Starship Asterisk*

by **Chris Peterson** » Wed Jan 04, 2012 6:47 pm

drollere wrote:
Chris Peterson wrote:"Resolved" is sometimes used to describe individual stars seen in other galaxies. In this case, it doesn't mean a star is spatially resolved, but that an individual star is detectable.
ann's usage was clear enough to me. what is the "correct" term for a star that is photographically identifiable as a separate point of light of some finite image scale diameter?

"Resolved" is the correct term both for a star imaged with a finite diameter and a star isolated from its background (as in another galaxy). Obviously, there is a potential for confusion here! The reason I asked Ann for clarification is because she was talking about the size of stars on the image, so it wasn't clear to me which meaning she intended.

There are no stars in this image that show a finite (real) diameter, but there are presumably some individual stars visible in IC 10, thus "resolved" in the second sense.

by **drollere** » Wed Jan 04, 2012 6:36 pm

Chris Peterson wrote:"Resolved" is sometimes used to describe individual stars seen in other galaxies. In this case, it doesn't mean a star is spatially resolved, but that an individual star is detectable.

ann's usage was clear enough to me. what is the "correct" term for a star that is photographically identifiable as a separate point of light of some finite image scale diameter?

the earlier discussion of galactic and cosmological age was interesting. i'd suggest that we can gain some traction by thinking of galaxies not as evolving one out of the other (e.g., ellipticals out of spirals, like land animals out of fish), but rather as galaxies on a thermodynamic continuum within an arbitrary volume of space, much as we think of different ecologies (e.g., marine animals vs. land animals). the animals that live in the niches are not older or younger, but the ecologies do have evolutionary significance and can be organized chronologically.

"grand spirals" are clearly pulling or have recently pulled gas and dust (and smaller galaxies) from their environment and are dynamically forming stars through the compression of large clouds of gas by gravitational contraction and spiral arm shock waves. ellipticals in contrast are devoid of star forming regions, are dynamically not unlike a perfect gas, are usually surrounded by an enormous cloud of hot gas, are characterized by "population II" stars, are not found at higher redshifts, rarely display supernova explosions, are more commonly found in clusters or groups, can be much more massive than the largest spiral galaxy, etc. ... all that implies that ellipticals characterize a *region of space* where galaxy formation began long before the regions of space where spirals or irregular galaxies appear, especially in isolation. galaxies do not necessarily evolve in a sequence, one type out of another, but they do represent stages in the transformation of matter into stars and the increasingly random balance between gravitation and the second law across multiple megaparsec distances.

supernovae explosions may be necessary for an irregular galaxy to remain irregular, but an equally necessary condition is their low mass. supernovae occur at the same rate in larger galaxies or more compact "starburst" galaxies, but their energies are less in relation to the total angular momentum.

this galaxy has no cutsie name. it's appalling. no one can possibly remember something as arcane as IC 10. i propose we hereafter call it the "cupcake galaxy". or maybe the "buns in the oven galaxy", since it has so many new stars on the way.

by **Wolf Kotenberg** » Wed Jan 04, 2012 6:30 pm

WOW !!! can we call this aggregate location an " galactic lagrange point " ??? By the way, remember when I said it would be cool for the soviet Grunt spacecraft to come back on my birthday ? Guess what ? it was announced to day it is ! Now if it misses my house that would be better.

by **Chris Peterson** » Wed Jan 04, 2012 6:02 pm

Ann wrote:It appears that I used the wrong terminology, then. I certainly didn't mean to imply that we were seeing the stars resolved in the sense that astronomers have (barely) resolved nearby supergiant star Betelgeuse.

I meant, rather, that we might be seeing individual supergiant stars in IC 10. These stars look "small" because they are (apparently) faint, due to the 2.5 million light-year distance to them, and even more due to the severe reddening of them due to thick curtains of intervening dust.

