About

John Simonetti is a professor in the Department of Physics at Virginia Tech, serving as the Associate Chair of the department and the Director of the Astronomy Outreach Program. His research field is Astronomical Sciences, and he is based at 225 Robeson Hall, Blacksburg, VA. His contact email is jhs@vt.edu, and his office phone number is (540) 231-8740. His work involves astronomical sciences, and he is actively engaged in outreach activities related to physics and astronomy.

Research topics

• Physics
• Astrophysics
• Astronomy
• Computer science
• Optics

Selected publications

• Searching for cosmic strings via black hole spin-down

  arXiv (Cornell University) · 2024-07-03 · 2 citations

  preprintOpen accessSenior author

  Cosmic strings that are attached to rapidly spinning black holes can extract significant amounts of rotational energy and angular momentum. Here we study the effect on primordial black holes, which are expected to form with one or more cosmic strings attached. Although large primordial black holes are predicted to rapidly spin up due to accretion soon after forming, we argue that cosmic strings will spin them down again. We show that if there are cosmic strings with tension greater than $10^{-20}$, the spins of large primordial black holes of mass greater than $30 M_\odot$ should consequently be observed to be near zero. We also investigate the effect on a supermassive black hole of capturing a cosmic string and the possibility of observing the subsequent spin down by its effect on a pulsar orbiting the black hole.

  PublisherOA PDFDOI

• Stability and observability of magnetic primordial black hole-neutron star collisions

  Journal of Cosmology and Astroparticle Physics · 2023-06-01 · 11 citations

  articleOpen accessSenior author

  Abstract The collision of a primordial black hole with a neutron star results in the black hole eventually consuming the entire neutron star. However, if the black hole is magnetically charged, and therefore stable against decay by Hawking radiation, the consequences can be quite different. Upon colliding with a neutron star, a magnetic black hole very rapidly comes to a stop. For large enough magnetic charge, we show that this collision can be detected as a sudden change in the rotation period of the neutron star, a glitch or anti-glitch.We argue that the magnetic primordial black hole, which then settles to the core of the neutron star, does not necessarily devour the entire neutron star; the system can instead reach a long-lived, quasi-stable equilibrium. Because the black hole is microscopic compared to the neutron star, most stellar properties remain unchanged compared to before the collision. However, the neutron star will heat up and its surface magnetic field could potentially change, both effects potentially observable.

  PublisherOA PDFDOI

• Quantum Gravity and Phenomenology: Dark Matter, Dark Energy, Vacuum Selection, Emergent Spacetime, and Wormholes

  arXiv (Cornell University) · 2022-02-10 · 1 citations

  preprintOpen access

  We discuss the relevance of quantum gravity to the frontier questions in high energy phenomenology: the problems of dark matter, dark energy, and vacuum selection as well as the problems of emergent spacetime and wormholes. Dark matter and dark energy phenomenology, and the problem of vacuum selection are discussed within the context of string theory as a model of quantum gravity. Emergent spacetime and wormholes are discussed in a more general context of effective theories of quantum gravity.

  PublisherOA PDFDOI

• Stability and Observability of Magnetic Primordial Black Hole-Neutron Star Collisions

  arXiv (Cornell University) · 2022-09-13

  preprintOpen accessSenior author

  The collision of a primordial black hole with a neutron star results in the black hole eventually consuming the entire neutron star. However, if the black hole is magnetically charged, and therefore stable against decay by Hawking radiation, the consequences can be quite different. Upon colliding with a neutron star, a magnetic black hole very rapidly comes to a stop. For large enough magnetic charge, we show that this collision can be detected as a sudden change in the rotation period of the neutron star, a glitch or anti-glitch.We argue that the magnetic primordial black hole, which then settles to the core of the neutron star, does not necessarily devour the entire neutron star; the system can instead reach a long-lived, quasi-stable equilibrium. Because the black hole is microscopic compared to the neutron star, most stellar properties remain unchanged compared to before the collision. However, the neutron star will heat up and its surface magnetic field could potentially change, both effects potentially observable.

  PublisherOA PDFDOI

• LIGO/Virgo S190425z: LWA1 observations.

