
A global array of telescopes reveals details on event horizon scales in Sgr A* - okket
https://www.mpifr-bonn.mpg.de/pressreleases/2018/7
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stephengillie
The angular resolution is mind-blowing. Combining these telescopes gives us
resolutions on the order of the orbit of Mercury around the sun, at a range of
our distance from the center of the galaxy. If the Earth were the size of our
eyes, it would be like seeing objects of diameter 11.5 meters (37.7 feet) from
about 7622 km (4736 mi) away. Almost like seeing a small apartment building in
London from Los Angeles, with the naked eye.

> _The increased angular resolution provided by the APEX telescope now reveals
> details in the asymmetric and not point-like source structure, which are as
> small as 36 million km. This corresponds to dimensions that are only 3 times
> larger than the hypothetical size of the black hole (3 Schwarzschild
> radii)._

> _“It reveals details in the central radio source which are smaller than the
> expected size of the accretion disk”, adds Thomas Krichbaum, initiator of
> the mm-VLBI observations with APEX._

Synthesizing with Wikipedia:

> _The current highest-resolution measurement, made at a wavelength of 1.3 mm,
> indicated an angular diameter for the source of 37 μas.[12] At a distance of
> 26,000 light-years, this yields a diameter of 44 million kilometers. For
> comparison, Earth is 150 million kilometers from the Sun, and Mercury is 46
> million kilometers from the Sun at perihelion. The proper motion of Sgr A_ *
> _is approximately −2.70 mas per year for the right ascension and −5.6 mas
> per year for the declination.[13]_ [0]

[0]
[https://en.wikipedia.org/wiki/Sagittarius_A*](https://en.wikipedia.org/wiki/Sagittarius_A*)

Diameter

    
    
      Earth 12,756,000 m
      Eye   0.025 m
      Ratio 510240000x

~~~
mozumder
The best part is that they have to know the alignment the telescopes within .5
mm of each other, across thousands of miles.

~~~
mikeash
Astounding. How can they do that?

~~~
NeutronStar
Maths and computers.

~~~
toomuchtodo
More precisely, motors and precision position encoders.

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SiempreViernes
Nothing new here, the data is from 2013 and this paper is probably just APEX
getting some ”longest baseline” fame in before the real results from the 2017
run, with a telescope on the south pole, relegate them to the ungloriuos
support role.

For an actual update about the event horizon telescope, see here:
[https://eventhorizontelescope.org/blog/eht-status-update-
may...](https://eventhorizontelescope.org/blog/eht-status-update-may-1-2018)

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nikhizzle
Can someone please explain simply?

~~~
Gibbon1
1\. They are ganging multiple radio telescopes to synthetically create a huge
telescope with an aperture of 10,000 km. That gives them enormously good
resolution (for a radio telescope). And using that to look at the giant black
hole at the center of our galaxy. (Sagittarius A _)

2\. There are limitations because the number of telescopes are small. That
makes the data they've collected somewhat ambiguous.

3\. As they add more radio telescopes they should get a clearer picture.

4\. Currently they can resolve to about 3 times the predicted 'radius' of
Sagittarius A_

5\. Ultimately I think they want to be able to actually resolve Sagittarius
A*. And they are getting close.

~~~
SiempreViernes
Data able to resolve the event horizon was taken last year, and analysis of it
has already started.

Probably that will be done before the end of the year, so realizing this
pressrelease is about 2013 data was pretty disappointing.

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mef51
journal paper:
[http://iopscience.iop.org/article/10.3847/1538-4357/aabe2e/m...](http://iopscience.iop.org/article/10.3847/1538-4357/aabe2e/meta)

~~~
privong
And the preprint:
[https://arxiv.org/abs/1805.09223](https://arxiv.org/abs/1805.09223)

~~~
Tepix
Thanks!

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basicplus2
The real beauty of Very Long Baseline Interferometry is that different sources
have different noise thus a common signal of large order of magnitude smaller
than the noise can be identified.

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Cyphase
The original link is HTTPS with a self-signed certificate. Here's the same
story from another source: [https://phys.org/news/2018-05-apex-glimpse-heart-
darkness.ht...](https://phys.org/news/2018-05-apex-glimpse-heart-
darkness.html)

~~~
vardump
It's not a self signed cert.

~~~
Cyphase
Whoops, my bad. I had disabled that CA (T-TeleSec GlobalRoot Class 2) in
Firefox at one point, along with all of the others, as an experiment to see
how many are really needed. I haven't had to re-enable one in ages.

