# Recent Observations of Gravitational Waves by LIGO and Virgo Detectors

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## Abstract

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## 1. Introduction

## 2. Gravitational-Wave Sources

## 3. Roger Penrose Contribution to Understanding Gravitational Waves

## 4. Detectors

## 5. First Detections of Gravitational Waves

## 6. Gravitational-Wave Observation in the First Half of the Third LIGO-Virgo Observing Run

#### 6.1. GW190412

#### 6.2. GW190425

#### 6.3. GW190521

#### 6.4. GW190814

#### 6.5. Gravitational Wave Transient Catalogue-2

**Masses.**We divide the events detected into two categories depending on whether the mass of the secondary component is less or greater than three solar masses.

**Spins.**Most of the compact objects observed in O3a possess zero spin measures within uncertainties, but some events have exhibited a slight deviation.Two systems have a probability greater than 50% that at least one of the BHs holding dimensionless spin magnitude ${\chi}_{i=\{1,2\}}>0.8$. (these parameters are equivalent to the a parameter of the Kerr solution discussed in Section 3). These are GW190517_055101 and GW190521. The analysis of O3a results has shown the presence of positive effective inspiral spin $\left({\chi}_{eff}\right)$ in 11 sources and GW190517_055101 has the highest value. There is no confident evidence of misaligned spins $({\chi}_{eff}<0)$, but GW190514_065416 likely has a small value of $-0.{19}_{-0.32}^{+0.29}$. This implies that the spin directions of BHs in binaries do not reveal the isotropic distribution with respect to their orbital angular momenta. Concerning precession for most binaries, the posterior on ${\chi}_{p}$ is comparable to the prior, indicating that the data is primarily equivocal about precession. There is however a clue of mild orbital precession in the systems GW190412 and GW190521.

**Localization.**The better sensitivity of the detectors has allowed us to identify the GW signals from larger distances as compared to O1 and O2. The farthest event, after considering for measurement uncertainties in the distance, is most plausibly GW190413_134308, with a predicted luminosity distance of ${D}_{L}=4.{45}_{-2.12}^{+2.48}$ Gpc. The nearest source identified in O3a is GW190425, with a suggested luminosity distance of ${D}_{L}=0.{16}_{-0.07}^{+0.07}$ Gpc. GW190814 is the most precisely localized event with an area of 19 deg${}^{2}$. On the other hand, GW190424_180648 is the worst localized event with an area of 28,000 deg${}^{2}$.

## 7. Future Detectors

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 3.**Plots of the first signal of GWs observed by the two LIGO detectors. The top two panels show data received at LLO and LHO and the waveform calculated, taking GR into account. The X-axis represents the time, and Y-axis represents the strain. Strain implies the slight variations in the distances. The bottom plot compares data from both detectors. There is a variation in the orientation of the instruments at the two sites. Therefore, LHO data have been inverted for comparison. There is also a shift in data to include the GW signals’ travel time between Livingston and Hanford (Courtesy Caltech/MIT/LIGO Laboratory) [11].

**Figure 4.**Masses of LIGO/Virgo discoveries. The network of detectors has observed the merger of different compact binaries. The BHs represent a diverse population with larger masses than what had been witnessed before, solely with X-ray observations. This plot shows the masses of the binary components before the merger and the mass of the postmerger object. [Image credit: LIGO-Virgo/Northwestern Univ./Frank Elavsky].

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**MDPI and ACS Style**

Królak, A.; Verma, P.
Recent Observations of Gravitational Waves by LIGO and Virgo Detectors. *Universe* **2021**, *7*, 137.
https://doi.org/10.3390/universe7050137

**AMA Style**

Królak A, Verma P.
Recent Observations of Gravitational Waves by LIGO and Virgo Detectors. *Universe*. 2021; 7(5):137.
https://doi.org/10.3390/universe7050137

**Chicago/Turabian Style**

Królak, Andrzej, and Paritosh Verma.
2021. "Recent Observations of Gravitational Waves by LIGO and Virgo Detectors" *Universe* 7, no. 5: 137.
https://doi.org/10.3390/universe7050137