Optics:   Ritchey–Chrétien 20" F/8.2 (4166mm FL) Processing:   PixInsight, Photoshop
Camera:   SBIG STXL-11000 with Adaptive Optics Date:   Jan - May 2014
11 Megapixel (4008 x 2672 16-bit sensor) Location:   Columbus, Texas
Exposure:   LRGB = 490:100:70:80 minutes Imager:   Kent E. Biggs
Update 2/7/2024: Super excited and honored that this image made NASA Astronomy Picture of the Day for February 7, 2024!. The image used was a cropped and rotated version of the above image to orient the galaxies to the more heart-shaped view as shown below!
Update 2/9/2024: It was subsequently picked up by National Geographic as an example of hearts in nature and published in their Travel Photo Gallery! Scroll about half way down to see the image.

Overview: This heart-shaped pair of galaxies are, in fact, physically attracted to each other, but not in any romantic way. Designated NGC 4038 and NGC 4039, they were two separate galaxies, each with 100s of billions of stars, and, at their cores, a supermassive black hole. Their physical attraction began about 1 billion years ago when they passed close enough to became enthralled in each other’s gravity. As a result, the compression of interstellar molecular clouds has created stellar nurseries which will birth over 1 billion new stars by the time the merger is complete. Also called the Antennae Galaxies, the antennae-like tails are the result of the expulsion of billions of stars and associated gas and dust. NGC 4038 (top) was a barred spiral galaxy while NGC 4039 (bottom) was a spiral galaxy. When the merger is complete, however, they will likely form a more massive elliptical galaxy with a single more massive core.
Details: The NGC 4038 Group of galaxies lies in the direction of the southern constellation Corvus, Latin for crow. This galaxy group contains between 13 and 27 galaxies, the most famous of which is the Antennae Galaxies, also known as the Ringtail Galaxy or Caldwell 60/61 pair. The group of galaxies lies somewhere between 45 and 65 million light years away from us and is half a million light years in size. They are moving at over 1600 kilometers per second away from us or nearly 10 times faster than mankind’s fastest space probe!

Young and Massive Globular Clusters: Studies of the Antennae galaxies have revealed to us something unusual about this galaxy pair. They contain a number of young, massive globular clusters. Globular clusters, such as M15 in our own galaxy, are spheroid in shape (slightly flattened spheres), and contain 10s of thousands to millions of stars, with a larger concentration of stars in their centers. Through telescopes they look like cotton balls, and only in the 20th century did astronomers realize they are not nebulae, but they are conglomerations of many stars. Globular clusters are found in many galaxies but usually contain very old stars, theorizing that these clusters themselves are very old with an average age a 12 billion years. This makes them among the oldest known objects in the universe! What is interesting about the Antennae galaxies is that by using the Hubble telescope, astronomers have discovered more than a thousand young, but massive globular clusters. As the two galaxies merge, they compress large massive molecular clouds. The largest and most massive of these molecular clouds is believed to be the birthplace of these young, massive globular clusters.

Interacting Galaxy. Imagine a billiard table with zero resistance where a billiard ball moves around, bouncing off the table sides forever, without slowing down. Then imagine each billiard ball is swarm of billions of stars gravitationally bound. As these balls of stars move around the frictionless surface, they inevitably come close to, or even collide, with another ball of stars. These close encounters and collisions are how galaxies interact with and disturb each other, occasionally merging with one another to form even more massive galaxies. Most galaxies probably experience at least one major interaction with another galaxy in their lifetime. While many galaxies seem to be the more boring elliptical type without arms or spiral structure. The spiral arms form when galactic density waves occur to align the galaxy into arms. One contributor to the density waves affect may be when galaxies interact with each other.

Starburst Galaxy. As galaxies interact or even merge, they often undergo a very high rate of star formation. The usual star formation rate in a galaxy like our own Milky Way galaxy is about 4 to 7 stars per year. During galaxy interactions, that rate increase up to 100 or more stars per year. We call a galaxy with this high rate of star formation a starburst galaxy. The high rate of star formation cannot go on forever, however, since the amount of material out of which stars form is limited. Once starburst galaxies consume all of this material, the rapid rate of new stars formed eventually decreases to normal or even below normal rates. This may be what has happened in many elliptical galaxies that seemed to have no dusty material remaining. They simply have already consumed most of the gas and dust available for star formation.

Discovery: In 1785, on February 7, William Herschel discovered the NGC 4038 and 4039 pair and cataloged them as a planetary nebula. It wasn’t until nearly 50 years later that William’s son, John Herschel, corrected his father and reclassified them as a galaxy, Latin for the term Milky Way or milky circle. Until the 20th century, galaxies were thought to be spiral nebulae and either unresolved star clusters or nebulae of gas and dust. Then in the early 20th century, astronomers made spectrographic studies of the brightest galaxies to determine their chemical composition as well as Doppler shifts. Surprisingly their Doppler shifts indicated that most of these galaxies were moving away from us at rates far greater than any star observed in our own galaxy. Using brightness of exploding stars called novae, astronomers soon realized that novae in galaxies were far fainter than they are in our own galaxy, hence they are much farther away from us. For years, the term island universes was then applied to both our own Milky Way galaxy as well as all other galaxies.

Annotations. The above image shows annotations when hovering over the image. In the center are the two galaxies NGC 4038 (top) and NGC 4039 (bottom). Highlighted and enlarged just below and to the left of these galaxies is a far more distant galaxy, uncatalogued, and likely in its own process if integration with a neighboring galaxy. Visible and labeled also are a relatively bright sun-like yellow star (top) and a red star (bottom); they are 5-10 times fainter than the faintest star visible with the human eye. Visible also are the wispy tidal arms; note the upper arm belongs to the lower galaxy, NGC 4039, while the lower arm belong to the upper galaxy, NGC 4038. The cores of both galaxy are clearly visible in the enlarged inset. These cores contain supermassive black holes, and eventually will merge into and even more massive black hole where 10s of millions of times the mass of our own star, the sun, will be squeezed into an infinitesimally small point.

Below Images: In the first image below, the same image has been processed to remove all foreground stars period these stars are all within our own Galaxy. This is what this view would appear like if we left our Galaxy looking outward period using a mouse to hover over the image comma brings all of the stars back. The second image below shows an enlarged and cropped versions of the galaxies. Third image below shows a wider field and cropped version of the image. The subsequent images, reveal comparison to previous processing showing generation 1, 2 and 3 processing techniques using the exact same data for all images.

Antenna Galaxies without Stars!

Antenna Galaxies Zoomed In #2

Gen 2 and Gen 3 Processing Compared

Gen 1 and Gen 2 Processing Compared