ASTRO: Draco Dwarf Galaxy reprocessed

The Draco Dwarf is also known as PGC 60095. When I took this 18 months
ago my processing abilities didn't allow me to process this one. 8
month's later I processed it but the galaxy was still very hard to pull
out. Now I'm trying again and the stars are now much easier to see.
This galaxy, located a bit over 250 million light years from us is a
satellite of our own galaxy. It wasn't discovered until 1954 using the
new Palomar Observatory Sky Survey plates. Even then it looked like a
rich but spread out open cluster as its stars covered more than a half
degree of sky by just under a half degree making it somewhat elliptical.
It is about 2500 light years across its major axis and 2000 light
years across its minor axis. That's small! But its distance showed it
to be beyond our galaxy and thus really a galaxy with only a few
thousand stars.

Motion of the stars within the galaxy is difficult to explain. Before
the discovery of dark matter it was thought tidal disruption was the
answer but there were some things this didn't explain. Dark matter
changed things. If you assume a very high concentration of dark matter
then the motions can be explained. The problem is the concentration has
to be so high this tiny galaxy would have a higher density of dark
matter than any known galaxy. Since it is close enough to us to be
tidally torn up (if it doesn't have this high density of dark matter)
the issue is still not settled though I sense a leaning toward the dark
matter side. But its the new kid on the block and it seems any new idea
suddenly becomes over popular in hindsight. Only time will tell who is
right here.

At least 75% and maybe up to 90% of its stars are over 10 billion years
old showing little new star formation though there's a small population
of 2 to 3 billion year old stars so something triggered a bit of star
formation at that time. Today we see too little dust and gas in it for
further star formation.

When I imaged it I used the coordinates that weren't all that accurate.
I should have checked but figured I'd see it in the focus images. But
I saw nothing so just assumed they were right. Big mistake as it is
well off center in my image because of this goof. The core is to the
upper left of center. All the reason to retake it in a few months with
a lot more exposure time.

14" LX200R @ F/10, L=4x10', RGB=4x10', STL-11000XM, Paramount ME

Rick


--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

Great picture Rick. Strange object indeed.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
ter.com...
The Draco Dwarf is also known as PGC 60095. When I took this 18 months
ago my processing abilities didn't allow me to process this one. 8
month's later I processed it but the galaxy was still very hard to pull
out. Now I'm trying again and the stars are now much easier to see.
This galaxy, located a bit over 250 million light years from us is a
satellite of our own galaxy. It wasn't discovered until 1954 using the
new Palomar Observatory Sky Survey plates. Even then it looked like a
rich but spread out open cluster as its stars covered more than a half
degree of sky by just under a half degree making it somewhat elliptical.
It is about 2500 light years across its major axis and 2000 light
years across its minor axis. That's small! But its distance showed it
to be beyond our galaxy and thus really a galaxy with only a few
thousand stars.

Motion of the stars within the galaxy is difficult to explain. Before
the discovery of dark matter it was thought tidal disruption was the
answer but there were some things this didn't explain. Dark matter
changed things. If you assume a very high concentration of dark matter
then the motions can be explained. The problem is the concentration has
to be so high this tiny galaxy would have a higher density of dark
matter than any known galaxy. Since it is close enough to us to be
tidally torn up (if it doesn't have this high density of dark matter)
the issue is still not settled though I sense a leaning toward the dark
matter side. But its the new kid on the block and it seems any new idea
suddenly becomes over popular in hindsight. Only time will tell who is
right here.

At least 75% and maybe up to 90% of its stars are over 10 billion years
old showing little new star formation though there's a small population
of 2 to 3 billion year old stars so something triggered a bit of star
formation at that time. Today we see too little dust and gas in it for
further star formation.

When I imaged it I used the coordinates that weren't all that accurate.
I should have checked but figured I'd see it in the focus images. But
I saw nothing so just assumed they were right. Big mistake as it is
well off center in my image because of this goof. The core is to the
upper left of center. All the reason to retake it in a few months with
a lot more exposure time.

14" LX200R @ F/10, L=4x10', RGB=4x10', STL-11000XM, Paramount ME

Rick


--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".