starship-design: Fwd: ISO detects signal from dark matter in a galaxy similar to the Milky Way

["L. Parker" <lparker@cacaphony.net>]

> ESA Science News
> http://sci.esa.int
>
> 17 Aug 1999
>
> ISO detects signal from dark matter in a galaxy similar to the Milky Way
>
> Galaxies are known to have much more matter than telescopes can currently
see.
> Up to 90% of the total mass of the galaxies is simply missing: it has to
be
> there, astronomers know, but it remains undetected. Is this so-called
'dark
> matter' made up of exotic, virtually undetectable particles, or is it
merely
> ordinary matter hidden to instruments for some reason? A new result
obtained by
> a Dutch team with the European Space Agency's infrared space telescope,
ISO,
> favours the last idea.
>
> They have detected in the disk of a galaxy the molecule of hydrogen,
considered
> an important component of the dark matter if it is of the normal, ordinary
type.
> Moreover, the molecular hydrogen is found precisely in the amount needed
to fill
> the missing-mass gap.
>
> "0ur results give a much stronger footing for the 'ordinary matter' simple
> solution of the dark matter problem, in the form of massive clouds in the
disks
> of galaxies", says the main author of the finding Edwin A. Valentijn, from
the
> Kapteyn Institute in Groningen (The Netherlands).
>
> Astronomers discovered the existence of the dark matter long ago, by
measuring
> the motion of the stars and gas in spiral galaxies: the velocity of this
motion
> corresponds to a certain amount of mass in the galaxy, and measurements
showed
> that the stars and the gas are moving too fast for the amount of mass
detected.
> Several hypotheses have been made to explain the nature of this missing
mass.
> While some consider it to be made of 'exotic' particles very difficult to
> detect, such as neutrinos, others point to ordinary matter -- 'baryonic
matter',
> in scientific terms --  which for some reason remains hidden.
>
> One of the findings helping to build the 'normal matter' explanation was
> obtained a decade ago by Valentijn himself. In 1989 he measured the
brightness
> of 2,500 spiral galaxies, to determine whether these objects were
transparent or
> opaque. Until then, most astronomers had assumed that spiral galaxies were
> basically transparent, this meaning that most light coming from the normal
> matter present would be freely emitted -- thus, the matter would be
bright. On
> the contrary, Valentijn found that spiral galaxies are heavily obscured by
their
> own interstellar dust. Could the dark matter, or at least part of it,
simply be
> the gas frequently associated with this interstellar dust?
>
> If that was the case, the gas had to be made up mostly of hydrogen in the
> molecular form. Hence,Valentijn and his co-author van der Werf started a
search
> for molecular hydrogen, which is extremely difficult to observe. Emission
from
> this molecule can only be detected with highly sensitive infrared
telescopes,
> and ESA's ISO has allowed the study of molecular hydrogen in unprecedented
detail.
>
> Using the spectrometer SWS on board ISO the Dutch team focused on a spiral
> galaxy called NGC 891, 30 million light-years away and very similar to our
own
> galaxy, the Milky Way. Measurements were made in 8 different positions in
the
> disk of NGC 891.
>
> "The surprise is that we detect molecular hydrogen everywhere where we
looked!
> Our team was the only one who thought the measurement was feasible, as no
other
> ISO-observations of this kind were programmed", Valentijn says.
>
> Moreover, the team found molecular hydrogen in the amount needed to
account for
> the missing mass. This is established as a value relative to the amount of
> hydrogen in the atomic form (one molecule of hydrogen is made of two atoms
of
> hydrogen). In NGC 891, Valentijn shows that there is 5 to 15 times more
> molecular than atomic hydrogen.
>
> As the Dutch astronomer explains, "it is well established that if there is
about
> 10 times as much molecular hydrogen as atomic hydrogen in the disks of
spiral
> galaxies, then the missing mass problem is resolved. In the case of NGC
891we
> find about 5-15 times as much molecular hydrogen as atomic hydrogen".
>
> Since NGC 891 is a rather common galaxy, it is "reasonable" -- the authors
say
> -- to expect the result to hold for other normal galaxies too. However,
the team
> warns that no other alternative dark matter model can be ruled out.
>
> According to Valentijn, "the problem is complex enough to avoid drawing
quick
> conclusions, and of course more observations should be made".
>
> The discovery has been accepted for publication in the Astrophysical
Journal Letters.
>
> FOOTNOTE ON ISO
>
> The European Space Agency's infrared space telescope, ISO, operated from
> November 1995 till May 1998, almost a year longer than expected. As an
> unprecedented observatory for infrared astronomy, able to examine cool and
> hidden places in the Universe, ISO successfully made nearly 30 000
scientific observations.
>
> FOR MORE INFORMATION AND ISO PICTURES
>
> ESA Public Relations Division
> Tel: +33(0)1.53.69.71.55, Fax: +33(0)1.53.69.76.90
>
> Martin F. Kessler (ISO Project Scientist)
> Tel: +34 918131254, mkessler@iso.vilspa.esa.es
>
> OTHER SCIENCE CONTACTS:
>
> Edwin Valentijn
> Kapteyn Institute
> Groningen (The Netherlands)
> valentyn@astro.rug.nl, Tel: +31 50 3634011
>
> Thijs de Graauw
> ISO SWS Principal Investigator
> Tel: +31-50-3634074, thijsdg@sron.rug.nl, Th.de.Graauw@sron.rug.nl
>
> USEFUL LINKS FOR THIS STORY
>
> ISO science web site
> http://isowww.estec.esa.nl
>
> NOAO images of NGC891
> http://www.noao.edu/image_gallery/html/im0002.html
>
> More about ISO
> http://sci.esa.int/iso
>
> ISO SWS page
> http://www.sron.rug.nl/iso/sws.html
>
> [NOTE: An image supporting this article is available at
> http://sci.esa.int/story.cfm?TypeID=1&ContentID=6311&Storytype=18]


If this is true, perhaps we can revive the interstellar ram jet idea...

Lee Parker

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       lparker@cacaphony.net

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