APOD: NGC 7331 Close Up (2020 Feb 07)

[APOD Robot]

NGC 7331 Close Up

Explanation: Big, beautiful spiral galaxy NGC 7331 is often touted as an analog to our own Milky Way. About 50 million light-years distant in the northern constellation Pegasus, NGC 7331 was recognized early on as a spiral nebula and is actually one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. Since the galaxy's disk is inclined to our line-of-sight, long telescopic exposures often result in an image that evokes a strong sense of depth. In this Hubble Space Telescope close-up, the galaxy's magnificent spiral arms feature dark obscuring dust lanes, bright bluish clusters of massive young stars, and the telltale reddish glow of active star forming regions. The bright yellowish central regions harbor populations of older, cooler stars. Like the Milky Way, a supermassive black hole lies at the core of spiral galaxy NGC 7331.

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[neufer]

Click to play embedded YouTube video.

<<In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the galaxy NGC 7331 is rotating in the opposite direction to the rest of the disk.>>

https://arxiv.org/abs/astro-ph/9602142

[Ann]

Angry cat.png (36.44 KiB) Viewed 4225 times

Interesting combination of physics and cat torture there, Art. Particularly when the cat landed on the hard ground.










On a different note, today's APOD is both beautiful and interesting, and it doesn't look brand new to me. Why not? Well, because its colors are so nice and a lot of filters must have been used to produce it!

Click to view full size image

NGC 7331. ESA/Hubble & NASA/D. Milisavljevic.

The image that is today's APOD was released slightly more than two years ago, on January 29, 2018. I strongly applaud all the filters that were used for the image. The ESA/Hubble page where this image was originally released lists no fewer than six filters that were used for this image, two ultraviolet ones, one blue, one yellow-green, one near infrared and one for Hα and NIII. As a result, we get a splendid image that does a superb job at detecting various stellar populations in NGC 7331.

(A more filter-economic example of a Hubble picture of a galaxy is this one, of galaxy NGC 2985, for which only two filters were used. In the case of NGC 2985, the two filters were Hα and near infrared.)

Click to view full size image

NGC 7331 and the Deer Lick Group.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

My favorite portrait of NGC 7331 (and the Deer Lick Group of background galaxies) is the one at right, however. With my peculiar sense of aesthetics, I do find the colors very beautiful.

David Galadí-Enríquez wrote about Vicent Peris picture:
Color is, also, a very important side of this photograph. The chromatic balance has been obtained assuming that all the light coming from the main galaxy, as a whole, is white. This reference allows to distinguish which parts of NGC 7331 are bluer or redder. This also makes possible to compare the hue of the main galaxy with that of its smaller neighbors and background objects.

So the colors of the Vicent Peris picture are "relative" compared to a "white standard". The colors emanating from various parts of the galaxy are either bluer or redder than the total light of the galaxy.

Click to view full size image

NGC 7337 of the Deer Lick Group.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

I highly recommend this page, which discusses details of the Vicent Peris picture of NGC 7331. Among other things, you can see two closeups of galaxies in the Deer Lick Group, of which the one at left is the most stunning. At least I think so.

Ann

[SpaceCadet]

Angry cat.png

Interesting combination of physics and cat torture there, Art. Particularly when the cat landed on the hard ground.










On a different note, today's APOD is both beautiful and interesting, and it doesn't look brand new to me. Why not? Well, because its colors are so nice and a lot of filters must have been used to produce it!

Click to view full size image

NGC 7331. ESA/Hubble & NASA/D. Milisavljevic.

The image that is today's APOD was released slightly more than two years ago, on January 29, 2018. I strongly applaud all the filters that were used for the image. The ESA/Hubble page where this image was originally released lists no fewer than six filters that were used for this image, two ultraviolet ones, one blue, one yellow-green, one near infrared and one for Hα and NIII. As a result, we get a splendid image that does a superb job at detecting various stellar populations in NGC 7331.

(A more filter-economic example of a Hubble picture of a galaxy is this one, of galaxy NGC 2985, for which only two filters were used. In the case of NGC 2985, the two filters were Hα and near infrared.)

Click to view full size image

NGC 7331 and the Deer Lick Group.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

My favorite portrait of NGC 7331 (and the Deer Lick Group of background galaxies) is the one at right, however. With my peculiar sense of aesthetics, I do find the colors very beautiful.

David Galadí-Enríquez wrote about Vicent Peris picture:
Color is, also, a very important side of this photograph. The chromatic balance has been obtained assuming that all the light coming from the main galaxy, as a whole, is white. This reference allows to distinguish which parts of NGC 7331 are bluer or redder. This also makes possible to compare the hue of the main galaxy with that of its smaller neighbors and background objects.

So the colors of the Vicent Peris picture are "relative" compared to a "white standard". The colors emanating from various parts of the galaxy are either bluer or redder than the total light of the galaxy.

Click to view full size image

NGC 7337 of the Deer Lick Group.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

I highly recommend this page, which discusses details of the Vicent Peris picture of NGC 7331. Among other things, you can see two closeups of galaxies in the Deer Lick Group, of which the one at left is the most stunning. At least I think so.

Ann

Thank you for sharing all of this information!

[Boomer12k]

Amazing close up... really seems active... but hard to see much else...

