There's a black hole in the Milky Way?!?! Physics buffs come talk to me

[Melodybe]

Why hasn't anyone been talking about this?

Sure it just means that in a few million years our solar system will eventually be crushed into darkness, but it's cool nonetheless.

So since I only read the first hundred pages of Hawkins' Brief History of Time, can someone give me in laymens terms what black holes mean to the shape of the universe.

I was always very fond of Hawkin's hourglass shape of the universe, he stopped using it because he forgot to factor time into the equation. I personally would leave time out of the equation, since it is a manmade construct, but are there any other reasons why that shape has been debunked?

With the proof that the universe is expanding does that support the hourglass shape?

Since I have never taken any physics classes, I am out in the cold on this one. I am very interested to see what DU phyics buffs have to say about all this.

[BlueEyedSon]

1. Theres a DU science forum, FYI

http://www.democraticunderground.com/discuss/duboard.php?az=show_topics&forum=228

[Goldmund]

2. I'm not sure I know what you're talking about...

...when you say "there's a black hole in the Milky way" -- as far as I know, this isn't news. Theoretical physicists have thought so for decades, and astronomers have been watching objects for a few years that they think are nearby black holes.

But it doesn't mean that in a few million years our solar system will be sucked in.

Remember this:

From large distances, a black hole affects the universe no differently than any other object of a similar mass would. It is only when you get nearby that shit starts getting whack.

[Melodybe]

4. I was just watching a program on the science channel and they made a big

honking deal out of it, with scary music and everything.

We got a good laugh out of it but I didn't know that there was a black hole in the Milky Way.

I also wanted to get some answers on my Hawkin's shape of the universe question.

So what is the current model?

[Goldmund]

19. I can't say I know much about that "hourglass shape"

At least when applied in this context... :D

[Incitatus]

21. Good laugh

If you want a good laugh watch "What The Bleep Do We Know".

[entanglement]

17. Yes, I remember reading that the tidal forces that 'tear' bodies apart

get really huge only quite close to a black hole

[Cleita]

3. Hmm. I thought most spiral galaxies had black holes in the

middle, but what do I know. :shrug: I also think since the universe is a kind of giant cosmic clock, it wouldn't be helpful to leave time out of the equation, but like I said, what do I know. Math and Science were not my best subjects. I hope someone comes along who does know and answers your questions. :-)

[Dudley_DUright]

10. You are correct. You actually must know a lot!

:-)

[Cleita]

14. Thanks for the vote of confidence.

I do try to read up on it and if I come away understanding about ten percent of what I've read, then it's a good day for me. :-)

[Occulus]

22. your analogy to a clock just feels right

and makes me wonder if this clock came with an alarm of some sort.

[salvorhardin]

5. Black holes seem to be essential in galaxy formation

http://hubblesite.org/newscenter/newsdesk/archive/releases/2000/22/
http://www.pitsco.com/the_cause/cause3aero.htm
http://www.physorg.com/news3014.html

[ninty]

6. ...

There is not one black hole in the center of the galaxy. There are hundreds or thousands or millions that combine to form one giant black hole. This is the way it is for all galaxies similar to ours, which are spiral galaxies. Other galaxies would have to have some sort of central gravitational pull as well, so I’m sure there are black holes in elliptical and irregular galaxies as well, or just a high density of stars.

This is the way it has been for 13.8 billion years, which is the age of the universe. Our solar system will not be crushed by it. Our solar system will die out when the sun explodes in 4 or 5 billion years.

It has been found that the mass of black holes and the gravity they create are not sufficient to hold everything together. We know that 70% of the mass of the universe is unaccounted for, because we need this mass to hold everything together. In comes in Dark Matter. This is what really shapes the universe. But until we can somehow find a way to measure it, we really can't use it to describe how it affects our surroundings.

[Dudley_DUright]

8. It is thought to be a single supermassive black hole

but you are right that it way formed by lots of individual stars/black holes that got sucked in early in the formation of our galaxy (when our galaxy was acting like a quasar)

[Dudley_DUright]

7. The black hole in the center of our galaxy is probably

about 2.6 million solar masses(which is still a small fraction of the mass of the galaxy with is of order 100 billion solar masses, at least for the visible stars, forgetting dark matter for the moment), but we are in no danger of falling into it .

http://www.sciencedaily.com/releases/1998/09/980908074632.htm

Rather we orbit the center of the galaxy and make one revolution roughly every 250 million years. Black holes mean very little to the overall shape of the universe since they do not comprise much of the critical mass needed to explain the current shape of the universe.

[Melodybe]

9. But what is the curren shape of the universe?

As I said I think that the hourglass makes sense, but Hawkins and the physics community is no longer using that model.

