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

[artitumis]

The Hubble already has a repalcement in the works. It is called The James Webb Space Telescope and is scheduled to go up in 2013. More about the JWST [nasa.gov]

Not really "close" to the main star as we know it.

[Ex Machina]

According to google calculator:

                  2 000 000 000 miles = 21.5155818 Astronomical Units

which puts it just inside the closest approach of Saturn, but well outside Jupiter's orbit.

Re:More.

[hattig]

As the FA points out: "it is the nearest Cepheid variable star. Cepheids' brightness variations are used to measure the distances of galaxies and the expansion rate of the universe"

So quite useful in astronomy.

Re:More.

[Anonymous Coward]

Actually I think what you actually meant was the "Restaurant at the End of the Universe". And the name refers to the temporal aspect, not locality.

Second star inside Neptune's orbit

[RobertB-DC]

From the article: "The companion proved to be less than two-tenths of an arcsecond from Polaris... At the system's distance of 430 light-years, that translates into a separation of about 2 billion miles."

I did a little googling, and found that Neptune's orbit is just over 2 billion miles from the Sun. So for reference, Hubble has directly imaged two distant objects that could fit inside our own solar system.

I think they could have gotten more "Oomph!" from their press release if they'd mentioned this fact. Also, they may have wanted to measure the distance in a standard publicity unit, such as roundtrip NY-LA distances ("A little over 350,000 round-trips from New York to Los Angeles").

Some perspective...

[Anonymous Coward]

TFA states that the close companion orbits at about 2 billion miles, or about 21.5 AU from the parent. That is a bit more than the orbit of Uranus (19.5 AU) in our own system. They had to stretch the Hubble to its limit to see something as bright as a STAR that was far enough away from the parent to fit most of our entire solar system inside. 490 light years is a long way away.

Re:some questions

[hattig]

It's a triple star system if they're all rotating around a common centre of gravity, even if PolarisB seems to be quite an outsider (although on the scale they're showing it is probably still at a distance similar to a Kuiper belt object (rough guess) whilst this Ab star is at Saturn distance from A.

I suppose it is possible that Ab is behind A and thus appears further away, but I'm sure they've done their maths and checked it over a lot before releasing the PR.

Re:some questions

[hcg50a]

There are three stars (Polaris A, Polaris B, and Polaris Ab) in orbit around each other (in various ways). That's why it's called a triple star.

A and B are indeed very far from each other. I don't know how long the period is, but it is probably on the order of hundreds or thousands of years. The center of mass of that orbit may be well outside of Polaris A.

A and Ab are in a very close orbit, with a period of around 30 years. The center of mass of that orbit may be well inside of Polaris A.

You can say Polaris B sucks, but that won't affect it, or the triple star system at all. Polaris B is easily visible in small amateur telescopes. It makes Polaris a very pretty star to look at.

Re:Just Beyond The Capabilities of My 125 ETX

[darkmeridian]

Adaptive optics systems are necessarily ground-based. The actuators and the lenses required are too bulky and heavy to be lugged into orbit. The atmosphere absorbs much incoming radiation. (Thank god, or we'd all literally be toast.) Scientists interested in the ultraviolet have to use space-based telescopes. Hence, the Hubble replacement does not focus on the visible because AO can take care of that from Earth, since we can build arbitrarily large arrays.

Re:I doubt this a a triple star system

[hcg50a]

Your first comment is true in the general 3-body problem, but certain cases are actually stable over a long period of time. Namely, when two of the bodies are in a very tight orbit which is not significantly perturbed by the 3rd body.

So, the system approximates a stable two body system.

Another similar case is 4 stars, where there are two close pairs in orbit around each other. This idea can be extrapolated to any number of stars as long as each pair is not significantly perturbed by its non-pair neighbors.

Re:Just Beyond The Capabilities of My 125 ETX

[Rolan]

Yes, someone always posts this when the death of the hubble is brought up, but what they never do is pay attention that the JWST can't see all that Hubble sees. They're built to look at different parts of the spectrum (yes, there is overlap), so one will never actually replace the capabilites of the other. They would however complement eachother's abilities.

Re:Just Beyond The Capabilities of My 125 ETX

[Moofie]

Since orbital astronomical telescopes aren't looking through atmospheres, adaptive optics are not necessary.

The surveillance ones, on the other hand, are another story.

Re:Not really "close" to the main star as we know

[tm2b]

Polaris A is big. Really, really big. You may think that it's a long walk...

Sorry.

But seriously, Polaris A [domeofthesky.com] is a supergiant, about 2400 times as bright as the sun, and Polaris Ab is a main sequence star. 22 AUs is really close for a couple of stars that size!

Welcome to Slashdot disinformation

[Anonymous Coward]

Why so? Most stars that can be seen naked-eye are in the range 4 to 1500 light-years. Stellar motion takes 100,000 years to be noticable, and those stars lifetimes are somewhere between tens of millions and tens of billions years. So considering the naked-eye stars "at this moment" doesn't change them much.

Re:Interesting...

[Anonymous Coward]

nuke the planet and you get robots. i miss the days of playing that in school cause it was "educational"

Why this is significant

[radtea]

Cepheid variable stars are one of the most basic "standard candles" on which our measurement of interstellar distances depends. Polaris is one of the closest Cepheids.

Cepheid periods depend on luminosity, but the period-luminosity relation is still semi-empirical. Knowing the mass of Polaris (which you can get from measuring the orbital elements of the companion star) pins down one of the important variables in the theoretical model of Cepheids, and so helps firm up one of the basic measuring instruments we use to determine the scale of the universe.

In the past, there have been significant changes in our beliefs about the scale of the universe due to problems with interpretation of variable star data--the discovery that some presumed Cepheids were actually RR Lyrae variables changed things by about a factor of two, IIRC.

Things are a lot better than that now, but it is still good to see that people are working to ensure our view of the universe is as consistent and accurate as possible.

Re:some questions

[hcg50a]

I think it is probably possible, though I suspect it will be difficult. Most reports I've seen it's an easy split in a 6" to 10" scope.

One guy has reported an easy split at 27x and 96x in an 80mm scope.

With 70mm aperture, I think the key will be high magnification. I would try at least 100x.

If this is a finder scope or binocular with limited power (ie., fixed at 10x or 8x), I doubt you will be able to split it.

Re:Looks like the Bard screwed that up...

[spaceyhackerlady]

"I am as constant as the Northern Star."

An astronomical detail Shakespeare got wrong. Thanks to the precession of the equinoxes (known in Roman times), there was no Northern Star in Julius Caesar's time. From the latitude of Rome the elevation of Polaris varied over a 2:1 range in 44 BC. There were no brighter stars closer to the pole in that epoch, either.

One of Isaac Asimov's essays discussed this.

...laura