Can a galaxy consume itself?

[SpeedFreek]

Also, the universe isn't "expanding". The redshift that leads to this conclusion was finally "calibrated" properly and there is no expansion as detailed in a previous SPACE.com article.

Try to keep up people!

I think this would be a major surprise to the scientific community. Any chance of a link to the article? Are you sure you understood it properly?

 

[ZenGalacticore]

Also, the universe isn't "expanding". The redshift that leads to this conclusion was finally "calibrated" properly and there is no expansion as detailed in a previous SPACE.com article.

Try to keep up people!

I think this would be a major surprise to the scientific community. Any chance of a link to the article? Are you sure you understood it properly?

Try to keep up Speedy!!! :lol: "Look, it's simple, let me explain it to you in language we can both understand..." :lol:

 

[ramparts]

Spouting unsubstantiated opinion that runs contrary to vast scientific consensus as fact without presenting any evidence - +1

EDIT: In response to maliaki's post. I didn't see this page! :lol:

 

[freeluna]

I have wondered if there wouldn't be an orbital energy exchange between the orbits of the various bits of stuff that make up a galaxy such that the fast orbitting stuff towards the galactic center wouldn't boost the orbits of the stuff away from the galactic center, but (1) I don't know if this is a real effect and (2) I don't know how long the process would take -- maybe hundreds or thousands of orbits of the galactic center. So I can imagine at a certain level, galaxies might be prone to eating and also dissipating on a very grand scale.

As for that menacing galactic black hole. As I understand it, our galaxy's black hole is just about the size of our solar system, maybe less. While that is huge in solar system terms, it hardly measures up as an obstacle in galactic terms. it might be (volume-wise) a tad larger than some of the largest stars in our galaxy -- mass-wise, it's huge of course. Given the vast expanses that make up our galaxy, which are able to contain the billions of solar systems that populate our galaxy, the earth would have a better chance of winning the lottery than colliding with Andromeda's black hole.

 

[FlatEarth]

As for that menacing galactic black hole. As I understand it, our galaxy's black hole is just about the size of our solar system, maybe less.

The Milky Way BH is around 1 million solar masses. It's not a 1 billion solar mass monster that are known to exist, but still a massive black hole.

 

[SippyCup]

Nope. Despite the supermassive black hole, almost all of the mass of the galaxy is orbiting around the center of mass far away from the center. For example we are ~ 26,000 light years from the center (about 1/3 of the way out) and are in an orbit that takes 220 million years to complete. It's a relatively stable orbit and will remain so for billions of years, at least until we collide with Andromeda (if we do).

I'm not disagreeing with your conclusion, but I don't think your argument is the right way to reach it. Regardless of the distance between us (or any other point in the galaxy) and the galactic center, we are orbiting the center, as is everything else in the galaxy, so obviously gravity still affects all of its mass. Knowing that, we're still left without an answer to the original question: If gravity is left to run its course, will it eventually crunch all the mass of our galaxy into the black hole at the center?

If we assume a perfect universe in which the Milky Way is totally undisturbed by outside forces and left to reach its own conclusion, then we have four possible scenarios:

1.) All the mass in our galaxy spirals into the core and creates some as yet unknown celestial entity (super mega ultra massive black hole?).
2.) Gravity is too weak to hold the galaxy together and it flies apart.
3.) Everything in the galaxy enters a perfectly stable orbit and remains that way infinitely.
4.) Some combination of the first three scenarios.

My long answer: At any given point in the galactic disc, if the orbit is currently decaying, then that point will end up in the black hole at the center, given enough time. If it's not decaying, it won't end up in the black hole. We're not only orbiting the center, we're also orbiting everything that lies INSIDE our orbit. If all that stuff ended up in the black hole, the mass inside our orbit wouldn't necessarily change, so the change in gravitational pull on our solar system will likely be very small. Thus, I believe the current state of our orbit--decaying or not decaying--is a good indicator of where we'll end up.

The short answer is "nobody knows," at least not yet. I don't think we've ever observed the end of a galaxy. There are some galactic collisions around, but as far as I know, nobody has ever spotted a galaxy that is on the verge of consuming itself. Since we have no president for an occurrence like this, all we can do is guess based on the knowledge we have. We need to know a lot more about the life cycle of a black hole than we know now before we can really start pondering how they affect the space and bodies around them.

Here are some good links that are referenced in the wiki article on galaxies:
http://www.astr.ua.edu/keel/galaxies/agnintro.html
Galaxies with active nuclei might "dry up" by blasting their matter out in jets.

http://www.astrosociety.org/pubs/mercur ... osmic.html
Check out the section on the Degenerate Era and onward.

 

[MeteorWayne]

Just a subtle techinicality, the objects in the Milky Way orbit the center of mass of the entire galaxy, called the barycenter. While it probably lies withing the event horizon of the center of the black hole, it is probably not at the precise center, which means that the black hole also orbits around the barycenter.

 

[SpaceTas]

NO 3 times

The stars etc are in orbit. This means there is a balance between the force of gravity and the tendency for the star to move off in a straight line. There is nothing to slow down the orbits to have the the stars "spiral in".

The orbit is determined by the total mass withing the orbit. So even if the central black hole grows in mass by feeding on mass nearby the orbit would not change. No Once.

Even during galaxy collisions most of the rearranged orbits don't pass near the central black holes. Even if the two central black holes merge, the extra mass is small compared to all the mass interior to the orbit of stars well away from the center. The merger process throws many stars out from the centers because of the triple star interactions with the merging central cores. No twice.

