Center of Our Galaxy - Nebula Orbits & Questions

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In summary, the center of our galaxy is a supermassive black hole called "Sagittarius A*" or "Sgr A*". It is not dead, but has flared up and swallowed stars in the past. Dark matter and energy are not located in the center of our galaxy, but are believed to be spread throughout the universe. Time does not require light and exists within black holes, but light cannot escape the event horizon of a black hole.
  • #1
doc.madani
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I was wondering what is at the center of our galaxy? could it possibly be large amounts of nebula's in which we are orbiting around?
 
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  • #2
doc.madani said:
I was wondering what is at the center of our galaxy? could it possibly be large amounts of nebula's in which we are orbiting around?

It's a supermassive black hole.
 
  • #3
Glennage said:
It's a supermassive black hole.

can black holes absorb other black holes?
 
  • #4
doc.madani said:
can black holes absorb other black holes?

Yes, they gain more mass, therefore it's event horizon(area of influence) would increase.
 
  • #5
does time exist in black holes?
 
  • #6
Yes I think it does, but say you have a "clock" outside a black hole, it would be ticking normally, at normal speed, but as you fell into a black hole, time would appear to go slower. But I believe time would "stop" at the event horizon..Not 100% sure but that's what I remember anyways. Trying to keep it simple for you.
 
  • #7
doc.madani said:
does time exist in black holes?

If you jump in, time exists at least as long as you do.

for someone outside, events that might happen inside a black hole do not happen at any time outside. I think that means that time doesn't exist in a black hole for someone outside.
 
  • #8
Glennage said:
It's a supermassive black hole.

And here are some pictures. We can't see the center of the Milky Way in visible light, but it can be observed in other frequencies. Here's a famous 2003 X-ray image from the Chandra space telescope. (reference link). The black hole itself is "Sagittarius A*" or "Sgr A*".
0203long_xray_label.jpg


See also this Chandra image from 2007, showing light echos from when the black hole was thought to have consumed a mass about the size of the planet Mercury.

A nice summary of evidence that the whole galaxy is pretty much orbiting this thing can be found in Is there a Supermassive Black Hole at the Center of the Milky Way?, by Mark Reid, in Int. J. Mod. Phys. D18:889-910, 2009, doi:10.1142/S0218271809014820, arXiv:0808.2624v1 [astro-ph]

Felicitations -- sylas
 
  • #9
I assume that the Black Hole in our galaxy is 'dead', I mean, it had already consumed all the nearby stars. So it does not work as quasar and does not generate jets.

But what happens when it 'swallows' a star? From time to time there must be stars flying too close? And how often does that happen?
 
  • #10
i was reading some articles and found that the centre of our galaxy is made up of dark matter and dark energy,, and these dark matter and dark energy is what keeps our galaxy together,, through its enormous gravitation.. what are these dark matter and energy?

another thing,, does time require light?? in which light is the only constant in our universe therefore time can only be calculated through measuring and recording light??
so.. light does not exist in black holes therefore time wouldn't exist too?
 
  • #11
Two responses in one...

Dmitry67 said:
I assume that the Black Hole in our galaxy is 'dead', I mean, it had already consumed all the nearby stars. So it does not work as quasar and does not generate jets.

But what happens when it 'swallows' a star? From time to time there must be stars flying too close? And how often does that happen?

Our black hole is not dead; just comparatively quiet when compared with what is seen in some galaxies. It has flared up a number of times; though what we see is radiation from material falling towards the horizon, not material from the hole itself. It is a very strong source of X-rays. I gave a link previously (here it is again) for light echos which are from major outbursts quite recently; and here is a report of a major outbust 300 years ago.

When we say a certain number of years ago, this actually means how long ago the outburst would have been seen at Earth, and then it would be another 26,000 years earlier still to the outburst itself. What we see now are echos of older outbusts.

We've also seen some flares directly quite recently. See Milky Way's Black Hole Sending Out Flares at UniverseToday (18 Nov 2008). A star falling into the hole would give a very large flare. According to this article at space today, such an event should occur about once every million years or so, although for a neutron star or a smaller black hole. That is quite often, on the time scales of a galaxy; not often enough for astronomers to expect to see it.

However, we can see such events in other galaxies. A possible such flare up is reported in New Scientist: Black hole seen devouring star in best detail yet (New Scientist 7 December 2006). This article suggests that a quiet black hole might swallow a star every 10,000 years or so.

doc.madani said:
i was reading some articles and found that the centre of our galaxy is made up of dark matter and dark energy,, and these dark matter and dark energy is what keeps our galaxy together,, through its enormous gravitation.. what are these dark matter and energy?

I think you have mixed up your article. Dark matter is believed to be an important part of our galaxy, but not in the center. It is thought to be associated as a large "halo" around the entire galaxy. Dark energy is not a part of the galaxy, but something hypothesized to be spread throughout all the space of the universe, and tends to accelerate cosmological expansion.

another thing,, does time require light?? in which light is the only constant in our universe therefore time can only be calculated through measuring and recording light??
so.. light does not exist in black holes therefore time wouldn't exist too?

No. Light is not the only constant (though what you might mean by that is very unclear). Light does exist within a black hole, in the sense that photons have no trouble passing across the boundary of the hole after which they proceed rapidly to the central singularity. Light can't get out of the hole, but that is a different question.
 
