Why is the Milky Way's blackhole so wimpy?

Has there been any studies done to explain why the Milky Way and
Andromeda galaxies with very similar overall masses to one another, have
such dissimilarly sized central blackholes?

Mass of the galaxies:
Overall mass of Milky Way: ~1,250 billion Msun http://is.gd/P9r95R
Overall mass of Andromeda: ~1,230 billion Msun http://is.gd/HgarRo

But the mass of the blackholes (according to http://is.gd/o21oyj):
Blackhole mass of Milky Way: ~4 million Msun (0.00032% of galactic mass)
Blackhole mass of Andromeda: ~140 million Msun (0.01138% of galactic mass)

I'm wondering if the Milky Way's blackhole is in a typical size range
for other galaxies of its size, or of galaxies of any size for that matter?

I'm wondering if this mass discrepancy has any implications for life in
various galaxies, too? Maybe like how it's impossible for life (or even
planets) to evolve in solar systems with too large stars at their
centers, perhaps there are galaxies with too large blackholes for life
to emerge in them? A larger blackhole would produce more radiation
throughout the rest of their galaxies.

Yousuf Khan

On 10/17/13 2:16 AM, Yousuf Khan wrote:
Has there been any studies done to explain why the Milky Way and
Andromeda galaxies with very similar overall masses to one another, have
such dissimilarly sized central blackholes?

Mass of the galaxies:
Overall mass of Milky Way: ~1,250 billion Msun http://is.gd/P9r95R
Overall mass of Andromeda: ~1,230 billion Msun http://is.gd/HgarRo

But the mass of the blackholes (according to http://is.gd/o21oyj):
Blackhole mass of Milky Way: ~4 million Msun (0.00032% of galactic mass)
Blackhole mass of Andromeda: ~140 million Msun (0.01138% of galactic mass)

I'm wondering if the Milky Way's blackhole is in a typical size range
for other galaxies of its size, or of galaxies of any size for that matter?

I'm wondering if this mass discrepancy has any implications for life in
various galaxies, too? Maybe like how it's impossible for life (or even
planets) to evolve in solar systems with too large stars at their
centers, perhaps there are galaxies with too large blackholes for life
to emerge in them? A larger blackhole would produce more radiation
throughout the rest of their galaxies.

Yousuf Khan



The difference in indicative of the cannibalistic history of each.

In article ,
Yousuf Khan writes:
Has there been any studies done to explain why the Milky Way and
Andromeda galaxies with very similar overall masses to one another, have
such dissimilarly sized central blackholes?

Mass of the galaxies:
Overall mass of Milky Way: ~1,250 billion Msun http://is.gd/P9r95R
Overall mass of Andromeda: ~1,230 billion Msun http://is.gd/HgarRo

But the mass of the blackholes (according to http://is.gd/o21oyj):
Blackhole mass of Milky Way: ~4 million Msun (0.00032% of galactic mass)
Blackhole mass of Andromeda: ~140 million Msun (0.01138% of galactic mass)

Understanding this in detail would take more work than I'm prepared
to do, but the "Magorrian relation" says that black hole mass
correlates with _spheroid mass_ (i.e., bulge mass for a spiral
galaxy), not with total galaxy mass. In other words, the galaxy disk
mass doesn't count towards expected black hole mass. There's also a
fair bit of scatter around the mean relation, though not usually as
much as indicated above.

Another thing to check is where that M31 BH mass value comes from,
though the first source I glanced at gives that value. (The Milky
Way BH mass comes from stellar orbits and should be reliable.)

Maybe this will be enough of a clue for someone else to work out the
details.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 17/10/2013 9:40 AM, Sam Wormley wrote:
The difference in indicative of the cannibalistic history of each.

I don't think so, over the past 13.8 billion years, they must've had
similar cannibalistic histories, being as they are from the same
neighbourhood.

Also surprising is that the Andromeda galaxy is actually slightly less
massive than the Milky Way, though probably identical masses within the
margins of error. Yet, M31's blackhole is 35 times more massive! If
there were a linear relationship between BH mass and galactic mass, then
M31 should be a brutally large elliptical galaxy already, 30 times
larger than the MW, and being the central galaxy of the Local Group. Or
alternatively, the MW should be a wimpy dwarf galaxy about the size of
the LMC. Yet somehow a wimpy 4M Msun blackhole is just as easily the
central anchor of this galaxy as a 140M Msun blackhole is of the
otherwise nearly identical M31 galaxy?!?

Yousuf Khan

On 18/10/2013 6:07 PM, Steve Willner wrote:
Understanding this in detail would take more work than I'm prepared
to do, but the "Magorrian relation" says that black hole mass
correlates with _spheroid mass_ (i.e., bulge mass for a spiral
galaxy), not with total galaxy mass. In other words, the galaxy disk
mass doesn't count towards expected black hole mass. There's also a
fair bit of scatter around the mean relation, though not usually as
much as indicated above.

