Starship Asterisk*

Why do I get the feeling that I'm being asked to do someone else's homework assignment

ErnieM wrote:What is the source of the heavier elements that a star "consumes" during the different stages of transformation?

Are the stages different between stars with planets and those with no planets?

From the debris of a exploded star. the next "generation of solar systems" is born. Do we know how many "generations" our solar system has gone through?

How about galaxies? Are new star systems formed from the ejected jets of debris as the central massive black hole ran out of solar systems to "digest"? Is there any evidence for or against this statement?

What then is the conceptual eventuality for the massive black hole?

Without the tell tale ejection jets, how can we detect the presence of massive black hole wandering in space? Is it gravitational lens effect only?

Presence of dark matter is not directly observed except through the gravitational lens effect.

Is there a know way to differentiate the gravitational lens effect between massive black holes and dark matter?

How do dark matter and massive black holes interact? Through gravity. Does massive black hole "consume" dark matter? If so, then it is conceivable that part of the ejected jet debris contains dark matter.

Chris Peterson wrote:

ErnieM wrote:

How about galaxies? Are new star systems formed from the ejected jets of debris as the central massive black hole ran out of solar systems to "digest"? Is there any evidence for or against this statement?

No star systems are observed to be forming in jets from active galaxies. But the released material might ultimately be incorporated into a star forming region in some different galaxy.

Ann wrote:http://asterisk.apod.com/viewtopic.php?f=29&t=28114

By following the above link you can see Minkowski's Object. A jet from a black hole in a giant elliptical galaxy hits a cloud of hydrogen gas and triggers star formation there. There may well be new star systems with planets there.

Ernie wrote:

1. What then is the conceptual eventuality for the massive black hole?
2. Without the tell tale ejection jets, how can we detect the presence of massive black hole wandering in space? Is it gravitational lens effect only?
3. Presence of dark matter is not directly observed except through the gravitational lens effect.
4. Is there a known way to differentiate the gravitational lens effect between massive black holes and dark matter?
5. How do dark matter and massive black holes interact? Through gravity. Does massive black hole "consume" dark matter? If so, then it is conceivable that part of the ejected jet debris contains dark matter.

In reply Chris wrote:

1. It is believed that all black holes eventually evaporate. For a supermassive black hole, the time required is huge compared with the current age of the Universe... but is, nevertheless, finite.

2. We can detect a black hole by the radiation emitted when matter falls into it (which isn't limited to the production of jets), or we can detect it by its gravitational effect on other bodies that we can see directly.

3. That is not so. There are many observations that indicate the presence of dark matter, such as the nature of galaxy rotation and the movement of galaxies in clusters.

4. I don't think a gravitational lens has ever been observed which can be associated with a supermassive black hole. As a rule, such objects are simply not massive enough. The black holes at the center of galaxies only represent a tiny fraction of the total mass of those galaxies- most of which is dark matter. When we observe a gravitational lens, we are seeing the effect of an entire galaxy. The only way to see lensing from a massive black hole would be to find an isolated one, which we haven't.

5. Black holes should consume dark matter in the same way they do ordinary matter. Jets are not produced from material consumed by a black hole, but are ordinary matter that is ejected before reaching the black hole, by a process that involves electromagnetic effects. Dark matter is not affected by electromagnetism, so there is no mechanism for its ejection from the vicinity of a black hole in jets. Presumably, it merely orbits black holes, and is only consumed if the orbital path crosses the event horizon.

ErnieM wrote:As massive black hole(s) at the center of a galaxy consumes its "ordinary" matter leaving only dark matter, its electromagnetic signatures including radio, will become undetectable by current technologies. In essence the galaxy goes dark, "invisible".

The only mechanism by which galaxies will go dark is the ultimate burning out of all the stars, leaving behind cold gas and dust too thin to initiate new star formation, and the hulks of old stars: black holes, neutron stars, and white dwarfs. The Universe is nowhere near old enough for that to have happened to any galaxy.

