Mergers and Acquisitions: Coming Attractions

MRK 1034This pair of galaxies, called MRK 1034, lies in the constellation of Triangulum (The Triangle) in the northern sky. The two similar galaxies, PGC 9074 and PGC 9071, are close enough to one another to be tied together by gravity, but because we are seeing them as they are just beginning to interact gravitationally, there aren’t any large distortions noticeable. Yet. Wait a few hundred million years.

We see both spiral galaxies top down from our point of view. At the bottom PGC 9074 shows a bright bulge and two spiral arms tightly wound around its nucleus, features which classify it as a type Sa galaxy. PGC 9071 isa type Sb galaxy with a fainter bulge and the spiral arms further apart. The spiral arms of both show dark patches of dust mixed with blue clusters of recently-formed stars. Older, cooler stars can be found in the glowing, compact yellowish bulge towards the galactic centers, and each galaxy is surrounded by a much fainter round halo of old stars.

So what would we likely see after waiting a few hundred million years? As these two neighbors attract each other, the process of star formation will be increased, and tidal forces will throw out long tails of stars and gas. Eventually, the interacting galaxies should merge together into a new, larger galaxy.

Image Credit: NASA

A Large Galaxy and Its Satellite

NGC1232The colors of the different regions of NGC 1232 stand out in this picture—the central areas contain older reddish stars while the spiral arms are populated by younger blue stars and many star-forming regions. This galaxy is about 100 million light-years away and about twice the size of our Milky Way galaxy. Note the companion galaxy at the lower left, shaped like the squashed greek letter “theta”. NGC 1232A, the satellite galaxy of NGC 1232, is thought to be the cause of unusual bending in the spiral arms in its larger neighbor.

Image Credit: ESO

A Galaxy Seen Head On

NGC1309_HLANGC 1309 lies on the banks of the constellation Eridanus (The River) about 100 million light-years away. It about 30,000 light-years across or about one third the size of our Milky Way galaxy. Bluish clusters of young stars and dust lanes trace out NGC 1309’s spiral arms, winding around an older yellowish star population at the galaxy’s core.

NGC 1309’s recent supernova and Cepheid variable stars are used to derive calibration data for the expansion of the Universe.

Image Credit: NASA / ESA

NGC 3185

potw1326Spiral galaxy NGC 3185 is about 80 million light-years away from us in the constellation of Leo (the Lion). The galaxy’s spiral arms swirl outward from the center of the galaxy toward the rim where they join a blue disk of young stars. At the galactic center of is a small but very bright nucleus containing a supermassive black hole. Supermassive black holes have masses many thousands of times that of our Sun, and they become active as matter falls towards them. When this happens the black hole lights up, sending away streams of particles and radiation at almost the speed of light.

ML_GalaxyNGC 3185 is a member of a four-galaxy group known as Hickson 44. NGC 3190 is a somewhat more famous member of the group. Apple used a blue-tinted image of it as the default wallpaper for its Mountain Lion operating system.

Image Credits: NASA, Apple

A Spiral on Edge

From our point of view we see galaxy NGC 3432, directly edge-on. The galaxy’s spiral arms and bright core are mostly hidden, and we instead see the thin strip of its outer stars. The dark bands of cosmic dust, patches of varying brightness and pink regions of star formation help with making out the true shape of NGC 3432—which we can do because we see spiral galaxies at every kind of orientation, and experience allows us to identify spirals on edge.

Image Credit: NASA / ESA

NGC 1232

NGC1232The colors of the different regions of NGC 1232 stand out in this picture—the central areas contain older reddish stars while the spiral arms are populated by younger blue stars and many star-forming regions. This galaxy is about 100 million light-years away and about twice the size of our Milky Way galaxy. Note the companion galaxy at the lower left, shaped like the sqashed greek letter “theta”.

Image Credit: ESO

NGC 3185

potw1326Spiral galaxy NGC 3185 is about 80 million light-years away from us in the constellation of Leo (the Lion). The galaxy’s spiral arms swirl outward from the center of the galaxy toward the rim where they join a blue disk of young stars. At the galactic center of is a small but very bright nucleus containing a supermassive black hole. Supermassive black holes have masses many thousands of times that of our Sun, and they become active as matter falls towards them. When this happens the black hole lights up, sending away streams of particles and radiation at almost the speed of light.

ML_GalaxyNGC 3185 is a member of a four-galaxy group known as Hickson 44. NGC 3190 is a somewhat more famous member of the group. Apple used a blue-tinted image of it as the default wallpaper for its Mountain Lion operating system.

