# Black hole or black ball

1. May 31, 2010

### fakts

I hear them always saying "black hole", my question is:
Is it a black hole that sucks stuff from one side, or is it like a black ball (sphere) that sucks thingies from all sides?

If asked or explained else where on the forum please refer me and I will delete this one
Thanks

2. May 31, 2010

### Nabeshin

They are indeed spheres which attract objects from any orientation.

3. Jun 2, 2010

### fakts

Then why whenever there is a doc about it on TV they show something like a swirling disk and things are going in circle around the hole (lol) then being sucked?!

4. Jun 2, 2010

### Staff: Mentor

It may just be artistic license or it may be a reflection of the fact that clouds of matter often take up disk shapes, making things look two dimensional (for example, spiral galaxies and our solar system are both arranged in disks).

5. Jun 2, 2010

### fakts

Hmm.. I know what you mean
But I'm having difficulties believing that matter will get sucked in a disk shape since the earlier guy replied saying it is a ball (Sphere) and not a hole.
So if it is a ball like thing then that means things should be sucked in a straight line from all directions, and not disks and things going in circle.
I'm I wrong?

6. Jun 2, 2010

### phyzguy

A non-rotating black hole is indeed spherically symmetric. But most real world black holes are rotating, usually rotating rapidly. So they are not spherically symmetric, they are cylindrically symmetric about the axis of rotation. The rapid rotation of the black hole distorts space around the black hole, and this is what causes there to be a disk (called the accretion disk) around the equator. Simulations show that infalling matter gets pulled into this disk, and some of the matter falls into the black hole, while some of it gets shot out along the poles, resulting in the jets you've probably seen. Exactly how the material gets shot into the jets is still being studied, but it is believed that magnetic fields in the ionized plasma of the accretion disk play a role.

7. Jun 2, 2010

### fakts

Well explained
Thanks

8. Jun 2, 2010

### Ich

That's not quite right. An accretion disk will be around any gravitating object, rotating or not, if there is infalling matter with some tangential motion.
They are alway showing the accretion disk as the Black Hole is not very photogenic, black against a dark background.

9. Jun 2, 2010

### Staff: Mentor

To expand on/take a different tack from what Ich explained, a black hole can only suck in matter that is around/near it, so if the matter around/near it is arranged spherically from it, it will suck it in from all directions, but if the matter is arranged in a disk, it will suck it in from two dimensions.

So why might matter be arranged in a disk instead of a sphere? As the examples I gave show, matter tends to be arranged in disks because matter is in orbit around other matter. An orbit is planar/disk-like. So the most obvious case (and also one of the most common for a black hole) is where a black hole is sucking matter away from a nearby companion object. Since the object is in orbit around the black hole, it is creating a disk shape and matter being sucked away remains in that disk because it is the most direct path to the black hole. Here's an artist's rendering of what I'm describing:
http://www.cosmographica.com/gallery/portfolio2007/content/bin/images/large/131_BlackHole.jpg

10. Jun 6, 2010

### Phrak

Yes, well, there may be as many as two distinguishable effects that contribute to the disk, then its reorientation. The first is due to collisions of matter in a plane perpendicular to the average momentum of the surrounding matter. The second force is due to frame drag, where the angular momenum of the object 'drags' spacetime with it and may reorentate the outboard disk.

11. Jun 6, 2010

### IanTBlack

That's a toughy. I've heard that "black holes" have event horizons. Which makes it sound like they are almost conical in shape. A sphere would also make sense. Although, "black holes" are supposed to condense everything to a single point. So why can't they just be a single point to begin with.

I recently read somewhere that "black holes" spew neutrinos. If there was a way to measure how many it could decipher which shape it is. If the neutrinos are coming in mass in one direction, then a cone like shape would be adequate. If there are neutrinos being spewed out in all directions, then a sphere would make sense.

12. Jun 6, 2010

### Ich

They are, in their mathematical description. There's a "point mass", and around it a spherical event horizon. Most frequently, you'll find the latter be identified with the "black hole" in the popular literature. So you'd say a black hole is a sphere.

13. Jun 18, 2010

### emergent

nice dialog here. i have been obsessing about climate for 6-7 years now, and believe it or not, it always seems to get entangled with the cosmos. i have ended up thinking about black holes a lot as a result. a black hole(i still wish it was call just dark space or something because hole does not suit it IMO) gives us many clues of itself, the most important is its galaxy. also they seem to exist in a galaxy's center. im not 100% but i think they all seem to spin in the same direction. they seems to be able to merge with one and other, or at the minimum share a level of attraction to each other. but most important a black hole can bend the path of light... amazing...
jeeze its 3:30 am im going to bed.
not many things as interesting, and still open to discussion. as a super massive black hole

14. Jun 18, 2010

### IanTBlack

I just bought the book, "Death by Black Hole" by Neil DeGrasse Tyson. It should be interesting.

Do you think that you would die if you came into contact with a black hole? How would anyone really know?