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Andromeda Galaxy (M31):
A New Look at a Close Neighbor
Andromeda, the nearest major galaxy to the Milky Way, is shown here in
this wide-field optical image from Kitt Peak. The central region of Andromeda
is shown in a composite image, with X-rays from NASA's Chandra X-ray
Observatory (blue) combined with the optical image. Astronomers believe
that Andromeda, also known as Andromeda Galaxy (M31), and the Milky Way will merge in a few
billion years.
In the composite image, hot, X-ray bright gas is seen to envelop the
central region of Andromeda. Point sources are also prominent, mostly
from pairs of stars that are interacting with each other.
Many of these
double stars are thought to include white dwarfs that are pulling large
amounts of material away from a companion star. When the amount of gas
being dumped onto the white dwarf gets too high a thermonuclear
explosion occurs on the surface of the white dwarf, emitting bright X-rays.
By taking multiple observations of these so-called novae with Chandra
and ESA's XMM-Newton observatories, a team of astronomers studied how
long the burst of X-ray emission lasts. They found that several novae
are bright in X-rays for surprisingly short periods of time, suggesting
that the corresponding nova explosions were missed in earlier
observations. Such short periods of bright X-ray emission, according to
theoretical calculations, indicate that the white dwarfs have relatively
high masses. This makes them good candidates for progenitors of Type Ia
supernovas, where a white dwarf reaches a mass limit and undergoes a
thermonuclear explosion and is completely destroyed. The high masses
suggested by the short X-ray outbursts suggests that the white dwarfs do
not have to gain very much mass before reaching their limit and being
destroyed. A long-running goal in stellar astrophysics has been to
identify the elusive stars that explode as Type Ia supernovas.
| Fast Facts for M31: |
| Credit |
X-ray: NASA/CXC/MPE/W.Pietsch et al; Optical: NOAO/AURA/NSF/T.Rector & B.A.Wolpa |
| Scale |
Inset is 12.8 by 9.7 arcmin |
| Category |
Normal Galaxies & Starburst Galaxies, Supernovas & Supernova Remnants |
| Coordinates (J2000) |
RA 00h 42m 44s | Dec +41º 16' 09" |
| Constellation |
Andromeda |
| Observation Dates |
11 pointings from Jul 2004-Feb 2005
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| Observation Time |
57 hours |
| Obs. IDs |
4719-4723, 5925-5928, 6177, 6202
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| Color Code |
Intensity |
| Instrument |
ACIS & HRC |
| Also Known As | Andromeda | | References | X-ray monitoring of optical novae in M31 from July 2004 to February 2005. Pietsch W. et al., 2007, A&A, 465, 375 |
| Distance Estimate |
About 2.9 million light years |
| Release Date |
May 22, 2007 |
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