| Topic: |
Science > Physics |
| User: |
"John Schutkeker" |
| Date: |
24 Mar 2007 05:34:38 PM |
| Object: |
I Doubt Andromeda Collision |
I just gave a close and critical reading to J. Dubinski's 10/06 article
in Sky & Telescope about the Andromeda Galaxy's eventual collision with
the Milky Way Galaxy, and I do not find the argument to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is heading
toward us with a radial velocity of 120 km/sec, but IMO, the absolute
lack of reliable evidence for it's transverse velocity make it
impossible to draw any conclusions at all from that datum.
It is equally likely that Andromeda is in orbit around the Milky Way,
with a transverse velocity equal to or greater than the radial velocity.
And even a fairly moderate transverse velocity, much smaller than the
radial velocity, would still put Andromeda into an orbit whose
eccentricity would not be too high. Only if the transverse velocity
were effectively negligible compared to the radial velocity would it be
destined for collision.
Dubinski says that there is no observational data for proper motion, but
he claims that *models* based on tidal and gravitational forces within
the local cluster estimate the proper motion to be between 0 and 150
km/sec. However, in the absence of observational data, results produced
by such models are notoriously unreliable. Information about initial
conditions, a critically important input into dynamical models, simply
does not exist, and the only way to get it would be to work backward
from an observation. IMO, this makes any such predictions about proper
motion completely unreliable.
Also, note that Dubinski's error range for the proper motion contains
the observed radial velocity, leaving open the possibility that the
proper and radial motions might be equal. This would put Andromeda into
a roughly circular orbit around us, completely contradicting the
conclusion about a collision.
As the old cliche says, extraordinary claims require extraordinary
evidence. As far as the argument presented in the S&T article is
concerned, although evidence is there, it is still not sufficient to
bolster an extraordinary claim.
.
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| User: "Steve Willner" |
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| Title: Re: I Doubt Andromeda Collision |
04 Apr 2007 04:13:39 PM |
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John Schutkeker wrote:
I just gave a close and critical reading to J. Dubinski's 10/06 article
in Sky & Telescope about the Andromeda Galaxy's eventual collision with
the Milky Way Galaxy, and I do not find the argument to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is heading
toward us with a radial velocity of 120 km/sec, but IMO, the absolute
lack of reliable evidence for it's transverse velocity make it
impossible to draw any conclusions at all from that datum.
One can estimate the _earliest_ possible date for a collision.
And even a fairly moderate transverse velocity, much smaller than the
radial velocity, would still put Andromeda into an orbit whose
eccentricity would not be too high. Only if the transverse velocity
were effectively negligible compared to the radial velocity would it be
destined for collision.
Add "on this pass." Because of dynamical friction, there has to be a
collision eventually, but it could be very far in the future. M33 will
also merge with the other two large spirals.
As the old cliche says, extraordinary claims require extraordinary
evidence.
It's hardly an extraordinary claim, but I agree that the evidence that
merger will occur _on the next pass_ is absent.
Someone else asked about refereed publications. I don't find anything
in ADS, not even conference proceedings.
.
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| User: "Agent Smith" |
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| Title: Re: I Doubt Andromeda Collision |
05 Apr 2007 10:21:43 PM |
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"Steve Willner" <willner@cfa.harvard.edu> wrote in
news:1175721219.027342.139780@l77g2000hsb.googlegroups.com:
John Schutkeker wrote:
I just gave a close and critical reading to J. Dubinski's 10/06
article in Sky & Telescope about the Andromeda Galaxy's eventual
collision with the Milky Way Galaxy, and I do not find the argument
to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is
heading toward us with a radial velocity of 120 km/sec, but IMO, the
absolute lack of reliable evidence for it's transverse velocity make
it impossible to draw any conclusions at all from that datum.
One can estimate the _earliest_ possible date for a collision.
And even a fairly moderate transverse velocity, much smaller than the
radial velocity, would still put Andromeda into an orbit whose
eccentricity would not be too high. Only if the transverse velocity
were effectively negligible compared to the radial velocity would it
be destined for collision.
Add "on this pass." Because of dynamical friction, there has to be a
collision eventually, but it could be very far in the future. M33 will
also merge with the other two large spirals.
As the old cliche says, extraordinary claims require extraordinary
evidence.
It's hardly an extraordinary claim, but I agree that the evidence that
merger will occur _on the next pass_ is absent.
Someone else asked about refereed publications. I don't find anything
in ADS, not even conference proceedings.
I couldn't find anything in Arxiv, so I sent Dubinski an e-mail, asking
for references.
