More to the North Star Than Meets the Eye

__roo writes "By stretching the capabilities of NASA's Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. This sequence of images shows that the North Star, Polaris is really a triple star system. 'The star we observed is so close to Polaris that we needed every available bit of Hubble's resolution to see it'" said astronomer Nancy Evans of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts."

Re:Just Beyond The Capabilities of My 125 ETX

[ajs]

Actually, I'm not sure that there's anything in this observation that Hubble is needed for. AO is limited in the ultraviolet, but this observation could have been made in the visisble spectrum, I would expect. As such, any of the more recent large telescopes with AO should have been able to make this observation. It just so happens that it was done with Hubble instead.

For those not aware, AO is "Addaptive Optics". This is how you use ground-based scopes, but compensate for the atmosphere. It usually involves deforming a physical mirror, though I think there are some AO systems that work purely digitally. I'm not sure. IANAA.

AO was perfected after Hubble went up, and many ground-based scopes have gotten imaging that's just as detailed (more so in some cases) as Hubble is capable of. I have an astronomer friend who was fond of showing off some photos that he had from AO scopes off of relatively old, retrofitted systems that he claimed were better imaging that Hubble had been able to get from the same objects.

Odd phrasing

[Kelson]

"With Hubble, we've pulled the North Star's companion out of the shadows and into the spotlight."

Of course, stars are easier to see surrounded by shadow than in the glare of a spotlight. Shouldn't this say, "We've pulled the North Star's companion out of the spotlight and into the shadows?"

Re:I doubt this a a triple star system

[coyote-san]

Where did you get this? There are many reasonably stable three-plus body systems. ("reasonably stable" meaning that they'll last the lifetime of the stars, but could still be disrupted by passing stars, etc.)

The classic example is a close binary with a distant third. The distant star essentially sees the binaries as a point. The binaries see the gravitational attraction of the third star as essentially flat (since the tidal forces drop off as 1/r^3). This doesn't mean non-zero, it just means that the attraction of the "near" star won't be higher than the attraction of the "far" star. IIRC that's why the moon is slowly pulling away from the earth -- the sun is slowly pulling the earth and the moon apart.

Another example is a pair of close binaries. Again each binary is overwhelmingly dominated by its pair, with the gravitational attraction of the other pair as essentially flat.

Re:Hubble

[amliebsch]

And what will really blow your mind is the knowledge that right at this moment, those stars are probably no longer in that configuration, if they even all still exist.