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NGC 6240:
Never Before Seen: Two Supermassive Black Holes in Same Galaxy
The Chandra image of NGC 6240, a butterfly-shaped
galaxy that is the product of the collision of two
smaller galaxies, revealed that the central region of
the galaxy (inset) contains not one, but two active
giant black holes.
Previous X-ray observatories had shown that the
central region was an X-ray source, but astronomers did
not know what was producing the X-rays. Radio,
infrared, and optical observations had detected two
bright nuclei, but their exact nature also remained a
mystery.
Chandra was able to show that the X-rays were coming
from the two nuclei, and determine their X-ray spectra. These
cosmic fingerprints revealed features that are
characteristic of supermassive black holes - an excess
of high-energy photons from gas swirling around a black
hole, and X-rays from fluorescing iron atoms in gas
near black holes.
Over the course of the next few hundred million years,
the two supermassive black holes, which are about 3000
light years apart, will drift toward one another and
merge to form one larger supermassive black hole. This
detection of a binary black hole supports the idea that
black holes grow to enormous masses in the centers of
galaxies by merging with other black holes.
NGC 6240 is a prime example of a "starburst"
galaxy in which stars are forming, evolving, and
exploding at an exceptionally rapid rate due to a
relatively recent merger (30 million years ago). Heat
generated by this activity created the extensive
multimillion degree Celsius gas seen in this image.
Note on Cosmic Look-Back Time: The
finite speed of light means that we must always be out
of date, no matter how hard we strive to keep up with
the times. Thus, the seemingly simple question - what
is happening right now on the Sun? - cannot be answered
by an observer on Earth, because it takes light 8
minutes to reach Earth from the Sun. For distant
galaxies, the light travel times are even longer, so
our information about the galaxy NGC 6240, which is 400
million light years away, is 400 million years out of
date! One consolation is that if astronomers on NGC
6240 are observing our Milky Way galaxy, they are
likewise 400 million years behind the times - our
times, that is. As Albert Einstein said, "The past, present and future are only illusions, even if stubborn ones." more
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Fast Facts for NGC
6240:
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Credit
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NASA/CXC/MPE/S.Komossa et al.
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Scale
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Full field is .35 x .3 arcmin; inset is 4 arcsec per side
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Category
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Black
Holes
Normal
Galaxies & Starburst Galaxies
Quasars
& Active Galaxies |
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Coordinates
(J2000)
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RA 16h 52m 59s | Dec +02º 24'
1.70" |
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Constellation
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Ophiuchus
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Observation
Date
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July 29, 2001
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Observation
Time
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10.2 hours
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Obs.
ID
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1590
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Color
Code
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Energy (0.5-1.5keV red; 1.5-5keV
green; 5-8keV blue)
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Instrument
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ACIS
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Reference
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S. Komossa et al. Astro-ph/0212099
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Distance
Estimate
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About 400 million light years
(redshift = 0.0245)
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Release Date
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November 19, 2002
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