Starship Asterisk*

The April, 2007, issue of Scientific American contains an interesting article on dwarf galaxy assimilation by the Milky Way (MW) Galaxy. The article is entitled "The Ghosts of Galaxies Past" by Ibata and Gibson, pp. 40-45.

The article documents streams of stars in and around our home galaxy that were formed in other galaxies now merged with the MW, stars that are different in composition and chemistry from our own home grown variety. Arcturus is given as one example.

If black holes are at the heart of every galaxy regardless of its size (my supposition), then the black holes of all those galaxies which have merged with the MW must be around somewhere, many probably located in the assimilated star streams.

I am curious about what effect such black holes would have, sprinkled as they may be in and around the MW galaxy:

• 1. Might these streaming black holes account for some of the dark matter effects observed?
  
  2. By what means could these unseen wanderers be detected in the MW?

Is it a given that every galaxy has a black hole? I hadn't thought that to be generally agreed upon.

Is it a possibility that assimilated black holes might have dropped into our own galatic center black hole? The attraction between them should be tremendous.

Would a supermassive black hole - e.g., what used to be a galactic core - distort what we're seeing behind it enough so that it might be detected, much the way entire galaxies create gravitational lenses? I wonder whether we've looked hard enough everywhere to say with assurance no such effects exist to be discovered.

-Noel

NoelC wrote:Is it a given that every galaxy has a black hole? I hadn't thought that to be generally agreed upon.

I think the consensus is that all galaxies have a black hole at their center. Recently, a supermassive black hole was discovered in a dwarf galaxy. See Even Dwarf Galaxies Have Supermassive Black Holes

Is it a possibility that assimilated black holes might have dropped into our own galatic center black hole?

More than likely.

The attraction between them should be tremendous.

Probably so.

Would a supermassive black hole - e.g., what used to be a galactic core - distort what we're seeing behind it enough so that it might be detected, much the way entire galaxies create gravitational lenses? I wonder whether we've looked hard enough everywhere to say with assurance no such effects exist to be discovered.

I do not know how much mass would be required to form a viable gravitational lens. The examples we see generally involve galactic clusters acting as the lens.

The sun deflects light beams, as observed by Eddington during a solar eclipse in 1919, exactly by the amount predicted by Einstein's theory of general relativity. I presume Jupiter might deflect light beams as well, but by an amount so small that it would be hard to measure.

However, I do recall reading in Is Anyone Out There?: The Scientific Search for Extraterrestrial Intelligence by Frank Drake and Dava Sobel that an observatory placed at about 500 AUs could use the sun as a gravitational lens. What that observatory could glean from such placement, I do not recall. For reference, Pluto lies between 30-50 AUs from the sun.

I am not a fan of SETI, but this book proved to be a fascinating recap of radio astronomy, worth reading for that purpose alone.

The sun deflects light beams, as observed by Eddington during a solar eclipse in 1919, exactly by the amount predicted by Einstein's theory of general relativity. I presume Jupiter might deflect light beams as well, but by an amount so small that it would be hard to measure.

Well, then, surely a black hole would deflect light from more distant stars/galaxies. As our recordings of the sky grow richer and older, we should have some ability to spot such distortion. Don't we have catalogs of "proper motion" of a huge number of stars already, to several significant digits? It would seem to me a black hole moving through our galaxy would impart "proper motions" to visually nearby (but actually more distant) objects in such a non-linear manner as to make it possible to detect the center of gravitation. Perhaps we just need more time observing and making highly accurate measurements. I'd think that if a widely spaced set of plates were superimposed visually (e.g., blinked or color-mapped), the distortion due to a black hole bending light should show up as a nice little ring of motion in surrounding stars. I was looking at an image I created from red and blue DSS plates exposed decades apart, and it was quite easy to spot a star that has moved.



Also, stars orbiting one another have been detected by measurement of distortions of spectra, I believe. Is there any reason to think a star could not orbit a black hole? The difference would be we would not be seeing two spectra, but one in that case.

And in a related sense, if a star orbited behind the event horizon of a black hole, would it not become invisible for a short period of time? They're claiming to find "hot Jupiter" planets orbiting around stars by the short dips in light output as the planets occult some of the starlight.

Notably, I've never heard of any of the above being observed.

-Noel

Hello All

Black holes are distributed throughout the milky way.At the centre there is a swam of large black holes and one very large.

Show us the evidence, Harry. I take it you've been out there, from your tone.

-Noel

Hello Noelc

I take it you do not know.