.
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| User: "Joseph Lazio" |
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| Title: Re: I Doubt Andromeda Collision |
11 Apr 2007 07:36:08 PM |
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"SW" == Steve Willner <willner@cfa.harvard.edu> writes:
SW> John Schutkeker wrote:
I just gave a close and critical reading to J. Dubinski's 10/06
article in Sky & Telescope about the Andromeda Galaxy's eventual
collision with the Milky Way Galaxy, and I do not find the argument
to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is
heading toward us with a radial velocity of 120 km/sec, but IMO,
the absolute lack of reliable evidence for it's transverse velocity
make it impossible to draw any conclusions at all from that datum.
[...]
SW> Someone else asked about refereed publications. I don't find
SW> anything in ADS, not even conference proceedings.
I thought that Mark Reid, Avi Loeb, and collaborators had been making
dynamical models for the Local Group, based in part on astrometric
measurements of M33 (and IC 10).
--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
.
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| User: "Sam Wormley" |
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| Title: Re: I Doubt Andromeda Collision |
25 Mar 2007 12:12:27 AM |
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John Schutkeker wrote:
I just gave a close and critical reading to J. Dubinski's 10/06 article
in Sky & Telescope about the Andromeda Galaxy's eventual collision with
the Milky Way Galaxy, and I do not find the argument to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is heading
toward us with a radial velocity of 120 km/sec, but IMO, the absolute
lack of reliable evidence for it's transverse velocity make it
impossible to draw any conclusions at all from that datum.
It is equally likely that Andromeda is in orbit around the Milky Way,
with a transverse velocity equal to or greater than the radial velocity.
And even a fairly moderate transverse velocity, much smaller than the
radial velocity, would still put Andromeda into an orbit whose
eccentricity would not be too high. Only if the transverse velocity
were effectively negligible compared to the radial velocity would it be
destined for collision.
Dubinski says that there is no observational data for proper motion, but
he claims that *models* based on tidal and gravitational forces within
the local cluster estimate the proper motion to be between 0 and 150
km/sec. However, in the absence of observational data, results produced
by such models are notoriously unreliable. Information about initial
conditions, a critically important input into dynamical models, simply
does not exist, and the only way to get it would be to work backward
from an observation. IMO, this makes any such predictions about proper
motion completely unreliable.
Also, note that Dubinski's error range for the proper motion contains
the observed radial velocity, leaving open the possibility that the
proper and radial motions might be equal. This would put Andromeda into
a roughly circular orbit around us, completely contradicting the
conclusion about a collision.
As the old cliche says, extraordinary claims require extraordinary
evidence. As far as the argument presented in the S&T article is
concerned, although evidence is there, it is still not sufficient to
bolster an extraordinary claim.
Hard to say without relative motion data in three dimensions. However
in the long run these two large neighbors are likely to merge.
Galactic Collision Reveals Fate of Milky Way Galaxy
http://cfa-www.harvard.edu/press/pr0429.html
Hubble Reveals Stellar Fireworks Accompanying Galaxy Collisions
http://hubblesite.org/newscenter/archive/releases/1997/34/astrofile/
Astrophysicists Run Largest Galactic Collision Simulations Ever on
NPACI's Blue Horizon
http://www.npaci.edu/online/v4.9/galaxies2.html
.
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| User: "John Schutkeker" |
|
| Title: Re: I Doubt Andromeda Collision |
27 Mar 2007 04:50:52 PM |
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Sam Wormley <swormley1@mchsi.com> wrote in
news:%wnNh.8316$oV.4167@attbi_s21:
John Schutkeker wrote:
I just gave a close and critical reading to J. Dubinski's 10/06
article in Sky & Telescope about the Andromeda Galaxy's eventual
collision with the Milky Way Galaxy, and I do not find the argument
to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is
heading toward us with a radial velocity of 120 km/sec, but IMO, the
absolute lack of reliable evidence for it's transverse velocity make
it impossible to draw any conclusions at all from that datum.
It is equally likely that Andromeda is in orbit around the Milky Way,
with a transverse velocity equal to or greater than the radial
velocity. And even a fairly moderate transverse velocity, much
smaller than the radial velocity, would still put Andromeda into an
orbit whose eccentricity would not be too high. Only if the
transverse velocity were effectively negligible compared to the
radial velocity would it be destined for collision.
Dubinski says that there is no observational data for proper motion,
but he claims that *models* based on tidal and gravitational forces
within the local cluster estimate the proper motion to be between 0
and 150 km/sec. However, in the absence of observational data,
results produced by such models are notoriously unreliable.
