The University of Valencia has participated in the discovery of a compact object of approximately 2.6 solar masses and places it in an interval between the most massive neutron star and the lightest black hole ever seen. The isolated observation of this wave, called GW190814, was made on Earth in August 2019 by Advanced Virgo detectors at the European Gravitational Observatory (in Italy) and the two Advanced LIGO (in the United States), but still not able to distinguish if this object is a black hole or a neutron star. The discovery was just published in The Astrophysical Journal Letters.
GW190814 is an object of about 2.6 solar masses, which places it within the “gap in the mass distribution”, an area that has a lack of observations of compact objects with masses between 2.5 and 5 solar masses. This area is in a range of masses apparently too small for a black hole and too large for a neutron star. Both neutron stars and black holes form when very massive stars use up their nuclear fuel and explode as supernovae. What remains after the explosion depends on how much of the star’s core remains. The less massive nuclei tend to form neutron stars, while the more massive ones collapse into black holes. For the scientific community, understanding if there is a gap in the mass distribution in this interval, and why, has been an enigma.
José Antonio Font, Professor of Astronomy at the University of Valencia and coordinator of the Virgo group in Valencia, highlights that “the nature of the object remains a mystery, since this observation of gravitational waves by themselves does not allow us to distinguish whether it is a black hole or of a neutron star. About 800 million years ago, the object merged with a 23 solar mass black hole and, in doing so, generated a final black hole about 25 times the mass of the Sun. The merger emitted an intense gravitational wave that the three instruments of the LIGO-Virgo network detected on August 14, 2019. “The signal associated with this Such unusual fusion was clearly detected with an overall signal-to-noise ratio of 25. Thanks mainly to the delay between the signal arrival times in the detectors, that is, the two Advanced LIGO in the USA and the Advanced Virgo in Italy, the network of the 3 detectors was able to locate the origin of the source that generated the wave in about 19 square degrees.
According to the research team, one of the peculiarities of this event is that the merger shows the most unusual proportion on record to date Among masses of a binary system, the largest mass is about 9 times more massive than the smallest mass. Likewise, they explain the probable reasons why this event was not seen in the electromagnetic spectrum. First of all, this event was six times farther away than GW170817, making it difficult to detect any electromagnetic signal. Second, if the collision involved two black holes, there were probably no emissions in the electromagnetic spectrum. Third, if the smallest object in the system was, in fact, a neutron star, its companion black hole 9 times more massive could have swallowed it whole; which would not produce any electromagnetic emission.
José Antonio Font points out that “The analysis of most of the signals announced by LIGO and Virgo to date has gone smoothly since the masses involved have facilitated the precise identification of the type of objects “. Font concludes that” fortunately, with GW190814, as also happened in part with GW190425, we enter a field where the conclusions are no longer so simple. This is an exciting sign in questioning our ideas about the formation of compact objects. Welcome! “.
The Virgo Collaboration
The Virgo Collaboration is comprised of approximately 550 members from 106 institutions in 12 countries different
The European Gravitational Observatory (EGO) houses the Virgo detector near Pisa, Italy, and is funded by the National Center for Scientific Research (CNRS) in France, the National Institute of Nuclear Physics (INFN) in Italy, and Nikhef, the National Institute for Subatomic Physics in the Netherlands.
Spanish contribution
Five groups in Spain are contributing to LIGO-Virgo gravitational wave astronomy in areas ranging from theoretical modeling of astrophysical sources to enhancing detector sensitivity for current and future observation periods. Two groups, in the University of the Balearic Islands (UIB) and at the Galician Institute of High Energy Physics (IGFAE) of the University of Santiago de Compostela (USC), are part of the LIGO Scientific Collaboration; while the University of Valencia (UV), the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the IFAE of Barcelona are members of Virgo.
The Spanish contribution is financed by the State Investigation Agency, he Ministry of Science, Innovation and Universities, through the AYA and FPN programs, Severo Ochoa and María de Maeztu Excellence programs, European Union funding, FEDER Fund, European social fund, Vice-presidency and Ministry of Innovation, Research and Tourism, Ministry of Education, and Universities of the Government of the Balearic Islands, Ministry of Innovation, Universities, Science and Digital Society of the Generalitat Valenciana, CERCA program of the Government of Catalonia, and have the support of the Spanish Supercomputing Network (RES).
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