Planets <--> solar systems <--> galaxies

[Loren Booda]

Have planets been observed outside of solar systems, or solar systems outside of galaxies?

[Sorry!]

Have planets been observed outside of solar systems, or solar systems outside of galaxies?

Just a rogue planet floating around without a star?... I though part of the definition of a plant was that it was in orbit around a star...

[Loren Booda]

Just a rogue planet floating around without a star?... I though part of the definition of a plant was that it was in orbit around a star...
Rogue it is.

[DaveC426913]

No. It is hard enough to find planets when we know almost exactly where to look and they're well lit by their star.

Even if we knew exactly where look, a rogue planet would be pretty much invisible in the darkness.

[russ_watters]

Our planet detection methods require them to be around stars.

[Loren Booda]

Our planet detection methods require them to be around stars.

A sensible definition for the present. It follows that binary planets are precluded.

What about the possibility of solar systems outside of galaxies?

[russ_watters]

A sensible definition for the present. It follows that binary planets are precluded. I'm not sure you understood me: It's not a definition, it is a matter of technological capability. What about the possibility of solar systems outside of galaxies? That, too is a matter of technological capability, but also a matter of the fact that the vast majority of stars are in galaxies.

[Wallace]

While a 'rogue' planet would be very difficult to detect, that is not to say they don't exist. The question comes down to the definition of a planet. We really don't know very much about the formation of very low mass stars (because they are very hard to see) so it is possible that when star clusters form, there are many 'stars' which form that are not sufficiently massive to start nuclear fusion. Technically, a ball of gas that is not burning at the core is a planet (such as the gas giants in our solar system) and as such there may well be many of these lone planets out there.

Detecting them would be very hard, and certainly the way we hunt for planets around stars would never find them. We could possibly see them via microlensing, if we got lucky.

[DaveC426913]

We could possibly see them via microlensing, if we got lucky.Now there's an understatement. :wink:

[Wallace]

Not really, the MACHO project in the late 90's found evidence for lone microlensing lenses with masses about twice that of Jupiter, and that was using a 40 inch telescope. In general, MACHO found a lot more microlensing events when looking towards the core of the Milky Way than expected, indicating the possible presence of many low mass stars/lone planets.

Modern microlensing surveys, e.g. see here (http://bustard.phys.nd.edu/MPS/) are most definately aimed at addressing this question (amongst others). You have to be lucky to see an individual event, but the theory behind these surveys is that if you keep watching enough stars you're effectively rolling the dice many times, so you end up getting lucky pretty often.

[Arch2008]

As to rogue stars, I read in Astronomy magazine that stars do get ejected from galaxies by passing near black holes.
http://www.universetoday.com/2008/01/28/hyperfast-star-ejected-from-the-large-magellenic-cloud/
Whether these rogue stars have a “system” of planets is not known.