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.