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NGC 5548:
Chandra Reads the Cosmic Bar Code of Gas Around a Giant Black Hole
This figure is the X-ray spectrum
of the central region of the galaxy, NGC 5548.
The spectrum shows the number of X-rays present at each
energy or wavelength, and amounts to a cosmic bar code.
It allows scientists to take an inventory of the gas
around the giant black hole in the center of the
galaxy. The deep valleys in the spectrum are produced
when a blanket of warm (few million degree) gas absorbs
X-rays of specific energies from hotter gas close to
the central black hole.
Absorption lines, or valleys, due to the elements
carbon, nitrogen, oxygen, neon and magnesium can be
seen in the figure. A peak in the spectrum due to
emission from oxygen is also identified. The Roman
numerals refer to how many electrons have been stripped
from the atoms. e.g. OVIII is an ion that has lost 7
electrons from its atomic shell, NeX has lost 9
electrons, etc. Detailed analysis shows that absorption
lines from elements silicon, sodium, and iron are also
present.
The exact position of the lines relative to laboratory
standards shows that the lines are shifted
systematically to shorter wavelengths by a fraction of
a percent. This shift is due to the gas moving away
from the source (Doppler effect). It indicates that the
blanket of absorbing gas is flowing away from the black
hole at about a million kilometers per hour (600,000
miles per hour), probably because of the enormous
amount of energy radiated by the extremely hot gas very
near the black hole.
Chandra X-ray Observatory Low Energy Transmission
Grating (LETG)/High Resolution Camera Image.
| Fast Facts for NGC 5548: |
| Credit |
NASA/SRON |
| Category |
Quasars & Active Galaxies |
| Coordinates (J2000) |
RA 14h 17m 59.50s | Dec +25° 08' 13" |
| Constellation |
Boötes |
| Observation Dates |
December 11, 1999
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| Observation Time |
24 hours |
| Obs. IDs |
330
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| Instrument |
LETG |
| Release Date |
February 17, 2000 |
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