Editor’s note: Astronomy Update is published on the third Saturday of the month, is provided by the Chippewa Valley Astronomical Society and is compiled by Lauren Likkel of the UW-Eau Claire department of physics and astronomy.
The first image of a supermassive black hole was released last week.
It is amazing, showing material surrounding the invisible black hole.
Not even light can escape from within the event horizon of a black hole, but the disk of material outside the event horizon is superheated and glows at every wavelength.
The colors in this false-color image represent the brightness of the millimeter wavelength radio waves emitted by the incredibly hot disk of gas.
This supermassive black hole is at the center of a huge active galaxy named Messier 87, located 55 million light years from Earth.
The disk is almost face-on but slightly tilted, as we expected because of a jet of glowing gas that extends toward us from the galaxy center, perpendicular to the disk.
The side of the disk moving toward us is enhanced in brightness due to relativistic beaming for particles moving near the speed of light.
The image was released by the Event Horizon Telescope project, a huge international collaboration.
To obtain the unprecedented clarity in the released image, a radio telescope would have to be almost as large as Earth itself.
The Event Horizon “Telescope” is actually a virtual telescope: it uses multiple radio telescopes together.
Individual telescopes spaced across the Earth simulate a giant telescope by using the interference of radio waves (interferometry).
Complicated computer analysis revealed the M87 black hole image by combining data recorded with seven telescopes observing the exact same sky location, at precisely the same time, at the same wavelength.
Our entire solar system would fit easily inside the dark area in the center of the image.
The size of the dark region reveals the mass of the black hole to be about 7 billion times the mass of our sun.
The central region is dark for three reasons based on general relativity.
First, no light can escape from within the event horizon, a distance determined by the black hole mass.
Next, nothing can orbit closer than 1.5 times the radius of the event horizon, although this distance is smaller for a rotating black hole.
This is because the speed needed for a stable orbit there exceeds the speed of light, and relativity tells us that nothing can travel faster than the speed of light.
And finally, the black hole bends light from the back into the black hole, so we can’t see light coming though the central area from behind.
This best-ever image of a black hole is very much like theoretically predicted simulated images.
We now have very clear evidence that supermassive black holes in galaxy centers really do exist and once again have validation of general relativity.
Lauren Likkel is a professor of physics and astronomy at UW-Eau Claire, and a member of the Chippewa Valley Astronomical Society.