APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Comments and questions about the APOD on the main view screen.
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APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by APOD Robot » Wed Jun 19, 2019 4:12 am

Image Our Galaxy's Magnetic Center

Explanation: What's the magnetic field like in the center of our Milky Way Galaxy? To help find out, NASA's SOFIA -- an observatory flying in a modified 747 -- imaged the central region with an instrument known as HAWC+. HAWC+ maps magnetism by observing polarized infrared light emitted by elongated dust grains rotating in alignment with the local magnetic field. Now at our Milky Way's center is a supermassive black hole with a hobby of absorbing gas from stars it has recently destroyed. Our galaxy's black hole, though, is relatively quiet compared to the absorption rate of the central black holes in active galaxies. The featured image gives a clue as to why -- a surrounding magnetic field may either channel gas into the black hole -- which lights up its exterior, or forces gas into an accretion-disk holding pattern, causing it to be less active -- at least temporarily. Inspection of the featured image -- appearing perhaps like a surreal mashup of impasto art and gravitational astrophysics -- brings out this telling clue by detailing the magnetic field in and around a dusty ring surrounding Sagittarius A*, the black hole in our Milky Way's center.

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by bystander » Wed Jun 19, 2019 4:41 am

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by RocketRon » Wed Jun 19, 2019 4:54 am

This doesn't quite seem to have a central point to it, or anything like it ?
Is that because its a 3D image displayed/compressed in 2 dimensions, or is there some other explanation for this ?

AND, if light etc can't escape a black hole, how is it that a magnetic field can ?
Or is the magnetic field being generated outside the black hole - by what ? - and drawn into it ?

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by BDanielMayfield » Wed Jun 19, 2019 5:22 am

Where exactly is Sag A* (our galaxy's supermassive BH) in this image? An X marks the spot overlay would be very helpful, along with a dashed line showing the Milky Way's mid plain.
"Happy are the peaceable ... "

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by Boomer12k » Wed Jun 19, 2019 5:44 am

Hmmm...it seems to... "bind the galaxy together...."....

Though compared to Earth's MF it is extremely weak.

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by AVAO » Wed Jun 19, 2019 7:49 am

BDanielMayfield wrote:
Wed Jun 19, 2019 5:22 am
Where exactly is Sag A* (our galaxy's supermassive BH) in this image? An X marks the spot overlay would be very helpful, along with a dashed line showing the Milky Way's mid plain.
To your question look at:


The view is like a bar-spiral galaxy...
(Source: https://public.nrao.edu/gallery/the-spi ... r-galaxy-2)

"In the heart of our 100,000 light-year wide spiral Milky Way Galaxy lies a miniature spiral of ionized gas only 10 light-years across. The Very Large Array (VLA) caught this gas in the act of orbiting around the supermassive black hole in the core of our Galaxy.
Credit: (NRAO/AUI/NSF)"


For a general understanding of the spatial dimensions in the pictures:

Diameter: 10LY
Diameter: 1LY (10 years of star tracking...)
Diameter: 0,1 LY (10 years of star tracking...)
Diameter: 0,01 LY WEBB (JWST) will solve it for us ...

Jack from the AVAO Team
Last edited by AVAO on Wed Jun 19, 2019 1:16 pm, edited 1 time in total.

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by orin stepanek » Wed Jun 19, 2019 11:11 am

Maybe Magnetism would be a good fuel for space travel! :shock:
Orin

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I know a HAWC from a handsaw.

Post by neufer » Wed Jun 19, 2019 1:11 pm

  • Oklahoma, ev'ry night my honey lamb and I
    Every night we sit alone and talk
    And watch a HAWC
    Makin' lazy circles in the sky
High-resolution Airborne Wideband Camera-Plus: HAWC altitude of 41,000 ft

High Altitude Water Cherenkov Experiment: HAWC altitude of 4100 meters
https://en.wikipedia.org/wiki/41_(number) wrote:
  • ...............................................................................
    41: In the 1959 Alfred Hitchcock film North by Northwest,
    Cary Grant is attacked by a crop-dusting airplane on Highway 41.
    ...............................................................................
    HAMLET: I am but mad north-north-west:
    • when the wind is southerly I know a HAWC from a handsaw.
    ...............................................................................
    Symphony No. 41, the longest and last symphony of Wolfgang Amadeus Mozart.

    41: The precinct number that appears on the NYC police car in the film
    Ghostbusters during the earthquake moment of the film's climax.

    41: Charlton Heston's designation as a Roman warship slave in the film Ben-Hur.

    41: Jonathan Pryce's destination level for his apartment in Terry Gilliam's Brazil.

    41: The district number where the "zombie virus" reappears in the film Doomsday.

    41: The race number worn by Sir Roger Bannister
    when he broke the mythical 4-minute mile barrier in 1954.

    41={1+[ln(262537412640768744)/π]2}/4
    ..............................................................................
    41: the largest lucky number of Euler:
    the polynomial f(k) = k2 − k + 41 yields primes
    for all the integers k with 1 ≤ k < 41.

