Credit: ESA/Hubble & NASA, D. Rosario et al.
For this Picture of the Week, the NASA/ESA Hubble Space Telescope turned its powerful eye towards an emission line galaxy called NGC 3749.
When astronomers explore the contents and constituent parts
of a galaxy somewhere in the Universe, they use various techniques and
tools. One of these is to spread out the incoming light from that galaxy
into a spectrum and explore its properties. This is done in much the
same way as a glass prism spreads white light into its constituent
wavelengths to create a rainbow. By hunting for specific signs of emission from various elements within a galaxy’s spectrum of light — so-called emission lines — or, conversely, the signs of absorption from other elements — so-called absorption lines — astronomers can start to deduce what might be happening within.
If a galaxy’s spectrum shows many absorption lines and few
emission lines, this suggests that its star-forming material has been
depleted and that its stars are mainly old, while the opposite suggests
it might be bursting with star formation and energetic stellar newborns.
This technique known as spectroscopy,
can tell us about a galaxy’s type and composition, the density and
temperature of any emitting gas, the star formation rate, or how massive
the galaxy’s central black hole might be.
While not all galaxies display strong emission lines, NGC
3749 does! It lies over 135 million light-years away, and is moderately
luminous. The galaxy has been used a “control” in studies of especially
active and luminous galaxies — those with centres known as active galactic nuclei,
which emit copious amounts of intense radiation. In comparison to these
active cousins, NGC 3749 is classified as inactive, and has no known
signs of nuclear activity.
Source: ESA/Hubble/potw