"Astronomers first suspected that there was an invisible, dark, galaxy, upon observing galaxy NGC 4254. This unusual-looking galaxy appears to be one partner in a cosmic collision. The only evidence is the following: gas is being siphoned away into a tenuous stream, and one of its spiral arms is being stretched out. The other partner in this collision is nowhere to be seen. The researchers calculated that an object with a mass of 1011 M☉ made close passage with NGC 4254 within the last 100 million years creating the gas stream and tearing at one of its arms. This was the clue that an invisible dark matter galaxy might be nearby.
Nature of dark galaxy

Origin
In 2000 astronomers found a gas cloud VIRGOHI21 and tried to find a theory of what it was and or why it could cause such a gravitational pull from NGC 4254 galaxy. After years of running out of other explanations some have concluded that VIRGOHI21 is a dark galaxy, due to the massive effect it had on NGC 4254.[1]

Size
The actual size of a dark galaxy is unknown, because they cannot be spotted with a normal telescope. There have been various estimations of the size of dark galaxies. Two potential sizes could be either double the size of the Milky Way[4] or the size of a small quasar.

Structure
Dark galaxies are composed of dark matter. Furthermore, dark galaxies are theoretically composed of hydrogen and dust.[1] Some scientists support the idea that dark galaxies may contain stars.[3] Yet the exact composition of dark galaxies is unknown because there is no conclusive way to spot them so far.

Methodology to observe dark bodies
Dark galaxies contain no visible stars, and are not visible using optical telescopes. The Arecibo Galaxy Environment Survey (AGES) is a current study using the Arecibo radio telescope to search for dark galaxies, which are predicted to contain detectable amounts of neutral hydrogen. The Arecibo radio telescope is useful where others are not because of its ability to detect the emission from this neutral hydrogen, specifically the 21 cm line.[5]

Alternative theories
Scientists do not have much explanation for some astronomic events, so some use the idea of a dark galaxy to explain these events. Little is known about dark galaxies, and some scientists believe dark galaxy is actually a newly forming galaxy. One such candidate is in the Virgo cluster. This candidate contains very few stars. Scientist classify this galaxy as a newly forming galaxy, rather than a dark galaxy.[6]

Potential dark galaxies

HE0450-2958
Main article: HE0450-2958
HE0450-2958 is an unusual quasar (a star like object that may send out radio waves and other forms of energy). This one in particular has many large red shifts.[7] HE0450-2958 has no visible host galaxy (a galaxy surrounding the quasar) detected around it. It has been suggested that this may be a dark galaxy in which a quasar has become active. However subsequent observations revealed that a normal host galaxy is probably present.[8]

HVC 127-41-330
Main article: HVC 127-41-330
HVC 127-41-330 is a cloud at high speed between the Andromeda and the Triangulum Galaxy. Astronomer Josh Simon considers this cloud to be a dark galaxy because of the speed of its rotation and its predicted mass.[9]

VIRGOHI21
Main article: VIRGOHI21
The discovery of VIRGOHI21 was announced in February 2005, and it was the first good candidate to be a true dark galaxy.[2][3][10][11] It was found when AGES was looking for the 21 cm-wavelength radio waves emitted by hydrogen (H). Its dynamics are apparently inconsistent with the predictions of the Modified Newtonian Dynamics (MOND) theory.[12] Some researchers have since discounted the possibility of VIRGOHI21 being a dark galaxy and believe it is more likely a "tidal tail"[13] of nearby galaxy NGC 4254, which is experiencing gravitational perturbations as it enters the Virgo cluster

ErnieM wrote:Chris wrote:

The only mechanism by which galaxies will go dark is the ultimate burning out of all the stars, leaving behind cold gas and dust too thin to initiate new star formation, and the hulks of old stars: black holes, neutron stars, and white dwarfs. The Universe is nowhere near old enough for that to have happened to any galaxy.

From Wipedia: http://en.wikipedia.org/wiki/Dark_galax ... l_evidence

"Astronomers first suspected that there was an invisible, dark, galaxy, upon observing galaxy NGC 4254. This unusual-looking galaxy appears to be one partner in a cosmic collision. The only evidence is the following: gas is being siphoned away into a tenuous stream, and one of its spiral arms is being stretched out. The other partner in this collision is nowhere to be seen. The researchers calculated that an object with a mass of 1011 M☉ made close passage with NGC 4254 within the last 100 million years creating the gas stream and tearing at one of its arms. This was the clue that an invisible dark matter galaxy might be nearby.