Information about initial conditions, a critically important input
into dynamical models, simply does not exist, and the only way to get
it would be to work backward from an observation. IMO, this makes
any such predictions about proper motion completely unreliable.
Also, note that Dubinski's error range for the proper motion contains
the observed radial velocity, leaving open the possibility that the
proper and radial motions might be equal. This would put Andromeda
into a roughly circular orbit around us, completely contradicting the
conclusion about a collision.
As the old cliche says, extraordinary claims require extraordinary
evidence. As far as the argument presented in the S&T article is
concerned, although evidence is there, it is still not sufficient to
bolster an extraordinary claim.
Hard to say without relative motion data in three dimensions.
However in the long run these two large neighbors are likely to
merge.
I reread the article again, and another bad assumption they made before
doing their simulation was to assume that the two galaxies are in a high
eccentricity orbit. The justification that Dubinski gives is that KBO's
are in high eccentricity orbits, which I think is a completely
unjustified analogy.
Assuming a high eccentricity orbit, effectively assumes the answer
before the analysis is even started. It's common knowledge that objects
come very close to each other at periapses of highly eccentric orbits.
Since galaxies are more like clouds than rigid objects, they merely need
to pass close to one another to initiate the coalescence process by
tearing each other apart.
Given their optimistic assumption, they shouldn't even need a simulation
to prove their conclusion. They should be able to do a back of the
envelope calculation to show that their assumption puts the results far
enough inside any envelope of uncertainty to make the outcome obvious.
Another way to support their assumption would be to have census data
showing that the majority of distant galaxies are in orbits of high
eccentricity. However, that data doesn't exist any more than proper
motion data for Andromeda.
S&T didn't give a reference, so would anybody happen to know where the
original paper was published? I'm hoping that my arthritis may have
subsided enough that I can get to the library this weekend.
.
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| User: "Me" |
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| Title: Re: I Doubt Andromeda Collision |
25 Mar 2007 08:32:08 AM |
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Well in 25 billion years time, I'll be nothing,so I don't care.
Where's my dinner tomorrow?
"Sam Wormley" <swormley1@mchsi.com> wrote in message
news:%wnNh.8316$oV.4167@attbi_s21...
John Schutkeker wrote:
I just gave a close and critical reading to J. Dubinski's 10/06 article
in Sky & Telescope about the Andromeda Galaxy's eventual collision with
the Milky Way Galaxy, and I do not find the argument to be compelling.
I have no quarrel with the Doppler measurement that Andromeda is heading
toward us with a radial velocity of 120 km/sec, but IMO, the absolute
lack of reliable evidence for it's transverse velocity make it impossible
to draw any conclusions at all from that datum.
It is equally likely that Andromeda is in orbit around the Milky Way,
with a transverse velocity equal to or greater than the radial velocity.
And even a fairly moderate transverse velocity, much smaller than the
radial velocity, would still put Andromeda into an orbit whose
eccentricity would not be too high. Only if the transverse velocity were
effectively negligible compared to the radial velocity would it be
destined for collision.
Dubinski says that there is no observational data for proper motion, but
he claims that *models* based on tidal and gravitational forces within
the local cluster estimate the proper motion to be between 0 and 150
km/sec. However, in the absence of observational data, results produced
by such models are notoriously unreliable. Information about initial
conditions, a critically important input into dynamical models, simply
does not exist, and the only way to get it would be to work backward from
an observation. IMO, this makes any such predictions about proper motion
completely unreliable.
Also, note that Dubinski's error range for the proper motion contains the
observed radial velocity, leaving open the possibility that the proper
and radial motions might be equal. This would put Andromeda into a
roughly circular orbit around us, completely contradicting the conclusion
about a collision.
As the old cliche says, extraordinary claims require extraordinary
evidence. As far as the argument presented in the S&T article is
concerned, although evidence is there, it is still not sufficient to
bolster an extraordinary claim.
Hard to say without relative motion data in three dimensions. However
in the long run these two large neighbors are likely to merge.
Galactic Collision Reveals Fate of Milky Way Galaxy
http://cfa-www.harvard.edu/press/pr0429.html
Hubble Reveals Stellar Fireworks Accompanying Galaxy Collisions
http://hubblesite.org/newscenter/archive/releases/1997/34/astrofile/
Astrophysicists Run Largest Galactic Collision Simulations Ever on
NPACI's Blue Horizon
http://www.npaci.edu/online/v4.9/galaxies2.html
.
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