APOD: NGC 253: Dusty Island Universe (2009 Nov 21)

[Chris Peterson]

Unless your large star, is trying to get to the same place another 30,000 stars, also want to get to.

I don't know of anywhere in the Universe where that situation is happening, though.

What happens to A huge Star,When another huge Star runs into it?

Presumably, it depends on the angle of the collision. The two could pull apart after transferring some material, or they might coalesce. In the latter case, the result would depend on where each was in its stellar evolution. You might end up with an unstable mass, or with more material to fuse. In any case, such collisions are extremely rare.

[The Code]

Unless your large star, is trying to get to the same place another 30,000 stars, also want to get to.

I don't know of anywhere in the Universe where that situation is happening, though.

What happens to A huge Star,When another huge Star runs into it?

Presumably, it depends on the angle of the collision. The two could pull apart after transferring some material, or they might coalesce. In the latter case, the result would depend on where each was in its stellar evolution. You might end up with an unstable mass, or with more material to fuse. In any case, such collisions are extremely rare.

Ok . Thanks Chris. Oh yeah, check this out.

http://www.telegraph.co.uk/science/spac ... alaxy.html

[bystander]

Ok . Thanks Chris. Oh yeah, check this out.

http://www.telegraph.co.uk/science/spac ... alaxy.html

No wonder you are so misinformed with your newspapers printing garbage like that. Try the Spitzer news release that came with the image. Nowhere do you see anything about black holes sucking up planets. But it must be true, it was in the newspaper.

http://www.spitzer.caltech.edu/Media/re ... ease.shtml

http://apod.nasa.gov/apod/ap090727.html
http://asterisk.apod.com/vie ... 11&t=17140
http://asterisk.apod.com/vie ... =9&t=17148

[Chris Peterson]

Ok . Thanks Chris. Oh yeah, check this out.
http://www.telegraph.co.uk/science/spac ... alaxy.html

It's still not sucking up much. Ignoring the dramatic headline, it consumes what "comes within it reach", and you can be certain that on the scale of the galaxy, that isn't much. Again, black holes at the center of galaxies have about the same gravitational effect as the center of a galaxy without a black hole. Near the black hole there is an accretionary region, and anything within that zone will lose energy and spiral into the center. But you only have to go a few light years away before there's no possibility of that happening. The vast majority of stars in this (or any) galaxy go about their orbits for their entire existence without being affected by any central supermassive black hole.

[The Code]

Spiral galaxies have a central bulge (probably always, even when the viewpoint might make it not apparent). The whirlpool effect you describe is an illusion. Material is not spiraling into the center of these galaxies, and the central black holes are only absorbing a tiny amount of matter from their surrounds, and those surrounds are far too small to be visible at the scale where you can see the entire galaxy.

What?

So can you please explain what we are seeing?

We are seeing a spiral shape. The brain tries to interpret spirals as material flowing into the center (or out of it), but that isn't usually what's going on. The Sun has orbited the Milky Way many times since it was formed, but our distance from the center hasn't changed. Likewise for all the stars you see in any spiral galaxy- each is orbiting in an approximately elliptical orbit (it's a little more complex than simple Keplerian orbit dynamics, because the mass is distributed), and each is staying about the same distance from the center over time. There is no inward flow of material in a spiral galaxy.

Quote From bystander's link:

The ring around the black hole is bursting with new star formation. An inflow of material toward the central bar of the galaxy is causing the ring to light up with new stars.

"The ring itself is a fascinating object worthy of study because it is forming stars at a very high rate," said Kartik Sheth, an astronomer at NASA's Spitzer Science Center. Sheth and Helou are part of a team that made the observations.

In the Spitzer image, infrared light with shorter wavelengths is blue, while longer-wavelength light is red. The galaxy's red spiral arms and the swirling spokes seen between the arms show dust heated by newborn stars. Older populations of stars scattered through the galaxy are blue. The fuzzy blue dot to the left, which appears to fit snuggly between the arms, is a companion galaxy.


