APOD: Mirach's Ghost (2017 Oct 27)

[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 left 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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[rj rl]

NGC 404 also known as Galaxy Not Found.

[Ann]

Yes, NGC 404 sounds like an error message.

Click to view full size image

Red carbon star T Lyrae, much redder than Mirach.
Source: http://picssr.com/photos/9885064@N05?nsid=9885064@N05

Click to view full size image

Yellow star Pollux, yellower than NGC 404.
Source: http://earthsky.org/brightest-stars/pol ... htest-star

What is most interesting about the picture to me is that it shows how much redder the star is than the galaxy. Mirach is an M-type giant, which makes it a quite red star in the sky, but not record red by any means. It is (probably) less red than Betelgeuse, whose B-V is 1.500 ± 0.500, versus 1.576 ± 0.010 for Mirach. Betelgeuse is definitely more infrared than Mirach, with a V-I index of 2.32 ± 0.02, versus 1.74 ± 0.03 for Mirach. That is actually not so red.

The only truly red stars are carbon stars like T Lyra or R Leporis. The B-V of R Leporis is 2.70 ± 0.510, and the B-V of T Lyra is 5.460 ± 0.510. Now we're talking red.

Click to view full size image

Visible and UV image of Mirach and NGC 404.

NGC 404, the galaxy that is "The Ghost of Mirach", is an S0-type galaxy and therefore made up almost exclusively of old "red" stars. But the overall light of the stars of typical S0 and elliptical galaxies is not so red. The B-V of NGC 404 is 0.940, which is a very normal B-V index for galaxies that have mostly stopped forming stars. It corresponds to a color redder than the Sun, but bluer than Pollux.

As the GALEX image at right shows, NGC 404 does have a faint ring of young stars that surrounds it.

One minute astronomer wrote:

Lenticular galaxies tend to have little star-forming activity. But astronomers have discovered NGC 404 is ringed by newly-formed stars and excited hydrogen gas. Studies suggest the little galaxy was jostled by the gravity of another galaxy about a billion years ago, an event which triggered a wave of star formation from the last remnants of gas within this tiny star group.

Ann

[sillyworm2]

That ring of younger blue stars...if we could see this Galaxy in current time......what would it look like? Would ANY of these young stars still exist? Would a group of newer young stars have been created? Is there a possibility that one day we may be able to "see" distant objects in a current time frame? Never say never!

[Chris Peterson]

That ring of younger blue stars...if we could see this Galaxy in current time......what would it look like? Would ANY of these young stars still exist? Would a group of newer young stars have been created? Is there a possibility that one day we may be able to "see" distant objects in a current time frame? Never say never!

We are seeing this galaxy in "current time". That's the only way it's possible to see it.

If we were still here to observe it 10 million years from now, it would likely look about the same.

[ta152h0]

my newscreamsaver

[sillyworm2]

Thanks Chris....I should have said 10 million years from now....and thinking about it..this galaxy is rather close.I should have realized that. Now If it was a Billion Light years away...would it look much different?

[sillyworm2]

Ok where is that editing button....Correction Would it look much different in a Billion years ? Or if say NGC 404 was a Billion Light Years away....would this ring of stars(and other scenarios I mentioned) look much different in a Billion years from now?

[Chris Peterson]

Ok where is that editing button....Correction Would it look much different in a Billion years ? Or if say NGC 404 was a Billion Light Years away....would this ring of stars(and other scenarios I mentioned) look much different in a Billion years from now?

Create an account for yourself and you'll have the ability to edit your posts.

[Visual_Astronomer]

Mirach's brightness makes seeing NGC 404 a challenge. As with Alnitak in Orion and the Flame Nebula (NGC 2024), it's best to pan the star out of the filed of view in order to see such a faint object.

[neufer]

NGC 404 also known as Galaxy Not Found.

<<In 2008, a study carried out by the telecommunications arm of the Royal Mail found that "404" became a slang synonym for "clueless" in the United Kingdom. Slang lexicographer Jonathon Green said that "404" as a slang term had been driven by the "influence of technology" and young people, but at the time, such usage was relatively confined to London and other urban areas.>>

[DL Martin]

Chris Peterson's assertion that objects such as stars and galaxies are only seen in "current time" is reminiscent of a pre telescope star gazer who thought the universe was pinholes on a black fabric. One might suppose that when Chris looks out the window he believes the Earth is flat, as well.

[HiYoSilver]

Chris Peterson's assertion that objects such as stars and galaxies are only seen in "current time" is reminiscent of a pre telescope star gazer who thought the universe was pinholes on a black fabric. One might suppose that when Chris looks out the window he believes the Earth is flat, as well.

Chris is familiar with the supposed reality that the image is what the galaxy looked like a long time ago, however long it was that the image's light left the galaxy. Chris was speaking of the viewer's present time as current time .. but obviously does not believe that anyone today has the ability to time travel, a possibility no one really knows except a time traveler if there is one, and perhaps some super secret Chinese or Russian or Indian or Japanese government agency (they being so far ahead in science and technology.) However, Chris could have been clearer, saying, 'we are viewing the image of that galaxy in current time.' (And I'm happy to help you out Chris, this time, well, not really happy, but I understand the effects of aging on mental processes involving proper use of words, us old folk do get tired.)

[Chris Peterson]

Chris Peterson's assertion that objects such as stars and galaxies are only seen in "current time" is reminiscent of a pre telescope star gazer who thought the universe was pinholes on a black fabric. One might suppose that when Chris looks out the window he believes the Earth is flat, as well.

