High res images of other stars

[Rdivine]

hey guys!

Is it possible to take high resolution pictures of other stars?

Here are some problems we would face:

-glare of the star would prevent us from getting to any surface details

-too distant

-too small

But, could we take photos of, say, proxima centuri and make out small details of the surface, or coronal ejections for that matter?

We could have a telescope fitted with a small circle ring in the middle to block out the main body of the star, and observe the star's outer layer.

If you have any knowledge of why this would/would not work , please comment below!

[YNM]

It'll be very hard. Stars that you'll likely able to resolve would be those very huge stars, evolved stars like RG and AGB, which means dense circumstellar dust and variability. An example of this is Betelgeuse, whose angular diameter goes around 43 to 56 miliarcsecond (ten millionth of a degree), and possibly irregular shaped. That being said, seems like our images of Betelgeuse are fairly resolved today that we can tell where the poles are located.

Edited July 24, 2015 by YNM

[Ralathon]

Suppose that proxima centauri is about the size of the sun and we want at least 10 pixels of resolution. This means the telescope needs an angular resolution of arctan(70e3km/4.8ly)~1.56e-9 rad.

We want to look at the star in visible light, so we have a wavelength of about 500nm. Plug these 2 numbers in the telescope equation and we find that we need a telescope with a main mirror 320 meters in diameter. The biggest telescope we have right now has a diameter of about 10 meters. The E-ELT that's in construction right now will have a diameter of almost 40 meters.

So we're about an order of magnitude short in terms of mirror diameter to see stars as anything other than point sources.

[lajoswinkler]

No, stars are literally points to our optical devices. Point like sources of light. That's one of the reasons why they shimmer when their light gets through our atmosphere.

[heng]

could someone kindly explain why very-long-baseline interferometry (VLBI) only works with radio telescopes?

why isn't this used with optical ones?

[cantab]

The much higher frequencies of visible light would demand correspondingly much higher precision in measuring and adjusting the timing of the signals. The slight variations in light travel time through the Earth's atmosphere would probably mess things up too.

[tater]

could someone kindly explain why very-long-baseline interferometry (VLBI) only works with radio telescopes?

why isn't this used with optical ones?

Light is light, it works, and small interferometers exist. A practical issue with optical is seeing. Meaning the the issues with the atmosphere which become worse when the paths for the light differ between instruments. Space-based optical interferometers have been proposed, and the Moon is a really good candidate for a VLA-like instrument (only optical, not radio).

[JetJaguar]

It turns out there are a handful of stars with images that have been resolved beyond a point source. I knew about Betelgeuse, being large and relatively close it's the first one to be directly imaged.

[Lukaszenko]

This thing is meant to block out a star's glare, but it's mainly meant for looking at exoplanets. Maybe it can also be used for OP's purpose?

https://en.wikipedia.org/wiki/New_Worlds_Mission

[K^2]

Our Sun is 1.5M km across. Visible light is about 500nm. That means, with a 1m telescope mirror, Sun would resolve to a single point at a distance of just 0.3 light years. From 4 light years, a telescope with a 12m mirror would still see our Sun as just a single point.

This basically means that even with largest conventional telescopes, best we can do are super-giants, and even then, all we get are a few pixels like that image above.

There is one more options. Interferometer telescope arrays can, in theory, image nearby stars. Quality of images such systems produce is pretty bad, but you can get some useful information out of it. I believe, prior to New Horizons, best images of Pluto were due to interferometer array. In theory, one of these arrays should be able to image Alpha Centauri stars, but there migth be some limitations I'm not taking into account, such as glare or atmosphere. Even then, you'd get something even uglier than that Betelgeuse image.

[livefree75]

You would need a HUGE telescope, probably space based.

I've heard it said that a typical star viewed from Earth has the same angular diameter as a walnut seen from 600 km away. (Correct me if I'm wrong.)