Because space is a special interest of mine (I mean, I’m the astronomer of the collective for a reason), I thought I’d spread some knowledge. So, today we’re going to be discussing galaxy classifications, what makes each unique, and I’ll be showing some examples of each.
First of all, there are three main types of galaxies; Spiral (with barred spiral being lumped in), Elliptical, and Irregular. We’ll talk about the Elliptical first.
Class- Elliptical
An elliptical galaxy is a galaxy that takes on a stretched out circle-like appearance, like an ellipse, hence the name. It’s unclear how common elliptical galaxies are, since they contain far less gas and dust than spirals, which are known for being hotbeds of star formation, and therefore fewer new (and brighter) stars are born in these galaxies. The majority of stars are much older and give off dimmer red light, and as a result, it’s tougher to see elliptical galaxies.
Example:
This is NGC 1316, an elliptical galaxy in the Fornax star cluster. Note how dim the light is around everything but its center, and how little dust there is, save for the black streaks around the inner ‘disk’ nearest the core. Given these characteristics, it becomes pretty clear why it takes longer for us to find them.
Sometimes we find elliptical galaxies that came about as a result of two spirals crashing into each other over billions of years.
Example:
Notice the two different cores of what used to be spiral galaxies. These are NGC 2292 and 2293, two spiral galaxies that collided in Canis Major, and flung their stars, gas and dust outward (note the ring of dust on the outer edge of the galaxy) and created an elliptical galaxy.
Class- Spiral Galaxy
Next, let’s talk about spiral galaxies. Everyone knows what a spiral looks like. It’s a pinwheel, with several self-perpetuating, long lived spinning arms and contains plenty of newborn and young stars, as well as a large enough amount of gas and dust to fuel star birth. Our own Milky Way is a spiral galaxy, as is the well known Andromeda galaxy, which we’re currently on a course to collide with in about 4-5 billion years.
It’s estimated that about 70% of the galaxies closest to us are spirals, and they make up most galaxies we discover. Spirals are known to be star forming factories, responsible for the majority of newborn stars, and therefore shine brighter than other galaxy types with older and dimmer stars.
Example:
This is Messier 81, or M81, a spiral galaxy in Ursa Major and the largest in its group. Note the distinct arms, the copious amounts of space dust and gasses, and the much brighter, much younger stars (as recent as a few million years old) in its arms while its oldest stars remain closer to the center.
At its center is a black hole of about 70 million solar masses, 15 times bigger than our own central black hole, Sagittarius A*. You can actually see this galaxy right now, being that it’s April at the time of posting this, through binoculars. Though, it will only look like a small, dim grey smudge. A small telescope, however, would be able to see its core if you point it in the right place.
Now. Barred spiral galaxies. Simply put, they’re just spiral galaxies that have a central bar shaped arm running through the middle made of stars and tend to look a little more squished than typical spirals.
Example:
This is NGC 1097, a barred spiral galaxy in the Fornax cluster. Note the somewhat almond shaped appearance, the strip of dust and stars running across the galaxy’s center. These bars are actually found in about half of all spiral galaxies, and a recent study headed by Debra and Bruce Elmegreen and Kartik Sheth confirms that the formation of bars is a sign of a galaxy reaching full maturity as the ‘formative years’ come to an end.
Class- Irregular
And finally, we come to irregular galaxies. The oddballs of the universe that don’t look like galaxies at all. They’re called irregular, because they can’t be placed neatly into the Hubble sequence, something Edwin Hubble came up with in 1926 to categorize galaxies. Some feature some structure, like a spiral’s arm, but not enough to place them into the sequence cleanly. Most have no distinct regular shape like spiral or elliptical galaxies, with no trace of a nuclear bulge or spiral arm structure. They’re thought to be deformed spiral or elliptical galaxies, ripped apart by uneven external gravitational forces.
Example:
This is NGC 1569, a dwarf irregular starburst galaxy with constant star formation activity (as denoted by the bright pink near the ‘center’) in Camelopardalis. Note the lack of a nuclear bulge, no distinct shape, and in particular for this one, the unusual amount of star birthing activity. It’s called ‘starburst’ for how fast it puts out stars, at a rate about 10 to the third power greater than a normal galaxy.
