PDA

View Full Version : Galaxy movement and Hubble Telescope



The_Radiation_Specialist
2007-Sep-23, 01:12 PM
I was wondering if Hubble can take detailed images so that we can see a little bit of change in the appearance of a galaxy such as movement. It would be cool to have before and after images of how a galaxy changed in maybe 10 years. Is that too short of a time?

StupendousMan
2007-Sep-23, 01:39 PM
I was wondering if Hubble can take detailed images so that we can see a little bit of change in the appearance of a galaxy such as movement. It would be cool to have before and after images of how a galaxy changed in maybe 10 years. Is that too short of a time?

Yes.

HST and other optical telescopes have resolutions of order 0.1 arcseconds. At the distance to the very close Andromeda galaxy, this corresponds to roughly 100,000 AU, or less than one light year. A typical angular velocity for material in the Andromeda galaxy is very roughly 10^(-8) radians per year. Therefore, a star in the outer regions of that galaxy's disk, a distance 100,000 light years from its center, will move by 10^(-3) light years each year.

In other words, it will take centuries or millenia for rotational motions of even the nearest galaxies to build up to movements we can discern with optical telescopes.

Nereid
2007-Sep-23, 02:33 PM
I was wondering if Hubble can take detailed images so that we can see a little bit of change in the appearance of a galaxy such as movement. It would be cool to have before and after images of how a galaxy changed in maybe 10 years. Is that too short of a time?I think some of this kind of differential astrometry, to detect proper motions, has been done with some stars in the closest (Milky Way) globular clusters, and some stars in some of the closest MW satellite dwarf galaxies.

The best 'beyond the Local Group' apparent proper motion observations - in the form of 'pictures' - that I can think of are those of the M87 jet, some of which were, indeed, taken by the HST (http://www.stsci.edu/ftp/science/m87/m87.html).

KaiYeves
2007-Sep-23, 06:13 PM
Nice avatar, Stupendous Man. Are you really six-year-old millionare Calvin?

Tobin Dax
2007-Sep-23, 08:00 PM
I think some of this kind of differential astrometry, to detect proper motions, has been done with some stars in the closest (Milky Way) globular clusters, and some stars in some of the closest MW satellite dwarf galaxies.
It definitely has been. I was trying to do something similar with M31 and M32 last year, based the globular cluster research, but we're barely there. (And it apparently wasn't interesting enough to get funding.)

Neverfly
2007-Sep-23, 08:32 PM
I think some of this kind of differential astrometry, to detect proper motions, has been done with some stars in the closest (Milky Way) globular clusters, and some stars in some of the closest MW satellite dwarf galaxies.

The best 'beyond the Local Group' apparent proper motion observations - in the form of 'pictures' - that I can think of are those of the M87 jet, some of which were, indeed, taken by the HST (http://www.stsci.edu/ftp/science/m87/m87.html).

Ok, now hang on.
My brain automatically wrapped around that "apparent motion" at 6 times c.

What does this mean exactly?!?!

StupendousMan
2007-Sep-23, 08:56 PM
Ok, now hang on.
My brain automatically wrapped around that "apparent motion" at 6 times c.

What does this mean exactly?!?!

It means that the material is moving at speeds which are "relativistic", meaning close to c (but NOT quite as fast as light), _and_ in almost directly towards the observer.

There are many good references which explain the apparent superluminal motion of material in jets from AGN and quasars. For example,


http://spiff.rit.edu/classes/phys314/lectures/superlum/superlum.html

Read this, then ask again if you still have questions.