In 2000 astronomers found a gas cloud VIRGOHI21 and tried to find a theory of what it was and or why it could cause such a gravitational pull from NGC 4254 galaxy. After years of running out of other explanations some have concluded that VIRGOHI21 is a dark galaxy, due to the massive effect it had on NGC 4254.

Dark galaxies are composed of dark matter. Furthermore, dark galaxies are theoretically composed of hydrogen and dust.[1] Some scientists support the idea that dark galaxies may contain stars.[3] Yet the exact composition of dark galaxies is unknown because there is no conclusive way to spot them so far.

Ann wrote:Surely a cloud of gas isn't a dark matter galaxy? Surely gas isn't dark matter?

I thought all galaxies contained at least some gas, at least some dust, at least some stars, and at least some dark matter. So what's the difference between dark matter galaxies and ordinary galaxies, if both contain the same "ingredients"?

And if a dark galaxy contains hydrogen, dust and stars as well as dark matter, why would it be so very hard to spot it?

Chris Peterson wrote:This is an entirely different thing. If dark matter galaxies exist, they are not galaxies that went dark. There hasn't been enough time for galaxies to go dark. This Wikipedia article is about hypothetical galaxies made from dark matter only. While interesting, I don't see the connection between them and the normal galaxies and supermassive black holes under discussion here.

http://knol.google.com/k/shape-of-the-universe#WMAP_Measurements wrote:WMAP Measurements
The Wilkinson Microwave Anisotropy Probe (WMAP) was designed to achieve more precise measurements of the anisotropy in CMB. Within the framework of the "Lambda-CDM Model" of the universe, the WMAP data indicate that the age of the universe is 12.73 ± 0.12 billion years old.

WMAP data also indicate that the current universe consists of 4.6% ordinary baryonic matter; 23% unknown dark matter; 72% dark energy; and less than 1% neutrinos. The ratio of the energy density to to the critical density was determined to be 1.0052 ± 0.0064 . These findings created big excitement in the scientific community. The academic papers [1][2] of the WMAP collaboration were among the most cited papers in history.

ErnieM wrote:Let us take a broader look at the evolution process of galaxies and let me present another way a galaxy can go dark. In the merging process of two or more galaxies, the dominant galaxy or galaxies eats up all the ordinary matter from the weakest one leaving only the dark galaxy with the central black hole and dark matter. From here, the dance between the galaxies continues for million if not billion of years until the weakest dark galaxy is either gobbled up by the dominant one or instantaneously thrown away in the jet stream ejection process or by the sling shot effect of gravity.

Our own Milky way is now accepted to have several small satellite dark galaxies partly responsible for the warping of the disk.

Correct me if I am wrong in presuming the the 4.6% atoms represent the ordinary matter today and the combined 17% photons and atoms were the ordinary matter 13.7 years ago. Dark matter is more dramatic, down to 23% from 63 %. Losing matter, dark and ordinary, at this rate must have happen not at solar system but at galactic scale.

Stars die at different rate. Some die faster and younger than others and galaxy compositions are also different specially at the early universe. So how can one be so conclusive that there is not enough time for galaxies to go dark.

ErnieM wrote:
Let us take a broader look at the evolution process of galaxies and let me present another way a galaxy can go dark. In the merging process of two or more galaxies, the dominant galaxy or galaxies eats up all the ordinary matter from the weakest one leaving only the dark galaxy with the central black hole and dark matter. From here, the dance between the galaxies continues for million if not billion of years until the weakest dark galaxy is either gobbled up by the dominant one or instantaneously thrown away in the jet stream ejection process or by the sling shot effect of gravity.

