BREAKING NEWS: Andromeda X--Andromeda's Newest Satellite Galaxy

The discovery of a new galaxy orbiting Andromeda gives a boost to the
leading theory of galaxy formation, say astronomers in Europe and the United
States. The new galaxy, named Andromeda X, is the dimmest satellite galaxy
ever seen around Andromeda. For the full story, including a
never-before-published color image of the new galaxy, see
http://KenCroswell.com/AndromedaX.html .

Other recent stories:
Most Stars Are Single (January 19, 2006):
http://KenCroswell.com/MostStarsAreSingle.html .
The Cosmic Origin of Carbon (January 11, 2006):
http://KenCroswell.com/OriginOfCarbon.html .
The Tenth Planet's First Anniversary (January 5, 2006):
http://KenCroswell.com/TenthPlanetFirstAnniversary.html .
Pulsar at the Galactic Center? (January 3, 2006):
http://KenCroswell.com/G359.html .
The Three Moons of Pluto (December 21, 2005):
http://KenCroswell.com/PlutoMoons.html .
The First Direct Distance to Andromeda (November 4, 2005):
http://KenCroswell.com/AndromedaDistance.html .

Correct email: MagnificentUniverse "at" yahoo "dot" com.

On Sun, 29 Jan 2006 20:34:19 -0800, "Magnificent Universe"
wrote:

The discovery of a new galaxy orbiting Andromeda gives a boost to the
leading theory of galaxy formation, say astronomers in Europe and the United
States. The new galaxy, named Andromeda X, is the dimmest satellite galaxy
ever seen around Andromeda. For the full story, including a
never-before-published color image of the new galaxy, see
http://KenCroswell.com/AndromedaX.html .


I hate when they compare absolute magnitudes of stars to extended
objects, it means NOTHING as far as visibility is concerned. Does
anyone know what the dimmest absolute magnitude star is that can be
seen with our current telescopes at the distance of the Andromeda
galaxy? If stars need to be absolute magnitude -7 or something to be
visible at all from Andromeda, it's no wonder there are possible
invisilble companion galaxies there.
-Rich

Rich wrote:
I hate when they compare absolute magnitudes of stars to extended
objects, it means NOTHING as far as visibility is concerned. Does
anyone know what the dimmest absolute magnitude star is that can be
seen with our current telescopes at the distance of the Andromeda
galaxy? If stars need to be absolute magnitude -7 or something to be
visible at all from Andromeda, it's no wonder there are possible
invisilble companion galaxies there.

The distance modulus for M31 is about 24.5, give or take. So if you're
talking about actually seeing it visually through an amateur-class
telescope, even a large one, you probably are limited to stars that are
absolute magnitude -7 or brighter. But for detection in images, we
can obviously see stars much dimmer than that. With something like a
Hubble Deep Field, you could see stars down to around sixth magnitude
or so, absolute magnitude.

Now, for purposes of detecting a galaxy, you need not detect the stars
to see the galaxy, especially if the galaxy is far enough away that you
don't resolve the individual stars.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html

Brian Tung wrote:

Now, for purposes of detecting a galaxy, you need not detect the stars
to see the galaxy, especially if the galaxy is far enough away that you
don't resolve the individual stars.

In this particular case, of course, the problem is that
the galaxy IS so close that we can and do resolve the
individual stars. That's one of the reasons it's so hard
to find dwarf galaxies in the Local Group: they only
appear when one looks in big catalogs of stars for
small regions of slightly higher stellar density ....

Michael Richmond