APOD: The Galactic Center in Radio from... (2022 Feb 02)

[APOD Robot]

The Galactic Center in Radio from MeerKAT

Explanation: What's happening at the center of our galaxy? It's hard to tell with optical telescopes since visible light is blocked by intervening interstellar dust. In other bands of light, though, such as radio, the galactic center can be imaged and shows itself to be quite an interesting and active place. The featured picture shows the latest image of our Milky Way's center by the MeerKAT array of 64 radio dishes in South Africa. Spanning four times the angular size of the Moon (2 degrees), the image is impressively vast, deep, and detailed. Many known sources are shown in clear detail, including many with a prefix of Sgr, since the galactic center is in the direction of the constellation Sagittarius. In our Galaxy's Center lies Sgr A, found here in the image center, which houses the Milky Way's central supermassive black hole. Other sources in the image are not as well understood, including the Arc, just to the left of Sgr A, and numerous filamentary threads. Goals for MeerKAT include searching for radio emission from neutral hydrogen emitted in a much younger universe and brief but distant radio flashes.

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[Ann]

The Galactic Center in Radio from MeerKAT Image Credit: Ian Heywood (Oxford U.), SARAO; Color Processing: Juan Carlos Munoz-Mateos (ESO)

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I would have liked to know a little more here.

Sgr A is the radio-bright region surrounding the supergiant central black hole of the Milky Way, Sgr A*. And SNR means supernova remnant, so the three sources marked SNR in today's APOD are remnants of exploding stars. And the word "Arc" is self-explanatory.

But what are Sgr B1, Sgr B2 and Sgr C? Are they UMWRSs? That is, are they Unidentified Milky Way Radio Sources?

Ann

[slyman]

Cool! Saw this similar image the other day from SARAO

https://www.popsci.com/science/center-o ... ay-images/

[Ann]

Cool! Saw this similar image the other day from SARAO

https://www.popsci.com/science/center-o ... ay-images/

Thanks, slyman!

I said in my previous post that the word "Arc" was self-explanatory. But it isn't. However, according to slyman's source, the arc(s) are...

The Jackson-Pollack-like red streaks are non-thermal filaments (NTFs), magnetized strands that can’t be found anywhere else in the galaxy.

So these strands are caused by magnetism. That sounds, and looks, reasonable.

Ann

[starduster]

Additional info here: https://chandra.harvard.edu/photo/2021/gcenter/

[orin stepanek]

Beautiful; but it looks like a dangerous place! It is busy; don't know
how those stars miss each other!?

[Chris Peterson]

MwCenter_MeerKATMunoz_1080_annotated.jpg

Beautiful; but it looks like a dangerous place! It is busy; don't know
how those stars miss each other!?

Those stars miss each other because they are still just dust motes in a giant room. It's still mostly empty space. But it's a messy gravitational environment- there will be no stable planetary systems in there.

[Fred the Cat]

Meerkat thinking, “You should see what the universe looks like through my eyes!

We have great eyesight and it’s way cooler than humans can see.”

[Cousin Ricky]

The colors are determined by spectral index, so I tried finding out what a spectral index is. My brain started hurting immediately.

[johnnydeep]

Very impressive image from MeerKAT. But no where can I seem to find what MeerKAT itself stands for? Wikipedia says the "KAT" part is Karoo Array Telescope (its former name), but what does "Meer" mean"? I might guess Millimetre Environment Explorer Radio (or Revealer)" if I'm being creative. Is it only named after the cute animal?

Particularly cool is the "Mouse", which is sadly not shown in this APOD image (though its tail is)! From https://www.sarao.ac.za/media-releases/ ... milky-way/ :

In the centre of the image is the supernova remnant G359.1-0.5. To the left is ‘the Mouse’, a runaway pulsar possibly formed and ejected by the supernova event. To the upper right is one of the longest and most famous radio filaments, known as ‘the Snake’. Credit: I. Heywood, SARAO.