  • #12
why does our galaxy become more denser and greater in diameter towards the centre?

can it be due to inactive black holes? or are there clumps of massive neutron stars
 
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  • #13
sylas, thank you for such detailed answer! I am checking the links.
 
  • #14
what is our universe expanding into? if we are expanding into nothing,,, what is the definition of nothing?
 
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  • #15
doc.madani said:
what is our universe expanding into? if we are expanding into nothing,,, what is the definition of nothing?

It is not expanding into anything. It is not expanding into nothing. There is no "into". It is just expanding. It means over time, there's more space between things.
 
  • #16
hmmm yes,, but i still don't understand how the universe is expanding,, hard to explain,, if we were to travel to the edge of the universe what would we see on the other side?
 
  • #17
doc.madani said:
hmmm yes,, but i still don't understand how the universe is expanding,, hard to explain,, if we were to travel to the edge of the universe what would we see on the other side?

There is no edge to the universe, as far as we know. There's no reason to think there is an edge.
 
  • #19
oh, does expanding of the universe simply mean the increase in space between other matter? if so, if we continue to expand at this rate, can the universe collapse on its self?
 
  • #20
How does expanding imply collapse?
 
  • #21
russ_watters said:
How does expanding imply collapse?

You misunderstand the question.

doc.madani said:
oh, does expanding of the universe simply mean the increase in space between other matter? if so, if we continue to expand at this rate, can the universe collapse on its self?

Yes, the expansion means that distances between objects increase with time. Whether the expansion will cease and reverse depends on the matter density in the Universe. You might be interested in the Swinburne Astronomy Online Encyclopedia entry on the http://astronomy.swin.edu.au/cosmos/D/Density+Parameter". Presently, we think there is far too little matter in the Universe to reverse the expansion and the Universe will continue to expand. In fact, as has been previously pointed out, the rate of expansion is currently accelerating.
 
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  • #22
^^ thanks for the links checking them out now
 
  • #23
No worries. The Swinburne Astronomy Online Cosmos Encyclopedia is written by professional astronomers and there are many more useful articles than the ones I linked to!
 
  • #24
A little to special relativity, if one spaceship traveling at 0.9c north passes another spaceship traveling at 0.9c south,, wouldn't the ship traveling north see the spaceship traveling south to be traveling at 1.8c,, but that's impossible.. how did Einstein explain this theory?
 
  • #25
doc.madani said:
A little to special relativity, if one spaceship traveling at 0.9c north passes another spaceship traveling at 0.9c south,, wouldn't the ship traveling north see the spaceship traveling south to be traveling at 1.8c,, but that's impossible.. how did Einstein explain this theory?
No. Nothing travels, or appears to travel, faster than the speed of light in any reference frame. When something is traveling that fast (or any velocity) the amount of time that passes, changes. Its called time dilation. No matter what your velocity, you will always see light travel the same speed, c.
 
  • #26
doc.madani said:
A little to special relativity, if one spaceship traveling at 0.9c north passes another spaceship traveling at 0.9c south,, wouldn't the ship traveling north see the spaceship traveling south to be traveling at 1.8c,, but that's impossible.. how did Einstein explain this theory?
It would see the other ship moving at approximately 0.994475c. In units such that c=1, the general formula is

[tex]\vec u\oplus\vec v=\frac{1}{1+\vec u\cdot\vec v}\bigg(\vec u+\vec v+\frac{\gamma_{\vec u}}{1+\gamma_{\vec u}}\vec u\times(\vec u\times\vec v)\bigg)[/tex]

where [tex]\gamma_{\vec u}=\frac{1}{\sqrt{1-v^2}}[/tex]

When the velocities are parallel, this reduces to

[tex]u\oplus v=\frac{u+v}{1+uv}[/tex]

The [itex]\oplus[/itex] notation isn't standard. It's just what I like to use.
 

What is the center of our galaxy?

The center of our galaxy is a supermassive black hole named Sagittarius A* (Sgr A*). It is located in the constellation Sagittarius and has a mass of about 4 million times that of our sun.

What is a nebula?

A nebula is a large cloud of gas and dust in space. It is typically created from the remains of a dying star or by the gravitational collapse of a giant molecular cloud. Nebulae can range in size from a few light-years across to hundreds of light-years.

What are the orbits of nebulae in our galaxy?

Nebulae can have a variety of orbits in our galaxy, depending on their location and the gravitational forces in their vicinity. Some may have circular orbits around the center of our galaxy, while others may have more elliptical or irregular orbits.

What are the different types of nebulae found in our galaxy?

There are three main types of nebulae found in our galaxy: emission nebulae, reflection nebulae, and dark nebulae. Emission nebulae emit light due to ionized gases, reflection nebulae reflect light from nearby stars, and dark nebulae absorb light, making them appear dark against a background of stars.

How do scientists study the center of our galaxy and nebulae orbits?

Scientists use a variety of tools and techniques to study the center of our galaxy and the orbits of nebulae. These include telescopes, radio telescopes, and satellites that can detect different wavelengths of light. Scientists also use computer simulations and models to study the complex dynamics of the center of our galaxy and the interactions between nebulae and other objects in our galaxy.

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