If objects/Stars are being created at a very high rate. One would assume other objects being crushed at the same time?

And the spiral i see, is not my imagination. Or any allusion. But newly created stars, spiraling out wards.

If I am on a moving train and I fire a Gun(Blanks) out of the window, Where does the smoke go?

If I am on a moving train and the air outside the train is going as fast as me and i fire the same blank starting pistol do I see the smoke for a lot longer?

Is not your spiral arm, an indication that dark matter is also traveling with us around and around?

The orbit of our planet and solar system around the galaxy Is a totally different concept to how spiral arms work. would you not say?

Mark.

ps
I appreciate every bodies input to this thread.

[rstevenson]

This article may get you started towards a better understanding of what spiral arms are in a galaxy. (I Googled "spiral arms galaxy simulations" and chose just this one link. There are many, and this may not be the best.)
http://nedwww.ipac.caltech.edu/level5/E ... lberg.html

Rob

[Chris Peterson]

If objects/Stars are being created at a very high rate. One would assume other objects being crushed at the same time?

Why? I don't see the logical connection between the two, and I don't think there is any actual suggestion that the latter is occurring. It is usual for stars to form in areas rich in gas and dust, particularly if a mechanism exists to produce shock fronts. This area is influenced by the central black hole, but material here isn't being consumed.

And the spiral i see, is not my imagination. Or any allusion. But newly created stars, spiraling out wards.

Nobody suggested that the spiral is an illusion. The illusion is that stars are moving inwards or outwards, rather than in fixed orbits. There are no stars spiraling outwards in this or any galaxy. There's no mechanism that could even provide that sort of orbital dynamic.

Is not your spiral arm, an indication that dark matter is also traveling with us around and around?

I don't see the connection. Dark matter orbits within and around galaxies, like all matter subject to gravity. But the spiral arms aren't evidence of that.

The orbit of our planet and solar system around the galaxy Is a totally different concept to how spiral arms work. would you not say?

No. Spiral arms are density concentrations- concentrations of individual stellar systems each in simple, precessing elliptical orbits. The orbital dynamics are easily described by simple classical mechanics.

[The Code]

Thanks rstevenson

I,ll take all that in. Over next few days.

Brb.

If objects/Stars are being created at a very high rate. One would assume other objects being crushed at the same time?

Why? I don't see the logical connection between the two, and I don't think there is any actual suggestion that the latter is occurring. It is usual for stars to form in areas rich in gas and dust, particularly if a mechanism exists to produce shock fronts. This area is influenced by the central black hole, but material here isn't being consumed.

Chris, your answers just give me new questions.

This is just one.


How can new stars form, when there is no input to feed them? Where does the new matter to feed new stars come from if there is nothing falling inwards? Hawking evaporation?

Then I read this:

The keys to understanding the amplification is the rotation of the disk and the idea of pumping a swing. To increase the amplitude of motion on a garden swing, it is crucial that the pushes be applied at the correct times, say at both the forward and backward ends of the swing. Such a tuning of an applied force to an oscillator is known as a resonance. In a galaxy the situation is a little more complicated than a swing. Stars do not travel around the disk in perfect circles, but orbit on precessing ellipses that can be conveniently thought of as the combination of motion around a circle combined with a small ``epicycle'' (as in the Ptolemaic theory of the solar system). Stars on orbits nearer the center go around the circle (not the epicycle) in a shorter time than those further out, an effect that will destroy any material feature within the disk of stars. The epicycles themselves generally have longer periods with increasing radius in the disk. However, it turns out that for the mass distributions of most galaxies the combination of the motion around the circle and half of the epicyclic frequency does not vary much with radius. That is, if a two-armed spiral pattern is created with a pattern speed that matches this combination of frequencies, than the stars on their slightly elliptical orbits will be able to respond in tune with this oscillation; that is, a wide range of radii will be near a resonance of the applied spiral wave so that it should grow in intensity. Ordinarily this spiral wave amplifier does not have a ``feedback'' circuit available, so the wave is excited, grows into the large visible spiral, and then fades away as the shearing forces overwhelm the amplifying forces.



