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NASA Astronomy Picture of the Day

🌌 NASA Astronomy Picture of the Day

The Double Nucleus of M31

Date: 1996-10-11

The Double Nucleus of M31

View HD Image

Explanation:

The center of M31 is twice as unusual as previously
thought. In 1991 the Planetary Camera then onboard the Hubble Space Telescope
pointed toward the center of our Milky Way's
closest major galactic neighbor: Andromeda (M31).
To everyone's surprise, M31's nucleus showed a double structure.
The nuclear hot-spots are quite close together when considering
Galactic distances: M31 is about 150,000 light years across while
the above shows only the central 30 light-years. Subsequent ground-based
observations have led to speculation that indeed two nuclei exist,
are moving with respect to each other,
that one nucleus is slowly tidally disrupting the other,
and that one nucleus may be the remains of smaller galaxy "eaten" by M31.
The nuclei of many galaxies, including M31, are known to be quite violent places,
and the existence of massive black holes
are frequently postulated to explain them.