Chris is familiar with the supposed reality that the image is what the galaxy looked like a long time ago, however long it was that the image's light left the galaxy. Chris was speaking of the viewer's present time as current time .. but obviously does not believe that anyone today has the ability to time travel, a possibility no one really knows except a time traveler if there is one, and perhaps some super secret Chinese or Russian or Indian or Japanese government agency (they being so far ahead in science and technology.) However, Chris could have been clearer, saying, 'we are viewing the image of that galaxy in current time.' (And I'm happy to help you out Chris, this time, well, not really happy, but I understand the effects of aging on mental processes involving proper use of words, us old folk do get tired.)

Well, you're sort of right. But I also meant it quite literally. As a physicist, I recognize that it's meaningless for the most part to give any concern to the light travel time of what we're seeing. In almost every useful sense, we can say we're seeing the galaxy as it is now.

[Ann]

Ok where is that editing button....Correction Would it look much different in a Billion years ? Or if say NGC 404 was a Billion Light Years away....would this ring of stars(and other scenarios I mentioned) look much different in a Billion years from now?

One-Minute Astronomer wrote:

Lenticular galaxies tend to have little star-forming activity. But astronomers have discovered NGC 404 is ringed by newly-formed stars and excited hydrogen gas. Studies suggest the little galaxy was jostled by the gravity of another galaxy about a billion years ago, an event which triggered a wave of star formation from the last remnants of gas within this tiny star group.

The event that created the blue-looking stars took place about a billion years ago, which means that most of the blue-appearing stars surrounding NGC 404 will also be around a billion years old. This fairly advanced age means that there should be no main sequence O or B-type stars left here, and hardly any A-type stars either. Perhaps we might find some late A-type stars in the ring around NGC 404, and certainly a lot of F-type stars.

A billion years is a non-negligible time in the life of a medium-mass star, but paradoxically, I don't think it will have that much of an effect on the appearance of the ring of stars around NGC 404. After two billion years there should certainly be no more A-type stars left, but there should be so few of them already that their complete absence shouldn't matter that much. By contrast, many of the F-type stars that are there today should still be there in another billion years.

If there has been one or more second wave of star formation in NGC 404 there may indeed be B-type stars there, and just possibly even a few O-type stars. If there are indeed some OB stars in NGC 404 now, but no new star formation will take place there - which is a possibility, since the galaxy may well have run out of gas - then another billion years will make a big difference in the galaxy's appearance. The color of the ring will change considerably if there are OB stars there now, but all the OB stars and many of the A-type stars disappear within a billion years.

Ann

[neufer]

Chris could have been clearer, saying, 'we are viewing the image of that galaxy in current time.'

Well, you're sort of right. But I also meant it quite literally. As a physicist, I recognize that it's meaningless for the most part to give any concern to the light travel time of what we're seeing. In almost every useful sense, we can say we're seeing the galaxy as it is now.

Then it would have been so easy to state that since the 'new' blue stars are about a billion years old they could not have changed much over the 10 million years it took for light to reach us.

Short cut explanations are seldom worth while.

[Chris Peterson]

Chris could have been clearer, saying, 'we are viewing the image of that galaxy in current time.'

Well, you're sort of right. But I also meant it quite literally. As a physicist, I recognize that it's meaningless for the most part to give any concern to the light travel time of what we're seeing. In almost every useful sense, we can say we're seeing the galaxy as it is now.

Then it would have been so easy to state that since the 'new' blue stars are about a billion years old they could not have changed much over the 10 million years it took for light to reach us.

I did say that.

[neufer]

As a physicist, I recognize that it's meaningless for the most part to give any concern to the light travel time of what we're seeing. In almost every useful sense, we can say we're seeing the galaxy as it is now.

Then it would have been so easy to state that since the 'new' blue stars are about a billion years old they could not have changed much over the 10 million years it took for light to reach us.

I did say that.

Only as an afterthought after quibbling about what
'observing something distant in current time' properly means
(when it was quite obvious to everyone what sillyworm2 meant).

[geckzilla]

I think when I learned that a photon experiences no passage of time from its point of view, if it could have a point of view, that changed how I thought about space. Clocks are useless to photons because not even the smallest slice of time passes between its "birth" and "death". One of the freakiest questions then is whether a photon knows where it's going to land before it actually lands.

[neufer]

One of the freakiest questions then is whether a photon knows where it's going to land before it actually lands.

Certainly not those photons with a slit personality.

[geckzilla]

I updated the first sentence of my previous post to be a complete sentence. Apparently it is hard to finish thoughts when one is being talked to and rushed.

[neufer]

I updated the first sentence of my previous post to be a complete sentence.
Apparently it is hard to finish thoughts when one is being talked to and rushed.

If you were a photon you could have stayed more focused.

[Chris Peterson]

I updated the first sentence of my previous post to be a complete sentence.
Apparently it is hard to finish thoughts when one is being talked to and rushed.

If you were a photon you could have stayed more focused.

Unless she got scattered.

[Chris Peterson]

Then it would have been so easy to state that since the 'new' blue stars are about a billion years old they could not have changed much over the 10 million years it took for light to reach us.

I did say that.

Only as an afterthought after quibbling about what
'observing something distant in current time' properly means
(when it was quite obvious to everyone what sillyworm2 meant).

What I took him to mean was that "now" meant that the system was "currently" 10 million years further along than we see it... a poor way of looking at things and one I will continue to correct in this forum.

The second sentence was the answer to his question, which was not an "afterthought".