I would argue that this should not be described as a galaxy going dark. It's just a galactic collision (a common thing) where the gravitational dynamics happen to operate like a filter, separating dark matter and ordinary matter unevenly. Indeed, an object was recently observed where the dark matter halo appears to have been substantially separated from the ordinary matter core. Nothing is going dark, however. You have the same total luminosity before and after. Nor is there any reason to think the central black hole wouldn't remain with the ordinary matter. Why assume it would end up with the dark matter? That seems dynamically unlikely.

"The Sagittarius Dwarf Galaxy, first discovered in 1994, is a satellite galaxy that is slowly being torn apart and ingested into the larger Milky Way. In the process, however, Sagittarius seems to have been making its presence felt. A group of astrophysicists at the University of Pittsburgh, the University of California, Irvine, and Florida Atlantic University simulated the gravitational infall of Sagittarius over the past few billion years to uncover what effects the dwarf galaxy may have had on the Milky Way."

ErnieM wrote:
Correct me if I am wrong in presuming the the 4.6% atoms represent the ordinary matter today and the combined 17% photons and atoms were the ordinary matter 13.7 years ago. Dark matter is more dramatic, down to 23% from 63 %. Losing matter, dark and ordinary, at this rate must have happen not at solar system but at galactic scale.

The Universe has a (presumably) fixed amount of energy, and during its early evolution, that energy changed form. When most of this was occurring, there were no galaxies.

ErnieM wrote:
Our own Milky way is now accepted to have several small satellite dark galaxies partly responsible for the warping of the disk.

Reference? I don't think anything like this is widely accepted... I don't even know that it has been proposed. It is suggested with good arguments that the warping of the disc is associated with dark matter, but not dark matter galaxies.

"The Magellanic Clouds are not the only satellites of the Milky Way. Astronomers have counted some two dozen. This video shows their three- dimensional position relative to the plane of the galaxy, where the sun and most other stars lie. Here, the mystery is why there are not more satellites: by rights, our galaxy should have hundreds. The Sloan Digital Sky Survey, which scanned the region shown by the pinkish cone, partially filled in the gap by finding another dozen satellites. They are extremely dim and composed mostly of dark matter. The rest of the satellites out there may be completely invisible."

"Dark matter is one of the great scientific mysteries of our time, but once astronomers accepted its existence, the answers to many other cosmic mysteries fell into place.
Whatever this unknown material may be, it seems to explain why the disk of our Milky Way galaxy has such a pronounced warp at its outer rim. Orbiting satellite galaxies naturally tend to distort the galaxy, but their gravitational effect would be too weak without the amplification that dark matter provides.

Another question dark matter answers is why the Milky Way appears to have fewer such satellite galaxies than models predict it should. It turns out that the satellites are probably out there, though composed almost entirely of dark matter, making them hard to detect."

ErnieM wrote:
Stars die at different rate. Some die faster and younger than others and galaxy compositions are also different specially at the early universe. So how can one be so conclusive that there is not enough time for galaxies to go dark.

We don't observe any galaxies consisting only of massive stars. Quite the opposite, every galaxy is dominated by low mass stars with lifetimes longer than the current age of the Universe. No theory that I'm familiar with predicts galaxies which could have gone dark. The lack of theory, combined with the lack of observation, makes a good case for no galaxies having "gone dark"

"New evidence suggests that hundreds of unseen dwarf galaxies made of dark matter encircle our Milky Way and other large, visible galaxies.
.
.
The scientists remain puzzled as to why these dark-matter galaxies contain few or no stars, however, given that 10 to 20 percent of their mass should exist as normal matter. "It's difficult to hide that much material," Dalal observes. The findings will appear in the June 10 issue of the Astrophysical Journal."

ErnieM wrote:

Chris wrote:I would argue that this should not be described as a galaxy going dark. It's just a galactic collision (a common thing) where the gravitational dynamics happen to operate like a filter, separating dark matter and ordinary matter unevenly. Indeed, an object was recently observed where the dark matter halo appears to have been substantially separated from the ordinary matter core. Nothing is going dark, however. You have the same total luminosity before and after. Nor is there any reason to think the central black hole wouldn't remain with the ordinary matter. Why assume it would end up with the dark matter? That seems dynamically unlikely.

