The Event Horizon Telescope (EHT) team that published the first-ever image of a black hole last year has now used its newly gained knowledge to analyze archival data from 2009 to 2013 and concluded that the shadow of the black hole has wobbled over the years. The results of the analysis have been published in the Astrophysical Journal.
Image Credit: Dotted Yeti via Shutterstock
The Event Horizon Telescope is an array of telescopes that uses a technique called Very Long Baseline Interferometry (VLBI) to form a virtual radio telescope with a dish diameter similar to the size of Earth.
In the period between 2009-2013, M87* (the supermassive black hole in the galaxy M87) was observed with prototype EHT telescopes, at four different sites. Eventually, the entire EHT array came into operation in 2017, with seven telescopes located in five locations around the Earth.
Although the observations from 2009-2013 contained much less data than those from 2017 (lacking the capacity to provide a picture of the black hole at that point in time), the EHT team was able to identify changes in the appearance of M87* between 2009 and 2017 using statistical models.
The researchers concluded that the diameter of the black hole's shadow remains consistent with the predictions of Einstein's general theory of relativity for black holes of 6.5 billion solar masses. But they also found something unexpected: the crescent-shaped ring of hot plasma around M87* wobbles! It is the first time astronomers have glimpsed the dynamic accretion structure so close to the event horizon of a black hole, where gravity is extreme.
Snapshots of the appearance of M87 *, obtained with images and geometrical models and the EHT array between 2009 and 2017. The diameter of the rings is the same, but the location of the bright side varies. - (Image Credit: M. Wielgus, D. Pesce & the EHT Collaboration)
One of the researchers, Sara Issaoun, stated in a NOVA press release that in applying the knowledge gained from the 2017 observations to older data, they discovered that the ring's size remained the same while the radiation from the gas around it changed over the years.
Professor of Theoretical High Energy Astrophysics at the University of Amsterdam, Sera Markoff, supplemented this statement by explaining that the brightness of the spot in the ring is dependant on the properties of gas surrounding the black hole, but also on its 'spin' and their relative orientations. The research team has already been able to discard several theoretical models for accretion, allowing scientists to test the laws of gravity around black holes more adequately.
If you are interested in a more detailed outlay of the study on M87*, be sure to check out the paper listed below this article. The EHT astronomers now possess a wealth of data on the dynamics of black holes. The team is currently analyzing 2018 data, which involved an additional telescope (in Greenland). In 2021, the array will be expanded even further with two additional telescopes!
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