  GCN · 2019-01-01

  article
  Publisher

• Accessing the axion via compact object binaries

  arXiv (Cornell University) · 2019-10-15

  articleOpen accessSenior author

  Black holes in binaries with other compact objects can provide natural venues for indirect detection of axions or other ultralight fields. The superradiant instability associated with a rapidly spinning black hole leads to the creation of an axion cloud which carries energy and angular momentum from the black hole. This cloud will then decay via gravitational wave emission. We show that the energy lost as a result of this process tends toward an outspiraling of the binary orbit. A given binary system is sensitive to a narrow range of axion masses, determined by the mass of the black hole. Pulsar-black hole binaries, once detected in the electromagnetic band, will allow high-precision measurements of black hole mass loss via timing measurements of the companion pulsar. This avenue of investigation is particularly promising in light of the recent preliminary announcements of two candidate black hole-neutron star mergers by LIGO/VIRGO (#S190814bv and #S190426c). We demonstrate that for such a binary system with a typical millisecond pulsar and a 3-solar-mass black hole, axions with masses between $2.7 \times 10^{-12}$ eV and $3.2 \times 10^{-12}$ eV are detectable. Recent gravitational wave observations by LIGO/VIRGO of binary black hole mergers imply that, for these binaries, gravitational radiation from the rotating quadrupole moment is a dominant effect, causing an inspiraling orbit. With some reasonable assumptions about the period of the binary when it formed and the spins of the black holes, these observations rule out possible axion masses between $3 \times 10^{-13}$ eV and $6 \times 10^{-13}$ eV. Future binary black hole observations, for example by LISA, are expected to provide more robust bounds. In some circumstances, neutron stars may also undergo superradiant instabilities, and binary pulsars could be used to exclude axions with certain masses and matter couplings.

  PublisherDOI

• Pulsar–black hole binaries as a window on quantum gravity

  International Journal of Modern Physics D · 2017-10-01 · 3 citations

  articleSenior author

  Pulsars (PSRs) are some of the most accurate clocks found in nature, while black holes (BHs) offer a unique arena for the study of quantum gravity. As such, PSR–BH binaries provide ideal astrophysical systems for detecting effects of quantum gravity. With the success of aLIGO and the advent of instruments like the Square Kilometer Array (SKA) and Evolved Laser Interferometer Space Antenna (eLISA), the prospects for discovery of such PSR–BH binaries are very promising. We argue that PSR–BH binaries can serve as ready-made testing grounds for proposed resolutions to the BH information paradox. We propose using timing signals from a PSR beam passing through the region near a BH event horizon as a probe of quantum gravitational effects. In particular, we demonstrate that fluctuations of the geometry outside a BH lead to an increase in the measured root-mean-square deviation of arrival times of PSR pulsar traveling near the horizon.

  PublisherDOI

• LIGO/Virgo G298048: LWA Detection

  GRB Coordinates Network · 2017-09-01

  article
  Publisher

• LIGO/Virgo G298048: LWA radio observations

  GRB Coordinates Network · 2017-08-01

  article
  Publisher

• SIMULTANEOUS OBSERVATIONS OF GIANT PULSES FROM PULSAR PSR B0950+08 AT 42 AND 74 MHz

  The Astronomical Journal · 2016-01-22 · 11 citations

  articleOpen access

  ABSTRACT We report the detection of giant pulse (GP) emission from PSR B0950+08 in 12 hr of observations made simultaneously at 42 and 74 MHz, using the first station of the Long Wavelength Array. We detected 275 GPs (in 0.16% of the pulse periods) and 465 GPs (0.27%) at 42 and 74 MHz, respectively. The pulsar is weaker and produces less frequent GPs than at 100 MHz. Here, GPs are taken as having 10 times the flux density of an average pulse (AP); their cumulative distribution of pulse strength follows a power law, with an index of −4.1 at 42 MHz and −5.1 at 74 MHz, which is much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a wide dispersion measure range from 1 to 5000 pc cm −3 . There were 128 GPs detected within the same periods from both 42 and 74 MHz, which means more than half of them are not generated in a wide band. The CLEAN-based algorithm was used to deconvolve the the effect of scattering broadening and we have concluded that the scattering effect from the interstellar medium at 42 and 74 MHz is weak and cannot be distinguished from the pulse profiles. We calculated the altitude r of the emission region using the dipolar magnetic field model. We found r (42 MHz) = 29.27 km (0.242% of R LC ) and r (74 MHz) = 29.01 km (0.240% of R LC ) for the AP, while for GPs, r (42 MHz) = 29.10 km (0.241% of R LC ) and r (74 MHz) = 28.95 km (0.240% of R LC ). GPs, which have a double-peak structure, have a smaller mean peak-to-peak separation compared to the AP.

  PublisherOA PDFDOI

Frequent coauthors

• Michael Kavic

  39 shared

• B. Dennison

  22 shared

• S. Cutchin

  National Postdoctoral Association

  17 shared

• J. Tsai

  Virginia Tech

  14 shared

• Gregory A. Topasna

  Virginia Military Institute

  13 shared

• Steven W. Ellingson

  Virginia Tech

  11 shared

• B. Bear

  Virginia Tech

  10 shared

• J. M. Cordes

  10 shared

Labs

• John Simonetti's LabPI

Education

• M.S., Ph.D., Astronomy and Space Sciences

  Cornell University

  1984