On 24/08/2017 00:01, Michael Moroney wrote:
Jeff-Relf.Me @. writes:

Sagittarius A* is THOUGHT to be the location of a supermassive black hole
https://en.wikipedia.org/wiki/Sagittarius_A*

"Thought", not "known".

"Thought" to a rather high degree of certainty.

Orbits of multiple stars are tracked orbiting "something"
with a mass of about 4.1 million solar masses but a radius of less than 45 AU
(otherwise the star S14 would collide with it).

https://upload.wikimedia.org/wikiped...tre_orbits.svg

Wiki claims Sgr A has Rs ~ 1.3x10^10 M which I make to be about 80AU
(in the section on Schwarzchild radii - which is suspect is out of date)

(although the page on Sgr A itself says 4.1M sun and about 45AU)

Star S14 must be getting awfully close to grazing the event horizon.

Is it possible to see and interpret gravitational and Doppler spectral
shifts for it as well as positional measurements?

Presumably we have to wait patiently for something chunky to go down the
gravitational plughole and then we will get to find out the period of
the last stable orbit more precisely.

--
Regards,
Martin Brown