What's wrong with the hourglass and what has replaced it?

[salvorhardin]

11. I would say

it is exactly universe shaped.

[Dudley_DUright]

12. The bottom line is that the overlall gravitational curvature of the

Universe seems to be zero (i.e. flat). This means that the mass of the universe is equal to the so called critical mass (or omega = 1).

http://map.gsfc.nasa.gov/m_uni/uni_101shape.html

[U4ikLefty]

13. Yes....and we call it Bush's brain!!!

n/t

[MisterP]

15. there's little chance of our falling into the Sag A hole, since it's

at the galaxy's center and we're in orbit around both it and the galactic center--it would be deceptive to say the hole is what we're orbiting around since it comprises only a tiny fraction of the Milky Way's mass, tremendous as it is.

[Peace Patriot]

16. Think of yourself as an ant trying to figure out the shape and true nature

of planet earth. That's where we stand in relationship to the great universe (only we're much smaller than the ant, and the cosmos is much bigger than the earth, in comparison).

Teensy-weensy ant-sized minds. Teensy-weensy telescopes. Wrong senses developed (ants--mostly scent). You get the picture. How can we even know there are oceans, if we don't live right next to one? And then it would just seem like the local puddle. A bit of deserty terrain, adjoining the tiny bit of forest that we inhabit--say a path tramped down by migrating goats--might be the most we ever know of the differing climates and habitats of earth.

Now think about hundreds of millions of galaxies each containing hundreds of millions of solar systems, many of the galaxies containing black holes where time freezes at the edge for any approaching object or lightbeam, and stretches out to eternity...

Yeah, we have a black hole at the center of our galaxy--that is now known--and the galaxy's outer arm rotation is NOT slower than the inner arm rotations. Figure THAT out. Nobody knows what the relationship of the black hole is to the swirl. It's a MYSTERY. So, in the ant metaphor, we've gotten as far as the deserty path; we don't know how it was created, or what's it's for, or who made it, or that someone made it, or why it's different than our inhabited terrain. We're just feeling around, sensing that it's hotter and brighter and dustier than our known ground, and contains mind-boggling puzzles.

What mysteries lay beyond--or even nearby--is anybody's guess. Ever hear of Dark Matter? Or String Theory? You'd be surprised how LITTLE we know (yet with minds that seem to WANT to know), and how wild the speculations are (given what we DO know) as to the true shape and nature and age and future of the Cosmos, and what rules MIGHT BE operating within it.

I once read an astrophysics paper that asserted that the universe is actually quite small, and that what we're seeing "out there" are merely mirrors--reflections of things that once were, and are no more.

Fun, huh?

Read up on it. It can give you a bit of perspective on our little political troubles here in the local sentient ant colony. And maybe some day--if we don't blow our little colony to smithereens--we'll figure out what goats are, and why they do what they do.

[JHB]

20. A few bits...

>Yeah, we have a black hole at the center of our
>galaxy--that is now known--and the galaxy's outer
>arm rotation is NOT slower than the inner arm
>rotations. Figure THAT out.

Actually, that one's pretty easy: it's just a matter of mass distribution. The orbital speed will decrease with distance from the center if essentially all the mass is at the center (or even just within the orbital radius), like in our solar system where about 99% of the mass is in the Sun.

But in a spiral galaxy, a significant portion of the mass is in the disk. It's been a long while since I had the exact numbers in my head for this, but the net effect is that the mass outside the orbital radius also has an effect, which results in the orbital speed being constant despite the orbital radius. Now, the weird part is that at some point the disk would end and everything outside that radius would have decreasing orbital speed, as with a central mass. But we can't detect the "drop-off limit", so that's where theories about Dark Matter and such come into play...

[wli]

18. not a physics buff, but anyway

"Black hole" is not quite as significant as it sounds. There is something called the Schwarzschild radius, which corresponds to the event horizon when things get dense enough for that radius to exceed the radius of the system itself.

All that's really required is that the density of a system of matter is sufficient for that radius to be outside it. A system of matter could easily appear organized while its Schwarzschild radius exceeds its own radius, and so you'd end up in a black hole without ever knowing it, and fall toward the center so slowly it's almost imperceptible.

Also, looking at black holes from the outside, they actually radiate quite a bit. For instance, the gravitational stress on matter being condensed while falling into it may be significant enough to give off X-rays and all sorts of other things. A black hole may not actually look much different from various other kinds of stars.

Anyway, there's a lot of material around about them. There shouldn't really be so much of a mystique about them. The fact light can't escape black holes doesn't make them particularly unique dangers. Sufficiently massive objects can have escape velocities high enough without being black holes to be unescapable by human means.