By Stacy Palen
In 2019, astronomers released the first image of the shadow of a black hole’s event horizon. Further processing of earlier data shows that the accretion disk has rotated.
Below are some questions to ask your students based on this article.
1). What is the black circle in the middle of the image?
Answer: This is the shadow of the event horizon. It is larger than the event horizon and shows where the light has been bent away from the line of sight and into the black hole.
2). What is the bright ring around the outside?
Answer: This is light coming from the accretion disk around the black hole. This light has been bent by the black hole’s gravity into our line of sight.
3). A series of models of the black hole are shown in the figure titled "M87* black hole appearance in 2009-2017." If the bright spot were on a clock face in 2009, it would have been at about 5:00 p.m. Where was it in 2017?
Answer: Nearly all the way around to 5:00 p.m. again, so about 6:00 p.m.
4). If this motion is periodic (that is, it repeats over and over, taking the same amount of time each time), what is the period?
Answer: 8 years.
5). How long will astronomers have to wait to find out if this motion is periodic?
Answer: At least one more period, so 8-16 years.
6). In the video and written text, the black hole is described as "sucking up light." Many astronomers object to this terminology, insisting that black holes don’t "suck in light" but that "light falls in." What distinction are astronomers trying to make?
Answer: Black holes have gravity rather than some super-strong supernatural force.