    1 : 41
    2 : 43 = 41 + 2
    3 : 47 = 43 + 4
    4 : 53 = 47 + 6
    5 : 61 = 53 + 8
    6 : 71 = 61 + 10
    7 : 83 = 71 + 12
    8 : 97 = 83 + 14
    9 : 113 = 97 + 16
    10 : 131 = 113 + 18
    11 : 151 = 131 + 20
    12 : 173 = 151 + 22
    13 : 197 = 173 + 24
    14 : 223 = 197 + 26
    15 : 251 = 223 + 28
    16 : 281 = 251 + 30
    17 : 313 = 281 + 32
    18 : 347 = 313 + 34
    19 : 383 = 347 + 36
    20 : 421 = 383 + 38
    21 : 461 = 421 + 40
    22 : 503 = 461 + 42
    23 : 547 = 503 + 44
    24 : 593 = 547 + 46
    25 : 641 = 593 + 48
    26 : 691 = 641 + 50
    27 : 743 = 691 + 52
    28 : 797 = 743 + 54
    29 : 853 = 797 + 56
    30 : 911 = 853 + 58
    31 : 971 = 911 + 60
    32 : 1033 = 971 + 62
    33 : 1097 = 1033 + 64
    34 : 1163 = 1097 + 66
    35 : 1231 = 1163 + 68
    36 : 1301 = 1231 + 70
    37 : 1373 = 1301 + 72
    38 : 1447 = 1373 + 74
    39 : 1523 = 1447 + 76
    40 : 1601 = 1523 + 78
    ..................................
    41 : 41x41 = 1601 + 80
Last edited by neufer on Thu Jun 20, 2019 12:46 am, edited 2 times in total.
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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by TheZuke! » Wed Jun 19, 2019 1:49 pm

It looks like a hairy, scary face!
B^)

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by BDanielMayfield » Thu Jun 20, 2019 4:18 pm

AVAO wrote:
Wed Jun 19, 2019 7:49 am
BDanielMayfield wrote:
Wed Jun 19, 2019 5:22 am
Where exactly is Sag A* (our galaxy's supermassive BH) in this image? An X marks the spot overlay would be very helpful, along with a dashed line showing the Milky Way's mid plain.
To your question look at:


The view is like a bar-spiral galaxy...
(Source: https://public.nrao.edu/gallery/the-spi ... r-galaxy-2)

"In the heart of our 100,000 light-year wide spiral Milky Way Galaxy lies a miniature spiral of ionized gas only 10 light-years across. The Very Large Array (VLA) caught this gas in the act of orbiting around the supermassive black hole in the core of our Galaxy.
Credit: (NRAO/AUI/NSF)"


For a general understanding of the spatial dimensions in the pictures:

Diameter: 10LY
Diameter: 1LY (10 years of star tracking...)
Diameter: 0,1 LY (10 years of star tracking...)
Diameter: 0,01 LY WEBB (JWST) will solve it for us ...

Jack from the AVAO Team
Thank you very sincerely Jack.
"Happy are the peaceable ... "

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by sallyseaver » Thu Dec 05, 2019 5:31 am

I'm wondering how to interpret the image.

In this APOD image, there are lines, also, the image includes color information: hue, saturation and brightness.

SOFIA is reading polarity of the far infrared radiation. Do the lines indicate the transverse direction of the radiation? Is the transverse direction orthogonal to the magnetic field? What does the color info tell us?

What in this image corresponds to one polarity versus another and how does this help us to understand the magnetic field depicted by the image.

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Re: APOD: Our Galaxy's Magnetic Center (2019 Jun 19)

Post by alter-ego » Thu Dec 12, 2019 2:51 am

sallyseaver wrote:
Thu Dec 05, 2019 5:31 am
I'm wondering how to interpret the image.

In this APOD image, there are lines, also, the image includes color information: hue, saturation and brightness.

SOFIA is reading polarity polarization of the far infrared radiation. Do the lines indicate the transverse direction of the radiation? Is the transverse direction orthogonal to the magnetic field? What does the color info tell us?
The lines directly map the magnetic field lines, and since the long axis of the dust grains are perpendicular to these lines then the FIR polarization is also perpendicular to the field lines. The heated dust grains preferentially emit light polarized along the long axis of the dust grain. It's more common to reference the polarization direction instead "transverse direction of the radiation." Therefore it's more clear to say the IR polarization is orthogonal the magnetic field lines. The color represents temperature: 10K (red) → 100K (blue)
What in this image corresponds to one polarity polarization versus another and how does this help us to understand the magnetic field depicted by the image.
Within a small region, it should be clear that the measured FIR polarization direction reveals the orthogonal field line direction. Subsequently, an array of this polarization-direction data will yield a family of mostly continuous magnetic field lines. The projection of a 3-D region of space to a 2-D image containing integrated line-of-sight FIR polarizations may limit magnetic field interpretation.

Edit: Although the simple rotational energy minimum for an elongated particle is for rotation about smaller axis, the reality is complicated by radiation-induced torques/forces, magnetic field strength, and particle properties (e.g. size, aspect ratio and if it's paramagnetic). The APOD states the grains are "rotating in alignment with the local magnetic field". That could mean the long axis is alignment with the field lines. In any case, the discussion still holds except that, instead of orthogonal, the field lines are parallel (or some other predicted angle) to the polarization direction. The case for parallel alignment is possible.
Interstellar Grain Alignment
Dust Grain Alignment in the Interstellar Medium
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