picture of the day
Composite X-ray (blue) and radio
(pink) image of the galaxy cluster Abell 400.
Credit: X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et al.; Radio:
May 01, 2006
Two "Black Holes"?
It seems that Abell 400, a galaxy cluster that has
long enchanted astronomers, is provoking a new round of speculations,
with little regard for the separation of fact and fiction.
The picture above combines X-ray and radio images of the galaxy cluster
Abell 400. According to the press release from the Chandra X-Ray
Observatory, the composite "shows radio jets immersed in a vast cloud of
multimillion degree X-ray emitting gas that pervades the cluster."
"The jets emanate from the vicinity of two super-massive black holes
(bright spots in the image)…. The peculiar dumbbell structure of this
galaxy is thought to be due to two large galaxies that are in the
process of merging."
Any substance with a temperature of "multimillion" degrees cannot
possibly be a gas: It will be a completely ionized
What the press release doesn’t say is that the X-rays in such cases are
almost exclusively synchrotron radiation, not thermal radiation. That
means the X-rays are emitted by very fast electrons spiraling in a
strong magnetic field. The Abell 400 galaxies are under extreme
But electricity is not something astronomers are eager to hear about.
They are not fond of electrical currents in space, because the
possibility that electricity generates large scale structure is alien to
their theoretical models. To generate the observed levels of energy seen
in Abell 400—using nothing but the puny force of gravity—more matter
would have to be squeezed into a galaxy than a galaxy could hold. But
the theorists are mathematicians, and they work with equations, not with
real objects. This permits them to ignore empirical limits on density
and let the amount of matter per unit volume increase without limit: The
"neutron stars" and "black holes" conjured through this mathematical
license can be placed wherever needed to explain away the stunning and
potentially embarrassing energy excesses.
The galaxies would still have to be large. But because of the two
"close" bright spots, astronomers now speculate about "colliding black
holes" that could form a "single super-supermassive black hole" in a few
million years—a mathematicians delight whether or not anything of this
sort actually occurs in the natural world.
But photographs of Abell clusters — there are over 4000 such clusters —
point to a different conclusion. Halton Arp, the
Galileo of the twentieth century, has shown that several are
aligned along the spine of the Virgo Cluster. Their x-ray
contours are elongated toward nearby active galaxies, and these galaxies
often have jets directed toward the Abell clusters.
Some members of the Abell clusters are paired with a quasar or a BL Lac
(a kind of fragmented quasar) across an active galaxy, presenting
astronomers with a now-familiar paradox. Because quasars and their kin
are small and faint and have rather larger redshifts than the active
galaxies, convention assumes they are large and bright but far away. But
as Arp points out, Hubble diagrams for Abell clusters have enormous
dispersion, placing the astronomers' assumptions about redshift in
doubt: "[T]here is no redshift-apparent magnitude relation for these
clusters like that which is claimed to demonstrate a redshift-distance
relation." [Seeing Red, p. 154] And their association with active
galaxies suggests that they are "grown up" BL Lacs — that they are not
far away, but actually small and faint and close to the nearby
active galaxy. Arp discusses this issue at length in his book,
Abell 400 is particularly interesting because it lies along the line of
Local Group objects extending from the minor axis of M31 (the
Andromeda galaxy), through M33, to 3C120 (the active galaxy with the
"faster-than-light" jet). Along that line are also nebulous clouds
"obviously interacting" with higher-redshift dwarf and low-luminosity
spiral galaxies, strong radio and x-ray sources, and quasar groupings.
Arp suggests that the objects in this line have been ejected from M31,
as may have been our own galaxy.
The Abell 400 cluster would be a part of the "umbilicus'"that still
connects us with our "mother", M31.
Submitted by Mel Acheson
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