:---[===] *

[orin stepanek]

I like all the very crisp detail that Hubble brought out!

[Alex_515]

It's always fascinating to relate the sense of depth given in such a spectacular image with the fact that relativistic phenomena are to be taken into account when viewing the image.

[TheOtherBruce]

Click to view full size image

NGC 7331 and the Deer Lick Group.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

My favorite portrait of NGC 7331 (and the Deer Lick Group of background galaxies) is the one at right, however. With my peculiar sense of aesthetics, I do find the colors very beautiful.

Does anyone else see the inner gas and dust clouds tilted at an angle to the outer spiral arms, or is it some sort of perspective effect? I think I can see the same thing in today's main picture.

[neufer]

Click to play embedded YouTube video.

Interesting combination of physics and cat torture there, Art.

Particularly when the cat landed on the hard ground.

[Chris Peterson]

It's always fascinating to relate the sense of depth given in such a spectacular image with the fact that relativistic phenomena are to be taken into account when viewing the image.

What "relativistic phenomena" must be taken into account? How would this image appear any different in a non-relativistic universe?

[Ann]

Click to view full size image

NGC 7331 and the Deer Lick Group.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

My favorite portrait of NGC 7331 (and the Deer Lick Group of background galaxies) is the one at right, however. With my peculiar sense of aesthetics, I do find the colors very beautiful.

Does anyone else see the inner gas and dust clouds tilted at an angle to the outer spiral arms, or is it some sort of perspective effect? I think I can see the same thing in today's main picture.

You are right. We are actually seeing the "ends" of a few spiral arms.

Click to view full size image

Highly inclined galaxy NGC 7331 with arms "ending" near bottom.
Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

Click to view full size image

Nearly face on galaxy NGC 6946 with arms "ending" at top.
Photo: Robert Gendler/ Subaru Telescope.

Ann

[DL MARTIN]

I'm still having trouble in seeing the scientific relevance of analyzing this galaxy without the qualifier that what is being examined took place 50 million years ago. Is astronomy an activity that advances looking backwards? If so, then let's be honest about it.

[Alex_515]

It's always fascinating to relate the sense of depth given in such a spectacular image with the fact that relativistic phenomena are to be taken into account when viewing the image.

What "relativistic phenomena" must be taken into account? How would this image appear any different in a non-relativistic universe?

On a picture of a galaxy like this one, side-viewed, antipodal objects on the external disk's boundary represent events separated by a huge amount of time wrt to the viewer, even though the time interval may be negligible according to the galaxy dynamics' timescale. This is not the case when the galaxy is face on. This is what I meant, please correct me if I'm wrong. I find it amazing.

Alex

[BDanielMayfield]

I'm still having trouble in seeing the scientific relevance of analyzing this galaxy without the qualifier that what is being examined took place 50 million years ago. Is astronomy an activity that advances looking backwards? If so, then let's be honest about it.

Astronomical objects are always studied with distance being one of the key factors involved in the analysis of the data. Also, in these general educational discussions in APOD distance in light-years is always reported for very distant objects.

And yes, astronomy very much is a science that advances by looking backwards in time, even into billions of years. This fact isn't being hidden, it's being celebrated!

[Chris Peterson]

It's always fascinating to relate the sense of depth given in such a spectacular image with the fact that relativistic phenomena are to be taken into account when viewing the image.

What "relativistic phenomena" must be taken into account? How would this image appear any different in a non-relativistic universe?

On a picture of a galaxy like this one, side-viewed, antipodal objects on the external disk's boundary represent events separated by a huge amount of time wrt to the viewer, even though the time interval may be negligible according to the galaxy dynamics' timescale. This is not the case when the galaxy is face on. This is what I meant, please correct me if I'm wrong. I find it amazing.

It is precisely because the time difference is tiny compared with the galaxy dynamics that the finite speed of light (which isn't the same as a relativistic phenomenon) doesn't matter. If light traveled infinitely fast, we'd see essentially no difference in this image, except for having rotated perhaps a quarter of the way further around its axis (which wouldn't make it look much different).

[Chris Peterson]

I'm still having trouble in seeing the scientific relevance of analyzing this galaxy without the qualifier that what is being examined took place 50 million years ago. Is astronomy an activity that advances looking backwards? If so, then let's be honest about it.

Until you're able to explain why you're having this trouble (which no astronomer has), I guess nobody is going to be able to help you. It's been explained to you many times why it's irrelevant.

[neufer]

On a picture of a galaxy like this one, side-viewed, antipodal objects on the external disk's boundary represent events separated by a huge amount of time wrt to the viewer, even though the time interval may be negligible according to the galaxy dynamics' timescale. This is not the case when the galaxy is face on. This is what I meant, please correct me if I'm wrong. I find it amazing.

NGC 7331 and the Deer Lick Group. Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

---

You are correct that there is a small distortion of the galactic wave structure due to synoptic observational time delay of the (~0.0005 c) galactic arm wave propagation.

It means that the most distant parts of NGC 7331 appear to be shifted to the right by at most 0.025% of the full width of the galaxy.

Likewise, the nearest parts of NGC 7331 also appear to be shifted to the right by at most 0.025% of the full width of the galaxy.

This small (though not totally negligible) relativistic distortion could be artificially adjusted for (to first order) but it hardly seems worth the effort.