Can we retire "Irregular Galaxy M82 (APOD 25 Mar 2008)

[djlncas]

M82 is a highly organized object. It is variously described as a "disk galaxy," "starburst galaxy," Spiral arms have been detected:

http://www.journals.uchicago.edu/doi/abs/10.1086/432644

These other labels better confer the structure of the object. The irregular classification is looking increasingly dated, some would say misleading.

Can we progress to terming it an edge-on spiral, that's certainly what it looks most like if you spend much time viewing edge-ons in the March-June evening sky.

[harry]

Hello djlncas


Galaxy Wars: M81 versus M82

http://antwrp.gsfc.nasa.gov/apod/ap080325.html

This is a fanatstic image

M8 as a spiral and M82 as an irregular galaxy. Both at different phases of evolution.


Basic Galaxy Properties by Type
http://www.astronomynook.com/galaxy_types.htm


The Hubble Tuning Fork
http://cas.sdss.org/dr6/en/proj/basic/g ... ngfork.asp

Hubble believed that galaxies started at the left end of the tuning fork when they were young, and moved toward the right as they aged. Therefore, he called elliptical galaxies "early galaxies" and spiral galaxies "late galaxies".

I partly agree with hubble

and yet

We now know he was mistaken in this belief. Spiral galaxies have a great deal of rotation and elliptical galaxies do not. There is no way an elliptical galaxy could spontaneously begin rotating, so elliptical galaxies cannot turn into spiral galaxies. Although Hubble was wrong about his theory of galaxy evolution, the confusing names have stuck: today, elliptical galaxies are still referred to as early galaxies and spirals as late galaxies.

I partly agree with the above statement.

When you put the both theories together you have a cyclic event.

Elliptical to spiral to irregular to ellipticl to spiral to irregular. This cyclic event keeps on going and is effected by other colliding galaxies.

One important point is that the so called black hole activity is directly related to the shape of the galaxy.

So!!!! M82 being an irregular galaxy has a very active black hole with jets ejecting matter at 90deg to the disc. In time this will transform the galaxy into an elliptical galaxy such as M87.

http://seds.org/messier/m/m087.html
which has a very active black hole
http://chandra.harvard.edu/photo/2001/0134/
http://chandra.harvard.edu/photo/2006/m87/
http://apod.nasa.gov/apod/ap950913.html

[djlncas]

Thanks for your response Harry. Sorry the thread is resisting my attempt to fix it, perhaps a moderator can edit?

Unfortunately the Hubble tuning fork read from left to right does not represent the sequence in time as galaxies develop.

The SEDS site is part of the problem. It would be great if they would update their description, because it is such a respected resource, as APOD .

The M82 description in http://www.wikipedia.org reflects a more current understanding. And here is a paragraph from Science Magazine that makes the point:

Science 12 May 2006:
Vol. 312. no. 5775, p. 815
DOI: 10.1126/science.312.5775.815a
Prev | Table of Contents | Next
EDITORS' CHOICE: HIGHLIGHTS OF THE RECENT LITERATURE
Galactic winds, driven by violent bursts of star formation, are thought to spread elements heavier than hydrogen between galaxies and throughout the cosmos. The ashes of former stars thereby live on in later generations of stars and may affect galactic evolution. The loss of gas due to winds may starve galaxies of fuel and could affect the growth of different galaxy types. The nearby edge-on spiral galaxy M82 has the most thoroughly studied strong wind; this galaxy is undergoing a violent burst of star formation in its heart, which expels a bi-conical superwind of hot ionized gas.
By examining infrared images acquired with the Spitzer Space Telescope, Engelbracht et al. find that M82 is surrounded by a spherical halo of warm dust into which the hot wind penetrates. Spidery dust filaments emanate outward in all directions, extending well beyond the galaxy and its wind. The spectra reveal that aromatic hydrocarbons survive in the dust despite close proximity to the hot superwind. The unusually wide extent and spherical shape of the M82 dust cocoon suggest that the dust was driven out of the galaxy before the superwind commenced, and is thus more pervasive than previously thought; possible explanations include interactions with neighboring galaxies or alternative wind-related mechanisms. -- JB

Astrophys. J. 642, L127 (2006).

If you'd like to enjoy the spectrum of chaotic irregular galaxies, I'd look at:

http://www.galaxyzoo.org

Cheers,
Dan

[harry]

Hello Djnlcas

You said

Unfortunately the Hubble tuning fork read from left to right does not represent the sequence in time as galaxies develop.

Its not a one way road.

I know what hubble said and know what others think.

In a cyclic universe its a combination of both.

Do you understand the following para:

EDITORS' CHOICE: HIGHLIGHTS OF THE RECENT LITERATURE
Galactic winds, driven by violent bursts of star formation, are thought to spread elements heavier than hydrogen between galaxies and throughout the cosmos. The ashes of former stars thereby live on in later generations of stars and may affect galactic evolution. The loss of gas due to winds may starve galaxies of fuel and could affect the growth of different galaxy types. The nearby edge-on spiral galaxy M82 has the most thoroughly studied strong wind; this galaxy is undergoing a violent burst of star formation in its heart, which expels a bi-conical superwind of hot ionized gas.
By examining infrared images acquired with the Spitzer Space Telescope, Engelbracht et al. find that M82 is surrounded by a spherical halo of warm dust into which the hot wind penetrates. Spidery dust filaments emanate outward in all directions, extending well beyond the galaxy and its wind. The spectra reveal that aromatic hydrocarbons survive in the dust despite close proximity to the hot superwind. The unusually wide extent and spherical shape of the M82 dust cocoon suggest that the dust was driven out of the galaxy before the superwind commenced, and is thus more pervasive than previously thought; possible explanations include interactions with neighboring galaxies or alternative wind-related mechanisms. -- JB

The above is part of the workings within a galaxy, but its not the driving force.

Their are two main forces that direct the formation of a galaxy, eletromagnetic and gravity, some say they are the same, but different forms.

In the centre of every galaxy there is one main black hole that has a direct hold on every star and other matter. The activity of the black hole determines the formation of the galaxy. There is no old or new galaxies , just different stages of evolution.