Posted on 06/02/2008 4:27:03 PM PDT by LibWhacker
ST. LOUIS — As if in a cosmic hug, the spiral arms of some galaxies wrap around themselves more tightly than others. The key to the bear hug: Galaxies holding heftier black holes at their centers also have more tightly wound spiral arms, an astronomer announced today.
The finding gives astronomers a way to weigh so-called supermassive black holes, which can have masses of millions to billions that of the sun, and are thought to reside at the centers of galaxies.
"This is a really easy way to determine the masses of these super-massive black holes at the centers of galaxies that are very far away," said researcher Marc Seigar, an astrophysicist at the University of Arkansas at Little Rock. "This gives us a way to measure the size of these black holes out to larger distances than ever before, up to 8 billion light-years away."
He announced the results here at a meeting of the American Astronomical Society (AAS).
Dark behemoths
A black hole is the evolutionary endpoint of a star packing at least 10 to 15 times the mass of the sun. Once the fat star has burned out, there are no outward forces to oppose gravity, causing the star to collapse in on itself. The stellar remnant eventually collapses to a point of zero volume and infinite density (called a singularity), and nothing, not even light, can escape its clutches.
Astronomers can't plop hefty black holes onto a cosmic scale; they can't even see them. Instead, they detect them indirectly and measure a black hole's mass by observing the orbital speed of nearby stars affected by its tremendous gravity. But this method is limited by the power of current telescopes.
"Even with the Hubble Space Telescope, to be able to resolve the stars at the center of the galaxy, you can only really look at the nearest 40 or so galaxies," Seigar said. "That's just maybe 20 million light-years away, something like that."
Tight hugs
The results come from a study of 27 spiral galaxies, including the Milky Way and our nearest neighbor the Andromeda Galaxy. Galaxies with the smallest black holes at their centers also showed the loosest "hugs," with angles of up to 43 degrees between the arms and the central bulge.
The tightest embraces came from galaxies boarding with the biggest black holes, such as the Andromeda Galaxy (its central black hole weighs about 180 million solar masses), which had just 7 degrees between the spiral arms and the central bulges.
Seigar and his colleagues are not sure why spiral arms wrap more tightly around heftier supermassive black holes and more loosely for the lightweight supermassive black holes.
But they think dark matter, mysterious matter thought to have played a critical role in the formation of the first galaxies after the Big Bang, could be the driving force.
"We think, although this is very speculative, the more concentrated the dark matter, the larger a black hole you get," Seigar told SPACE.com. "And also the more concentrated the dark matter the tighter the spiral arms. So we think it's the dark matter that's driving everything."
(Of the total matter in the universe, dark matter makes up 85 to 90 percent, and visible matter (normal matter, baryonic matter) makes up the rest — about 10 to 15 percent. Of the total mass in the universe, about 74 percent is dark energy, 22 percent is dark matter and 4 percent or so is normal matter.)
The dark-matter connection makes sense, he said: "The more dark matter you have, the more matter you have, so the more stuff that's there to create first of all a bulge, and the more mass there is to create a bigger black hole."
Seigar's future research will aim to show whether dark matter is the driving force.
For starters it speaks of fat stars becoming black holes having masses of only 10-15 times the mass of the sun and those are held forth as examples for what follows in the article that being how black holes shape galaxies. It then outlines how black holes shape galaxies. If black holes, whether big or small relatively speaking, formed all over a galaxy then galaxies would constantly be being reshaped and wouldn’t be neat pinwheels. The black holes wouldn’t always be at the center. There would be some really ugly galaxies being pulled this way and that from dozens of different points.
No, no, no, no... Only supermassive black holes have anything to do with shaping a galaxy. An ordinary black hole has no more influence on the galaxy than the individual star from which it formed.
Well the difference in black hole formation rates in the arms of a galaxy versus at the center of the galaxy is significant. Stars are so close together in the core, it's possible for them to actually collide in the center. So it would be with all of the black holes that inevitably form.
Black holes that form from dying supermassive stars in the arms would be nowhere near large enough to wreak havoc on a galactic scale. Of course one passing through a solar system would destroy that system's orbital arrangement utterly.
OK, that makes sense. Do super massive black holes not form away from the center? I think the post after yours touches on an answer to that.
I see the logic in that. The sheer number of stars near the center is so high that it increases the odds of them forming there plus they combine being so close together. Relatively speaking. Still I have to think then that super massive black holes aren’t formed from single star collapses or there would still be mini-centers scattered around the galaxy. I could see an explanation that after much time the center black hole becomes so massive that nothing in the periphery effects the whole significantly. But there should be quite a difference in younger galaxies. We should also see smaller black holes being drug across the galaxy towards the center creating a pattern like a comet by its gravity creating disarray amongst stars in or near its path.
Why? The black hole retains the angular momentum and vector of the original stellar mass. Admittedly they have huge footprints and can disrupt systems, but they would orbit the galaxy similar to the ways stars orbit the galaxy. Out in our neck of the woods the closest star is 4.26 ly away (Prox centauri). Even a 10 solar mass black hole at that distance is not going to do anything to our solar system.
Space is mind bogglingly huge compared to the matter in it.
Sun: Child's Soccer ball (8 inch diameter)
Earth: peppercorn
Pluto: pinhead
Distance from Soccer ball(sun) to peppercorn (Earth): 26 yards.
Distance from Soccerball (sun)to pinhead (Pluto): 1019 yards
Distance from Soccerball (sun) to another soccerball (Alpha Centauri) : 4000 MILES (or NYC to Berlin)
I am aware of the vast expanses of space.
