Starship Asterisk*

montylc2001 wrote: ↑Sun Jan 24, 2021 9:45 pm What is the black dot located lower left in the core area? It's not present in other images, and does not seem to be a camera artifact or other processing artifact.

Chris Peterson wrote: ↑Sun Jan 24, 2021 5:42 pm

johnnydeep wrote: ↑Sun Jan 24, 2021 5:38 pm

Chris Peterson wrote: ↑Sun Jan 24, 2021 4:12 pm
Well, the Milky Way is very much at the high end in terms of massive galaxies.

Really? I've been trying to find a graph of galaxy mass versus frequency to no avail. Is the MW on the high end of spiral galaxy mass? What about if elliptical galaxies are also included? Is it even the most massive galaxy in the local group? WikiPedia says Andromeda is a close contender at (1.5±0.5)×10¹² M☉ (from https://en.wikipedia.org/wiki/Andromeda_Galaxy)

I do know dwarf galaxies make up at least 95% (19 out of 20) or so of all galaxies. Or so the Atlas Of the Universe site implies at all size scales (e.g., http://www.atlasoftheuniverse.com/virgo.html). And https://www.quantamagazine.org/the-prob ... y-20190109 says there may be even more:

Bullock argues that around 1,000 tiny galaxies likely orbit every large galaxy like the Milky Way. In addition, dwarf galaxies also overrun the vast stretches of seemingly empty space between large galaxies. As such, there could be as many as 100,000 dwarf galaxies for every large galaxy in the universe.

Today, astronomers estimate that there are likely 100 billion galaxies across the observable universe. But these are Milky-Way-size galaxies. If you extend the count down to these mini-galaxies, then there might be more like 10 million billion galaxies in all.

Ellipticals are the most massive. But among spirals, the MW is definitely at the high end. There are a lot more spiral galaxies that are less massive than the MW than more.

Chris Peterson wrote: ↑Sun Jan 24, 2021 5:44 pm

Lasse H wrote: ↑Sun Jan 24, 2021 5:16 pm

JohnD wrote: ↑Sun Jan 24, 2021 3:31 pm
And with LasseH, do you refer to the Black Dot at 8 o'clock, on the edge of the central clearance? As you say, it must be ENORMOUS!

Yes, I think you mean the same object as I do. I didn't say it was enormous but it must be, if it is an object belonging to the galaxy. Near to it there are about 10 similar sized, round objects, but they are white and look like stars. So, what is the "black sheep" doing there?

Again, this isn't an object. It's an imaging artifact. Caused, for example, by a hot spot on a calibration frame. There are more such black spots in the image, you just need to look a little closer for them because they're in lower contrast areas.

https://en.wikipedia.org/wiki/NGC_2841 wrote:

Click to play embedded YouTube video.

Click to play embedded YouTube video.

<<The rotational behavior of NGC 2841 suggests there is a massive nuclear bulge, with a low-ionization nuclear emission-line region (LINER) at the core; a type of region that is characterized by spectral line emission from weakly ionized atoms. A prominent molecular ring is orbiting at a radius of 2–6 kpc, which is providing a star-forming region of gas and dust. The nucleus appears decoupled and there is a counter-rotating element of stars and gas in the outer parts of the nucleus, suggesting a recent interaction with a smaller galaxy.

A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O⁺, N⁺, and S⁺. Conversely, the spectral line emission from strongly ionized atoms, such as O⁺⁺, Ne⁺⁺, and He⁺, is relatively weak. The class of galactic nuclei was first identified by Timothy Heckman in the third of a series of papers on the spectra of galactic nuclei that were published in 1980.

LINER galaxies are very common; approximately one-third of all nearby galaxies (galaxies within approximately 20-40 Mpc) may be classified as LINER galaxies. Approximately 75% of LINER galaxies are either elliptical galaxies, lenticular galaxies, or S0/a-Sab galaxies (spiral galaxies with large bulges and tightly wound spiral arms). LINERs are found less frequently in Sb-Scd galaxies (spiral galaxies with small bulges and loosely wound spiral arms), and they are very rare in nearby irregular galaxies. LINERs also may be commonly found in luminous infrared galaxies (LIRGs), a class of galaxies defined by their infrared luminosities that are frequently formed when two galaxies collide with each other. Approximately one-quarter of LIRGs may contain LINERs.

