APOD: High Energy Andromeda (2016 Jan 07)

[APOD Robot]

High Energy Andromeda

Explanation: A mere 2.5 million light-years away, the Andromeda Galaxy, also known as M31, really is just next door as large galaxies go. In this (inset) scan, image data from NASA's Nuclear Spectrosopic Telescope Array has yielded the best high-energy X-ray view yet of our large neighboring spiral, revealing some 40 extreme sources of X-rays, X-ray binary star systems that contain a black hole or neutron star orbiting a more normal stellar companion. In fact, larger Andromeda and our own Milky Way are the most massive members of the local galaxy group. Andromeda is close enough that NuSTAR can examine its population of X-ray binaries in detail, comparing them to our own. The background image of Andromeda was taken by NASA's Galaxy Evolution Explorer in energetic ultraviolet light.

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[Glima49]

Sorry if this is completely unrelated, but I think SIMBAD says that M31's nucleus has very low level of activity. Interesting.

[Ann]

Sorry if this is completely unrelated, but I think SIMBAD says that M31's nucleus has very low level of activity. Interesting.

Interesting indeed, and lucky for us. Personally I don't think it would be good for us if the central black hole of Andromeda suddenly had a gigantic outburst. A jet from Andromeda likely wouldn't be headed our way, since Andromeda is so inclined from our line of sight, but I still don't like the thought of Andromeda launching a tremendous jet from its nucleus, thereby certainly stirring up and heating up the intergalactic medium between our two galaxies.

Nevertheless, the low activity of the nucleus of M31 notwithstanding, the blue object in today's APOD just might be the central black hole of Andromeda anyway. There is a Chandra image of high-energy sources that you can see here, and part of the captions says,

The blue source at the center is at the position of the supermassive black hole.

In X-ray imagery, a blue source is likely to represent particularly energetic X-rays. So the blue source in today's APOD might be the nucleus of M31 and its supermassive central black hole after all.

Ann

[Ron-Astro Pharmacist]

Thanks for link sources of X-rays. It was very informative piece which helped me get a better understanding of how X-rays are measured and what they represent. I will have to listen to a many more of them.

[isblech@gmail.com]

Andromeda is a lenticular galaxy. It finishes its active live long ago.
Its spirals are closed into rings and which need a lot of time.

[neufer]

Nevertheless, the low activity of the nucleus of M31 notwithstanding, the blue object in today's APOD just might be the central black hole of Andromeda anyway. There is a Chandra image of high-energy sources that you can see here, and part of the captions says,

The blue [Chandra 0.2–10 keV X-ray telescope] source at the center is at the position of the supermassive black hole.

In X-ray imagery, a blue source is likely to represent particularly energetic X-rays. So the blue [NuSTAR 3 - 79 keV high-energy X-ray telescope] source in today's APOD might be the nucleus of M31 and its supermassive central black hole after all.

The blue [NuSTAR high-energy X-ray] source in today's APOD (straight down from the peak of the right hand insert picture) is certainly not anyway near the center of the GALAX UV image; rather the bright yellow [~8 keV X-ray ] NuSTAR source seems to be closest to the nucleus of M31.

[Ann]

Andromeda is a lenticular galaxy. It finishes its active live long ago.
Its spirals are closed into rings and which need a lot of time.

That's not quite true, isblech. Check out this (rather large) portrait of Andromeda by Bill Snyder. You can see a lot of pink nebulas in there. (Their visibility has been enhanced by Bill Snyder's use of an Ha filter, along with red, green and blue filters, for his image.) Many of the pink nebulas visible in Bill Snyder's picture, although not necessarily all of them, are sites of ongoing star formation.

But even though there is definitely some (starforming) activity going on inside Andromeda, there is not a lot of activity going on in there compared with many other spiral galaxies. Andromeda is not "red and dead", in the sense that it lacks star formation altogether (it doesn't), but it is pretty "red" in the sense that it is heavily dominated by tremendous numbers of old red (make that yellow) stars.

There is a category of galaxies sometimes called "green valley galaxies". Many of the galaxies belonging to the "green valley" are also called red spiral galaxies.

Wikipedia wrote:
The Milky Way and the Andromeda Galaxy are assumed to lie in the green valley because their star formation is slowing down due to running out of gas.

Ann

[MarkBour]

The blue [NuSTAR high-energy X-ray] source in today's APOD (straight down from the peak of the right hand insert picture) is certainly not anyway near the center of the GALAX UV image; rather the bright yellow [~8 keV X-ray ] NuSTAR source seems to be closest to the nucleus of M31.

Interesting that the point of high X-ray emission is offset from the brightest spot in visible and UV light at the center of Andromeda. If I understand the prevailing theory from the Wikipedia article, perhaps a cluster of stars are in elliptical orbits around the black hole. That seems like a recipe for future outbursts. Of course I have no idea if the size or frequency of outbursts would be low or high as typical galaxies go.

[neufer]

The blue [NuSTAR high-energy X-ray] source in today's APOD (straight down from the peak of the right hand insert picture) is certainly not anyway near the center of the GALAX UV image; rather the bright yellow [~8 keV X-ray ] NuSTAR source seems to be closest to the nucleus of M31.

