How do supermassive blackholes stop star formation?

This article has me wondering a few things.

SPACE.com -- Huge Black Holes Stifle Star Formation
"As matter falls towards a black hole, momentum forces it to flatten out
into a dense, hot disk. A lot of the matter never makes it into the
black hole and is ejected in jets that travel at a significant fraction
of light-speed, emanating from the poles of the black hole. Those jets
might do such a good job of heating gas near the center of a galaxy that
there is little fuel available for the creation of new stars, Yi said. "
http://www.space.com/scienceastronom...e_tuesday.html


If you need cold gas to start star formation, then how cold is cold? And
what temperature do these jets heat the surrounding gas upto that
prevents the star formation? Is it preventing star formation throughout
the whole galaxy, or just around the vicinity of the blackhole? If it's
the whole galaxy, then is the temperature of space within that whole
galaxy quite high?

Yousuf Khan

"YK" == Yousuf Khan writes:

YK This article has me wondering a few things.
SPACE.com -- Huge Black Holes Stifle Star Formation "As matter
falls towards a black hole, momentum forces it to flatten out into
a dense, hot disk. A lot of the matter never makes it into the
black hole and is ejected in jets that travel at a significant
fraction of light-speed, emanating from the poles of the black
hole. Those jets might do such a good job of heating gas near the
center of a galaxy that there is little fuel available for the
creation of new stars, Yi said. "
http://www.space.com/scienceastronom...e_tuesday.html

Yes, this is a topic of active research.

YK If you need cold gas to start star formation, then how cold is
YK cold?

The gas in molecular clouds from which stars form might have
temperatures as low as 10 K. In the center of our own Galaxy, the
molecular cloud temperatures appear to be somewhat higher, perhaps 100
K, though stars continue to form.

YK And what temperature do these jets heat the surrounding gas upto
YK that prevents the star formation?

The jets may very well ionize the material around them, which would
heat the gas to thousands of degrees.

YK Is it preventing star formation throughout the whole galaxy, or
YK just around the vicinity of the blackhole? If it's the whole
YK galaxy, then is the temperature of space within that whole galaxy
YK quite high?

Probably just in the immediate vicinity. Part of this issue of course
concerns the direction of the jet. Gas at large angles from the jet
is probably relatively unaffected.


Note that a similar effect is thought to occur in clusters of
galaxies. Here the gas surrounding the galaxies should cool and start
to produce stars. This isn't observed, and one possible explanation
is that a jet from the center of one of the galaxies in the cluster
can keep the gas "stirred up" enough that it cannot cool.

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Joseph Lazio wrote:
YK If you need cold gas to start star formation, then how cold is
YK cold?

The gas in molecular clouds from which stars form might have
temperatures as low as 10 K. In the center of our own Galaxy, the
molecular cloud temperatures appear to be somewhat higher, perhaps 100
K, though stars continue to form.

Okay, so anywhere upto 100 Kelvin seems to be ideal. I assume the gas
is denser in the galactic core than in the galactic disk, so that's why
100K is okay in the centre, but 10K is better in the disk?

YK And what temperature do these jets heat the surrounding gas upto
YK that prevents the star formation?

The jets may very well ionize the material around them, which would
heat the gas to thousands of degrees.

What is the maximum radius of ionization from the centre of the jet?
Would it be expressed in the 10's, or 100's, or 1000's of light-years?
Or maybe a more fun way to ask would be if a starship were travelling
above or below the plane of a galaxy towards its central axis, would it
feel "a wind" and get blown off-course at some distance away from the
central axis? :-)

Note that a similar effect is thought to occur in clusters of
galaxies. Here the gas surrounding the galaxies should cool and start
to produce stars. This isn't observed, and one possible explanation
is that a jet from the center of one of the galaxies in the cluster
can keep the gas "stirred up" enough that it cannot cool.

Is there a significant amount of gas between the galaxies in a cluster?
Enough gas to produce another galaxy perhaps?

Yousuf Khan

In article ,
Yousuf Khan writes:
SPACE.com -- Huge Black Holes Stifle Star Formation

The preprint is at http://arxiv.org/abs/astro-ph/0608517 . I've had
it lying around for a couple of weeks now but haven't had time to
read it.

"[QSO] jets
might do such a good job of heating gas near the center of a galaxy that
there is little fuel available for the creation of new stars, Yi said. "

Is it preventing star formation throughout
the whole galaxy, or just around the vicinity of the blackhole?

Bearing in mind that I haven't read the preprint...

Jets should easily disrupt star formation in any clouds they hit, but
I don't see how jets can affect a very large fraction of the galaxy.
Jets occupy too small a solid angle. But presumably the authors know
that, so maybe they have a new idea.

The idea that star-forming clouds can be disrupted by radiation from
an accretion disk -- as opposed to jets -- is not new. There is
evidence that such disruption is important in the most luminous
objects, but I don't think there is a good understanding of when it's
important and when it isn't. Whatever effect there may be, there are
distant galaxies that show evidence of rapid star formation despite
having a luminous active nucleus.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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"SW" == Steve Willner writes:

SW In article , Yousuf Khan
SW writes:
SPACE.com -- Huge Black Holes Stifle Star Formation

SW The preprint is at http://arxiv.org/abs/astro-ph/0608517 . [...]

"[QSO] jets might do such a good job of heating gas near the center
of a galaxy that there is little fuel available for the creation of
new stars, Yi said. "

Is it preventing star formation throughout the whole galaxy, or
just around the vicinity of the blackhole?

