Why does Sag A* exist?

[llivinglarge]

If it isn't the super-massive black hole, why do we associate it with it (specifically, the event horizon)?

 

[thespeculator]

This should tell you about it.<br />http://heasarc.nasa.gov/docs/objects/galaxies/sag-a_star.html<br /><br /><br />The event horizon on a black hole is the distance from the center of its mass where gravitational pull overpowers and pulls in light... Or it could also be distroying the light waves at that distance instead. I'm not entirely sure which it does.<br /> <br /><br />EDIT:Whoops. I'm sorry I think I misread your question. I thought Sag A* was a black hole...? Did I miss something?

 

[CalliArcale]

Sag A* is a powerful radio source, now believed to be a supermassive black hole. The radio waves are emissions from its accretion disk.<br /><br />The event horizon of a black hole is the average altitude above the center at which escape velocity is exactly c (light speed). You can actually orbit closer than that without being sucked in, but you will never escape that orbit. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[Saiph]

Sag A is, I believe, a black hole, not a "supermassive" black hole. The difference is really only in scale. Stellar sized BH's are on sizes about those of stars, from about the mass of the sun, to a 100x greater.<br /><br />Calli: Actually, you can't have a stable orbit inside the event horizon...all the space-time paths lead to the singularity. Screwy, but true. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[phobophile]

Light can theoreticly be trapped in an orbit about the singularity as calliarcale said if it's at the right position around the black hole itself. This is called the photon sphere and it occurs at 1.5 of the swartzchild radii from the black holes singularity "center."<br /><br /><br />

 

[Saiph]

well, at 1.5x the swartzchild radius (probably misspelled there) that's outside the event horizon, not inside it as calli said.<br /><br />But, that is a neat fact I'd entirely forgotten about. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>