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edi.becker
2008-Sep-25, 08:44 PM
I just heard that the Milky Way galaxy (our home) has a super massive Black hole at the center (where else would could it be?). Is our black hole generating a Relativistic jets perpendicular to our galactic plane?

Thank you.

alainprice
2008-Sep-25, 08:57 PM
Nope.

There are active Quasars, and dormant ones. I figure the Milky Way is dormant.

parejkoj
2008-Sep-25, 10:25 PM
Not only is the Milky Way not a quasar, it doesn't even have an "active galactic nucleus" because our own personal supermassive black hole (Sgr A*) is very quiescent.

It's not the jets that determine whether something is a quasar or not (some quasars do not have bright jets, and some galaxies that aren't very active do), but the amount the black hole is accreting, and thus how bright it is. A quasar has a large black hole that is accreting a lot of material very rapidly, and thus is highly luminous.

closetgeek
2008-Sep-27, 01:35 AM
It is speculated that it was a quasar at one point, though, right?

Neverfly
2008-Sep-27, 01:47 AM
I think it spits out some anti matter, though...;)

sohh_fly
2008-Sep-27, 02:56 AM
i think the black hole in our centre is feeding at a rate of something like the mass of the earth per year at this point.
which is more like a quick sip before hitting the track again so to speak.

but when it does start feeding at a violent rate ,what would we see from earth or would we not know that it is happening?
i've been thinking about this all day , we would surely see the jets shooting out no??

parejkoj
2008-Oct-05, 01:56 AM
It is speculated that it was a quasar at one point, though, right?

Actually, it probably never was. The mass of our central black hole is "only" ~4 million solar masses. The growth rate of most quasars would get them above that in a fairly short order, and for quasars where we can most directly measure the mass of the black hole, we find a mass around a billion (109) solar masses.

But, since the Milky Way has a fairly well defined bulge, it probably underwent at least one significant merger (besides the minor "acquisitions" that resulted in things like the Sagittarius dwarf stream (http://www.astro.virginia.edu/~mfs4n/sgr/)), so it would certainly have been classified as having an active galactic nucleus (AGN) at some point its history. Quasars are just the upper-end of the AGN luminosity function; classically there is a dividing line at a certain absolute magnitude, but it's pretty arbitrary since we now know it to be a continuous distribution of luminosities. Think of Quasars as the "big kids on the block" - not too many of them around, but they are easily noticed!


I think it spits out some anti matter, though...;)

uh... only sorta. There is probably some pair-production from the energies of the magnetic field at the inner edge of the accretion disk, but it isn't particularly significant in terms of the overall energy production. Though Fermi (née GLAST) (http://fermi.gsfc.nasa.gov/) will help answer that question quantitatively.


i think the black hole in our centre is feeding at a rate of something like the mass of the earth per year at this point.
which is more like a quick sip before hitting the track again so to speak.

Pretty close, though I think the best upper-limits are a bit lower than that: Marrone et al. (2007) (http://adsabs.harvard.edu/abs/2007ApJ...654L..57M), give an upper limit of ~10-7 solar masses per year, which is ~1/10 the mass of the Earth. It appears to sporadically go a good bit above that value for short periods (http://adsabs.harvard.edu/abs/2006MNRAS.366..358C). But you're definitely correct that it's just sippin', not slurpin'.


but when it does start feeding at a violent rate ,what would we see from earth or would we not know that it is happening?
i've been thinking about this all day , we would surely see the jets shooting out no??

Again, jets aren't necessarily associated with high accretion rates; plenty of very weakly accreting AGN have quite prominent jets. In fact, there is reason to suspect that very strong accretion can actually quench the jets (though I can't provide a citation for that at the moment). But in answer to the first part of your question, it would be a while before we would see anything here on Earth: in the optical part of the spectrum, there is very extreme extinction in the direction of Sgr A*: ~30 magnitudes in V-band! If the black hole suddenly started accreting strongly, it would have to sublimate most of that dust before we'd be able to see anything in optical light. But X-ray and IR observations would pick something out fairly quickly, since those cut through the dust.

Related to this, there were several (http://arxiv.org/abs/0809.3548) papers (http://arxiv.org/abs/0809.4490) recently (http://arxiv.org/abs/0809.4677) posted to astro-ph about direct imaging of the accretion disk using Very Long Baseline Interferometry at sub-millimeter wavelengths. It won't be too long before we've actually got images (interferometric images, but still...) of the accretion disk structure around Sgr A*. Now that's cool!

