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Dr. Drake - Arecibo Message will reach M13

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#1 Jason H.

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Posted 17 August 2010 - 10:50 AM

Hello,
I had the good fortune of speaking with Dr. Frank Drake (a nice gentleman) this weekend at SETIcon about the Arecibo Message (and other SETI-related things) and whether M13 was going to be there or not; I then referred to the 1999 Cornell release

http://www.news.corn...message.ws.html

Which in one part states

"...Ironically, the globular cluster at which the signal was aimed won't be there when the message arrives. It will have moved well out of the way in the normal rotation of the galaxy."

(Someone here in this Cloudy Nights forum had recently indicated that this could not be true, so I just had to ask him about it :^)

Dr. Drake believes that the statement that M13 will not be there is incorrect, and that the message will arrive there.

I also asked some other Arecibo Message-related questions that I haven't been able to find information about on the internet, specifically, did he know if there is someplace that might be recorded the exact RA/DEC used for the transmission, his answer was that they aimed it at the exact center of M13 and that it's center was easy to determine from the sphere of M13 (so I guess I should take that as a no? anyway...)

A few years ago I noticed that there were a few stars in the Tycho catalog that are much closer to the Earth than M13, and I knew that Arecibo's beam width at the transmission frequency was only a few arc minutes wide, and M13 is probably closer to 20 arc minutes wide, so I had to ask if Arecibo swept M13 (i.e. Earth's rotation swept the message over M13 and no one part got all of it) but before I could finish he positively/emphatically (but in a gentle voice) stated that Arecibo was tracking M13.

Then I asked if he recalled Arecibo's beamwidth at that frequency, and he said it was around 2 arc min. (close to what I had seen posted for other work at Arecibo at that frequency.)

After I mentioned the Tycho catalog stars in the field of view and possibly in the path, he also said there there are perhaps something like 30 stars between M13 and us (more than I thought there were, but I don't know what's in surveys other than Tycho catalog either.)

The Cornell release also stated

" There are stars closer to our solar system than that, but none of them is in the path of the message."

I wonder if any of those ~30 closer stars fit in the 2 arc minute centroid window of M13 (with room for dish pointing error.)

This is getting long so I'll stop here; I'll post other things Dr. Drake, Jill Tarter, Seth Shostak, and top planet hunting Astronomers, minor planet finders, astrobiologists and a meteorite hunter all said to me personally in response to my questions, and other things they spoke about at the conference in other threads.

Regards, Jason Higley
______________________________________
My SETI website http://setisociety.org

#2 Maryland Mike

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Posted 18 August 2010 - 06:50 AM

Fascinating stuff, Jason, thanks for posting. Wish I could have gone.

Is the metallicity of globulars so poor as to greatly reduce the likelihood of their developing life?

#3 GlennLeDrew

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Posted 18 August 2010 - 09:54 PM

The absolute proper motion (in the ICRS reference frame, and with respect to the Sun) of M13 is ~3.4 mas/yr. Given a distance of 25,000 l-y, during this period the cluster will move across our line of sight ~1.4 arcminutes.

I haven't considered the contribution from the Earth's ~30 km/sec orbital velocity about the Sun, but I should think it's small enough to ignore for this purpose.

#4 Greg K.

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Posted 20 August 2010 - 02:48 PM

Fascinating stuff, Jason, thanks for posting. Wish I could have gone.

Is the metallicity of globulars so poor as to greatly reduce the likelihood of their developing life?


Certainly the night sky from a planet in or near a globular would be spectacular!

#5 llanitedave

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Posted 20 August 2010 - 03:48 PM

I don't know how much metallicity a star needs in order to support planet formation. It is pretty low in globulars, but not zero.

#6 Jason H.

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Posted 20 August 2010 - 10:05 PM

Fascinating stuff, Jason, thanks for posting. Wish I could have gone.

Is the metallicity of globulars so poor as to greatly reduce the likelihood of their developing life?


Hi Mike, the short answer IMO, often yes. That said there are some globulars that are metal rich, I believe NGC 6791 is one

http://en.wikipedia.org/wiki/NGC_6791

Interestingly, this metal-rich globular cluster is within Kepler's FOV.

