18 July 2003
	*DRAFT*	Gen-X Science: Executive Summary *DRAFT*
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Generation-X will:
 * observe the birth of the first black holes, and their
effect on the formation of galaxies;

 * probe the behavior of matter in extreme environments

 * address a wide range of science objectives, on all scales of
astrophysics, including the evolution of galaxies from the earliest
times.

These primary goals, set by NASA Goals and OSS Enterprise Objectives,
require a poweful mission, that must be able to reveal the deepest
Universe, out to z = 10 -20, when the Universe was only 1-2% of its
present age (100-300 million years), to the time before stars.

What was happening at these depths in the young Universe is now only a
matter of theoretical speculation. This era is when the first collapse
of matter in the present day forms was beginning, to give rise to the
first structures that have evolved into clusters and galaxies. This is
when the first black holes may have formed, that gave rise to quasars,
to later evolve into the silent massive black holes found with
$Hubble$ in the nuclei of virtally all large galaxies.

Generation X is the missing element of the current effort of
understanding the early Universe.  The young Universe cannot be
observed in the optical band, because the UV photons emitted at those
depth are absorbed by the intergalactic Hydrogen.  The JWST will
explore the optical-near-UV emission of the nascent galaxies, that
reaches us in the near IR. ALMA will detect the IR dust emission of
these galaxies in the millimeter band. Generation-X will explore the
unabsorbed harder ($>2$~keV) emission of these young galaxies and
quasars, redshifted into the soft X-rays ($> 0.1$~keV). In addition,
Gen-X will also provide an unique (CHECK!) understanding of the
chemical evolution of the Universe, and will detect the hot gas that
traces the large scale distribution of matter.

The X-ray band is where the primordial black holes can be uniquely
detected.  With Gen-X we will understand how do the first Black Holes
form, why do they have the distribution of masses we observe, why do
the black holes in galaxy nuclei grow in synchrony with their
surrounding galaxy, and why are most now dormant.  We will be able to
study the evolution of black holes from their inception on up to later
times. We will directly study the feedback of the black hole onto the
larger scale surrounding environment, and how that affects the flow of
matter into the black hole.

The X-ray band is also where we can detect the fossil evidence of
element abundances in the gas lying in the closed systems of clusters
of galaxies. The evolution of this metal content provides unique
constraints to the star formation history of the Universe, the black
hole formation and evolution, and the supernova rate of galaxies.
Gen-X will reveal the pattern of formation of the elements that place
us in the Universe.

The cosmic variance evident from $Hubble$ deep fields bears witness to
the existence of large scale structures in the Universe. Gen-X will
directly trace the distribution of matter in the Universe (dark matter
included) by means of the hot plasma trapped in these potential wells
(FEAS??).
 * The nature of the unseen components of the Universe: Dark Matter
and Dark Energy?


These ambitious scientific goals require: (1) A very large collecting
area (100sq.m), to detect the nascent back holes at z = 20, and obtain
spectra of the hot intracluster medium at z = 1 - 2; (2) Angular
resolution $< 1''$ (goal 0.1'') to be able to resolve the deep
Universe and distinguish the point-like emission from accreting
black-holes from the surrounding galaxy emission. (3) A band-width
extending down to 0.1~keV, to detect the X-ray emission from z = 10-
20, and up to $\sim 8$~keV, to be able to follow the evolution of
black holes and clusters to the present day; (4) a D > 4 arcmin field
of view, to be able to study clusters and trace the hot gaseous
component trapped in the large-scale structures of the deep Universe;
(5) Spectral resolution (R>1000) sufficient to separate spectral lines
to diagnose conditions at all redshifts.

While Gen-X was conceived to address the fundamental astrophysics
goals described above, this powerful observatory will also open up the
study of the whole gamut of celestial phenomena, from comets to
quasars, to study in X-rays. For example, X-ray astronomers have
studied X-ray binaries since the dawn of the subject, yet we still
know little about: the detailed physics of accretion disks, especially
at the inner radii; the equation of state of matter at neutron star
densities; the presence of exotic forms of matter (e.g. quark stars);
how XRB form and evolve in a wide range of galaxies and environments.
Gen-X provides a unique capability for approaching these important
questions, combining a large area that will provide a torrent of
photons; good angular resolution, that will pick out XRBs cleanly in
other galaxies; and high spectral resolution that will reveal the
dynamics of the accretion process.

Beyond SEU objectives, Gen X will also provide a novel way to explore
other NASA OSS objectives: the Sun-Earth connection, by studying other
`Suns' at various ages; the physical properties of space plasma, by
producing 3-D maps of a variety of stellar coronae; and the harsh
X-ray environment of planets, thus reducing the candidates for
life-bearing planets.

Projecting forward to describe the most exciting science 20 years from
now is inherently uncertain. The Gen-X mission parameters describe an
observaotry that explores large new volumes of `Discovery Space'. This
makes the Gen-X concept robust and powerful even in the face of major
upheavals in our current understanding of the Universe.