The study of compact objects, like (binary) black holes, (binary) neutron stars,
their mergers and subsequent formation of a single compact object surrounded by
an accretion disk are very important for contemporary astrophysics (and physics) for several reasons.
Binary neutron-star systems are particularly interesting, because they are the best candidate source for
explaining a class of gamma-ray bursts, which are in general the most energetic explosions in the Universe.
Gamma-ray bursts are observed daily by satellites and telescopes,
but their origin and mechanism is not known in detail.

Binary neutron-star and/or black-hole systems are also powerful sources of gravitational radiation.
Gravitational waves are a fundamental prediction of General Relativity and,
after huge experimental efforts worldwide especially with laser interferometric detectors,
have been measured for the first time only recently:
the first binary black-hole merger in September 2015 and the first binary neutron-star merger in August 2017.
The measurement of gravitational waves has opened a completely new observational window on the Universe,
through which we will get to know things that are completely or partially inaccessible to electromagnetic observations,
like black-hole dynamics, the internal structure of compact stars, the equation of state of ultra-high density matter,
and so on, in addition to the internal engine of gamma-ray bursts, as mentioned above.

These measurements were performed by interferometers in the US (LIGO)
and Italy (Virgo), while the Japanese KAGRA detector is fully part of
the observational network since 2023.

In order to physically interpret the measurements, accurate knowledge of gravitational waveforms is
of crucial importance and hence numerical simulations of the sources are necessary.
Given the high nonlinearity of the Einstein equations for General Relativity,
numerical solutions are in fact often the only means to study the internal structure and
the most violent dynamics of such objects in detail.

Luca Baiotti is currently part of
the OUTAP group (Osaka University Theoretical AstroPhysics group)
in the Department of Earth and SpaceScience.
Prospective students, in particular, are invited to look at the web pages of the OUTAP group.

Merger and Postmerger of Binary Neutron Stars with a Quark-Hadron Crossover Equation of State

Huang, Y.-J., Baiotti L., Kojo T., Takami K., Sotani H., Togashi H., Hatsuda T., Nagataki S., Fan Y.-Z.

Physical Review Letters 129 (2022) 181101

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Gravitational waves from neutron star mergers and their relation to the nuclear equation of state

Baiotti L.

Progress in Particle and Nuclear Physics 109 (2019) 103714

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Binary neutron-star mergers: a review of Einstein's richest laboratory

Baiotti L., Rezzolla L.,

Reports on Progress in Physics 80 (2017) 096901

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Constraining the equation of state of neutron stars from binary mergers

Takami K., Rezzolla L., Baiotti L.,

Phys. Rev. Lett. 113 (2014) 091104

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The missing link: Merging neutron stars naturally produce jet-like structrues and can power short gamma-ray bursts

Rezzolla L., Giacomazzo B., Baiotti L., Granot J., Kouveliotou C., Aloy M.A.,

Ap. J. Lett. 732 (2011) L6

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Analytic modelling of tidal effects in the relativistic inspiral of binary neutron stars

Baiotti L., Damour T., Giacomazzo B., Nagar A., Rezzolla L., Phys. Rev.

Lett. 105 (2010) 261101

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Accurate evolutions of inspiralling neutron-star binaries: prompt and delayed collapse to black hole

**Baiotti L.**, Giacomazzo B., Rezzolla L. Phys. Rev. **D78** (2008) 084033

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Accurate simulations of the dynamical bar-mode instability in full General Relativity

**Baiotti L.**, De Pietri R., Manca G.M., Rezzolla L. Phys. Rev. **D75** (2007) 044023

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Challenging the paradigm of singularity excision in gravitational collapse

**Baiotti L.**, Rezzolla L. Phys. Rev. Lett. **97** (2006) 141101

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Three-dimensional relativistic simulations of rotating neutron-star collapse to a Kerr black hole

**Baiotti L.**, Hawke I., Montero P., Lö̈ffler F., Rezzolla L., Stergioulas N., Font J. A., Seidel E. Phys. Rev. **D71** (2005) 024035

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Luca Baiotti received his Ph.D. in astrophysics at SISSA (International School of Advanced Studies), in Trieste (Italy) in 2004. He then worked as a postdoc at the Max-Plank-Institut für Gravitationsphysik, Albert-Einstein-Institut, in Potsdam (Germany) in the period 2004-2007 and as a JSPS fellow at the University of Tokyo (2007-2008) and at Kyoto University (2009).

He is presently Associate Professor in the International College and the Graduate School of Science of Osaka University.