The Sculptor galaxy is similar in many respects to our Milky Way. It is about the same size and mass, with a similar spiral structure. But while it is impossible to get a full view of the Milky Way from the vantage point of Earth because we are inside the galaxy, Sculptor is perfectly positioned for a good look.
Astronomers have done just that, releasing an ultra-detailed image of the Sculptor galaxy on Wednesday obtained with 50 hours of observations using one of the world's biggest telescopes, the European Southern Observatory's Chile-based Very Large Telescope.
The image shows Sculptor, also called NGC 253, in around 4,000 different colors, each corresponding to a specific wavelength in the optical spectrum.
Because various galactic components emit light differently across the spectrum, the observations are providing information at unprecedented detail on the inner workings of an entire galaxy, from star formation to the motion of interstellar gas on large scales. Conventional images in astronomy offer only a handful of colors, providing less information.
The researchers used the telescope's Multi Unit Spectroscopic Explorer, or MUSE, instrument.
"NGC 253 is close enough that we can observe it in remarkable detail with MUSE, yet far enough that we can still see the entire galaxy in a single field of view," said astronomer Enrico Congiu, a fellow at the European Southern Observatory in Santiago, and lead author of research being published in the journal Astronomy & Astrophysics.
"In the Milky Way, we can achieve extremely high resolution, but we lack a global view since we're inside it. For more distant galaxies, we can get a global view, but not the fine detail. That's why NGC 253 is such a perfect target: it acts as a bridge between the ultra-detailed studies of the Milky Way and the large-scale studies of more distant galaxies. It gives us a rare opportunity to connect the small-scale physics with the big-picture view," Congiu said.
Sculptor is about 11 million light-years from Earth, making it one of the closest big galaxies to the Milky Way. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
Like the Milky Way, it is a barred spiral galaxy, meaning it has an elongated structure extending from its nucleus, with spiral arms extending from the ends of the bar. Its diameter of about 88,000 light-years is similar to the Milky Way's, as is its total mass. One major difference is Sculptor's rate of new star formation, estimated to be two to three times greater than that of the Milky Way.
Nearly 30% of this star formation is happening near the galaxy's nucleus in what is called a starburst region, as revealed in colorful emissions shown in the new image.
The observations have given information on a wide range of properties such as the motion, age and chemical composition of stars and the movement of interstellar gas, an important component of any galaxy.
"Since the light from stars is typically bluer if the stars are young or redder if the stars are old, having thousands of colors lets us learn a lot about what stars and populations of stars exist in the galaxy," said astronomer Kathryn Kreckel of Heidelberg University in Germany, a study co-author.
"Similarly for the gas, it glows in specific bright emission lines at very specific colors, and tells us about the different elements that exist in the gas, and what is causing it to glow," Kreckel said.
The initial research being published from the observations involves planetary nebulae, which are luminous clouds of gas and dust expelled by certain dying stars. Despite their name, they have nothing to do with planets. These nebulae can help astronomers measure the precise distances of faraway galaxies.
The researchers marveled at the scientific and aesthetic value of the new view of Sculptor.
"I personally find these images amazing," Congiu said. "What amazes me the most is that every time I look at them, I notice something new - another nebula, a splash of unexpected color or some subtle structure that hints at the incredible physics behind it all."
