How does a collapsing star look?

Abstract

Time evolution of an optical image of a pressureless star under gravitational collapse is studied in the geometric optics approximation. The star surface is assumed to emit radiation obeying Lambert's cosine law but with an arbitrary spectral intensity in the comoving frame. We develop a formalism for predicting observable quantities by photon counting and by radiometry, in particular, spectral photon flux and spectral radiant flux. Then, this method is applied to the two cases: One is monochromatic radiation, and the other is blackbody radiation. The two kinds of spectral flux are calculated numerically for each case. It is reconfirmed that the redshift factor remains finite and the star becomes gradually invisible due to decay of the photon flux. We also develop an approximate method to present analytic formulas that describe the late time behavior. A possible connection of our study to observation of high-energy neutrinos is briefly discussed.

arXiv comment55 pages, 21 figures, published version

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Cited by in corpus (16)

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• Deflection angle of a light ray reflected by a general marginally unstable photon sphere in a strong deflection limit
• Nonlogarithmic divergence of a deflection angle by a marginally unstable photon sphere of the Damour-Solodukhin wormhole in a strong deflection limit
• Gravitational lensing by using the 0th order of affine perturbation series of the deflection angle of a ray near a photon sphere
• Affine perturbation series of the deflection angle of a ray near the photon sphere of a Reissner-Nordström black hole
• Universal $10^{20}$Hz stochastic gravitational waves from photon spheres of black holes
• Do black hole shadows merge?
• Observing axions through photon ring dimming of black holes
• Circular light orbits of a general, static, and spherical symmetrical wormhole with $Z_2$ symmetry
• Gravitational lensing by two photon spheres in a black-bounce spacetime in strong deflection limits
• Gravitational lensing inside and outside of a marginally unstable photon sphere in a general, static, spherically symmetric, and asymptotically-flat spacetime in strong deflection limits
• Notes on primordial black hole origin for thermal gamma-ray bursts
• Shadow formation in gravitational collapse: Redshift and blueshift by spacetime dynamics
• Erratum: Primordial black hole origin for thermal gamma-ray bursts