Credit: NASA/JPL-Caltech/SINGS Team
How many rings do you see in this striking new image of the galaxy
Messier 94 (NGC 4736) as seen by the infrared eyes of NASA’s Spitzer
Space Telescope? While at first glance one might see a number of them,
astronomers believe there is just one.
Historically, Messier 94
was considered to have two strikingly different rings: a brilliant,
compact band encircling the galaxy’s core, and a faint, broad, swath of
stars falling outside its main disk.
Astronomers have recently
discovered that the outer ring, seen here in the deep blue glow of
starlight, may actually be more of an optical illusion. Their 2009 study
combined infrared Spitzer observations with ultraviolet data from
NASA’s Galaxy Evolution Explorer, and ground-based surveys in visible
(Sloan Digital Sky Survey) and near infrared light (Two Micron All Sky
Survey). This more complete picture of Messier 94 indicates that we are
really seeing two separate spiral arms that, from our perspective, take
on the appearance of a single, unbroken ring.
The bright inner
ring of Messier 94 is very real, however. This area is sometimes
identified as a “starburst ring” because of the frenetic pace of star
formation in this confined area. Starbursts like this can often be
triggered by gravitational encounters with other galaxies, but in this
case may instead be caused by the galaxy’s oval shape.
Tucked in
between the inner starburst ring and the outer ring-like arms we find
the galaxy’s disk, striated with greenish filaments of dust. While, at
first glance, these dusty arcs look like a collection of rings, they
actually follow tightly wound spiral arcs.
Messier 94 is about 17
million light years away, making it a distant neighbor of our own Milky
Way galaxy. It was first discovered by Charles Messier’s assistant,
Pierre Méchain, in 1781 and was added to his supervisor’s famous
catalog two days later.
Infrared light with wavelengths of 3.6 and
4.5 microns is shown as blue/cyan, showing primarily the glow from
starlight. 8 micron light is rendered in green, and 24 micron emission
is red, tracing the cooler and warmer components of dust, respectively.
The observations were made in 2004, before Spitzer ran out of cryogen.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer
Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Data
are archived at the Infrared Science Archive housed at the Infrared
Processing and Analysis Center at Caltech. Caltech manages JPL for
NASA.
Source: Spitzer/Caltech
