pretty cool news from the European Southern Observatory
[phys.org] GRAVITY instrument breaks new ground in exoplanet imaging
[phys.org] GRAVITY instrument breaks new ground in exoplanet imaging
ESO/GRAVITY: First Direct Observation of an Exoplanet Using Optical Interferometry
- Thread starter SPCTRE
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Wake me when the find another "Earth" - preferable one that hasn't been mucked up by it's inhabitants!
(Still a big step in the right direction.)
(Still a big step in the right direction.)
Realised that I left university so long ago that, while I know a bit about radio interferometry, I know sod all about this form of optical interferometry. I assume the long baseline (large effective aperture) allows the signal from the planet to be distinguished from its parent star. Though exactly how the interferometer made these measurements, I'm not sure. Goes off to find info on this as I'm not sure the paper contains enough detail on this subject given what little I know.
https://www.eso.org/public/archives/releases/sciencepapers/eso1905/eso1905a.pdf
https://www.eso.org/public/archives/releases/sciencepapers/eso1905/eso1905a.pdf
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You have the basics correct. Three (or more - in this case four apparently) optical systems separated by a long baseline and the resultant image can be used to "clear out" anything other than what you want to look at.
It's kind of like a 3-D camera system, in some ways.
Still, it's not at the quality level that you could literally look at a planet over interstellar distances. They can see enough details to infer what the general conditions and environment should be like.
It's kind of like a 3-D camera system, in some ways.
Still, it's not at the quality level that you could literally look at a planet over interstellar distances. They can see enough details to infer what the general conditions and environment should be like.
Orange clouds and purple sky? Fuuuck.
That's an actual photograph shown? Whoa.
That's an actual photograph shown? Whoa.
^Haha, erm no, but you knew that.
Each telescope uses separate optical fibres to direct light from the planet and the parent star into a spectrometer and the difference is measured at each wavelength. It's how the data from the four telescopes is combined and analysed to distinguish the star's signal from the planet's signal that I haven't quite grasped. I assume the planet's signal is extracted after the star's contribution to the signal has been removed by averaging over multiple phases at each wavelength (effectively, destructive interference to cancel it out). The planet itself was not imaged. Only its spectrum was investigated.
Unfortunately, the description on the ESO website is a bit vague:
https://www.eso.org/sci/facilities/paranal/instruments/gravity/inst.html
Each telescope uses separate optical fibres to direct light from the planet and the parent star into a spectrometer and the difference is measured at each wavelength. It's how the data from the four telescopes is combined and analysed to distinguish the star's signal from the planet's signal that I haven't quite grasped. I assume the planet's signal is extracted after the star's contribution to the signal has been removed by averaging over multiple phases at each wavelength (effectively, destructive interference to cancel it out). The planet itself was not imaged. Only its spectrum was investigated.
Unfortunately, the description on the ESO website is a bit vague:
https://www.eso.org/sci/facilities/paranal/instruments/gravity/inst.html
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I did indeed, but, boy, did the caption in the OP article totally imply that it was!
Do we even have the ability to photograph stars directly yet?
I thought even the strongest telescopes will likely never be able to resolve them beyond a point of light.
I thought even the strongest telescopes will likely never be able to resolve them beyond a point of light.
Optical interferometers can image larger or closer stars to the extent that their oblateness can be determined and large starspots rendered visible. We're talking diameters that are the order of milliarcseconds (mas) as seen from Earth.
At a distance of one parsec (1 pc = 3.26 light years or about 31 trillion km), one Astronomical Unit (1 AU = the Earth-Sun distance or about 150 million km) subtends an angle of one arcsecond so the Sun would appear to be about 10 mas across. (One arcsecond is about 1/1800 of the apparent diameter of the Moon as seen from Earth.)
The limiting resolution, theta, in arcseconds (as) of a telescope with aperture D in metres at optical wavelengths (about 550 nanometres) is approximately theta = 0.138/D as, so you'd need a telescope with an aperture of D = 0.138/0.01 = 13.8 metres to barely resolve the Sun as a disc from a distance of 1 pc.
A long baseline between telescopes creates an effective aperture that is much larger than that of a single telescope. However, the light gathering power is just the sum of that of the individual instruments. Of course, spectroscopy and stellar seismometry are also invaluable tools.
At a wavelength (measured in metres), Lambda, the limiting resolution formula is approximately theta = 250 * Lambda/D as, where D is measured in kilometres. Radio interferometers need very large baselines as the wavelength of radio waves is much greater than for visible light.
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