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This is the thing that strikes me as immediately weird about this result: as you point out, we can resolve stars in other galaxies. We've been able to for a lon
by tjradcliffe 12y ago
This is the thing that strikes me as immediately weird about this result: as you point out, we can resolve stars in other galaxies. We've been able to for a long time.
So why hasn't anyone ever noticed this extra-galactic population? They'd show up as anomalous field stars, probably with odd proper motions.
If you think of it in terms of the Local Group, every galaxy should have a "halo" of these free stars around it in a radius comparable to half the distance between galaxies. Admittedly that's pretty low density, but is it really low enough that no one has ever seen one of these objects?
Or are they only present at very high redshift (and if so, what happened to them?)
- JoeAltmaier 12y agoAre there discernible proper motion to extra-galactic objects? Our seasonal excursion of 186 million miles around the Sun looks pretty tiny in comparison.
- Florin_Andrei 12y agoThe parallax can only be used for things inside this galaxy (and until very recently, only in our immediate vicinity within). It's the very first step outside the solar system in the cosmic distance ladder. Other methods must be used outside the galaxy. http://en.wikipedia.org/wiki/Cosmic_distance_ladder http://en.wikipedia.org/wiki/Cosmic_distance_ladder
- Florin_Andrei 12y agoI guess two reasons: - the population density of extra-galactic stars is super low - outside our galaxy we're only discerning a fraction of the biggest nearest stars anyway You're looking for the odd ball at the remote end of a huge concert hall packed with regular balls.