The authors imply the entire galaxy.

SW Bearing in mind that I haven't read the preprint...

SW Jets should easily disrupt star formation in any clouds they hit,
SW but I don't see how jets can affect a very large fraction of the
SW galaxy. Jets occupy too small a solid angle. But presumably the
SW authors know that, so maybe they have a new idea.

In my quick skim of the paper, I find no stated mechanism for the
quenching effect. Rather, the logic appears to be the following:

They conducted ultraviolet observations of a series of early-type
galaxies (ellipticals). They found that the amount of UV emission,
which traces star formation, is anti-correlated with stellar velocity
dispersion (i.e., how fast stars are moving). The stellar velocity
dispersion is known to be correlated with central black hole mass.
Thus, there appears to be an anti-correlation between black hole mass
and star formation, from which the authors infer that central black
holes affect their entire galactic environment.

I didn't see them state explicitly how this would occur, other than
by removing gas from the galaxy which would imply strong winds and/or
jets.

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"b" == bbbl67 writes:

b Joseph Lazio wrote:
YK If you need cold gas to start star formation, then how cold is
YK cold?
The gas in molecular clouds from which stars form might have
temperatures as low as 10 K. In the center of our own Galaxy, the
molecular cloud temperatures appear to be somewhat higher, perhaps
100 K, though stars continue to form.

b Okay, so anywhere upto 100 Kelvin seems to be ideal. I assume the
b gas is denser in the galactic core than in the galactic disk, so
b that's why 100K is okay in the centre, but 10K is better in the
b disk?

It's a value that's accurate to astronomical accuracy. There are
large deviations, how the temperature is measured can lead to
different results, etc. Nonetheless, if one wants some kind of
"typical" value, 10 K certainly works.


YK And what temperature do these jets heat the surrounding gas upto
YK that prevents the star formation?
The jets may very well ionize the material around them, which
would heat the gas to thousands of degrees.

b What is the maximum radius of ionization from the centre of the
b jet? Would it be expressed in the 10's, or 100's, or 1000's of
b light-years?

I don't know the ionization radius off the top of my head. The jets
themselves, at least down at their bases, can be fairly narrow, tens
of lightyears. However, I would expect that the area potentially
influenced by their radiation could be much larger.

Also, I just posted a response to Steve Willner in which I noted that
the original paper does not specify in any great detail the mechanism
by which they think that the black holes suppress star formation.


Note that a similar effect is thought to occur in clusters of
galaxies. Here the gas surrounding the galaxies should cool and
start to produce stars. This isn't observed, and one possible
explanation is that a jet from the center of one of the galaxies in
the cluster can keep the gas "stirred up" enough that it cannot
cool.

b Is there a significant amount of gas between the galaxies in a
b cluster? Enough gas to produce another galaxy perhaps?

In a typical cluster, there's more gas in the intra-cluster medium
than in galaxies. However, much of it is way too hot, 10^7 K or
hotter, to cool and condense into stars.


While typing this response, it occurred to me that perhaps what the
authors of the original paper had in mind was something similar to
what is thought to happen in clusters. The observed effect is seen
for early-type galaxies, i.e., those with large bulges and little or
no disk. Thus, one might suspect that these galaxies formed from
large, roughly spherical clouds of gas. If the black hole injected a
jet into a large cloud of gas, it could induce significant turbulence,
which might have the effect of shutting down star formation.

--
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No means no, stop rape. | http://patriot.net/%7Ejlazio/
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In article ,
Joseph Lazio writes:
In my quick skim of the paper, I find no stated mechanism for the
quenching effect. Rather, the logic appears to be the following:

They conducted ultraviolet observations of a series of early-type
galaxies (ellipticals). They found that the amount of UV emission,
which traces star formation, is anti-correlated with stellar velocity
dispersion (i.e., how fast stars are moving).
....
I didn't see them state explicitly how this would occur, other than
by removing gas from the galaxy which would imply strong winds and/or
jets.

Thanks, Joe. As we all know, correlation does not imply causality.

My _guess_ would be that big bulges (indicated by the large velocity
dispersions) come from past mergers, which converted gas to stars.
Thus current star formation is absent because there is no gas left.
That would also explain the absence of dust around luminous active
galactic nuclei (AGN), as discovered years ago. The absence might
have nothing to do with the AGN itself. As we now know (but didn't
back then), luminous AGN are markers for massive bulges.

As Joe and probably most readers realize, this is a very active topic
of ongoing research, and the very complex relations among galaxy
assembly, star formation, and active nuclei are not understood. I've
certainly been wrong plenty of times before, and the suggestion above
should be treated as speculation and nothing more.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

I wrote:
My _guess_ would be that big bulges (indicated by the large velocity
dispersions) come from past mergers, which converted gas to stars.
Thus current star formation is absent because there is no gas left.

Good thing I labelled this as speculation! I've just come from a
colloquium given by Christy Tremonti (U. Arizona). She and her
colleagues have been studying post-starburst galaxies, and in some of
the galaxies they found Mg II absorption lines blue-shifted by about
1000 km/s. That indicates strong gas outflows. Thus simply using up
all the gas doesn't seem to be the whole story.

It is still an open question whether the outflows were powered by an
AGN or something else (presumably some aspect of the star formation
process).

As I wrote before, this is a very active topic of current research!