Planet formation around HL Tau, 450 light years from Earth



This image is from an array of RADIO telescopes!

ALMA is a billion-dollar, international astronomy project consisting of about 50 40-foot diameter radio telescopes in Chile. They are connected as a big interferometer, so they can make ridiculously high resolution images, such as the one in the article.

I am working on a prototype telescope for this array that was built ten years ago, and is now on Kitt Peak in Arizona, to do similar observations but with even higher resolution by using scopes that are on different continents.


Only 450 light years from Earth sounds to me like we’re seeing it more or less as it is. I’m assuming planetary accretion takes millions or even billions of years. This will be a solar system when humans will probably be long gone.

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Yes, this is a much younger solar system that ours.

The ALMA folks ought to be able to take more pictures of other systems in various stages of development, now that they have shown that their interferometer works well enough to do this. Expect to see this image in textbooks soon.

Is it just me, or are radio telescopes pretty simple devices in that they simply aim at a particular point in the sky and collect the various frequencies passing by? They don’t require ultra-fine optics or mirrors and they don’t need to move a great deal except to maintain a particular position and direction. And yeah, I realize they can’t actually be that simple, but I’ve always wondered why we couldn’t just throw up three or five radio telescopes to orbit the sun at equal intervals such that we effectively would have a radio telescope with a larger gathering area than the sun.
And yeah, I realize that in space, nothing is that easy.

Radio telescopes tend to be simpler than optical telescopes, as the antenna doesn’t need to be nearly as flat as an optical mirror. We do have roomfuls of electronics to process the radio signals into spectra, but that stuff is now getting small.

There have been radio telescopes in aircraft, but getting them into space is not considered necessary, as the ALMA array is demonstrating to us.

There are some folks down the hall from me who do terahertz observing using helium balloons circling Antarctica. The receivers at that frequency range are highly experimental items.

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Very cool! Link to original BBC article (missing from the post?)

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That’s what I was thinking. At the relatively low frequency of radio waves that these telescopes observe, the atmosphere is pretty close to completely transparent. What I would like to know though is whether earth’s magnetic field, Schumann resonances and other man-made and natural sources of local radio emissions are much of a problem for these big directional telescopes.

Do you ever get reflections off the ionosphere that cause freaky signals at the dish?

The only atmospheric problems we get are from either water, which absorbs the signal and is why ALMA is at 15,000 feet ASL, or oxygen or ozone lines that render a few frequencies unusable. There isn’t much man-made RF at hundreds of gigahertz.

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