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Observations of nature tend to throw up unexpected results and new mysteries – whether you're investigating the rain forest or outer space. When radio astronomy took off in the 1950s, we had no idea that it would be possible for us to have galaxies such as our own terrifyingly wide black holes at their center – millions to billions of times the mass of the sun.
A few decades later, we are still able to prove that these beasts – dubbed supermassive black holes – actually exist. But our new research, published in the Monthly Notices of the Royal Astronomical Society.
Early radio astronomers discovered that some galaxies emit radio waves (a type of electromagnetic radiation). They knew that galaxies sometimes collide and merge, and naturally wondered about this phenomenon. Better observations, however, rewrite this idea over the years.
They also discovered that radio waves were emitted as narrow jets, meaning that the power came from a tiny region in the nucleus. The radio power was so huge – often surpassing the luminosity of the stars in the galaxy taken together. Various suggestions were made to such a huge amount of energy that could be produced, and it was in the 1970s that scientists finally proposed that a supermassive black hole could be the culprit. The objects are nowadays known as quasars.
Theoretical models estimated that these objects would have a mass of an average size comparable to Earth's orbit around the sun. But because only some galaxies produce energetic outbursts, it was unclear how common supermassive black holes would be. With the advent of the Hubble Space Telescope in 1990, the centers of nearby galaxies that did not emit radio bursts could finally be investigated. Did they contain supermassive black holes too?
It turned out that many did – astronomers saw signs of gravitating masses influencing the matter around it without emitting any light. Even the Milky Way has been shown to be a supermassive black hole at the center, now known as Sgr A *. At this point, astronomers have become aware that supermassive black holes were a reality and could plausibly explain the extreme energetic outbursts of some galaxies.
However, there is no definitive proof yet. That is despite the fact that some supermassive black holes emit jets – these come from the inside of the black hole rather than the black hole itself. So how do you prove the existence of something completely dark? A black hole as defined by Einstein's theory of general relativity is a region of space bounded by a horizon – a surface from which no light or material object can ever escape. So, it's a pretty difficult task for astronomers: they need to see something that emits nothing.
For smaller black holes, the size of a stellar mass, a proof of the fact that they have a great deal of merge, they emit gravitational waves, a tiny wobbling of space that was first recorded in 2015. , that they sometimes form peers and that they are indeed merge. This was a tremendous success, honored with the Nobel prize in 2017.
We also have a good understanding of where we have grown up. But both the existence and the origin of supermassive black holes are shrouded in mystery.
Spinning black holes
We have found many indications that many of the radio jets produced by supermassive black holes may be the result of these objects, orbiting each other. We did this by comparing the maps of our regions with our computer models.
The presence of a second black hole would make the jets produced by the first one change direction. We realized that the cyclic change in the direction of the galaxy center.
Lobes are created by the jets depositing energy to surrounding particles. Author provided
We found evidence of such a pattern in about 75% of our sample of "radio galaxies" (galaxies that emit radio waves), suggesting that supermassive black hole is the rule, not the exception. Such peers are actually expected to form after galaxies merge. Each galaxy contains a supermassive black hole, and they are heavier than the individual stars, they sink to the center of the newly formed galaxy where they first form a close pair and then merge under emission of gravitational waves.
Whereas it is important to know for the existence of supermassive black holes, it is not a proof. What we observe are still the effects that the black holes somehow cause indirectly. Just like with normal black holes, a full proof of the existence of supermassive black hole peers requires detection of gravitational waves emitted by them.
Current gravitational wave telescopes can only detect gravitational waves from stellar mass black holes. The reason is that they orbit one another much faster, which leads to the production of higher gravitational waves that we can detect. The next generation of instruments will be able to be able to register low frequency gravitational waves as well – potentially from supermassive black hole pairs. This would finally prove their existence – half a century after they were first proposed. It's an exciting time to be a scientist.
This article is republished from the Creative Commons license. Read the original article.
<p class = "canvas-atom-canvas-text Mb (1.0em) Mb (0) – sm Mt (0.8em) – sm" type = "text" content = "Martin Krause receives funding from Deutsche Forschungsgemeinschaft (DFG), Excellence Cluster Universe (Garching, Germany), European Science Foundation, Australian Research Council, International Space Science Institute (Bern, Switzerland), Ernst-Rudolf-Schloeßmann Stiftung (Max-Planck Society, Germany). "data-reactid =" 102 ">Martin Krause receives funding from Deutsche Forschungsgemeinschaft (DFG), Excellence Cluster Universe (Garching, Germany), European Science Foundation, Australian Research Council, International Space Science Institute (Bern, Switzerland), Ernst-Rudolf-Schloeßmann Stiftung (Max-Planck Society, Germany).
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