8.1.3 Astrophysics
The term particle astrophysics was initially synonymous with cosmic ray studies
but within the last several decades it has become increasingly apparent that there
are still undiscovered fundamental particles that may play a dominant role in the
composition of “dark matter”. This is the form of matter believed to account for
approximately 85% of the matter in the universe, and about a quarter of its total
mass-energy density. The scope of particle astrophysics has expanded to include
dark matter studies, although scientists cannot yet be certain that it will actually
yield to a particle physics solution.
In addition to the study of electrically charged particles, high energy gammarays, and possibly neutrons of extra-solar origin, neutrinos have now also emerged
as another member of the realm of particles. The fluxes of high energy neutrinos
in the tera-electron-volt (TeV) to exa-electron-volt (EeV) range are closely related
to cosmic acceleration processes, and may provide “smoking gun” evidence for
the sources of both galactic and extragalactic cosmic rays. For the latter, cosmogenic EeV neutrinos will be direct byproducts of intergalactic scattering of the
highest energy cosmic rays, and will have the potential to probe cosmic ray accelerators back to the earliest epochs of cosmic ray sources.
Balloon-borne payloads are active contributors to all of these particle astrophysics topics. After listing some of those flights, we shall discuss several cases in
detail.
• BOOMERANG flew in the early 1990’s creating one of the first detailed
maps of Cosmic Microwave Background (CMB) temperature fluctuations,
and demonstrating the Euclidean geometry of the universe. This led to the
2006 Balzan Prize for Astronomy and Physics, and influenced follow-on
space missions such as the Cosmic Background Explorer (COBE) and its
successors WMAP and Planck.
• During a 2007 flight, the Advanced Thin Ionization Calorimeter (ATIC) saw
a surprising excess of cosmic ray electrons at energies of 300 GeV. Along
with positron evidence obtained by the PAMELA spacecraft, these observations prompted speculation that the anomaly might represent the “annihilation signature” of dark matter particles, although current belief now favors
a relatively nearby unidentified object such as a pulsar as the source.
• The Trans-Iron Galactic Element Recorder (TIGER) which flew in 20062007 yielded precise measurements of the abundances of elements from
atomic numbers 26 Fe to 34 Se. This led to some of the best evidence that
acceleration of galactic cosmic rays occurs in OB star associations. (The
seven main types are, hottest to coolest O-B-A-F-G-K-M. Our Sun is of
type G). Stars in OB associations are young, hot and very luminous. The
ensuing SuperTIGER mission is further detailed below.
8.1 Scientific Discovery Examples 181
The term particle astrophysics was initially synonymous with cosmic ray studies
but within the last several decades it has become increasingly apparent that there
are still undiscovered fundamental particles that may play a dominant role in the
composition of “dark matter”. This is the form of matter believed to account for
approximately 85% of the matter in the universe, and about a quarter of its total
mass-energy density. The scope of particle astrophysics has expanded to include
dark matter studies, although scientists cannot yet be certain that it will actually
yield to a particle physics solution.
In addition to the study of electrically charged particles, high energy gammarays, and possibly neutrons of extra-solar origin, neutrinos have now also emerged
as another member of the realm of particles. The fluxes of high energy neutrinos
in the tera-electron-volt (TeV) to exa-electron-volt (EeV) range are closely related
to cosmic acceleration processes, and may provide “smoking gun” evidence for
the sources of both galactic and extragalactic cosmic rays. For the latter, cosmogenic EeV neutrinos will be direct byproducts of intergalactic scattering of the
highest energy cosmic rays, and will have the potential to probe cosmic ray accelerators back to the earliest epochs of cosmic ray sources.
Balloon-borne payloads are active contributors to all of these particle astrophysics topics. After listing some of those flights, we shall discuss several cases in
detail.
• BOOMERANG flew in the early 1990’s creating one of the first detailed
maps of Cosmic Microwave Background (CMB) temperature fluctuations,
and demonstrating the Euclidean geometry of the universe. This led to the
2006 Balzan Prize for Astronomy and Physics, and influenced follow-on
space missions such as the Cosmic Background Explorer (COBE) and its
successors WMAP and Planck.
• During a 2007 flight, the Advanced Thin Ionization Calorimeter (ATIC) saw
a surprising excess of cosmic ray electrons at energies of 300 GeV. Along
with positron evidence obtained by the PAMELA spacecraft, these observations prompted speculation that the anomaly might represent the “annihilation signature” of dark matter particles, although current belief now favors
a relatively nearby unidentified object such as a pulsar as the source.
• The Trans-Iron Galactic Element Recorder (TIGER) which flew in 20062007 yielded precise measurements of the abundances of elements from
atomic numbers 26 Fe to 34 Se. This led to some of the best evidence that
acceleration of galactic cosmic rays occurs in OB star associations. (The
seven main types are, hottest to coolest O-B-A-F-G-K-M. Our Sun is of
type G). Stars in OB associations are young, hot and very luminous. The
ensuing SuperTIGER mission is further detailed below.
8.1 Scientific Discovery Examples 181