Eroica
2008-Oct-05, 04:45 PM
... we would surely see the jets shooting out no??
One theory is that radio-loud active galaxies (which are usually characterized by jets and radio lobes) are associated with accreting supermassive black holes with very high angular momentum - they're spinning at very high rates.

This could occur if two large galaxies merge, their supermassive black holes merging to form an even bigger black hole with the combined angular momentum of its parents.

Such mergers are believed to produce giant elliptical galaxies, and the host galaxies of most radio-loud active galaxies are indeed large ellipticals.

timb
2008-Oct-20, 08:11 PM
This could occur if two large galaxies merge, their supermassive black holes merging to form an even bigger black hole with the combined angular momentum of its parents.


That doesn't seem right. Adding two vectors can't make a vector with magnitude greater than twice the larger of the two vectors, and most likely the vectors wouldn't be perfectly aligned. Accretion disks can spin black holes up.

m1omg
2008-Oct-20, 08:13 PM
This question seems to me like asking "Is Trabant a Ferrari Enzo?" or "Is my paper model rocket a Saturn V?".

timb
2008-Oct-20, 08:19 PM
This question seems to me like asking "Is Trabant a Ferrari Enzo?" or "Is my paper model rocket a Saturn V?".

Or, "Is the Sun a black hole?"

connor240287
2008-Oct-20, 08:33 PM
Nope The Milky Way is Not a Quasar

And if you Was going to Ask Was the Milky Way a Quasar in the distant past?

The Answer to That is

Our Galaxy does have a supermassive black hole at the center, which is what astronomers believe powers the enormous emission in quasars. However, whether or not it was ever a quasar is still up for debate. It's entirely possible that it was, but we don't have any proof one way or the other.

Invader Xan
2008-Oct-20, 08:35 PM
Not only is the Milky Way not a quasar, it doesn't even have an "active galactic nucleus" because our own personal supermassive black hole (Sgr A*) is very quiescent.

At least it is right now. Some believe there's evidence suggesting it was a lot more active active as little as 300 years ago (http://www.esa.int/esaSC/SEMV9Z3XQEF_index_0.html)... ;)

sohh_fly
2008-Oct-20, 11:48 PM
if the smbh at our center started feeding,would we feel anything?
the optical light would take some time reach us , but how about the jets,
im sure that they would have to be moving some of the dust clouds/lanes.
which would start a chain reaction pushing outward from the center?

if this was to be the case,i would imagine that this cause would have some kind of effect for the rest of the galaxy.
i think there would be so many things to consider, maybe the heating of the galaxy, spin rotation might differ,also i think the supernova's would be a dime a dozen then.


are any of these ideas plausible?
just wondering whats the effects are?

also has the BH at our center ever been active since the solar system evolved or at least since humans evolved?

parejkoj
2008-Oct-21, 01:39 AM
And if you Was going to Ask Was the Milky Way a Quasar in the distant past?

The Answer to That is

Our Galaxy does have a supermassive black hole at the center, which is what astronomers believe powers the enormous emission in quasars. However, whether or not it was ever a quasar is still up for debate. It's entirely possible that it was, but we don't have any proof one way or the other.

No, not really. No debate, I'd say. See my comment above (http://www.bautforum.com/questions-answers/79305-milky-way-quasar.html#post1337200). Basically, Sgr A* is too small to have ever been a "classical quasar." But it certainly was "on" at various times in the past; otherwise it wouldn't be as big as it is. There are also quite a few signs (Invader Xan links to one), from shock heating and other processes in the galactic center, that it has been "on" at various points in the relatively recent past (~few thousand years).

As to its effects on us, were it to "turn on" now... I'd bet that Phil Plait's new book, "Death from the Skies!" has a chapter on that. I should order myself a copy, just to be sure. :)

For those who are paying attention, I'm not really defining what "on" means in this case. There is a broad range of AGN feeding rates, and thus a broad range in AGN luminosities, and thus a broad range in their effects on their surroundings. In general (though not quite always), "secular growth" (not merger driven) isn't strong enough to cause major feedback, like the kind that might affect us here on Earth, while merger-induced growth often (but not always) is. So, there may be some interesting fireworks when M31 and the Milky Way merge in a few billion years...

