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3

M87 was actually the easiest black hole for the Event Horizon Telescope (EHT) to attempt, and was thus sensibly its first target. For the EHT to work you need 1) an active BH accreting matter such that it is a strong radio source, and 2) that it be close and massive enough to be angularly large. While M87 is some 20x further away than, say M31 or M33, it ...


29

M33 does not appear to contain a supermassive black hole: in fact there's no evidence that it contains a central black hole at all. The upper limit on the mass of a central black hole based on the dynamics of the core region is a few thousand solar masses. Merritt et al. (2001) "No Supermassive Black Hole in M33?" derive an upper limit of 3000 solar masses ...


2

I think your recreation is essentially correct. For example, if you look at Figure 1 in that paper, you can see that the potential goes from positive to negative as a function of the azimuthal angle ("phase"). What you're missing is that the potential and density functions they define are perturbations, which are intended to be added to an axisymmetric ...


4

Capitalization is critical here. (As is knowing which classification system is being used.) The traditional spiral stages (going back to Hubble) are Sa - Sb - Sc; this was a sequence from more centrally concentrated (more dominant central "bulge") + smoother disk + more tightly wrapped spiral arms (Sa) to less centrally concentrated (smaller or even ...


1

The comment that the picture is an artists`s impression is strictly valid. But as more major surveys of stars are performed and analysed (Gaia in the visible, with distances but difficulties due to the thick dust in the Galactic plane, and VVV in the infrared, which allows dust penetration but distances have to be inferred) our picture of the bar becomes ...


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Even though it arised for historical reasons outlined in the other answers, the distinction between metals and non-metals as defined by astronomers does continue to make sense today. Metals are formed in stars and supernovas, whereas non-metals preexist stars. Therefore, the distinction is relevant when considering nucleosynthesis.


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Galaxies move though space independently of the orientation of their axis of rotation. That this is true can be appreciated from the fact that their direction through space is relative; that is, in the reference frame of an observer that is passing the galaxy in its plane, it is moving like a frisbee, whereas in the reference frame of an observer who is ...


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The key to understanding this is that dark matter and, effectively, stars are collisionless, whereas gas is collisional. Structure formation As written in the second quote, structure forms in a hierarchical, bottom-up fashion. That is, small halos of gas and dark matter (DM) collapse first on small scales, and these halos then merge to form larger halos. ...


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