Black holes from prediction to detection
On 14 September 2015, the LIGO/VIRGO instruments detected the first statistically significant signal of a gravitational wave passing through Earth, one hundred years after the publication of the theory of General Relativity. The signal was identified as originating from the merger of two stellar black holes orbiting each other. Black holes, since their theoretical conception from Albert Einstein and Karl Schwarzschild, have played an integral role both in theoretical physics and later on in astronomy and astrophysics.
Currently, black holes are thought to be important, both as probes of the most extreme regime of gravity, but also as regulators of their environments both on stellar and galactic scales. Nature journals have published key results relating to black holes, including some of the most highly cited papers in astronomy. This collection showcases the presence of black holes in scientific research over the last 50 years and the evolution of our understanding of black holes in astronomy and astrophysics.
In the Research tab, you will find a collection of some of the most important discoveries relating to black holes that were published in Nature journals. From the association of black holes to the most luminous galaxies in the Universe, to Hawking radiation, and quantum black holes, this tab offers a slice of some of the most exciting research in astronomy.
In the News, Views and Comments tab, you will find the reaction of the community to what today is considered rather commonplace knowledge. What would happen if one lowers a rope with a mass tied to its end inside a black hole? Why is the detection of gravitational waves such an important breakthrough? Click through to find more.
In the Theory and Predictions tab, you will find papers that have dealt with black holes on a theoretical level, making predictions about both the observational signatures of black holes and the properties of the black holes themselves. Despite their blackness, black holes power some of the most luminous objects in our Universe through the accretion of matter and the gravitational release of energy.
Black holes come in all sizes (and potentially shapes). In the Quantum to stellar black holes tab, we take a closer look at black holes with small masses (up to a few hundred or thousand solar masses). These can be found scattered around galaxies, the end product of stellar evolution, and even presumably in the primordial Universe, products of quantum fluctuations and extremely high-energy processes.
Milky Way and beyond takes a step back and looks at the most massive black holes we currently know. From the black hole hiding at the centre of our very own galaxy to the giant black holes found in other galaxies in our local Universe and beyond. In this tab, you will find papers about stars being destroyed by black holes, the evidence for a black hole at the centre of the Milky Way, the missing intermediate-mass black holes and even systems of binary supermassive black holes whose gravitational wave signature will eventually be observed by LISA.
The observational detection of a black hole is extremely challenging because they do not emit any detectable radiation. In 1971, Alistair Cameron investigated the binary epsilon Aurigae, concluding that the companion object of the supergiant residing in the system must be a black hole. His argumentation was based on the peculiarities observed during the eclipses of the main star by this secondary object. Stellar evolution theory precluded the possibility that the companion can be either a proto-star or a star on the Main Sequence. Image credit: NASA/JPL-Caltech
Only a few months after the initial claim, Pierre Demarque & Stephen Morris sent a correspondence to Nature to voice their disagreement with the recent results on epsilon Aurigae. The authors claim that a slightly evolved O-star could be embedded within a disk formed by mass loss from the primary supergiant. While they found the idea of a black hole intriguing, the lack of knowledge about how black holes interact with ordinary matter made them hesitant to ascribe the observational signatures in this system to such an exotic object. Recent observations of the system, however, seem to contradict the presence of a stellar black hole. It remains a puzzling object.
One of the most striking predictions made about black holes was that they actually radiate through what is now known as Hawking radiation (you can find the original paper in this collection as well). While inconsequential for currently observable black holes (of stellar or galactic origin), this process can lead to rapid mass loss and subsequent evaporation of primordial black holes of very small mass (1015 grams). In 2014, Jeff Steinhauer managed to create a charged black hole analogue by means of an atomic Bose-Einstein condensate. The author showed that self-amplifying Hawking radiation is observed from this analogue black hole, providing a confirmation of the initial prediction. Image credit: NASA
A hundred years after the publication of Einstein's seminal work on General Relativity and how mass shapes the space–time continuum around it, gravitational waves — a direct prediction of that theory — were finally detected by the LIGO/VIRGO collaboration. This was a major milestone for physics and an additional robust confirmation of General Relativity. However, the source of the gravitational waves was a surprise itself. It was a binary black hole rather than a binary neutron star that was the first such event to be detected. Krzysztof Belczynski et al. were able to explain this surprising turn of events and showed the reprecussions that this detection has on our understanding of stellar evolution theory and the rarity (or lack thereof) of binary black holes.