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[bystander]

Very impressive image from MeerKAT. But no where can I seem to find what MeerKAT itself stands for? Wikipedia says the "KAT" part is Karoo Array Telescope (its former name), but what does "Meer" mean"? I might guess Millimetre Environment Explorer Radio (or Revealer)" if I'm being creative. Is it only named after the cute animal? ...

Why MeerKAT?

The telescope was originally known as the Karoo Array Telescope (KAT) that would consist of 20 receptors. When the South African government increased the budget to allow the building of 64 receptors, the team re-named it “MeerKAT” – ie “more of KAT”. The MeerKAT (scientific name Suricata suricatta) is also a much beloved small mammal that lives in the Karoo region.

[johnnydeep]

Very impressive image from MeerKAT. But no where can I seem to find what MeerKAT itself stands for? Wikipedia says the "KAT" part is Karoo Array Telescope (its former name), but what does "Meer" mean"? I might guess Millimetre Environment Explorer Radio (or Revealer)" if I'm being creative. Is it only named after the cute animal? ...

Why MeerKAT?

The telescope was originally known as the Karoo Array Telescope (KAT) that would consist of 20 receptors. When the South African government increased the budget to allow the building of 64 receptors, the team re-named it “MeerKAT” – ie “more of KAT”. The MeerKAT (scientific name Suricata suricatta) is also a much beloved small mammal that lives in the Karoo region.

Ah, thanks. All the way at the bottom of that page! So apparently "meer" means "more" in ... Afrikaans! - https://www.wordhippo.com/what-is/the-m ... 6ba74.html, and I guess that's also how the animal got its name.

[Chris Peterson]

Very impressive image from MeerKAT. But no where can I seem to find what MeerKAT itself stands for? Wikipedia says the "KAT" part is Karoo Array Telescope (its former name), but what does "Meer" mean"? I might guess Millimetre Environment Explorer Radio (or Revealer)" if I'm being creative. Is it only named after the cute animal? ...

Why MeerKAT?

The telescope was originally known as the Karoo Array Telescope (KAT) that would consist of 20 receptors. When the South African government increased the budget to allow the building of 64 receptors, the team re-named it “MeerKAT” – ie “more of KAT”. The MeerKAT (scientific name Suricata suricatta) is also a much beloved small mammal that lives in the Karoo region.

Ah, thanks. All the way at the bottom of that page! So apparently "meer" means "more" in ... Afrikaans! - https://www.wordhippo.com/what-is/the-m ... 6ba74.html, and I guess that's also how the animal got its name.

Probably from Dutch meer, "lake" (or sometimes "sea", like in German).

[Starski2]

When I first saw the image it looked like a crouching, muscular monster with SagA* at its head and two outstretched arms. It's throwing SNR's this way. Sorry, I have an active imagination.

[VictorBorun]

is there a way to tell if at least SuperNova remnants are at the same distance as SgA, or are they in the foreground or are they in the background?

And can Arc connect to SgA magnetic poles, the top one and the bottom one?

Update. I guess I am wrong to take the almost ring (that I want to connect with SgA magnetic poles) for the Radio Arc (that is not a ring or even an arc but a straight lane).

Or I can not read properly.

The complex, cirrus-like emission from the Galactic centre super bubble dominates this image. This is traversed by the Radio Arc, a complex of many parallel radio filaments. The radio bubble nestles against the diffuse Sagittarius A region in the lower centre of the image. The bright dot near the centre of this region is Sagittarius A*, a 4 million solar mass black hole. This image captures the chaotic complexity of the very heart of our Galaxy. Credit: I. Heywood, SARAO.

Click to view full size image

[johnnydeep]

Ah, thanks. All the way at the bottom of that page! So apparently "meer" means "more" in ... Afrikaans! - https://www.wordhippo.com/what-is/the-m ... 6ba74.html, and I guess that's also how the animal got its name.

