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M101 - Quasisoft Sources
Enigmatic X-ray Sources Point to Possible New Black Hole Population
Chandra observations of the spiral galaxy M101 and several other nearby
galaxies have revealed a possible new class of X-ray sources.
These mysterious X-ray sources, marked with green diamonds in the image, are
called "quasisoft" sources because they have a temperature in the range
of one to four million degrees Celsius.
The power output of quasisoft sources is comparable to or greater than
that of neutron stars or stellar-mass black holes fueled by the infall
of matter from companion stars. This implies that the region that
produces the X-rays in a quasisoft source is dozens of times larger.
One explanation is that these sources are produced by intermediate-mass
black holes that have masses a hundred or more times greater than the
mass of the Sun. Such objects would have much larger event horizons,
which would account for the larger sizes and lower temperatures
associated with the quasisoft sources. Alternatively, they could be standard
neutron stars or stellar black holes where the associated region of hot
gas is for some as yet unknown reason much larger than usual.
"Hard" X-ray sources, such as neutron stars or stellar-mass black holes
have temperatures greater than ten million degrees. The "supersoft"
X-ray sources due to white dwarfs have temperatures of several
hundred-thousand-degrees. A total of 72 quasisoft sources were
discovered in the four galaxies: M101, M83, M51, and NGC 4697.
Until a few years ago, astronomers only knew of two sizes of black
holes: stellar black holes with masses about ten times that of the Sun,
and supermassive black holes located at the centers of galaxies, with
masses ranging from millions to billions times that of the Sun. Recent
evidence, however, suggests that a class of "intermediate-mass" black
holes may also exist. Theories for the formation of intermediate-mass
black holes involve the collapse of extremely massive stars, or the
merger of many stellar-mass black holes.
As more quasisoft sources are discovered, the types of galaxies in which
they reside and where they are located in a galaxy should give
astronomers additional clues as to their nature and how they are formed.
The present study indicates that quasisoft occur in various locations in
elliptical as well as spiral galaxies.
| Fast Facts for M101:
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Credit
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NASA/CXC/SAO/R.DiStefano et al. |
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Scale
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Image is 14 arcmin per side |
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Category
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Normal and Starburst Galaxies |
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Coordinates
(J2000)
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RA 14h 03m 10.50s | Dec +54º 21' 34.80" |
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Constellation
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Ursa Major |
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Observation
Date
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March 26, 2000 |
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Observation
Time
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26.1 hrs |
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Obs.
ID
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934 |
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Color
Code
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Energy (Red: 0.3-1.0 keV, Green: 1.0-2.0 keV, Blue: 2.0-8.0 keV) |
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Instrument
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ACIS
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Reference
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R. DiStefano and A. Kong, astro-ph0311375 |
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Distance Estimate
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About 20 million light years |
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Also Known As:
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NGC 5457, the Pinwheel Galaxy |
| Release Date |
March 1, 2004 |
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