A New Science Strategy for Space Astronomy and Astrophysics (1997) / Chapter Skim
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3 Stars and Stellar Evolution
3 Stars and Stellar Evolution
Pages 21-34
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From page 21... ...
These black hole transients have many properties in common with the more massive variety of black holes thought to reside in galactic nuclei, including their nonthermal spectra and the capability of producing superluminal jets. Therefore, they give the opportunity to deepen our understanding of black holes on all scales.
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From page 22... ...
Key Questions About Stellar Evolution Important questions remaining to be answered about stellar evolution include the following: · What physical processes determine the mass functions of single and binary stars, from their formation to their demise as compact stellar remnants such as white dwarfs, neutron stars, and black holes? · How do rotation and magnetic fields influence stellar evolution?
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From page 23... ...
EUVE also provided critical constraints on magnetic white dwarf accretion flow by establishing the vertical extent of the accretion spot and the spectrum of the heated white dwarf. New insight into the ultimate evolution of white dwarf binaries came from ROSAT observations of supersoft x-ray sources, many of which are accreting white dwarfs undergoing steady nuclear burning on their surfaces so that the white dwarfs are increasing in mass.
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From page 24... ...
Massive stars, in excess of 8 solar masses, end their lives by gravitational collapse that triggers supernovae, forms neutron stars and black holes, and ejects a significant fraction of the synthesized elements into space. Supernova (SN)
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From page 25... ...
Many issues, ranging from the origin of millisecond pulsars to the fate of old neutron stars and the question of whether or not any of them have high magnetic fields, remain to be clarified. The most useful observations will require large-collecting-area, high-resolution
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From page 26... ...
The new class of black hole transients raises fundamental questions about how stellar-mass black holes are formed. Several systems appear to have black holes of only 5 solar masses, which is both too large for plausible collapse of neutron stars and yet too small for formation from the massive helium cores of stars too massive to form neutron stars or supernovae.
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From page 27... ...
While all main sequence stars lose mass in winds, this process is especially severe in massive stars whose mass can be substantially depleted on the hydrogen-burning time scale. While great progress has been made toward understanding spherically symmetric, radiation-driven winds emanating from massive stars, there are still difficulties in understanding time-dependent, nonspherical mass loss in massive stars such as luminous blue variables and Wolf-Rayet stars.
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From page 28... ...
This process, linking pulsating red-giant stars to white dwarfs, is poorly understood. Moreover, it has parallels with other mass-ejection processes in objects ranging from protostars to supernova progenitors.
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From page 29... ...
How do black holes create relativistic jets of matter, and what is the composition of the jets? How does matter behave near the event horizons of black holes?
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From page 30... ...
Measurement of this frequency yields an estimate of the black hole's mass as a function of its angular momentum, thereby indicating whether the black hole has Schwarzschild or Kerr geometry. Jets Jets are phenomena common to protostellar disks, planetary nebula, accreting stellar black holes, and galactic black holes but are not, interestingly, an obvious product of accreting neutron stars.
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From page 31... ...
What fraction of the dark matter is composed of brown dwarfs and compact objects (white dwarfs, neutron stars, and black holes)
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From page 32... ...
Searches for massive compact halo objects (MACHOs) have turned up microlensing events that indicate small stellar objects that may or may not be white dwarfs.
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From page 33... ...
The fate of blue stragglers and stripped giants remains to be determined with high-resolution images and spectra and with theoretical studies. The origin and evolution of white dwarfs and neutron stars in globular clusters, and thus both initial mass functions and the dynamical evolution of clusters, can be studied with high-resolution optical, ultraviolet, and x-ray imaging.
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From page 34... ...
The use of stars to measure the cosmological distance scale, deceleration parameter, and age of the universe is central to modern cosmology. Important tasks include accurate determinations of the parallax distances and hence ages of globular clusters.
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