No, you didn't use the wrong terminology, it's just that the terminology in use is potentially confusing, given that "resolved" can mean two completely different things when referring to stars.

by **Ann** » Wed Jan 04, 2012 5:53 pm

Chris Peterson wrote:
Ann wrote:Well, I thought there might be. According to Wikipedia, IC 10 and the Andromeda Galaxy are at about the same distance from us. This picture of giant OB association NGC 206 in M 31 shows resolved stars, or so I thought anyway.
It depends on how we define "resolved". Normally, it means that we can extract spatial information. In the case of stars, only a handful have been resolved in this sense- ones that are very close and very large (like Betelgeuse). And even those are only barely resolved. Certainly, there are no spatially resolved stars in other galaxies.

"Resolved" is sometimes used to describe individual stars seen in other galaxies. In this case, it doesn't mean a star is spatially resolved, but that an individual star is detectable.

In any wide field image like today's APOD, every star- whether in our galactic foreground, or in extragalactic objects, is a dimensionless point optically, spread out by atmospheric effects, diffraction, bad optics, scatter in the camera, and any number of other issues. In any image we see, the apparent size of the stars tells us nothing about the actual size of those stars, only how bright they are at the camera.

It appears that I used the wrong terminology, then. I certainly didn't mean to imply that we were seeing the stars resolved in the sense that astronomers have (barely) resolved nearby supergiant star Betelgeuse.

I meant, rather, that we might be seeing individual supergiant stars in IC 10. These stars look "small" because they are (apparently) faint, due to the 2.5 million light-year distance to them, and even more due to the severe reddening of them due to thick curtains of intervening dust.

Ann

by **Chris Peterson** » Wed Jan 04, 2012 4:52 pm

Ann wrote:Well, I thought there might be. According to Wikipedia, IC 10 and the Andromeda Galaxy are at about the same distance from us. This picture of giant OB association NGC 206 in M 31 shows resolved stars, or so I thought anyway.

It depends on how we define "resolved". Normally, it means that we can extract spatial information. In the case of stars, only a handful have been resolved in this sense- ones that are very close and very large (like Betelgeuse). And even those are only barely resolved. Certainly, there are no spatially resolved stars in other galaxies.

"Resolved" is sometimes used to describe individual stars seen in other galaxies. In this case, it doesn't mean a star is spatially resolved, but that an individual star is detectable.

In any wide field image like today's APOD, every star- whether in our galactic foreground, or in extragalactic objects, is a dimensionless point optically, spread out by atmospheric effects, diffraction, bad optics, scatter in the camera, and any number of other issues. In any image we see, the apparent size of the stars tells us nothing about the actual size of those stars, only how bright they are at the camera.

by **Sergio** » Wed Jan 04, 2012 4:46 pm

Hello

Dont want to start a discussion but a bit of info related the equipment
The TMB (7" f8) used 1420 mm of focal length and a 4020 chip gives a resolution arround 1.07 arc seconds per pixel. I my humble opinion will be hard to resolve the IC 10 stars. I might resolve some clusters but this galaxy is 4.2 Mio lights years away (according to SEDS). Another thing could be the SML or LMC were stars can be noticed.

Nevertheless it is an Amazing picture
Impeccable acquisition and the processing of Dietmar is beautiful as usual

Congrats to Torsten and Diets !!

Sergio

by **Ann** » Wed Jan 04, 2012 4:30 pm

Chris wrote:
Ann- I'm confused about the point you're trying to make here. You're not suggesting that there are any resolved stars, are you?

Well, I thought there might be. According to Wikipedia, IC 10 and the Andromeda Galaxy are at about the same distance from us. This picture of giant OB association NGC 206 in M 31 shows resolved stars, or so I thought anyway. Of course there is a huge difference between M31 and IC 10 in that IC 10 is reddened by many magnitudes by dust in our galaxy.

In "The Color Atlas of Galaxies", Jame D Wray has a UBV closeup of NGC 206, which according to James D Wray shows resolved stars. Of course I don't know if he was correct about that.

If you say that it is impossible to see resolved stars in IC 10 in today's APOD, then I'm not arguing.

Ann

by **Chris Peterson** » Wed Jan 04, 2012 3:01 pm

Ann wrote:Note how the Milky Way star field is full of stars of a certain size. But as you go inside IC 10, the "large" Milky Way stars disappear, and instead you get sprinklings of small well-resolved stars, looking like colorful sprinkles on top of a cupcake. These "sprinkles stars" are small-looking because they are 2.5 million light-years away, whereas the Milky Way stars that we can see in Cassiopeia are, at most, a few thousand light-years away. The fact that many of the stars that are sprinkled across the face of IC 10 are almost the same brightness although they are differently colored shows, or so James D Wray argued in his book "The Color Atlas of Galaxies", that they are resolved supergiant stars.