Image Credits: NASA, Apple

A Matter of Perspective

Spiral galaxies are pancake-shaped collections stars and vast clouds of gas and dust. This video illustrates how their observed shapes can differ change depending on the angle at which they are observed. This video pictures models of the spiral galaxies NGC 4302 (left) and NGC 4298 (right) in three dimensions and rotates them to show how they might look if viewed from other perspectives. The models are based on observations by the Hubble and Spitzer space telescopes, as well as on the statistical properties of galaxies. Because we see NGC 4302 nearly edge on, and its structure is not well-defined—its model is based upon observations of the spiral galaxy Messier 51.

Video Credits: NASA / ESA / STScI

NGC 1288

FORS1 First Light - Spiral galaxy NGC 1288This is the spiral galaxy NGC 1288 in the southern constellation Fornax. The distance to this galaxy is about 300 million light-years, and it is receding from us at around of 4500 km/s. It’s roughly 200,000 light-years or about twice the diameter of the Milky Way.

Image Credit: ESO

The Calm Before the Storm?

NGC 799 & NGC 800This pair of galaxies, NGC 799 (below) and NGC 800 (above), is located in the constellation of Cetus (The Whale) about 300 million light-years away. Our face-on point of view lets us see these objects are both spiral galaxies with characteristic long arms winding towards a bright bulge at the center.

It may appear that these spiral galaxies are coexisting in an everlasting peace, but that is unlikely. What we see is probably the calm before the storm. Typically, when two galaxies are close enough, they interact over hundreds of millions of years through mutual gravitational attraction. In some cases, only minor interactions occur, causing shape distortions, but sometimes galaxies collide, merging to form a single, new and larger galaxy.

We’ll have to check back in a few hundred million years.

Image Credit: ESO

The Great Barred Spiral Galaxy

NGC 1365NGC 1365 is enormous. It is one of the largest galaxies known to astronomers—over 200,000 light-years across. This, plus the sharply defined bar of old stars across its structure is why it is also known as the Great Barred Spiral Galaxy. Astronomers believe that the Milky Way, which is only half as big, may look very similar to this galaxy. The bright centre of the galaxy is thought to be caused by huge amounts of superhot gas ejected from the ring of material circling a central black hole. Young luminous hot stars, born in the interstellar clouds, give the arms their blue color. The bar and spiral pattern rotates, with one full turn taking about 350 million years. NGC 1365 is about 61 million light-years away in the constellation Fornax (the Furnace).

Image Credit: ESO

NGC 1232

NGC1232The colors of the different regions of NGC 1232 stand out in this picture—the central areas contain older reddish stars while the spiral arms are populated by younger blue stars and many star-forming regions. This galaxy is about 100 million light-years away and about twice the size of our Milky Way galaxy. Note the companion galaxy at the lower left, shaped like the sqashed greek letter “theta”.

Image Credit: ESO

A Cosmic Black Eye

M64_Black_Eye_GalaxyThe collision of two galaxies has resulted in this, M64 (aka The Black Eye Galaxy). To the casual observer M64 looks fairly normal, except for the huge band of dust blocking part of our view of the nucleus. All its star orbit the galactic center in the same direction, clockwise in this image from Hubble, but recent observations show that the interstellar gas in the outer regions of M64 rotates in the opposite direction from the gas and stars in the inner regions. This is believed to trigger the creation of many new stars around the boundary between the regions where the oppositely rotating gases collide.

The small satellite galaxy that merged with its larger neighbour has now been almost completely destroyed. Its stars have either entered the main galaxy or scattered into intergalactic space, but signs of the collision persist in the retrograde motion of gas at the outer edge of M64.

Image Credit: NASA

Messier 83

This video fades between views of Messier 83 in visible light and infrared images captured at European Southern Observatory’s La Silla Observatory in Chile. The dust that obscures many stars becomes nearly transparent in the infrared image. That image may seem less dramatic, but it shows a swarm of new stars that are otherwise invisible.

Video Credit: ESO / M. Gieles
Acknowledgement: Mischa Schirmer

A Spiral in an Air Pump

IC 2560There’s a constellation in the southern sky called Antlia (The Air Pump). It was named by a French Astronomer in honor of the invention of the air pump in the 17th century. Spiral galaxy IC 2560 is about 110 million light-years away in the constellation Antlia. It is a relatively nearby spiral galaxy, and is part of the Antlia cluster, a group of over 200 galaxies held together by gravity. Unlike most other galaxy clusters, the Antlia cluster doesn’t appear to have one big dominant galaxy within it.

