help

Why did the EHT Choose to Image the Black Hole in M87 Rather Than Cygnus X1?

-- Gavin | March 16, 2020

EHT image of event horizon in the central supermassive black hole of M87

Question:

I hope this isn’t a stupid question. Black hole [in M87 imaged by the EHT in 2019] is about 53 Mly away, but first discovered Cygnus X-1 is only 6,000 ly away. Why wouldn’t have that been a better chance for a more detailed picture of a black hole?

-- Gavin

Answer:

This is a very good question. Both M87 and Cygnus X1 would have been observable by the telescopes which comprise the EHT. I believe that the main reason that the EHT scientists chose to image M87 rather than Cygnus X1 is that the black hole in M87 is much more massive than that in Cygnus X1. The black hole in M87 has a mass of about 6.5 billion times the mass of our Sun, while the mass of the black hole in Cygnus X1 is about 15 times the mass of our Sun. Since the effect on the warping of space near a black hole is proportional to its mass, M87 produces a much larger gravitational effect that can be measured.

-- Jeff Mangum

The National Radio Astronomy Observatory is a facility of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
	Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.
	The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."
	AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.