Comments and questions about the APOD on the main view screen.
Posts: 11
Joined: Sun Jul 17, 2005 3:17 am
Location: Canada


Post by Frank » Sat Sep 03, 2005 4:44 am

I found the article about Albireo very interesting and have a few questions to ask.

The distance to Albireo is reported to be 380 light years from our Sun, but the distance between the two stars was not mentioned although they take 75,000 years to orbit each other. Is it possible to determine their average distance from each other?

Another question I have is how far can two stars be apart and yet orbit each other? Have orbiting or twin stars evolved from their births or are they captured at a later time?

What percentage of stars orbit one or more other stars?

Are there any "twins" or "trios" that are existing without being part of a galaxy?
Thank you for answering any of my questions. Frank :D

Posts: 2019
Joined: Tue Oct 12, 2004 5:25 pm

Re: Albireo

Post by makc » Mon Sep 05, 2005 6:24 am

Frank wrote:What percentage of stars orbit one or more other stars?
100%. No, really - gravity is everywhere (but if you wouldn't use "or more" part, answer would be different;) )

Posts: 16
Joined: Tue Jun 14, 2005 11:10 pm

Post by Odegard » Tue Sep 06, 2005 3:07 am

Take a quick peek at Kepler's laws.

"The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit."

P^2 = a^3

P is measured in years, and a is the semimajor axis measured in AU (mean distance Earth-Sun, ~150million kilometers)

So, 380^2 = 144400, and 144400^(1/3) = 52,5

Of one of the stars were the sun, the other would be 25% farther out that Pluto (Sun-Pluto = 40AU)

The answer to your other question is: it depends.

It depends on the surroundings. Two bodies orbit eachother if no other external force of gravity is strong enough to pull them from eachother. Since gravity is infinite in reach, you could in theory have two stars orbiting eachother at a distance of several billion lightyears if there was nothing else closer by.

Stars are often born in groups, and naturally form multisystems of stars. Then, some stars "capture" other stars. I don't know the ratio of the two.

I've heard somewhere that most stars live in doublestar systems but I can't vouch for it.

For something to not be part of our galaxy, they would have to be dominated by some external force of gravity, another galaxy. I don't think there are many single/double/multi stars between galaxies, where should they have formed?
Maintainer of the Norwegian mirror