For decades, scientists have been using long-range probes and telescopes to discover and study the bodies that inhabit our galaxy and beyond. The results have sparked numerous reports on deep-space phenomena and bodies such as stars, nebulae and black holes.
The latter features have captured the imagination of many in a particular way. This is due to telemetry that portrayed black holes as massive, powerful objects capable of such things as pulling in the matter around them and perhaps turning the same into nothing.
The true strength of black holes
Black holes have become linked to impressive properties such as massive X-ray emissions, the ability to spit out what they swallow at near-light speeds and prodigious magnetic fields. These indications were the results of old measurements taken with what would be outdated detection systems by now. New studies of black holes, using modern spectroscopy, give a clearer picture of what the best-studied black holes are capable of in reality.
Unfortunately, this may put a sizeable dent in the image of black holes that humanity has built up over the years.
Studies of black holes depend on telescopy that detects radiation of the short-wave, infra-red, visible and X-ray varieties. This, in turn, requires that the black hole in question emit a ‘jet’ of particles that make it extremely bright, from the telescope’s point of view, at least. These ‘jets’ may occur when the black hole experiences an abrupt upsurge of its accretion, or the negation of the matter around it. V404 Cygni is a black hole orbited by a red giant known for its ‘jets’. For example, a particular outburst of particles made V404 Cygni the brightest object visible from Earth in 2015. This event gave astronomers and physicists around the world a chance to apply up-to-date telescopy to its study and an updated look at its properties.
This study was published in the December 2017 edition of Science magazine. Approximately 60 scientists are credited as its authors, working at astrophysics centers in the UK, US, India, Japan, Spain and Italy. It reported the results from data they collected using spectroscopy (of the wavelengths as outlined above) directed at V404 Cygni while it ‘flared’.
The analysis gave results on the rate of decay seen in the outbursts over time, how the plasma found in the black hole behaved during this process, the approximate size of the black hole, and a re-assessment of its magnetic field. V404 Cygni, which is about 40 miles in ‘diameter’, was reported to have a magnetic field of 461 ± 12 gauss, which was measured at its corona, which is a feature somewhat like that of a star’s, which is thought to be the focus of matter accretion.
This figure sounds pretty impressive. However, it is also 400 times less than the previous estimation of the same black hole’s magnetic field. This new figure also disrupts the current models of black holes, which partially explain their behavior through early observations of kilo-gauss coronal magnetic fields. Other studies on black holes have also reported that they emit X-rays with energies equivalent to at least 10,000 electron-volts. These findings may also be incompatible with the new magnetic field readings.
This data was collected through the use of installations such as the CIRCE (Canarias InfraRed Camera Experiment) infrared camera, the William Herschel telescope and the Gran Telescopio, which are located on the Canary Islands. The UK’s Arcminute Microkelvin Imager radio telescope and NASA’s extraterrestrial NuSTAR telescope were also used in this study.
Gran Telescopio Canarias. (CC BY-SA 3.0)
Their data, while possibly more accurate than previous estimations, fail to explain exactly how black holes suck in matter. However, now that coronal magnetism may be taken out of this equation, astrophysicists could move on to other features of black holes. This study also discovered more about how the plasma observed within V404 Cygni cools post-outburst, through synchotron radiation.
Time will tell
Unfortunately, the researchers behind the new study may have to wait a long time for another chance to study this particular black hole. The lead author of the study, Yigit Dalilar of the University of Florida, notes that V404 Cygni produced ‘jets’ for only a few weeks in 2015, which is the first time it had done so for 26 years. In addition, no-one knows exactly why black holes do this in the first place, although the data gathered by Dalilar and the whole team may contribute to uncovering this in the future. The same data may also inform areas of science such as nuclear physics for some time to come.
The general public understanding of black hole physics has led to idealized constructs of amazing, possibly dangerous entities that can ‘kill’ or eliminate things that get too close to them. However, improved knowledge and understanding may now diminish them slightly in the collective consciousness.
On the other hand, the new findings on V404 Cygni maintain their reputation of being huge celestial bodies with many fascinating properties. Black holes may now be seen as objects that achieve their classic attributes of matter accretion and particle jets in mysterious ways we have yet to define.
Top image: This artist’s impression shows the surroundings of a supermassive black hole, typical of that found at the heart of many galaxies. The black hole itself is surrounded by a brilliant accretion disc of very hot, infalling material and, further out, a dusty torus. There are also often high-speed jets of material ejected at the black hole’s poles that can extend huge distances into space. Observations with ALMA have detected a very strong magnetic field close to the black hole at the base of the jets and this is probably involved in jet production and collimation. (CC BY 4.0)
Dallilar Y, Eikenberry SS, Garner A, et al. A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni. Science (New York, N.Y.). 2017;358(6368):1299-1302.
UF News. How strong are black holes really?. Shorthand Social. 2017. Available at: https://social.shorthand.com/UFNews/uyeqsNATm8u/how-strong-are-black-holes-really