There's some indication that the MW is a barred spiral galaxy, rather
than a standard spiral. That might indicate that it's got an extended
central bulge. Is it possible that there are other mid-sized blackholes
(i.e. 100,000 Msun) anchoring the outer parts of the bar?

Another thing to check is where that M31 BH mass value comes from,
though the first source I glanced at gives that value. (The Milky
Way BH mass comes from stellar orbits and should be reliable.)

Even if M31's BH mass isn't completely accurate, I'm sure it's within
50% of the final determination. I remember before the MW's BH was
well-established, they were guessing between 3 million and 6 million
Msun, which is remarkably close to the finally established 4 million
Msun mass.

And anyways, I might be wrong, but M31's BH mass was apparently recently
fully established. I think they got stellar velocity data around its BH too.

Yousuf Khan

In article ,
Yousuf Khan writes:
There's some indication that the MW is a barred spiral galaxy, rather
than a standard spiral. That might indicate that it's got an extended
central bulge.

It's not clear to me whether bars count as part of the bulge. I
don't know of any papers addressing the question, but this is not a
subject I follow in detail.

In general, spiral galaxies can have pretty much any ratio between
bars and bulges; the presence of one doesn't imply or deny the other.

Is it possible that there are other mid-sized blackholes
(i.e. 100,000 Msun) anchoring the outer parts of the bar?

"Intermediate mass black holes" have been searched for but with no
success that I know of. Even if they exist, they wouldn't have any
significant dynamical effect on a bar with far larger mass.

Even if M31's BH mass isn't completely accurate, I'm sure it's within
50% of the final determination.

Why are you sure of that? Typical indirect measurements have
uncertainties of at least a factor of two or three with much larger
errors in individual cases.

I remember before the MW's BH was well-established, they were
guessing between 3 million and 6 million Msun, which is remarkably
close to the finally established 4 million Msun mass.

This is not at all comparable. Those estimates were based on direct
measurements of motions within 0.1 pc of the black hole. They could
hardly be wrong by much.

What you'd really want to compare with are guesses before the motions
were measured. There were certainly papers claiming zero black hole
mass, and I'm pretty sure I remember guesses much larger than 10^7,
maybe larger than 10^8.

And anyways, I might be wrong, but M31's BH mass was apparently recently
fully established. I think they got stellar velocity data around its BH too.

If that last is the case, which I haven't checked, the mass should be
accurate.

The Magorrian relation says the bulge mass is about 2000 times the
black hole mass. That would make the bulges about 8E9 solar masses
for the Milky Way and 3E11 for M31. Are these inconsistent with
direct measurements of the respective bulge masses?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 23/10/2013 6:10 PM, Steve Willner wrote:
In article ,
Yousuf Khan writes:
There's some indication that the MW is a barred spiral galaxy, rather
than a standard spiral. That might indicate that it's got an extended
central bulge.

It's not clear to me whether bars count as part of the bulge. I
don't know of any papers addressing the question, but this is not a
subject I follow in detail.

It would be an interesting question to have answered.

Is it possible that there are other mid-sized blackholes
(i.e. 100,000 Msun) anchoring the outer parts of the bar?

"Intermediate mass black holes" have been searched for but with no
success that I know of. Even if they exist, they wouldn't have any
significant dynamical effect on a bar with far larger mass.

My understanding is that there are several examples of intermediate
blackholes found, such as this one:

Rare Black Hole Survives Galaxy's Destruction | Intermediate-Mass Black
Hole HLX-1 | Dwarf Galaxies | Space.com
http://www.space.com/14586-middlewei...rf-galaxy.html

Even if M31's BH mass isn't completely accurate, I'm sure it's within
50% of the final determination.

Why are you sure of that? Typical indirect measurements have
uncertainties of at least a factor of two or three with much larger
errors in individual cases.

I remember before the MW's BH was well-established, they were
guessing between 3 million and 6 million Msun, which is remarkably
close to the finally established 4 million Msun mass.

This is not at all comparable. Those estimates were based on direct
measurements of motions within 0.1 pc of the black hole. They could
hardly be wrong by much.

What you'd really want to compare with are guesses before the motions
were measured. There were certainly papers claiming zero black hole
mass, and I'm pretty sure I remember guesses much larger than 10^7,
maybe larger than 10^8.

And anyways, I might be wrong, but M31's BH mass was apparently recently
fully established. I think they got stellar velocity data around its BH too.

If that last is the case, which I haven't checked, the mass should be
accurate.

I think this article pretty much proves that they've been photographing
the interior of the Andromeda's bulge, near the SMB. So with so much
detail, they really should know the mass of their SMB to a great degree.