Ann- I'm confused about the point you're trying to make here. You're not suggesting that there are any resolved stars, are you?

In any image like this, the apparent size of the stars is purely a function of their intensity at the camera... in other words, a combination of their intrinsic brightness and their distance. That's why more distant stars usually appear smaller. But a nearby dim star could look smaller than a distant bright one.

by **orin stepanek** » Wed Jan 04, 2012 2:03 pm

Makes you wonder what is causing the starburst activity as it seems to be away from nearby galaxies!

by **Celestine** » Wed Jan 04, 2012 1:05 pm

This is a very interesting thread! I am truly fascinated by the mysteries of the universe. It's hard to wrap my head around sometimes...

by **Ann** » Wed Jan 04, 2012 12:40 pm

starstruck wrote:Ann, that's very interesting. Your comments raise a further thought making me wonder then, how old is the universe? By that, I do not mean what is it's age, but how far along is it in it's lifespan? Is it currently a baby, a toddler, a child, a teenager, a young adult, thirty-something, middle-aged, pensionable, or what? If the universe is still fairly young, then how will it change as it ages and what will it be like in it's dotage? Is it possible for us to even predict? What might the night sky look like to someone in the future standing and staring up at the stars when the universe is old?

The future of the universe is not really known, but it does look as if the universe will not only keep expanding but also keep accelerating in the future, perhaps indefinitely. In that case, the universe may never "die", or at least never "disappear", but it must get ever more "diluted". In such a universe, the galaxies must eventually become so widely separated that they disappear behind each other's "event horizons". Or, to put it differently, in the distant future it will not be possible to spot any galaxies at all apart from the galaxies of the Local Group. Building larger and more powerful telescopes here on Earth (or elsewhere in our own galaxy) will not help. The other galaxies will have disappeared from the part of the universe that we can see. The reason is that the universe will expand so fast that it will send the other galaxies "speeding away from us" at a velocity that is larger than the speed of light. So the light from the other galaxies will approach us at the speed of light, but the distance between us and the other galaxies will grow larger at a speed that is greater than the speed of light, meaning that the light from the other galaxies will never catch up with us.

But you should ask Chris to expound on this subject.

Ann

by **starstruck** » Wed Jan 04, 2012 12:24 pm

Ann, that's very interesting. Your comments raise a further thought making me wonder then, how old is the universe? By that, I do not mean what is it's age, but how far along is it in it's lifespan? Is it currently a baby, a toddler, a child, a teenager, a young adult, thirty-something, middle-aged, pensionable, or what? If the universe is still fairly young, then how will it change as it ages and what will it be like in it's dotage? Is it possible for us to even predict? What might the night sky look like to someone in the future standing and staring up at the stars when the universe is old?

by **Ann** » Wed Jan 04, 2012 10:10 am

saturno2 wrote:I think that the galaxies have 3 ages:
1. Irregular galaxy
2.- Eliptical galaxy
3.- Spiral galaxy

Well, there is no clear relationship between the morphological type of a galaxy and its age. But generally, irregular galaxies are small, whether they are old or young. However, the reason why the irregular galaxies are irregular is almost always that they contain many young stars. These hot massive stars have strong stellar winds and end in titanic supernova explosions, which disrupt the galaxies into irregular shapes. Also, the small mass of these galaxies mean that the massive stars and their outbursts can distort most or all of the galaxy, not just a small part of it.

Large galaxies have generally settled into more regular shapes. In the distant past, elliptical galaxies were less common than they are today. Spiral galaxies can evolve into ellipticals through collisions with other galaxies, but there are, to my knowledge, no known examples of (large) elliptical galaxies evolving into spiral galaxies.

Please note, too, that there was more "free gas" in the distant universe than there is today. Stars form out of gas, so if the gas supply is running dry, star formation must also go down. In the past, when there was a lot of gas available, starburst galaxies must have been much more common than they are today.