Probably from Dutch meer, "lake" (or sometimes "sea", like in German).

Looks like you are at least partially correct.

'Meerkat' derives from the Dutch name for a kind of monkey, which in turn comes from the Old High German mericazza, possibly as a combination of meer ('lake') and kat ('cat'). This may be related to the similar Hindi: मर्कट (markat, or monkey), deriving from Sanskrit, though the Germanic origin of the word predates any known connections to India. The name was used for small mammals in South Africa from 1801 onward, possibly because the Dutch colonialists used the name in reference to many burrowing animals.[4][5] The native South African name for the meerkat is 'suricate', possibly deriving from the French: surikate, which in turn may have a Dutch origin. In Afrikaans the meerkat is called graatjiemeerkat or stokstertmeerkat; the term mierkatte or meerkatte can refer to both the meerkat and the yellow mongoose (Afrikaans: rooimeerkat). In colloquial Afrikaans mier means 'ant' and kat means 'cat', hence the name probably refers to the meerkat's association with termite mounds.[2][6][7]

So apparently the "meer" in MeerKAT the observatory means "more", but the "meer" in meerkat the animal means "lake".

[Ann]

is there a way to tell if at least SuperNova remnants are at the same distance as SgA, or are they in the foreground or are they in the background?

And can Arc connect to SgA magnetic poles, the top one and the bottom one?

Update. I guess I am wrong to take the almost ring (that I want to connect with SgA magnetic poles) for the Radio Arc (that is not a ring or even an arc but a straight lane).

Or I can not read properly.

The complex, cirrus-like emission from the Galactic centre super bubble dominates this image. This is traversed by the Radio Arc, a complex of many parallel radio filaments. The radio bubble nestles against the diffuse Sagittarius A region in the lower centre of the image. The bright dot near the centre of this region is Sagittarius A*, a 4 million solar mass black hole. This image captures the chaotic complexity of the very heart of our Galaxy. Credit: I. Heywood, SARAO.

Click to view full size image

If you ask me, a supernova remnant that appears to be located close to the center of our galaxy - so that it can be clearly seen in an infrared, radio or X-ray image that portrays the center of our galaxy - is almost certainly truly located near the center of our galaxy.

The caption that you quoted does not discuss the magnetic features of the center of the Milky Way, as you no doubt noted yourself.

Ann

[VictorBorun]

Click to view full size image

If you ask me, a supernova remnant that appears to be located close to the center of our galaxy - so that it can be clearly seen in an infrared, radio or X-ray image that portrays the center of our galaxy - is almost certainly truly located near the center of our galaxy.

A nameless SN remnant! So it's just a bubble shell brightly illuminated by Sgr A, not a magnetic loop at all.

And how distant from us is the straight lane called the Radio Arc, visually striking through that nameless SNR?
It must be well outside the SNR to look so independent of the SNR. Either in front of or behind. And still close enough to Sgr A to look so similar to other magnetic filaments.

[VictorBorun]

I wonder if Milky Way's core is much wider than this 2° = 1 kly wide view.
Leaving out red dwarfs, we can count the good half of the non-dwarf stars in far infra red pics, cannot we?

[neufer]

Click to view full size image

If you ask me, a supernova remnant that appears to be located close to the center of our galaxy - so that it can be clearly seen in an infrared, radio or X-ray image that portrays the center of our galaxy - is almost certainly truly located near the center of our galaxy.

A nameless SN remnant! So it's just a bubble shell brightly illuminated by SgA*, not a magnetic loop at all.

And how distant from us is the straight lane called the Radio Arc, visually striking through that nameless SNR?
It must be well outside the SNR to look so independent of the SNR. Either in front of or behind. And still close enough to SgA* to look so similar to other magnetic filaments.

