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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO,General Relativity and Quantum Cosmology, gr-qc
Abstract:
Sagittarius A*, lying the Galactic Center $8$ kpc from Earth, hosts the
closest supermassive black hole known to us. It is now inactive, but there are
evidences indicating that about six million years ago it underwent a powerful
outburst where the luminosity could have approached the Eddington limit.
Motivated by the fact that in extragalaxies the supermassive black holes with
similar masses and near-Eddington luminosities are usually strong X-ray
emitters, we calculate here the X-ray luminosity of Sagittarius A*, assuming
that the outburst was due to accretion of gas or tidal disruption of stars,
both scenarios having been considered to trigger the previous outburst. We show
that in both cases Sagittarius A* could precipitate on Earth an X-ray ($h\nu>2$
keV) irradiance comparable to that from the current quiescent sun. The
irradiance in harder energy band $20~{\rm keV}<h\nu<100~{\rm keV}$, however,
surpasses that from an X-class solar flare, and the irradiation timescale is
also much longer, ranging from weeks to $10^5$ years depending on the outburst
scenario. This level of radiation would disturb the ozone and ionosphere around
the ancient earth, and affect the abundance of organic molecules in dense
interstellar environments around the solar neighbourhood, but these prospects
have not been adequately explored so far. Our results indicate that the
activity of supermassive black hole and the origin and evolution of life may be
more closely linked than previously has been thought.
