Sagittarius A*


by shounakbhatta
Tags: sagittarius
shounakbhatta
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#1
Dec17-12, 06:16 AM
P: 268
Hello,

Reading through internet I came across that Sagittarius A*, located at the center of our galaxy, is the location of super massive black hole. On the other hand, Sagittarius A is located at the Sagittarius constellation.

Where is the link?

Thanks,

-- Shounak
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D H
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#2
Dec17-12, 10:06 AM
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Constellations are collections of stars and other objects that are at more or less the same inclination and declination. Distance is not a part of the equation. Example: The Andromeda galaxy lies within the Andromeda constellation. The only connection between that galaxy and the stars in our galaxy that comprise the constellation is that all of those objects lie in the same patch of sky from our Earthly perspective.

Similarly, the only connection between Sagittarius A and the stars that comprise the Sagittarius constellation is direction from our Earthly perspective. There is a connection between Sagittarius A and Sagittarius A*. All three features that comprise Sagittarius A, Sagittarius A East, Sagittarius A West, and Sagittarius A*, lie at the center of the galaxy.
P_I
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#3
Dec17-12, 11:24 AM
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Like when I drive my car around and around a tree, the tree might be said to be located in a certain window of my car, just becasue that's where I always see it. But in fact, it's nowhere near my window at all.

shounakbhatta
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#4
Dec17-12, 12:47 PM
P: 268

Sagittarius A*


Ok. Thanks for all the help. Sagittarius A* contains the super massive black holes right?

-- Shounak
shounakbhatta
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#5
Dec17-12, 12:53 PM
P: 268
One more thing. Galaxy is the super set and within that comes the stars right? So any galaxy G, should have constellations within G, right?
Drakkith
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#6
Dec17-12, 03:41 PM
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Quote Quote by shounakbhatta View Post
One more thing. Galaxy is the super set and within that comes the stars right? So any galaxy G, should have constellations within G, right?
A galaxy is made up of stars, gas, dust, and other material. I don't understand your question about the constellations however. The constellations are purely random patterns formed by the stars in the sky. If we move about a hundred or so light years in any direction practically all the constellations will no longer be the same.
P_I
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#7
Dec17-12, 04:11 PM
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Shounakbhatta, you've piqued my curiosity with Saggitarius A*, I had no idea what it was till now, thanks. And the info I found says that teh black hole at the centre of our galaxy is just located pretty much where Saggitarius A* is.
davenn
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#8
Dec17-12, 07:29 PM
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you need to realise than when you look in the direction of Saggitarius, you are actually looking towards the centre of our galaxy.

that is the link :)

We cannot optically "see" the centre of our galaxy from our location, as there is too much intervening dust and gas etc. but using infra-red scopes and radio telescopes we can "see" deep into that region

Dave
shounakbhatta
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#9
Dec17-12, 10:51 PM
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Hello P_I,

Sagittarius A*(Sgr A*) is the seat for a super massive black hole and it is at the heart of our Galaxy, the Milky Way. If I am not wrong, on October '2012, Sgr A* erupted. Source 2, S2 is the star, closest to Sgr A* and have been seen changing position, which gives the proof of the existence of a super massive black hole.
Astrofan
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#10
Jan6-13, 07:06 PM
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Quote Quote by shounakbhatta View Post
Hello P_I,

Sagittarius A*(Sgr A*) is the seat for a super massive black hole and it is at the heart of our Galaxy, the Milky Way. If I am not wrong, on October '2012, Sgr A* erupted. Source 2, S2 is the star, closest to Sgr A* and have been seen changing position, which gives the proof of the existence of a super massive black hole.
Hello shounakbhatta,

The stellar motion of multiple stars around the ''center Black Hole" of our galaxy has been tracked for quite some time now (more than 10 years); a list is on the wiki site http://en.wikipedia.org/wiki/Sagittarius_A*. As an afternote, in the current day, we in this field consider that every galaxy hosts a super massive black hole (SMBH) at its center.
But concerning the statement you used
Quote Quote by shounakbhatta View Post
which gives the proof of the existence of a super massive black hole.
Currently this is considered only as an indirect proof of a very massive object there with mass compatible of being a SMBH, however, a 'proof' of a black hole relies on the actual imaging of the black holes event horizon, which is an ongoing project for both Sgr A* and M87 (an elliptical galaxy with a black hole >100 times more massive than in our galaxy)
shounakbhatta
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#11
Jan7-13, 06:23 AM
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Hello Astrofan,

Thank you very much for informing. Does that mean, a BH or a SMBH has not actually been SIGHTED as yet?
Astrofan
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#12
Jan7-13, 07:31 AM
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Quote Quote by shounakbhatta View Post
Hello Astrofan,

Thank you very much for informing. Does that mean, a BH or a SMBH has not actually been SIGHTED as yet?
As far as i know it, there is to this day no direct sighting of a BH/SMBH yet.

They are getting close though, refer to this article for a bit of info: (but don't take the whole thing too seriously, lots of it is still uncertain)
http://www.sciencemag.org/content/ea...itversion=true
shounakbhatta
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#13
Jan7-13, 10:47 AM
P: 268
Hello Astrofan,

Thank you for the reply. Yes, I also think in that way. We haven't viewed BH or SMBH, we are just speculating.....
D H
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#14
Jan7-13, 11:32 AM
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Quote Quote by shounakbhatta View Post
We haven't viewed BH or SMBH, we are just speculating.....
Nonsense. Think of what you said along the lines of "we haven't viewed the iron core at the center of the Earth, we are just speculating."

We will *never* see the black hole at the center of the galaxy; it's black. Everything we can see, including huge velocities of stars at periapsis, an accretion disc, infalling material, gravitational lensing, etc. is indirect. That does not mean it's speculation. There is surprisingly little stuff that we can "see" directly.
shounakbhatta
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#15
Jan7-13, 12:19 PM
P: 268
Right, thanks.


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