Black holes and their activity are typically tracked with spectral telescopy. This is because the actions they are best known for – the destruction of matter that gets too close – have become associated with certain types of emissions in the optical to X-ray ranges.
For example, scientists at MIT picked up the radio signature corresponding to a tidal disruption flare, a term for what happens when a black hole consumes an entire star. However, these researchers also detected other types of emission linked to the same black hole. This is an exciting discovery that may indicate that the black hole also emitted energy proportional to that of the star it had ‘eaten’.
Tidal Disruption Flares
The initial signs of this black hole were detected by multiple radio telescopes worldwide in 2014. Both objects were estimated to be located 300 million light years away. The signals as recorded were deemed to be associated with a tidal disruption flare, a wash of electromagnetic energy associated with the death of the star.
This location has also become the main focus of many telescopes since, including those run by researchers at Johns Hopkins and MIT. Two of these scientists, Dheeraj Pasham and Sjoert van Velzen, have just published a second paper on subsequent emanations from the same black hole.
The new emission was a 16GHz radio signal that matched up with the 2014 emission of the flare resulting from the same tidal disruption, which was code-named ASASSN-14li. However, it was also accompanied by a burst of X-ray energy, reported to have been in the 0.3 to 1 keV range.
This X-ray emission preceded the radio transmission by approximately 13 days. Whilst both emissions had a 90% similarity, indicating that they did indeed originate from the same place - the black hole. Therefore, the two emissions may represent two different, yet connected, events or facets of the tidal disruption.
Dr. Pasham, who completed this research at the Kavli Institute for Astrophysics and Space Research within MIT, proposes that the X-ray emissions are associated with the accretion disk of the black hole, and the radio emissions with a more novel feature of the body.
It may have indicated a jet, which is a stream of particles emitted by a black hole after something falls into it. This phenomenon was predicted by Stephen Hawking in the course of his work on black holes. It suggests that not all the matter, energy or both is lost when an object passes into such a body, which were originally thought to utterly annihilate anything that came near them.
Above: A schematic of the Milky Way Galaxy showing the electromagnetic radiation emitted by technological civilizations that formed in succession. Each civilization emits radiation during a lifetime. The full circle represents a civilization that is still emitting radiation. The other three civilizations with larger outer circles started emitting radiation longer ago and have since died and ceased emitting, leaving holes in their centers. (Courtesy of Geoff Marcy, UC-B, and Claudio Grimaldi, Ecole Polytechnique Fédérale de Lausanne.)
Increasing our understanding of black hole function
In the case of this study, it could mean that a jet ensued as the result of the star’s integration into the black hole. The researchers, who also published their work in the Astrophysical Journal, also believe that the accretion disk regulates this jet. Therefore, they posit that the release of the jet is proportional to the rate at which the star is being consumed by the black hole. If this theory is backed up by more similar evidence, it could greatly enhance our understanding of black hole function.
The researchers’ new thesis is particularly important as their new observations are at odds with current models of how ASASSN-14li behaves. However, ascribing the radio emissions to a jet resolves this incompatibility. Given that radio emissions are typically associated with the movement of high-energy electrons, the 16GHz signal could be related to a jet – however, it could also be associated with external factors, such as shocks acting on the more internal parts of the black hole. Therefore, more similar events need to be identified and assessed with microscopy before its actual origin can be confirmed.
A new publication claims to document a possible jet of high-energy particles resulting from a previously-recorded black hole event. This occurrence, known as ASASSN-14li, concerns what happens when a star runs afoul of a black hole. Scientists have been able to track ASASSN-14li for nearly four years by observing its X-ray emissions through a global network of telescopes. However, the most recent emissions detected by researchers also included an additional radio signal. Two authors from MIT and Johns Hopkins have written a paper on these new findings. They propose that the radio emissions are related to the jet; furthermore, it is being released from the black hole in a manner determined by the accretion ring of the black hole. Should this new theory of tidal disruption functions be corroborated by more data, it may represent a new direction for black hole science.
Top image: Artist's impression of an inner accretion flow and a jet from a supermassive black hole when it is actively feeding, for example, from a star that it recent tore apart. Image: ESO/L. Calçada
Dheeraj RP, Sjoert van V. Discovery of a Time Lag between the Soft X-Ray and Radio Emission of the Tidal Disruption Flare ASASSN-14li: Evidence for Linear Disk–Jet Coupling. The Astrophysical Journal. 2018;856(1):1.
Chu J. Scientists detect radio echoes of a black hole feeding on a star. MIT News. 2018. Available at: http://news.mit.edu/2018/scientists-detect-radio-echoes-black-hole-feeding-star-0319