# How do we know that the discovered M87 black hole isn't just a star surrounded by a dust disk?

To an untrained eye like mine, pictures of stars surrounded by dust discs look very much similar to the picture of the M87 black hole.

Here are some pictures of these dust discs:

And here is a picture of the M87 Black Hole:

I find it quite difficult to differentiate between the two in a meaningful, non-hand-wavy way. What is the scientific explanation for the distinction? I'm not doubting the scientific explanation, I just don't understand it.

• Notice how all the dust-disk images have artificial black regions in their centers -- this is where light from the central star has been blocked out, to make the disks more visible. There is no such central blocking in the M87 image. Jul 18 '20 at 13:26

In the case of M87, these measurements were first conducted in the late 1970s (Sargent et al., Young et al.). Both groups noted that the velocity dispersions near the nucleus required a central mass on the order of $$\sim5\times10^9M_{\odot}$$. Mass/luminosity ratio profiles were also calculated based on photometry, and both sets of observations noted a steep rise in $$M/L$$ near the center. Neither group was able to rule out other possible explanations, like a compact star cluster, but a supermassive black hole was - to quote Young et al. - "the most attractive of the models considered". Further observations over the last four decades have ruled out those other options.