• Sagittarius A East

<<This feature is approximately 25 light-years in width and has the attributes of a supernova remnant from an explosive event that occurred between 35,000 and 100,000 BC. However, it would take 50 to 100 times more energy than a standard supernova explosion to create a structure of this size and energy. It is conjectured that Sgr A East is the remnant of the explosion of a star that was gravitationally compressed as it made a close approach to the central black hole.>>

Surface brightness and velocity field of the inner part of Sagittarius A West

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• Sagittarius A West

<<Sgr A West has the appearance of a three-arm spiral, from the point of view of the Earth. For this reason, it is also known as the "Minispiral". This appearance and nickname are misleading, though: the three-dimensional structure of the Minispiral is not that of a spiral. It is made of several dust and gas clouds, which orbit and fall onto Sagittarius A* at velocities as high as 1,000 kilometers per second. The surface layer of these clouds is ionized. The source of ionisation is the population of massive stars (more than one hundred OB stars have been identified so far) that also occupy the central parsec.

Sgr A West is surrounded by a massive, clumpy torus of cooler molecular gas, the Circumnuclear Disk (CND). The nature and kinematics of the Northern Arm cloud of Sgr A West suggest that it once was a clump in the CND, which fell due to some perturbation, perhaps the supernova explosion responsible for Sgr A East. The Northern Arm appears as a very bright North—South ridge of emission, but it extends far to the East and can be detected as a dim extended source. The Western Arc (outside the field of view of the image shown in the right) is interpreted as the ionized inner surface of the CND. The Eastern Arm and the Bar seem to be two additional large clouds similar to the Northern Arm, although they do not share the same orbital plane. They have been estimated to amount for about 20 solar masses each. On top of these large scale structures (of the order of a few light-years in size), many smaller cloudlets and holes inside the large clouds can be seen. The most prominent of these perturbations is the Minicavity, which is interpreted as a bubble blown inside the Northern Arm by the stellar wind of a massive star, which is not clearly identified.>>

[VictorBorun]

Surface brightness and velocity field of the inner part of Sagittarius A West

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I struggle to fit the two pictures. The posted 2° wide MeerKAT image is 200 times wider and Sgr A spot in that panorama is too bright anyhow to see any details

[Chris Peterson]

is there a way to tell if at least SuperNova remnants are at the same distance as SgA, or are they in the foreground or are they in the background?

No, at that distance we don't really have any good way of determining if we're seeing something in front of or behind Sgr A. But I agree with Ann that what we're seeing is close to it in either case.

[neufer]

Surface brightness and velocity field of the inner part of Sagittarius A West

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I struggle to fit the two pictures.

The posted 2° wide MeerKAT image is 200 times wider and Sgr A spot in that panorama is too bright anyhow to see any details.

It certainly doesn't help that the

"Surface brightness and velocity field of
. the inner part of Sagittarius A West"

is only about half an arc minute wide

[VictorBorun]

The MeerKAT's article shows these angular seconds of Sgr A blindingly bright radio spot as follows.
Both images are tilted so the plane of Milky Way disk has a downward slope (◺)

A desaturated view of the 1.28 GHz

A spectral index view (based on 4,096 spectral channels across .856–1.712 GHz) is blanked for pixels of low brightness; I would rather painted them black.

They say that "The mini-spiral structure is apparently connected to two streams of material that flow through the center of the bipolar structure. "

To my eye the jets from Sgr A* central black hole look vertical in this image therefore tilted in relation to Milky Way's spin and most filaments in the core

[VictorBorun]

Surface brightness and velocity field of the inner part of Sagittarius A West

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I struggle to fit the two pictures.

The posted 2° wide MeerKAT image is 200 times wider and Sgr A spot in that panorama is too bright anyhow to see any details.

It certainly doesn't help that the

"Surface brightness and velocity field of
. the inner part of Sagittarius A West"

is only about half an arc minute wide

I think I fitted the two

Sgr A center.jpg (15.18 KiB) Viewed 7713 times

Sgr A center-.jpg (26.7 KiB) Viewed 7713 times

using the half angular minute ticks of