Arp 273, two interacting spiral galaxies (UGC 1810 and UGC 1813) | Motion Effect by rexisky 

Galaxy NGC 7714 After Collision : Is this galaxy jumping through a giant ring of stars? Probably not. Although the precise dynamics behind the featured image is yet unclear, what is clear is that the pictured galaxy, NGC 7714, has been stretched and distorted by a recent collision with a neighboring galaxy. This smaller neighbor, NGC 7715, situated off to the left of the featured frame, is thought to have charged right through NGC 7714. Observations indicate that the golden ring pictured is composed of millions of older Sun-like stars that are likely co-moving with the interior bluer stars. In contrast, the bright center of NGC 7714 appears to be undergoing a burst of new star formation. NGC 7714 is located about 100 million light years away toward the constellation of the Fish . The interactions between these galaxies likely started about 150 million years ago and should continue for several hundred million years more, after which a single central galaxy may result. via NASA


Scanning the skies for galaxies, Canadian astronomer Paul Hickson and colleagues identified some 100 compact groups of galaxies, now appropriately called Hickson Compact Groups (HCGs). This sharp Hubble image shows one such galaxy group, HCG 90, in startling detail. Three galaxies, two visible here, are revealed to be strongly interacting: a dusty spiral galaxy stretched and distorted in the image center, and two large elliptical galaxies. The close encounter will trigger furious star formation. On a cosmic timescale, the gravitational tug of war will eventually result in the merger of the trio into a large single galaxy. The merger process is now understood to be a normal part of the evolution of galaxies, including our own Milky Way.

Image Credit: NASA; ESA, Hubble Legacy Archive; Processing: Oliver Czernetz

The Whirlpool Galaxy and Beyond : Follow the handle of the Big Dipper away from the dippers bowl, until you get to the handles last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messiers famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy , NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. Though M51 looks faint and fuzzy to the human eye, the above long-exposure, deep-field image taken earlier this year shows much of the faint complexity that actually surrounds the smaller galaxy. Thousands of the faint dots in background of the featured image are actually galaxies far across the universe. via NASA


Hubble Sees the Beautiful Side of Galaxy IC 335: This new NASA/ESA Hubble Space Telescope image shows the galaxy IC 335 in front of a backdrop of distant galaxies. IC 335 is part of a galaxy group containing three other galaxies, and located in the Fornax Galaxy Cluster 60 million light-years away.

As seen in this image, the disk of IC 335 appears edge-on from the vantage point of Earth. This makes it harder for astronomers to classify it, as most of the characteristics of a galaxys morphology the arms of a spiral or the bar across the center are only visible on its face. Still, the 45000 light-year-long galaxy could be classified as an S0 type.

These lenticular galaxies are an intermediate state in galaxy morphological classification schemes between true spiral and elliptical galaxies. They have a thin stellar disk and a bulge, like spiral galaxies, but in contrast to typical spiral galaxies they have used up most of the interstellar medium. Only a few new stars can be created out of the material that is left and the star formation rate is very low. Hence, the population of stars in S0 galaxies consists mainly of aging stars, very similar to the star population in elliptical galaxies.

As S0 galaxies have only ill-defined spiral arms they are easily mistaken for elliptical galaxies if they are seen inclined face-on or edge-on as IC 335 here. And indeed, despite the morphological differences between S0 and elliptical class galaxies, they share some common characteristics, like typical sizes and spectral features.

Both classes are also deemed early-type galaxies, because they are evolving passively. However, while elliptical galaxies may be passively evolving when we observe them, they have usually had violent interactions with other galaxies in their past. In contrast, S0 galaxies are either aging and fading spiral galaxies, which never had any interactions with other galaxies, or they are the aging result of a single merger between two spiral galaxies in the past. The exact nature of these galaxies is still a matter of debate.

European Space Agency
Credit: ESA/Hubble and NASA


Hubble Spots Two Interacting Galaxies Defying Cosmic Convention

Some galaxies are harder to classify than others. Here, Hubble’s trusty Wide Field Camera 3 has captured a striking view of two interacting galaxies located some 60 million light-years away in the constellation of Leo. 
The more diffuse and patchy blue glow covering the right side of the frame is known as NGC 3447 — sometimes NGC 3447B for clarity, as the name NGC 3447 can apply to the overall duo. The smaller clump to the upper left is known as NGC 3447A. 

The Andromeda constellation is one of the 88 modern constellations and should not be confused with our neighboring Andromeda Galaxy. The Andromeda constellation is home to the pictured galaxy known as NGC 7640.

Many different classifications are used to identify galaxies by shape and structure — NGC 7640 is a barred spiral type. These are recognizable by their spiral arms, which fan out not from a circular core, but from an elongated bar cutting through the galaxy’s center. Our home galaxy, the Milky Way, is also a barred spiral galaxy. NGC 7640 might not look much like a spiral in this image, but this is due to the orientation of the galaxy with respect to Earth — or to Hubble, which acted as photographer in this case! We often do not see galaxies face on, which can make features such as spiral arms less obvious.

There is evidence that NGC 7640 has experienced some kind of interaction in its past. Galaxies contain vast amounts of mass, and therefore affect one another via gravity. Sometimes these interactions can be mild, and sometimes hugely dramatic, with two or more colliding and merging into a new, bigger galaxy. Understanding the history of a galaxy, and what interactions it has experienced, helps astronomers to improve their understanding of how galaxies — and the stars within them — form.

Image credit: ESA/Hubble & NASA

Text credit: European Space Agency

Time And Space


What’s The Largest Galaxy In The Universe?

“Interacting spiral galaxies can have their arms greatly extended and disrupted, with NGC 6872 spanning 522,000 light years from tip-to-tip. Ultra-low surface brightness galaxies can see their stars extend even farther, with Malin 1 reaching 650,000 light years across. […]  But the largest and most massive galaxies aren’t spirals, but supergiant ellipticals, like NGC 4874 in the Coma Cluster.”

From our vantage point within the Milky Way, it sure does appear impressive. Hundreds of billions of stars shine in our own cosmic backyard, with our galaxy spanning a whopping 100,000 light years from end-to-end. Yet not only is that small compared to our nearest large neighbor, Andromeda, but it’s not even 20% as large as the largest spiral galaxies we find. While tidal disruption might create the largest spiral galaxies, we have giant ellipticals that are many times larger than a spiral will ever achieve. Some of the biggest ones of all are found at the centers of massive galaxy clusters, but in the scheme of the entire observable Universe, only one galaxy can truly be the largest.

Which is it, and how do we know? Find out on this edition of Mostly Mute Monday!

🌌 Seyfert’s Sextet 🌌, a group of galaxies 190 million light years away located in the constellation of Serpens. This sextet actually only contains 4 interacting galaxies as the face-on spiral galaxy in the Hubble image lies in the distant background and is coincidentally aligned with the main group. Though the misty condensation in the upper left may appear to be a separate galaxy, it’s likely a tidal tail of stars created by the gravitational interactions of these galaxies. 

📸Image Credit: Hubble Legacy Archive, NASA, ESA

Why do many galaxies appear as spirals? A striking example is M101, shown above, whose relatively close distance of about 27 million light years allows it to be studied in some detail. Observational evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. These waves compress existing gas and cause star formation. One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies.

Object Names: M101, Pinwheel Galaxy

Image Type: Astronomical

Credit: Subaru Telescope (NAOJ), Hubble Space Telescope, European Southern Observatory

Procesing and Copyright: Robert Gendler

Time And Space