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This blog is all about science and technology (with occasional math thrown in for fun). The goal of this blog is to try and pass on the sense of excitement and wonder I feel when I read about these topics. I hope you enjoy the posts.

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Viewing The Milky Way's Supermassive Black Hole

Posted June 11, 2015 11:12 AM by Bayes

Sagittarius A*

In the center of the Milky Way there is a very bright, compact radio source. Found near the constellations Sagittarius and Scorpius in the night sky, Sagittarius A*(Sgr A*) is believed to be the location of a supermassive black hole similar to those observed to exist at the center of other galaxies.

Due to dust and gas, astronomers have been unable to observe Sgr A* in the optical spectrum. Attempts have been made to view it using radio telescopes.

Event Horizon Telescope

The Event Horizon Telescope is a project to create a large millimeter telescope array combining data from radio telescope stations from around the Earth using very-long-baseline interferometry (VLBI) to observe the immediate environment of the Milky Way's supermassive black hole Sgr A* with angular resolution comparable to the event horizon.

The group will combine existing and planned millimeter/submillimeter facilities into a high-sensitivity, high angular resolution Event Horizon Telescope. The effort will include development and deployment of submillimeter dual polarization receivers, highly stable frequency standards to enable VLBI at 230-450 GHz, higher-bandwidth VLBI backends and recorders, as well as commissioning of new submillimeter VLBI sites.

New York Times Video on the Event Horizon Telescope

Here is an excellent video discussing the Event Horizon Telescope and it's mission to observe Sgr A*

NYT Video

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Guru

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#1

Re: Viewing The Milky Way's Supermassive Black Hole

06/12/2015 11:10 AM

I find it incredible that they can get the timing sufficiently accurate to guarantee the simultaneity of observations taken at such diverse locations! Without that timing, I think the observations would be nearly useless.

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Engineering Fields - Aerospace Engineering - Retired South Africa - Member - The Rainbow-nation Engineering Fields - Engineering Physics - Relativity & Cosmology Popular Science - Cosmology - The Big Picture!

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#2
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Re: Viewing The Milky Way's Supermassive Black Hole

06/12/2015 12:32 PM

I do not think the synchronized atomic clocks used at the different locations are error free enough - they have a very sophisticated processing technique called closure phase, a type of self-calibration to combine the images.

"Roger Jennison developed this novel technique for obtaining information about visibility phases in an interferometer when delay errors are present. Although his initial laboratory measurements of closure phase had been done at optical wavelengths, he foresaw greater potential for his technique in radio interferometry. In 1958 he demonstrated its effectiveness with a radio interferometer, but it only became widely used for long baseline radio interferometry in 1974. A minimum of three antennas are required. This method was used for the first VLBI measurements, and a modified form of this approach ("Self-Calibration") is still used today. The "closure-phase" or "self-calibration" methods are also used to eliminate the effects of astronomical seeing in optical and infrared observations using astronomical interferometers."

Very impressive...

-J

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#3
In reply to #2

Re: Viewing The Milky Way's Supermassive Black Hole

06/12/2015 1:05 PM

I checked out "closure phase": I do understand complex numbers (to a limited extent), but this is just a bit, or maybe a lot, beyond my comprehension.

Thanks!

Dick

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