The Weekend Image : Andromeda Galaxy's Supermassive Black Hole
http://www.dailygalaxy.com/my_weblog...lack-hole.html

The Magorrian relation says the bulge mass is about 2000 times the
black hole mass. That would make the bulges about 8E9 solar masses
for the Milky Way and 3E11 for M31. Are these inconsistent with
direct measurements of the respective bulge masses?

I don't know, I've only recently found out about the Magorrian
Relationship, so I don't know what the bulge masses of either galaxy
are. Let's see if Google or Wolfram turns up anything?

This paper suggests that the bulge mass of the MW is 2E+10 Msun, while
its length is 5E+9 Lsun.

http://www.astro.caltech.edu/~george...y20-Lec16x.pdf

I'll have to search for similar info on Andromeda. I found this paper,
but I haven't had time to search through it all yet. There does seem to
be a table of masses for the bulges of various nearby galaxies, though I
don't think MW or Andromeda are included.

Yousuf Khan

In article ,
Yousuf Khan writes:
My understanding is that there are several examples of intermediate
blackholes found, such as this one:

Rare Black Hole Survives Galaxy's Destruction | Intermediate-Mass Black
Hole HLX-1 | Dwarf Galaxies | Space.com
http://www.space.com/14586-middlewei...rf-galaxy.html

While it's intermediate in mass, it still was (apparently) formed at
the center of a galaxy. I think of "intermediate mass" as suggesting
formation a different way, perhaps at the core of a globular cluster.
Regardless of the semantics, few intermediate mass BHs are known.

I think this article pretty much proves that they've been photographing
the interior of the Andromeda's bulge, near the SMB. So with so much
detail, they really should know the mass of their SMB to a great degree.

The Weekend Image : Andromeda Galaxy's Supermassive Black Hole
http://www.dailygalaxy.com/my_weblog...lack-hole.html

You are might well be right, but an image is not a spectrum. If I
had time to pursue this topic, I'd track down the source of the M31
mass estimate.

This paper suggests that the bulge mass of the MW is 2E+10 Msun, while
its length is 5E+9 Lsun.
http://www.astro.caltech.edu/~george...y20-Lec16x.pdf

That's not a paper, but it should be a good source. ("George" is
George Djorgovski, Caltech professor.) If the bulge mass is 2E10,
the BH mass should be 1E7, which isn't far off the measured 4E6.

What's needed is a bulge mass for M31. I had a quick look, and there
seems to be a fair bit of controversy. A couple of sources suggest
M31 bulge mass is not much bigger than the Milky Way's. On the other
hand, one source suggests the BH mass isn't out of line for the bulge
mass, but finding actual numbers was harder than it should have been,
and I gave up. Anyway, these seem to be the lines to pursue: what's
the real M31 bulge mass, and how reliable is the BH mass estimate?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 10/29/13, 5:33 PM, Steve Willner wrote:
In article ,
Yousuf Khan writes:
My understanding is that there are several examples of intermediate
blackholes found, such as this one:

Rare Black Hole Survives Galaxy's Destruction | Intermediate-Mass Black
Hole HLX-1 | Dwarf Galaxies | Space.com
http://www.space.com/14586-middlewei...rf-galaxy.html

While it's intermediate in mass, it still was (apparently) formed at
the center of a galaxy. I think of "intermediate mass" as suggesting
formation a different way, perhaps at the core of a globular cluster.
Regardless of the semantics, few intermediate mass BHs are known.

I think this article pretty much proves that they've been photographing
the interior of the Andromeda's bulge, near the SMB. So with so much
detail, they really should know the mass of their SMB to a great degree.

The Weekend Image : Andromeda Galaxy's Supermassive Black Hole
http://www.dailygalaxy.com/my_weblog...lack-hole.html

You are might well be right, but an image is not a spectrum. If I
had time to pursue this topic, I'd track down the source of the M31
mass estimate.

This paper suggests that the bulge mass of the MW is 2E+10 Msun, while
its length is 5E+9 Lsun.
http://www.astro.caltech.edu/~george...y20-Lec16x.pdf

That's not a paper, but it should be a good source. ("George" is
George Djorgovski, Caltech professor.) If the bulge mass is 2E10,
the BH mass should be 1E7, which isn't far off the measured 4E6.

What's needed is a bulge mass for M31. I had a quick look, and there
seems to be a fair bit of controversy. A couple of sources suggest
M31 bulge mass is not much bigger than the Milky Way's. On the other
hand, one source suggests the BH mass isn't out of line for the bulge
mass, but finding actual numbers was harder than it should have been,
and I gave up. Anyway, these seem to be the lines to pursue: what's
the real M31 bulge mass, and how reliable is the BH mass estimate?



Thank you.