This really is just the tip of the iceberg when it comes to exploring galaxies (I didn’t even touch on lenticular galaxies or Seyfert spirals), but I hope this little glance at the universe was informative all the same.
writing sci fi is fucking exhausting bc i have a whole degree in aerospace systems now so my brain simply Will Not let me write a scene without doing the setting justice
me:they land on a planet
the part of my brain that remembers my airspace control and orbit mechanics courses: this is a trading planet so it would be high traffic, they’d be looking to avoid congestion. so they’d probably start in a graveyard orbit, assuming there’s some kind of air traffic control network in geostationary, and then it’d be a series of transfers down, they’d probably be waiting say eight hours for an appropriate transfer path? to they have any structures in low orbit? maybe an intercept and they just park in LEO? what happens if you don’t have standardised docking equipment? what if you need repairs? how about refuelling? what are they even using for fuel? would reusable/tradeable solar batteries work? could you park solar systems in geostationary for people just passing through? do they even need to land at all?
me: oh my fucking god get ON WITH IT
Yeah but the jixtaposition comedy of “oh you expected a Hollywood entrance? Yeah. Not until they call us back with our gate number.”
TheSidera Lodoicea are four of Saturn’s moons discovered by Giovanni Domenico Cassini at the Paris Observatory.Sidera Lodoicea translates to Louisian Stars, named in honor of King Louis XIV of France. One of the moons, Dione, has interesting thin, white bands on its surface that are highly reflective. When first photographed by Voyager, it was hypothesized that Dione was geologically active, possibly from cryovolcanism, or ice volcanoes, causing surface cracks to erupt. Closeup images of Dione from Cassini proved that hypothesis wrong and revealed that these features are actually cliffs of ice created by tectonic fractures.
Obscured Sirius reveals Gaia 1 cluster por European Space Agency Por Flickr: Space Science image of the week: If you gazed at the night sky over the past few weeks, it is possible that you stumbled upon a very bright star near the Orion constellation. This is Sirius, the brightest star of the entire night sky, which is visible from almost everywhere on Earth except the northernmost regions. It is, in fact, a binary stellar system, and one of the nearest to our Sun – only eight light-years away. Known since antiquity, this star played a key role for the keeping of time and agriculture in Ancient Egypt, as its return to the sky was linked to the annual flooding of the Nile. In Ancient Greek mythology, it represented the eye of the Canis Major constellation, the Great Dog that diligently follows Orion, the Hunter. Dazzling stars like Sirius are both a blessing and a curse for astronomers. Their bright appearance provides plenty of light to study their properties, but also outshines other celestial sources that happen to lie in the same patch of sky. This is why Sirius has been masked in this picture taken by amateur astronomer Harald Kaiser on 10 January from Karlsruhe, a city in the southwest of Germany. Once the glare of Sirius is removed, an interesting object becomes visible to its left: the stellar cluster Gaia 1, first spotted last year using data from ESA’s Gaia satellite. Gaia 1 is an open cluster – a family of stars all born at the same time and held together by gravity – and it is located some 15 000 light-years away. Its chance alignment next to nearby, bright Sirius kept it hidden to generations of astronomers that have been sweeping the heavens with their telescopes over the past four centuries. But not to the inquisitive eye of Gaia, which has been charting more than a billion stars in our Milky Way galaxy. Mr Kaiser heard about the discovery of this cluster during a public talk on the Gaia mission and zealously waited for a clear sky to try and image it using his 30 cm-diameter telescope. After covering Sirius on the telescope sensor – creating the dark circle on the image – he succeeded at recording some of the brightest stars of the Gaia 1 cluster. Gaia 1 is one of two previously unknown star clusters that have been discovered by counting stars from the first set of Gaia data, which was released in September 2016. Astronomers are now looking forward to Gaia’s second data release, planned for 25 April, which will provide vast possibilities for new, exciting discoveries. More information about opportunities for amateur astronomers to follow up on Gaia observations here. Credit: H. Kaiser