Eroica
2008-Oct-21, 09:53 AM
That doesn't seem right. Adding two vectors can't make a vector with magnitude greater than twice the larger of the two vectors, and most likely the vectors wouldn't be perfectly aligned. Accretion disks can spin black holes up.I don't know the details, but wouldn't angular momentum be conserved in such a merger?

timb
2008-Oct-21, 12:20 PM
I don't know the details, but wouldn't angular momentum be conserved in such a merger?

Yes, but my point was that adding together two lots of angular momentum doesn't make a giant amount of angular momentum. The orbital angular momentum of the SMBHs would also contribute, probably more than the rotational angular momenta of the two SMBHs. Is this what you were referring to? In that case I agree, the merger of two SMBHs could create a SMBH which is spinning much faster.

ASEI
2008-Oct-21, 12:52 PM
Quick question - I once heard something to the effect that the radiated energy that matter emmits as it falls into a black hole is equal to the total mass-energy of the matter - in which case, what is the black hole getting out of the deal?

timb
2008-Oct-21, 12:58 PM
Quick question - I once heard something to the effect that the radiated energy that matter emmits as it falls into a black hole is equal to the total mass-energy of the matter - in which case, what is the black hole getting out of the deal?

Nothing in that scenario, so that can't be right. Matter doesn't have to emit any energy as it falls into a black hole.

Eroica
2008-Oct-22, 11:01 AM
Quick question - I once heard something to the effect that the radiated energy that matter emmits as it falls into a black hole is equal to the total mass-energy of the matter - in which case, what is the black hole getting out of the deal?The radiated energy is approximately equal to one tenth of the rest mass-energy of the accreting matter. The remaining 90% is added to the black hole's mass.

Eroica
2008-Oct-22, 11:07 AM
Yes, but my point was that adding together two lots of angular momentum doesn't make a giant amount of angular momentum. The orbital angular momentum of the SMBHs would also contribute, probably more than the rotational angular momenta of the two SMBHs. Is this what you were referring to? In that case I agree, the merger of two SMBHs could create a SMBH which is spinning much faster.Yes, I see the point you are making. The final spin rate will depend on the way in which the SMBHs merge as they approach one another.

It's like a close binary star system in which the separation between the two stars is gradually diminishing. They orbit their common centre of mass faster and faster, and when they merge this orbital angular momentum is conserved in the rotational angular momentum of the merged star. Right?

timb
2008-Oct-23, 12:56 AM
Yes, I see the point you are making. The final spin rate will depend on the way in which the SMBHs merge as they approach one another.

It's like a close binary star system in which the separation between the two stars is gradually diminishing. They orbit their common centre of mass faster and faster, and when they merge this orbital angular momentum is conserved in the rotational angular momentum of the merged star. Right?

That's basically my understanding too. So you have to sum three "spins": those of the two BHs and their mutual orbit. Note that some of these may be retrograde relative to each other and cancel out. Angular momentum is a vector quantity, like velocity, not a scalar, like mass.

Due to the magic of general relativity (http://en.wikipedia.org/wiki/Gravitational_radiation#Energy.2C_momentum.2C_and_ angular_momentum_carried_by_gravitational_waves) some of the angular momentum is radiated as gravitational waves, so the sum will be less than the total of the parts in general.

snowflakeuniverse
2008-Oct-23, 04:40 AM
Hi EdiBecker and Parejkoj

Parejkoj said the following

Think of Quasars as the "big kids on the block" - not too many of them around, but they are easily noticed!


There are over a million quasars discovered so far and the count is not complete. .


Photometric Quasars: The One Million Mark and 9-D SDSS+Spitzer Selection
American Astronomical Society, AAS Meeting #211, #142.02
12/2007
Abstract
We describe a photometrically selected catalog that includes 1,175,097 unresolved quasar candidates to i=21 from 8417 sq. deg. of imaging from the Sloan Digital Sky Survey's (SDSS) Data Release 6. With an expected efficiency in excess of 95% for 17<i<20; and an overall efficiency of 85.6%, the catalog is expected to contain approximately 1 million quasars. We further discuss the optimal selection and photometric redshift estimation of quasars from combined SDSS plus Spitzer-IRAC photometry. Using only the deeper 3.6 and 4.5 micron bands of Spitzer-IRAC and single epoch SDSS photometry, we reliably identify 2580 quasar candidates in the Spitzer FLS, ELAIS-N1/N2, and Lockman Hole fields --- roughly a density of 110 per square degree and 10 times the density of the SDSS spectroscopic sample. Photometric redshifts are estimated to be accurate to 4 percent or better for 86 percent of the sample.


