#irregular galaxies

[cosmicfunnies]

Morning! Here’s an updated comic on irregular galaxies! This is part 1

Source: https://science.nasa.gov/universe/galaxies/types/

[livingforstars]

A Magellanic Mural - February 3rd, 1998.

"Two galaxies stand out to casual observers in Earth's southern hemisphere: the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). These irregular galaxies are two of the closest galaxies to our Milky Way galaxy. Observations of the LMC (on the left) have determined that it is on a nearly circular orbit around our galaxy, and have even helped in the determination of the composition of dark matter in our galaxy. The above photograph spans 40 degrees. Visible on the lower left of the LMC is the Tarantula Nebula (in red). In the foreground to the right of the SMC is globular cluster 47 Tucanae, appearing here as a bright point of light."

[zespaceblog]

The Humming Bird Galaxy

Yes, this is actually a thing ! Otherwise known as ARP 142, and 300 million light years from us in the constellation of Hydra, this crazy humming bird shape is actually a spiral galaxy that got too close to a large elliptical galaxy (the bright egg like object under it).

It's actually a spiral galaxy like our Milky Way being torn to shreds in the throws of it's eventual merger.

When galaxies meet, there's often a huge amount of star formation as gravity pushes and pulls dust and gas into concentrations that easily collapse and form bright blue giant stars. These stars don't live very long, a couple of million years at most, before collapsing, some of which will go supernova.

What's left of the galaxy will quickly fall towards the centre of the elliptical, consume what is left of the dust and gas, and settle back into a larger elliptical galaxy, with little to no trace of this once spiral galaxy left to the casual viewer.

As an extra to the picture, these two stars are very much in the Milky Way, and not connected to what looks like a comets tail. That is in fact PGC 1237172 an irregular galaxy a little closer to us, at 230 million light years, but just happens to line up with a star in our own galaxy currently.

[er-cryptid]

It is thought that most irregular galaxies (oddly-shaped galaxies) are formed by two other galaxies crashing into each other.

[autodidact-adventures]

Some Astronomy: Galaxies

There are about 100 billion galaxies in the Universe.  They contain nearly all ordinary matter, and some dark matter.  Most contain billions of stars, and clouds of dust & gas.  They can be 10,000 - 200,000 light years in diameter.  Most galaxies are named with a combination of letters & numbers.

Galaxies are usually grouped into clusters of 20 - several thousand galaxies.

Clusters are grouped into superclusters.

Superclusters form filaments (broad bands), with large voids between them.

Galaxy Shapes

There are five basic galaxy shapes:

Elliptical galaxies are roughly oval-shaped, with a smooth profile.  Their brightness profile is nearly featureless.  They are more three-dimensional than spiral galaxies, and their stars are in random orbits around the centre

Elliptical galaxy.

Lenticular galaxies are disc-shaped.  They have lost or used up most of their interstellar matter, and therefore have very little star formation occurring.

Two lenticular galaxies.

Spiral galaxies are also disc-shaped.  They are a flat, rotating disc which contains stars, dust and gas.  The central concentration stars is called the “bulge”.

They have spiral arms extending outwards, and star formation occurs here..  They are brighter than the surrounding disc, because they have young, hot stars in them.

Spiral galaxy.

Barred spiral galaxies are the same as spiral galaxies, but with a central bar-shaped structure extending from the central bulge.  The spiral arms begin at the ends of the bar.  There are about twice as many barred spiral galaxies as regular spiral galaxies.

Barred spiral galaxy.

Irregular galaxies are exactly that - irregular.

One example of an irregular galaxy - but there are many, many different shapes!

Black Holes & Quasars

Quasars are remote, highly energetic objects, and they have puzzled astronomers since the 1960′s.  It is now believed that they were caused by the formation of black holes in the centres of early galaxies.

Black holes are areas of extremely compressed matter.  It is believed that most large galaxies have black holes.

[livingforstars]

Distant Galaxies - June 22nd, 1997.

"This Hubble Space Telescope image of a group of faint galaxies "far, far away" is a snap shot of the Universe when it was young. The bluish, irregularly shaped galaxies revealed in the image are up to eight billion light-years away, and seem to have commonly undergone galaxy collisions and bursts of star formation. Studying these objects is difficult because they are so faint, however they may provide clues to how our own Milky Way galaxy formed."

[zespaceblog]

NGC 2814 - Irregular Galaxy

Not all galaxies fit the classical shapes of spiral, elliptical or lenticular, some appear to have no obvious form, and these are classified as irregular. Many have found there way to this state through interaction with other galaxies, while others we can only speculate to how they came to be as they are.

This recent Hubble image shows NGC 2814 which is 84 million light years from us in the constellation of Ursa Major, and a close companion to a number of other galaxies which make up the Holmberg 124 group.

[zespaceblog]

I Zwicky 18

One of the most peculiar of galaxies, I Zwicky 18 has been for some time thought to be a close resemblance to early galaxies.

The galaxy has very poor metallicity, meaning most of the stars are being born from hydrogen and helium, with little other element involved.

This is peculiar because the galaxy also shows huge star formation, and stars fuse hydrogen and helium into metals, and so it was assumed this galaxy itself must be incredibly young, just a few million years old.

That was until Hubble started looking at it a decade or more ago, and found stars of all types, G, K and M types with ages most likely in their billions, if not right back to the start of the universe itself.

So, how did this galaxy avoid star formation for so long, it's a bit of a mystery. We know JWST has since discovered galaxies in the early universe were not anything like what we imagined, and while that may reduce some interest in I Zwicky 18, the mysteries of it's creation and history will certainly keep astronomers focused on this.

The galaxy also has companions, which also seem to follow the same bizarre construction.

The best guess is, that the galaxy sits in an area of rather pure hydrogen, and gravitational interactions over its histories (including recently) have pushed that gas inwards and into densities that have sparked star formation, of particularly large O and B type stars, which themselves don't last so long.