Study plunges standard Theory of Cosmology into Crisis
New insights into Milky Way satellite galaxies raise awkward questions for cosmologists
Do we have to modify Newton's theory of gravitation as it fails to
explain so many observations? Voices are increasingly being heard that support
this heretical hypothesis. Two new studies conducted by physicists at the
University of Bonn, in collaboration with scientists from Austria and Australia,
are likely to provide yet more grist for the mill. Their latest results about
so-called "satellite galaxies" at the periphery of the Milky Way could rock the
theoretical foundations of standard physics.
As modern
cosmologists rely more and more on the ominous "dark matter" to explain
otherwise inexplicable observations, much effort has gone into the detection of
this mysterious substance in the last two decades, yet no direct proof could be
found that it actually exists. Even if it does exist, dark matter would be
unable to reconcile all the current discrepancies between actual measurements
and predictions based on theoretical models. Hence the number of physicists
questioning the existence of dark matter has been increasing for some time now.
Competing theories of gravitation have already been developed which are
independent of this construction. Their only problem is that they conflict with
Newton's theory of gravitation. "Maybe Newton was indeed wrong", declares
Professor Dr. Pavel Kroupa of Bonn University´s Argelander-Institut für
Astronomie (AIfA). "Although his theory does, in fact, describe the everyday
effects of gravity on Earth, things we can see and measure, it is conceivable
that we have completely failed to comprehend the actual physics underlying the
force of gravity".
This is a problematical hypothesis that has
nevertheless gained increasing ground in recent years, especially in Europe. Two
new studies could well lend further support to it. In these studies, Professor
Kroupa and his former colleague Dr. Manuel Metz, working in collaboration with
Professor Dr. Gerhard Hensler and Dr. Christian Theis from the University of
Vienna, and Dr. Helmut Jerjen from the Australian National University, Canberra,
have examined so-called "satellite galaxies". This term is used for dwarf galaxy
companions of the Milky Way, some of which contain only a few thousand stars.
According to the best cosmological models, they exist presumably in hundreds
around most of the major galaxies. Up to now, however, only 30 such satellites
have been observed around the Milky Way, a discrepancy in numbers which is
commonly attributed to the fact that the light emitted from the majority of
satellite galaxies is so faint they remain invisible.
A detailed study
of these stellar agglomerates has revealed some astonishing phenomena: "First of
all, there is something unusual about their distribution", Professor Kroupa
explains, "the satellites should be uniformly arranged around their mother
galaxy, but this is not what we found". More precisely, all classical
satellites of the Milky Way - the eleven brightest dwarf galaxies - lie more or
less in the same plane, they are forming some sort of a disc in the sky. The
research team has also been able to show that most of these satellite galaxies
rotate in the same direction around the Milky Way - like the planets revolve
around the Sun.
Contradiction upon Contradiction
The physicists do belief that this phenomenon can only be explained if
the satellites were created a long time ago through collisions between younger
galaxies. "The fragments produced by such an event can form rotating dwarf
galaxies", explains Dr. Metz, who has recently moved across to the Deutsches
Zentrum für Luft- und Raumfahrt (German Aero-space Center). But there is an
interesting catch to this crash theory, "theoretical calculations tell us that
the satellites created cannot contain any dark matter". This assumption,
however, stands in contradiction to another observation. "The stars in the
satellites we have observed are moving much faster than predicted by the
Gravitational Law. If classical physics holds this can only be attributed to the
presence of dark matter", Manuel Metz states.
Or one must assume that
some basic fundamental principles of physics have hitherto been incorrectly
understood. "The only solution would be to reject Newton´s classical theory of
gravitation", says Pavel Kroupa. "We probably live in a non-Newton universe. If
this is true, then our observations could be explained without dark matter".
Such approaches are finding support amongst other research teams in Europe, too.
It would not be the first time that Newton's theory of gravitation had
to be modified over the past hundred years. This became necessary in three
special cases: when high velocities are involved (through the Special Theory of
Relativity), in the proximity of large masses (through the theory of General
Relativity), and on sub-atomic scales (through quantum mechanics). The
deviations detected in the satellite galaxy data support the hypothesis that in
space where extremely weak accelerations predominate, a "modified Newton
dynamic" must be adopted. This conclusion has far-reaching consequences for
fundamental physics in general, and also for cosmological theories. Famous
astrophysicist Bob Sanders from the University of Groningen declares: "The
authors of this paper make a strong argument. Their result is entirely
consistent with the expectations of modified Newtonian dynamics (MOND), but
completely opposite to the predictions of the dark matter hypothesis. Rarely is
an observational test so definite."
Metz, Manuel; Kroupa, Pavel; Theis,
Christian; Hensler, Gerhard; Jerjen, Helmut: Did the Milky Way dwarf satellites
enter the halo as a group? (The Astrophysical Journal 2009; doi:
10.1088/0004-637X/697/1/269)
Metz, Manuel; Kroupa, Pavel; Jerjen,
Helmut: Discs of Satellites: the new dwarf spheroidals (Monthly Notices of the
Royal Astronomical Society 2009;
doi: 10.1111/j.1365-2966.2009.14489.x)
Contact:
Professor Dr. Pavel Kroupa
Argelander-Institut für Astronomie der Universität Bonn
Telephone:
0228/73-6140, E-Mail: [Email protection active, please enable JavaScript.]
Dr.
Manuel Metz
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Telephone:
0228/447-511, E-Mail: [Email protection active, please enable JavaScript.]