LINERs have been at the center of two major debates. First, astronomers have debated the source of energy that excites the ionized gas in the centers of these galaxies. Some astronomers have proposed that active galactic nuclei (AGN) with supermassive black holes are responsible for the LINER spectral emission. Other astronomers have asserted that the emission is powered by star formation regions. The other major issue is related to how the ions are excited. Some astronomers have suggested that shock waves propagating through the gas may ionize the gas, while others have suggested that photoionization (ionization by ultraviolet light) may be responsible.

These debates are complicated by the fact that LINERs are found in a wide variety of objects with different brightnesses and morphologies. Moreover, the debate over the energy sources for LINERs is entangled with a similar debate over whether the light from star formation regions or the light from AGN produce the high infrared luminosities seen in LIRGs.

A number of surveys have been performed to explore the connection between star formation and LINER activity. If a connection can be found between star formation activity and LINER activity, then this strengthens the possibility that LINERs are powered by the hot gas found in star formation regions. However, if star formation cannot be found in LINERs, then this definitively excludes star formation as powering LINER emission.

Recent observations with the Spitzer Space Telescope show a clear connection between LINER emission in luminous infrared galaxies (LIRGs) and star formation activity. The mid-infrared spectra of LIRGs with LINERs have been shown to look similar to the mid-infrared spectra of starburst galaxies, which suggest that infrared-bright LINERs are powered by star formation activity. However, some mid-infrared spectral line emission from AGN have also been detected in these galaxies, indicating that star formation may not be the only energy sources in these galaxies.

Normal nearby galaxies with LINERs, however, appear to be different. A few near-infrared spectroscopic surveys have identified some LINERs in normal galaxies that may be powered by star formation. However, most LINERs in nearby galaxies have low levels of star formation activity. Moreover, the stellar populations of many LINERs appear to be very old, and the mid-infrared spectra, as observed by the Spitzer Space Telescope, do not appear similar to the spectra expected from star formation. These results demonstrate that most LINER in nearby normal galaxies may not be powered by star formation, although a few exceptions clearly exist.>>

Lasse H wrote: ↑Sun Jan 24, 2021 5:16 pm

JohnD wrote: ↑Sun Jan 24, 2021 3:31 pm
And with LasseH, do you refer to the Black Dot at 8 o'clock, on the edge of the central clearance? As you say, it must be ENORMOUS!

Yes, I think you mean the same object as I do. I didn't say it was enormous but it must be, if it is an object belonging to the galaxy. Near to it there are about 10 similar sized, round objects, but they are white and look like stars. So, what is the "black sheep" doing there?

Lasse H wrote: ↑Sun Jan 24, 2021 5:16 pm

JohnD wrote: ↑Sun Jan 24, 2021 3:31 pm
And with LasseH, do you refer to the Black Dot at 8 o'clock, on the edge of the central clearance? As you say, it must be ENORMOUS!

Yes, I think you mean the same object as I do. I didn't say it was enormous but it must be, if it is an object belonging to the galaxy. Near to it there are about 10 similar sized, round objects, but they are white and look like stars. So, what is the "black sheep" doing there?

johnnydeep wrote: ↑Sun Jan 24, 2021 5:38 pm

Chris Peterson wrote: ↑Sun Jan 24, 2021 4:12 pm

johnnydeep wrote: ↑Sun Jan 24, 2021 4:08 pm

"It is one of the more massive galaxies known." Really? The Milky Way seems to be MUCH more massive! From https://en.wikipedia.org/wiki/Milky_Way:



And from https://en.wikipedia.org/wiki/NGC_2841 (note: the article doesn't list size or number of stars):



So, the Milky Way would seem to be at least 10 times as massive as NGC 2841.

Well, the Milky Way is very much at the high end in terms of massive galaxies.