Generally speaking though, many globs are known for their lack of metals, and are therefore speculated to not be conducive places for our brand of life. Planet formation is possible though (indeed M4 is known to have a planet orbiting a pulsar), but most of the planets contemplated to be in metal-poor globulars are generally considered to possibly be around stars on the main sequence and probably will be gas giant planets without metals, again, probably devoid of our kind of life?

OTOH, if you think a civilization is interested in relocating (their star reaches the end of its life and they want to relocate, or they are a machine race who only cares about stability or energy) globs are thought to possess many white dwarfs which might be a nice place to move if you are tired of relocating to less long-lived systems? (bring your other resources though.) It also might be a great place to set up a beacon (everybody looks at globular clusters and there's lots of free energy to be exploited.)

One other thing, globular clusters are known to have picked up some so-called straggler stars; these are much higher in metals and might be good targets of investigation.

Jason Higley

#7 Maryland Mike

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Posted 21 August 2010 - 11:39 AM

Good points. The long-lived stability of these stars could make them an attractive destination for a civilization, if not necessarily conducive to birthing them.

#8 GlennLeDrew

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Posted 21 August 2010 - 08:34 PM

One other thing, globular clusters are known to have picked up some so-called straggler stars; these are much higher in metals and might be good targets of investigation.


I've not read of known cases of globs capturing stragglers. But the phenomenon of the so-called 'blue straggler' is generally attributed to the coalescing of a tight binary. This now more massive singleton enjoys a new lease on life, so to speak, as the gain in mass makes it both brighter and hotter/bluer, and so it moves up and to the left in the H-R diagram.

A fair number of open clusters also have blue stragglers, they being more likely the older and richer the cluster.

If there is evidence that these stragglers have higher metallicity, by how much? Would it be too much to account for via the extra processing which would occur after a binary merges into a more massive singleton?

#9 Jason H.

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Posted 22 August 2010 - 06:55 PM

Hello Glenn, I think I have (incorrectly) made an association of the following two concepts:

Capture of Field Stars by Globular Clusters in Dense Bulge Regions

http://arxiv.org/PS_...3/9703166v1.pdf

And M4's Methusela

http://science.nasa....0jul_psrplanet/

"...He bases this conclusion on the fact a planet was uncovered in such an unlikely place: orbiting two captured stars..."

In the first paper there is reference to the "contamination" of the globular population, which I recall skimming a similar article a long time ago. In the second I should have more carefully considered the "captured stars" as I've apparently mis-interpreted (probably from skimming it too?), leading to a doubly bad inference on my part. Sorry.

Jason Higley

#10 GlennLeDrew

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Posted 23 August 2010 - 02:25 PM

Jason,
I wouldn't dare to say you've mis-interpreted those papers, as I haven't read them myself. I was only recounting my own ignorance. Here are some off-the cuff guesses on my part...

It's certainly possible for a cluster to capture field stars, but from dynamical considerations I'm aware of the probablity should be rather low, except, I suppose, for those clusters that lie on orbits which keep them confined to one or both the denser, inner bulge region or disk. Another critical factor is the velocity difference between cluster and the mean motion for the field star population through which the cluster moves. Finally, the so-called 'impact parameter' leading to a capture event would necessarily be narrowly bound, given that most captures would have to be accomplished by a very close passage between a field star and a cluster member star (or more likely a binary), unless the relative motion is so small that the gravitational potential of the cluster as a whole can do its work.

To better grasp this, note that the velocity dispersion in a typical globular is of order ~5 km/s, if memory serves. This is a not fast orbital velocity for a cluster star. A field star passing through a glob at a velocity much larger than this will therefore not generally be captured.

Throghout the region where most globs orbit, their velocity about the galactic center is more than 200 km/s. The disk's motion is very well ordered, with velocity dispersions being for the most part no larger than 10-30 km/s, depending on object age. So a glob would have to lie on a not highly inclined orbit to begin to have a chance to capture a disk star as it plunges through the disk. But in the bulge, the stars are on a very wide range of orbits at all possible inclinations and orbital eccentricity. This leads to a better possibility of a capture due to the greater potential number of stars which would share a fairly similar orbit to that of the glob.

Interesting stuff!


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