Starship Asterisk*

The Antlia Cluster of Galaxies

Explanation: Galaxies dot the sky in this impressively wide and deep image of the Antlia Cluster. The third closest cluster of galaxies to Earth after Virgo and Fornax, the Antlia cluster is known for its compactness and its high fraction of elliptical galaxies over (spirals. Antlia, cataloged as Abell S0636, spans about 2 million light years and lies about 130 million light years away toward the constellation of the Air Pump (Antlia). The cluster has two prominent galaxy groups - bottom center and upper left -- among its over 200 galactic members, but no single central dominant galaxy. The vertical red ribbon of gas on the left is thought related to the foreground Antlia supernova remnant and not associated with the cluster. The featured image composite, taken from New Zealand, resulted from 150+ hours of exposures taken over six months.

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Rolf Olsen is one of the best astrophotograpers at this site. Congratulations, Rolf, your picture looks gorgeous, and your APOD is so well-deserved!

Ann

Really awesome...

Must be an awfully old SNR....
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The third closest cluster of galaxies to Earth after Virgo and Fornax, the Antlia cluster is known for its compactness and its high fraction of elliptical galaxies over (spirals.

I think this round bracket is opened in second sentence accidentally.

This is an amazing image that was actually released last year! While the galaxy cluster is very far away, the Antlia Supernova Remnant is very close and also adds an interesting dimension to things. It is probably the closest supernova remnant and is currently being studied by a few astronomers.

Boomer12k wrote:Really awesome...

Must be an awfully old SNR....
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Apparently it's age might be 1.8 million years?

Someone correct me please if this observation is wrong. The text says there are ca. 200 galaxies in this cluster that is only two million light years across. Isn't that even smaller than the distance from earth to Andromeda? Are we talking about an awesome sky for a planet in the middle of this!

Also forgot to mention, the Antlia Supernova Remnant has a size of 26 degrees!! I would love to see a Ha mosaic of the whole supernova remnant by John Gleason!

A virtual smorgasbord of galaxies here! You see fine examples of near-perfect spirals, irregulars, ring, ellipticals, you name it. Now I wonder what our Local Group would look like from that distance.

The cosmology of our universe is a thing to behold. To call today's APOD a small part of it just seems wrong but thanks for the view.

Think there were supernovae during the 6 months of the imaging

The blue-ringed spiral near the bottom-center of the image is very interesting. Upon close inspection it looks like there is a small round object silhouetted in front of it. Is this real, or an artifact?

Visual_Astronomer wrote:The blue-ringed spiral near the bottom-center of the image is very interesting. Upon close inspection it looks like there is a small round object silhouetted in front of it. Is this real, or an artifact?

Good eye, to have noticed that. I really like the coloring of that galaxy. I hope you find out what the black speck is, and that it's something amazing. I wonder if it is anywhere near the galaxy.

MarkBour wrote:

Visual_Astronomer wrote:The blue-ringed spiral near the bottom-center of the image is very interesting. Upon close inspection it looks like there is a small round object silhouetted in front of it. Is this real, or an artifact?

Good eye, to have noticed that. I really like the coloring of that galaxy. I hope you find out what the black speck is, and that it's something amazing. I wonder if it is anywhere near the galaxy.

The image author talks about it on his website! Here's a link to an image he made comparing with some other observations (what an amazing comparison by the way... a 12.5" newtonian on par with telescopes with apertures in meters!) http://www.rolfolsenastrophotography.co ... -fgcM3NZ/A

And here's a link he gives to a paper about the dust cloud:
http://iopscience.iop.org/article/10.10 ... ld.iop.org

NCTom wrote:
Someone correct me please if this observation is wrong. The text says there are ca. 200 galaxies in this cluster that is only two million light years across. Isn't that even smaller than the distance from earth to Andromeda? Are we talking about an awesome sky for a planet in the middle of this!

The Large and Small Magellanic Clouds are separated by ~21º ... imagine them filling the entire sky with that average spacing and that average brightness.

florid_snow wrote:

MarkBour wrote:

Visual_Astronomer wrote:The blue-ringed spiral near the bottom-center of the image is very interesting. Upon close inspection it looks like there is a small round object silhouetted in front of it. Is this real, or an artifact?