There is a a limit to the rate at which a black hole can swallow material. Eventually radiation pressure stops more material falling in. This limit is called the Eddington limit. For a 100 million solar mass black (about the largest found) this limit is about 0.003156 solar mass per year. 1 solar mass in 317 years. So to consume say the Milky Way with 200 billion solar mass of stars+gas would take about 63400 billion years. Longer than age of Universe even by heat death. No 3 times

Calculation done by setting Eddington limit of 1.3x10^37 Watts = 1/2 * m * c^2 (E=MC^2)
the initial 1/2 because only half gravitational energy is released in falling into black hole, m is the mass of accreted matter per second (recall Watts = Joules/sec). I solar mass 2x10^30 kg.

Super Eddington accretion is possible, in a non- spherical flow; but all input matter is not swallowed, some goes out in jets. But even out by factor 100, above conclusion still holds. Minimal accretion time is longer than projected age of universe.

 

[neilsox]

Hi Maliaki: Just because it was in a space.com article or Wikipedia does not mean it will become mainstream opinion, ever! Admittedly the scientific community is slow to adopt new ideas when they come from a scientist who is not part of the in crowd. So maybe we were once part of a dwarf galaxy and Sol came from the Sagittarius galaxy. Perhaps our sun and/or the Sagittarius galaxy orbit at right angles to the plain of the galactic disk. Perhaps not. Please note; I did not use many capital letters. Neil

 

[MeteorWayne]

The sun does not orbit perpendicular to the plane of the galaxy.

 

[JozefGibb]

Maliaki please may you post the link to that article?.

 

[Fallingstar1971]

This should help

http://blogs.discovermagazine.com/badas ... er-galaxy/


Star

 

[SporeFreak]

Also, the universe isn't "expanding". The redshift that leads to this conclusion was finally "calibrated" properly and there is no expansion as detailed in a previous SPACE.com article.

Try to keep up people!

Really? They "calibrated" that the universe isn't expanding? Despite all of the evidence on professional sites and shows on the Science and Discovery channels which state that the universe IS expanding? I'm not saying you're wrong or anything but could you get me a link to the article that states that? Thank you. :mrgreen:

 

[SporeFreak]

Also, the universe isn't "expanding". The redshift that leads to this conclusion was finally "calibrated" properly and there is no expansion as detailed in a previous SPACE.com article.

Try to keep up people!

Also, as Stephen Hawking once said to Fred Hoyle, "The quantity you are talking about diverges."

 

[space_futurist]

Well i have to agree with some people. I just want to give an example, because it can help understanding the trick with the black hole. The black hole is actually a self-consumed Super Giant Star. There are two types of stars, Red Giant and Super Red Giant. Red Giant is something our sun will become, since it isn't big enough, it will eventually die and there will be only the cold core floating in the space. Super Red Giant would either become Neutron Star, or it would consume itself and become a Black Hole. Now we get the picture. There had to be really big star in the center of the galaxy. So now we can say, that the black hole is just a very strong gravity epicenter. Now we can contrast the black hole and something like Gas Giant, like Jupiter (it isn't the black hole but it will help explaining). Jupiter has so much gravity strength, that it would consume any space ship floating to close to it, but it's moons are just orbiting the massive planet. The same thing with our galaxy, the black hole has a lot of power, so much that on some distance it can make sun systems orbit it like a planet. What i think is that all of the sun systems in the radio galaxy are slowly moving towards the central black hole, to their death and they will be consumed eventually. That's why the old stars are in the center, and young ones are floating further from the galaxy's center. I believe that there are always systems born in our galaxy, and that makes a balance between consumed stars, and outer layers of the galaxy. The only mystery for my is how we can see strong light coming from the center of radio galaxy? Why the black hole doesn't consume it?

 

[MeteorWayne]

Sorry, a few misconceptions in there. Just as Jupiter does not swallow all spacecraft that come near it, the black hole will not swallow all the stars in a galaxy. The key is, how fast is the spacecraft (or star) moving. If it has sufficient energy, it glides right on past, possibly with it's trajectory changed. If it has just the right amount of speed or energy, it is in an orbit, and will stay in that orbit unless acted on by some outside force.

As for this:
"The only mystery for my is how we can see strong light coming from the center of radio galaxy? Why the black hole doesn't consume it?"

The energy we see comes from outside the event horizon. Only material (or light) that gets too close is absorbed. Meanwhile, material in close proximity gets very hot from compression, and emits the energy (light, radio waves, X-rays, etc). Since it's not to close, the EM radiation travels merrily away at the speed of light. This further demonstrates that the black hole doesn't swallow everything, just stuff 9or light) that gets too close. Everything outside of that distance just sees it as a reallyreallyreally heavy star

 

[moreandless]

MW, i was just reading this thread and links concerning the consumption of the
Sag Dwarf Galaxy and found myself wondering if any of the stars nearby have
been identified as belonging to that group?

 

[MeteorWayne]

I'm not aware of any nearby stars, but it's been a while since I checked.

And just so the previous poster isn't confused, it is the Milky Way Galaxy consuming a number of other dwarf galaxies, not the Black Hole at the center of the MW.

 

[space_futurist]

Well, nobody spoke about speed. I just set an example about gravity with Jupiter, because this planet is the biggest in solar system, and therefore has more gravity. Again we can even build a theory =) If ship has certain speed - X, then we can fly right near the black hole, without any danger, getting * vacuumed* right into it.