From article Star-Crossed: Milky Way's......http://www.scientificamerican.com/artic ... ite-spiral
I would argue that over time, Sagittarious Dwarf can become another dark satellite galaxy.

No argument. And massive black holes, alone or in dark galaxies, is another form of energy but not visible.

ErnieM wrote:

Chris wrote:

ErnieM wrote:Our own Milky way is now accepted to have several small satellite dark galaxies partly responsible for the warping of the disk.

Reference? I don't think anything like this is widely accepted... I don't even know that it has been proposed. It is suggested with good arguments that the warping of the disc is associated with dark matter, but not dark matter galaxies.

From article "How Dark Matter Messes....http://www.scientificamerican.com/artic ... our-galaxy

From article "The Dark Side of the Milky Way" http://www.scientificamerican.com/artic ... -milky-way

"Dark matter is one of the great scientific mysteries of our time, but once astronomers accepted its existence, the answers to many other cosmic mysteries fell into place.
Whatever this unknown material may be, it seems to explain why the disk of our Milky Way galaxy has such a pronounced warp at its outer rim. Orbiting satellite galaxies naturally tend to distort the galaxy, but their gravitational effect would be too weak without the amplification that dark matter provides.

ErnieM wrote:From article Dark-Matter Dwarf Galaxies..http://www.scientificamerican.com/artic ... rf-galaxie

"New evidence suggests that hundreds of unseen dwarf galaxies made of dark matter encircle our Milky Way and other large, visible galaxies.
.
.
The scientists remain puzzled as to why these dark-matter galaxies contain few or no stars, however, given that 10 to 20 percent of their mass should exist as normal matter. "It's difficult to hide that much material," Dalal observes. The findings will appear in the June 10 issue of the Astrophysical Journal."

Chris Peterson wrote:

ErnieM wrote:
From article Dark-Matter Dwarf Galaxies..http://www.scientificamerican.com/artic ... rf-galaxie

"New evidence suggests that hundreds of unseen dwarf galaxies
made of dark matter encircle our Milky Way and other large, visible galaxies.
..............................................................
The scientists remain puzzled as to why these dark-matter galaxies contain few or no stars, however, given that 10 to 20 percent of their mass should exist as normal matter. "It's difficult to hide that much material," Dalal observes. The findings will appear in the June 10 issue of the Astrophysical Journal."

This is a ten-year old article. It would be interesting to check up on what these researchers have published recently. In any case, however, this is all made confusing by conflicting terminology. In general, a "dark matter galaxy" these days refers to a hypothetical isolated galaxy. What this article is discussing is clumps of dark matter orbiting inside or just outside the dark matter halo of large galaxies. Calling a non-homogeneous mix of dark matter around a large galaxy a halo with dark satellite galaxies confuses two different concepts. And in the context of the earlier discussion, these clumps of dark matter (if they exist) don't seem to be associated with any ordinary matter- including supermassive black holes.

I don't think so. What happens is that the Sagittarius Dwarf Galaxy is gradually absorbed into the Milky Way- a type of merger that occurs all over the Universe. Nothing is going dark, and there's nothing to suggest that the dark matter of the SDG will remain distinct from the dark matter of the Milky Way.

This is a ten-year old article. It would be interesting to check up on what these researchers have published recently. In any case, however, this is all made confusing by conflicting terminology. In general, a "dark matter galaxy" these days refers to a hypothetical isolated galaxy. What this article is discussing is clumps of dark matter orbiting inside or just outside the dark matter halo of large galaxies. Calling a non-homogeneous mix of dark matter around a large galaxy a halo with dark satellite galaxies confuses two different concepts. And in the context of the earlier discussion, these clumps of dark matter (if they exist) don't seem to be associated with any ordinary matter- including supermassive black holes.

This is a ten-year old article. It would be interesting to check up on what these researchers have published recently. In any case, however, this is all made confusing by conflicting terminology. In general, a "dark matter galaxy" these days refers to a hypothetical isolated galaxy. What this article is discussing is clumps of dark matter orbiting inside or just outside the dark matter halo of large galaxies. Calling a non-homogeneous mix of dark matter around a large galaxy a halo with dark satellite galaxies confuses two different concepts.