Really? I've been trying to find a graph of galaxy mass versus frequency to no avail. Is the MW on the high end of spiral galaxy mass? What about if elliptical galaxies are also included? Is it even the most massive galaxy in the local group? WikiPedia says Andromeda is a close contender at (1.5±0.5)×10¹² M☉ (from https://en.wikipedia.org/wiki/Andromeda_Galaxy)

I do know dwarf galaxies make up at least 95% (19 out of 20) or so of all galaxies. Or so the Atlas Of the Universe site implies at all size scales (e.g., http://www.atlasoftheuniverse.com/virgo.html). And https://www.quantamagazine.org/the-prob ... y-20190109 says there may be even more:

Bullock argues that around 1,000 tiny galaxies likely orbit every large galaxy like the Milky Way. In addition, dwarf galaxies also overrun the vast stretches of seemingly empty space between large galaxies. As such, there could be as many as 100,000 dwarf galaxies for every large galaxy in the universe.

Today, astronomers estimate that there are likely 100 billion galaxies across the observable universe. But these are Milky-Way-size galaxies. If you extend the count down to these mini-galaxies, then there might be more like 10 million billion galaxies in all.

Chris Peterson wrote: ↑Sun Jan 24, 2021 4:12 pm

johnnydeep wrote: ↑Sun Jan 24, 2021 4:08 pm

APOD Robot wrote: ↑Sun Jan 24, 2021 5:05 am Massive Nearby Spiral Galaxy NGC 2841

Explanation: It is one of the more massive galaxies known. A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk. Dust lanes, small, pink star-forming regions, and young blue star clusters are embedded in the patchy, tightly wound spiral arms. In contrast, many other spirals exhibit grand, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way. The featured composite image merges exposures from the orbiting 2.4-meter Hubble Space Telescope and the ground-based 8.2-meter Subaru Telescope. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

"It is one of the more massive galaxies known." Really? The Milky Way seems to be MUCH more massive! From https://en.wikipedia.org/wiki/Milky_Way:

Mass (0.8–1.5)×10¹² M☉
Number of stars 100-400 billion
Size Stellar disk: 185 ± 15 kly
Dark matter halo: 1.9 ± 0.4 Mly (580 ± 120 kpc)

And from https://en.wikipedia.org/wiki/NGC_2841 (note: the article doesn't list size or number of stars):

Mass 7×10¹⁰ M☉

So, the Milky Way would seem to be at least 10 times as massive as NGC 2841.

Well, the Milky Way is very much at the high end in terms of massive galaxies.

Bullock argues that around 1,000 tiny galaxies likely orbit every large galaxy like the Milky Way. In addition, dwarf galaxies also overrun the vast stretches of seemingly empty space between large galaxies. As such, there could be as many as 100,000 dwarf galaxies for every large galaxy in the universe.

Today, astronomers estimate that there are likely 100 billion galaxies across the observable universe. But these are Milky-Way-size galaxies. If you extend the count down to these mini-galaxies, then there might be more like 10 million billion galaxies in all.

JohnD wrote: ↑Sun Jan 24, 2021 3:31 pm
And with LasseH, do you refer to the Black Dot at 8 o'clock, on the edge of the central clearance? As you say, it must be ENORMOUS!

johnnydeep wrote: ↑Sun Jan 24, 2021 4:08 pm

APOD Robot wrote: ↑Sun Jan 24, 2021 5:05 am Massive Nearby Spiral Galaxy NGC 2841

Explanation: It is one of the more massive galaxies known. A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk. Dust lanes, small, pink star-forming regions, and young blue star clusters are embedded in the patchy, tightly wound spiral arms. In contrast, many other spirals exhibit grand, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way. The featured composite image merges exposures from the orbiting 2.4-meter Hubble Space Telescope and the ground-based 8.2-meter Subaru Telescope. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

"It is one of the more massive galaxies known." Really? The Milky Way seems to be MUCH more massive! From https://en.wikipedia.org/wiki/Milky_Way:

Mass (0.8–1.5)×10¹² M☉
Number of stars 100-400 billion
Size Stellar disk: 185 ± 15 kly
Dark matter halo: 1.9 ± 0.4 Mly (580 ± 120 kpc)

And from https://en.wikipedia.org/wiki/NGC_2841 (note: the article doesn't list size or number of stars):

Mass 7×10¹⁰ M☉

So, the Milky Way would seem to be at least 10 times as massive as NGC 2841.