Good eye, to have noticed that. I really like the coloring of that galaxy. I hope you find out what the black speck is, and that it's something amazing. I wonder if it is anywhere near the galaxy.

The image author talks about it on his website! Here's a link to an image he made comparing with some other observations (what an amazing comparison by the way... a 12.5" newtonian on par with telescopes with apertures in meters!) http://www.rolfolsenastrophotography.co ... -fgcM3NZ/A

And here's a link he gives to a paper about the dust cloud:
http://iopscience.iop.org/article/10.10 ... ld.iop.org

Thanks for posting that, florid_snow! It is hugely interesting, and it underscores Rolf Olsen's fantastic skill and dedication as an astrophotographer.

I googled the Antlia Cluster and looked for pictures, but I found nothing that is the least bit comparable with Rolf's great image. Again, thanks, Rolf!

The dust cloud in the blue-ringed galaxy near bottom center is very interesting for several reasons. You have to wonder how such a strange feature formed, but this dark dust patch also underscores how little dust there seems to be in the Antlia Cluster galaxies in general. The most obvious dust I can spot is a dust ring in a yellow galaxy near top center. Of course there are other galaxies with visible dust as well, but in general, the galaxies here are not dusty.

There are two other galaxies I find interesting. One is a "perfect spiral" at center right. It is fantastically well-formed, and because it isso regular in shape, I would guess there is not much star formation in it.

The other is a "chunky-looking" yellow galaxy to the upper right of the bright elliptical galaxy at bottom center. The chunky galaxy has a bright, obvious halo that comes to a sudden "stop" - it is truncated. I can find no other galaxy with such a strange halo in the image.

Again, this is a fantastic image!

Ann

Muppet wrote:Of course we've all seen this one by now.

https://www.engadget.com/2016/10/16/uni ... -galaxies/

10 X the supposed # of galaxies in the universe.

http://asterisk.apod.com/viewtopic.php?f=31&t=36458

florid_snow wrote:

MarkBour wrote:

Visual_Astronomer wrote:The blue-ringed spiral near the bottom-center of the image is very interesting. Upon close inspection it looks like there is a small round object silhouetted in front of it. Is this real, or an artifact?

Good eye, to have noticed that. I really like the coloring of that galaxy. I hope you find out what the black speck is, and that it's something amazing. I wonder if it is anywhere near the galaxy.

The image author talks about it on his website! Here's a link to an image he made comparing with some other observations (what an amazing comparison by the way... a 12.5" newtonian on par with telescopes with apertures in meters!) http://www.rolfolsenastrophotography.co ... -fgcM3NZ/A

And here's a link he gives to a paper about the dust cloud:
http://iopscience.iop.org/article/10.10 ... ld.iop.org

Thanks for the link. Such beautiful work, with a 12.5" Newtonian. I'm just floored by Rolf Olsen's dedication.

Anyway, back to the dark blob. The paper you linked was a bit hard for me to follow, but it seemed to be favoring the guess that it is probably a foreground object in our own galaxy, right? I *do* find this quite amazing, then. This kind of observation can start out seeming small, but can snowball into something quite significant. Suppose we conclude that there are quite a number of Jupiter-sized clouds in the interstellar medium surrounding us. The paper mentioned that they would probably not contribute too much to a mass estimate for the galaxy. But the light they block from our view might do a lot more to contribute to the mass we should infer to be out there around us. It would be awfully hard to develop a survey of such objects. But it seems it would dovetail nicely with the survey of galaxies issue that muppet just referenced in this same thread.

MarkBour wrote:Anyway, back to the dark blob. The paper you linked was a bit hard for me to follow, but it seemed to be favoring the guess that it is probably a foreground object in our own galaxy, right? I *do* find this quite amazing, then. This kind of observation can start out seeming small, but can snowball into something quite significant. Suppose we conclude that there are quite a number of Jupiter-sized clouds in the interstellar medium surrounding us. The paper mentioned that they would probably not contribute too much to a mass estimate for the galaxy. But the light they block from our view might do a lot more to contribute to the mass we should infer to be out there around us. It would be awfully hard to develop a survey of such objects. But it seems it would dovetail nicely with the survey of galaxies issue that muppet just referenced in this same thread.