Not quite. They operate on the extreme macro scale just the same as stars. Orbital mechanics and all that. It's just that when you get closer in, like within half an AU or so that the gravity pull goes up like an asymptotic graph of y=1/x.
They do become heavier with the more mass they take in, but most of that mass is going to have an inpendent velocity and can orbit at a far distance just like it would any other stellar sized object like a star, neutron star or exotic matter star.
Supermassive black holes start from collapsed stars (10-100 solar masses or so) but OVER geological scales of TIME in the galatic core, these black holes start colliding and merging. So eventually you get one uber-huge black hole oscillating around the center of the galaxy.
Stellar collapse is how they start; collisions and merges later is how the really big ones show up.
However it is a good guess, just a guess mind you, that early in the life of a galaxy many super massive stars form in the dense center of the galaxy. Large stars, very large stars have short lives, a few million years or so, then go super Nova and the remains collapse into a black hole. Well if you've got lots of black holes fairly close to one another and a super nova goes BOOM, chances are good that some of the black holes will collide and form an even bigger black hole. Etc, Etc, Etc, until you wind up with a super massive black hole int the center of a stable galaxy. Everything should be fine until your stable galaxy collides with another Galaxy and then all hell breaks out again.
That makes good sense to me and so does the explanation that objects maintain orbits in similar fashion. A gravitational body is a gravitational body.
But the explanation of geological time scales begs the question I put forth before. When we look into deep space and see young galaxies they should look quite different. Before the colliding and merging take place there should be some galaxies that look rather swiss cheesy or in some way less organized.
OK, but, unless I misunderstood, the article was offering a theory of how they form. Keeping within that context I was looking for answers to some apparent contradictions as I see them. Again, the composition of young galaxies ought to reflect the proposed theory of "first there was a bunch of black holes, then there was one black hole."
Also, not all galaxies are spirals. There are lenticular, ellipse, and irregular galaxies too. It might also be that superlarge black holes encourage spiral galaxy formation from other types and that the larger blackholes impose a tighter spiral pattern.
Yes that was basically the thesis of this article. The bigger the black hole the tighter the spiral. I know not all galaxies are spirals and was kind of wondering why they didn't tie those in with the theory to bolster it. ie lack of a massive black hole at the center leads to less organized shape etc. It's an interesting subject all around. Just thought I would poke at some of loose threads in the theory and see what kind of answers I got.
That's a good question. In short, I don't think they know yet how every galaxy managed to get a supermassive black hole at its center. And it's beginning to look like every (large?) galaxy does indeed have one.
The Science Channel had a show on supermassive black holes not too long ago (and is my source for all this stuff...hehehe) and they mentioned that the very fact that every large galaxy they look at has a supermassive black hole at its center very strongly suggests that there is some previously unsuspected but fundamental relationship between supermassive black holes and galaxy formation that they don't understand. Did the galaxy form around the supermassive black hole? Or was the black hole born in the galaxy, grow up in the galaxy, and ultimately reshape the galaxy so that it was at the center. Or perhaps it somehow migrated to the center?
The point you made elsewhere in this thread is 100% correct: If it's the latter, that is, if the galaxy was there first, then we should be able to look out at the "edge" of the known universe and see baby galaxies that don't have supermassive black holes at their centers yet.
Not that it's worth anything since I'm not a scientist, just a fascinated layperson, but personally I think the supermassive black holes had to come first, born in the Big Bang, and galactic nebulae condensed around them.
I have a big problem seeing how one could migrate to the center of a galaxy given the orbital velocities and momentum considerations you guys were talking about earlier. And to have a galaxy form around a pre-existing supermassive black hole that's floating out in intergalactic space, where you wouldn't think there would be sufficient matter to make an entire galaxy, doesn't ring true either, at least not to my ears. Steady State theories have been ruled out. So the only way I can really imagine it happening is the black holes were formed during the Big Bang and they seeded all the galaxies that we see today during the so-called "Dark Age" of the universe, i.e., the first 300,000 years or so. </theorizing from peanut gallery!...lol>
Same here but it sounds like you've stayed at more Holiday Inn's than I have. heh
I'm hep enough to get exactly what you're saying here and those explanations make perfect sense to me. I also have to think that super massive black holes preceded galaxy formation and/or are the ground for galactic existence themselves. If they actually exist.
Perhaps they do more than simply suck matter in never to be seen again. Maybe they introduce/reintroduce matter into the surrounding space in a way not yet postulated. The wormhole idea may work but not in moving matter to some remote place or other dimension but into its own vicinity instead in some sort of balanced galactic ecology.
Today's astronomy pic of the day kind of answers my question (maybe) about how organized a galaxy actually is. IOWs not as much as I was imagining. Things are little rougher out on the interstellar high seas than the charts indicate.
Thoughts on the scale of things and the relative gravitational power that you guys have put to me come into play. In a sense we're both right; there are smatterings of black holes (or really big somethings) all around the galaxy but they are not big enough to distort the larger pattern of the galaxy.
If you go back to post #3 on this thread and look at the Triangulum galaxy and its black hole estimated to be only 1,500 times the mass of the sun that is where I lose confidence in the theory. It’s not nearly as tight as Andromeda but it has a very defined shape. How can such a small black hole exert such far reaching influence? 1,500X solar mass just isn’t much on that scale.
Also, check out the parent site: The Black Hole Encyclopedia
Yes, I was thinking about that, too. Quasars throw out matter, and maybe it isn't all infalling matter that couldn't go down the drain.
Loved the APOD of the day, thanks!
Wow! That first link looks like it was made to fit our discussion. And an Encyclopedia of Black Holes? Thanks, that is too cool. The APOD is really something isn’t it? Did you go to the site and play with the high res version? Lots of interesting “blobs” in our Milky Way.
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