The reason why the gas supply of the universe is going down is that much of the gas is "locked up" inside small red dwarfs of spectral class M. These stars are not going to give back the gas they are made of to the universe until the universe is many times older than its present age.

Ann

by **saturno2** » Wed Jan 04, 2012 9:41 am

I think that the galaxies have 3 ages:
1. Irregular galaxy
2.- Eliptical galaxy
3.- Spiral galaxy

by **Ann** » Wed Jan 04, 2012 9:24 am

This is a great picture!

Note how the Milky Way star field is full of stars of a certain size. But as you go inside IC 10, the "large" Milky Way stars disappear, and instead you get sprinklings of small well-resolved stars, looking like colorful sprinkles on top of a cupcake. These "sprinkles stars" are small-looking because they are 2.5 million light-years away, whereas the Milky Way stars that we can see in Cassiopeia are, at most, a few thousand light-years away. The fact that many of the stars that are sprinkled across the face of IC 10 are almost the same brightness although they are differently colored shows, or so James D Wray argued in his book "The Color Atlas of Galaxies", that they are resolved supergiant stars. Undoubtedly some of the bright "clumps" here must be unresolved clusters, too. The delightful pink spots and clouds are of course emission nebulae.

We are seeing IC 10 through the curtain of dust in the plane of the Milky Way. The brightest blue star in the picture, to the lower left of IC 10, is a star with the watching-friendly name of TV Cas. Although the star is variable, it is classified as a main sequence star of spectral class B9. Such a star should have a negative B-V index, but that is not the case for TV Cas. Although the star is "only" about 500 light-years away, it is nevertheless suffciently far away to be significantly reddened by dust in the Milky Way. Imagine, then, how reddened IC 10 must be, since it is behind "the full curtain of dust" of the galactic plane of our galaxy.

IC 10 is seen close to the star farthest to the right in the "W"-shape of Cassiopeia, Beta Cassiopeia. Almost directly to the lower left of Beta Cassiopeia is the reflection nebula Van den Bergh 1. The reflection nebula is being lit up by blue main sequence stars of spectral class B. As you can see in the picture I linked to here, this is a star formation area. Two stars appear to be in the process of being born here, V376 and V633. But these are small stars, nothing like the giant stars that are being born in the churning dust of starburst galaxy IC 10!

Thank you for this great picture, Dietmar Hager and Torsten Grossmann!

Ann

by **bystander** » Wed Jan 04, 2012 6:09 am

Case wrote:
APOD wrote:< | Archive | Index | Search | Calendar | RSS | Education | About APOD | Discuss | >
Link for ‘Discuss’ doesn't work/points to non-existing page. Perhaps because of the old host name?

I've reported it. I don't think the old host name is the problem. I think it has to do with the phpBB update.

by **Case** » Wed Jan 04, 2012 6:02 am

APOD wrote:< | Archive | Index | Search | Calendar | RSS | Education | About APOD | Discuss | >

Link for ‘Discuss’ doesn't work/points to non-existing page. Perhaps because of the old host name?
* The link works now. *

by **APOD Robot** » Wed Jan 04, 2012 5:43 am

Starburst Galaxy IC 10

Explanation: Lurking behind dust and stars near the plane of our Milky Way Galaxy, IC 10 is a mere 2.3 million light-years distant. Even though its light is dimmed by intervening dust, the irregular dwarf galaxy still shows off vigorous star-forming regions that shine with a telltale reddish glow in this colorful skyscape. In fact, also a member of the Local Group of galaxies, IC 10 is the closest known starburst galaxy. Compared to other Local Group galaxies, IC 10 has a large population of newly formed stars that are massive and intrinsically very bright, including a luminous X-ray binary star system thought to contain a black hole. Located within the boundaries of the northern constellation Cassiopeia, IC 10 is about 5,000 light-years across.

<< Previous APOD

Discuss Any APOD

Next APOD >>

[/b]

Starship Asterisk*

APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Post a reply

Expand view Topic review: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

Re: APOD: Starburst Galaxy IC 10 (2012 Jan 04)

APOD: Starburst Galaxy IC 10 (2012 Jan 04)