions of years for a merger like this to happen.
There are other effects that could be to blame for the brightness variations in PKS. The variation in the black hole jet could be caused by wobbles and changes in direction over time. The explanation of the orbital motion is simpler and more likely to be true according to the astronomer. That is an acceptable model to use until further data supports or undermines it. It might be due to something else.
This could be an example of a black hole to study. It is possible that more could be waiting for us to discover them if it is possible to find them by looking for variability. That would be a huge boon to astronomy, so I keep room for doubt, but I am hoping this blazar turns out to be one of these rare cases.
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