Starship Asterisk*

When was the last time anyone dusted that thing?

[float=left][img3=""]https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/Cataract_in_human_eye.png/300px-Cataract_in_human_eye.png[/img3][/float][quote="Chris Peterson" post_id=292248 time=1557931434 user_id=117706]

Hmmm. Since this lack of star forming activity likely stems from a loss of free hydrogen, and therefore a relative increase in metallicity, perhaps we should not see it as [i]anemic[/i], but rather as [url=https://en.wikipedia.org/wiki/Polycythemia][i]polycythemic[/i][/url].[/quote]
Not enough plasma :?:

:arrow: Looks more like a cataract to me.

[quote="orin stepanek" post_id=292246 time=1557921723 user_id=100812]
I did notice that you can see several distant galaxies through and behind NGC 4921! :shock: 8-) :thumb_up:
[/quote]

See an annotated view [url=https://spacetelescope.org/images/heic0901b/]here[/url].

Hmmm. Since this lack of star forming activity likely stems from a loss of free hydrogen, and therefore a relative increase in metallicity, perhaps we should not see it as [i]anemic[/i], but rather as [url=https://en.wikipedia.org/wiki/Polycythemia][i]polycythemic[/i][/url].

How 'bout that pair of Milky Way stars just "below" the center. I wonder if we know whether those are companions or if they just happen to line up closely in our line of sight.

I did notice that you can see several distant galaxies through and behind NGC 4921! :shock: 8-) :thumb_up:

I really like today's APOD! :D


[float=right][img2]https://montasefilm.com/wp-content/uploads/2017/11/a-ghost-story.jpg[/img2][c][size=85]Galaxy-colored ghost?[/size][/c][/float]


Okay, first off, I want to say that the bluish color of NGC 4921 is not "true color". Since there are such low levels of star formation in NGC 4921, the galaxy is clearly dominated by yellow stars. Nevertheless, the milky bluis-white colors suit this galaxy. After all, you've never heard of a yellow ghost, have you?




[float=left][img2]https://mk0astronomynow9oh6g.kinstacdn.com/wp-content/uploads/2015/07/ngc4921_colombari_940x400-326x245.jpg[/img2][c][size=85]Ghost-colored galaxy?[/size][/c][/float]





Today's APOD reveals a lot of lovely little details. Star formation is heavily concentrated to the gas-rich dust clouds in the galaxy. Strong intergalactic winds sculpt "pillars of creation" in the striking dust lane at right, which almost appears to [url=https://png.pngtree.com/element_origin_min_pic/16/06/29/16577380e71a05a.jpg]be on blue fire[/url] due to star formation. The bulge of the galaxy looks pale and wan, as if it, too, was a ghost. Diffuse little satellite galaxies can be seen right "above" the galaxy, and at lower right.

NGC 4921 is a handsome ghost of a galaxy.

Ann

I thought I'd seen it all, but ... as has happened multiple times before, this professional astronomer is flummoxed by an APOD! Wow!

It appears to be common in the coma cluster. Hydrogen is being stripped off by the intergalactic medium, leaving galaxies deficient... this galaxy has a high relative velocity...7,560 km/s, which probably does not help...

Many galaxies in the vicinity look in similar condition.

:---[===] *

[url=https://apod.nasa.gov/apod/ap190515.html] [img]https://apod.nasa.gov/apod/calendar/S_190515.jpg[/img] [size=150]Anemic Spiral NGC 4921 from Hubble[/size][/url]

[b] Explanation: [/b] How far away is spiral galaxy NGC 4921? It's surpringly important to know. Although presently estimated to be about 300 million [url=http://chandra.harvard.edu/photo/cosmic_distance.html]light years[/url] distant, a more precise determination could be coupled with its known [url=http://en.wikipedia.org/wiki/Metric_expansion_of_space]recession speed[/url] to help humanity better calibrate the [url=http://apod.nasa.gov/debate/debate96.html]expansion rate[/url] of the entire [url=https://apod.nasa.gov/apod/ap180508.html]visible universe[/url]. Toward [url=http://archive.stsci.edu/proposal_search.php?mission=hst&id=12476]this goal[/url], several [url=http://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=NGC%204921&posfilename=&poslocalname=&posfilecount=&listdelimiter=whitespace&listformat=degrees&RA=195.358960&Dec=27.885940&Radius=0.020833&inst-control=all&inst=ACS&inst=ACSGrism&inst=WFC3&inst=WFPC2&inst=NICMOS&inst=NICGRISM&inst=COS&inst=WFPC2-PC&inst=STIS&inst=FOS&inst=GHRS&imagetype=best&prop_id=&spectral_elt=&proprietary=both&preview=1&output_size=256&cutout_size=12.8|ra=&dec=&sr=&level=&image=&inst=ACS%2CACSGrism%2CWFC3%2CWFPC2%2CNICMOS%2CNICGRISM%2CCOS%2CWFPC2-PC%2CSTIS%2CFOS%2CGHRS&ds=]images were taken[/url] by the [url=http://en.wikipedia.org/wiki/Hubble_Space_Telescope]Hubble Space Telescope[/url] in order to help identify key stellar distance markers known as [url=http://en.wikipedia.org/wiki/Cepheid_variable]Cepheid[/url] [url=http://www.phys.ufl.edu/~buchler/ceph/anim.html]variable[/url] stars. Since [url=http://en.wikipedia.org/wiki/NGC_4921]NGC 4921[/url] is a member of the [url=https://apod.nasa.gov/apod/ap180326.html]Coma Cluster of Galaxies[/url], refining [url=http://adsabs.harvard.edu/abs/2016ApJ...819...77L]its distance[/url] would also allow a better [url=http://abyss.uoregon.edu/~js/ast123/lectures/lec13.html]distance determination[/url] to one of the largest nearby clusters in the local universe. The magnificent spiral [url=http://www.youtube.com/watch?v=6uAjKlkiQ_I]NGC 4921[/url] has been informally dubbed [url=http://en.wikipedia.org/wiki/Anemic]anemic[/url] because of its low rate of [url=https://spaceplace.nasa.gov/search/stars/]star[/url] formation and [url=http://nedwww.ipac.caltech.edu/level5/March01/Impey/frames.html]low surface brightness[/url]. [url=http://www.spacetelescope.org/news/html/heic0901.html]Visible[/url] in [url=http://www.astrobin.com/403935/]the featured image[/url] are, from the center, a bright nucleus, a bright [url=https://apod.nasa.gov/apod/ap050825.html]central bar[/url], a prominent [url=https://apod.nasa.gov/apod/ap991212.html]ring[/url] of dark [url=http://en.wikipedia.org/wiki/Cosmic_dust]dust[/url], blue [url=https://apod.nasa.gov/apod/ap081209.html]clusters[/url] of recently formed stars, several smaller [url=https://apod.nasa.gov/apod/ap080909.html]companion galaxies[/url], unrelated [url=https://apod.nasa.gov/apod/ap180305.html]galaxies in the far distant universe[/url], and unrelated stars in our [url=http://cass.ucsd.edu/public/tutorial/MW.html]Milky Way Galaxy[/url].


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