It’s easy to make out IC 2560’s spiral arms and barred structure in this Hubble image. IC 2560 is a Seyfert-2 galaxy, a type of spiral galaxy characterized by an extremely bright nucleus and very strong emission lines from the elements hydrogen, helium, nitrogen, and oxygen. The bright center of the galaxy is thought to be the result of the ejection of huge amounts of super-hot gas from the region around a central black hole.

Image Credit: NASA

Oh, one more thing … Seyfert galaxies were first identified by Carl Seyfert, who I had a chance to meet as a kid in a local astronomy club in Nashville. Dr. Seyfert was director of the Dyer Observatory at Vanderbilt University. In the ’50s he was also the weatherman on the local news at WSM-TV.

NGC 3185

potw1326Spiral galaxy NGC 3185 is about 80 million light-years away from us in the constellation of Leo (the Lion). The galaxy’s spiral arms swirl outward from the center of the galaxy toward the rim where they join a blue disk of young stars. At the galactic center of is a small but very bright nucleus containing a supermassive black hole. Supermassive black holes have masses many thousands of times that of our Sun, and they become active as matter falls towards them. When this happens the black hole lights up, sending away streams of particles and radiation at almost the speed of light.

ML_GalaxyNGC 3185 is a member of a four-galaxy group known as Hickson 44. NGC 3190 is a somewhat more famous member of the group. Apple uses a blue-tinted image of it as the default wallpaper for its Mountain Lion operating system.

Image Credits: NASA, Apple

Another Galactic Collision

The messy result of a galactic collisionThis new image from the Hubble Space Telescope shows a collision between two galaxies—a spiral galaxy colliding with a lenticular galaxy. There’s an almost 3D appearance to the picture as the spiral arms embrace the lenticular galaxy’s bulge.

There’s more evidence of the collision in the image. Look at the stream of stars coming out from the merging galaxies toward the top of the image. The bright spot in the middle of the plume is the unique feature of this collision. That spot is believed to be the former nucleus of the spiral galaxy ejected from the system during the collision. It’s now being disassembled by tidal forces producing the stream of stars.

Image Credit: NASA

A Starry Spider Web

Like a spider’s web swirled into a spiral, Galaxy IC 342 appears as a delicate pattern of dust. Captured in infrared light by NASA’s Spitzer Space Telescope, faint starlight gives way to the glowing bright patterns of dust found throughout the galaxy’s disk. IC 342 is relatively close by galactic standards, only about 10 million light-years away, however our vantage point places it directly behind the disk of our own Milky Way. The intervening dust makes it difficult to see in visible light, but infrared light penetrates easily.

IC 342 is nearly face-on to us, giving a clear, top-down view of the structure of its disk. It’s surface appears fairly dim compared to other spiral galaxies, indicating a lower density of stars (seen here as a blue haze). Its dust structures show up much more vividly (red). (The blue dots are stars closer to us in our own Milky Way.) New stars are forming in the disk at a rapid rate. The center glows brightly in the infrared because of an enormous burst of star formation in this tiny region. A small band of dust and gas on either side of the central region is helping to fuel the star formation.

Data from Spitzer’s infrared array camera are shown in blue (3.6 microns), green (4.5 microns) and red (5.8 and 8.0 microns).

Image Credit: NASA

Warp Factor

How did spiral galaxy ESO 510-13 get bent out of shape? The disks of many spiral galaxies are thin and flat, but with the gaps between star they are not solid. Spiral disks are loose conglomerations of billions of stars and diffuse gas all gravitationally orbiting a galaxy center. The common flat disk shape  is thought to be created by sticky collisions of large gas clouds early in the galaxy’s formation. Warped disks are not uncommon, though, and even our own Milky Way Galaxy is thought to have a bit of warp. The causes of spiral warps are still being investigated, but some warps are thought to result from interactions or even collisions between galaxies. ESO 510-13, shown in the digitally sharpened Hubble image above, is about 150 million light years away and about 100,000 light years across.

Image Credit: NASA

NGC1073

Many spiral galaxies have bars across their centers. Our own Milky Way Galaxy is thought to have a modest central bar. The prominently barred spiral galaxy NGC 1073 was captured in spectacular detail in this recently released image taken by the Hubble Space Telescope. The image shows dark filamentary dust lanes, young clusters of bright blue stars, red emission nebulas of glowing hydrogen gas, a long bright bar of stars across the center, and a bright active nucleus that likely houses a supermassive black hole. NGC 1073 is about 55,000,000 light years away and is about 80,000 light years across. It can be seen with a moderately-sized telescope looking toward the constellation of Cetus (the Sea Monster).

Image Credit: NASA