Interesting that the point of high X-ray emission is offset from the brightest spot in visible and UV light at the center of Andromeda. If I understand the prevailing theory from the Wikipedia article, perhaps a cluster of stars are in elliptical orbits around the black hole. That seems like a recipe for future outbursts. Of course I have no idea if the size or frequency of outbursts would be low or high as typical galaxies go.

• You also seem to have little idea of the size/scale of the expanded NuSTAR (inset)
  scan image in today's APOD... which I estimate at about 60 ly/pixel.

The surmised Wikipedia elliptical orbits around the black hole are only on the order of ~10 ly in diameter.

---

<<In 1991 Tod R. Lauer used WFPC, then on board the Hubble Space Telescope, to image M31's inner nucleus. The nucleus consists of two concentrations separated by 4.9 ly. The brighter concentration, designated as P1, is offset from the center of the galaxy. The dimmer concentration, P2, falls at the true center of the galaxy and contains a black hole measured at 110–230 million M_☉ in 2005. Scott Tremaine has proposed that the observed double nucleus could be explained if P1 is the projection of a disk of stars in an eccentric orbit around the central black hole. The eccentricity is such that stars linger at the orbital apocenter, creating a concentration of stars. >>

[MarkBour]

• You also seem to have little idea of the size/scale of the expanded NuSTAR (inset)
  scan image in today's APOD... which I estimate at about 60 ly/pixel.

The surmised Wikipedia elliptical orbits around the black hole are only on the order of ~10 ly in diameter.

Ah. So in the NuSTAR image here, the bright yellow and bright blue locations are about 12,000 to 15,000 ly apart?

[neufer]

• You also seem to have little idea of the size/scale of the expanded NuSTAR (inset)
  scan image in today's APOD... which I estimate at about 60 ly/pixel.

The surmised Wikipedia elliptical orbits around the black hole are only on the order of ~10 ly in diameter.

Ah. So in the NuSTAR image here, the bright yellow and bright blue locations are about 12,000 to 15,000 ly apart?

2,500 ly apart (horizontally)?

[MarkBour]

• You also seem to have little idea of the size/scale of the expanded NuSTAR (inset)
  scan image in today's APOD... which I estimate at about 60 ly/pixel.

The surmised Wikipedia elliptical orbits around the black hole are only on the order of ~10 ly in diameter.

Ah. So in the NuSTAR image here, the bright yellow and bright blue locations are about 12,000 to 15,000 ly apart?

2,500 ly apart (horizontally)?

No, I'm just lost. (Not that it matters ... there is a correct answer, and I'm sure the creators of the image know it with great precision and confidence. You probably know it, too. Whether or not I have a good method for figuring it out is not very important.) But if you're not bored with this, then: I downloaded the image and counted about 213 pixels between the two spots (a 122 x 175 rectangle). That gave me about 213*60 = 12,800 from your figure. I put a question mark after my answer, since I doubted it; my pixels may not have matched your pixels at all. If the outer image is a pretty complete image of Andromeda (is it?) and we believe that's 220,000 ly, then I get a yardstick for comparison (on my image, I got 2561 ly / in). That also ignores any aberration of the image as plotted on a flat page. The larger inset appears to be magnified about 1.7 times the original, so I end up with about 3 in = 7682 / 1.7 = 4545 ly between the 2 points. I don't seem to get 2500 ly. From what I'm doing, you can see all of these are just measures as if things are all equidistant from the viewer ... which is what I think you may have meant by "horizontally" in your post. Although in this case, I assume the objects in the NuSTAR inset image are not at all close to equidistant from us, so these measurements are of course only crude lower bounds on the actual distances in space.

The main thing, though, I think, is that you pointed out to me that these are indeed a lot farther apart than I imagined, and so the yellow source is definitely not something just a few light years from the blue source. As a neophyte to the subject of Andromeda's core, it looks to me like it's a complicated place, with many structures and varied parts interacting.

[neufer]

I downloaded the image and counted about 213 pixels between the two spots (a 122 x 175 rectangle).

You downloaded a hi-res version of the APOD image...that was unfair

If the outer image is a pretty complete image of Andromeda (is it?) and we believe that's 220,000 ly.

I was assuming it was only about 2/3's that at most.

[alter-ego]

I downloaded the image and counted about 213 pixels between the two spots (a 122 x 175 rectangle).

You downloaded a hi-res version of the APOD image...that was unfair

If the outer image is a pretty complete image of Andromeda (is it?) and we believe that's 220,000 ly.

I was assuming it was only about 2/3's that at most.

The FoV of todays (cropped) GALEX image ~ 2.8°along Andromeda's long axis. At a distance of 2.54 Mly, the FoV ≈ 125,000 ly.

Even in the linked APOD GALEX image, the image diagonal spans 4°, or 178 kly. You would need a very deep image spanning 5° to reveal galaxy detail out to 220 kly. Interestingly, I've not found an image that shows a 5°-diameter Andromeda, neither the IR/Spitzer or UV/GALEX images really reach/exceed 4°

This eye-catching, scaled composites convey the eyeball deep-image views showing M31 with about a 3.5°span.
http://sploid.gizmodo.com/the-incredibl ... 1493036499
http://apod.nasa.gov/apod/ap061228.html

Click to view full size image

Click to view full size image