Infrared Spectroscopy

Our Galaxy

One way astronomers can study our galaxy's structure is to map the intensity of certain spectral lines over the entire Milky Way as seen from Earth orbit. In the infrared, certain lines can be used to map the distribution of star forming regions and cool interstellar clouds throughout our galaxy. For example, the 2 images below show all sky maps of the intensity of C+ (ionized carbon) and N+ (ionized nitrogen) from the COBE satellite. In these images the plane of the Milky Way is horizontal across the middle of the map with the center of our galaxy in the center of the image. The C+ line intensity map shows the distribution of the cold interstellar clouds while the N+ line intensity map shows the distribution of the warm interstellar regions which surround hot stars.


All sky intensity map of the 158 micron C+ line.

All sky intensity map of the 205 micron N+ line.

The nucleus (central region) of our Milky Way galaxy is a complex and fascinating region. Our galactic center has a very high density of stars, a high probability of stellar collisions, dense high velocity clouds, and a possible massive black hole. Infrared studies have shown that the stars in the galactic center are distributed in a rotating bar. The study of our galactic center gives us the only chance to get a detailed picture of what goes on in the nucleus of a galaxy - other galaxies are too far away. Our galactic center is hidden from optical view by thick layers of dust. Infrared light, however, can pass through this dust and allow us to peer into the very heart of our galaxy.

Infrared spectra of the stars in the galactic center have helped show that massive star formation occured throughout the galactic center no longer than 10 million years ago.


Infrared spectra of the galactic center from ISO.
From "SWS observations of the Galactic center" , D.Lutz.

Infrared spectral studies of the galactic center show a wide range of lines from ionized atoms. This information allowed astronomers to determine that the average temperature of the stars is about 35,000 degrees Kelvin (the temperature of large, young stars). This evidence points to a very active period of intense star formation in the galactic center which occured only a few million years ago (a few million years is a short time on a galactic scale - for example, our Sun is about 4.6 billion years old).

Ionized neon has a characteristic infrared wavelength of 12.8 microns. At this wavelength we can study ionized clouds of gas very close to the center of our Galaxy. Studies show that there are very high velocity clouds near the Galactic center which indicate that there is a dark, extremely high mass object (perhaps ten million times the mass of our Sun) embedded in these clouds.


Infrared Spectroscopy Index | What is Spectroscopy? | Infrared Spectroscopy | Solar System | Interstellar Space | Star Forming Regions | Older Stars | Search For Life | Our Galaxy | Other Galaxies | Cosmology