Did I say complex? Guys please don,t scare me away. I really do want to understand.

Thanks Rob.

[Chris Peterson]

How can new stars form, when there is no input to feed them? Where does the new matter to feed new stars come from if there is nothing falling inwards?

There is some material spiraling inwards. But it isn't being "sucked" in the way a lot of the stories suggest. Except for material very close to the black hole, most of the dust and gas is only very gradually losing energy to local collisions and getting closer to it. The effect of the black hole is to concentrate material in a large ring or disc, where it provides an environment where stars can form. Given long enough, this stuff will end up in the center, but it may take a good long time. Nothing moves directly towards the black hole, it just orbits, and can't get swallowed up until the orbit decays down to the size of the event horizon. That's a pretty long process.

Even in this very active galaxy, though, the mass of material involved is small compared to the mass of the galaxy as a whole.

[rstevenson]

Today's (Nov. 27th, 2009) APOD provides an interesting adjunct to this discussion.
http://apod.nasa.gov/apod/ap091127.html

Quoting the Oct. 2005 article at the last link on the APOD page ("massive black hole")...

...images showing in unprecedented detail how matter spirals toward the black hole at the centre of a galaxy...

...a detailed view of the channelling process of matter, from the main part of the galaxy down to the very end in the nucleus...

...These observations provide astronomers with new insights on how supermassive black holes lurking inside galaxies get fed...

It's clear from the rest of the article and the images that an area of about 5500 Ly is involved in "feeding" the black hole, though it also seems obvious that the area just outside this radius is piling up with gas and dust, perhaps some of it being pushed out of the central area by radiation pressure.

There's a natural tendency, already discussed above, to interpret the spirals as the path of material falling towards the black hole. But I've read lots of background material lately (prompted by this discussion) that reinforces the idea that the spirals are illusions caused by coincidental clustering of material as it orbits. Nvertheless, material is infalling, though as the paper says (and Chris said above), "...only a small amount of gas and stars are apparently being swallowed by the black hole at any given moment."

A very interesting thread.

Rob

[The Code]

I actually think, that the black hole is consuming dead star matter. Gas, Dust, But as Chris points out, not all gets past the Event Horizon. Most of the matter just converges to form new stars. but, here comes the interesting bit. They move outwards . Small particles, gas, dust, move inwards. and heavy objects like stars move the other way. but on a time scale that is very hard to see. When i look at the above picture of our milky way. I do not see stars spiraling inwards. i see them spiraling out wards, like on a production line. All be it very very slowly.

Agreed. excellent Thread.

[bystander]

I actually think, that the black hole is consuming dead star matter. Gas, Dust, But as Chris points out, not all gets past the Event Horizon. Most of the matter just converges to form new stars. but, here comes the interesting bit. They move outwards . Small particles, gas, dust, move inwards. and heavy objects like stars move the other way. but on a time scale that is very hard to see. When i look at the above picture of our milky way. I do not see stars spiraling inwards. i see them spiraling out wards, like on a production line. All be it very very slowly.

Why would you think that gravitational affects would be different for dust and gas than for stars? I don't think it's the mass by itself that matters, it's the angular momentum that counts.

[The Code]

Why would you think that gravitational affects would be different for dust and gas than for stars? I don't think it's the mass by itself that matters, it's the angular momentum that counts.

Is it not what happens when big objects become small objects?
What happened when a planet smashed into the earth? Did they not become big again?

Small objects momentum is easily changed?

[SKY DOGS]

whats the story with the arms being made by gravity waves and not a spinning in motion?

[Chris Peterson]

whats the story with the arms being made by gravity waves and not a spinning in motion?

"Gravity waves" is not the correct term- those are something completely different and are not what causes spiral arms. The arms are density concentrations, and there are several links already posted in this thread that discuss the mechanisms behind their formation.