clarification needed

[surivitna]

If it is the black hole which is present at the centre of our galaxy,how is it discovered?Black holes are discovered by its effects on other objects,right.

 

[MeteorWayne]

Welcome to Space.com!

There is a supermassive black hole at the center of the galaxy, but it and all the stars orbit the center of mass of the whole galaxy. the pull is that of gravity. However, since eveything is in orbit, nothing is heading toward the center of the galaxy, although the black hole already resides there. It's the same as the earth orbiting the center of mass of the solar system, which is currenly inside the sun. We are falling toward the sun, but moving sideways at the same speed, so we just go round and round

 

[michaelmozina]

what is at the centre of our galaxy?

http://chandra.harvard.edu/photo/2005/felines/
http://chandra.harvard.edu/photo/2005/f ... ration.jpg

This is a link to an illustration of what the core is thought to look like. As Wayne pointed out, gravity is the thing that keeps us in orbit around the core, and as he notes, most of the stuff is simply in orbit around the core, it's not necessarily going to fall into the event horizon. It should be noted that the whole thing is surrounded by an accretion disk of material that is swirling around the black hole and that material can eventually fall into the event horizon. The spinning cores and accretion disks can also also form "jets" around the poles that spew material away from the black hole at very high velocity. It's not a given that any specific particle is actually going to fall into the event horizon, even if it starts out headed toward the event horizon. The interactions with the materials around the black hole will have a great influence on where the falling body ends up. A lot of the material in that falling body could end up in a outbound jet, or get trapped in the accretion disk around the event horizon.

 

[SpeedFreek]

Here is an animation showing the positions of the central stars in our galaxy, over the decade from 1992 to 2002. The are orbiting an unseen object and their motions show that object to have a very large mass, relative to those stars.

[youtube]http://www.youtube.com/watch?v=UM4o9xft1Lw[/youtube]

 

[neilsox]

The Moon is attracted by the gravity of Earth, but it does not fall to Earth because it is orbiting fast enough for the centrifugal force to cancel the pull of gravity. In like manner, the stars of our galaxy are attracted by the gravity of the super massive black hole, but they don't fall in (with rare exceptions) because the stars are orbiting the black hole and other mass, such that the centrifugal force cancels the gravity of the super massive black hole. The arrangement is reasonably stable, such that orbit changes due to collisions and near misses rarely produce a new orbit that intersects the super massive black hole. Neil

 

[MeteorWayne]

Sorry nelisox, too many errors to let pass. There is no such thing as centrifigal force. Look it up.

"In Newtonian mechanics, the term centrifugal force is used to refer to one of two distinct concepts: an inertial force (also called a "fictitious" force) observed in a non-inertial reference frame or a reaction force corresponding to a centripetal force."

The only force involved is gravity, which curves what would otherwise be a straight path of the object into an elliptical orbit.

Second, as stated above, stars do not orbit the black hole per se, they orbit the net center of mass of the entire galaxy. The two are very closely colocated, but are not the same thing.

MW

 

[chris1996]

I do not believe that anything exists in the center of the universe. :roll:
We are actually moving away from the center at enormous speeds.

 

[surivitna]

thanks guys for your explanation.

 

[Saiph]

except, MW, that the centrifugal force is not illusory if you set up your equations in a rotating reference frame

The way neil posed the answer is technically correct, even if it can cloud the real issue of how orbits work.

 

[lionheart01]

new constelation maby found

I thing i have discovered my own constelation, or made one either i just want to ask you if you know who i can get in touch with so i can make the new constelation official and i also want to know that if i discover it then do i get to name it and the main stars that make it. Please reply as soon as possible. Thank you.

 

[MeteorWayne]

Well, you really acn't discover a new Constellation:

(from Wiki)
"The 88 official constellations defined by the IAU (International Astronomical Union) are mostly based upon those of the ancient Greek tradition, passed down through the Middle Ages, which includes the 'signs of the zodiac,' twelve constellations through which the sun passes and which thus have had special cultural significance. The rest consist of constellations which were defined in the early modern era by astronomers who studied the southern hemisphere's skies, which were invisible to the Greeks.

The constellation boundaries now used by the International Astronomical Union were drawn up in 1930 by Eugène Delporte. He drew them along vertical and horizontal lines of right ascension and declination. However, he did so for the epoch B1875.0, the era when Benjamin A. Gould made the proposal on which Delporte based his work. The consequence of this early date is that due to precession of the equinoxes, the borders on a modern star map (e.g., for epoch J2000) are already somewhat skewed and no longer perfectly vertical or horizontal. This skew will increase over the years and centuries to come.

A star pattern may be widely known but may not be used by the International Astronomical Union. One famous example is the asterism known as the Big Dipper; this term is not used by the IAU as the stars are considered part of the larger constellation of Ursa Major.

SO what you have found may be an asterism (a collection of stars in a recognizeable pattern) such as the big or little dipper, the Pleiades, or the teapot asterism in Saginttarius.

Can you give us more info on wht you found?

 

[lionheart01]

I found a small collection of starts that i believe look similar to a dog, its nothing much but i look up at the night sky and straight away i can see the image of a dog, it consists of 7 stars but if you look carefully and have a good imagination then you can easily see the image of a dog, if its not a constellation and its just an asterism then thats ok, as long as you know that its there then thats fine, i just wanted to know if it could be reconised by everyone who looks for it.

Thanks for your help anyway its been much appreciated and i thank you for your time.

 

[MeteorWayne]

I wonder if you are seeing the Pleiades, also called the Seven Sisters? Is the grouping very small? Then it might be that asterism, which is in the constellation Taurus. It's quite distnctive, really a favorite for almost anyone who looks at the Autumn sky.

Here's some information on the cluster with a close up picture:

http://en.wikipedia.org/wiki/Pleiades_(star_cluster)

Wayne

 

[lionheart01]

no i dont think that this is what im seeing and im having some trouble sending you an image of the collection of stars, if i could show you then it would give you more info, do you know how i could send you some sort of image

 

[surivitna]

If it is a black hole which is at the centre,how was it discovered?Because i read in a book that black holes are discovered only through its effects on another object?

 

[surivitna]

why is all the stars,planets,and moons in spherical shape? :?:

 

[MeteorWayne]

why is all the stars,planets,and moons in spherical shape? :?:

Actually, the answer to both your questions is the same...gravity.

Regarding the Milky Way's central black hole, we can observe the strs orbiting the MW center, and can therefore calculate the mass. When you conbine the mass with the size the object occupies, the only option is a black hole.

And gravity is what makes round stars, planets, and moons. When an object is gas, liquid, or even solid if large enough, the gravity pulls everything toward the center equally. The lowest energy state for such a situation is a globe shaped object. Smaller objects such as asteroids don't have enought gravity to overcome the strength of the rock, so retain their beat up, potato like, and angular shapes.