Now with well over 100,000 million galaxies observed in our Universe, one could argue that then number of quasars are “proportionally” small.

However, this leads to the question as to where did these large massive quasars go if they are not the progenitors of Galaxies? Astronomers have established that our galaxy is larger than most. Also, there are no galaxies observed that appear to have thousands of times the mass of our galaxy.

This then leads to the Mass problem you mentioned, which I believe I first mentioned in this Against the Mainstream thread. http://www.bautforum.com/against-mainstream/71117-white-black.html

Snowflake

StupendousMan
2008-Oct-23, 01:51 PM
Now with well over 100,000 million galaxies observed in our Universe, one could argue that then number of quasars are “proportionally” small.


Right. If we pick some volume of the universe and look within that volume, we might find a few active quasars, but we'll find thousands or millions of galaxies -- most of which are piddly little items like the Magellanic Clouds.



However, this leads to the question as to where did these large massive quasars go if they are not the progenitors of Galaxies?


When the mass accretion rate of a super-massive black hole (SMBH) falls to low levels, it stops emitting enough radiation to qualify as a "quasar". Astronomers would then call the object "a very large and massive galaxy with an inactive SMBH at its center", if they can make the detailed observations necessary to detect the SMBH; or, if astronomers don't have lots of high-resolution spectra of the central regions, and so don't detect the SMBH, they would call it "a very large and massive galaxy."



Astronomers have established that our galaxy is larger than most.


Yes, that's right. The great majority of galaxies are tiny little insignificant objects like the Magellanic Clouds.



Also, there are no galaxies observed that appear to have thousands of times the mass of our galaxy.


That's true. The mass of the Milky Way is roughly 5 x 10^(11) solar masses, within a radius of 50 kpc, and rises to perhaps 2 x 10^(12) solar masses at large radii; see

http://arxiv.org/abs/astro-ph/0608343

The largest galaxies in big clusters have masses which may be larger by factors of 10 to 100, but not 1000, as far as I know. A brief scan of the recent literature, for example, turns up

http://adsabs.harvard.edu/abs/2007ApJ...662..781R
http://adsabs.harvard.edu/abs/2007MNRAS.376..180N

and other papers which use gravitational lensing to measure the masses of galaxies at large radii.





This then leads to the Mass problem you mentioned, which I believe I first mentioned in this Against the Mainstream thread.

Here you cross the line into ATM. Please keep your ATM ideas in the ATM forum.

parejkoj
2008-Oct-23, 01:51 PM
Now with well over 100,000 million galaxies observed in our Universe, one could argue that then number of quasars are “proportionally” small.

The number of quasars is absolutely "proportionally" small. They are quite rare objects.



However, this leads to the question as to where did these large massive quasars go if they are not the progenitors of Galaxies? Astronomers have established that our galaxy is larger than most. Also, there are no galaxies observed that appear to have thousands of times the mass of our galaxy.

About our galaxy: it depends on how you define "galaxy" and how you define "larger" and how you define "most." And the thing to compare, when talking about the SMBHs at the center of galaxies, is not the total galaxy mass, but the bulge velocity dispersion, which is somewhat related to galaxy mass, but traces the history in a different way.

As to your first question, I gave a talk with nearly that title back in February... Remember, a quasar is a massive black hole that is actively accreting material at a high rate. Remove the material, and the massive black hole is still there, it just isn't easily visible. M87 is an example of a galaxy hosting a "former quasar" - there is a large SMBH but no cool gas for it to accrete. As far as we can tell, the present day analogs of the quasars we see in the distant universe are the brightest cluster galaxies. Big, massive ellipticals with little to no star formation and a very large central object.

snowflakeuniverse
2008-Oct-25, 01:09 AM
First
Quasars are the progenitors of large galaxies.

Second
1 million quasars represents a significant quantity. It is proportionally a small fraction of the over 100,000 million galaxies observed, but it is still a large number.

Third,
The True proportional amount of quasars to galaxies is not 1/100,000.

When we look into deep space, we see galaxies that have existed for billions of years. Quasars have a much shorter duration, and are only observed in the distant past. This distorts our true perception of the number of quasars with respect to the number of galaxies.

