Brightest cluster galaxies ( BCGs ) in the cores of galaxy clusters have distinctly different properties from other low redshift massive ellipticals .
The majority of the BCGs in cool-core clusters show signs of active star formation .
We present observations of NGC 4696 , the BCG of the Centaurus galaxy cluster , at far-infrared ( FIR ) wavelengths with the Herschel space telescope .
Using the PACS spectrometer , we detect the two strongest coolants of the interstellar medium , [ C ii ] at 157.74 \mu m and [ O i ] at 63.18 \mu m , and in addition [ N ii ] at 121.90 \mu m. The [ C ii ] emission is extended over a region of 7 kpc with a similar spatial morphology and kinematics to the optical H \alpha emission .
This has the profound implication that the optical hydrogen recombination line , H \alpha , the optical forbidden lines , [ N ii ] \lambda~ { } 6583 \AA , the soft X-ray filaments and the far-infrared [ C ii ] line all have the same energy source .

We also detect dust emission using the PACS and SPIRE photometers at all six wavebands .
We perform a detailed spectral energy distribution fitting using a two-component modified black-body function and find a cold 19 K dust component with mass 1.6 \times 10 ^ { 6 } ~ { } M _ { \odot } and a warm 46 K dust component with mass 4.0 \times 10 ^ { 3 } ~ { } M _ { \odot } .
The total FIR luminosity between 8 \mu m and 1000 \mu m is 7.5 \times 10 ^ { 8 } ~ { } L _ { \odot } , which using Kennicutt relation yields a low star formation rate of 0.13 M _ { \odot } ~ { } \mathrm { yr } ^ { -1 } .
This value is consistent with values derived from other tracers , such as ultraviolet emission .
Combining the spectroscopic and photometric results together with optical H \alpha , we model emitting clouds consisting of photodissociation regions ( PDRs ) adjacent to ionized regions .
We show that in addition to old and young stellar populations , there is another source of energy , such as cosmic rays , shocks or reconnection diffusion , required to excite the H \alpha and [ C ii ] filaments .