I will look up the links for you.

You could also google for it.

Be Back soon

Hello All

Black Holes

The Swarm
http://antwrp.gsfc.nasa.gov/apod/ap050128.html

At the Center of the Milky Way
http://antwrp.gsfc.nasa.gov/apod/ap051023.html

Black Hole Blows Bubble Between The Stars
http://pda.physorg.com/lofi-news-black- ... _5756.html

"We already knew that supermassive black holes at the centre of other galaxies produce enormous amounts of energy, but this finding proves that something similar is happening in our backyard," said Elena Gallo of the University of Amsterdam, lead author of the paper which will appear in this week's issue of Nature.

"Remarkably, it also means that, after a massive star dies and turns into a black hole, it is still capable of energising its surroundings, by means of completely different mechanisms."

"The importance of this result is that it demonstrates that black holes such as Cygnus X-1, of which there may be millions within our galaxy alone, do not swallow all of the infalling matter and energy, but rather redirect a considerable fraction of it back into space," added Rob Fender of the University of Southampton, second author on the paper.

Black Holes
http://imagine.gsfc.nasa.gov/docs/scien ... holes.html


Is there any evidence that black holes exist?
http://cosmology.berkeley.edu/Education/BHfaq.html#q7


Black Hole Boldly Goes Where No Black Hole Has Gone Before
http://chandra.harvard.edu/press/07_rel ... 10307.html

Black Hole Boldly Goes Where No Black Hole Has Gone Before
Astronomers have found a black hole where few thought they could ever exist, inside a globular star cluster. The finding has broad implications for the dynamics of stars clusters and also for the existence of a still-speculative new class of black holes called 'intermediate-mass' black holes.

The discovery is reported in the current issue of Nature. Tom Maccarone of the University of Southampton in England leads an international team on the finding, made primarily with the European Space Agency's XMM-Newton satellite.

Globular clusters are dense bundles of thousands to millions of old stars, and many scientists have doubted that black holes could survive in such an exclusive environment. Computer simulations show that a newly formed black hole would first sink towards the centre of the cluster but quickly get gravitationally slingshot out entirely when interacting with the cluster's myriad stars.


Artist's impression of globular star cluster
(Credit: ESA/Hubble)
The new finding provides the first convincing evidence that some black hole might not only survive but grow and flourish in globular clusters. What has astonished astronomers is how quickly the black hole was found.

Puny black holes can eject Milky Way's stars
http://space.newscientist.com/article/d ... ef=dn10020

Close encounters
The smaller black holes are about 10 times more massive than the Sun. Some studies suggest as many as 25,000 small black holes may orbit the supermassive black hole at the galaxy's centre, having migrated there from other parts of the galaxy after being nudged out of their original orbits by passing stars.

When one of these little black holes near the galactic centre passes very close to a star, it can sometimes fling the star out of the galaxy, while itself moving closer to the supermassive black hole, the study says.

This process could eject stars at an even greater rate than the disruption of binary stars by the supermassive black hole itself, Loeb says. "The rate could account for a substantial fraction or maybe most of the events we have seen so far," he told New Scientist.

There are many more links:

RJ,

Harry beat me to it, but I was going to say that the quincunx of black holes at our galactic center may be the 'assimilated extra-galactic center black holes' you are looking for. As I remember there are 4 smaller ones orbiting the larger central one, in our galactic center. This may infer that our galaxy has 'eaten' four smaller galaxies of various types sometime in the past. By the size of the eaten black holes it may reflect on the size of the object eaten.

Or they may be products of early super-size aggregations of material forming massive lumps within our galaxy that ended up as massive compact objects, and are not assimilated extra-galactic object cores. More study is needed.

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As Tycho Brahe taught us by example, collection of accurate data is the first step in understanding the Universe.

Hello Kovil


You said

Harry beat me to it, but I was going to say that the quincunx of black holes at our galactic center may be the 'assimilated extra-galactic center black holes' you are looking for. As I remember there are 4 smaller ones orbiting the larger central one, in our galactic center. This may infer that our galaxy has 'eaten' four smaller galaxies of various types sometime in the past. By the size of the eaten black holes it may reflect on the size of the object eaten.

You may be right.

There is another option:

Black hoels grow and grow in the spirals of the MW and as they make their way to the centre they become bigger and less in number. Its like a game of tennis. You start with many, than quarter finals and semis than finals.

What is interesting is how a black hole can be shot out of the centre. Now thats a good trick.

Darn my comp froz.