Starship Asterisk*

BDanielMayfield wrote:What is the galactic escape velocity for Zeta Oph and stars in the Sun's neighborhood?

Bruce

TildalWave at Stack Exchange Space Exploration wrote:
RAVE took a sample of 90 high-velocity Milky Way stars (some moving at over 300 km/s) for which their position and velocity was determined sufficiently precise, and then compared their movement to models of other, similar spiral galaxies, to reach an estimate of Milky Way's total mass at about 1.6 trillion solar masses. Once they had that, they could calculate estimated escape velocities for our stellar neighbourhood, for which mass distribution and radial velocity with respect to the galactic barycenter are of course most well understood.

Solar system's orbital velocity is estimated at roughly 220 km/s, and galactic escape velocity for our vicinity at about 537 km/s. So in the direction of Solar system's velocity vector, velocity required to escape Milky Way is ~ 317 km/s. And much more, if this Solar system's own orbital momentum cannot be used to full extent and a launch in other directions is required. This is of course assuming you can launch on a trajectory that avoids getting too close to gravitational influence of other solar systems.

The RAVE survey: the Galactic escape speed and the mass of the Milky Way, Piffl et al., 17 Sep 2013 (Complete PDF)

The RAVE Survey: Constraining the Local Galactic Escape Speed, Smith et al., 9 May 2007 (Complete PDF)

Ann wrote: So in the direction of Solar system's velocity vector, velocity required to escape Milky Way is ~ 317 km/s. And much more, if this Solar system's own orbital momentum cannot be used to full extent and a launch in other directions is required. This is of course assuming you can launch on a trajectory that avoids getting too close to gravitational influence of other solar systems.
Ann

NCTom wrote:Given this came from Spitzer and enhanced with false color, what does the heavy green represent even to coloring a nice spiral galaxy near the bottom? I also wondered about the red dots, the left one of which has a pretty halo.

De58te wrote:

NCTom wrote:Given this came from Spitzer and enhanced with false color, what does the heavy green represent even to coloring a nice spiral galaxy near the bottom? I also wondered about the red dots, the left one of which has a pretty halo.

The "stunning infrared portrait" link says, " For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red. "

cytophile wrote:The measurement of the velocity of the star seems to imply consideration of a particular inertial frame of reference, appropriate to this context. Is it's motion assumed to be relative to the sun, the galactic center, the whole cosmos?

Ann wrote:

BDanielMayfield wrote:What is the galactic escape velocity for Zeta Oph and stars in the Sun's neighborhood?

Bruce

Well, what do I know, Bruce, but at least I found this:

... Solar system's orbital velocity is estimated at roughly 220 km/s, and galactic escape velocity for our vicinity at about 537 km/s. So in the direction of Solar system's velocity vector, velocity required to escape Milky Way is ~ 317 km/s.

Ann

Chris Peterson wrote:

De58te wrote:

NCTom wrote:Given this came from Spitzer and enhanced with false color, what does the heavy green represent even to coloring a nice spiral galaxy near the bottom? I also wondered about the red dots, the left one of which has a pretty halo.

The "stunning infrared portrait" link says, " For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red. "

FWIW, that nominally translates to 450° C material for blue, 90° C material for green, and -150° C material for red. (Those are the blackbody peaks; the curves are very broad, of course, so the numbers only give a sense of the temperature range for each filter.)

cytophile wrote:The measurement of the velocity of the star seems to imply consideration of a particular inertial frame of reference, appropriate to this context. Is it's motion assumed to be relative to the sun, the galactic center, the whole cosmos?

Ann wrote:

Chris Peterson wrote:

De58te wrote: The "stunning infrared portrait" link says, " For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red. "

FWIW, that nominally translates to 450° C material for blue, 90° C material for green, and -150° C material for red. (Those are the blackbody peaks; the curves are very broad, of course, so the numbers only give a sense of the temperature range for each filter.)

450^o C doesn't do justice to 32,000K Zeta Ophiuchi.

BDanielMayfield wrote:Wikipedia says that the radial velocity of Zeta Oph is -15 km/s, so it is moving away from the Sun at 15 km/s.

heehaw wrote:Hey, now THERE"S a project for NASA!! Let's get this solar system OUT of this darned galaxy that we're currently stuck in! Let's hit the road! Outside this mucky interstellar medium we are at the moment surrounded by, we'd get a much cleaner view of that lovely universe out there! And we could look back and really see our own Galaxy for the first time!

BDanielMayfield wrote:

BDanielMayfield wrote:Wikipedia says that the radial velocity of Zeta Oph is -15 km/s, so it is moving away from the Sun at 15 km/s.

That means this star once was much closer to us than it is now. I wonder how close it was to the Sun when its partner popped?

An object in motion tends to remain in motion in a straight line.

Chris Peterson wrote:

BDanielMayfield wrote:

BDanielMayfield wrote:Wikipedia says that the radial velocity of Zeta Oph is -15 km/s, so it is moving away from the Sun at 15 km/s.

That means this star once was much closer to us than it is now. I wonder how close it was to the Sun when its partner popped?

A negative radial velocity means it is getting nearer to us (although the actual direction is determined by combining the radial and tangential velocities).