APOD: Mirach's Ghost (2021 Oct 28)

[APOD Robot]

Mirach's Ghost

Explanation: As far as ghosts go, Mirach's Ghost isn't really that scary. Mirach's Ghost is just a faint, fuzzy galaxy, well known to astronomers, that happens to be seen nearly along the line-of-sight to Mirach, a bright star. Centered in this star field, Mirach is also called Beta Andromedae. About 200 light-years distant, Mirach is a red giant star, cooler than the Sun but much larger and so intrinsically much brighter than our parent star. In most telescopic views, glare and diffraction spikes tend to hide things that lie near Mirach and make the faint, fuzzy galaxy look like a ghostly internal reflection of the almost overwhelming starlight. Still, appearing in this sharp image just above and to the right of Mirach, Mirach's Ghost is cataloged as galaxy NGC 404 and is estimated to be some 10 million light-years away.

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[Ann]

Mirach's Ghost. Image Credit & Copyright: John Chumack

Mirach's Ghost. Image Credit & Copyright: Kent Wood

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As you can see, these two images of Mirach and Mirach's Ghost look very different. One is much redder than the other. One displays much longer och brighter star spikes of Mirach than the other. Kent Wood's image makes Mirach sparkle and blaze like a combination of a yellow-white diamond and a searchlight.

The orientation of the two images is also different. It is the orientation of John Chumack's image that is the "correct" one, or at least the conventional one.

As for Mirach's Ghost, isn't it funny that its NGC number is 404, like an error message?

And speaking of NGC 404...

NGC 404, Mirach's Ghost, imitating a galactic pumpkin. Image: NASA.

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NGC 404, Mirach's Ghost. Image: Alchetron, the free encyclopedia (and Hubble?)

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Would you look at that!!! Two different images of Mirach's Ghost, NGC 404, one where it looks like a galactic pumpkin and one where it looks like a galaxy!!!

Of course NGC 404 isn't as orange as a pumpkin in space, and Mirach isn't as red as it seems to be in today's APOD.

But see here what NGC 404 looked like when NASA's now defunct ultraviolet-detecting space telescope GALEX took a peek at it:

NGC 404. Image: GALEX/NASA/JPL-Caltech.

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What's that blue ring? Well, take a look at that Alchetron picture of NGC 404, and I think you can see the blue stars there. They seem to be very widely scattered in an extremely loose ring, and the dust that we can see near the nucleus of NGC 404 seems to have no connection with the scattered blue stars. They are probably rather modest stars of spectral classes A and late B, like Sirius, Vega and Regulus.

And by the way, where is Mirach in the GALEX image? Well, can you see that unremarkable yellow star to the lower left of NGC 404, at 7 o'clock? That's Mirach. It looks so small because GALEX only detected ultraviolet light, and Mirach is very faint at shorter wavelengths.

And what about the "true" color of Mirach? Well, think of it like this. Mirach is considerably paler in color than Betelgeuse. So if Betelgeuse isn't that red, then Mirach most certainly isn't.

Image: Freestarcharts.

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But why don't you go out and take a look for yourself?

Ann

[orin stepanek]

Beautiful Star & Galaxy! So; if M31 & M33 are gravitationaly
attractioned to each other; we could be involved in a triple
galactic merger!

[neufer]

<<The HTTP 404, 404 not found, 404, 404 error, page not found or file not found error message is a hypertext transfer protocol (HTTP) standard response code, in computer network communications, to indicate that the browser was able to communicate with a given server, but the server could not find what was requested. The 404 error may also be used when a server does not wish to disclose whether it has the requested information.>>

Click to play embedded YouTube video.

NGC 404 galaxy by Hubble Space Telescope

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Click to play embedded YouTube video.

<<NGC 404 is a very isolated dwarf lenticular galaxy, a bit more luminous and smaller than the Small Magellanic Cloud. Unlike many other early-type galaxies, it is very rich in neutral hydrogen, most of it concentrated on a pair of large rings around it. It also has star formation both on its center and on its outermost regions, albeit at a low level,

Both the outer gas disk and its star formation are assumed to have been triggered by one or several mergers with smaller galaxies roughly 1 billion years ago and it has been proposed NGC 404 is a former spiral galaxy that was transformed into a lenticular one by that event.

NGC 404 contains a low-ionization nuclear emission-line region (LINER), a type of region that is characterized by spectral line emission from weakly ionized atoms. A nuclear star cluster is also present as well as -likely- a supermassive black hole, with a mass of several tens of thousands solar masses.