Where do you get "Jupiter-sized cloud"? Such a cloud couldn't exist. A reasonable estimate for the size of the cloud is given as 400 AU, meaning it's the size of the entire solar system out to the heliopause.

In fact, such clouds should have distinctive IR signatures, and be quite obvious in IR surveys. So I doubt they're very common. If there were enough around to actually block our view significantly, the sky would be glowing in IR.

Chris Peterson wrote:

MarkBour wrote:Anyway, back to the dark blob. The paper you linked was a bit hard for me to follow, but it seemed to be favoring the guess that it is probably a foreground object in our own galaxy, right? I *do* find this quite amazing, then. This kind of observation can start out seeming small, but can snowball into something quite significant. Suppose we conclude that there are quite a number of Jupiter-sized clouds in the interstellar medium surrounding us. The paper mentioned that they would probably not contribute too much to a mass estimate for the galaxy. But the light they block from our view might do a lot more to contribute to the mass we should infer to be out there around us. It would be awfully hard to develop a survey of such objects. But it seems it would dovetail nicely with the survey of galaxies issue that muppet just referenced in this same thread.

Where do you get "Jupiter-sized cloud"? Such a cloud couldn't exist. A reasonable estimate for the size of the cloud is given as 400 AU, meaning it's the size of the entire solar system out to the heliopause.

In fact, such clouds should have distinctive IR signatures, and be quite obvious in IR surveys. So I doubt they're very common. If there were enough around to actually block our view significantly, the sky would be glowing in IR.

Sorry, I misquoted from the Heithausen (2004) paper at: http://iopscience.iop.org/article/10.10 ... /fulltext/ where the author refers to: "clumpuscules with sizes of about 100 AU and Jupiter mass (10-3 M⊙)". So I should have said "Jupiter-mass clouds" and I apologize, I should have noted that they would be way, way larger than Jupiter in their volume, so far less dense. He points out that such objects should not be stable, even with that correction.

As to your comment about them being obvious in IR surveys, perhaps the paper is before the time of that data being available(?), so perhaps you have just explained a reason to discount Heithausen's "Such clouds thus provide an ideal means to hide matter from the observer." and in the B. DIRSCH, T. RICHTLER, AND M. GÓMEZ paper, a comment that "Their properties suggest that they may be an abundant structural feature of the ISM."

Chris Peterson wrote:If there were enough around to actually block our view significantly, the sky would be glowing in IR.

By the way, I'm still thinking about this. It's not the first time I've thought along such lines, and this statement makes quite a challenge for me to consider. Perhaps I need to alter my intuition. As a thought experiment, though, I have not found myself being convinced either way. This reminds me of Olber's Paradox, one thing I have thought about a little.

I'd like to invite a further response, if there is a topic in basic astronomy, or an article, or famous experiment or debate, you might point me to, that might steer me better on this question of "What if there is something out there absorbing or blocking light? What can we say about it?"

MarkBour wrote:

Chris Peterson wrote:If there were enough around to actually block our view significantly, the sky would be glowing in IR.

By the way, I'm still thinking about this. It's not the first time I've thought along such lines, and this statement makes quite a challenge for me to consider. Perhaps I need to alter my intuition. As a thought experiment, though, I have not found myself being convinced either way. This reminds me of Olber's Paradox, one thing I have thought about a little.

I'd like to invite a further response, if there is a topic in basic astronomy, or an article, or famous experiment or debate, you might point me to, that might steer me better on this question of "What if there is something out there absorbing or blocking light? What can we say about it?"

I'll look around. But in general, consider that an absolutely clear sky is essentially the temperature of the microwave background. If you have any sort of absorbing material (like dust) it doesn't just radiate to that background, but it absorbs photons (energy) from everything around it that's glowing. It heats up, and is warmer than the background. That's why it stands out against the background in IR (even if it's still very cold in absolute terms).

This is similar to the reason that cloudy nights are warmer than clear ones.