VLT Image of Supernova 2007af in the Spiral Galaxy NGC 5584 in Virgo

[Blob]

Until now NGC 5584 was just one galaxy among many others, located to the West of the Virgo Cluster. Known only as a number in galaxy surveys, its sheer beauty is now revealed in all its glory in a new VLT image. Since 1 March, this purple cosmic rose also holds the brightest stellar explosion of the year, known as SN 2007af.
Located about 75 million light years away towards the constellation Virgo, NGC 5584 is a galaxy slightly smaller than the Milky Way. It belongs, however, to the same category: both are barred spirals.

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[RussT]

Will This...
http://www.narrabri.atnf.csiro.au/pu...mages/ngc2915/

Evolve into this...???
http://www.eso.org/outreach/press-re.../pr-16-07.html

Put 2 windows up and keep going back and forth between the two.

[HenrikOlsen]

They do seem to have several similarities.

[Peter Wilson]

Pictured is the blue compact dwarf (BCD) galaxy NGC 2915. In visible light, shown in yellow, this galaxy appears to be a normal dwarf galaxy, as indicated by the yellow smudge in the image center. Yet when imaged in a neutral hydrogen gas (called HI), a whole spiral galaxy appears. Much about BCD galaxies remains mysterious, such as...why there is so much dark matter?

Because there's so little light matter?

[RussT]

Quote:

Originally Posted by Narrabi
Pictured is the blue compact dwarf (BCD) galaxy NGC 2915. In visible light, shown in yellow, this galaxy appears to be a normal dwarf galaxy, as indicated by the yellow smudge in the image center. Yet when imaged in a neutral hydrogen gas (called HI), a whole spiral galaxy appears. Much about BCD galaxies remains mysterious, such as...why there is so much dark matter?

Because there's so little light matter?

Precisely! DM is universal and so the more that stars are made in any particular galaxy, the more that the DM is "IN" (both in elements and 'going through' the stars at "c") the stars and seen as baryonic matter. SO, the more evolved a galaxy is the less DM is 'seen' as necessary to account for the speeds of the HI/HII and stars in the outer parts of the disc.

SO, the Dark Matter Galaxies need the most DM, then the BCD's, and then the LSB's and so on through the Sa/Sc's and up to the Ellipticals, which need the least amount of DM to account for rotation speeds.

BUT back to comparing the two galaxies. This is still listed as a BCD, (Blue Compact "Dwarf"), but as it says right in the quote... [Yet when imaged in a neutral hydrogen gas (called HI), a whole spiral galaxy appears.].

You can actually see where the "Bar" will form once this evolves closer to the LSB stages. What is actually being shown here is "First Light" from a spiral galaxy!!!

http://www.astro.uni-bonn.de/~webgk/ws98/thuan_r.html

[Peter Wilson]

Thanks.

That's what I was thinking

[Cougar]

DM is universal and so the more that stars are made in any particular galaxy, the more that the DM is "IN" (both in elements and 'going through' the stars at "c") the stars and seen as baryonic matter. SO, the more evolved a galaxy is the less DM is 'seen' as necessary to account for the speeds of the HI/HII and stars in the outer parts of the disc.... SO, the Dark Matter Galaxies need the most DM, then the BCD's, and then the LSB's and so on through the Sa/Sc's and up to the Ellipticals, which need the least amount of DM to account for rotation speeds.... http://www.astro.uni-bonn.de/~webgk/ws98/thuan_r.html

Interesting paper. (I've read both of Thuan's books -- the first much better than the second.) But I don't know how you are reaching your conclusion about the amount of dark matter in these various galaxies (other than ellipticals). I don't see any data showing the rotation curves or the "speeds of the HI/HII and stars in the outer parts of the disc" of your blue compact dwarfs mentioned above...

[RussT]

Thanks.

That's what I was thinking

You're welcome.

[RussT]

Interesting paper. (I've read both of Thuan's books -- the first much better than the second.) But I don't know how you are reaching your conclusion about the amount of dark matter in these various galaxies (other than ellipticals). I don't see any data showing the rotation curves or the "speeds of the HI/HII and stars in the outer parts of the disc" of your blue compact dwarfs mentioned above...

You know, now that you mention it like this, I don't think that I have read one paticular paper or article that talks about it like this.

I was reading something (racking my brain) the other night that was saying something to this affect, and had to read it 3 times to make sure it was saying this very thing correctly (that is, agreeing with what I am saying here), but it was not talking about specific types of galaxies like I am doing here. I think it was more of a mass to light ratio thing.

I'll check some of the other LSB and BCD things I have saved and see if I can find a more specific reference related to this.

I know it says something to this affect in here (at least for this galaxy).

http://kencroswell.com/FirstDarkGalaxy.html

[RussT]

Here are several links to papers on this.

http://www.bautforum.com/showthread.php?t=26983

The first is most directly relevent.

http://arxiv.org/abs/astro-ph/0405439

I have talked about this in several different ways, but what really needs to be understood here, is that if they aren't careful, they are going to (if they haven't already) 'constrain themselves' right out of the truth about all of this!

[RussT]

Interesting paper. (I've read both of Thuan's books -- the first much better than the second.) But I don't know how you are reaching your conclusion about the amount of dark matter in these various galaxies (other than ellipticals). I don't see any data showing the rotation curves or the "speeds of the HI/HII and stars in the outer parts of the disc" of your blue compact dwarfs mentioned above...

http://www.spacetoday.net/Summary/2814

Cardiff University astronomers found the galaxy, designated VIRGOHI21, at radio wavelengths using the Lovell Telescope. The radio telescope data revealed a large mass of ordinary hydrogen atoms weighing 100 million solar masses. However, the rate of rotation of the hydrogen derived from the radio observations implied the existence of 1,000 times more mass, which astronomers believe is in the form of invisible dark matter. Visible-light observations of the region showed no sign of any stars of other ordinary matter that might otherwise explain the observations.

These are the kind of DM VS rotational speeds I was talking about.