For example,
Lets say the galaxies in the Universe have existed in the Universe for 10,000 million years. (U.S. 10 billion) (Order of magnitude calculation)

Lets assume that the galaxies ability to produce the prodigious amounts of energy associated with the quasar phase of the galaxy is “short lived”, lasting 10 million years.

So in the “fractional observation window” that quasars can be seen is only
1/1, 000 of window allowing the observation of galaxies. This would result in the quasar to galaxy ratio to be 1/10 during the quasar era in our Universes evolution.

In this example, quasars are not “rare”.

Now there are other kinds of modeling or assumptions that can be made which would significantly alter the proportional relationships of galaxies to quasars, but the primary point or issue this example is given is to show that true proportional representation of quasars to galaxies is much higher than 1/100,000, once the proper historical perspective is used. Arguably my sample estimates could be construed as being somewhat exaggerated, but it does illustrate the issue.

P.S.
I am not a “professional”, just a rather serious amateur. Some of the points I am making may be somewhat counter to what some “professionals” may be asserting.


Snowflake

parejkoj
2008-Oct-25, 05:07 AM
Quasars are the progenitors of large galaxies.

Not exactly, no. A quasar is the actively accreting black hole at the center of what will likely eventually be a large elliptical galaxy. But the quasar that we see on the sky is not the galaxy itself, just the accreting SMBH. For very distant sources (z~>4), the galaxy is too dim to be seen beyond the light of the quasar, but for nearer sources, HST can distinguish the quasar light from the galaxy light (http://hubblesite.org/newscenter/archive/releases/1996/35/image/a/).

Haven't we been through this before?


1 million quasars represents a significant quantity. It is proportionally a small fraction of the over 100,000 million galaxies observed, but it is still a large number.

What does "still a large number" mean? 1023 is also "a large number", but that many molecules of hydrogen barely make a gram of mass. 1 million photometrically-selected quasars in the SDSS field down to r~20 is certainly a large number, considering 15 years ago only some few thousands were known. But compared to the number of non-active galaxies it is effectively nothing. I will repeat my true statement, and then give some numbers to back it up:

'The number of quasars is absolutely "proportionally" small. They are quite rare objects.'

Look at the final two plots (18 & 19) in Richards et al. (2008) (submitted) (http://arxiv.org/abs/0809.3952), which is the paper related to the AAS talk that you quoted above. Those plots give the quasar number density (on the sky) and luminosity function (in 3-d space). Figure 18 shows that there are around a hundred quasars per square degree at i~= 20, and Figure 19 shows that there is ~1 "dim" quasar per ~107 cubic megaparsecs, and ~1 "bright" quasar per ~108 cubic megaparsecs at a redshift of 2 (the quasar space density is redshift dependent, which Figure 19 also demonstrates).

Contrast that with galaxies (http://arxiv.org/abs/0806.4930) (that was the first "general" galaxy luminosity function paper I found in 10 seconds of searching), which have a sky density of many thousands per square degree down to i~=15 and a real space density of ~1 per 100 cubic Mpc for galaxies as bright as the Milky Way. In comparing the sky densities of quasars and galaxies, note that the flux limits I'm quoting are two orders of magnitude dimmer for quasars; if we were counting galaxies down to the same flux limit, the number of galaxies per square degree would be drastically larger.

Do you see now that the claim "a million is a large number" is rather meaningless? And that quasars really are rare objects in the universe? To say nothing of their increasing rarity in recent epochs...



When we look into deep space, we see galaxies that have existed for billions of years. Quasars have a much shorter duration, and are only observed in the distant past. This distorts our true perception of the number of quasars with respect to the number of galaxies.

No, you are confused. As an example, M87 is not a quasar, but it has a supermassive black hole at its center. Quasars are rapidly accreting supermassive black holes. If you want to count the space density of supermassive black holes above a given mass whether they are accreting or not, you can--and it's been done (http://adsabs.harvard.edu/cgi-bin/bib_query?2007ApJ...658..721H): just search ADS for other examples--but that is not the same thing as counting the space density of quasars. Do you understand the distinction?



...[made-up numbers snipped for brevity]

In this example, quasars are not “rare”.


Seeing as I've given observational data above that directly contradicts your claim, will you withdraw that statement, or concede that you are confusing quasars and SMBHs? With that out of the way, what, exactly are you claiming?



I am not a “professional”, just a rather serious amateur. Some of the points I am making may be somewhat counter to what some “professionals” may be asserting.

But the "points" that you are making are counter to the observational evidence! So why are your "points" even worth considering?