At least two techniques have been used to measure distances to NGC 404. The infrared surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 404 using this technique in 2003 is 9.9 ± 0.5 Mly. However, NGC 404 is close enough that red supergiants can be imaged as individual stars. The light from these stars and knowledge of how they should compare to nearby stars within the Milky Way galaxy allows for direct measurement of the distance to the galaxy. This method is referred to as the tip of the red giant branch (TRGB) method. The estimated distance to NGC 404 using this technique is 10.0 ± 1.2 Mly. Averaged together, these distance measurements give a distance estimate of 10.0 ± 0.7 Mly. In 2018 a possible satellite designated Donatiello I was identified. Donatiello I is a dwarf spheroidal galaxy with little recent star formation. Difficulty in establishing the exact distance to the galaxy leaves its status as a satellite unconfirmed.>>

[Joe Stieber]

But why don't you go out and take a look for yourself?

Ann

Indeed, and I have done so many times over the years, primarily with a 12.5 inch (318 mm) Newtonian on a Dobsonian mount. I remember the first time I saw it about 15 years ago. My friend Jeremy spotted a fuzzy patch near Mirach (Beta And). We wondered, was it an internal reflection in the eyepiece or was it an actual object? When the scope was moved around a little, the spacing and orientation remained the same, unlike an internal reflection. Then a check of Sky & Telescope's Pocket Sky Atlas showed that it was the ironically numbered NGC 404. I still have that old S&T PSA, it's all beat up now.

[johnnydeep]

So, the Wikipedia link - https://en.wikipedia.org/wiki/NGC_404 - shows a Hubble image of the entirety of NGC 404 with a fov of 1.68' x 1.68'. But the stat box says the apparent size of NGC 404 is 3′.5 × 3′.5. How can this make sense? And for that matter, shouldn't that be 3.5' x 3.5'?

[Chris Peterson]

So, the Wikipedia link - https://en.wikipedia.org/wiki/NGC_404 - shows a Hubble image of the entirety of NGC 404 with a fov of 1.68' x 1.68'. But the stat box says the apparent size of NGC 404 is 3′.5 × 3′.5. How can this make sense? And for that matter, shouldn't that be 3.5' x 3.5'?

I'd take any reference to the angular size of a galaxy with a big grain of salt. It depends so much on the depth of the image. Galaxies don't always have very clearly defined edges.

Stylistically, angular units used with decimal values can be placed with the integer part of the value or at the end (e.g. 3°.5, 3.5°). You'll see both used. But Wikipedia should stick with just one format. Mixing them this way is poor.

[johnnydeep]

So, the Wikipedia link - https://en.wikipedia.org/wiki/NGC_404 - shows a Hubble image of the entirety of NGC 404 with a fov of 1.68' x 1.68'. But the stat box says the apparent size of NGC 404 is 3′.5 × 3′.5. How can this make sense? And for that matter, shouldn't that be 3.5' x 3.5'?

I'd take any reference to the angular size of a galaxy with a big grain of salt. It depends so much on the depth of the image. Galaxies don't always have very clearly defined edges.

Stylistically, angular units used with decimal values can be placed with the integer part of the value or at the end (e.g. 3°.5, 3.5°). You'll see both used. But Wikipedia should stick with just one format. Mixing them this way is poor.

Ok, sure, a galaxy's size is surely debatable (they being quintessentially "fuzzy" objects), but in what universe of reasonable is it to say that a galaxy that pretty clearly fits totally in a 1.68' square FOV, is also 3.5' in diameter? ... Then again, I just found this reference that confirms the 3.5'-ish diameter with a circle representing the extent of the galaxy - https://theskylive.com/sky/deepsky/ngc404-object#dss2

DSS2 image of NGC 404 in the Red band. The green region on the image is a representation of the major (3.4 arcmin) and minor (3.37 arcmin) axes of the object's apparent size.

It still seems to be wildly exaggerating the diameter to me though.

[Chris Peterson]

So, the Wikipedia link - https://en.wikipedia.org/wiki/NGC_404 - shows a Hubble image of the entirety of NGC 404 with a fov of 1.68' x 1.68'. But the stat box says the apparent size of NGC 404 is 3′.5 × 3′.5. How can this make sense? And for that matter, shouldn't that be 3.5' x 3.5'?

I'd take any reference to the angular size of a galaxy with a big grain of salt. It depends so much on the depth of the image. Galaxies don't always have very clearly defined edges.

Stylistically, angular units used with decimal values can be placed with the integer part of the value or at the end (e.g. 3°.5, 3.5°). You'll see both used. But Wikipedia should stick with just one format. Mixing them this way is poor.

Ok, sure, a galaxy's size is surely debatable (they being quintessentially "fuzzy" objects), but in what universe of reasonable is it to say that a galaxy that pretty clearly fits totally in a 1.68' square FOV, is also 3.5' in diameter? ... Then again, I just found this reference that confirms the 3.5'-ish diameter with a circle representing the extent of the galaxy - https://theskylive.com/sky/deepsky/ngc404-object#dss2


ngc 404 apparent size.JPG


It still seems to be wildly exaggerating the diameter to me though.

It is not at all obvious to me that this galaxy "clearly fits totally in a 1.68' square FOV". I have no problem believing that we are only seeing the central, brightest part in that image.

[neufer]

Click to play embedded YouTube video.