APOD Robot wrote: ↑Sun Jan 24, 2021 5:05 am Massive Nearby Spiral Galaxy NGC 2841

Explanation: It is one of the more massive galaxies known. A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk. Dust lanes, small, pink star-forming regions, and young blue star clusters are embedded in the patchy, tightly wound spiral arms. In contrast, many other spirals exhibit grand, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way. The featured composite image merges exposures from the orbiting 2.4-meter Hubble Space Telescope and the ground-based 8.2-meter Subaru Telescope. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

Mass (0.8–1.5)×10¹² M☉
Number of stars 100-400 billion
Size Stellar disk: 185 ± 15 kly
Dark matter halo: 1.9 ± 0.4 Mly (580 ± 120 kpc)

Mass 7×10¹⁰ M☉

De58te wrote: ↑Sun Jan 24, 2021 3:10 pm @John D, I see a lot of blue star clusters, particularly in the arms at the top of the photo. You just got to view the enlarged image. In the small image it does look overall pink with a yellow nucleus. Blue stars are scattered all over the arms with the exception of one solid pink arm, second from the foreground spiral. This seems to be at least an area some 50,000 light years long (if the entire galaxy is 150,000 light years large ) without any blue clusters at all.

Now I have a question about observation. As already mentioned the galaxy is tilted from our viewpoint. At first I thought we are viewing it from above and the closer arms to us are the ones at the bottom of the image. Then I glanced away for awhile and looking again I had the impression that I am looking from below and the galaxy is above us like a ceiling fixture and the arms at the top are the ones closer to us. So which is it? Is there an astronical way of measuring which of the arms are closer to us?

Also at the west end of the yellow nucleus there seems to be a black spot where presumably there shouldn't be a black spot in the bright nucleus. Given the size of the galaxy I would guess the black spot is more than 10 light years wide at least. What could it be? A telescope glitch, a black spot in the Milky Way foreground, or maybe the first visible dark matter caught on camera?

VictorBorun wrote: ↑Sun Jan 24, 2021 6:09 am trying to imagine a 3d, it's easy to see dusty outskirts as wide tyre around a thin plate wheel.

The part near the core is more puzzling. There surely is a large ghostly shine bulge through which we see the far side of the arms' ends.
But what are the dusty lanes seen very close to the core due to the backlight of the core?
They look like lying strictly in the plane.
How come the dust lanes obey the flattening viscosity of the gas disk and the stellar population of bulge does not?
Is dust more glued into near-core thinning gas then the stars?

JohnD wrote: ↑Sun Jan 24, 2021 11:24 am I think this may be one for Anne, but did something go wrong with the way this photo was printed?
Quote from blurb, "Dust lanes, small, pink star-forming regions, and young blue star clusters are embedded in the patchy, tightly wound spiral arms", when the whole galaxy looks pink, with precious few blue stars!

John

VictorBorun wrote: ↑Sun Jan 24, 2021 8:32 am

Click to view full size image

and what about visibiliy of the dust in say 1 kly from us just outside the disk?
Is it dark against the galaxy bulge?
Does it disappear the other way round, where it catch the light from the core of the Milky Way and is as bright as its background of the distant stellar haze?
Or are we too far from too small a bulge for such play?

It seems we are too far from the bulge of the Milky Way for its light to brighten the dust outside the disk and against the background of distant stellar haze.

VictorBorun wrote: ↑Sun Jan 24, 2021 6:09 am trying to imagine a 3d, it's easy to see dusty outskirts as wide tyre around a thin plate wheel.

The part near the core is more puzzling. There surely is a large ghostly shine bulge through which we see the far side of the arms' ends.
But what are the dusty lanes seen very close to the core due to the backlight of the core?
They look like lying strictly in the plane.
How come the dust lanes obey the flattening viscosity of the gas disk and the stellar population of bulge does not?
Is dust more glued into near-core thinning gas then the stars?